Texas/New Mexico/Louisiana/Mexico Obs And Discussion Thread Part 4

[bubba hotep]

The GFS has been hinting at a wet Christmas for DFW for a few days now. It went dry for a few runs but was back on the precip today with 12z being the most intriguing run for our area.

[Srain]

The overnight guidance suggests a potent storm complex and associated trough/Canadian cold front will sweep S Wednesday. Modest moisture returns begin on Tuesday that may bring our next chance for showers/isolated storms Wednesday as the storm system ejects. ENE from Colorado into the Mid West. At that time a potent Winter Storm appears to wrap up bringing potentially heavy snows and possibly near blizzard conditions across the Panhandle to the Great Lakes Region. Snow may well extend as far S as the Colorado front range into the Southern Plains. In the warm sector, the SPC as outlined a Slight Risk for severe weather across Arkansas/Northern Louisiana/W Tennessee.

Freezing temps for inland locations are expected Thursday night into Friday across most of Texas. There still is some uncertainty, but another storm system perhaps tracking a bit further S across the US is expected on Christmas as the progressive pattern continues. The 00Z Operational Euro and its ensembles are down right chilly across New Mexico/Texas/Oklahoma/Louisiana following the Christmas storm, but that is day 9/10 in model world, so expect changes.

[Ed Lizard]

As a fan of interesting weather, the 12Z GFS, just beyond the resolution lobotomy, is full of win.

[Srain]

Afternoon AFD's from FWD:

A STRONG SYSTEM...CURRENTLY LOCATED EAST OF THE KAMCHATKA

PENINSULA...IS PROGGED TO MOVE FIRST INTO THE GULF OF ALASKA AND

THEN INTO THE PACIFIC NORTHWEST SUNDAY MORNING. THE GFS AND ECMWF

THEN MOVE THE UPPER SYSTEM INTO THE SOUTHERN PLAINS. EVEN THOUGH

IT IS A LONG WAYS OFF AND THERE WILL BE NUMEROUS MODEL

CHANGES...IT APPEARS THAT NORTH TEXAS WILL SEE A MAJOR COOL OFF

WITH AT LEAST DECENT CHANCES FOR RAIN BY THE MIDDLE OF NEXT WEEK.

SHOULD THE UPPER SYSTEM TRACK FAR ENOUGH SOUTH...THIS COULD ALSO

BRING WINTER WEATHER TO AT LEAST PARTS OF NORTH TEXAS.

THE 12Z ECMWF TRACKS THE LOW ACROSS NORTH TEXAS CHRISTMAS

EVENING...AND WITH HEIGHTS AT ITS CENTER OF 538 DM IT IS A STRONG

SYSTEM. HOWEVER...THE 12Z GFS MOVES THE LOW SLOWER...AND HAS THE

UPPER TROF CENTERED IN EASTERN NEW MEXICO AT THAT TIME. IT IS

ALSO NOT AS STRONG WITH LOWEST HEIGHTS IN NORTH TX ABOVE 541 DM.

WITH BOTH MODELS BRINGING A STRONG COLD FRONT THROUGH TUESDAY

AFTERNOON...THE TEMPERATURES WILL DROP QUICKLY BELOW FREEZING

TUESDAY EVENING AND IF THERE IS ANY MOISTURE LEFT IN THE

ATMOSPHERE AND ANY FORCING TO LIFT IT...WINTRY PRECIP WOULD BE

EXPECTED.

AGAIN...IT IS MUCH TOO EARLY TO GUARANTEE A WINTER EVENT...MODEL

SOLUTION ERRORS TEND TO GROW LARGE THAT FAR IN THE FUTURE. WE CAN

SAY WITH SOME CONFIDENCE THAT WE CAN EXPECT SOME TYPE OF

EVENT THAT MAY INCLUDE WINTER WEATHER. MUCH COOLER TEMPERATURES

ARE ALSO POSSIBLE AFTER CHRISTMAS DAY. WITH MUCH OF THE COUNTRY

TRAVELING FOR THE HOLIDAYS...THIS LARGE AND POWERFUL SYSTEM HAS

THE POTENTIAL TO IMPACT AIR AND ROAD TRAVEL ON A LARGE SCALE

AS IT MOVES ACROSS THE COUNTRY. BE AWARE THAT CHANGES ARE COMING

AND KEEP TRACK OF THE FORECAST AS THE EVENT EVOLVES. UPDATE YOUR

WINTER WEATHER PLAN.

LUB:

INTERESTING SYSTEM TO WATCH AT THE VERY END OF

THE PERIOD...IE MONDAY AND BEYOND. CERTAINLY WAY TOO EARLY TO PUT

VERY MUCH FAITH IN SPECIFICS BUT ECMWF AND GFS HAVE COME A LITTLE

MORE IN LINE WITH 12Z RUNS WITH DEPICTION OF DEEPENING UPPER LOW

DIGGING SOUTH ACROSS THE ROCKIES MONDAY AND TUESDAY OF NEXT WEEK.

GIVEN DRY PROGRESSIVE PATTERN...WILL NOT INSERT MENTIONABLE POPS AT

THIS TIME...BUT GIVEN THE UPCOMING CHRISTMAS HOLIDAY THIS SYSTEM

CERTAINLY BEARS WATCHING.

SJT:

NOW THAT WE ARE PAST THE MIDPOINT OF DECEMBER...THE WEATHER

FORECAST FOR CHRISTMAS IS BEGINNING TO COME INTO PLAY. BOTH THE

ECMWF AND GFS ARE SHOWING A STRONG TROUGH MOVING ACROSS THE

ROCKIES BY 00Z TUESDAY. THERE ARE SOME SUBTLE DIFFERENCES IN THE

SMALLER SCALE FEATURES BUT THIS IS TO BE EXPECTED AT F180. THE

ECMWF IS A BIT FASTER WITH THE COLD FRONT /AND DEEPER WITH THE

SURFACE LOW/ WITH MUCH COLDER TEMPERATURES ANTICIPATED FOR

TUESDAY. NEITHER OF THE MODELS DEVELOP MUCH QPF OVER THE

CWA...KEEPING THE BULK OF THE PRECIPITATION TO OUR NORTH AND EAST.

THE ECMWF AND GFS HAVE EFFECTIVELY SWAPPED ROLES TODAY...WITH THE

GFS BEING THE DEEPEST OF THE TWO...WITH REGARD TO THE

AFOREMENTIONED TROUGH.. THE POTENTIAL FOR WINTRY PRECIPITATION

DOES EXIST BUT IT IS A LOW PROBABILITY EVENT AT THIS JUNCTURE. IT

WILL REQUIRE A WATCHFUL EYE OVER THE COMING DAYS.

[Ed Lizard]

Glass overflowing optimisitic on a good soaking for the lawn this morning. OK, that is beyond NowCast into Hindcast territory...

Natural optimism, I reject the 18Z GFS because it is beyond the wave number truncation. (Not like the 12Z wasn't, but I'm a natural optimist/wishcaster)

[Ed Lizard]

Mixed- my brother and Mom were planning to drive down that day to visit us in Houston. But sleet and snow, and barely beyond wave number truncation so it isn't really fantasy land and similar to 12Z GFS... Yuprian keeps serious snow North of Red River...

[DoctorMu]

^ Interesting. The Euro bringin' da heat....errrrrr cold.

[ams30721us]

Uhm, I know I am new to the area over in Lake Charles but NEVER thought I would wake up to the day I read this type of AFD wording this far south! haha

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX

500 AM CST TUE DEC 18 2012

.DISCUSSION...

SOUTHEAST TEXAS WEATHER WILL UNDERGO MUCH CHANGE AS WE HEAD THROUGH

THIS WEEK LEADING UP TO CHRISTMAS. THE OFFICIAL START OF WINTER

IS FRIDAY MORNING AND THE WEATHER PATTERN THE FIRST WEEK OF WINTER

MAY ACTUALLY LIVE UP TO ITS SEASONAL BILLING. RECENT NPW ENSEMBLE

RUNS ALL EVOLVE A POTENT STORM SYSTEM ACROSS THE INTERCONTINENTAL

DIVIDE EARLY NEXT WEEK...TAKING A DEEP TROUGH (WITH A FOLLOWING

VERY COLD AIR MASS IN ITS WAKE) ACROSS TEXAS CHRISTMAS DAY THROUGH

EARLY WEDNESDAY. A BIT TOO EARLY TO NAIL DOWN THE SPECIFICS...BUT

IT DOES APPEAR THAT THE PROBABILITY OF HEAVIER WEATHER IS ON THE

RISE ON OR AROUND CHRISTMAS DAY. AS THE DAYS UNFOLD...THE QUESTION

WILL BE WHETHER WE WILL EXPERIENCE STRONG TO SEVERE WEATHER AND/OR

WINTRY PRECIPITATION OVER THE HOLIDAY.

NO RAIN UNTIL MONDAY...THIS IS WHEN THE FORECAST BECOMES

QUITE INTERESTING. THE DAYS LEADING UP TO CHRISTMAS WILL BECOME

MILD...WINDIER AND MORE HUMID...WITH INCREASING RAIN PROBABILITIES.

RELATIVELY HIGH RAIN CHANCES IN THE EXTENDED AS RECENT RUN-TO-RUN

EXTENDED PROGS ALL INDICATE A VERY WET PATTERN JUST BEFORE...DURING

...AND POSSIBLY AFTER CHRISTMAS DAY. THE LATTER PROGNOSTICATION

IS INTERESTING AS...WITH LINGERING MOISTURE AND THE CLOSE PROXIMITY

OF A DEEP UPPER LOW SUGGESTS WINTRY PRECIPITATION. ALL CLICHES

ASIDE...BUT STAY TUNED! 31

[Srain]

Afternoon e-mail from Jeff:

Forecast over the next week will be filled with rapid changes as several powerful weather systems move across the central part of the US.

High pressure is shifting eastward today allowing the return of onshore winds and influx of western Gulf of Mexico moisture. Strong upper level trough will dive into the southern plains tonight and Wednesday with rapid deepening of low pressure over the TX/OK panhandle region. Strong pressure falls will result in strong onshore winds developing on Wednesday with sustained S winds of 15-25mph and gust to 30-35mph. Already starting to see northward moving cloud cover SSE of Brownsville and this moisture/cloud cover will advect rapidly northward tonight and early Wednesday. Shallow moist layer will be capped off by SW winds above the surface suggesting only a slight chance of drizzle or light rain on Wednesday. Big changes blast into the region on Wednesday night as warm temperatures with highs in the upper 70’s and low 80’s on Wednesday is quickly ended by a strong cold front.

Front should rapidly cross the region with the possibility of a thin line of showers and may be a thunderstorms mainly along and SE of US 59. Of greater issue appears to be very strong WNW to NW surface winds on Thursday as the deepening storm system to our NE spreads a strong gradient across our area. Winds of 20-30mph with gust to 40mph will be possible and this coupled with rapid surface drying will support an enhanced fire danger situation across our NW and W counties where rainfall on Sunday was on the lighter side. Fine fuels have been cured by freezes last week and overall conditions are dry so the spread of wildfire will be high on Thursday. Could be near critical fire weather conditions and Red Flag Warning criteria from College Station toward Victoria on Thursday. Other big change will be a cold Canadian air mass pouring into the region with highs on Thursday in the 50’s under mainly sunny skies…or nearly a 20-25 degree drop from Wednesday.

Light freeze is likely early Friday morning for most areas NW of US 59, but no freeze warning will be required as all of these areas froze multiple mornings last week. Quick hitting cold air mass begins to shift east on Friday afternoon as the next storm system digs down into the SW US. Winds will swing back around to the SE late Friday and the process starts all over again.

Should see a fairly rapid influx of moisture over next weekend with a chance for a few showers in the strong warm air advection pattern over TX. A powerful upper trough will develop over the Rockies and is expected to bring an “impactful” winter storm to the central US the week of Christmas. Models continue to struggle with the longer range prospects on both the amount of rainfall and the amount of cold air. Recent GFS and ECMWF runs have trended warmer with the storm system suggesting a better severe weather versus winter weather event. With that said, there is some mighty cold air that has been bottled up over NW Canada for weeks now and it remains possible that some of this could become ingested into the system. Would not be expecting winter precipitation threat into this region, but for N and NC TX there is some potential around Christmas into the days following Christmas. For now will go with a fairly warm and increasing wet pattern from Saturday into Christmas Day with lows in the 60’s and highs in the 70’s under 30-40% rain chances. Rain chances look to really increase Christmas Day into the 26th ahead of a potentially very strong cold front which could bring freezing temperatures to a large part of the area following Christmas.

[Quixotic1]

quarter sized hail imby

[bubba hotep]

quarter sized hail imby

Back-to-back over performers! Looks like a nice little line rolling in!

ETA: That was legit but no hail for us.

[Quixotic1]

Back-to-back over performers! Looks like a nice little line rolling in!

ETA: That was legit but no hail for us.

i saw a return earlier out west and thought it must be dust.

hopefully next weeks storm will overperform as well!

[Srain]

LOL @ the 00Z Euro for early next week. A deep neutral trough dropping S into the Rio Grande Valley with a storm track across Central/E Texas on into Louisiana.

[Quixotic1]

LOL @ the 00Z Euro for early next week. A deep neutral trough dropping S into the Rio Grande Valley with a storm track across Central/E Texas on into Louisiana.

2004 redux?

[Srain]

Morning e-mail from Jeff:

Powerful cold front sweeping into the Gulf of Mexico

Very strong NW winds blasting across the area this morning with frequent gusts to 45-50mph.

Red Flag Warning in effect for today.

Cold front has moved well into the Gulf of Mexico clearing the coast around 300am. Since then very strong winds have affected the area with the following gust recorded:

N Jetty: 61

Palacios: 48

Sugar Land: 46

Conroe: 47

College Station: 43

Eagle Point: 40

Impressive surface pressure rises are ongoing across the area and expect winds to weaken slightly over the next 1-2 hours only to pick back up into the 30-40mph range by mid morning. Think the strongest winds associated with the frontal passage are over, but would not be surprised to see a few more 40-45mph gust today especially across the coastal counties and in the corridor from Columbus to Victoria.

Region-wide wind advisory and coastal Gale Warnings are in effect.

Fire Weather:

RH has fallen from 61% to 28% in the last 3 hours as the very dry and cold air mass pours into the region. With winds of 30-40mph expected, very dry air, and dry fuels, fire weather concerns will be high today. Some areas, mainly east of I-45 did see a quick .10 to .50 of an inch of rainfall with the front overnight, but the bone dry air mass will dry any surface moisture quickly this morning. Feel the highest fire weather threat will be west of I-45 and north of I-10 where fuels are driest. Strong winds will make fire containment difficult. Air mass is even drier on Friday, but winds will be much lower with high pressure overhead.

Marine:

Very hazardous on the open waters (lakes/bays/Gulf) this morning with frequent gusts at or above 45mph. Gale Warning is in effect for all Gulf waters and the inland bays through this afternoon for winds of 30-45mph. NW winds are currently pushing water out of Galveston Bay and tidal forecasting models show water level falling to nearly 1-2 feet below MSL by this afternoon…hence a Low Water Advisory is in effect for the risk of vessel groundings in the Bay and Houston Ship Channel.

Long Range:

Little agreement within the models for the Christmas week storm system. GFS and ECMWF have nearly switch positions from yesterday on their track of the upper level system on Christmas Day and the associated weather across the state. Given the ongoing blizzard over the central plains yesterday with a decent snow pack from CO to IA this morning and the fact that shallow arctic air masses tend to bleed southward more than forecast by models….I am leaning toward the colder ECMWF solution. Suspect the strong frontal boundary may reach the region faster than currently shown in the models (around the 26th). Models will really not have a good grasp on this system until likely Sunday when it moves into the western US sounding network.

For now will go with a gradual warming trend over the weekend under increasing southerly flow and humidity. By Monday we will be back near record highs and it will feel very much like yesterday. Rain chances begin to increase Monday evening and peak on Tuesday. Christmas appears warm, but if the front is faster than expected a sharp drop in temperatures would occur during the day on Tuesday. Upper trough in the ECMWF comes across in the cold air on Christmas night with winter precipitation across much of NC and N TX. For now, any winter precipitation looks to remain well north of our area, but the whole system and evolution of factors over the next 48-72 hours does bear watch

[ams30721us]

12z Euro showing accum. snow across East TX Northern LA next week

[Srain]

HGX:

A SLOW WARMUP WILL CONTINUE THROUGH SATURDAY BEFORE A RETURN OF

ONSHORE FLOW LEADS TO MUCH WARMER CONDITIONS SUNDAY AND MONDAY.

MODELS HAVE COME INTO FAIRLY GOOD AGREEMENT WITH THE TIMING OF THE

UPPER LEVEL STORM SYSTEM THAT WILL AFFECT THE REGION EARLY NEXT

WEEK. UNFORTUNATELY THEY ARE SOLIDIFYING AROUND A SOLUTION THAT

WILL PRODUCE A WET CHRISTMAS DAY FOR MUCH OF SOUTHEAST TEXAS. THE

ECMWF CONTINUES TO BE SLIGHTLY STRONGER AND SLOWER WITH THIS

SYSTEM WHICH COULD PRODUCE JUST A BRIEF WINDOW FOR SOME OF OUR

NORTHERN COUNTIES TO SEE RAIN CHANGE OVER TO SNOW...BUT SURFACE

TEMPERATURES WOULD BE TOO WARM TO SUPPORT ANY SORT OF ACCUMULATION

AND NO SIGNIFICANT IMPACTS ARE EXPECTED AT THIS TIME. DRIER AND

COOLER WEATHER IS EXPECTED FOR THE LATTER HALF OF NEXT WEEK.

OUN:

THE MAIN CONCERN OVER THE NEXT SEVERAL DAYS WILL BE THE

PROGRESSION OF A SHORTWAVE TROUGH MOVING OUT OF THE NPAC AND

ONSHORE EARLY MONDAY MORNING...PERHAPS PHASING WITH ANOTHER

SHORTWAVE TROUGH FURTHER NORTH. MOST OF THE NWP MODELS TEND TO

AGREE THAT AMPLIFICATION WILL OCCUR AND WITH A DIGGING TROUGH

MOVING INTO THE ROCKIES...OR JUST WEST...BY CHRISTMAS EVE NIGHT.

THE ECMWF CONTINUES TO DIG THE TROUGH WITH THE MAIN VORT MAX

MOVING ACROSS CENTRAL TEXAS. THIS IS LIKELY DUE TO THE

MAINTENANCE OF SLIGHTLY STRONGER MERIDIONAL UPPER JET ON ITS

BACK SIDE. MEANWHILE...THE REST OF THE MODELS FAVOR A MORE

NORTHERLY TRACK WITH THE POSSIBILITY OF A CLOSED LOW. FROM SOUTH

TO NORTH THE GFS...GEMNH...AND THEN DGEX. FOR NOW...PRECIPITATION

CHANCES LOOK SLIGHTLY BETTER CONSIDERING THE CONSENSUS SO POPS

WERE NUDGED UP JUST A BIT ESPECIALLY ACROSS THE NORTHERN HALF OF

OK...BUT QPF AMOUNTS ARE RELATIVELY LOW/QUICKLY MOVE OUT OF THE

REGION. OF COURSE CONFIDENCE REMAINS FAIRLY LOW WITH REGARDS TO

SNOWFALL AMOUNTS...LOCATIONS AND PERHAPS THE OPPORTUNITY FOR LIGHT

PRE-ICING.

SJT:

THE 12Z ECMWF HAS COME MORE INTO ALIGNMENT WITH THE LATEST GFS AS

TO THE EVOLUTION OF THE NEXT SIGNIFICANT STORM SYSTEM THAT WILL

DEVELOP OVER THE WESTERN STATES AT THE BEGINNING OF NEXT WEEK.

THE MODELS HAVE THE UPPER LOW DIGGING INTO NORTHERN TEXAS ON

CHRISTMAS DAY WITH A COLD FRONT BACKED BY A STRONG POLAR

REINFORCEMENT PUSHING THROUGH THE FORECAST AREA. AS A

CONSEQUENCE...HIGHS CHRISTMAS DAY WILL ONLY BE IN THE 40S ACROSS

THE NORTHERN CWA AND THE 50S OVER THE SOUTHERN HALF. THIS FAST

MOVING FRONTAL BOUNDARY SHOULD BE MIDWAY THROUGH THE FORECAST

AREA BY NOON. THERE WILL BE A SLIGHT CHANCE OF RAIN AHEAD OF THE

COLD FRONT PRIMARILY IN THE AFTERNOON OVER THE SOUTHEASTERN

COUNTIES. AS FOR SNOW...THERE WILL BE A SLIGHT CHANCE OF LIGHT

SNOW OR SNOW FLURRIES OVER THE NORTHERN BIG COUNTRY AS

TEMPERATURES DROP BELOW FREEZING BY EVENING. WILL CONTINUE THE

SLIGHT CHANCE OF SNOW THROUGH CHRISTMAS NIGHT OVER THE NORTHERN

BIG COUNTRY ONLY.

FWD:

MONDAY THROUGH WEDNESDAY...ON MONDAY WE WILL BE CLOSELY WATCHING

THE PROGRESS AND INTENSITY OF THE COLD FRONT AS IT MOVES SOUTH

THROUGH THE PLAINS. AS THE PREVIOUS FORECAST DISCUSSION

MENTIONED...THE SPEED AND BAROCLINICITY OF THIS FRONT WILL PLAY A

ROLE IN WHERE OUR CHRISTMAS DAY STORM SYSTEM MOVES OVER THE

SOUTHERN PLAINS ON TUESDAY AND TUESDAY NIGHT. THE

GFS/ECMWF/CANADIAN ALL SHOW AT LEAST A SHALLOW COLD FRONT SINKING

SOUTH ALL THE WAY THROUGH THE CWA BY MONDAY AFTERNOON. NEARLY ALL

GUIDANCE SHOWS THIS FRONT MOVING THROUGH NORTH TX DRY...DUE TO

LIMITED DEPTH OF MOISTURE AND LACK OF UPPER LEVEL SUPPORT MONDAY

AFTERNOON. AS A RESULT...WENT AHEAD AND SHAVED POPS BACK TO THE

FAR SOUTHEAST PORTIONS OF THE FORECAST AREA FOR MONDAY AFTERNOON

AND ONLY MENTIONED RAIN SHOWERS AT THIS TIME.

WHERE THE MODELS SEEM TO DIFFER MOST SIGNIFICANTLY IS ON THE SPEED

OF STRONG COLD AIR ADVECTION DOWN THE HIGH PLAINS LATE MONDAY

AFTERNOON THROUGH THE OVERNIGHT HOURS. THIS IS MOST EVIDENT BY

LOOKING AT PROGGED H850 WINDS AND TEMPERATURES ALONG THE HIGH

PLAINS DURING THIS TIME FRAME. THE GFS IS ANYWHERE FROM 6 TO 12

HRS SLOWER WITH AN INTRUSION OF COLD...CANADIAN AIR DOWN THE HIGH

PLAINS FROM EARLY CHRISTMAS/TUESDAY MORNING THROUGH THE DAYTIME

HOURS. AS A RESULT...THE GFS TAKES THE NEXT POWERFUL UPPER LEVEL

STORM SYSTEM ON A MORE NORTHERLY TRACK OVER THE SOUTHERN PLAINS

TUESDAY AFTERNOON WITH THE ECMWF AND CANADIAN OFFERING UP THE MORE

SOUTHERLY TRACKS. ASSUMING THIS STRONG LOW-LEVEL COLD AIR

ADVECTION PLAYS AN IMPORTANT ROLE IN HOW FAR SOUTH THE UPPER LOW

WILL GO...FAVOR THE ECMWF AND CANADIAN TRACKS MORE SO THAN THE GFS

AT THIS TIME. THE PRIMARY REASON FOR THIS IS BECAUSE COLD AIR

TYPICALLY RACES SOUTH DOWN THE HIGH PLAINS MUCH FASTER THAN MEDIUM

RANGE GUIDANCE INDICATES. THEREFORE...TEND TO FAVOR THE MODELS

THAT SHOW A FASTER TRACK OF THE COLD AIR...AND A MORE SOUTHERLY

TRACK TO THE UPPER LOW OVER THE SOUTH PLAINS.

WITH THE DECISION MADE TO FAVOR THE MORE SOUTHERLY TRACK...WENT

AHEAD AND MENTIONED A CHANCE FOR PRECIPITATION TO CHANGE OVER TO

SNOW OR A RAIN/SNOW MIX AFTER SUNSET ON CHRISTMAS DAY FOR PORTIONS

OF NORTH TX. AT THIS TIME IT LOOKS AS THOUGH A CHANGE OVER TO SNOW

WILL BE TRYING TO KEEP PACE WITH PRECIPITATION ENDING FROM WEST TO

EAST ACROSS NORTH TX AS DRY MID-LEVEL AIR BUILDS OVER THE REGION

BEHIND THE UPPER LOW. AS SUCH...THINK THAT ANY SNOW WILL TEND TO

BE LIGHT AND ONLY LAST A COUPLE OF HOURS BEFORE ENDING TUESDAY

NIGHT. HAVE SOME CHANCE FOR SNOW...OR A RAIN/SNOW MIX MENTIONED IN

THE FORECAST TUESDAY NIGHT FOR MOST LOCATIONS NORTHWEST OF A LINE

FROM CANTON TO TEMPLE. AT THIS TIME...BECAUSE THE CHANGE OVER TO

SNOW APPEARS TO OCCUR AFTER WE LOSE ANY CONNECTION TO GULF

MOISTURE...VERY LITTLE IMPACT IS EXPECTED AT THIS TIME. HAVE

SNOWFALL OF ONE TENTH OF AN INCH OR LESS IN THE FORECAST AT THIS

TIME.

THERE REMAINS A GREAT DEAL OF UNCERTAINTY IN THE FORECAST...AS WE

ARE STILL STRUGGLING WITH FORECASTING THE PLACEMENT OF

LARGE/SYNOPTIC SCALE FEATURES. SMALLER SCALE DETAILS WILL HAVE A

LARGE IMPACT ON THIS SYSTEM...INCLUDING CHANCES AND AMOUNTS OF

SNOW POSSIBLE. THE FORECAST MAY UNDERGO LARGE CHANGES TO EITHER A

COMPLETELY DRY FORECAST TO MORE ACCUMULATING WINTRY WEATHER

DEPENDING ON THESE SMALLER SCALE...BUT VERY IMPORTANT CONCERNS.

THESE SMALLER SCALE FORECAST DETAILS WILL NOT LIKELY BE WELL

HANDLED UNTIL SUNDAY NIGHT INTO MONDAY AS WE GET A BETTER

CONSENSUS ON THE SPEED AND INTENSITY OF THE INITIAL COLD FRONT

MOVING SOUTH THROUGH THE PLAINS.

EXTENDED...THE POWERFUL UPPER LEVEL STORM SYSTEM MOVES EAST ON

WEDNESDAY LEAVING A DRY FORECAST AND BELOW NORMAL TEMPERATURES

OVER THE REGION FOR THE REMAINDER OF THE WEEK.

SHV:

WE WILL SOON BE SETTING UP FOR OUR NEXT RAINMAKER DURING THE

WEEKEND. THE MODELS CONTINUE TO BE BACK AND FORTH AMONGST

THEMSELVES CURRENT AND PREVIOUS RUNS. NOW THE EURO IS COLDER FOR

CHRISTMAS AND THAT NIGHT WITH SNOW A POSSIBILITY. THE GFS IS NOT

AS COLD BUT STILL BRINGS SNOW WITH CHILLY TEMPS ALOFT. SO WILL

SETTLE ON A SLIGHT MENTION TO CONTINUE IN THE FORECAST FOR

OVERNIGHT AND THE DAY AFTER CHRISTMAS. MAV/MEX NUMBERS HAVE BEEN

BLENDED INTO THE EXTENDED PACKAGE AS THE ROLLER COASTER LINGERS

INTO THE NEW SEASON. THE WINTER SOLSTICE WILL OCCUR IN THE EARLY

MORNING HOURS AT 05:12 A.M. THE EARLIEST START TO THE WINTER SEASON

SINCE 1896.

AMA:

CHRISTMAS DAY AND CHRISTMAS NIGHT REMAINS THE PERIOD OF MOST CONCERN

THROUGH THE NEXT WEEK. THIS REMAINS A HIGH UNCERTAINTY

FORECAST...THOUGH MODELS ARE BEGINNING TO COME INTO SLIGHTLY BETTER

AGREEMENT. AT THIS POINT...THERE SEEMS TO BE RELATIVELY GOOD

AGREEMENT THAT THIS SYSTEM WILL BE AN OPEN WAVE PROGRESSIVE TROUGH

DIGGING SOUTHEAST FROM THE PACIFIC NW. WITH THIS ASSUMPTION...THERE

ARE THREE POSSIBLE SOLUTIONS. FIRST...THE CMC AND PREVIOUS RUNS OF

THE GFS...SHOW THE TROUGH TAKING A FAR SOUTH TRACK DIGGING FROM THE

FOUR CORNERS REGION DOWN TO CENTRAL TEXAS. THIS WOULD BE THE COLDEST

AND POSSIBLY SNOWIEST SOLUTION. THE SECOND SOLUTION IS THE LEAST

AMPLIFIED TROUGH WITH THE FURTHEST NORTH TRACK. THE PRIMARY HAZARD

WITH THIS SOLUTION WOULD BE A PERIOD OF STRONG WINDS.

THE THIRD SOLUTION...AND MOST LIKELY SOLUTION...IS CLOSE TO THE 12Z

GFS SOLUTION WITH THE UPPER LEVEL TROUGH DIGGING SOUTHEAST FROM CO

OVER THE PANHANDLES...TO CENTRAL OK. WITH THIS SOLUTION...THERE IS A

CHANCE FOR SNOW ACROSS THE PANHANDLES ON CHRISTMAS DAY...BEHIND THE

MAIN FRONT. HIGHEST CHANCES FOR SNOW WOULD BE VERY DEPENDENT ON THE

TRACK...BUT AT THIS POINT LOOK TO BE IN THE OK PANHANDLE AND NE TX

PANHANDLE. WITH THIS SOLUTION...STRONGEST WINDS WOULD BE MUCH FURTHER

SOUTH...UNDER THE LARGER MID AND UPPER LEVEL HEIGHT

GRADIENTS...THOUGH WINDS OF 15 TO 25 MPH ARE STILL POSSIBLE IN THE

PANHANDLES. THE BEST WINDOW OF OPPORTUNITY LOOKS TO BE CHRISTMAS

MORNING...AS BY 18Z THE GFS ALREADY IS BEGINNING TO DEPICT ISENTROPIC

DESCENT AND DRY AIR ADVECTION. HAVE KEPT POPS CLOSE TO THE PREVIOUS

FORECAST...THOUGH IF THIS SOLUTION CONTINUES TO BE THE MOST PROBABLE

ONE...SNOW CHANCES AFTER 00Z ARE VERY UNLIKELY. THE MOST UNCERTAIN

FACTOR IN THIS SYSTEM IS SNOW AMOUNTS ACROSS THE REGION...BUT AT THIS

POINT...DO NOT EXPECT MORE THAN A FEW INCHES AT MOST.

[bubba hotep]

FWD...

THERE REMAINS A GREAT DEAL OF UNCERTAINTY IN THE FORECAST...AS WE

ARE STILL STRUGGLING WITH FORECASTING THE PLACEMENT OF

LARGE/SYNOPTIC SCALE FEATURES. SMALLER SCALE DETAILS WILL HAVE A

LARGE IMPACT ON THIS SYSTEM...INCLUDING CHANCES AND AMOUNTS OF

SNOW POSSIBLE. THE FORECAST MAY UNDERGO LARGE CHANGES TO EITHER A

COMPLETELY DRY FORECAST TO MORE ACCUMULATING WINTRY WEATHER

DEPENDING ON THESE SMALLER SCALE...BUT VERY IMPORTANT CONCERNS.

THESE SMALLER SCALE FORECAST DETAILS WILL NOT LIKELY BE WELL

HANDLED UNTIL SUNDAY NIGHT INTO MONDAY AS WE GET A BETTER

CONSENSUS ON THE SPEED AND INTENSITY OF THE INITIAL COLD FRONT

MOVING SOUTH THROUGH THE PLAINS.

This will cause a lot of heartburn for the model huggers out there

I just hope that we can squeeze another round of rain out of this system. Any kind of snow

will just be bonus.

[Terpeast]

Good AFD out of DFW about the xmas storm.

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE FORT WORTH TX

845 PM CST THU DEC 20 2012

.UPDATE...

THE DEWPOINTS ARE NEAR 0 DEG F AND THE PRECIPITABLE WATER VALUE IS

NEAR A TENTH OF AN INCH. THIS IS ABOUT THE DRIEST AIR I CAN RECALL

IN MANY YEARS. THE DRY AIR AND CLEAR SKIES WILL HELP TEMPS FALL

INTO THE TEENS AND 20S TONIGHT...WITH BIG VARIATIONS IN OVERNIGHT

LOWS FROM LOCATION TO LOCATION BASED ON LOCAL TOPOGRAPHY AND SOIL

TYPE. SURFACE HIGH WILL SETTLE IN OVER THE HILL COUNTRY WHICH

WILL KEEP A LIGHT WEST WIND IN PLACE TONIGHT...AND THIS LIGHT WIND

COMBINED WITH HEAT STORED UP IN THE SOIL WILL KEEP TEMPS 10-20

DEGREES ABOVE THEIR DEWPOINT. NO CHANGES WERE MADE...WITH COLDEST

TEMPS GENERALLY IN THE SW ZONES NEARER TO THE HIGH CENTER.

YOUR REGULARLY SCHEDULED UPDATE AFD ENDS HERE. SINCE IT IS A QUIET

NIGHT...ITS WEATHER CLASSROOM AND LAB TIME FOR THOSE INTERESTED...

THE CHRISTMAS NIGHT FORECAST IS ON EVERYONE/S MIND. WE HAVE BEEN

WATCHING THIS SYSTEM IN THE EXTENDED MODELS FOR SEVERAL DAYS...AND

CONTINUE TO RIGHTLY ASSESS THAT A POTENTIAL FOR A WINTER EVENT

EXISTS. UNFORTUNATELY MODEL GUIDANCE DOES NOT HAVE THE SKILL IN

THAT TIME RANGE TO ACCURATELY PREDICT THE INTENSITY AND LATITUDE

THE UPPER LEVEL SYSTEM WILL TAKE BECAUSE OF THE UNCERTAINTY ON

EXACTLY WHERE A COLD FRONT WILL BE ON TUESDAY. AS WE HAVE SAID IN

THE LAST 2 AFDS...THIS COLD FRONT IS THE KEY TO THE FORECAST.

BUT TO UNDERSTAND WHY...IT IS HELPFUL TO DISCUSS BAROCLINICITY

AND ITS AFFECTS ON THE MOVEMENT AND STRENGTH OF WEATHER SYSTEMS.

ESSENTIALLY THESE STORM SYSTEMS ARE BLOBS OF UPPER LEVEL

ENERGY...OR VORTICITY...OFTEN CALLED SHORTWAVES OR DISTURBANCES.

IN AN ATMOSPHERE WHERE THERE IS VERY LITTLE TEMPERATURE DIFFERENCE

FROM LOCATION TO LOCATION...THE MOTION OF THESE DISTURBANCES IS

BASICALLY DICTATED BY THE FLOW THEY ARE A PART OF. THEY BEHAVE

MUCH LIKE A LEAF WOULD IF IT WERE FLOATING DOWN A RIVER.

HOWEVER WHEN HORIZONTAL TEMPERATURE GRADIENTS EXIST...SUCH AS

WHEN A COLD FRONT IS NEARBY...THIS SIMPLE RULE GOES OUT THE

window. THIS IS CALLED A BAROCLINIC ATMOSPHERE. A DISTURBANCE THAT

MOVES INTO A BAROCLINIC ZONE WILL INTENSIFY. THIS IS BECAUSE LOW

LEVEL TEMPERATURE ADVECTION BEGINS TO INTERFACE WITH THE UPPER

LEVEL SYSTEM. IN SHORT...THERMAL ADVECTION IN THE LOW LEVELS

CAUSE HEIGHT CHANGES IN THE UPPER LEVELS...WHICH IN TURN

STRENGTHEN THE UPPER LEVEL VORTICITY CENTER...WHICH IN TURN

STRENGTHENS THE LOW LEVEL THERMAL ADVECTION...AND ETC. THE WHOLE

THING BECOMES A FEEDBACK LOOP. AN UPPER DISTURBANCE UNDERGOING

BAROCLINIC INTENSIFICATION WILL TRANSFORM INTO A CYCLONE AND WILL

NO LONGER MOVE WITH THE MEAN FLOW...BUT WILL CURVE TOWARD THE

POLE. IN THE PROCESS OF TURNING TOWARD THE POLE THE CYCLONE

OFTEN OCCLUDES...MEANING THEY LOSE THEIR ACCESS TO THE TEMPERATURE

GRADIENTS AND THEY WEAKEN. WE HAVE ALREADY SEEN MANY MODEL RUNS OF

A BIG WINTER CYCLONE DEVELOPING OVER THE SOUTHERN PLAINS AND

CURVING OFF TO THE NORTH. IN THE LATEST MODELS WE NO LONGER SEE

THAT SOLUTION AND SEE A WEAK TROUGH MOVING OVERHEAD.

THE REASON WHY THE MODELS HAVE BEEN ALTERNATING BETWEEN A POWERFUL

WINTER CYCLONE IN THE PLAINS AND A WEAK DISTURBANCE HAS BEEN DUE

TO THE LOCATION OF THE BAROCLINIC ZONE /OR COLD FRONT/ WHEN THE

DISTURBANCE REACHES THE SOUTHERN PLAINS. THE TREND IN MOST OF THE

MODELS HAS BEEN TO MOVE THE FRONT/BAROCLINIC ZONE INTO SOUTH

TEXAS. AS A RESULT THE UPPER LEVEL DISTURBANCE TRAVELS OVER TEXAS

WITHOUT STRENGTHENING BECAUSE THE TEMPERATURE GRADIENTS ARE WEAK

SO FAR BEHIND THE FRONT. THE SYSTEM THUS DOES NOT INTENSIFY UNTIL

IT REACHES THE NORTHERN GULF COAST WHERE A BAROCLINIC ZONE EXISTS.

THIS SCENARIO...WHICH WE ARE CURRENTLY FORECASTING...IS ONE THAT

WOULD ONLY PRODUCE LIGHT AMOUNTS OF WINTER PRECIP. THIS IS BECAUSE

THE SYSTEM WILL BE WEAK AND HAS NO ACCESS TO THE THERMAL GRADIENTS

IT NEEDS TO INTENSIFY. AN INTENSIFYING LOW WOULD BE ABLE AUGMENT

THE WIND FIELDS AND THUS TAP INTO THE GULF FOR MOISTURE.

IN ORDER TO GET A SIGNIFICANT SNOW STORM HERE...WE WOULD NEED THE

FRONT TO BE FARTHER NORTH THAN CURRENTLY FORECAST...BUT NOT SO FAR

NORTH THAT THE SYSTEM BEGINS ITS POLEWARD TURN AND STAYS NORTH OF

THE REGION ALTOGETHER. WE NEED A GOLDILOCKS POSITION OF THIS

FRONT. AGAIN...KNOWING THE PRECISE LOCATION OF A FRONT BEYOND 5

DAYS IS THE DIFFICULTY WITH THIS FORECAST. THANKFULLY THE LEAD

SHORTWAVE RESPONSIBLE FOR THE LOCATION OF THIS FRONT WILL BE

ONSHORE IN CALIFORNIA SATURDAY AND WILL BE SAMPLED BY THE BALLOON

NETWORK. IN ADDITION...WE WILL BE IN RANGE OF THE NAM BY TOMORROW

FOR HAVING ANOTHER OPINION ON THIS FRONT/S STRENGTH AND LOCATION

MONDAY NIGHT AND TUESDAY...EVEN IF WE DONT GET AN EXPLICIT DEC

25TH FORECAST FROM THE NAM UNTIL SATURDAY.

TR.92

[bubba hotep]

WE NEED A GOLDILOCKS POSITION OF THIS

FRONT.

Lock it up

[DoctorMu]

Well, the family vote is that we on to Florida tomorrow, so I can GUARANTEE snow X-mas eve!

[bubba hotep]

Most important GFS run of this young winter starting in 15 min! (i'm being sarcastic) I've always wondered why we don't have any hardcore weenies from our area? It seems like every other subforum has them. Anyway, I liked the trends in the overnight guidance and it seems like the winter weather option is still somewhat on the table IMBY.

[Quixotic1]

Most important GFS run of this young winter starting in 15 min! (i'm being sarcastic) I've always wondered why we don't have any hardcore weenies from our area? It seems like every other subforum has them. Anyway, I liked the trends in the overnight guidance and it seems like the winter weather option is still somewhat on the table IMBY.

I think the reality of our situation keeps us on the leash. Yes, it can snow, but on average once or twice a winter out of half a dozen chances. So its easy to be a bit pessimistic when you hear "snow" but, given how poor forecasting winter events in Texas can be, even if they say "flurries" there's hope. (Collin County March 2010 where "flurries" became 7" for example or even February 2010 when a forecast of 2" turned into a foot).

Besides, we're more weenie-esque when it comes to severe wx.

[Srain]

I think we just tend to be a bit more cautious and keep our inner weenie in check...way down here. I suspect that if the trends continue, our region will get a lot more active. After all we are the calm/quiet sub forum that never has any issues like those back E do...

[bubba hotep]

I like the GFS trends @ 00z

[somethingfunny]

FWD:

MEDIUM RANGE GUIDANCE IS FINALLY STARTING TO AGREE FAIRLY WELL

WITH REGARDS TO THE MOVEMENT OF THE UPPER TROUGH AND THE ARRIVAL

OF MUCH COLDER AIR INTO NORTH TEXAS. ALTHOUGH THE MODELS DO VARY A

BIT ON THE EXACT TRACK OF THE UPPER LOW...THE GENERAL CONSENSUS IS

THAT THE CENTER OF THE LOW WILL REMAIN JUST SOUTH OF THE RED RIVER

CHRISTMAS DAY. ALL MODELS ARE HOLDING OFF ON THE INTRUSION OF COLD

AIR UNTIL THE UPPER TROUGH AXIS PASSES. THIS IS IN LINE WITH THE

PREVIOUS FORECAST PACKAGE AND WE HAVE MADE VERY LITTLE

MODIFICATIONS TO POPS OR PRECIP TYPE CHRISTMAS AFTERNOON/CHRISTMAS

NIGHT. SO IN SUMMARY...EXPECT SHOWERS CHRISTMAS MORNING WITH A MIX

OR CHANGE OVER TO LIGHT SNOW GENERALLY NORTH OF INTERSTATE 20

CHRISTMAS AFTERNOON. SOME LINGERING WRAP AROUND LIGHT SNOW IS

POSSIBLE IN THE NORTH/NORTHEAST DURING THE EVENING OF THE 25TH BEFORE

THE SYSTEM MOVES INTO THE CENTRAL PLAINS. GIVEN THIS SCENARIO...LITTLE

OR NO ACCUMULATIONS OR TRAVEL IMPACTS IN NORTH TEXAS ARE EXPECTED.

ALTHOUGH STRONG AND GUSTY WIND IS EXPECTED CHRISTMAS EVENING

BEHIND THE COLD FRONT...WE FEEL THAT ANY SNOW THAT FALLS SHOULD BE

WET AND BLOWING SNOW SHOULD NOT CREATE ANY MAJOR IMPACTS.

THERE IS ONE FLY IN THE OINTMENT THAT HAS OUR ATTENTION AND THAT

IS THE POSSIBILITY THAT THE COLD AIR COULD ARRIVE EARLIER THAN

EXPECTED AS OFTEN HAPPENS WITH ARCTIC INTRUSIONS SINCE THEY

PROPAGATE ON THEIR OWN WEIGHT. THEREFORE....CAREFUL SURFACE

ANALYSIS MUST CONTINUE OVER THE NEXT TWO DAYS. IF THE COLD AIR

DOES ARRIVE EARLIER THAN PROGGED IT COULD HAVE SUBSTANTIAL IMPACTS

TO THE FORECAST SUCH AS THE POSSIBILITY OF A DEEPER AND SLOWER

UPPER LOW...LONGER DURATION OF PRECIPITATION...AND POTENTIAL FOR

SNOW ACCUMULATIONS. FOR NOW...WE WILL KEEP THE FORECAST IN LINE

WITH MODEL CONSENSUS BUT THIS SYSTEM NEEDS TO BE WATCHED VERY

CLOSELY.

[Quixotic1]

it would be funny if we got dry-slotted. that low looks lke its going to comr directly over dfw.

[bubba hotep]

FWD:

THERE IS ONE FLY IN THE OINTMENT THAT HAS OUR ATTENTION AND THAT

IS THE POSSIBILITY THAT THE COLD AIR COULD ARRIVE EARLIER THAN

EXPECTED AS OFTEN HAPPENS WITH ARCTIC INTRUSIONS SINCE THEY

PROPAGATE ON THEIR OWN WEIGHT. THEREFORE....CAREFUL SURFACE

ANALYSIS MUST CONTINUE OVER THE NEXT TWO DAYS. IF THE COLD AIR

DOES ARRIVE EARLIER THAN PROGGED IT COULD HAVE SUBSTANTIAL IMPACTS

TO THE FORECAST SUCH AS THE POSSIBILITY OF A DEEPER AND SLOWER

UPPER LOW...LONGER DURATION OF PRECIPITATION...AND POTENTIAL FOR

SNOW ACCUMULATIONS. FOR NOW...WE WILL KEEP THE FORECAST IN LINE

WITH MODEL CONSENSUS BUT THIS SYSTEM NEEDS TO BE WATCHED VERY

CLOSELY.

Yep, it seems like that almost always happens. I just wonder if it will be significant enough to actually alter the development of the system.

[Ed Lizard]

Even w/ the difference in low tracks, I think I can see both GFS and Euro supporting possible elevated (maybe barely elevated) supercells Christmas morning with a chance for decent hail. 12Z skew-T in main forum thread.

FWD's AFD mentioned supercells in their Southern counties, BTW...

[DFWWeather]

12z MEX MOS shows DFW at 18°F for Tuesday night and 32°F for a high on Wednesday, despite adequate insolation. I have never known MOS guidance to be too cold. If anything, it is usually too warm during Arctic outbreaks.