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OKpowdah

Weekend winter storm

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We've all seen the multiple 1040mb+ arctic highs that are projected to roll down the lee of the Rockies.

There's a lot of uncertainty in the timing of the cold front, along with amount of moisture that gets lifted behind front. The NAM is printing out a very icy scenario for parts of Oklahoma (albeit it is the NAM at 78-84hrs). The Euro also produces wintry precip. Whereas the GFS keeps precip ahead of the front.

 

I don't have time to really write up something, but I thought we should consolidate discussion in this thread, for the upcoming wintry period across the region.

 

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The WPC is mentioning the possibilities of icing on the high plains this weekend.

 

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1022 AM EST TUE NOV 19 2013

VALID 12Z FRI NOV 22 2013 - 12Z TUE NOV 26 2013


THE SPLIT FLOW AT THE MEDIUM RANGE HAS BEEN PROBLEMATIC FOR THE
GLOBAL NUMERICAL MODELS DURING THE LAST FEW DAYS' WORTH OF DATA
RUNS. THE TIMING AND AMPLITUDE OF THE STRONGER SHORTWAVES WITHIN
BOTH STREAMS HAVE BEEN DISPARATELY HANDLED--BOTH INTER- AND
INTRAMODEL. IN SOME CASES, THE SOLUTIONS HAVE INDICATED A
SUBSTANTIAL DEGREE OF PHASING BETWEEN THE STREAMS, WHICH HAS
RESULTED IN SPRAWLING, DEEP CYCLONES AROUND THE PERIPHERY OF THE
CONTIGUOUS UNITED STATES. EXAMPLES OF SUCH PHASING INCLUDED BOTH
THE 00Z/19 AND 06Z/19 GFS, AND THE 00Z/18 AND 12Z/18 ECMWF--WITH
THE SYSTEM CROSSING THE GREAT LAKES EARLY IN THE PERIOD AFFECTED.
THE ENSEMBLE MEANS--PARTICULARLY THE ECENS MEAN--HAVE NOT HAD AS
STRONG OF A PHASING SIGNATURE. THE MOST RECENT ECENS MEAN FROM THE
00Z/19 DATA CYCLE SEEMS TO BEST REFLECT THE MULTI-DAY AVERAGES AND
TRENDING THAT KEEP THE NORTHERN STREAM DOMINANT. LATE IN THE
PERIOD, THE CLOSED LOW NEAR BAJA CALIFORNIA DAY 3 SHOULD FINALLY
MAKES ITS WAY TO THE GULF OF MEXICO, WHERE IT WILL HAVE SOME ROOM
TO EXPAND NORTHWARD.

THE MAJOR SENSIBLE WEATHER THREATS WILL BE THE COLD DELIVERED INTO
THE NORTH CENTRAL STATES DAYS 3 AND 4, AND THE MULTI-DAY
PRECIPITATION THREAT OVER THE SOUTHWEST. WITH COLD AIR BANKED WELL
DOWN THE ROCKY MOUNTAIN CHAIN, EXPECT SNOWS TO PILE
UP--PARTICULARLY OVER THE SOUTHERN ROCKIES. THE WEDGE OF LOW-LEVEL
COLD AIR EXTENDING INTO THE SOUTHERN HIGH PLAINS MAY AFFORD THE
VERTICAL THERMAL STRUCTURE FOR ICE THERE LATER IN THE FORECAST.



CISCO

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FGF mentioning snow chances for the Red River Valley Wednesday night but it's all going to depend on where the best frontogenesis is. Both the NAM and the GFS are showing precip, albeit minor amounts, for Wednesday into Thursday.

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The 12Z Euro trended bit slower with the E movement of the 5H cutoff low near San Diego. Typically these SW 5H lows give the guidance fits until about 24-36 hours out and often produce very heavy snow totals across the higher elevations N of I-40. It is also noteworthy that the Euro does suggest a Coastal Low developing SE of Corpus Christi on Sunday into Monday producing over running precip N of the frontal boundary as the low opens up and shears out with a secondary trough axis over Texas.

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20/00Z ECMWF lives up to its "Dr. No" moniker for the Friday/Saturday wave. Little more than 0.10" QPF anywhere in our region. Definitely discounting the NAM solution until the other guidance moves.

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I think the main concern has always been the ejection of the SW 5H cold core low over the shallow arctic air mass at the surface that should be relatively insolated with a low/middle cloud deck and the development of the Coastal Low previously mentioned on Sunday. ABQ will likely issue Winter Storm Watches later today and change that to a Warning that will likely extend into Monday for their entire forecast area. The OP GFS/Euro solutions have come into better agreement as well as the ensembles suggesting a further E development of a closed cold core low and slowly ejecting that feature E across New Mexico Saturday evening and across Texas on Sunday into Monday. It does appear that the Coastal Low will be far enough offshore of the Lower/Middle Texas Coast to allow a stiff NE wind and wedge the very cold air mass almost down to the Coastal Counties to provide at least a chance of freezing rain and sleet across portions of West Texas into the Hill Country/Edwards Plateau extending E to just W of the Dallas/ Ft Worth area and possibly as far S as the Bryan/College Station to Lake Livingston area of Northern SE Texas. While it is still several days out and these SW cold core 5H lows are extremely difficult to forecast and tend to give guidance fits, some of the parameters we look for in past storm situations at least raise an eyebrow and we have seen that trend this morning with various WFO's across Texas. Further N into Oklahoma this may be a bit less of an issue at the moment, but with any shift N and E in the 5H Low/trough over the weekend would tend to put those areas extending into SW MO and NE AR in an area worth monitoring.

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GFS has moved a bit toward the NAM depiction at H5 over the past 24 h, and suggests at least modest QPF after the frontal passage Friday into Saturday morning. I generally agree with the NWS OUN forecast right now; I think at least minor icing looks increasingly likely. The potential for something bigger is there, but less than a 50% chance right now.

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From a cursory glance of the last three runs of the SREF (the most recent being 15Z) the trend certainly seems to be toward an icing event. The probabilities of freezing rain keep bouncing around from 10-30% on all the members but there's a definite growth in the area being pegged as ZR in both the NCEP and SPC classification schemes. 

 

SREF_LIKELY__f069.gif

 

SREF_LIKELY__f063.gif

 

SREF_LIKELY__f057.gif

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Winter Weather Advisories up for roughly the western 3/4 of Kansas. Looks like a lot of rain here where I'm at. 

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The NAM and SREFs remain very aggressive with the freezing rain potential for a good portion of western Texas, although the QPF output behind the 0*C surface isotherm has been backed off a bit with the initial frontal surge. Both jam the shallow arctic armass down to where it approximately follows the course of the Balconies Escarpment.

 

As Srain noted above, the most interesting bit may be with the actual ejection of the shortwave/closed low out of the desert SW. The 18Z NAM is again very interesting as it begins ejecting the trough at the end of the run. Even though the NAM is noticeably faster with the ejection of the trough, it bears mentioning that the cold air remains firmly entrenched through the end of the run, with any modification taking place being equally offset by cold air advection.

 

In my location at least, I'm somewhat excited about the prospect of getting perhaps up to 2 inches of rainfall through the duration of the event with some elevated convection that looks like it could set up shop on or near the quasi-stationary 850 mb front and over my head. It'll be cold and miserable to be in, but should be interesting enough to observe.

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I was looking over it and it looks to me like a possible serious ice event. I just dont honestly think the models are handling it quite right. I believe the cold air will be too shallow to produce snow like that. I'm thinking more of an overrunning situation more than anything.

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Yeah, I'm more concerned with icing as well. With a moist mid level flow coming from the SW around the closed low, it's hard to not get a warm layer aloft in all but the coldest part of winter. I suspect we'll see the same issue here. It's also worth noting that the NAM is very fast with the ejection of the mid level closed low from the SWUS and the WPC and others are treating it's handling of the feature as an outlier.

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A complex and complicated forecast for much of Texas and Oklahoma is unfolding this morning regarding the timing of the arrival of the much talked about Arctic front and what we may see weather wise into the weekend extending into early Tuesday.

Currently surface observations suggest the Arctic boundary is moving faster than previously though and is running a good 12-18 hours faster than was expected. As is usually the case with a very dense and cold air mass, this is not too surprising that the computer model would under estimate the speed. First things first…showers are moving N to NE from the Gulf and that should continue today and increase in coverage across the Region and we should begin to see some storms develop to our NW across Oklahoma and N Texas later tonight. A line of showers and storms will sweep S during the overnight hours tonight ushering in the arrival of the coldest air of the season on Friday.

Wintry Weather Advisories have been issued across Oklahom/Kansas and will likely be needed later today across the Panhandle and further S into the Permian Basin and the Big Country near Midland/Odessa. There is a chance that Winter Weather Advisories or even a Winter Storm Watch will be hoisted for the Dallas/Ft Worth area as freezing temps at the surface and over running precip begins to fall leading to an ice threat mainly on elevated surfaces by Friday afternoon into the evening hours.

We may see a brief break from the over running precip as the much talked about upper air cold core close low develops in Southern California. This feature is expected to deepen rather rapidly and there are some strong indications that this low will be near the 3 standard deviation below normal for late November standards making it a strong storm system that we usually do not see this time of year. Abundant tropical moisture from the Pacific will wrap up this storm system and indications are that it will be a bit further E over Arizona bringing flooding rains to the Phoenix area and heavy higher elevation snow to Eastern AZ into New Mexico.

This storm system appears to stay rather strong and remain a closed low as it cross New Mexico on Saturday and moves E into Texas on Sunday. The current projected storm track appears to be just S of Lubbock to near Austin and then very close to SE Texas during the morning hours of Monday. The latest run of the 06Z GFS brings this upper air feature very close to Bryan/College Station and Montgomery County, so it will be worth monitoring. There still remains relative good agreement that a Coastal Low will develop along the Middle Texas Coast on Sunday and slide NE toward Lake Charles on Monday into Tuesday. Currently the latest HPC/WPC Day 3 Outlook does suggest an icing potential for portions of Central and E Texas. Temperature profiles at the surface continue to drop with each run of the computer models, but warmer air above the shallow dense cold air at the surface do not support snow. What we may see is a chance of sleet as the cold air layer deepens a bit to about 3000 ft. Areas near Dallas may see heavy sleet thus warranting a Winter Storm Watch. Temps across SE Texas are expected to drop into the mid 30’s or very close to freezing Sunday night into Monday morning. Regardless, it is going to feel very cold with brisk N to NE winds and very chilly rain at the least.

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
342 AM EST THU NOV 21 2013

VALID 12Z THU NOV 21 2013 - 12Z SUN NOV 24 2013


...DAY 1 ...

...NORTHERN TO CENTRAL ROCKIES/ADJACENT HIGH PLAINS...

SNOW WILL CONTINUE TO SETTLE SOUTH OVER THE CENTRAL ROCKIES AND
ADJACENT PORTIONS OF THE WESTERN HIGH PLAINS TODAY AND TONIGHT AS
ARCTIC HIGH PRESSURE TO THE NORTH FORCES THE BEST BAROCLINICITY
SOUTH. STRONG UPPER DIVERGENCE AFFORDED BY RIGHT-ENTRANCE REGION
DYNAMICS ALONG WITH STRENGTHENING UPSLOPE FLOW AND LOW-MID LEVEL
FRONTOGENESIS SHOULD LEAD TO INCREASING SNOWS ACROSS THE FAVORED
TERRAIN OF WESTERN WY WHICH THEN SAGS SOUTH AND EAST. LIGHTER
AMOUNTS ARE EXPECTED TO EXTEND INTO THE NORTHERN-CENTRAL HIGH
PLAINS WHERE THE THERMAL PROFILES ARE FORECAST TO SUPPORT
SNOW...BUT ASCENT WILL BE WEAK AND SHORT-LIVED.

THE POTENTIAL FOR FREEZING RAIN DEVELOPS OVER PARTS OF KS/OK LATE
IN THE PERIOD...WITH ENOUGH POTENTIAL TO WARRANT A SLIGHT RISK.

...CENTRAL SIERRA NEVADA INTO THE GREAT BASIN...

AN AREA OF PRECIPITATION OUT AHEAD OF A DEVELOPING MID LEVEL TROF
WILL BRING SNOW TO PORTIONS OF THE CENTRAL SIERRA INTO THE
MOUNTAINS OF CENTRAL NV AS THE TROF MOVES INLAND. SNOW LEVELS
SHOULD BE INITIALLY PRETTY HIGH BUT DECREASE AS HEIGHTS/THICKNESS
VALUES LOWER.

...DAYS 2 AND 3...

...SOUTHERN CA COASTAL RANGES/CENTRAL-SOUTHERN SIERRA TO THE
ROCKIES...

THE SYSTEM WHICH BEGINS TO BRING SNOW TO THE HIGHER ELEVATIONS OF
THE CENTRAL SIERRA WILL CONTINUE DIGGING SOUTH LATE THU INTO
FRI...CLOSING OFF A DEEP CENTER THAT IS FORECAST TO SPIN SOUTH TO
THE COAST OF SOUTHERN CA. THIS WILL BRING SNOWS FURTHER TO THE
SOUTH THROUGH THE SIERRA. SNOWS WILL CONTINUE TO MOVE SOUTH ALONG
THE WASATCH AND DEVELOP ALONG THE MOGOLLON RIM OF NORTHERN AZ AS
WELL. THE HEAVIEST OF THE ACCUMULATIONS OF THE PERIOD HOWEVER ARE
EXPECTED ALONG THE SAN JUANS WHERE A MODERATE RISK AND EVEN A
SMALL HIGH RISK FOR A FOOT OR MORE IS INDICATED IN THE DAY 2
OUTLOOK. AN UPPER JET COUPLET...LOW-MID LEVEL FRONTOGENESIS AND
OROGRAPHIC EFFECTS ARE EXPECTED TO ALL CONTRIBUTE TO THE HEAVY
SNOW THREAT ACROSS THIS REGION.

MEANWHILE FURTHER TO THE EAST...A SHALLOW ARCTIC AIR IS FORECAST
TO UNDERCUT MOIST SOUTHERLY FLOW ALOFT. WHILE WIDESPREAD
ACCUMULATIONS OF GREATER THAN A QUARTER-INCH STILL APPEAR
UNLIKELY...THERE IS STILL ENSEMBLE AND NOW SOME OPERATIONAL
GUIDANCE TO SUPPORT THE POSSIBILITY OF ENOUGH PRECIPITATION
OCCURRING AT THIS TIME IN WHICH TO WARRANT SPOTTY AREAS OF ICING
CONCERNS...PARTICULARLY FROM THE TX PANHANDLE EASTWARD INTO
PORTIONS OF CENTRAL AND EASTERN TX
INTO EASTERN KS.


WPC PROBABILITIES GAVE MORE WEIGHT TO THE ECMWF/GFS THROUGH THE
PERIOD...DISCOUNTING THE NAM WHICH MOVED TO THE MORE PROGRESSIVE
SIDE OF THE GUIDANCE WITH RESPECT TO THE DEVELOPING UPPER LOW.

BANN

 

 

 

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Forecast update from Meteorologist Jeff L (Harris County Flood Control District:

 

 

Major changes coming in the next 24 hours as a powerful cold front sweeps across the state.

 

Today-early Friday:

 

Warm and moist onshore flow off the Gulf will provide an increasing chance of showers and thunderstorms today-Friday. Temperatures will be in the humid 70’s for most of the entire period. Waves of showers will move inland off the Gulf of Mexico and northward across the area as moisture deepens ahead of a strong cold front on Friday. This will be the last warm day for a while!

 

Starting to push dewpoints over the near shore water temperatures so expect areas of dense sea fog to begin to form today and especially tonight as onshore winds weaken and persist until the front crosses the area on Friday.

 

Friday-Saturday:

 

Powerful polar cold front roars across the state bringing much colder weather. Dense shallow air mass should arrive across our NW counties near sunrise Friday and be off the coast by early afternoon. High temperatures will occur prior to the frontal passage in the upper 70’s and then plummet into the 40’s and 50’s behind the front. SE winds of 10mph will shift to the north and increase to 20-30mph behind the front. Strong frontal lifting and a moist air mass will support widespread shower and thunderstorm development along the boundary. Shallow nature of the dense cold air will result in continued warm Gulf air mass being lifted up and over the frontal surface across the entire into Saturday with widespread periods of light to moderate rainfall continuing into Saturday. Temperatures on Saturday will hold nearly steady in the low to mid 40’s with gusty N winds. Rainfall amounts Friday-Saturday will average .5 to 1.5 inches.

 

Saturday night-Sunday night:

 

Winter Storm heads for TX

 

Strong upper level storm system over the SW US begins to move eastward toward TX with a firm cold air mass in place. Expect dry but cloudy conditions across SE TX most of Sunday as the cold dome deepens. Strong upper level system approaching from the west will result in the forcing of surface low pressure off the lower TX coast which will begin to swing moisture back over the surface cold dome. Expect to see increasing light rainfall by Sunday evening west and north of SE TX. Highs Sunday will hold in the 40’s.

While forecast soundings show a warm nose, it appears that enough dry air in the mid to surface layer may result in enough cooling to onset precipitation as sleet from near Fort Worth along and west of I-35 to NW of San Antonio. Surface temperatures in this region will be just above freezing, but could drop to freezing allowing some accumulation of sleet/ice Sunday night into Monday morning west of I-35. This area is being monitored for the issuance of a Winter Storm Watch.

Locally, looking at forecast soundings at both CLL and UTS for Monday morning suggest dewpoints in the upper 20’s at the surface and surface temperatures in the mid 30’s. This would suggest a brief window for some evaporative cooling from College Station to Lufkin at the onset of light rain Sunday night. Such setups in the past have resulted in P-type of sleet or rain/sleet mix at the onset of the precipitation and this is a possibility. With surface temperatures expected to be above freezing and the ground still very warm do not expect any accumulation over our area.

 

Monday-Tuesday:

 

Winter storm pushes across TX with accumulating ice/sleet possible over W/NW/N TX and portions of the Hill Country. Southward surface low will move NE along the TX coast resulting in widespread cold rain and windy conditions. Expect rain to develop from SW to NE early Monday as warm Gulf air is lifted over the cold air locked in at the surface. Surface winds will increase out of the ENE on Monday and tide levels will begin to rise along the coast as winds increase. Surface low should progress across our coastal waters early Tuesday resulting in peak winds late Monday night and greatest rainfall potential Monday afternoon and evening. Highs Monday will again be locked in the 40’s. Surface low moving east of the area on Tuesday will likely end rain chances and shift winds around to the NW keeping the cold air in place. Highs Tuesday may stay in the 40’s also…but could reach the lower 50’s depending on if any sun breaks through late in the day.

 

Thanksgiving Outlook:

 

TX should lie between storm systems, but cold air will remain in place across the state. Lows in the 30’s on Thursday with highs in the 50’s under partly cloudy to mostly cloudy skies. GFS continues to show a shallow moist layer trapped in the frontal inversion both Wednesday and Thursday which may keep low clouds locked in place and highs colder than the 50’s. Looks like the cold finally begins to modify in about a week or the Friday after Thanksgiving.

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Grand Forks International Airport picked up an inch of snow last night with the NWS office reporting .8 of an inch. Further N and W of here some places saw between 3.5 and 5.0 inches last night. The models did a pretty darn good job of depicting the placement of the strongest band.

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The front just passed through Oklahoma City in the past hour.  It was 68 F when I left for lunch at about 12:15 pm.  It was 55 F with a howling north wind less than an hour later. 

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Looks like we are getting some minor icing in NW OK already, with a lot of the Mesonet anemometers not reporting:

 

current.gustarrows.gif

 

Gage, OK:

KGAG 212053Z AUTO 35014KT 4SM BR OVC007 M02/M03 A3024 RMK AO2 PK WND 35027/2033 SLP245 60000 T10171028 51023

 

Woodward, OK:

KWWR 212055Z AUTO 34014G19KT 4SM BR OVC005 00/M01 A3026 RMK AO2

 

Alva, OK:

KAVK 212050Z AUTO 36017G24KT 2SM -RA OVC006 00/M01 A3024 RMK AO2

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The front just passed through Oklahoma City in the past hour.  It was 68 F when I left for lunch at about 12:15 pm.  It was 55 F with a howling north wind less than an hour later. 

 

...and as of about 15 minutes ago (3 pm observation), OKC was reporting 43 F with a dewpoint of 39 F.  That, my friends, is a cold front.   

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SJT issues Winter Storm Watch while MAF issues Winter Weather Advisory.

 

Edit to add LUB to WSW list.

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...and as of about 15 minutes ago (3 pm observation), OKC was reporting 43 F with a dewpoint of 39 F.  That, my friends, is a cold front.   

 

Yeah, officially a 23 F drop in two hours at the Mesonet here, almost completely owing to advection (no precipitation and little change in cloud cover over that period).

 

Gusts of 40-50 mph becoming common over W OK, with 53 mph at slightly-elevated Medicine Park. Good day to hibernate.

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Yeah, officially a 23 F drop in two hours at the Mesonet here, almost completely owing to advection (no precipitation and little change in cloud cover over that period).

 

Gusts of 40-50 mph becoming common over W OK, with 53 mph at slightly-elevated Medicine Park. Good day to hibernate.

 

As of the 4 pm observations, Wiley Post is down to 37 F (with a dewpoint of 34 F) and OKC is down to 40 F (with a dewpoint of 36 F).  At this rate, the metro (especially the north side) might be below freezing before this evening is too far along.  I am assuming the evening rush hour will be okay, but I am not so sure we will stay above freezing much longer after that.  If we actually get anything falling from the sky heavier than a mist, those temps are going to get down to freezing darn quickly.    

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