Severe Weather Risk 12/25-12/26

[ICEHOCEY77]

DAY 4-8 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0358 AM CST FRI DEC 21 2012 VALID 241200Z - 291200Z ...DISCUSSION... THE MEDIUM RANGE MODELS BEGIN THE DAY 4 TO 8 PERIOD WITH AN UPPER-LEVEL TROUGH MOVING FROM THE FOUR CORNERS REGION ON MONDAY/DAY 4 TO THE GREAT PLAINS ON TUESDAY/DAY 5. THE ECMWF AND GFS HAVE SIMILAR TIMING AND CLOSE-OFF THE SYSTEM OVER THE ARKLATEX ON TUESDAY. AS THIS OCCURS...THE MODELS STRENGTHEN A PRONOUNCED LOW-LEVEL JET AND BRING MOISTURE NWD INTO THE LOWER MS VALLEY TUESDAY AFTERNOON WHERE A THREAT FOR STRONG THUNDERSTORMS COULD DEVELOP. IF MORE MOISTURE CAN RETURN NWD INTO THE LOWER MS VALLEY ON TUESDAY THAN IS CURRENTLY FORECAST...A SUBSTANTIAL SEVERE THREAT COULD DEVELOP TUESDAY AFTERNOON. THE SEVERE THREAT COULD PERSIST EWD ACROSS THE GULF COAST STATES FROM TUESDAY NIGHT INTO WEDNESDAY AS THE SYSTEM PROGRESSES ACROSS THE REGION. AT THIS POINT...WILL NOT ISSUE AN ENHANCED SEVERE THREAT MAINLY DUE TO UNCERTAINTIES CONCERNING MOISTURE RETURN AND DIFFERENCES IN MODEL SOLUTIONS.

The models are trending along the I-20/I-85 corridor with some pretty incredible winds

Cape will obviously be limited, but the GFS is picking up some 500 J/KG.

[metalicwx366]

Does this threat include S GA and N Fl?

[Brick Tamland]

I'm dreaming of a windy Christmas...

[buckeyefan1]

Does this threat include S GA and N Fl?

Yes...anywhere from se TX and points east.

[deltadog03]

EURO would certainly be a potential NASTY setup for some in the SE for the Christmas storm

[metalicwx366]

..DISCUSSION...

THE MEDIUM RANGE MODELS MOVE A PROGRESSIVE UPPER-LEVEL TROUGH

QUICKLY ESEWD ACROSS THE ROCKIES MONDAY NIGHT AND INTO THE SRN

PLAINS ON TUESDAY/DAY 4. STRONG LARGE-SCALE ASCENT AND MOISTURE

RETURN AHEAD OF THE SYSTEM WILL ALLOW SCATTERED TO NUMEROUS

THUNDERSTORMS TO DEVELOP ACROSS THE TX COASTAL PLAINS AND IN THE

LOWER MS VALLEY FROM LATE MONDAY NIGHT INTO TUESDAY. AS THE EXIT

REGION OF A POWERFUL MID-LEVEL JET NOSES INTO THE LOWER MS

VALLEY...SEVERE STORMS WILL BE POSSIBLE DUE TO STRONG DEEP LAYER

SHEAR AND WIDESPREAD ASCENT. THE PROGRESSIVE NATURE OF THE SYSTEM

MAY ENABLE A SQUALL-LINE TO ORGANIZE AND QUICKLY MOVE EWD ACROSS THE

LOWER MS VALLEY ON TUESDAY AND INTO THE CNTRL GULF COAST STATES. IT

APPEARS THAT A SUBSTANTIAL SEVERE WEATHER THREAT WILL BE POSSIBLE ON

TUESDAY AND TUESDAY NIGHT ACROSS A BROAD CORRIDOR FROM SE TX

EXTENDING ENEWD ACROSS LA...MS ...AL AND INTO THE FL PANHANDLE.

AS THIS SYSTEM CONTINUES TO MOVE ENEWD INTO THE CAROLINAS ON

WEDNESDAY/DAY 5...A SEVERE THREAT WILL CONTINUE TO BE POSSIBLE. AN

ENHANCED SEVERE THREAT COULD OCCUR IF A LINEAR MCS OR A CLUSTER OF

SEVERE STORMS MOVES INTO THE REGION FROM THE WEST LATE TUESDAY

NIGHT. AT THIS POINT...WILL NOT ISSUE AN OUTLOOK AREA FOR THE

CAROLINAS UNTIL CONFIDENCE IS A BIT GREATER CONCERNING THE TIMING OF

THE UPPER-LEVEL TROUGH. BY LATE IN THE DAY 4 TO 8 PERIOD...THE

MODELS MOVE ANOTHER UPPER-LEVEL TROUGH INTO THE CNTRL U.S. THIS

COULD BE FAVORABLE FOR STRONG THUNDERSTORMS IN THE LOWER TO MID MS

VALLEY AGAIN ON FRIDAY/DAY 7 BUT MUCH UNCERTAINTY EXISTS AT THIS

RANGE.

[ICEHOCEY77]

12Z NAM is picking up EHI above 1! But compared to the GFS, it's wind fields are coming in a tad bit less strong.

vs.

[andyhb]

We have a thread in the main forum for this, since it may impact areas through Southern TX/LA as well...

http://www.americanwx.com/bb/index.php/topic/38454-major-national-winter-storm-dec-25-28/#entry1938146

[NavarreDon]

Link to MOB SWS:

http://forecast.weat...on=1&glossary=0

Morning AFD also:

[CHRISTMAS DAY]...

...SIGNIFICANT INCREASE IN SEVERE WEATHER WILL OCCUR FROM EARLY

CHRISTMAS MORNING THROUGH THE EVENING HOURS...

AN EXTREMELY POWERFUL UPPER LEVEL SHORTWAVE OVER NORTH TEXAS IN THE

MORNING WILL MOVE VERY QUICKLY TOWARD EAST THEN NORTHEAST...REACHING

WESTERN TENNESSEE BY MIDNIGHT. AN 80 TO 100 KNOT JET STREAK AT 500

MB WILL ACCOMPANY THIS SYSTEM...BUT MORE IMPRESSIVELY IS THE 50 TO

55 KNOT JET MAX AT 850 MB THAT WILL EXTEND FROM NEW ORLEANS TO

BIRMINGHAM BY LATE IN THE AFTERNOON.

AT THE SURFACE...A VERY STRONG SURFACE LOW CENTERED ACROSS TEXAS

WILL MOVE QUICKLY EAST-NORTHEAST OVER NORTHERN MISSISSIPPI BY LATE

AFTERNOON AND DEEPEN TO 998 MB...PLACING THE ENTIRE FORECAST AREA

WELL WITHIN THE WARM SECTOR. PLENTY OF MOISTURE WILL BE AVAILABLE TO

FEED INTO THE SYSTEM WITH 850 MB DEWPOINTS RANGING FROM 8C TO 11C

AND SURFACE DEWPOINTS IN THE LOWER 60S F ACROSS THE FORECAST AREA.

ATTENDANT STRONG COLD FRONT APPROACHING FROM THE WEST WILL REACH THE

MISSISSIPPI RIVER BY LATE AFTERNOON AND THEN QUICKLY SWEEP THROUGH

THE FORECAST AREA FROM MID EVENING THROUGH JUST AFTER MIDNIGHT.

CHRISTMAS DAY LOOKS TO HAVE ALL THE INDICATIONS OF A CLASSIC SEVERE

WEATHER EVENT SETTING UP. UNLIKE THE LAST EVENT WHICH EXHIBITED LOW

TOPPED / LOW LIGHTNING CONVECTION...THIS EVENT IS MORE CONDUCIVE TO

DEEP CONVECTION AS 500-300 MB LAPSE RATES WILL BE NEAR 8 C/KM AND

MUCAPES APPROACH 1600 J/KG. WE ARE EXPECTING A DUAL THREAT WITH

SUPERCELLS IMPACTING THE AREA DURING THE DAY AHEAD OF AN AREA OF LOW

PRESSURE AND COLD FRONT...AND THEN WITH BOWING RADAR STRUCTURES/LINE

ECHO WAVE PATTERNS IMPACTING THE AREA DURING THE EVENING ALONG AND

AHEAD OF THE COLD FRONT.

BRN INDICES GREATER THAN 10 AND SFC-3 KM STORM RELATIVE HELICITY

BETWEEN 300 AND 400 M^2/S^2 SUGGEST THAT SUPERCELLS ARE FAVORABLE.

IN ADDITION...MOST OF THIS HELICITY RESIDES IN THE SFC-1 KM LAYER

AND EHI VALUES ACROSS THE FORECAST WILL BE BETWEEN 1 (ONE) AND 3

(THREE)...SUGGESTING THE FORMATION OF STRONG CONVECTIVE SUPERCELLS

WITH EF-2 AND EF-3 TORNADOES POSSIBLE.

WITH THE DECREASED STABILITY...CLOUD TOPS ARE NOW PROJECTED TO BE

NEAR 50000 FEET AND MAXIMUM VERTICAL VELOCITIES NEAR 50 M/S. WITH

THIS...AND THE FACT THAT THE MODELS ARE NOW BRINGING A LAYER OF DRY

AIR INTO THE MID LEVELS...INDICATE THAT LARGE HAIL THROUGHOUT THE

DAY IS POSSIBLE WITH THE STRONGEST OF STORMS.

DUE TO EXTREMELY STRONG DEEP LAYER WINDS RESULTING IN STORMS MOVING

TOWARD THE NORTHEAST AT 50 TO 60 MPH...ANY STORMS DEVELOPING IN THIS

ENVIRONMENT HAVE A FAVORABLE CHANCE OF DAMAGING WINDS. ANY SEVERE

WEATHER THREATS WILL LIKELY HAPPEN VERY QUICKLY IF A WARNING IS

ISSUED UPSTREAM FROM YOU. DO NOT VENTURE OUTSIDE OR WAIT FOR A

THREAT TO APPEAR IMMINENT BEFORE TAKING ACTION. STAY TUNED TO

FURTHER DEVELOPMENTS AND INFORMATION AS THEY BECOME AVAILABLE.

HIGH TEMPERATURES MONDAY AND TUESDAY WILL RANGE FROM 68 TO 73

DEGREES. LOW TEMPERATURES MONDAY NIGHT WILL ONLY FALL INTO THE UPPER

50S NORTH TO MID 60S ALONG THE COAST. COOLER OVERNIGHT LOWS BEHIND

THE FRONT ARE EXPECTED TUESDAY NIGHT...FALLING INTO THE UPPER 30S TO

LOWER 40S NORTHWEST OF I-65...WITH MID 40 TO LOWER 50S TO THE

SOUTHEAST. /22

[deltadog03]

12z NAM Severe parameters look very strong for MS/AL/FL and a little bit weaker (LI and Cape) in GA....BUT MORE than adequate in GA for severe. SC would have some as well.

[buckeyefan1]

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0229 AM CST SUN DEC 23 2012

VALID 251200Z - 261200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN

PLAINS...LOWER MS VALLEY AND CNTRL GULF COAST STATES...

...GULF COAST STATES...

AN IMPRESSIVE UPPER-LEVEL SYSTEM IS FORECAST TO MOVE EWD INTO THE

SRN PLAINS EARLY TUESDAY MORNING AS THE EXIT REGION OF A POWERFUL

MID-LEVEL JET MOVES INTO THE GULF COAST STATES. AHEAD OF THE

SYSTEM...MOISTURE IS FORECAST TO RETURN NWD INTO THE LOWER MS VALLEY

AND CNTRL GULF COAST STATES WITH MODERATE INSTABILITY DEVELOPING

ACROSS THE SRN AND WRN PART OF THE SLIGHT RISK AREA EARLY IN THE DAY

ON TUESDAY. A CLUSTER OF THUNDERSTORMS OR SQUALL-LINE MAY BE ALREADY

DEVELOPED BY DAYBREAK ON TUESDAY ACROSS EAST TX WITH ADDITIONAL

STORMS POSSIBLY ONGOING ACROSS THE LOWER MS VALLEY. MODEL FORECASTS

INCREASE CONVECTIVE COVERAGE ACROSS THE LOWER MS VALLEY AND APPEAR

TO MOVE A WELL-DEVELOPED MCS EWD ACROSS THE REGION DURING THE DAY.

FORECAST SOUNDINGS AT MIDDAY TUESDAY IN THE LOWER MS VALLEY DEVELOP

AN IMPRESSIVE SHEAR ENVIRONMENT AS THE MID-LEVEL JET APPROACHES THE

REGION FROM THE WEST. NAM FORECAST SOUNDINGS VALID TUESDAY AT 21Z

JUST SOUTHWEST OF JACKSON MS SHOW MLCAPE VALUES AROUND 1500 J/KG

WITH ABOUT 60 KT OF DEEP LAYER SHEAR. THIS COMBINED WITH 0-3 KM

STORM RELATIVE HELICITIES AROUND 400 M2/S2 COULD BE FAVORABLE FOR

SUPERCELLS AND TORNADOES. IF MANY CELLS CAN REMAIN DISCRETE...THEN

CONDITIONS COULD ALSO BE FAVORABLE FOR STRONG TORNADOES AS THE

LOW-LEVEL JET MOVES EWD ACROSS THE CNTRL GULF COAST STATES FROM

TUESDAY MORNING INTO THE AFTERNOON. AT THIS POINT...THE POTENTIAL

FOR WIDESPREAD WIND DAMAGE APPEARS JUST AS VIABLE. THE MAGNITUDE OF

THESE THREATS MAY DEPEND UPON THE DOMINANT STORM MODE. IF THE

FAVORED MODE ENDS UP BEING LINEAR...THEN WIND DAMAGE COULD BE THE

GREATER THREAT.

FORECAST SOUNDINGS ACROSS THE LOWER MS VALLEY AND CNTRL GULF COAST

STATES TUESDAY INTO TUESDAY NIGHT SHOW POTENTIAL FOR A SUBSTANTIAL

SEVERE WEATHER EVENT. THE COMBINATION OF SHEAR AND INSTABILITY

COMBINED WITH A POTENT WEATHER SYSTEM SUGGESTS A 30 PERCENT

PROBABILITY AND SIGNIFICANT SEVERE HATCHED AREA ARE WARRANTED. THE

SEVERE THREAT SHOULD CONTINUE INTO TUESDAY EVENING AND POSSIBLY INTO

THE OVERNIGHT PERIOD AS THE UPPER-LEVEL TROUGH MOVES QUICKLY EWD

ACROSS THE GULF COAST STATES.

..BROYLES.. 12/23/2012

[audioguy3107]

Waiting for SPCs update this afternoon, but the last update mentions some potentially ominous things

NAM FORECAST SOUNDINGS VALID TUESDAY AT 21Z JUST SOUTHWEST OF JACKSON MS SHOW MLCAPE VALUES AROUND 1500 J/KG WITH ABOUT 60 KT OF DEEP LAYER SHEAR. THIS COMBINED WITH 0-3 K STORM RELATIVE HELICITIES AROUND 400 M2/S2 COULD BE FAVORABLE FOR SUPERCELLS AND TORNADOES. IF MANY CELLS CAN REMAIN DISCRETE...THEN CONDITIONS COULD ALSO BE FAVORABLE FOR STRONG TORNADOES AS THE LOW-LEVEL JET MOVES EWD ACROSS THE CNTRL GULF COAST STATES FROM TUESDAY MORNING INTO THE AFTERNOON.

Looks like the worst will potentially be south of I-20, but if things keep going this way and some of the CAPE values are realized, we could have a Christmas day moderate risk on our hands. Wonder if that's ever happened before?

[CandymanColumbusGA]

Here's the sounding for Columbus, GA Christmas Night. We've got great shear with a strengthening 850mb jet set to move in with the storms (925 mb for next time frame is above 50 kts.... :/) There's a bit of mid-level dry air attempting to work in after the warm front lifts which could lead to stronger storms and the potential for hail. Even though it won't be as bad in GA as MS, at least that's my current thinking, we could still be in for a long night with winds, hail and an isolated tornado along a squall line. As AudioGuy said... A moderate risk is possible Christmas Day. It could be bad news for those in LA/MS/AL/FL as these storms get going Christmas morning and afternoon while many people are opening presents and may not have the TVs on. Heck, if we see some sunshine in between the warm front lifting north and sunset... Those in eastern Alabama and western Georgia could be looking at potentially stronger storms than currently thought Christmas night.

[SquatchinNY]

This will be my first severe weather outbreak with Radarscope, and I may pick up GR3 as well.

[Shawn]

This will be my first severe weather outbreak with Radarscope, and I may pick up GR3 as well.

GR3 is wonderful. You can use it free for the event if you've never installed it. GR2AE is great to see storm structure also. I aslo recommend a free website called simuawips (google it) it's a web based version of AWIPS that NOAA uses but with far less features currently; that you may like better than Radarscope.

[SquatchinNY]

GR3 is wonderful. You can use it free for the event if you've never installed it. GR2AE is great to see storm structure also. I aslo recommend a free website called simuawips (google it) it's a web based version of AWIPS that NOAA uses but with far less features currently; that you may like better than Radarscope.

That looks cool! Thank you so much!

[ICEHOCEY77]

Don't see that very often in December.

[SquatchinNY]

Don't see that very often in December.

Wow!

Latest NAM

[Disc]

Don't see that very often in December.

The ingredients for this was lowered, thus making it easier to attain higher readings. Seeing a large area of 50 showing up is still telling regardless.

[MichaelJ]

We are a little too far North for severe weather here and I am thankful for that. Not a good sign for the SE when it is almost the first of a new year and we are dealing with thunderstorms instead of wintry weather.

[Disc]

We are a little too far North for severe weather here and I am thankful for that. Not a good sign for the SE when it is almost the first of a new year and we are dealing with thunderstorms instead of wintry weather.

Yeah, you're probably too far N and E in NC to see much severe weather, but some parameters through central and E NC already look potentially bad for the 26-27 timeframe. Some large curved hodos from that area already showing up.

[ICEHOCEY77]

0z NAM is out. First time I've seen an EHI of 3 for the storm.

[Disc]

0z NAM is out. First time I've seen an EHI of 3 for the storm.

FWIW, newest SREF sigtor has a much larger 50 area showing up now than previous runs.

[brettjrob]

The hodographs across much of AL/MS after dark are completely off the hook, almost reminiscent of 2011-04-27. Instability, of course, is quite marginal as progged by the global and regional models at this stage. In particular, even despite rather small CAPE values, the EL is relatively high (for December) which equates to ultra-skinny CAPE. Progged H5 LI values are well above -4 C except along the immediate Gulf Coast. Overall, I don't have much hope of seeing sig svr here in the HSV area where I'm staying for the holidays, but it should be mighty interesting near the I-10 corridor. The 24/00z NAM has trended slower, too, favoring LA and even far E TX before sunset on Christmas Day.

[calculus1]

0z NAM is out. First time I've seen an EHI of 3 for the storm.

OK, I don't usually get too active in the severe threads because I don't know all the lingo too well. Plus, tornadoes don't happen that often in western NC. All that being said, I'd still like to understand what I'm reading here. Can you (or anyone else who wants to chime in) explain what I'm looking at in this map you just posted? What is EHI? What are the implications of a grade of 3? What is the scale for this measurement? Apparently, it's bad news (or good news, depending on how you look at it) implying really severe storms.

[Disc]

OK, I don't usually get too active in the severe threads because I don't know all the lingo too well. Plus, tornadoes don't happen that often in western NC. All that being said, I'd still like to understand what I'm reading here. Can you (or anyone else who wants to chime in) explain what I'm looking at in this map you just posted? What is EHI? What are the implications of a grade of 3? What is the scale for this measurement? Apparently, it's bad news (or good news, depending on how you look at it) implying really severe storms.

This link may help: http://www.theweatherprediction.com/habyhints/314/

[calculus1]

This link may help: http://www.theweathe.../habyhints/314/

Thanks! So, with an EHI of 3, there's a pretty decent chance of a few tornadoes of significance, I take it.

[Disc]

A couple of hodos from various areas in the SE:

Alexandria, LA:

Natchez, MS:

[Disc]

Thanks! So, with an EHI of 3, there's a pretty decent chance of a few tornadoes of significance, I take it.

Yes, there is a possibility of several strong tornadoes locally with EHI pushing 3-5, but it's just one ingredient of severe weather people look at to determine where you will be more likely to see tornadic supercells.

[ICEHOCEY77]

A couple of hodos from various areas in the SE:

Alexandria, LA:

Natchez, MS:

Wow, that's incredible.