Post-Christmas severe weather outbreak?

[CrazyC83]

The SPC seems to think so on December 26 and 27:

ZCZC SPCSWOD48 ALL
ACUS48 KWNS 221013
SPC AC 221013

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0413 AM CST MON DEC 22 2008

VALID 251200Z - 301200Z

...DISCUSSION...
PRIMARY FOCUS OF THIS OUTLOOK WILL BE ON POST-CHRISTMAS WEEKEND
SEVERE POTENTIAL...AS 00Z ECMWF AND 00Z GFS/GEFS REMAIN IN
RELATIVELY GOOD GENERAL AGREEMENT WITH THE OVERALL PATTERN INTO THE
WEEKEND. GIVEN THIS MODEL CONSENSUS...IT SEEMS INCREASINGLY LIKELY
THAT A CONSIDERABLE UPPER TROUGH WILL DEEPEN/SPREAD EASTWARD ACROSS
THE ROCKIES/CENTRAL STATES THROUGH DAY 5 FRIDAY. WHILE INHERENT
VARIABILITY REMAINS IN THE LARGE SCALE DETAILS...AND SOME CONCERN
EXISTS REGARDING THE NEUTRAL/SLIGHTLY POSITIVE TILT OF THE UPPER
TROUGH AND ITS LATE NIGHT ARRIVAL...OF NOTE WILL BE THE POTENTIAL
FOR GREATER MOISTURE AVAILABILITY AS COMPARED TO THE PREVIOUS EARLY
WEEK SYSTEM. THUS...CURRENT THINKING IS THAT AN APPRECIABLE SEVERE
RISK MAY MATERIALIZE ACROSS PORTIONS OF THE ARKLATEX/MID-SOUTH AND
LOWER/MIDDLE MISSISSIPPI VALLEY FOR DAY 5/FRIDAY INTO DAY
6/SATURDAY. WILL OUTLOOK DAY 5/FRIDAY FOR PRESUMED EVENING/NIGHTTIME
SEVERE POTENTIAL...WITH SUBSEQUENT OUTLOOKS BETTER ABLE TO
EVALUATE/DELINEATE THE POSSIBLE SEVERE RISK INTO DAY 6/SATURDAY.

..GUYER.. 12/22/2008

[Ed Mahmoud]

My "No Intelligence Needed" quicklook of the Euro's 850 mb LLJ being colorful and 500 mb flow at and angle and somewhat divergent says sort of yes for Thursday and a big yes for Friday severe.



Big area of 50 knot 850 mb winds.

[CrazyC83]

Looks like 2008 will end the way it began. If we can have a major outbreak on January 7, we can also have one on December 26.

[Ed Mahmoud]

Looking at 12Z GFS, Eastern Oklahoma and Arkansas look like potential hotspots.





Look at GFS forecast sounding for Fort Smith Friday late afternoon. Not super-impressive instability, but enough for t-storms, and strong low level winds. Not quite enough directional shear to be mother of all tornado outbreaks kind of bad, but impressive anyway.

[CrazyC83]

This looks bad now:

ZCZC SPCSWOD48 ALL
ACUS48 KWNS 231000
SPC AC 231000

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0400 AM CST TUE DEC 23 2008

VALID 261200Z - 311200Z

...DISCUSSION...
PRIMARY FOCUS OF THIS OUTLOOK REMAINS THE POST-CHRISTMAS WEEKEND
SEVERE POTENTIAL...SPECIFICALLY DAYS 4/5 FRIDAY INTO SATURDAY. THE
MOST RECENT 00Z ECMWF HAS TRENDED TOWARD A SLOWER CENTRAL STATES
TROUGH SOLUTION IN CONCERT WITH THE 00Z UKMET...SLOWER THAN THE
PREVIOUS 12Z ECMWF AND MOST RECENT 00Z GFS/GEFS GUIDANCE. IN
COLLABORATION WITH HPC...WILL LEAN TOWARD THIS TREND OF A MORE
AMPLIFIED/SLOWER UPPER TROUGH...WITH RAMIFICATIONS FOR A POTENTIALLY
MORE WIDESPREAD SEVERE RISK INTO DAY 5/SATURDAY.

SOME CONCERN DOES EXIST REGARDING THE NEUTRAL TO SLIGHTLY POSITIVE
TILT OF THE UPPER TROUGH...BUT OF NOTE IS THE LIKELIHOOD FOR A
RATHER BROAD AND ESPECIALLY MOIST PREFRONTAL WARM SECTOR FOR THE
SEASON...WITH A GENERAL CONSENSUS OF MODEL SOLUTIONS LEADING
CREDENCE TO THE POSSIBILITY OF 60 F DEWPOINTS MAKING IT AS FAR NORTH
AS THE MIDDLE MISSISSIPPI/OHIO VALLEY BY DAY 5/SATURDAY. IN
ALL...CURRENT THINKING IS THAT A MULTIFACETED/ALL HAZARDS SEVERE
RISK WILL MATERIALIZE ACROSS PORTIONS OF FAR EASTERN
OK/OZARKS/ARKLATEX TO THE MIDDLE MISSISSIPPI VALLEY/OHIO VALLEY FOR
DAY 4/FRIDAY INTO DAY 5/SATURDAY.

..GUYER.. 12/23/2008

CLICK TO GET WUUS48 PTSD48 PRODUCT

[Ed Mahmoud]

Late Friday when the outbreak could be starting, a winter severe forecasted sounding, just enough instability for thunderstorms, around 500 J/Kg, but extremely strong shear.

Western Arkansas



When the storms seem to be at their height, overnight Friday into Saturday, GFS shows almost no surface based instability at soundings just ahead of the heaviest rain, but good elevated instability as seen in total-totals aoa 50, and extremely strong and veering low level winds. I kind of wish the NIU Storm Machine Sounding Machine had 6 hour sounding increments that far out, because I suspect the 6Z soundings ahead of the intensifying surface low might look ominous.

[CrazyC83]

Something similar to January 7 of this year?

[CrazyC83]

I'm looking at models - this could be the worst December outbreak on record if some of them hold up...

[CKB 38]

any chance that could get as far north as central illinois?

[Ed Mahmoud]

any chance that could get as far north as central illinois?

Strong maybe

http://www.spc.ncep.noaa.gov/products/exper/day4-8/

[Dave]

Possible strong storms for SW, Central, Southern Indiana Friday night into Saturday

Paducah KY NWS Statement

http://forecast.weather.gov/showsigwx.php?warnzone=INZ086&warncounty=INC163&firewxzone=INZ086&local_place1=Evansville+IN&product1=Hazardous+Weather+Outlook

Louisville KY NWS Statement (very close to my area if not in it)

http://forecast.weather.gov/showsigwx.php?warnzone=KYZ030&warncounty=KYC111&firewxzone=KYZ030&local_place1=3+Miles+NNW+Louisville+KY&product1=Hazardous+Weather+Outlook

[Ed Mahmoud]

Places like Tulsa and Fort Smith may see some action, based on GFS, Friday afternoon and evening when diurnal heating is maximized, but heaviest rain and most widespread storm action is in the overnight and morning hours Saturday.
Even near peak heating, not super-high instability





Then storms seem to really fire up with heating Saturday.



Tupelo should be just ahead of the storms per GFS Saturday afternoon/evening...
Not particularly high instability, and none in the lowest 3,000 feet or so, which would limit tornado chances, but 50 knot plot winds just above the deck look favorable for damaging straight line winds.



If the GFS is correct, this quickly evolves into a potent squall line, with some tornado risk, but a more substantial straight line wind damage risk.

Disclaimer: Amateur and unofficial opinion.

[CrazyC83]

CAPE should be fairly low, but shear and helicity could be outrageous. Those are a nightmare to forecast.

[Ed Mahmoud]

No hatched areas, but with a 30% area, might get an upgrade to MODERATE when the Day 1 SWODY comes out tonight, but no mention of that in the text.

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1252 AM CST THU DEC 25 2008

VALID 261200Z - 271200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS EASTERN OK/NORTHEAST
TX/AR TO THE MIDDLE MISSISSIPPI VALLEY...

...SYNOPSIS...
A PROGRESSIVE BROAD/LONGWAVE UPPER TROUGH WILL TRANSITION EASTWARD
OVER THE ROCKIES/HIGH PLAINS ON FRIDAY. A LEAD/NORTHERN IMPULSE AND
PRIMARY SURFACE LOW WILL SPREAD NORTHEASTWARD ACROSS THE NORTHERN
PLAINS/UPPER MIDWEST...WHILE THE SOUTHERN PORTION OF THE TROUGH/JET
ALOFT ADVANCES OVER THE SOUTHERN ROCKIES/SOUTHERN HIGH PLAINS. AHEAD
OF THE APPROACHING UPPER TROUGH...AN UNSEASONABLY WARM/MOIST AIRMASS
ACROSS THE LOWER SOUTHERN PLAINS/MISSISSIPPI VALLEY WILL CONTRIBUTE
TO AN UPSWING IN TSTM/SEVERE POTENTIAL ON FRIDAY.

...EASTERN OK/NORTHEAST TX/MUCH OF AR AND SOUTHERN/EASTERN MO...
AS HEIGHT FALLS OCCUR ACROSS THE PLAINS THROUGH THE DAY...A VERY
MOIST/WARM AIRMASS FOR THE SEASON WILL CONTINUE TO ADVECT NORTHWARD
ACROSS THE ARKLATEX/MISSISSIPPI VALLEY ON FRIDAY...WITH NEAR 60F
SURFACE DEWPOINTS LIKELY TO DEVELOP AS FAR NORTH AS EASTERN
MO/SOUTHERN IL BY EVENING. AS THE SOUTHERN PORTION OF THE UPPER
TROUGH SPREADS EASTWARD...SURFACE CYCLOGENESIS WILL OCCUR ACROSS THE
SOUTH CENTRAL PLAINS...WITH AN INCREASINGLY SHARP LOW LEVEL
BAROCLINIC ZONE/MOIST AXIS BECOMING ESTABLISHED ACROSS THE
ARKLATEX/MIDDLE MISSISSIPPI VALLEY. WITH THE ARRIVAL OF LARGE SCALE
FORCING FOR ASCENT ESPECIALLY POST-SUNSET...SURFACE BASED TSTMS
SHOULD STEADILY INCREASE ACROSS THE REGION PARTICULARLY DURING THE
EVENING/OVERNIGHT HOURS...WITH INITIAL DEEP CONVECTIVE DEVELOPMENT
AND AN INCREASING SEVERE THREAT PERHAPS AS EARLY AS LATE AFTERNOON.

WITH THE PRESENCE OF A VERY MOIST AIRMASS /60-65 F SURFACE
DEWPOINTS/...PRE-SURFACE LOW/COLD FRONT SBCAPES WILL LIKELY REACH
1000-1200 J/KG BY EVENING ACROSS EASTERN OK/NORTHEAST TX/WESTERN
AR...WHILE SBCAPES WILL BE MORE ON THE ORDER OF 500-1000 J/KG ACROSS
SOUTHERN MO. A STRONGLY SHEARED ENVIRONMENT WILL FAVOR THE
DEVELOPMENT OF WELL-ORGANIZED TSTMS INCLUDING SUPERCELLS AND
LEWPS/BOWS THROUGH THE EVENING/OVERNIGHT. IN SPITE OF RATHER
FAVORABLE MOISTURE PROFILES FOR THE SEASON AND THE HIGH DEGREE OF
SHEAR/SRH...MID LEVEL LAPSE RATES WILL NOT BE PARTICULARLY STEEP
GIVEN THE ORIENTATION OF THE UPPER TROUGH...WHILE BACKING FLOW ALOFT
IS SUGGESTIVE OF A TENDENCY FOR A LINEAR CONVECTIVE MODE
OVERNIGHT/EARLY SATURDAY. NEVERTHELESS...VERY STRONG /50-65 KT/ FLOW
AROUND 1 KM WILL SUPPORT A DISTINCT RISK FOR TORNADOES THROUGH THE
EVENING/OVERNIGHT WITH ANY QUASI-DISCRETE TSTMS AND/OR LINE-EMBEDDED
CIRCULATIONS. THIS IS IN ADDITION TO AN APPRECIABLE THREAT FOR
DAMAGING WINDS AND SOME HAIL. MOST LIKELY IN THE FORM OF A BROKEN
SQUALL LINE...THE SEVERE THREAT WILL STEADILY SPREAD EASTWARD TOWARD
THE MID-SOUTH/MIDDLE MISSISSIPPI VALLEY THROUGH THE EARLY MORNING
HOURS OF SATURDAY.

..GUYER.. 12/25/2008

CLICK TO GET WUUS02 PTSDY2 PRODUCT

NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z

[CrazyC83]

I would have at least hatched it based on the wording.

[CrazyC83]

SPC AC 251731

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1131 AM CST THU DEC 25 2008

VALID 261200Z - 271200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN PLAINS
INTO AR/MO FROM MAINLY FRIDAY AFTERNOON THROUGH FRIDAY NIGHT...

...SYNOPSIS...
DEEP UPPER TROUGH LOCATED OVER THE INTERMOUNTAIN WEST AT 12Z FRIDAY
WILL PROGRESS EWD REACHING THE HIGH PLAINS LATE IN THE FORECAST
PERIOD...AS A ATTENDANT SHORT WAVE TROUGH DIGS SEWD INTO THE DESERT
SW...BEFORE TRACKING MORE EWD FRIDAY NIGHT INTO NM/SRN ROCKIES. IN
THE LOW LEVELS...A PACIFIC COLD FRONT...ACCOMPANYING THE WRN TROUGH
AND PHASED CANADIAN TROUGH...IS FORECAST TO MOVE EWD INTO THE
CENTRAL STATES DURING DAY 2. A SURFACE LOW WILL TRACK FROM THE
CENTRAL PLAINS THROUGH THE UPPER MS VALLEY TO NWRN ONTARIO WITH THE
COLD FRONT TRAILING SWWD AT 12Z SATURDAY FROM THE LOW THROUGH THE
UPPER MS VALLEY TO ERN KS/CENTRAL OK TO SW TX. A SECOND LOW IS
EXPECTED TO DEVELOP ESEWD FROM SERN CO TO CENTRAL/ERN OK BY END OF
THE FORECAST PERIOD.

...CENTRAL-ERN OK/NE TX/MUCH OF AR/SERN KS INTO CENTRAL MO...
MODELS REMAIN FAIRLY SIMILAR WITH THE EWD PROGRESSION OF THE DEEP
WRN TROUGH ON FRIDAY...BUT ARE SUGGESTING LOW LEVEL MOISTURE WILL
RETURN FARTHER WWD INTO NORTH CENTRAL TX/CENTRAL OK THAN INDICATED
BY EARLIER MODEL RUNS /SEE NAM TREND/. THIS MAY BE DUE TO A
SLIGHTLY SLOWER MOVEMENT OF THE SWRN TROUGH FRIDAY NIGHT. THIS WWD
TREND SUGGESTS INSTABILITY...THOUGH NOT OVERLY STRONG...WILL DEVELOP
FURTHER WWD. FOR THIS REASON...COMBINED WITH STRENGTHENING DEEP
LAYER SSWLY WIND FIELDS AHEAD OF THE APPROACHING WRN TROUGH WILL
RESULT IN CONDITIONS FAVORABLE FOR SEVERE STORMS/CATEGORICAL SLIGHT
RISK TO EXTEND WWD INTO CENTRAL PART OF OK AND N TX LATE FRIDAY
NIGHT/EARLY SATURDAY MORNING.

THE REST OF THE SLIGHT RISK REMAINS THE SAME AS INDICATED BY THE
INITIAL DAY 2 OUTLOOK. AS HEIGHT FALLS OCCUR ACROSS THE PLAINS
THROUGH THE DAY...A VERY MOIST/WARM AIRMASS FOR THE SEASON WILL
CONTINUE TO ADVECT NWD ACROSS THE ARKLATEX/MS VALLEY ON FRIDAY...
WITH NEAR 60F SURFACE DEWPOINTS LIKELY TO DEVELOP AS FAR NORTH AS
ERN MO/SRN IL BY EVENING. AS THE SOUTHERN PORTION OF THE UPPER
TROUGH SPREADS EASTWARD...SURFACE CYCLOGENESIS WILL OCCUR ACROSS THE
SOUTH CENTRAL PLAINS...WITH AN INCREASINGLY SHARP LOW LEVEL
BAROCLINIC ZONE/MOIST AXIS BECOMING ESTABLISHED ACROSS THE
ARKLATEX/MID MS VALLEY. WITH THE ARRIVAL OF LARGE SCALE FORCING FOR
ASCENT ESPECIALLY POST-SUNSET...SURFACE BASED TSTMS SHOULD STEADILY
INCREASE ACROSS THE REGION PARTICULARLY DURING THE EVENING/
OVERNIGHT HOURS...WITH INITIAL DEEP CONVECTIVE DEVELOPMENT AND AN
INCREASING SEVERE THREAT PERHAPS AS EARLY AS LATE AFTERNOON.

WITH THE PRESENCE OF A VERY MOIST AIRMASS /60-65 F SURFACE
DEWPOINTS/...PRE-SURFACE LOW/COLD FRONT SBCAPES WILL LIKELY REACH
1000-1200 J/KG BY EVENING ACROSS CENTRAL-ERN OK/NORTHEAST TX/WRN
AR...WHILE SBCAPES WILL BE MORE ON THE ORDER OF 500-1000 J/KG ACROSS
SRN MO. A STRONGLY SHEARED ENVIRONMENT WILL FAVOR THE
DEVELOPMENT OF WELL-ORGANIZED TSTMS INCLUDING SUPERCELLS AND
LEWPS/ BOWS THROUGH THE EVENING/OVERNIGHT. IN SPITE OF RATHER
FAVORABLE MOISTURE PROFILES FOR THE SEASON AND THE HIGH DEGREE OF
SHEAR/SRH...MID LEVEL LAPSE RATES WILL NOT BE PARTICULARLY STEEP
GIVEN THE ORIENTATION OF THE UPPER TROUGH...WHILE BACKING FLOW ALOFT
IS SUGGESTIVE OF A TENDENCY FOR A LINEAR CONVECTIVE MODE
OVERNIGHT/ EARLY SATURDAY. NEVERTHELESS...VERY STRONG /50-65 KT/
FLOW AROUND 1 KM WILL SUPPORT A DISTINCT RISK FOR TORNADOES THROUGH
THE EVENING/OVERNIGHT WITH ANY QUASI-DISCRETE TSTMS AND/OR
LINE-EMBEDDED CIRCULATIONS. THIS IS IN ADDITION TO AN APPRECIABLE
THREAT FOR DAMAGING WINDS AND SOME HAIL. MOST LIKELY IN THE FORM OF
A BROKEN SQUALL LINE...THE SEVERE THREAT WILL STEADILY SPREAD
EASTWARD TOWARD THE MID-SOUTH/MIDDLE MISSISSIPPI VALLEY THROUGH THE
EARLY MORNING HOURS OF SATURDAY.

..PETERS.. 12/25/2008

CLICK TO GET WUUS02 PTSDY2 PRODUCT

NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0700Z
CURRENT UTC TIME: 1755Z (12:55PM), RELOAD THIS PAGE TO UPDATE THE TIME

[Ed Mahmoud]

Snip from Tulsa AFD

THE LATEST SHORT/MID RANGE MODELS HAVE FINALLY BEGUN TO COME INTO
SOME BETTER AGREEMENT ON THE FRONTAL PASSAGE TIMING FOR LATE
FRIDAY NIGHT AND SATURDAY...WITH THE 18Z NAM AND 12Z GFS/ECMWF
BRINGING THE FRONT IN THE VICINITY OF A TULSA TO ARDMORE LINE BY
12Z SATURDAY. WITH THE VERY MOIST AIR AHEAD OF THE FRONT...SBCAPES
APPROACHING 1000 J/KG ARE EXPECTED TO BE IN PLACE IMMEDIATELY
ALONG AND AHEAD OF THE BOUNDARY. 130 KT UPPER JET WILL AID IN
PRODUCING 0-6KM SHEAR OF 60-70 KTS...VALUES MORE THAN SUPPORTIVE
OF SEVERE STORMS. THE FRONTAL TIMING IS STILL INDICATIVE OF A
NOCTURNAL EVENT...WITH STORMS MOST LIKELY INITIATING AFTER 06Z
SATURDAY ALONG THE COLD FRONT. THIS SHOULD RESULT IN A
LINEAR/SQUALL LINE STORM MODE WITH DAMAGING WINDS AND HAIL AS THE
PRIMARY THREAT. HOWEVER...WITH THE 60 KT LOW LEVEL JET IN PLACE
OVER EASTERN OKLAHOMA AND WESTERN ARKANSAS...0-1KM SHEARS WILL BE
VERY HIGH...INCREASING THE POSSIBILITY OF TORNADOES ON THE LEADING
EDGE OF THE SQUALL LINE. THE SEVERE THREAT IS EXPECTED TO LINGER
OVER FAR EASTERN OKLAHOMA AND WESTERN ARKANSAS THROUGH 18Z
SATURDAY. IT SHOULD BE NOTED THAT IF THE FRONT SLOWS MUCH AT ALL
FROM THE CURRENT PROJECTIONS /AS IN THE 06Z AND 12Z NAM RUNS FROM
THIS MORNING/...SEVERE WEATHER THREATS AND THE POSSIBILITY OF
DISCRETE SUPERCELLS WILL INCREASE ON SATURDAY AFTERNOON IN
NORTHWEST ARKANSAS ESPECIALLY.

[PurdueWx80]

saturday looks like the more impressive day to me, with the secondary low rapidly developing over missouri (per the 12z NAM and UKMET). the models are probably underplaying the amount of warming (and resulting instability) ahead of the front. could be tornadoes as far north as northern indiana and illinois late saturday, but more likely from the st. louis area through most of AR and LA.

even more horrifying is the amount of flooding some of these areas may see - hydromets in chicago are already talking about record flooding from the combo of rapid snow melt and torrential rain.

there will probably also be a narrow band of heavy icing and snow on the back side saturday night. this one's a biggie.

[Dave]

Hydrologic Prediction Center (HPC) forecast rainfall through Sunday




http://www.crh.noaa.gov/news/display_cmsstory.php?wfo=ilx&storyid=20489&source=0

Flash Flood Watches already in place for a large part of IL & MO while we have Flood Warnings already issued for parts of western and sw Indiana.

[Dave]

North Central River Forecast Center River Forecast



http://www.crh.noaa.gov/ncrfc/content/water/fop.php