Tornado outbreak - February 10-11, 8+ dead

[Dave]

High wind watch posted for central & southern Indiana, all of Ky, and a large part of Oh from wednesday thru thursday morning, including me.

"Wednesday: Showers likely, then showers and thunderstorms after noon. Some storms could be severe, with damaging winds. High near 63. Windy, with a south wind 16 to 19 mph becoming west between 28 and 31 mph. Winds could gust as high as 55 mph. Chance of precipitation is 90%. New rainfall amounts between a quarter and half of an inch possible."

http://forecast.weather.gov/MapClick.php?site=ind&map.x=264&map.y=188

Still holding cloud cover this morning, temp 51 dewpoint 50 humidity 96% at 8:30 am.

Got a load of sleep last night so ready to go...looks like wednesday for me.

[Dave]

ZCZC SPCPWOSPC ALL
WOUS40 KWNS 101102
ARZ000-LAZ000-OKZ000-TXZ000-101900-

PUBLIC SEVERE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0502 AM CST TUE FEB 10 2009

...SEVERE WEATHER OUTBREAK EXPECTED OVER THE ARKLATEX LATER THIS
AFTERNOON AND TONIGHT...

THE NWS STORM PREDICTION CENTER IN NORMAN OK IS FORECASTING THE
DEVELOPMENT OF A FEW STRONG...LONG-TRACK TORNADOES AND WIDESPREAD
DAMAGING WINDS OVER PARTS OF THE ARKLATEX LATER THIS AFTERNOON AND
TONIGHT.

THE AREAS MOST LIKELY TO EXPERIENCE THIS ACTIVITY INCLUDE

WESTERN AND CENTRAL ARKANSAS
NORTHWEST LOUISIANA
EASTERN OKLAHOMA
NORTH-CENTRAL AND NORTHEAST TEXAS

ELSEWHERE...SEVERE STORMS ARE ALSO POSSIBLE FROM THE MID MISSISSIPPI
VALLEY INTO CENTRAL AND SOUTHEAST TEXAS.

A POWERFUL WINTER STORM SYSTEM OVER THE LOWER COLORADO VALLEY THIS
MORNING WILL MOVE EAST THROUGH THE SOUTHERN ROCKIES INTO THE
SOUTHERN PLAINS BY TONIGHT. LOW-LEVEL MOISTURE WILL CONTINUE TO
INCREASE TODAY OVER LOWER ELEVATIONS OF THE SOUTHERN PLAINS INTO
LOWER MISSISSIPPI VALLEY AS SOUTHERLY WINDS STRENGTHEN IN ADVANCE OF
THE UPPER-LEVEL STORM SYSTEM. THIS MOISTURE WILL COMBINE WITH
DAYTIME HEATING AND COOLING TEMPERATURES ALOFT TO CREATE A
MODERATELY UNSTABLE AIR MASS BY AFTERNOON GENERALLY ALONG AND EAST
OF THE I-35 CORRIDOR OF OKLAHOMA AND TEXAS.

RAPID THUNDERSTORM DEVELOPMENT IS EXPECTED BY MID TO LATE AFTERNOON
ALONG A DRYLINE FROM NEAR OR SOUTH OF OKLAHOMA CITY SOUTHWARD TO THE
DALLAS-FORT WORTH METROPLEX AS THE APPROACHING UPPER-LEVEL SYSTEM
BEGINS TO EXERT AN INFLUENCE ON THE DESTABILIZING AIR MASS. THE
COMBINATION OF STRONG VERTICAL SHEAR AND A MODERATELY UNSTABLE AND
EXPANDING WARM SECTOR SUGGESTS THE LIKELIHOOD OF A FEW SUPERCELLS
CAPABLE OF PRODUCING STRONG...POTENTIALLY LONG-TRACKED TORNADOES.
THIS TORNADO THREAT APPEARS TO BE GREATEST OVER SOUTHEAST
OKLAHOMA...NORTHEAST TEXAS...WEST-CENTRAL AND SOUTHWEST ARKANSAS
INTO NORTHWEST LOUISIANA LATE THIS AFTERNOON INTO TONIGHT.

ADDITIONAL STORMS...LIKELY IN THE FORM OF A SQUALL LINE...ARE
EXPECTED TO DEVELOP OVER PARTS OF EASTERN OKLAHOMA INTO EASTERN
TEXAS TONIGHT AS A FAST-MOVING PACIFIC FRONT OVERTAKES THE DRYLINE.
WHILE A FEW TORNADOES AND SOME HAIL WILL BE POSSIBLE WITH THESE
STORMS...IT APPEARS THAT DAMAGING WINDS WILL BE THE PRIMARY SEVERE
WEATHER HAZARD. THIS DAMAGING WIND THREAT WILL LIKELY CONTINUE
EASTWARD INTO PARTS OF ARKANSAS AND LOUISIANA OVERNIGHT.

THIS IS POTENTIALLY A VERY DANGEROUS SITUATION. THOSE IN THE
THREATENED AREA ARE URGED TO REVIEW SEVERE WEATHER SAFETY RULES AND
TO LISTEN TO RADIO...TELEVISION...AND NOAA WEATHER RADIO FOR
POSSIBLE WATCHES...WARNINGS...AND STATEMENTS LATER TODAY.

..MEAD.. 02/10/2009

http://www.spc.noaa.gov/products/outlook/pwo.html

[Extremeweatherguy]

The 12z RUC is very aggressive with the moisture return. It brings 60-degree dewpoints all the way north to the KS/OK border by this evening, with the dry-line sitting just west of I-35 at 7pm. CAPE values are also shown to reach 1000-2000 J/kg at that same time with Lifted Indexes as low as -8 to -10.

[Ed Mahmoud]

12Z NAM is out...



Several spooky forecast soundings, Corsicana looks spookiest

[CrazyC83]

Those look like an upgrade is very possible at 1630Z.

That would be only the third time that I know of that there was a high risk in February - the others were February 10, 1998 and February 5, 2008.

[RL3AO]

Dewpoints up to 62 in Dallas.

[Extremeweatherguy]

Higher dew-points are quickly spreading north into Oklahoma...

[jasons2k]

From Jeff Lindner 7:00 AM

Strong to severe thunderstorms expected tonight.

Powerful storm system will move into the plains today with large scale outbreak of severe weather including potential for very damaging tornadoes. Low level warm advection pattern is in full swing this morning with strong south winds pumping copious moisture northward into developing low pressure over NW TX. Surface dryline extends southward through W TX while a powerful upper level shortwave digs across Utah.

Water vapor images show impressive upper level system moving rapidly SE and will eject strong dynamics and tremendous wind energy across much of TX starting late today. Mid level flow in the base of the trough increases to near 90kt after 300pm today with a 120kt upper level jet streak plowing across the state by early evening. Large warm sector east of the W TX dryline will become increasingly unstable as 850mb and 700mb layer cools with approach of the upper level trough. Capping will hold through most of the early afternoon before building instability gives way and busts the cap as the mid levels cool. Expect discrete supercells to develop in the strong warm advection regime over NE and NC TX by mid afternoon. Powerful wind energy and strong turning with height suggest a strong tornado potential with these cells and a few tornadoes could be high EF events.

Strong forcing arrives into TX before sunset as the dryline and Pacific cold front swing eastward. With cooling mid levels and strong surface convergence along the front expect a large squall line to develop from C OK to C TX with the southern extent being determined by the cap intensity over C TX. Strong jet dynamics and associated wind energy points to a severe wind threat with this line. Given 90kts of mid level flow into the backside of the squall line a widespread damaging wind event along the leading edge of this line looks likely. Discrete cells developing ahead of the squall line and rooted near the surface will exhibit strong low level rotation and a tornado threat.

Southern end of a severe squall line will reach our NW counties around midnight and sweep quickly across most of the area by 400am. Cap intensity looks strong enough around Matagorda Bay to preclude much development in that region although the rest of the area appears to be under the gun tonight. Strongest storms and greatest tornado threat will be along and N of HWY 105 where best moisture, dynamics, and least capping will be found. Squall line may be more broken across areas south of I-10.

SPC has issued a slight risk for severe storms for our entire region….although the Matagorda area is likely on the tail southern end with a moderate risk area outlining the increased tornado and widespread wind damage threat which approaches our N counties. As short range/meso models firm up the track of the surface low and quality of Gulf air mass is realized this afternoon adjustments to the risk areas and possible upgrade to high risk for portions of TX may be needed. Main threats across SE TX will be straight line winds of 60-70mph along the leading edge of the squall line. While the air mass will exhibit strong low level shearing discrete cells this afternoon should develop just north of our region with the main tornado threat across NC and NE TX into SE OK and AR. A few violent tornadoes will be possible and forward motions of 45-60mph will be possible leading to very short lead warning times. Widespread tornado/severe threat will continue through tonight and into Wednesday across the southern US.

[CrazyC83]

Not only might we see a high risk, they may have to greatly expand the moderate risk, all the way to the Gulf and back to about Wichita.

[srainhoutx]

If SPC upgrades to High Risk, it would probably come at 20Z after 18Z soundings...

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SHREVEPORT LA
931 AM CST TUE FEB 10 2009

DISCUSSION

12Z KSHV RAOB SHOWS A MOIST...MODERATELY UNSTABLE AMS IN
PLACE...W/DEEP LAYER SHEAR ON THE INCREASE. WE/LL BE DOING AN 18Z
RELEASE TO BETTER ASSESS PRE-STORM ENVIRONMENT. FOR THE MORNING
UPDATE...ONLY CHANGES TO GRIDS WILL BE TO ADJUST AFTERNOON HIGHS A
BIT...IN LIEU OF CLOUD COVER AND WARM FRONT. TO MAINTAIN
CONTINUITY...WX GRIDS LOOK FINE. UPDATES OUT SHORTLY.

[CrazyC83]

1630Z - MDT expanded but no HIGH yet...

[RL3AO]

HAVE CHOSEN
TO MAINTAIN CATEGORICAL MODERATE RISK FOR THIS AFTERNOON DUE TO
CONTINUED CONCERNS OVER THE QUALITY OF LOW LEVEL MOISTURE...BUT AN
UPGRADE TO HIGH RISK WILL REMAIN POSSIBLE AT 20Z.

[CrazyC83]

I think they are waiting for the 18Z model runs. A mesoscale discussion around 19Z will likely tell the tale.

[CrazyC83]

SPC AC 101621

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1021 AM CST TUE FEB 10 2009

VALID 101630Z - 111200Z

...THERE IS A MDT RISK OF SVR TSTMS OVER PORTIONS OF CENTRAL/EASTERN
OK...NORTH CENTRAL AND NORTHEAST TX...NORTHWEST LA...AND MUCH OF
AR...

...THERE IS A SLGT RISK OF SVR TSTMS OVER MUCH OF THE SOUTHERN
PLAINS AND LOWER/MID MS VALLEY...

...A SIGNIFICANT SEVERE WEATHER OUTBREAK -- INCLUDING SUPERCELLS
WITH STRONG TORNADOES -- IS EXPECTED THIS AFTERNOON INTO TONIGHT FOR
ERN OK/NE TX...INTO WRN/CENTRAL AR AND NW LA...

MORNING WATER VAPOR SHOWS A VIGOROUS AND DIGGING SHORTWAVE TROUGH
OVER EASTERN AZ. THIS FEATURE WILL ROTATE INTO TX THIS
EVENING...WHILE 110+ KT MID LEVEL JET NOSES INTO THE BIG BEND
REGION. PARAMETERS REMAIN VERY FAVORABLE FOR NUMEROUS SEVERE
THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN PLAINS THIS AFTERNOON AND
TONIGHT WITH A RISK OF WIDESPREAD DAMAGING WINDS...STRONG
TORNADOES...AND LARGE HAIL.

15Z SURFACE ANALYSIS SHOWS LOW LEVEL MOISTURE RETURNING RAPIDLY
NORTHWARD ACROSS EAST TX INTO OK/AR. BY MID AFTERNOON...IT APPEARS
LIKELY THAT THE SURFACE DRYLINE WILL BECOME ESTABLISHED ROUGHLY
ALONG A LINE FROM W OF OKC...LAW...ABI. HIGH CLOUDS ARE CLEARING
OUT OF THIS REGION...AND LOW CLOUDS WILL SLOWLY ERODE THIS MORNING.
THIS WILL ALLOW RELATIVELY STRONG HEATING ALONG THE DRYLINE AND LEAD
TO AFTERNOON MLCAPE VALUES AROUND 1000 J/KG. FARTHER EAST...GREATER
LOW LEVEL MOISTURE WILL OFFSET MORE CLOUD COVER WITH MLCAPE OF OVER
1000 J/KG EXPECTED.

...DRYLINE INITIATION OK/TX...
GIVEN LATEST MODEL GUIDANCE AND OBSERVATIONAL TRENDS...
THUNDERSTORMS ARE EXPECTED TO DEVELOP 20-22Z ALONG DRYLINE OVER
WESTERN OK AND NORTHWEST TX. THESE STORMS WILL LIKELY BE
SUPERCELLULAR WITH A RISK OF VERY LARGE HAIL AND TORNADOES. THE
STORMS WILL BECOME MORE NUMEROUS BY EARLY EVENING /AFTER DARK/ AND
TRACK NORTHEASTWARD INTO NORTHEAST TX AND EASTERN OK. MUCH STRONGER
VERTICAL SHEAR PROFILES IN THIS REGION /EFFECTIVE HELICITY OF 400+
M2/S2/ WILL ALSO INCREASE THE RISK OF STRONG TORNADOES. HAVE CHOSEN
TO MAINTAIN CATEGORICAL MODERATE RISK FOR THIS AFTERNOON DUE TO
CONTINUED CONCERNS OVER THE QUALITY OF LOW LEVEL MOISTURE...BUT AN
UPGRADE TO HIGH RISK WILL REMAIN POSSIBLE AT 20Z.

...MAIN SQUALL LINE TX/EASTERN OK...
BY LATE AFTERNOON...THE PRIMARY UPPER FORCING WILL ARRIVE ALONG THE
DRYLINE/PACIFIC FRONT OVER NORTHWEST TX. THIS WILL LIKELY RESULT IN
THE RAPID DEVELOPMENT OF AN INTENSE SQUALL LINE. THIS ACTIVITY IS
EXPECTED TO TRACK EASTWARD ACROSS NORTH-CENTRAL AND CENTRAL TX
DURING THE EVENING WITH A RISK OF WIDESPREAD DAMAGING WINDS. LOW
AND DEEP LAYER VERTICAL SHEAR PROFILES WILL BE VERY FAVORABLE FOR
EMBEDDED MESOCYCLONES AND THE RISK OF TORNADOES. FORECAST SOUNDINGS
ALSO SUGGEST ONLY A WEAK CAP AHEAD OF THE SQUALL LINE...POSING THE
RISK OF MORE DISCRETE TORNADIC SUPERCELLS DURING THE EVENING.
STRONG TORNADOES WILL BE POSSIBLE OVER THIS REGION AS WELL.

...OVERNIGHT LA/AR/MO...
WIDESPREAD THUNDERSTORMS WILL ACCELERATE THROUGH THE EVENING AND
SWEEP EASTWARD INTO PARTS OF LA/AR/MO OVERNIGHT. THE 500MB JET MAX
WILL INCREASE TO OVER 120 KT DURING THIS PERIOD...SUGGESTING A
CONTINUED RISK OF WIDESPREAD DAMAGING WINDS AND EMBEDDED TORNADOES
THROUGH MUCH OF THE NIGHT. STORMS MAY REACH SOUTHERN IL/WEST
TN/NORTHWEST MS BY 11/12Z.

...NORTHERN OK/SOUTHERN KS...
MODEL GUIDANCE SUGGESTS THAT PRIMARY SURFACE LOW WILL BECOME
ESTABLISHED BY LATE AFTERNOON OVER SOUTHWEST KS...WITH BACKED LOW
LEVEL WINDS AND INCREASING MOISTURE INTO PARTS OF NORTHWEST
OK/SOUTHERN KS. FULL SUNSHINE WILL LEAD TO STEEP LOW LEVEL LAPSE
RATES AND SUFFICIENT INSTABILITY FOR THE DEVELOPMENT OF ISOLATED
THUNDERSTORMS BY EARLY EVENING. VERTICAL SHEAR PROFILES ARE WEAKER
IN THIS REGION THAN FARTHER SOUTHEAST. HOWEVER... PARAMETERS
SUGGEST THE RISK OF A FEW SUPERCELLS CAPABLE OF LARGE HAIL AND
ISOLATED TORNADOES.

..HART.. 02/10/2009

CLICK TO GET WUUS01 PTSDY1 PRODUCT

NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z
CURRENT UTC TIME: 1630Z (11:30AM), RELOAD THIS PAGE TO UPDATE THE TIME

[CrazyC83]

I think it will be around 20Z that we see the watches come out as well. I'm guessing at least 1 or 2 of them will be PDS watches.

[RL3AO]

I'm thinking SC Oklahoma is where things will first start to pop. Just a guess though.

[CrazyC83]

ZCZC SPCPWOSPC ALL
WOUS40 KWNS 101715
ARZ000-LAZ000-OKZ000-TXZ000-110115-

PUBLIC SEVERE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1115 AM CST TUE FEB 10 2009

...SEVERE THUNDERSTORMS EXPECTED OVER PARTS OF THE SOUTHERN PLAINS
INTO THE MID AND LOWER MISSISSIPPI VALLEY THIS AFTERNOON AND
TONIGHT...

THE NWS STORM PREDICTION CENTER IN NORMAN OK IS FORECASTING THE
DEVELOPMENT OF TORNADOES...LARGE HAIL AND DAMAGING WINDS OVER PARTS
OF THE SOUTHERN PLAINS INTO THE MID AND LOWER MISSISSIPPI VALLEY
THIS AFTERNOON AND TONIGHT.

THE AREAS MOST LIKELY TO EXPERIENCE THIS ACTIVITY INCLUDE

WESTERN 2/3 OF ARKANSAS
NORTHWEST LOUISIANA
MUCH OF THE EASTERN HALF OF OKLAHOMA
NORTHEAST TEXAS

ELSEWHERE...SEVERE STORMS ARE ALSO POSSIBLE FROM THE MIDDLE TEXAS
COAST EASTWARD TO THE MOUTH OF THE MISSISSIPPI RIVER...AND AS FAR
NORTH AS KANSAS...MISSOURI...AND ILLINOIS.

A STRONG MIDDLE- AND UPPER-LEVEL STORM SYSTEM CONTINUES MOVING
ACROSS THE FOUR CORNERS REGION...AND WILL EMERGE INTO THE CENTRAL
AND SOUTHERN PLAINS LATER THIS AFTERNOON. AHEAD OF THIS SYSTEM...A
MOIST LOW-LEVEL AIRMASS CONTINUES STREAMING NORTHWARD ACROSS TEXAS
AND LOUISIANA INTO EASTERN OKLAHOMA AND THE OZARKS REGION. DAYTIME
HEATING OF THE MOISTENING BOUNDARY LAYER WILL INCREASE THROUGH THE
AFTERNOON ACROSS OKLAHOMA AND TEXAS AS INITIAL CLOUD COVER SHIFTS
EASTWARD. THIS COMBINED WITH COOLING ALOFT IN CONJUNCTION WITH THE
APPROACHING STORM SYSTEM LATER TODAY WILL RESULT IN AIRMASS
DESTABILIZATION -- SUPPORTIVE OF THUNDERSTORM DEVELOPMENT BY MID TO
LATE AFTERNOON.

INITIAL STORM MODE IS FORECAST TO BE SUPERCELLULAR...AS A VERY
STRONG WIND FIELD -- VEERING/INCREASING WITH HEIGHT THROUGH THE
LOWER TROPOSPHERE -- RESULTS IN FAVORABLE SHEAR FOR STORM ROTATION.
AS STORMS DEVELOP FROM CENTRAL OKLAHOMA SOUTHWARD INTO NORTH CENTRAL
TEXAS LATER THIS AFTERNOON...EXPECT LARGE HAIL AND LOCALLY-DAMAGING
WINDS ALONG WITH THE POTENTIAL FOR ISOLATED STRONG TORNADOES.

OVERNIGHT...AS A COLD FRONT APPROACHES FROM THE WEST...STORMS SHOULD
BECOME ORGANIZED IN A MORE LINEAR FASHION ALONG THE FRONT...AND THEN
SPREAD RAPIDLY EASTWARD TOWARD THE MISSISSIPPI VALLEY. ALONG WITH A
CONTINUED THREAT FOR HAIL AND ISOLATED TORNADOES...WIDESPREAD
DAMAGING WINDS SHOULD BECOME INCREASINGLY LIKELY.

THOSE IN THE THREATENED AREA ARE URGED TO REVIEW SEVERE WEATHER
SAFETY RULES AND TO LISTEN TO RADIO...TELEVISION...AND NOAA WEATHER
RADIO FOR POSSIBLE WATCHES...WARNINGS...AND STATEMENTS LATER TODAY.

..GOSS.. 02/10/2009

$$

[CrazyC83]

Day 2: 45% removed

SPC AC 101720

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1120 AM CST TUE FEB 10 2009

VALID 111200Z - 121200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE OH/TN VALLEY REGION
INTO THE NRN GULF STATES...

...OH VALLEY/TN VALLEY...

INTENSE MID LEVEL HEIGHT FALLS...ON THE ORDER OF
240-270M/12HR...WILL DEVELOP ACROSS THE MID MS/OH VALLEY REGION
DURING THE DAY2 PERIOD AS STRONG SPEED MAX...120KT AT
500MB...INTENSIFIES AND EJECTS ACROSS AR INTO OH BY LATE AFTERNOON.
AT THE SURFACE...DEEPENING CYCLONE WILL LIFT NEWD FROM NEAR STL AT
12Z INTO SWRN LOWER MI BY 00Z. A NARROW AXIS OF BOUNDARY LAYER
MOISTURE...SFC DEW POINTS INTO THE UPPER 50S...WILL ADVECT NWD AHEAD
OF SFC LOW AND ATTENDANT COLD FRONT AS IT SURGES EAST ACROSS MO INTO
IL/IND DURING THE MORNING HOURS PROVIDING SUFFICIENT INSTABILITY FOR
THUNDERSTORMS ALONG WIND SHIFT. ALTHOUGH INSTABILITY WILL BE
SOMEWHAT MARGINAL...STRONG/FOCUSED ASCENT WILL UNDOUBTEDLY ENHANCE
CONVECTIVE POTENTIAL WITHIN STRONGLY SHEARED
ENVIRONMENT...ESPECIALLY ACROSS THE OH VALLEY. FORECAST SOUNDINGS
SUGGEST THUNDERSTORMS THAT DEVELOP AHEAD OF STRONG COLD FRONT WILL
MOVE RAPIDLY NEWD...SPEEDS IN EXCESS OF 50KT...ENHANCING THE THREAT
FOR DAMAGING WINDS. IN ALL LIKELIHOOD AN ELONGATED SQUALL LINE WILL
EMERGE ALONG SHARP BOUNDARY FROM IL INTO WRN TN EARLY...THEN MOVE
RAPIDLY NEWD ACROSS THE OH/TN VALLEY REGION BY LATE AFTERNOON INTO
WRN PA DURING THE EVENING HOURS. AIRMASS EAST OF THE APPALACHIANS
WILL PROVE SOMEWHAT HOSTILE FOR MAINTAINING STRONG/ORGANIZED
UPDRAFTS GIVEN THE MARGINAL MOISTURE/INSTABILITY EXPECTED DURING THE
OVERNIGHT HOURS. FARTHER SOUTH ACROSS THE CNTRL GULF COAST...LAPSE
RATES SHOULD REMAIN TOO WEAK TO WARRANT ANY MEANINGFUL THREAT FOR
ROBUST ORGANIZED UPDRAFTS GIVEN THAT SIGNIFICANT LARGE SCALE UPPER
SUPPORT SHOULD SPREAD WELL NORTH OF THIS REGION.

..DARROW.. 02/10/2009

CLICK TO GET WUUS02 PTSDY2 PRODUCT

NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0700Z
CURRENT UTC TIME: 1724Z (12:24PM), RELOAD THIS PAGE TO UPDATE THE TIME

[RL3AO]

Clouds are probably going to prevent a high risk day.



Also, there are some scattered showers near San Antonio.

[Dave]

AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON OH 929 AM EST TUE FEB 10 2009

SYNOPSIS

AN ELEVATED FRONTAL BOUNDARY WILL STALL NEAR THE OHIO RIVER THIS AFTERNOON. THIS BOUNDARY WILL LIFT NORTH AS A WARM FRONT TONIGHT. A COLD FRONT WILL SWEEP ACROSS THE OHIO VALLEY ON WEDNESDAY...AS A RAPIDLY DEEPENING SURFACE LOW TRACKS ACROSS THE LOWER GREAT LAKES.

NEAR TERM /UNTIL 6 PM THIS EVENING/

ELEVATED FRONTAL BOUNDARY HAS JUST ABOUT STALLED OUT NEAR THE OHIO RIVER THIS MORNING. A MOIST SW FLOW ALONG AND AHEAD OF THIS BOUNDARY...COMBINED WITH SOME EMBEDDED UPR LVL WX DISTURBANCES...WILL KEEP SCATTERED SHOWERS GOING ACROSS THE SOUTHERN AND SOUTHEASTERN ZONES THROUGH THE AFTN HOURS. THE REMAINDER OF THE REGION WILL REMAIN MAINLY DRY. HAVE UPDATED ZONES/GRIDS TO REFLECT THIS CURRENT THINKING. WILL KEEP AN EYE ON RADAR TRENDS SHOULD SHOWERS BECOME MORE WIDESPREAD THAN EXPECTED. HIGH TEMPERATURES IN THE LOWER TO MID 60S STILL LOOK GOOD AT THIS POINT.

----------------------------
SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY

CHANCE OF SHOWERS WILL EXPAND NORTHWARD TONIGHT AS THE ELEVATED BOUNDARY LIFTS BACK NORTH INTO NORTHERN OHIO BY 12Z. STREAM OF WARM AIR BEHIND THIS WARM FRONT WILL KEEP TEMPS MILD OVERNIGHT WITH LOWS IN THE LOW TO MID 50S.

MAIN FOCUS THIS PERIOD IS WEDNESDAY AND WEDNESDAY NIGHT...AS AN UPPER SHORTWAVE ACROSS THE SOUTHERN PLAINS EJECTS INTO THE OHIO VALLEY...TAKING ON A STRONG NEGATIVE TILT. THIS RESULTS IN RAPID DEEPENING OF A SURFACE LOW WHICH WILL QUICKLY TRACK FROM NEAR ST LOUIS AT 12Z WEDS...TO NEAR DETROIT BY 00Z THURS...AND INTO FAR SOUTHEAST ONTARIO BY 12Z THURS. THE LOW IS FORECAST TO DEEPEN TO NEAR 998 MB BY THIS TIME. THE RESULTING WIND FIELD TO THE SOUTH OF THE LOW WILL BE VERY STRONG...WITH 850 HPA WIND SPEEDS OVER 70 KT...AND WINDS IN EXCESS OF 50 KT AS LOW AS 925 HPA.

BECOMING INCREASINGLY CONCERNED THAT THERE MAY BE A SIGNIFICANT SEVERE WEATHER EVENT ACROSS THE ENTIRE CWA ON WEDNESDAY. WITH THE AFOREMENTIONED WIND FIELD...SHEAR AT ALL LEVELS OF THE ATMOSPHERE WILL BE AT THE HIGH END OF THE SPECTRUM BY WEDS AFTERNOON. MODELS ARE INDICATING 0-1 KM SHEAR AROUND 40-KT...0-1KM AND 0-3KM HELICITY OF 200-300 M2/S2...AND 0-6 KM SHEAR A WHOPPING 70-KT+.

WHILE COLD-SEASON SHEAR VALUES AROUND THESE LEVELS ARE NOT UNCOMMON...THEY USUALLY ARE ACCOMPANIED BY INSTBY THAT IS ALMOST NIL. HOWEVER...THIS CASE APPEARS DIFFERENT...AS PERSISTENT SOUTHERLY WINDS OVER THE NEXT 2 DAYS WILL EASILY BE ABLE TO TRANSPORT AN UNSEASONABLY WARM AND MOIST AIRMASS INTO THE REGION. BOTH NAM AND GFS ARE FORECASTING DEWPOINTS IN THE LOW TO MID 50S ADVECTING INTO MUCH OF SOUTHERN OHIO BY WEDS AFTERNOON...WHICH DOES NOT SEEM AT ALL UNREASONABLE...GIVEN THAT LOW 50S DEWPOINTS ARE JUST A STATE AWAY IN WESTERN KENTUCKY. IF SFC HEATING IS ADEQUATE...THIS WOULD ALLOW FOR SFC-BASED CAPE VALUES BETWEEN 500-1000 J/KG WHICH WOULD FAVOR CONVECTION DEVELOPING ALONG A COLD FRONT WHICH WILL RAPIDLY SWEEP THROUGH THE AREA LATE WEDS AFTERNOON AND EARLY EVENING. IF THESE CAPE VALUES ARE IN FACT REALIZED...THE COMBINATION OF ADEQUATE INSTBY...VERY STRONG LOW- LEVEL SHEAR...LOW LCLS...AND DRYING MIDLEVELS WOULD POINT TO A RAPIDLY-PROGRESSING SQUALL LINE WITH EMBEDDED LEWPS AND MESOCYLONES...RESULTING IN WIDESPREAD DAMAGING WINDS AND AT LEAST A FEW TORNADOES. THIS SITUATION WILL NEED TO BE CLOSELY WATCHED.

BIGGEST CONCERN ACTING AGAINST THE SEVERE THREAT IS THAT THE DEEP-LAYER SHEAR WILL BE TOO STRONG AND OUT OF PROPORTION WITH THE WEAK INSTBY...WHICH MAY NOT ALLOW UPDRAFTS TO ORGANIZE ADEQUATELY BEFORE BEING RIPPED APART. SEVERE THREAT WILL BE HIGHLY DEPENDENT ON THE DEGREE OF DESTABILIZATION...AND THIS IS A SITUATION WHICH WILL NEED TO BE CLOSELY MONITORED. SECOND CONCERN IS WEDS NIGHT AFTER THE FRONT PASSES...AS STRONG LOW-LEVEL COLD AIR ADVECTION BRINGS THETA-SURFACES NEARLY VERTICAL. THIS SHOULD ALLOW EASY TRANSPORT OF 50-KT+ LOW-LEVEL WINDS TO THE SFC...AND MAY BRING A WIDESPREAD HIGH WIND EVENT WITH GUSTS IN EXCESS OF 50-KT POSSIBLE. TRANSPORT TECHNIQUES EVEN SUGGEST THE POTENTIAL FOR GUSTS AS HIGH AS 60-70 MPH WEDS NIGHT...THOUGH DONT THINK GUSTS WILL GET QUITE THIS HIGH BEING NIGHT TIME AND NO SFC HEATING. FOR THIS REASON...A HIGH WIND WATCH HAS BEEN POSTED FOR WEDS AFTERNOON AND WEDS NIGHT.

http://kamala.cod.edu/in/latest.fxus61.KILN.html