2009 Severe Weather thread

[RL3AO]

First watch of the year.



URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 1
NWS STORM PREDICTION CENTER NORMAN OK
935 AM CST SAT JAN 3 2009

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

SOUTHEAST LOUISIANA
SOUTHERN MISSISSIPPI
COASTAL WATERS

EFFECTIVE THIS SATURDAY MORNING AND AFTERNOON FROM 935 AM UNTIL
500 PM CST.

HAIL TO 1.5 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

[Ed Mahmoud]

I've had my eye on the Gulf Coast for Tuesday and Wednesday for a couple of years.


While my amateur prognostications of Atlantic Basin tropical cyclones had a decidely mixed record, with a few notable failures, I did fairly well on severe weather long range spotting, beating SPC on general time and area a couple of times on the Days 3 and Days 4 to 8 convective outlooks.

[CrazyC83]

The first tornadoes of 2009 reported today.

[RL3AO]

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0344 AM CST THU FEB 12 2009

VALID 151200Z - 201200Z

...PREDICATABILITY IS TOO LOW TO DELINEATE A SVR THREAT AREA...

BARRING A SUBSTANTIAL COLD INTRUSION INTO THE GULF OF MEXICO...THE
BOUNDARY LAYER OVER THE GULF OF MEXICO SHOULD REMAIN FAVORABLE FOR A
QUICK INLAND RETURN FLOW OF MOISTURE...GIVEN SIGNIFICANT SURFACE
CYCLONE DEVELOPMENT TO THE LEE OF THE CENTRAL/SOUTHERN ROCKIES.
AND...12/00Z OPERATIONAL GFS AND ECMWF BOTH ONCE AGAIN INDICATE THAT
THIS IS A POSSIBILITY DURING THE EARLY TO MIDDLE PART OF NEXT
WEEK...WITH A SIGNAL FOR INCREASING SEVERE THUNDERSTORM POTENTIAL
FROM PARTS OF THE SOUTHEASTERN PLAINS/LOWER MISSISSIPPI VALLEY INTO
THE SOUTHEASTERN STATES. HOWEVER...THE SPREAD AMONG MEDIUM ENSEMBLE
MEMBERS HAS BEEN LARGE THE PAST SEVERAL DAYS...CONCERNING SHORT WAVE
DEVELOPMENTS WITHIN THE PREVAILING SPLIT UPPER FLOW PATTERN AT THIS
EXTENDED RANGE.

..KERR.. 02/12/2009

----

Some of the models are hinting at something early next week. If it becomes more likely, a separate thread can be created.

[Ed Mahmoud]

SPC has a risk area along the Northeast Gulf for Day 5 (Wednesday into Thursday morning).

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0327 AM CST SAT FEB 14 2009

VALID 171200Z - 221200Z

...DISCUSSION...

MODEL CONSENSUS IS THAT ACTIVE PROGRESSIVE UPPER FLOW REGIME WILL
PERSIST THROUGH DAY 5. GFS...ECMWF AND MREF HAVE SHOWN RUN TO RUN
CONTINUITY AND ARE IN REASONABLE AGREEMENT THAT A STRONG UPPER JET
WILL EJECT INTO THE PLAINS DAY 4. THIS FEATURE WILL CONTINUE EAST
THROUGH THE TN VALLEY AND MID ATLANTIC REGION WEDNESDAY...DAY 5.
STRONG CYCLOGENESIS IS FORECAST TO COMMENCE BY DAY 4 OVER THE CNTRL
PLAINS AS THE UPPER JET CROSSES THE ROCKIES.

SEVERE WEATHER PROSPECTS WILL BE CONTINGENT ON EXTENT OF MOISTURE
RETURN AHEAD OF THIS SYSTEM. DEEPEST FRONTAL INTRUSION WILL OCCUR
OVER THE CNTRL AND ERN GULF MONDAY. STRENGTHENING SLY LOW LEVEL FLOW
OVER THE WRN GULF DUE TO THE DEVELOPING DEEP CYCLONE WILL ALLOW
PARTIALLY MODIFIED GULF AIR TO BEGIN RETURNING NWD THROUGH ERN TX
AND THE LOWER MS VALLEY LATER DAY 4. ELEVATED STORMS CAPABLE OF
PRODUCING MOSTLY HAIL MAY DEVELOP IN ASSOCIATION WITH THIS MOISTURE
RETURN FROM ERN TX INTO THE LOWER MS VALLEY.

A MORE SIGNIFICANT SEVERE THREAT IS NOT EXPECTED TO DEVELOP UNTIL
DAY 5. PARTIALLY MODIFIED GULF MOISTURE WILL LIKELY ADVECT NEWD
THROUGH THE SERN STATES AND TN VALLEY AS THE UPPER JET AND SURFACE
LOW EJECTS EWD THROUGH THE OH VALLEY. CONVECTION WILL LIKELY
CONTINUE DEVELOPING WITHIN THE MOISTENING WARM SECTOR ACROSS THE
SERN U.S. WHERE DEEP LAYER FLOW AND VERTICAL SHEAR WILL STRENGTHEN.
SUFFICIENT INSTABILITY MAY DEVELOP IN PRE-FRONTAL WARM SECTOR FOR A
THREAT OF SEVERE STORMS.

ANOTHER GULF FRONTAL SURGE WILL OCCUR BY DAY 6 AS THE LOW EXITS THE
ERN SEABOARD WITH LOW POTENTIAL FOR SEVERE WEATHER DAY 6-8.

..DIAL.. 02/14/2009

[RL3AO]

Not looking too impressive. GFS is showing some moderate instability (500 to 750 CAPE) and some 60+ dewpoints in most of AL and MS. Right now I'd say its maybe showing a high end slight risk.

[RL3AO]

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0223 AM CST MON FEB 16 2009

VALID 181200Z - 191200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF THE SERN
STATES...

...SYNOPSIS...

MODEL CONSENSUS IS THAT SRN BRANCH UPPER JET WILL ADVANCE INTO THE
LOWER MS...TN AND OH VALLEYS WED WHERE IT WILL INTENSIFY AS IT
MERGES WITH AMPLIFYING NRN STREAM. SUBSEQUENT CONSOLIDATION AND
AMPLIFICATION OF THE TROUGH WILL CONTINUE OVER THE ERN STATES WED
NIGHT. SURFACE LOW TRACK WILL REMAIN TIED TO STRONGER FORCING WITHIN
UPPER JET EXIT REGION. THIS FEATURE WILL LIFT NE THROUGH THE OH
VALLEY DURING THE DAY. TRAILING COLD FRONT WILL SWEEP EWD THROUGH
THE OH VALLEY AND SERN STATES.

...SERN STATES...

DEGREE OF SEVERE WEATHER THREAT REMAINS CONTINGENT ON AMOUNT OF
INSTABILITY THAT CAN DEVELOP IN WARM SECTOR. DEEPER GULF FRONTAL
INTRUSION WILL OCCUR MONDAY OVER THE CNTRL AND ERN GULF AS AREA OF
SURFACE HIGH PRESSURE ADVANCES THROUGH THE SERN STATES. EFFECTS OF
THE COLD ADVECTION WILL BE MUCH LESS OVER A PORTION OF THE SWRN GULF
WHERE DEWPOINTS WILL REMAIN IN THE UPPER 60S. BY WEDNESDAY AN AXIS
OF PARTIALLY MODIFIED GULF AIR WILL ADVECT NWD THROUGH THE LOWER MS
VALLEY AND A PORTION OF THE SERN STATES ALONG A STRONG SWLY LOW
LEVEL JET ASSOCIATED WITH THE EWD MIGRATING CYCLONE. ELEVATED STORMS
WILL BE ONGOING OVER A PORTION OF THE SERN U.S. AND OH VALLEY WITHIN
ZONE OF STRONG ISENTROPIC ASCENT. THE STORMS WILL SHIFT EAST DURING
THE DAY...BUT IN THEIR WAKE...WIDESPREAD CLOUDS WILL LIKELY PERSIST
OVER MUCH OF WARM SECTOR WHICH WILL TEND TO LIMIT INSTABILITY.

CLUSTERS OF STORMS MAY REDEVELOP ALONG AND EAST OF ADVANCING FRONT
WITHIN ZONE OF HEIGHT FALLS AND LOW LEVEL CONFLUENT FLOW REGIME FROM
THE LOWER MS VALLEY INTO PARTS OF THE SERN STATES. ACTIVITY WILL BE
EMBEDDED WITHIN VERY STRONG KINEMATIC PROFILES WHICH WOULD SUPPORT
AN ORGANIZED SEVERE THREAT INCLUDING POTENTIAL FOR SUPERCELLS AND
BOWING STRUCTURES WITH ANY SURFACE BASED DEEP CONVECTION. POTENTIAL
FOR A MARGINAL THERMODYNAMIC ENVIRONMENT COULD STILL POSE A LIMITING
FACTOR FOR A HIGHER END SEVERE EVENT.

...SRN PORTIONS OF THE OH VALLEY...

COLDER AIR ALOFT AND PLUME OF STEEPER MID LEVEL LAPSE RATES WILL
ATTEND THE UPPER JET EXIT REGION THROUGH SRN PARTS OF THE OH
VALLEY...AND THIS COULD COMPENSATE FOR MORE LIMITED LOW LEVEL
MOISTURE IN THIS AREA. STRONG AGEOSTROPHIC FORCING ATTENDING THE
UPPER JET WILL LIKELY CONTRIBUTE TO REDEVELOPMENT OF CONVECTION
SOUTH AND EAST OF SURFACE LOW TRACK. PRIMARY UNCERTAINTY AT THIS
TIME IS HOW MUCH THE BOUNDARY LAYER CAN DESTABILIZE IN WAKE OF
MORNING CONVECTION GIVEN POTENTIAL FOR LOW CLOUDS TO PERSIST. STRONG
VERTICAL SHEAR AND STEEP LAPSE RATES IN THIS REGION WOULD SUPPORT
ORGANIZED SEVERE STORMS. HOWEVER...DUE TO THE CONDITIONAL NATURE OF
THE THREAT ONLY 5% SEVERE PROBABILITIES WILL BE ADDED AT THIS
TIME...BUT AN CATEGORICAL RISK MIGHT BE NEEDED FOR A PORTION OF THIS
REGION IN LATER OUTLOOKS.

..DIAL.. 02/16/2009

[RL3AO]

12z NAM is a little slower and shows more instability by Wednesday evening.
12z GFS is a little faster and doesn't show as much instability.

Looks like a another high shear, low instability event in the south.

[RL3AO]

0z models hinting at a little more instability near and just ahead of the cold front.

[AirNik]

[somethingfunny]

The Weather Channel is suddenly very bullish on severe weather here in Texas and Oklahoma tonight. Local on the 8s (and the NWS) aren't even giving it a 10% chance, but Carl Parker keeps on saying things like "areas that took a very hard hit last week" (Lone Grove/Ardmore/Texomaland) and specifically mentioning DALLAS...."Areas like Dallas, Tulsa, and Little Rock are going to be having a very long night ahead of us, make sure your weather radios are turned on," etc.

Carl Parker's been there a long time and he generally doesn't throw around blatant errors (like mistaking Mississippi for Alabama or something, like some of their OCMs do)....but I'm not seeing any evidence or chatter to support a SVR WX outbreak in my area. What gives?

[RL3AO]

Carl Parker's been there a long time and he generally doesn't throw around blatant errors (like mistaking Mississippi for Alabama or something, like some of their OCMs do)....but I'm not seeing any evidence or chatter to support a SVR WX outbreak in my area. What gives?

Extreme NE Texas was under a slight risk earlier, but not any more. The only severe storms will be late tonight/after midnight where the threat will be hail and rain over parts of MS, AL, AR, and TN

[Ed Mahmoud]

Not watching TWC, but Carl Parker went there from KPRC-TV 2 in Houston. KPRC recently stopped using AccuWeather, not sure where the forecasts now come from, but they have "semi-pro mets". All of them seem to be radio/television/film or journalism majors who took a 60 hour course on "broadcast meteorology" from Mississippi State.

Early TWC "OCM's like Jeanetta Jones had no scientific background at all, although I think most/all have some kind of training now.


That said, Dr. Forbes, the 'severe weather specialist', has a PhD and studied under the famous Dr. Fujita.

[Dave]

MESOSCALE DISCUSSION 0116
NWS STORM PREDICTION CENTER NORMAN OK
0544 PM CST TUE FEB 17 2009

AREAS AFFECTED...SRN/CENTRAL AR AND ARKLATEX REGION -- PORTIONS NE
TX...NWRN LA...SWRN AR...EXTREME SERN OK.

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 172344Z - 180215Z

TSTMS ARE FCST TO DEVELOP AND INCREASE IN COVERAGE GRADUALLY THROUGH
EVENING -- SPREADING FROM SW-NE ACROSS ARKLATEX REGION TOWARD LOWER
MS VALLEY. MAIN CONCERN WILL BE HAIL.

SFC MESOANALYSIS INDICATES DIFFUSE/FRAGMENTED WARM FRONTAL ZONE
EVIDENT FROM S-CENTRAL OK SWD THEN EWD ACROSS CENTRAL/E-CENTRAL
TX...S OF TYR...TO CENTRAL LA. WARM FRONT SHOULD CONSOLIDATE
SOMEWHAT AND LIFT NEWD ACROSS MUCH OF E TX AND LA THROUGH 06Z.
MEANWHILE STG ELEVATED WAA REGIME IS MAINTAINED TO ITS NE ALONG
SLOPED FRONTAL/ISENTROPIC SFC...AND AMIDST STRENGTHENING/45-60 KT
LLJ. INCREASINGLY MOIST PARCELS -- EMANATING FROM COASTAL AREAS
WITH DEW POINTS UPPER 60S F AT SFC AND 10-13 DEG C AT 850 MB -- WILL
BE LIFTED TO LFC BENEATH MUCAPES BETWEEN 500-1000 J/KG. AS BUOYANCY
ALOFT STRENGTHENS/DEEPENS WITH TIME...SO WILL BOTH EFFECTIVE SHEAR
AND EFFECTIVE SRH -- 50-60 KT AND 200-300 J/KG RESPECTIVELY --
AVAILABLE TO THOSE ELEVATED INFLOW PARCELS. STORM ORGANIZATION
SHOULD INCREASE ACCORDINGLY...WITH MOST FAVORABLE LARGE HAIL
POTENTIAL FROM TSTMS THAT CAN MAINTAIN THEIR IDENTITY LONG ENOUGH TO
BUILD LOW-MIDDLE LEVEL MESOCYCLONES. ROBUST STABLE LAYER NEAR SFC
WILL BE MAINTAINED OVER DISCUSSION AREA THROUGH EVENING...WITHOUT
APPRECIABLE DRYING ABOVE...WHICH SHOULD MINIMIZE POTENTIAL FOR
ORGANIZED SVR WIND. HOWEVER...ISOLATED GUSTS APCHG SVR LEVELS
CANNOT BE RULED OUT FROM MOST INTENSE TSTMS -- ESPECIALLY OVER NE TX
WHERE PRE WARM-FRONTAL STABLE LAYER WILL BE SHALLOWEST.

..EDWARDS.. 02/17/2009

[RL3AO]

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 22
NWS STORM PREDICTION CENTER NORMAN OK
705 PM CST TUE FEB 17 2009

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

SOUTHERN AND EASTERN ARKANSAS
NORTHERN LOUISIANA
NORTHERN MISSISSIPPI
FAR SOUTHWEST TENNESSEE

EFFECTIVE THIS TUESDAY NIGHT AND WEDNESDAY MORNING FROM 705 PM
UNTIL 200 AM CST.

HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 80
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 45 MILES WEST OF EL
DORADO ARKANSAS TO 15 MILES NORTH NORTHEAST OF OXFORD
MISSISSIPPI. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU2).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

DISCUSSION...ELEVATED THUNDERSTORMS WILL CONTINUE TO INCREASE IN
BOTH COVERAGE AND INTENSITY ACROSS THIS REGION THROUGH THE EVENING
WITHIN BROAD LOW LEVEL WAA REGIME. 00Z SOUNDINGS INDICATE STEEP MID
LEVEL LAPSE RATES...WITH PARCELS TAPPING LOW LEVEL MOISTENING NEAR
H85 EXPANDING NEWD INTO THE MID SOUTH. THIS WILL SUPPORT MODEST
MUCAPE WITHIN STRONG CLOUD-LAYER SHEAR. STRONGER CORES WILL BE
CAPABLE OF LARGE HAIL...WITH ELEVATED SUPERCELLS INCREASING
POTENTIAL FOR SEVERE HAIL BY LATER THIS EVENING.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 400. MEAN STORM
MOTION VECTOR 25035.


...EVANS

[RL3AO]

Just some regular thunderstorms. No warnings yet.

[CajunMama]

Looking at your radar, i have no clue where that is. Could you please give a description when posting something like that? Thanks

[RL3AO]

I tried to zoom out enough to show where it was. Arkansas in the middle. TX/OK on left.

Since then more storms have developed with most being near the MO/OK/AR border.

[RL3AO]

Wow. They went with a moderate risk (15%H tornado).






DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1159 PM CST TUE FEB 17 2009

VALID 181200Z - 191200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF FAR ERN
MS...CNTRL AL AND SRN AL......

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE LOWER MS
VALLEY...TN VALLEY AND ERN GULF COAST STATES......

...LOWER MS VALLEY/TN VALLEY/ERN GULF COAST STATES...
AN UPPER-LEVEL TROUGH OVER THE NRN STATES WILL DIG SEWD INTO THE MS
VALLEY TODAY AS A POWERFUL 90 TO 100 KT MID-LEVEL JET MOVES EWD
ACROSS THE TN VALLEY AND SRN APPALACHIAN MTNS. SOUTHEAST OF THE
UPPER-LEVEL TROUGH...AN IMPRESSIVE 60 TO 70 KT LOW-LEVEL JET WILL BE
ORIENTED ALONG THE MS RIVER THIS MORNING WITH NUMEROUS ELEVATED
THUNDERSTORMS ONGOING ALONG THE AXIS OF THE JET. THE SRN EXTENT OF
THIS ACTIVITY SHOULD PERSIST EWD ACROSS TN...NRN AL AND NRN GA
THROUGH MIDDAY. FORECAST SOUNDINGS IN SRN TN...NRN MS AND NRN AL
SHOW COLD AIR ALOFT AND SUFFICIENT INSTABILITY FOR A HAIL THREAT
WITH THE ACTIVITY. BY THIS AFTERNOON...MODEL FORECASTS INITIATE
SFC-BASED THUNDERSTORMS FROM FAR ERN MS ENEWD ACROSS CNTRL AL INTO
WRN GA. STORM COVERAGE SHOULD GRADUALLY EXPAND WITH MCS DEVELOPMENT
APPEARING LIKELY BY THIS EVENING ACROSS SRN AL AND SW GA. THIS LINE
OF STORMS SHOULD REACH THE FL PANHANDLE AND THE NRN FL PENINSULA
DURING THE OVERNIGHT PERIOD.

AT THE SFC...A MOIST AXIS IS FORECAST TO BE LOCATED FROM SRN LA
EXTENDING ENEWD ACROSS SRN MS INTO WRN AL. THIS AREA SHOULD BE
MOSTLY FREE OF CONVECTION THROUGH MIDDAY ALLOWING FOR THE
DEVELOPMENT OF AN INSTABILITY/THERMAL AXIS EXTENDING ENEWD ACROSS
THE MODERATE RISK AREA. STRONG SFC-BASED THUNDERSTORMS APPEAR LIKELY
TO INITIATE FIRST IN NCNTRL AND NERN AL EARLY THIS AFTERNOON WITH
THE ACTIVITY EXPANDING WSWWD ACROSS THE MODERATE RISK AREA ALONG THE
INSTABILITY AXIS DURING THE AFTERNOON. FORECAST SOUNDINGS ACROSS
CNTRL AL SHOW STRONG VERTICAL SHEAR PROFILES/0-6 KM SHEAR OF 80 TO
90 KT/ WITH 0-3 KM SRH VALUES RANGING FROM 250 SOUTH OF TUSCALOOSA
TO 450 M2/S2 EAST OF MONTGOMERY. THIS SHOULD BE MORE THAN SUFFICIENT
FOR DISCRETE TORNADIC SUPERCELLS CAPABLE OF PRODUCING A FEW STRONG
TORNADOES. AS STORM COVERAGE EXPANDS ACROSS THE MODERATE RISK
AREA...THE SHEAR SHOULD KEEP THE STORMS DISCRETE RESULTING IN A
PERSISTENT TORNADO THREAT THROUGH EARLY EVENING. FURTHER WEST
SOUTHEAST INTO SCNTRL MS...ISOLATED SUPERCELLS WITH A TORNADO/HAIL
THREAT MAY ALSO INITIATE. HOWEVER...THE GREATER THUNDERSTORM
COVERAGE SHOULD EXIST ACROSS SRN AL AND SW AL AS THUNDERSTORMS
BECOME QUITE NUMEROUS DURING THE EVENING. A TRANSITION TO A MORE
LINEAR STRUCTURED MCS MAY OCCUR WITH THE WIND DAMAGE THREAT
INCREASING. ALTHOUGH A WIND DAMAGE THREAT MAY ALSO EXIST IN SW GA
DURING THE LATE EVENING...THUNDERSTORMS IN THE ERN PART OF THE
SLIGHT RISK AREA SHOULD BECOME ELEVATED DURING THE OVERNIGHT PERIOD.
THE WIND DAMAGE THREAT MAY CONTINUE INTO THE FL PANHANDLE LATE IN
THE PERIOD.

..BROYLES.. 02/18/2009

[Ed Mahmoud]

They expanded the MODERATE RISK area all the way to New Orleans.