Archive for the ‘USA Forecasts’ Category

Tornadoes and very large hail across NE TX becoming likely today!

Robust setup once again over TX today with a slight eastward progressing on the system. Conditons are coming together for another round of severe storms over NE TX where instability, shear/SREH will be maximized. An OFB moving from SE OK southwards should interact with a coming front from the west across NE TX.

SPC issued a large SLGT risk for these areas across SE OK/NE TX and parts of LA/AR while another SLGT risk was issued for IL/IN/SW OH and KY…

10% area for tornadoes in NE TX and 30% hatched for large hail…

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1125 AM CDT TUE APR 03 2012

VALID 031630Z – 041200Z

…THERE IS A SLGT RISK OF SVR TSTMS TODAY AND TONIGHT FROM PARTS OF THE SRN PLAINS INTO LOWER MS VALLEY…

…THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT ACROSS PORTIONS OF THE OH VALLEY…

..SYNOPSIS

MID AND UPPER-LEVEL LOW OVER ERN NM WILL PROGRESS SLOWLY EWD THIS PERIOD IN RESPONSE TO ONSHORE DEVELOPMENT OF AN UPSTREAM TROUGH INTO THE PACIFIC NW. MORNING WATER VAPOR IMAGERY SHOWS A VORTICITY MAXIMUM PIVOTING AROUND THE UPPER LOW ACROSS WRN TX WITH THIS FEATURE LIFTING NEWD ACROSS PORTIONS OF OK/KS TODAY INTO TONIGHT. ELSEWHERE…AN ELONGATED VORTICITY MAXIMUM FROM THE OZARKS TO CNTRL GULF COAST WILL CONTINUE EWD/NEWD WITHIN INCREASINGLY CONFLUENT FLOW REGIME IN PLACE ACROSS THE ERN THIRD OF THE NATION.

IN THE LOW LEVELS…SURFACE CYCLONE OVER NRN IL WILL DEVELOP EWD ACROSS IND TODAY IN CONJUNCTION WITH NRN EXTENSION OF ELONGATED VORTICITY MAXIMUM MENTIONED ABOVE. THIS LOW WILL BE TRAILED BY A COLD FRONT WHICH WILL SETTLE SWD THROUGH THE MID MS VALLEY/OZARKS. THE WRN EXTENSION OF THIS BOUNDARY ACROSS SRN KS WILL REMAIN MORE QUASI-STATIONARY IN RESPONSE TO A WEAK SURFACE LOW DEVELOPING FROM NWRN TX INTO S-CNTRL KS. FARTHER S…A PACIFIC FRONT WILL MOVE SLOWLY EWD FROM W-CNTRL INTO CNTRL TX…BOUNDED ON THE N BY A W-E ORIENTED OUTFLOW BOUNDARY STRETCHED ACROSS NRN PARTS OF TX/LA.

..SRN PLAINS INTO LOWER MS VALLEY TODAY INTO TONIGHT

A N-S BAND OF STRONG-SEVERE…ELEVATED TSTMS HAS EVOLVED THIS MORNING OVER N-CNTRL TX/S-CNTRL OK IN RESPONSE TO INCREASED FORCING FOR ASCENT ATTENDANT TO VORTICITY MAXIMUM PIVOTING AROUND NM UPPER LOW. 12Z FWD SOUNDING SHOWED A MOIST BOUNDARY LAYER BENEATH STEEP MIDLEVEL LAPSE RATES YIELDING MUCAPE OF 2000-2500 J/KG. GIVEN THE PRESENCE OF 40-50+ KT OF EFFECTIVE BULK SHEAR…EMBEDDED SUPERCELL STRUCTURES WILL BE POSSIBLE WITH AN ASSOCIATED RISK FOR LARGE HAIL.

BREAKS IN THE CLOUDS ACROSS NRN/CNTRL TX SHOULD ALLOW FOR SUFFICIENT BOUNDARY LAYER HEATING SUCH THAT ONGOING STORMS WILL BECOME PROGRESSIVELY SURFACE-BASED BY AFTERNOON…WITH ADDITIONAL STORMS POSSIBLE ALONG AND AHEAD OF TRAILING PACIFIC FRONT. THE COMBINATION OF A MOIST AND MODERATELY UNSTABLE AIR MASS /I.E. AFTERNOON MLCAPE OF 1000-2500 J PER KG/ AND 40-60 KT OF DEEP-LAYER SHEAR ORIENTED LARGELY ORTHOGONAL TO THE PACIFIC FRONT WILL SUPPORT SUPERCELLS CAPABLE OF LARGE HAIL AND DAMAGING WIND GUSTS. A FEW TORNADOES ARE ALSO POSSIBLE /ESPECIALLY ACROSS PARTS OF N-CNTRL AND NERN TX/ GIVEN MODESTLY STRONG LOW-LEVEL FLOW AND PRE-EXISTING OUTFLOW BOUNDARIES WHICH WILL LOCALLY ENHANCE LOW-LEVEL SHEAR.

ELSEWHERE…STORMS WILL LIKELY INCREASE IN COVERAGE AND INTENSITY TODAY ALONG OUTFLOW BOUNDARY/GRAVITY WAVE SURGING EWD/SEWD INTO W-CNTRL MS…CNTRL/SRN LA AND SERN TX. WHILE VERTICAL SHEAR WILL REMAIN WEAKER THAN POINTS TO THE W…THE PRESENCE OF A MOIST/UNSTABLE INFLOW AIR MASS /REF. 12Z LCH SOUNDING/ WILL SUPPORT
VIGOROUS UPDRAFTS CAPABLE OF DAMAGING WINDS AND PERHAPS SOME HAIL.

..OH VALLEY

12Z ILX SOUNDING SHOWED STEEP MIDLEVEL LAPSE RATES WHICH WILL COMBINE WITH DAYTIME HEATING AND BOUNDARY LAYER DEWPOINTS INCREASING THROUGH THE 50S TO AROUND 60 F TO YIELD AFTERNOON MLCAPE OF 1000-1500 J/KG. INCREASED FORCING FOR ASCENT ASSOCIATED WITH VORTICITY MAXIMUM LIFTING NEWD THROUGH THE MID MS VALLEY…COUPLED
WITH LOW-LEVEL UPLIFT ALONG SURFACE FRONT ARE EXPECTED TO FOSTER SCATTERED TSTMS LATER THIS AFTERNOON ACROSS PORTIONS OF IL/IN. VERTICAL SHEAR WILL REMAIN RELATIVELY WEAK…BUT THE PRESENCE OF STEEP LOW TO MIDLEVEL LAPSE RATES WILL PROMOTE VIGOROUS UPDRAFTS CAPABLE OF DAMAGING WINDS AND SEVERE HAIL. STORMS ARE EXPECTED TO GROW UPSCALE INTO AN MCS WITH AN ASSOCIATED WIND/HAIL THREAT SPREADING SEWD INTO PARTS OF KY TONIGHT.

..SERN U.S

REMNANT MCV OVER THE FL PNHDL…HEATING ALONG THE HIGH TERRAIN OF THE CNTRL/SRN APPALACHIANS…AND WARM FRONT SLOWLY LIFTING NWD THROUGH THE PIEDMONT AND COASTAL PLAINS WILL ALL SERVE AS FOCI FOR STRONG-MARGINALLY SEVERE TSTM DEVELOPMENT THIS AFTERNOON INTO EVENING. THE PRIMARY HAZARD WILL BE LOCALLY STRONG WIND GUSTS…THOUGH SOME HAIL IS POSSIBLE.

..MEAD/GARNER.. 04/03/2012

Stay tuned!

Mesoscale discussion and SVR TSTORM watch #0129 out for S KS/W OK/E TX PANH/NW TX!

A mesoscale discussion out for areas from SSW KS through W OK, E TX Panh into NW TX concerning severe potential for explosive development of severe storms near the Pacific front and dryline intersection in SW KS as well as further south along the sharpening dryline…

MESOSCALE DISCUSSION 0415
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT MON APR 02 2012

AREAS AFFECTED…NWRN TX…ERN OK/TX PANHANDLES…SWRN KS…WRN OK

CONCERNING…SEVERE POTENTIAL…WATCH LIKELY

VALID 022000Z – 022200Z

A TORNADO WATCH WILL LIKELY BE NEEDED FOR PORTIONS OF NWRN TX…THE ERN OK/TX PANHANDLES…SWRN KS AND WRN OK THIS AFTERNOON AND EVENING.

MID-AFTERNOON MESOANALYSIS SHOWS A COLD FRONT WAS LOCATED FROM SWRN KS INTO ERN NM…WHICH IS BEGINNING TO STALL IN RESPONSE TO PRESSURE FALLS AHEAD OF A POTENT NEGATIVELY TILT MIDLEVEL SHORTWAVE TROUGH. A DRYLINE ACCOMPANIED BY DEEPENING CUMULUS EXTENDED SWD FROM THE KS PORTION OF THE COLD FRONT…WHILE A PACIFIC FRONT WAS BEGINNING TO ENTER W TX. SURFACE TEMPERATURES ALONG THE DRYLINE HAVE WARMED INTO THE MID 80S…AND DEWPOINTS E OF THE BOUNDARY RESIDE IN THE UPR 50S TO MID 60S. THE WARM/MOIST AIRMASS LOCATED ACROSS THE WARM SECTOR COMBINED WITH STEEP MIDLEVEL LAPSE RATES /IN EXCESS OF 8 C PER KM IN THE 700-500 MB LAYER/ ARE CONTRIBUTING TO A VERY UNSTABLE ENVIRONMENT…WITH MLCAPE VALUES NEAR 3000 J/KG.

AS THE UPPER DISTURBANCE LIFTS NWD ACROSS THE SRN HIGH PLAINS THIS AFTERNOON AND EVENING…SHORT-TERM MODEL GUIDANCE INDICATES SURFACE CYCLOGENESIS WILL RAPIDLY TAKE PLACE OVER NERN NM AND THE TX PANHANDLE. STRONG LOW-LEVEL SWLY WINDS OVER W TX…POSSIBLY ACCOMPANYING AN EWD SURGE OF THE PACIFIC FRONT…WILL QUICKLY SPREAD EWD TOWARD THE DRYLINE…RESULTING IN STRENGTHENING LOW-LEVEL CONVERGENCE. AS THIS TAKES PLACE…SCATTERED THUNDERSTORM ARE FORECAST TO DEVELOP FROM THE KS TRIPLE POINT SWD ALONG THE DRYLINE BY 22-00Z.

DURING THE EARLY STAGES OF THIS CONVECTIVE EPISODE TEMPERATURE-DEWPOINT SPREADS WILL BE NEAR 20F OVER THE WARM SECTOR…AND MIDLEVEL FLOW/DEEP LAYER SHEAR WILL BE MARGINAL FOR SUPERCELLS…WHICH MAY NEGATIVELY INFLUENCE THE POTENTIAL FOR TORNADOES DUE TO EXCESSIVE OUTFLOW. HOWEVER…IF STORMS CAN REMAIN QUASI-DISCRETE INTO THE EVENING…THEN A COOLER/MORE HUMID BOUNDARY LAYER COUPLED WITH BACKING/STRENGTHENING 0-1 KM FLOW MAY LEAD TO A MORE SUBSTANTIAL THREAT OF TORNADOES. OTHERWISE…STORMS WILL POSE A THREAT FOR VERY LARGE HAIL GIVEN THE PRESENCE OF LARGE BUOYANCY AND VERY STEEP LAPSE RATES…IN ADDITION TO LOCALLY DAMAGING WIND GUSTS.

..GARNER.. 04/02/2012

A SVR TSTORM watch has been issued soon after for the same area… linear hodographs preclude TORNADO watch attm as shear is mostly uniderectional… very large hail the main threat!

Tornadoes
Probability of 2 or more tornadoes Low (20%)
Probability of 1 or more strong (F2-F5) tornadoesLow (5%)

Wind
Probability of 10 or more severe wind eventsMod (30%)
Probability of 1 or more wind events > 65 knotsMod (30%)

Hail
Probability of 10 or more severe hail eventsHigh (70%)
Probability of 1 or more hailstones > 2 inchesMod (60%)

Combined Severe Hail/Wind
Probability of 6 or more combined severe hail/wind eventsHigh (80%)

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

SOUTHWEST KANSAS
WESTERN OKLAHOMA
NORTHWEST TEXAS INCLUDING THE EASTERN PANHANDLE

EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 340 PM UNTIL 1100 PM CDT.

HAIL TO 3 INCHES IN DIAMETER…THUNDERSTORM WIND GUSTS TO 70 MPH…AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

DISCUSSION…TSTM DEVELOPMENT IS ANTICIPATED WITHIN THE NEXT HOUR OR TWO ALONG STATIONARY FRONT OVER SWRN KS INTO THE NRN TX PNHDL…AS WELL AS ALONG DRYLINE INTO W-CNTRL TX. AMBIENT AIR MASS HAS BECOME STRONGLY UNSTABLE THIS AFTERNOON WITH MLCAPE APPROACHING 3000-3500 J/KG WHICH WILL SUPPORT INTENSE STORM DEVELOPMENT. AREA VAD/PROFILER DATA AND MODEL FORECAST HODOGRAPHS INDICATE THAT VERTICAL SHEAR /BOTH IN THE LOW LEVELS AND THROUGH A DEEP LAYER/ IS MARGINALLY SUPPORTIVE OF SUPERCELLS. WHEN COUPLED WITH RATHER LARGE TEMPERATURE-DEWPOINT SPREADS…THE EXPECTATION IS THAT VERY LARGE HAIL AND DAMAGING WIND GUSTS WILL BE THE PRIMARY HAZARDS. BY 03/00-03Z…BOTH LOW AND DEEP-LAYER SHEAR ARE FORECAST TO STRENGTHEN…AND THE POTENTIAL FOR TORNADOES WILL INCREASE WITH STORMS THAT REMAIN MORE DISCRETE. THUS…CONDITIONS WILL BE MONITORED FOR A POSSIBLE UPGRADE TO A TORNADO WATCH LATER THIS EVENING.

Several SVR TSTORM watches remain in effect for E TX ino SE OK/SW AR/LA where a weak upper low/MCS-MCV maintain intense severe storms and moving NNE-wards.

Stay tuned!


Severe storms with giant hail and few torns along the dryline from S KS to CNTRL TX

An interesting, robust and very complex setup shaping up for S-CNTRL Plains today with a trough closing off into a cut off low across southern Rockies and moving across NM into W TX. At surface, a quasi-stationary SFC low wobbles over TX Panh during most of the day/night. A Pacific front lies NE-SW oriented across KS while a sharp dryline extends southwards across W-CNTRL OK in CNTRL TX. Severe storms are expected to initiate along the dryline at peak daytime heating hours. Very high MLCAPE in excess of 3000-3500 J/kg and strong shear will support robust supercells with primary threat of large to very large hail and a couple of tornadoes especially across N TX into S OK (Red River) where directional shear is the most favorable. Areas for towards NNW into S KS will have hodographs too parallel and could support more linear storm modes or splitting cells, there a squall-line is expected along the cold front progression. Later overnight, storms will cluster into a few big system trailing eastwards and bring local intense rain and severe winds.

SPC has issued a large SLGT risk over south-central Plains…

… with 5% broad area for TORNS, 15%/30% for severe winds and hail… more likely higher wind threat in KS along the Pacific cold front and very large hail threat over N TX/S OK where CAPE/shear profiles are maximized…

YDAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0756 AM CDT MON APR 02 2012

VALID 021300Z – 031200Z

…THERE IS A SLGT RISK OF SVR TSTMS FROM A LARGE PART OF TX N AND
NE INTO PARTS OF THE CNTRL PLNS AND LWR MS VLY…

…SYNOPSIS…
A COMPLEX UPR PATTERN WILL PREVAIL THIS PERIOD…WITH SVR TSTM POTENTIAL LARGELY TIED TO UPR SYSTEM NOW CLOSING OFF NEAR THE FOUR CORNERS. THE LOW SHOULD ELONGATE W-E AS IT DRIFTS ESE ACROSS NM LATER TODAY/TNGT. ONE OF THE RESULTING VORT LOBES ALREADY IS BECOMING APPARENT IN SATELLITE IMAGERY ATTM OVER SRN NM. THIS FEATURE SHOULD PIVOT NNE ACROSS W TX LATER TODAY…AND NWD ACROSS THE TX PANHANDLE TNGT…AS UPSTREAM LOBE MOVES S ACROSS AZ.

SE OF THE FOUR CORNERS LOW…VWP AND SATELLITE DATA INDICATE THAT A FAIRLY BROAD MCV HAS EVOLVED OVER S CNTRL/SE TX FROM CONVECTIVE COMPLEX THAT CROSSED THE REGION OVERNIGHT. ALSO LINGERING IN THE AREA IS REMNANT OF THE SMALL UPR LVL CIRCULATION THAT FORMED OVER THE TX GULF CST YESTERDAY. THE COMBINED CIRCULATIONS SHOULD MOVE GENERALLY NNE ACROSS THE REMAINDER OF E TX AND LA/AR LATER TODAY/TNGT AS THEY BECOME ABSORBED WITHIN STRENGTHENING MID/UPR LVL FLOW DOWNSTREAM FROM THE FOUR CORNERS LOW.

FARTHER N…NRN PART OF TROUGH THAT GAVE BIRTH TO THE FOUR CORNERS SYSTEM WILL TRACK E ACROSS MT AND THE DAKOTAS AS A HIGH AMPLITUDE RIDGE PERSISTS FROM THE ERN GULF CST TO THE UPR GRT LKS. EWD MOTION OF THE MT/DAKOTAS IMPULSE WILL MAINTAIN STEADY EWD ADVANCE OF ASSOCIATED COLD FRONT NOW OVER THE NRN/CNTRL PLNS…WITH THIS BOUNDARY EXPECTED TO EXTEND FROM ERN WI TO CNTRL MO BY 12Z TUE. A MORE COMPLEX SFC EVOLUTION LIKELY WILL EXIST OVER THE SRN PLNS. APPROACH OF AFOREMENTIONED NM VORT LOBE SHOULD DRIVE PACIFIC COLD FRONT/DRY LINE E/NE ACROSS W CNTRL TX AND THE TX PANHANDLE THIS AFTN…WHILE ASSOCIATED SFC LOW REMAINS QSTNRY NEAR AMA. FARTHER S…COLD POOL FROM OVERNIGHT S TX MCS LIKELY WILL HAVE SOME
LINGERING INFLUENCE ON LOW LVL CONVERGENCE/UPLIFT PATTERNS FROM S CNTRL TX NEWD INTO LA.

…W TX NNE INTO WRN/CNTRL KS AND SE NEB THIS AFTN/EVE…
CONDITIONS SHOULD BECOME INCREASINGLY FAVORABLE FOR STRONG TO SVR STORMS ALONG AN ARC FROM W CNTRL TX NWD THROUGH WRN OK…SW KS…N CNTRL KS…AND SE NEB LATER TODAY AS SFC HEATING DESTABILIZES REGION ALONG AND AHEAD OF MERGING DRY LINE AND PACIFIC COLD FRONT.

EVOLUTION OF STORMS AND THEIR ATTENDANT SVR THREATS WILL BE COMPLICATED BY THE VARIABLE WIND FIELDS THAT WILL EXIST ACROSS THIS REGION THROUGH SPACE AND TIME AS NM VORT LOBE PIVOTS NE ACROSS REGION. ATTM IT APPEARS THAT THE MOST FAVORABLE JUXTAPOSITION OF DEEPLY VEERING WIND PROFILES…STEEP LOW TO MID LVL LAPSE RATES…AND LOW LVL MOISTURE WILL EXIST FROM WRN N TX N AND NNW THROUGH WRN OK INTO SW KS LATE THIS AFTN. EARLY PASSAGE OF THE VORT LOBE IN TX ADDS A FURTHER COMPLICATION TO THE SITUATION. BUT OVERALL COMBINATION OF PERSISTENT LOW LVL CONVERGENCE ALONG DRY LINE/COLD FRONT…STRONG INSTABILITY /SBCAPE 2500-3500 J PER KG/…AND WIND PROFILES THAT WILL BE SUFFICIENT FOR SUSTAINED STORMS/SUPERCELLS EXPECTED TO YIELD A SIGNIFICANT SVR THREAT NONETHELESS.

LARGE HAIL SHOULD BE THE DOMINANT SVR RISK…ALTHOUGH SOME POTENTIAL ALSO WILL EXIST FOR TORNADOES…ESPECIALLY IN SW KS AND WRN OK WHERE LOW LVL WINDS ARE APT TO REMAIN BACKED NE OF TX PANHANDLE SFC LOW. FARTHER N…MORE SLOWLY-MOVING PORTION OF COLD FRONT IN NRN KS AND SE NEB SHOULD BE THE FOCUS FOR HAIL AND LOCALLY DMGG WIND. THE STORMS MAY EVOLVE INTO TWO OR THREE CLUSTERS THIS EVE…WITH A GRADUALLY DIMINISHING RISK FOR SVR HAIL AND WIND.

…E TX INTO MUCH OF LA/AR LATER TODAY THROUGH THIS EVE…
SFC HEATING OF MOIST ENVIRONMENT DOWNSTREAM FROM S TX MCV WILL LEAD TO MODERATE INSTABILITY ACROSS MUCH OF E TX…LA…AND AR LATER TODAY…WITH SBCAPE LIKELY TO BE ON THE ORDER OF 2000 /KG. FORCING FOR ASCENT ATTENDANT TO THE N TO NE-MOVING CIRCULATION SHOULD FOSTER FAIRLY WIDESPREAD TSTM DEVELOPMENT. WHILE DEEP SHEAR WILL REMAIN COMPARATIVELY MODEST /AROUND 30 KTS/…SETUP COULD YIELD SCTD STRONG TO SVR WIND GUSTS AND HAIL. GIVEN THE PRESENCE OF FAVORABLE STORM INTERACTIONS AND/OR SMALL SCALE CIRCULATIONS WITHIN EXPECTED STORM CLUSTERS/BANDS…A CONDITIONAL RISK ALSO WILL EXIST FOR WEAK TORNADOES.

..CORFIDI/COHEN.. 04/02/2012

My initial target today would be somewhere around Wichita Falls, TX and then adjusting prior to the storm initiation.

As this will again be a rather slow moving closed low across the southern Plains in the next few days, it could result in large rainfall accumulations once again over the Plains, surely very positive for soil moisture improvements.

Stay tuned for future updates!