May 21, 2011 2000 UTC Day 1 Convective Outlook | |
Updated: Sat May 21 20:02:11 UTC 2011 | |
Probabilistic to Categorical Outlook Conversion Table |
Categorical Graphic |
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Probabilistic Tornado Graphic |
Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point. |
Probabilistic Damaging Wind Graphic |
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point. |
Probabilistic Large Hail Graphic |
Probability of hail 1" or larger within 25 miles of a point. Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point. |
SPC AC 211958 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0258 PM CDT SAT MAY 21 2011 VALID 212000Z - 221200Z ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MID MO VALLEY INTO PARTS OF THE LOWER MS VALLEY AND SRN TX... ...SRN PLAINS INTO MID MS VALLEY... ONLY MINOR CHANGES MADE TO 1630Z OUTLOOK. EXTENDED SLIGHT RISK SWWD INTO SRN TX...REFERENCE WW 316...AS EXIT REGION OF 60 KT JET MAX MOVING NEWD INTO THE ARKLATEX HAS INCREASED CONVERGENCE ALONG DRYLINE. VERY UNSTABLE AIR MASS...MLCAPES NEAR 3500 J/KG... AND DEEP LAYER SHEAR AROUND 40 KT WILL SUPPORT SUPERCELLS WITH SEVERE HAIL THE PRIMARY THREAT. ALSO SHIFTED THE SRN PORTION OF SLIGHT RISK IN TX SWD...SINCE SOME OF THE HIGH RESOLUTION MODELS INDICATE A FEW OF THE STORMS DEVELOPING EAST OF THE DRYLINE IN CENTRAL TX WILL SHIFT EWD ALONG AND NORTH OF INTERSTATE 10. RELATIVELY THICK LOW CLOUDS ACROSS NERN TX/SERN OK SHOULD DECREASE THROUGH THE AFTERNOON AS JET MAX MOVES NEWD AND LARGE SCALE LIFT INCREASES ACROSS THE REGION...WITH A THREAT FOR SEVERE STORMS LATE AFTERNOON/EVENING. THE STORMS MAY CONTINUE NEWD FROM CENTRAL AR INTO WRN TN OVERNIGHT...BUT STORMS SHOULD WEAKEN IN INTENSITY AS THEY MOVE INTO A LESS UNSTABLE ENVIRONMENT. ....ERN SD/SRN MN INTO CENTRAL PLAINS... HAVE RAISED TORNADO PROBABILITIES TO 5% IN FAR SERN NEB AND WRN IA WHERE LOW LEVEL WIND PROFILES MAY IMPROVE ENOUGH FOR A BRIEF TORNADO OR TWO. SLIGHT RISK WAS EXTENDED WWD ACROSS FAR SRN NEB AND NRN KS AS VISIBLE SATELLITE SHOWS CONVECTION DEVELOPING ALONG SURFACE TROUGH MOVING EWD INTO THE AREA. ALSO INCREASED WIND PROBABILITIES ACROSS NRN MO AND IA WHERE STORMS ARE EXPECTED TO CONGEAL INTO A SMALL LINEAR MCS THIS EVENING...WITH GREATER COVERAGE OF DAMAGING WINDS POSSIBLE. ..IMY.. 05/21/2011 .PREV DISCUSSION... /ISSUED 1117 AM CDT SAT MAY 21 2011/ ...ERN SD/SRN MN INTO CNTRL PLAINS... IN THE WAKE OF INITIAL VORTICITY MAXIMUM LIFTING NWD THROUGH THE MID MO VALLEY...MORNING WATER VAPOR IMAGERY SHOWS THE NEXT UPSTREAM IMPULSE OVER WRN PARTS OF NEB/KS. THIS LATTER FEATURE IS FORECAST TO PIVOT NEWD THROUGH THE MID MO VALLEY TODAY PROVIDING FAVORABLE LARGE-SCALE FORCING FOR ASCENT FOR STRONG-SEVERE TSTM DEVELOPMENT. WEAK COLD FRONT/PRESSURE TROUGH CURRENTLY EXTENDING FROM SURFACE LOW S OF BIS SEWD INTO ERN NEB WILL LIKELY SERVE AS THE FOCUS FOR THIS STORM DEVELOPMENT AS IT SLOWLY PROGRESSES EWD ACROSS THE REGION. 12Z OAX SOUNDING SHOWED THAT THE PRE-FRONTAL AIR MASS IS ONLY WEAKLY CAPPED WITH STEEP MIDLEVEL LAPSE RATES APPROACHING 8 C/KM. DAYTIME HEATING...COUPLED WITH BOUNDARY LAYER DEWPOINTS IN THE LOWER 60S AND THE STEEP MIDLEVEL LAPSE RATES WILL YIELD A MODERATELY UNSTABLE AIR MASS BY AFTERNOON WITH MLCAPE VALUES APPROACHING 1500-2500 J/KG. VERTICAL SHEAR PROFILES WILL REMAIN SOMEWHAT CHAOTIC...EXHIBITING A VEERING-BACKING PATTERN. NONETHELESS...THE PRESENCE OF THE STEEP LAPSE RATES AND SEASONABLY COOL MIDLEVEL TEMPERATURES WILL BE QUITE SUPPORTIVE OF LARGE HAIL WITH THE MOST INTENSE STORMS. FARTHER S INTO ERN KS AND MO...12Z TOP SOUNDING INDICATED A STRONGER CAP RELATIVE TO OAX WITH STORM INITIATION LIKELY BEING DELAYED UNTIL LATER THIS AFTERNOON INTO EVENING. LATEST MODEL GUIDANCE SUGGESTS THAT AREAS GENERALLY N OF I-70 WILL SEE THE GREATEST COVERAGE OF TSTMS...WITH AREAL COVERAGE DECREASING WITH SWD EXTENT. HERE TOO...THERMODYNAMIC ENVIRONMENT WILL BE CHARACTERIZED BY STEEP LAPSE RATES AND MLCAPE OF 2000-2500 J/KG. WHEN COUPLED WITH 30-35 KT OF DEEP WLY SHEAR...SETUP WILL SUPPORT THE DEVELOPMENT OF ORGANIZED MULTICELL AND SUPERCELL STRUCTURES WITH LARGE HAIL BEING THE PRIMARY HAZARD. STORMS MAY GROW UPSCALE INTO AN MCS WITH SOME THREAT FOR GUSTY WINDS AND HAIL CONTINUING ACROSS THE LOWER MO VALLEY OVERNIGHT. ...SRN PLAINS INTO LOWER MS VALLEY... MID MORNING SURFACE ANALYSIS SHOWS THAT THE MARITIME TROPICAL AIR MASS --SEE 12Z BRO/CRP SOUNDINGS-- EXTENDS FROM THE TX HILL COUNTRY INTO SRN LA...ALONG AND S OF OUTFLOW BOUNDARY ASSOCIATED WITH A NOCTURNAL MCS...THE REMAINS OF WHICH ARE STILL IN PROGRESS OVER W-CNTRL LA. IT DOES APPEAR THAT THIS HIGH THETAE AIR WILL BE ADVECTED NWD INTO NERN TX/SERN OK TODAY AHEAD OF DRYLINE THAT IS FORECAST TO MIX EWD TO NEAR OR E OF THE I-35 CORRIDOR. THIS MOISTURE COMBINED WITH THE NRN FRINGE OF STEEP MIDLEVEL LAPSE RATE PLUME WILL CONTRIBUTE TO A MODERATELY TO STRONGLY UNSTABLE WARM SECTOR BY LATE AFTERNOON WITH MLCAPE OF 2000-3500 J/KG. WEAK MIDLEVEL IMPULSE OVER WRN TX /EVIDENT IN WATER VAPOR IMAGERY/ WILL TRANSLATE EWD AND PROVIDE FAVORABLE BACKGROUND FORCING FOR DRYLINE TSTM DEVELOPMENT LATE THIS AFTERNOON INTO EVENING. REGIONAL PROFILER/VAD DATA INDICATE THE PRESENCE OF A 50-60 KT MIDLEVEL JET STREAK ACROSS REGION TODAY WHICH WILL RESULT IN MORE THAN SUFFICIENT VERTICAL SHEAR FOR SUPERCELLS GIVEN THE DEGREE OF INSTABILITY. INITIALLY...LARGE HAIL WILL BE THE PRIMARY THREAT. HOWEVER...A RISK FOR TORNADOES WILL INCREASE THIS EVENING AS LOW-LEVEL SHEAR STRENGTHENS IN RESPONSE TO THE DEVELOPMENT OF A SLY LLJ. THEREAFTER...THERE IS SOME INDICATION THAT STORMS MAY GROW UPSCALE INTO AN MCS WITH A WIND/HAIL THREAT CONTINUING THROUGH TONIGHT INTO PORTIONS OF THE LOWER MS VALLEY/MID SOUTH. ...OH VALLEY... CONSIDERABLE UNCERTAINTY EXISTS WITH RESPECT TO DIURNAL TSTM DEVELOPMENT GIVEN THE ABSENCE OF ANY WELL-DEFINED FORCING MECHANISMS. DIFFUSE WARM FRONT EXTENDING FROM NRN IL INTO CNTRL IND AS OF LATE MORNING MAY SERVE AS THE FOCUS FOR ISOLATED TSTM DEVELOPMENT THIS AFTERNOON. AMBIENT ENVIRONMENT IS CHARACTERIZED BY VERTICALLY VEERING WIND PROFILES INVOF WARM FRONT WITH A RELATIVELY MOIST BOUNDARY LAYER WITH DEWPOINTS IN THE LOW/MID 60S. THE PRIMARY FACTORS LIMITING A MORE ROBUST SEVERE WEATHER THREAT APPEAR TO BE THE MARGINAL DEEP-LAYER SHEAR AND WEAK MIDLEVEL LAPSE RATES WHICH WILL LIMIT THE DEGREE OF DESTABILIZATION. STILL...ISOLATED STRONG-SEVERE STORMS WILL BE POSSIBLE WITH A RISK FOR GUSTY WINDS...SOME HAIL AND PERHAPS A BRIEF TORNADO. CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z