SPC 2000Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0258 PM CDT WED MAY 02 2012 VALID 022000Z - 031200Z ...THERE IS A MDT RISK OF SVR TSTMS THIS EVE ACROSS PARTS OF CNTRL/ERN NEBRASKA...SOUTHEASTERN SOUTH DAKOTA...SOUTHWESTERN MINNESOTA...WESTERN IOWA... ...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN AND EVE ACROSS PARTS OF THE NORTH CENTRAL PLAINS EASTWARD THROUGH THE SOUTHERN GREAT LAKES/OH VALLEY REGION...INTO PARTS OF THE MID ATLANTIC... ...20Z OUTLOOK UPDATE... WEAK MID-LEVEL HEIGHT RISES ARE ONGOING ACROSS MUCH OF THE PLAINS INTO THE GREAT LAKES REGION AND MID ATLANTIC COAST. AND MID/UPPER FORCING FOR UPWARD VERTICAL MOTION ASSOCIATED WITH THE SIGNIFICANT SHORT WAVE IMPULSE LIFTING THROUGH THE NORTHERN ROCKIES WILL LIKELY SPREAD INTO THE SOUTH CENTRAL CANADIAN PROVINCES...WELL NORTH OF THE MID MISSOURI VALLEY...AS LARGE-SCALE UPPER TROUGHING AMPLIFIES OFF THE PACIFIC COAST. UNCERTAINTIES REMAIN CONCERNING CONVECTIVE POTENTIAL ON THE NORTHERN PERIPHERY OF BROADER SCALE SUBTROPICAL RIDGING GRADUALLY BECOMING MORE PROMINENT FROM PORTIONS OF THE SOUTHEASTERN PLAINS INTO THE MID ATLANTIC SEABOARD. HOWEVER...MODESTLY STRONG DEEP LAYER WESTERLY MEAN FLOW FIELDS AND SHEAR REMAIN CONDUCIVE TO THE EVOLUTION OF ORGANIZED STORM CLUSTERS...FROM THE NORTH CENTRAL PLAINS THROUGH THE SOUTHERN GREAT LAKES REGION INTO PARTS OF THE MID ATLANTIC STATES...AS THE BOUNDARY LAYER DESTABILIZES. ...NORTH CENTRAL PLAINS INTO UPPER MIDWEST... THE MOST PROMINENT SURFACE FEATURE REMAINS A RESIDUAL CONVECTIVE OUTFLOW BOUNDARY...EXTENDING FROM REMNANTS OF AN OVERNIGHT CONVECTIVE COMPLEX...NOW CENTERED OVER NORTH CENTRAL ILLINOIS... WEST NORTHWARD INTO THE VICINITY OF THE MID MISSOURI VALLEY. LOW-LEVEL CONVERGENCE IS WEAK...BOTH ALONG THIS BOUNDARY...AND ALONG A WEAK SURFACE TROUGH EXTENDING FROM WESTERN KANSAS INTO CENTRAL NEBRASKA. BUT OBJECTIVE ANALYSIS INDICATES THAT MIXED LAYER CAPE IS BECOMING MODERATELY LARGE ACROSS THIS REGION...AS INSOLATION CONTINUES BENEATH STEEP MID-LEVEL LAPSE RATES. AND A SIGNIFICANT SIGNAL PERSISTS IN MODEL GUIDANCE SUGGESTING A RAPID STRENGTHENING IN LOWER/MID TROPOSPHERIC WARM ADVECTION ACROSS CENTRAL NEBRASKA INTO THE MID MISSOURI VALLEY BY 03-06Z. BASED LARGELY ON THESE TWO POINTS...IT STILL APPEARS THAT POTENTIAL EXISTS FOR THE EVOLUTION OF A SIGNIFICANT MESOSCALE CONVECTIVE SYSTEM BY LATE THIS EVENING...IF NOT BEFORE. THIS ACTIVITY COULD FORWARD PROPAGATE AS FAR EAST AS PORTIONS OF THE UPPER MISSISSIPPI VALLEY BY 12Z THURSDAY...ACCOMPANIED BY CONTINUING POTENTIAL FOR DAMAGING WINDS AND HAIL. ...SOUTHERN GREAT LAKES... SOME CHANGES TO PROBABILITY/CATEGORICAL LINES HAVE BEEN MADE TO ACCOUNT FOR ONGOING TRENDS IN CONVECTION/DESTABILIZATION. THIS INCLUDES A SLIGHT SOUTHWARD ADJUSTMENT OF SLIGHT RISK PROBABILITIES ACROSS PORTIONS OF WEST CENTRAL OHIO AND CENTRAL INDIANA...TO ACCOUNT FOR POSSIBLE CONTINUED INTENSIFICATION OF CONVECTION NOW DEEPENING ALONG OUTFLOW BOUNDARY UPSTREAM. ..KERR.. 05/02/2012 .PREV DISCUSSION... /ISSUED 1130 AM CDT WED MAY 02 2012/ ...CNTRL PLAINS LATE... MORNING SURFACE/UA ANALYSIS REVEALS DEEP-LAYER FRONTAL ZONE EXTENDING SW TO NE OVER THE CNTRL PLAINS TO A SURFACE LOW PRESSURE CENTER IN SRN ONTARIO. THE FRONT IS EMBEDDED WITHIN A BAND OF MODEST 40-50KT SWLY FLOW AT MID LEVELS AND...AT THE SURFACE...THE FRONT IS INTERSECTED BY AN OUTFLOW BOUNDARY OVER ERN NEB. MID/UPPER LEVEL FLOW OBSERVED ON WATER VAPOR DEPICTS A SHORT WAVE TROUGH MOVING ACROSS MT BUT OTHERWISE CAN BE DESCRIBED AS NON-DESCRIPT WITH REGARD TO MORE PROMINENT SHORT WAVE FEATURES THAT MAY AID ASCENT ACROSS THE PLAINS TODAY. IN FACT...MOST GUIDANCE INDICATES WEAK MID LEVEL HEIGHT RISES WILL OCCUR ACROSS MUCH OF THE REGION THROUGH THE DAYLIGHT HOURS. IN ADDITION...SUBSTANTIAL CAPPING ACROSS THE GREAT PLAINS...ESPECIALLY SOUTH OF THE FRONT/OUTFLOW INTERSECTION...WILL LIKELY LIMIT STORM INITIATION AND SUBSEQUENT SEVERE THREAT ACROSS THE MDT RISK AREA UNTIL THIS EVENING. WHILE ENVIRONMENT IS CURRENTLY HOSTILE TO MORE ROBUST TSTM DEVELOPMENT...THAT DOES NOT MEAN THAT A TREMENDOUS AMOUNT OF INSTABILITY CANNOT DEVELOP. IT SEEMS REASONABLE TO EXPECT SBCAPE TO CLIMB TO AROUND 5000 J/KG LATER THIS AFTERNOON BASED ON MORNING SOUNDINGS AND FORECAST HIGH TEMPERATURES IN AREAS EXPERIENCING MAXIMUM HEATING. IT IS POSSIBLE THAT PERSISTENT MESOSCALE CONVERGENCE/LIFT NEAR THE FRONT AND ALONG AND NORTH OF OUTFLOW...FROM ERN NEB ACROSS IA...COULD RESULT IN TSTM DEVELOPMENT IN THESE AREAS BY LATER AFTERNOON. ANY STORMS THAT CAN BREAK THE CAP IN THESE AREAS WILL POSE A THREAT OF LARGE HAIL AND DAMAGING WINDS...AND PERHAPS EVEN A TORNADO...GIVEN THE MAGNITUDE OF INSTABILITY AND EFFECTIVE SHEAR ON THE ORDER OF 40-50KT. WHILE SOME GUIDANCE DOES FORECAST THIS POTENTIAL NEAR THE IA/MN/WI BORDERS BY LATE AFTERNOON...OTHER GUIDANCE DOES NOT. THUS...RELATIVELY HIGH UNCERTAINTY EXISTS IN THIS SCENARIO. MORE CONFIDENCE EXISTS THAT STORMS WILL INITIATE OVER THE CNTRL HIGH PLAINS LATE TODAY THROUGH A COMBINATION OF DIABATIC INFLUENCES AND GREATER LARGE SCALE SUPPORT WITH THE UPPER TROUGH APPROACHING FROM MT. THE ACTIVITY WILL TRACK EAST INTO THE INSTABILITY AXIS FROM NRN KS INTO NEB THIS EVENING AND SHOULD INTENSIFY AND EXPAND INTO ONE OR TWO FORWARD-PROPAGATING STORM COMPLEXES. VERY LARGE HAIL POTENTIAL WILL EXIST WITH EARLY DEVELOPMENT. INCREASE IN NOCTURNAL LOW LEVEL JET SHOULD FURTHER SUSTAIN MASS INFLOW AND KINEMATIC REGIME APPEARS SUPPORTIVE OF WIDESPREAD SEVERE WIND GUSTS SPREADING EAST ACROSS NEB/SERN SD AND PARTS OF SWRN MN AND WRN IA THROUGH LATE TONIGHT. ...UPPER MIDWEST/NRN IA ACROSS WI/NRN IL... FORECAST UNCERTAINTY ALREADY MENTIONED FOR STORMS ACROSS SOME OF THIS AREA LATER THIS AFTERNOON. A MORE LIKELY SCENARIO WOULD BE STORMS INCREASING ALONG/NORTH OF THE RETREATING OUTFLOW/WARM FRONT LATER THIS EVENING AHEAD OF THE BOWING/MCS COMPLEX FARTHER WEST. LARGE HAIL WOULD BE A THREAT WITH THIS DEVELOPMENT GIVEN MAGNITUDE OF UPSTREAM INSTABILITY. VERY HEAVY RAIN POTENTIAL WILL ALSO EXIST ACROSS SOME OF THE AREA GIVEN THE POSSIBILITY OF BACKBUILDING/TRAINING CONVECTION. ...SERN MI ACROSS OH/WRN PA... WATER VAPOR IMAGERY REFLECTS A LOW AMPLITUDE MID-LEVEL TROUGH PROGRESSING EASTWARD OVER LOWER MI/LAKE HURON VICINITY EARLY THIS AFTERNOON. ON THE SOUTHERN PERIPHERY OF THIS FEATURE...IT SEEMS LIKELY THAT TSTMS WILL INCREASE THIS AFTERNOON WITHIN AN INCREASINGLY WARM/UNSTABLE AIRMASS ALONG/SOUTH OF A WARM FRONT ACROSS THE REGION...WITH 2000-3000 J/KG MLCAPE LIKELY WITHIN THE WARM SECTOR. GIVEN THE DEGREE OF INSTABILITY...AND THAT THE REGION/WARM FRONTAL ZONE COINCIDES WITH THE SOUTHERN FRINGE OF MODERATELY STRONG MID-LEVEL WESTERLIES...SUFFICIENT VERTICAL SHEAR /25-35 KT/ WILL EXIST FOR SUSTAINED MULTICELLS/PERHAPS SOME SUPERCELLS. SEVERE HAIL/PERHAPS A BRIEF TORNADO WILL BE POSSIBLE...BUT MORE SO...STORMS SHOULD TEND TO CONGEAL/ORGANIZE AND MOVE EAST-SOUTHEASTWARD WITH A DAMAGING WIND THREAT INTO THIS EVENING. ...MID ATLANTIC... STRONG HEATING/DESTABILIZATION WILL OCCUR THIS AFTERNOON ALONG/SOUTHWEST OF A NEARLY STALLED FRONTAL ZONE FROM WV ACROSS NRN VA TO TIDEWATER...WITH THE MOST AGGRESSIVE DESTABILIZATION LIKELY TO OCCUR NEAR THE APPALACHIANS INTO SOUTHERN/WESTERN VA AND MUCH OF NC. THE STRONGEST WEST-NORTHWESTERLY FLOW ALOFT/VERTICAL SHEAR WILL BE RELATED TO NEAR THE AFOREMENTIONED FRONTAL ZONE...BUT THE DEGREE OF LAPSE RATES/DESTABILIZATION WILL AT LEAST SUPPORT AN ISOLATED/EPISODIC POTENTIAL FOR SEVERE WIND/HAIL THIS AFTERNOON/EARLY EVENING. ...MS DELTA... WEAK AND SLOW MOVING UPPER IMPULSE/MCV WILL AID IN TSTM DEVELOPMENT FROM THE DELTA INTO CNTRL MS AND SRN AL THROUGH THE AFTERNOON. WHILE FLOW IS WEAK...VERY WARM AND MOIST AIRMASS WILL BOOST INSTABILITY SO THAT A FEW STORMS IN THE FORM OF MULTICELLULAR CLUSTERS COULD POSE A THREAT OF SOME HAIL AND DAMAGING WET MICROBURSTS.
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_2000.html
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