SPC 2000Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0300 PM CDT TUE JUL 09 2013 VALID 092000Z - 101200Z ...THERE IS A SLGT RISK OF SVR TSTMS FROM PORTIONS OF THE CENTRAL PLAINS EWD INTO THE OHIO VALLEY... TWO PRIMARY CHANGES HAVE BEEN MADE WITH THIS OUTLOOK. FIRST...REMOVED SLIGHT RISK ACROSS MUCH OF WI/NERN MN WHERE STABILIZING INFLUENCE OF MORNING CONVECTION AND WIDESPREAD CLOUD COVER HAVE MITIGATED AFTERNOON DESTABILIZATION...WITH VALUES GENERALLY AOB 1000 J/KG OF MLCAPE. AN ISOLATED SVR TSTM CANNOT BE RULED OUT WHERE MODEST ADDITIONAL DESTABILIZATION IN THE VICINITY OF SURFACE BOUNDARIES AND 30-40 KTS OF EFFECTIVE BULK SHEAR IS PRESENT...BUT COVERAGE IS EXPECTED TO BE TOO SPARSE FOR 15 PERCENT PROBS AND SLIGHT RISK. THE SECOND SIGNIFICANT CHANGE IS TO EXTEND THE SLIGHT RISK FARTHER WEST ACROSS PORTIONS OF IOWA WHERE HEATING/DESTABILIZATION HAS OCCURRED IN ADVANCE OF SURFACE TROUGH/FRONT. SURFACE DEW POINTS IN THE LOWER TO MID 70S RESIDE BENEATH ERN EDGE OF STEEPER MID-LEVEL LAPSE RATES...RESULTING IN MLCAPE VALUES BETWEEN 2000 AND 3000 J/KG. EFFECTIVE SHEARS WOULD BE SUPPORTIVE OF ORGANIZED TSTMS WITH A SVR WIND AND HAIL THREAT WITH ANY STORM THAT DEVELOPS. NO OTHER CHANGES WERE MADE TO PREVIOUS OUTLOOK. ..BUNTING.. 07/09/2013 .PREV DISCUSSION... /ISSUED 1129 AM CDT TUE JUL 09 2013/ A LARGE UPPER RIDGE IS PRESENT TODAY OVER THE SOUTHERN AND CENTRAL UNITED STATES...WHILE A SHORTWAVE TROUGH EMBEDDED IN THE STRONGER WESTERLIES TRACKS ACROSS THE DAKOTAS/MN. A LARGE MCS ASSOCIATED WITH THE NORTHERN TROUGH HAS PROGRESSED MUCH FASTER AND FARTHER EAST THAN FORECAST BY OVERNIGHT MODEL SOLUTIONS. THIS HAS RESULTED IN SIGNIFICANT FORECAST CHANGES FOR THIS UPDATE...WITH REDUCED SEVERE PROBABILITIES OVER MUCH OF THE MIDWEST AND MS VALLEY. ...GREAT LAKES INTO MID MS VALLEY... THE LEADING EDGE OF THE LARGE MCS CURRENTLY EXTENDS FROM WI INTO IL. THIS ACTIVITY MAY PERSIST EASTWARD ACROSS LAKE MI INTO WESTERN LOWER MI THIS AFTERNOON WITH A CONTINUED RISK OF LOCALLY SEVERE STORMS. DAMAGING WINDS APPEAR TO BE THE MAIN THREAT. PERSISTENT CLOUD COVER OVER EASTERN/NORTHERN LOWER MI AND MUCH OF UPPER MI SHOULD LESSEN INSTABILITY AND THE RESULTING SEVERE RISK AS STORMS MOVE EASTWARD THIS EVENING. ...MO/KS... A TRAILING SURFACE BOUNDARY EXTENDS FROM SOUTHEAST NEB INTO NORTHERN KS. THIS BOUNDARY SHOULD SETTLE INTO NORTHERN MO BY MID AFTERNOON...WHEN SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP. STRONG HEATING IN THIS REGION WILL YIELD STEEP LOW LEVEL LAPSE RATES AND MODERATE CAPE...OFFSETTING ONLY MARGINAL VERTICAL SHEAR. A FEW ORGANIZED MULTICELL OR WEAK SUPERCELL STRUCTURES ARE POSSIBLE ALONG THE BOUNDARY OVER NORTHERN MO AND KS THIS AFTERNOON WITH A RISK OF DOWNBURSTS OR HAIL IN THE STRONGEST CORES. ...IN/OH/WV/KY... A MOIST AND QUITE UNSTABLE AIR MASS IS IN PLACE TODAY OVER THE OH VALLEY...WITH STRONG HEATING OCCURRING OVER MUCH OF THE AREA. 12Z MODEL SOLUTIONS SHOW SCATTERED THUNDERSTORM DEVELOPMENT THIS AFTERNOON. PWAT VALUES OF NEAR 2 INCHES COMBINED WITH 25-35 KNOT WESTERLY MID LEVEL FLOW MAY BE SUFFICIENT FOR ISOLATED SEVERE STORMS CAPABLE OF DAMAGING WINDS AND HAIL. ...AZ... LATEST VWP FROM IWA SHOWS 20+ KNOTS OF NORTHEASTERLY MID LEVEL WINDS OVER SOUTHERN AZ. MEANWHILE...EASTERLY LOW LEVEL WINDS HAVE DRAWN LOW TO MID 60S DEWPOINTS INTO THE PHX AREA. MOST MODEL SOLUTIONS SUGGEST THE POTENTIAL FOR SCATTERED THUNDERSTORM DEVELOPMENT OVER THE HIGHER TERRAIN OF EAST-CENTRAL AND SOUTHEAST AZ LATER TODAY. STEERING FLOW AND PROPAGATION MIGHT HELP THESE STORMS PERSIST INTO THE LOWER DESERTS THIS EVENING. ANY STORMS THAT CAN SURVIVE WOULD HAVE A THREAT OF DAMAGING WINDS.
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_2000.html
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