The SPC is forecasting ...severe thunderstorms expected over parts of the upper midwest into the ohio valley this afternoon and tonight.... Please read the latest public statement about this event. View What is a Watch? clip.
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| 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. |
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| 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. |
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| 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. |
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SPC AC 121220 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0720 AM CDT WED JUN 12 2013 VALID 121300Z - 131200Z ...THERE IS A MDT RISK OF SVR TSTMS TODAY ACROSS PARTS OF EASTERN IOWA...THROUGH MUCH OF NORTHERN AND CENTRAL ILLINOIS...INDIANA AND WESTERN OHIO... ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MODERATE RISK AREA ACROSS UPPER PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY...THE SOUTHERN GREAT LAKES REGION...OHIO VALLEY AND PARTS OF THE MID ATLANTIC COAST STATES... ...THERE IS A SLGT RISK OF SVR TSTMS TODAY ACROSS MUCH OF CENTRAL AND EASTERN MONTANA AND ADJACENT AREAS OF NORTHERN WYOMING... ...SYNOPSIS... THE REMNANTS OF A SIGNIFICANT SHORT WAVE IMPULSE...WHICH HAVE EMERGED FROM THE GREAT BASIN...ARE CURRENTLY PROGRESSING THROUGH BROADER SCALE UPPER RIDGING ACROSS THE NORTH CENTRAL PLAINS INTO THE MIDDLE MISSOURI VALLEY. THE PRIMARY PERTURBATION STILL APPEARS TO BE OVER THE DAKOTAS...WITH AT LEAST ONE OTHER NOTABLE PERTURBATION TO ITS SOUTH AND EAST...SHIFTING INTO IOWA. THESE FEATURES WILL REMAIN PROGRESSIVE TODAY...BUT LIKELY WILL TAKE A SOUTHEASTWARD TURN EAST OF THE MISSISSIPPI RIVER...TOWARD THE OHIO VALLEY/CENTRAL APPALACHIANS REGION...IN RESPONSE TO UPSTREAM AMPLIFICATION IN THE LARGE-SCALE PATTERN. AS UPPER TROUGHING CONTINUES TO DIG SOUTHWARD ALONG THE PACIFIC COAST...UPPER RIDGING IS EXPECTED TO AMPLIFY ACROSS THE GREAT PLAINS INTO THE CANADIAN PRAIRIES. AT THE SAME TIME...ANOTHER SIGNIFICANT IMPULSE ASSOCIATED WITH STRONGER WESTERLIES WILL GRADUALLY DIG SOUTHWARD ACROSS ONTARIO INTO THE GREAT LAKES REGION...ALTHOUGH CONSOLIDATION WITH THE IMPULSE NOW OVER THE NORTH CENTRAL PLAINS IS NOT FORECAST TO OCCUR UNTIL TOMORROW. IN RESPONSE TO THESE DEVELOPMENTS...LOWER/MID TROPOSPHERIC COOLING WILL OCCUR FROM THE CENTRAL PLAINS/MID MISSOURI AND UPPER MISSISSIPPI VALLEY REGION THROUGH MUCH OF THE MIDDLE MISSISSIPPI AND LOWER OHIO VALLEY BY 12Z THURSDAY. GUIDANCE IS SUGGESTIVE THAT COOLING AT MID-LEVELS WILL PRECEDE LOW-LEVEL COOLING IN THE WARM SECTOR OF A SURFACE FRONTAL WAVE...WHICH IS FORECAST TO MIGRATE ACROSS UPPER PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY INTO SOUTHERN PORTIONS OF THE GREAT LAKES REGION LATER TODAY AND TONIGHT. VERY WARM ELEVATED MIXED LAYER AIR FROM THE INTERMOUNTAIN WEST IS NOW PRESENT ACROSS MUCH OF THIS REGION...AS WELL AS MUCH OF THE CENTRAL U.S...FROM THE ROCKIES TO THE APPALACHIANS. THIS IS CURRENTLY CAPPING FAIRLY MOIST LOW-LEVELS...BUT SUPPORTING LARGE CAPE. WITH DAYTIME HEATING OF A BOUNDARY LAYER WITH SURFACE DEW POINTS AROUND 70F...MIXED LAYER CAPE OF 2000-3000+ J/KG APPEARS LIKELY BY LATE AFTERNOON ACROSS A BROAD AREA OF THE MIDDLE MISSISSIPPI INTO LOWER OHIO VALLEYS...AND MUCH OF THE SOUTHEAST. MEANWHILE...WEAK MID-LEVEL COOLING AHEAD OF THE PACIFIC COAST UPPER TROUGH MAY ALSO CONTRIBUTE TO SUBSTANTIVE DESTABILIZATION /MIXED LAYER CAPE ON THE ORDER OF 1000 J PER KG/ ACROSS MUCH OF CENTRAL...EASTERN MONTANA AND ADJACENT AREAS OF NORTHERN WYOMING BY LATE THIS AFTERNOON. ...MISSISSIPPI VALLEY TO ATLANTIC COAST... AROUND THE PERIPHERY OF THE STRONGLY CAPPING ELEVATED MIXED LAYER AIR...SCATTERED CONVECTIVE DEVELOPMENT...MOSTLY WEAK...IS ONGOING ACROSS PARTS OF THE UPPER MIDWEST AND SOUTHERN GREAT LAKES REGION INTO PARTS OF THE CENTRAL APPALACHIANS. THIS IS MOST LIKELY ASSOCIATED WITH AREAS OF ENHANCED LOWER/MID TROPOSPHERIC WARM ADVECTION...AND AT LEAST SOME OF THIS ACTIVITY COULD PERSIST TODAY. IF THIS OCCURS...IT IS NOT OUT OF THE QUESTION THAT CONVECTION COULD EVENTUALLY BECOME ROOTED IN A DESTABILIZING BOUNDARY LAYER ACROSS PARTS OF THE UPPER OHIO VALLEY INTO THE MID ATLANTIC STATES AND...PERHAPS...TO THE SOUTH OF THE SOUTHERN APPALACHIANS...ACROSS PARTS OF GEORGIA AND SOUTH CAROLINA. HOWEVER...PRIMARY CONVECTIVE POTENTIAL APPEARS TO EXIST TO THE NORTH AND WEST...ACROSS PARTS OF THE UPPER MIDWEST SOUTHEASTWARD THROUGH THE SOUTHERN GREAT LAKES REGION AND LOWER/MIDDLE OHIO VALLEY. THIS IS EXPECTED AS CONVECTIVE INHIBITION WEAKENS IN RESPONSE TO MID-LEVEL COLD ADVECTION AND LIFT...AS THE NORTH CENTRAL PLAINS SHORT WAVE TROUGH FINALLY DIGS SOUTHEAST OF THE MISSISSIPPI VALLEY. VARIABILITY EXISTS AMONG THE MODELS CONCERNING WHEN AND JUST HOW THIS OCCURS...AND THIS PROBABLY WILL HAVE CONSIDERABLE IMPACT ON THE LOCATION AND CHARACTER OF ENSUING CONVECTIVE DEVELOPMENT. BASED LARGELY ON THE SPC STORM-SCALE ENSEMBLE DATA...HIGHEST SEVERE PROBABILITIES AND THE MOST SIGNIFICANT SEVERE WEATHER POTENTIAL...STILL APPEAR FOCUSED IN A CORRIDOR ACROSS EAST CENTRAL IOWA INTO NORTHERN ILLINOIS LATE THIS AFTERNOON AND EVENING...INTO NORTHERN INDIANA AND WESTERN OHIO LATER TONIGHT. IN THE PRESENCE OF STRONG SHEAR AND INSTABILITY...DISCRETE SUPERCELL STORMS MAY OCCUR INITIALLY...BEFORE CONVECTION CONSOLIDATES AND GROWS UPSCALE INTO ONE OR MORE ORGANIZED CONVECTIVE CLUSTERS. STRENGTHENING SOUTHWESTERLY 850 MB FLOW TO 30-50 KT ACROSS THE LOWER OHIO VALLEY THIS EVENING MAY CONTRIBUTE TO THE RISK FOR A FEW VERY STRONG AND DAMAGING WIND GUSTS ACROSS PARTS OF NORTHERN AND CENTRAL ILLINOIS/INDIANA INTO OHIO. THE WESTERN FLANK OF THE ANTICIPATED EVOLVING MESOSCALE CONVECTIVE SYSTEM AND ASSOCIATED SURFACE COLD POOL PROBABLY WILL TEND TO PROPAGATE SOUTHWARD OR SOUTHEASTWARD TOWARD THE LOWER OHIO VALLEY...AND MODERATE RISK SEVERE PROBABILITIES HAVE BEEN ADJUSTED SOUTHWARD ACROSS ILLINOIS AND INDIANA TO ACCOUNT FOR THIS. THE RISK FOR POTENTIALLY DAMAGING WIND GUSTS MAY PERSIST WITH VIGOROUS CONVECTION THROUGH THE WESTERN SLOPES OF THE CENTRAL APPALACHIANS...AND PERHAPS ACROSS THE UPPER OHIO VALLEY INTO THE MID ATLANTIC COAST REGION...OVERNIGHT. ...CENTRAL/EASTERN MONTANA AND ADJACENT NORTHERN WYOMING... STRONGER FORCING FOR UPWARD VERTICAL MOTION AHEAD OF THE PACIFIC COAST TROUGH IS EXPECTED TO SUPPORT THE DEVELOPMENT OF SCATTERED THUNDERSTORMS IN A PLUME FROM THE NORTHERN GREAT BASIN...ACROSS AND NORTHEAST OF THE NORTHERN ROCKIES BY LATE THIS AFTERNOON. IN THE PRESENCE OF WEAK TO MODERATE INSTABILITY...LARGEST TO THE NORTHEAST OF THE HIGHER TERRAIN...ACROSS CENTRAL AND EASTERN MONTANA...VERTICAL SHEAR WILL BE SUFFICIENT FOR SCATTERED SEVERE STORMS...INCLUDING A FEW SUPERCELLS. ..KERR/LEITMAN.. 06/12/2013 CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z |