SPC 2000Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0257 PM CDT SUN JUL 26 2015 VALID 262000Z - 271200Z ...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTERNOON AND EVENING ACROSS THE NORTHERN AND CENTRAL HIGH PLAINS... ...THERE IS A MRGL RISK OF SVR TSTMS ACROSS SURROUNDING AREAS OF THE PLAINS... ...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PARTS OF THE OHIO VALLEY...ALLEGHENY PLATEAU INTO THE HUDSON VALLEY... ...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PARTS OF SOUTHWEST THROUGH CENTRAL MONTANA... ...SUMMARY... A FEW SEVERE STORMS ARE POSSIBLE THIS AFTERNOON ACROSS PARTS OF THE NORTHERN AND CENTRAL HIGH PLAINS. WIDELY SCATTERED STRONG STORMS ARE ALSO POSSIBLE ACROSS PARTS OF THE OHIO VALLEY...AND THE ALLEGHENY PLATEAU REGION INTO THE HUDSON VALLEY...AS WELL AS ACROSS PARTS OF SOUTHWESTERN INTO CENTRAL MONTANA. ...20Z OUTLOOK UPDATE... CATEGORICAL AND PROBABILISTIC LINES HAVE BEEN ADJUSTED TO ACCOUNT FOR THE LATEST TRENDS CONCERNING CONVECTIVE DEVELOPMENT AND DESTABILIZATION. ...PLAINS... WIDELY SCATTERED THUNDERSTORM DEVELOPMENT IS ALREADY UNDERWAY NEAR THE LEE SURFACE TROUGH ACROSS THE CENTRAL AND NORTHERN HIGH PLAINS...LIKELY TO DUE AT LEAST THE APPROACH OF CONVECTIVE TEMPERATURES...WHERE LOW-LEVEL CONVERGENCE HAS BECOME LOCALLY ENHANCED. THIS ACTIVITY IS EXPECTED TO PERSIST AND GRADUALLY INTENSIFY THROUGH LATE AFTERNOON IN AN ENVIRONMENT THAT APPEARS CHARACTERIZED BY STEEP LOWER/MID TROPOSPHERIC LAPSE RATES...SIZABLE CAPE AND WEAK TO MODEST SHEAR. AN INCREASE IN STORM COVERAGE IS ALSO PROBABLE...PARTICULARLY ACROSS PARTS OF EASTERN COLORADO AND NORTHWEST KANSAS INTO WESTERN NEBRASKA...LIKELY AIDED BY FORCING ASSOCIATED WITH A WEAK IMPULSE EMBEDDED WITHIN THE MID-LEVEL MOIST PLUME WRAPPING AROUND THE WESTERN PERIPHERY OF THE SOUTHERN PLAINS SUBTROPICAL HIGH CENTER. ...OHIO VALLEY INTO NORTHEAST... LOW PROBABILITIES FOR MARGINALLY SEVERE HAIL AND WIND ARE BEING MAINTAINED ALONG AN AXIS OF MODEST BOUNDARY LAYER DESTABILIZATION WHICH HAS TAKEN PLACE WITH DAYTIME HEATING ACROSS PARTS OF THE OHIO VALLEY...AND THE ALLEGHENY PLATEAU INTO THE HUDSON VALLEY. IN THE PRESENCE OF WEAK DEEP LAYER MEAN FLOW AND SHEAR...SUBSTANTIVE FURTHER CONVECTIVE INTENSIFICATION DOES NOT SEEM TOO LIKELY...BUT CONSIDERABLE THUNDERSTORM ACTIVITY IS ALREADY UNDERWAY. ...MIDDLE MISSISSIPPI VALLEY... CONVECTIVE OUTFLOW HAS STABILIZED THE BOUNDARY LAYER NEAR THE IMMEDIATE VICINITY OF THE MISSISSIPPI RIVER ACROSS MISSOURI/ ILLINOIS AND IOWA. ON THE WESTERN FLANK OF A REMNANT OUTFLOW BOUNDARY NOW ARCING ACROSS WESTERN TENNESSEE AND NORTHEAST ARKANSAS INTO PARTS OF SOUTH CENTRAL MISSOURI...MOISTURE CONTENT REMAINS SEASONABLY HIGH AND IS CONTRIBUTING TO LARGE MIXED LAYER CAPE. ALTHOUGH SOME RECENT INCREASE IN THUNDERSTORMS IS NOTED TO THE EAST AND SOUTHEAST OF FORT LEONARD WOOD...THE TENDENCY FOR WARMING ALOFT IN CONJUNCTION WITH GENERALLY WEAK FORCING FOR ASCENT...DEEP LAYER MEAN FLOW AND SHEAR SEEM TO LIMIT CONVECTIVE POTENTIAL THROUGH THE REMAINDER OF THE PERIOD. ...NORTHERN ROCKIES... THE LACK OF MORE SUBSTANTIVE POST-FRONTAL BOUNDARY LAYER MOISTENING AND DESTABILIZATION APPEARS THE MAIN LIMITING FACTOR AS THUNDERSTORMS DEVELOP ACROSS THE MOUNTAINS OF SOUTHWEST INTO CENTRAL MONTANA IN RESPONSE TO STRENGTHENING FORCING FOR ASCENT. DEEP LAYER SHEAR IS SUFFICIENT TO SUPPORT ORGANIZED SEVERE STORMS...INCLUDING SUPERCELLS. HOWEVER...AT THIS POINT...TOO MUCH UNCERTAINTY REMAINS TO SUPPORT ANYTHING BEYOND MARGINAL SEVERE PROBABILITIES. ..KERR.. 07/26/2015 .PREV DISCUSSION... /ISSUED 1130 AM CDT SUN JUL 26 2015/ ...CNTRL/NRN HIGH PLAINS... MORNING SATELLITE IMAGERY DEPICTS MOSTLY CLEAR SKIES ACROSS THE HIGH PLAINS FROM THE RIO GRANDE TO CANADIAN BORDER. DIURNAL HEATING/MIXING AND WEAK BACKGROUND ASCENT/HEIGHT FALLS FROM ERN CO NWD SHOULD CONTRIBUTE TO WIDELY SCATTERED CONVECTIVE INITIATION ALONG/AHEAD OF HIGH PLAINS LEE/THERMAL TROUGH LATER THIS AFTERNOON. DESPITE VERY WARM MID-LEVEL TEMPS DELINEATING LOWER LAYER OF EML PLUME...DEEPER BOUNDARY LAYER MIXING/HEATING SHOULD BE ABLE TO AID IN OVERCOMING CONVECTIVE INHIBITION WITH AT LEAST A FEW STORMS ABLE TO TAP INTO STRONG SURFACE-BASED INSTABILITY. EFFECTIVE SHEAR ON THE ORDER OF 25-30KT SHOULD SUPPORT A COUPLE OF MORE PERSISTENT STORM UPDRAFTS/SUPERCELLS WITH THE CAPABILITY OF PRODUCING HAIL AND HIGH WINDS. SOMEWHAT GREATER STORM COVERAGE AND PERSISTENCE MAY EXIST ACROSS ERN CO WHERE STORMS MAY DRIFT TOWARD AXIS OF GREATER LOW LEVEL MOISTURE/DESTABILIZATION ALONG THE CO/KS BORDER WITH TIME. SOME OF THIS ACTIVITY MAY ALSO PERSIST INTO THE NIGHTTIME HOURS AS MASS TRANSPORT AND LOW LEVEL ASCENT ARE MAXIMIZED ON THE NOSE OF PLAINS LLJ. ...MIDWEST/TO NORTH OF OH VALLEY/ALLEGHENY PLATEAU... FORECAST IS COMPLICATED ACROSS THE MIDWEST GIVEN THE DECAYING REMNANTS OF A PAIR OF OVERNIGHT MCS/S...ONE NOW CROSSING THE LOWER OH RIVER VALLEY IN WRN KY AND THE MO BOOTHEEL...THE OTHER MOVING INTO WRN IL FROM SERN IA AND ERN MO. NRN SYSTEM APPEARS TO BE ASSOCIATED WITH A RELATIVELY STRONG SHORTWAVE TROUGH EVIDENT ON WATER VAPOR SATELLITE IMAGERY OVER MN/IA...AND A PACKET OF STRONGER 30-35 KT MIDLEVEL FLOW PER REGIONAL VWP OBSERVATIONS. STRONG HEATING IN THE WAKE OF THE SHORTWAVE/MCV ACROSS MN/IA WILL CONTRIBUTE TO AN AXIS OF STRONG INSTABILITY ALONG THE EDGE OF THE PLAINS CAPPING INVERSION/EML. WHILE LARGE SCALE SUPPORT FOR ASCENT WILL PROBABLY BE WANING ALONG THIS CORRIDOR...A CONDITIONAL SEVERE HAIL/WIND RISK WILL BE MAINTAINED IN THE EVENT ISOLATED STORMS CAN DEVELOP GIVEN CONTINUING LOW LEVEL CONVERGENCE ALONG RESIDUAL FRONT AND OUTFLOW BOUNDARIES REMAINING IN THE PRESENCE OF STRONG TO LOCALLY EXTREME DESTABILIZATION. FARTHER EAST....FROM IND TO PA...INSTABILITY AND WEAK LIFT WILL BE FOCUSED ALONG THE STALLED FRONT SITUATED ACROSS THESE AREAS. A FEW AFTERNOON OR EARLY EVENING STORMS COULD RESULT IN LOCALLY STRONG GUSTS AND PERHAPS A COUPLE OF TREE-DOWN EVENTS. ...NORTHEAST... MODEST WARM SECTOR DESTABILIZATION WAS UNDERWAY WITH LATEST OBJECTIVE DATA INDICATING MLCAPE OF AROUND 1000 J/KG ACROSS MUCH OF NY AND LITTLE IN THE WAY OF INHIBITION. LARGE SCALE PATTERN ACROSS NEW ENGLAND IS MARGINALLY SUPPORTIVE OF SEVERE STORMS IF STORMS CAN DEVELOP WITHIN THE WARM SECTOR...AND NEAR/ALONG CT RIVER VALLEY WARM FRONT LATER THIS AFTERNOON. NWLY FLOW AT MIDLEVELS AND WEAK SLY/SELY FLOW NEAR THE SURFACE WILL RESULT IN LOCALLY SUFFICIENT SHEAR FOR A FEW STRONGER UPDRAFTS CAPABLE OF GUSTY WINDS AND PERHAPS SOME HAIL. MAIN LIMITING FACT IS THE LACK OF STRONGER DEEP-LAYER ASCENT AS PRIMARY SHORTWAVE TROUGH APPEARS TO BE CROSSING THE REGION NOW FOLLOWED BY NEUTRAL TO WEAK HEIGHT RISES AROUND THE TIME OF MAXIMUM STORM INITIATION POTENTIAL. NONETHELESS...IF STORMS CAN DEVELOP...THERE MAY EVOLVE A BRIEF PERIOD OF SEVERE WEATHER IN THE FORM OF MARGINALLY STRONG WIND GUSTS AND HAIL LATER THIS AFTERNOON. ...NRN ROCKIES... AN AMPLIFYING MID/UPPER TROUGH ACROSS BC AND THE PACIFIC NORTHWEST WILL SUPPORT THE INTENSIFICATION OF A SWLY MID/UPPER JET ACROSS THE NRN ROCKIES THIS PERIOD. HEATING ACROSS THE HIGHER TERRAIN SHOULD AID IN CONVECTIVE INITIATION LATER THIS AFTERNOON GIVEN DECREASING STATIC STABILITY AND SUFFICIENT MOISTURE TO SUPPORT MLCAPE ON THE ORDER OF 500 J/KG. WITH MEAN WIND AROUND 50KT AND MODEST DIRECTIONAL SHEAR AROUND CLOUD BASE THERE IS THE POSSIBILITY FOR A FEW FAST-MOVING LOW-TOPPED SUPERCELLS WITH SOME CHANCE FOR HAIL AROUND AN INCH AND LOCALLY NEAR-SEVERE WIND GUSTS.
from SPC Convective Outlooks http://1.usa.gov/1OIoOEG
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