SPC AC 191733
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1233 PM CDT FRI JUN 19 2015
VALID 201200Z - 211200Z
...THERE IS AN ENH RISK OF SVR TSTMS OVER A SMALL PART OF THE UPPER
MS VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE UPPER MS
VALLEY/CORN BELT...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE LEE OF THE CNTRL
APPALACHIANS TO THE DELMARVA...
...THERE IS A MRGL RISK OF SVR TSTMS OVER THE CNTRL HIGH/NRN
PLAINS...
...THERE IS A MRGL RISK OF SVR TSTMS FROM THE LOWER MO VALLEY TO THE
MIDWEST...
...THERE IS A MRGL RISK OF SVR TSTMS FROM THE UPPER OH VALLEY TO THE
MID-ATLANTIC...
...SUMMARY...
A CLUSTER OF SEVERE STORMS IS EXPECTED ACROSS PARTS OF THE UPPER
MISSISSIPPI VALLEY LATE AFTERNOON TO EVENING ON SATURDAY...WITH ALL
HAZARDS POSSIBLE. SCATTERED SEVERE STORMS WILL BE POSSIBLE IN THE
AFTERNOON AND EVENING FROM THE LEE OF THE CENTRAL APPALACHIANS TO
THE DELMARVA AREA.
...SYNOPSIS...
QUASI-ZONAL MID-LEVEL FLOW WILL PERSIST OVER THE
NORTHWEST/NORTH-CENTRAL STATES WITH THE FASTEST BELT OF WLYS
EXPECTED TO BE CENTERED FROM THE CENTRAL HIGH PLAINS TO THE UPPER
GREAT LAKES AT 21/00Z. A FEW LOW-AMPLITUDE IMPULSES WILL BE EMBEDDED
WITHIN THIS REGIME WITH A LEAD IMPULSE NEAR THE LAKE SUPERIOR AREA
BY SAT EVENING. A COLD FRONT ASSOCIATED WITH THIS LEAD IMPULSE
SHOULD ADVANCE SE ACROSS THE UPPER MS VALLEY TO CENTRAL GREAT
PLAINS...WITH TRAILING PORTION STALLING OVER KS ON SAT NIGHT. IN THE
EAST...SHORTWAVE TROUGH REMNANT OF TC BILL SHOULD ACCELERATE ENE
FROM THE TN VALLEY TO THE MID-ATLANTIC STATES.
...UPPER MS VALLEY/CORN BELT REGION...
A DECAYING MCS WILL LIKELY BE ONGOING ACROSS PARTS OF MN/IA AT
20/12Z. THIS ACTIVITY SHOULD FURTHER WEAKEN SAT MORNING BUT SHOULD
YIELD AN OUTFLOW BOUNDARY/EFFECTIVE DIFFERENTIAL HEATING CORRIDOR AS
ROBUST DIABATIC HEATING OCCURS TO THE SW. AMIDST UPPER 60S TO LOWER
70S SURFACE DEW POINTS BENEATH A STOUT EML...MLCAPE SHOULD BECOME
QUITE LARGE AOA 2500 J/KG OVER THE LOWER MO VALLEY. CONVERGENCE
ALONG THE FRONT AND RESIDUAL OUTFLOW BOUNDARIES SHOULD BE SUFFICIENT
TO OVERCOME WEAKENING MLCIN FOR SCATTERED TSTMS TO FORM INVOF
CNTRL/ERN IA. ALTHOUGH THERE SHOULD BE A PRONOUNCED N/S GRADIENT IN
THE STRENGTH OF MID-LEVEL WLYS...A FEW SUPERCELLS MAY FORM IN THE
FIRST COUPLE HOURS OF DEVELOPMENT WITH ALL SEVERE HAZARDS POSSIBLE.
CONVECTION SHOULD GROW UPSCALE INTO AN MCS IN THE EVENING WITH
PREDOMINANT SEVERE WIND/HAIL RISKS.
...LEE OF THE CENTRAL APPALACHIANS TO DELMARVA AREA...
30-45 KT SWLYS AT 500 MB WILL OVERSPREAD MUCH OF THIS REGION
DOWNSTREAM YIELDING A BROAD SWATH OF AT LEAST SEMI-ORGANIZED SEVERE
POTENTIAL. ALTHOUGH MID-LEVEL LAPSE RATES WILL BE WEAK...DIABATIC
HEATING OF A PERSISTENT RICHLY MOIST AIR MASS SHOULD YIELD POCKETS
OF AT LEAST MODEST BUOYANCY. AS NUMEROUS TSTMS LIKELY FORM DURING
THE AFTERNOON...SOME OF THESE SHOULD ORGANIZE INTO MULTICELL
CLUSTERS WITH RISKS FOR DAMAGING WINDS AND PERHAPS MARGINALLY SEVERE
HAIL.
...CENTRAL HIGH/NRN PLAINS...
DEEP-LAYER SHEAR WILL BE STRONG ACROSS THE CENTRAL HIGH PLAINS AND
BLACK HILLS AREA WITH A WLY MID-LEVEL JET AND POST-FRONTAL SURFACE
ELYS. LATEST GUIDANCE HAS GENERALLY TRENDED DRIER WITH
BOUNDARY-LAYER MOISTURE THROUGH EARLY EVENING ON SAT...RENDERING LOW
CONFIDENCE IN THE SUSTENANCE/COVERAGE OF DEEP CONVECTION. SHOULD A
STORM DEVELOP...THE CONDITIONAL LARGE HAIL RISK IS QUITE HIGH GIVEN
THE QUITE FAVORABLE STEEP LAPSE RATE/VERY STRONG DEEP SHEAR
COMBINATION. THE MORE LIKELY SCENARIO IS FOR A BAND OF ELEVATED
STORMS BUT WITH A MORE MARGINAL HAIL RISK ON SAT NIGHT WITHIN A
CORRIDOR OF STRENGTHENING LOW-LEVEL WAA/ISENTROPIC ASCENT. FOR
NOW...WILL MAINTAIN LOW SEVERE PROBABILITIES GIVEN THE CONCERNS OF
SURFACE-BASED TSTM COVERAGE.
FARTHER N...A COUPLE OF MARGINALLY SEVERE HAIL/WIND EVENTS MIGHT
OCCUR ALONG A WEAK SURFACE TROUGH CENTERED NEAR CNTRL ND AT PEAK
HEATING.
..GRAMS.. 06/19/2015
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