SWODY1
SPC AC 131959
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0259 PM CDT MON SEP 13 2010
VALID 132000Z - 141200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF THE CNTRL
PLAINS AND UPPER MS VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS FROM SERN NY INTO SRN NEW
ENGLAND...
...CNTRL PLAINS AREA...
A QUASI-STATIONARY FRONT EXTENDS FROM A WEAK SURFACE LOW NEAR HILL
CITY KS EWD ACROSS N-CNTRL AND NERN KS INTO NWRN MO. SECONDARY E-W
FRONT DEMARCATING THE MOISTURE GRADIENT EXTENDS THROUGH CNTRL NEB
INTO SWRN IA AND NERN MO. ANOTHER BOUNDARY EXTENDS SWWD FROM THE LOW
THROUGH WRN KS. IN ADDITION TO PREVIOUSLY MENTIONED BOUNDARIES A N-S
CONVERGENCE ZONE WAS ALSO INDICATED ACROSS N-CNTRL KS JUST W OF
CONCORDIA WHERE BOUNDARY LAYER CUMULUS HAS BEEN INCREASING. WARM
SECTOR HAS BECOME QUITE UNSTABLE FROM N-CNTRL KS THROUGH S-CNTRL NEB
WITH MLCAPE FROM 2500-3000 J/KG INDICATED ON LATEST OBJECTIVE
ANALYSIS. STORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON IN VICINITY
OF THE PREVIOUSLY MENTIONED BOUNDARIES FROM NRN KS INTO SRN NEB WITH
FORCING FOR DEEPER ASCENT POSSIBLY AUGMENTED BY A VORT MAX MOVING
EWD THROUGH NERN CO AND WRN NEB. EFFECTIVE SHEAR FROM 40-50 KT WILL
SUPPORT SUPERCELL STRUCTURES WITH VERY LARGE HAIL AND ISOLATED
DAMAGING WIND THE MAIN THREATS. HODOGRAPHS SIZE WILL INCREASE FROM
LATE AFTERNOON INTO THE EVENING AS THE LOW LEVEL JET STRENGTHENS
WITH A WINDOW FOR ISOLATED TORNADOES. STORMS WILL LIKELY CONSOLIDATE
INTO AN MCS OVERNIGHT AS THE LOW LEVEL JET STRENGTHENS.
...NERN STATE...
THREAT FOR MAINLY ISOLATED LARGE HAIL WILL CONTINUE NEXT FEW HOURS
MAINLY WITH CLUSTER OF SUPERCELLS MOVING SEWD THROUGH SERN NY INTO
NERN PA AND NRN NY. THREAT SHOULD DIMINISH THIS EVENING AS VORT MAX
MOVES OFF SHORE AND THE BOUNDARY LAYER BEGINS TO COOL.
..DIAL.. 09/13/2010
.PREV DISCUSSION... /ISSUED 1123 AM CDT MON SEP 13 2010/
...LOWER GREAT LAKES INTO THE LOWER HUDSON VALLEY/SWRN NEW
ENGLAND...
MORNING WATER VAPOR IMAGERY AND 12Z UPPER-AIR ANALYSIS SHOW A
WELL-DEFINED SHORT WAVE TROUGH AND AN ASSOCIATED 50-70 KT MIDLEVEL
JET STREAK RAPIDLY TRANSLATING SEWD THROUGH SWRN ONTARIO AND THE
LOWER GREAT LAKES. FORCING FOR ASCENT ATTENDANT TO THIS SYSTEM
SHOULD SUPPORT A GRADUAL INCREASE IN COVERAGE AND INTENSITY OF
ONGOING STORMS CURRENTLY FROM THE ADIRONDACKS SWWD TO S OF THE
MOHAWK VALLEY OF UPSTATE NY. GIVEN THE NOTABLE UPSTREAM COOLING
OBSERVED BY 12Z BUF SOUNDING AND POTENTIAL FOR STRONGER DIABATIC
HEATING...IT APPEARS THAT THE REGION FROM CNTRL NY EWD/SEWD THROUGH
ALB AND THE LOWER HUDSON VALLEY WILL HAVE THE HIGHEST POTENTIAL FOR
EXPERIENCING STRONG TO SEVERE TSTMS THIS AFTERNOON. HERE...THE
COMBINATION OF STEEPENING LOW-LEVEL LAPSE RATES...SBCAPE OF 500-1000
J/KG AND STRENGTHENING DEEP NWLY SHEAR WILL BE SUPPORTIVE OF BOWING
LINE SEGMENTS CAPABLE OF DAMAGING WINDS AND SOME HAIL.
...CNTRL PLAINS/MID MO VALLEY...
15Z MESOANALYSIS SHOWED A SURFACE LOW N OF HLC WITH AN ASSOCIATED
WARM OR QUASI-STATIONARY BOUNDARY EXTENDING GENERALLY EWD ALONG THE
KS-NEB BORDER INTO NRN MO. AN INVERTED TROUGH WAS ALSO OBSERVED
FROM THIS LOW NWWD THROUGH WRN NEB TO A SECONDARY SURFACE LOW OVER
ERN MT. BASED ON LATEST MODEL GUIDANCE...IT APPEARS THAT THE
PRIMARY FOCUS FOR DIURNALLY-ENHANCED TSTM DEVELOPMENT WILL BE A ZONE
NEAR OR N OF THE SURFACE LOW AND WARM/STATIONARY FRONT. HERE...THE
COMBINATION OF MID/UPPER 60S BOUNDARY LAYER DEW POINTS AND
STEEPENING MIDLEVEL LAPSE RATES WILL YIELD A MODERATELY UNSTABLE AIR
MASS BY AFTERNOON WITH MLCAPE INCREASING TO 1500-2500 J/KG.
WHILE LARGE-SCALE FORCING FOR ASCENT IS NOT EXPECTED TO BE
PARTICULARLY STRONG...IT APPEARS THAT SOME BACKGROUND FORCING WILL
BE MAINTAINED THROUGH THE PEAK OF THE DIURNAL HEATING CYCLE BY: 1)
BROAD ISENTROPIC ASCENT INTO RIGHT ENTRANCE REGION OF UPPER JET
STREAK OVER THE GREAT LAKES REGION...AND 2) THE INCREASING INFLUENCE
OF WEAK MIDLEVEL IMPULSE CURRENTLY CRESTING RIDGE AXIS OVER WY/CO.
AS SUCH...EXPECT ISOLATED TO SCATTERED SURFACE-BASED STORMS TO FORM
BY MID/LATE AFTERNOON FROM PORTIONS OF CNTRL/SRN NEB INTO NRN KS.
GIVEN PRONOUNCED VEERING OF WINDS THROUGH THE LOWEST 3-4 KM AGL AND
35-45 KT OF DEEP-LAYER SHEAR...SETUP WILL FAVOR THE DEVELOPMENT OF
SUPERCELLS CAPABLE OF LARGE HAIL. THE POTENTIAL FOR ISOLATED
TORNADOES WILL INCREASE BY 14/00Z WITH ANY SUSTAINED STORMS OWING TO
THE STRENGTHENING OF THE LLJ AND RESULTANT ENHANCEMENT OF LOW-LEVEL
SHEAR.
ACTIVITY SHOULD GROW UPSCALE INTO CLUSTERS TONIGHT OVER THE
MID/LOWER MO VALLEY AS LOWER-TROPOSPHERIC FORCING INCREASES IN EXIT
REGION OF NOCTURNAL LLJ. GIVEN THE PRESENCE OF THE STEEP MIDLEVEL
LAPSE RATES AND SUFFICIENT VERTICAL SHEAR...THE THREAT FOR DAMAGING
WINDS AND HAIL WILL CONTINUE WITH THE MORE INTENSE STORM CLUSTERS.
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