SPC AC 301336
DAY 1 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0836 AM CDT THU APR 30 2009
VALID 301330Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE SRN AND CNTRL
PLNS INTO THE OH VLY...
CORRECTED FOR GENERAL THUNDER FORECAST
...SYNOPSIS...
LOW AMPLITUDE CYCLONIC FLOW WILL ONCE AGAIN PREVAIL OVER MOST OF THE
NATION...ALONG SRN FRINGE OF ELONGATED TROUGH OVER THE N CNTRL
STATES. S OF THE MAIN BELT OF WLYS OVER THE NRN TIER...A WEAKER SRN
BRANCH WILL PERSIST OVER THE SRN RCKYS/SRN PLNS...AND OVER THE OH
VLY. TWO VORT MAXIMA IN THE LATTER BAND OF FLOW...BOTH DERIVED
LARGELY FROM SRN PLNS CONVECTIVE CLUSTERS...COULD AFFECT STORM
DEVELOPMENT OVER AR/MO AND THE OH VLY LATER TODAY.
AT LWR LVLS...COLD FRONT ASSOCIATED WITH NRN STREAM TROUGH WILL MOVE
SE ACROSS THE UPR MS VLY AND CNTRL/SRN PLNS THIS PERIOD. FARTHER
SE...DIFFUSE WARM FRONT NOW OVER THE MID MS/LWR OH VLYS SHOULD
REDEVELOP NE ACROSS THE UPR OH VLY/LWR GRT LKS TODAY AS A WAVE OF
LOW PRESSURE ASSOCIATED WITH LEAD MCV MOVES FROM CNTRL IL TO NEAR
TORONTO.
...ARKLATEX NE INTO OH VLY...
LEAD SRN STREAM VORT/MCV...NOW OVER NRN IL...SHOULD CONTINUE ENE TO
NEAR DETROIT THIS EVE. ENHANCED /40-50 KT/ WSWLY MID LVL FLOW ON S
SIDE OF VORT...AND 30-40 KT SSW LLJ AHEAD OF IT...WILL TRANSPORT
FAIRLY RICH MOISTURE /PW AROUND 1.5 INCHES/ NE ACROSS THE MID OH
VLY...YIELDING AT LEAST MARGINAL DESTABILIZATION.
HEATING WILL BE LIMITED CLOSE TO TRACK OF VORT. BUT SATELLITE DATA
SUGGEST GREATER HEATING MAY OCCUR CLOSER TO THE OH RVR ACROSS PARTS
OF IND/KY/OH. ALTHOUGH WIND PROFILES WILL FEATURE MODERATE DEEP
UNIDIRECTIONAL WSW FLOW AT MID LVLS...CONSIDERABLE LOW LVL
DIRECTIONAL SHEAR WILL EXIST IN THE LOWEST 200 MB...ESPECIALLY NEAR
SEGMENTS OF AFOREMENTIONED WARM FRONT. IF INDIVIDUAL STORMS ARE
ABLE TO FORM IN THIS REGION...SETUP COULD YIELD A COUPLE TORNADOES
NEAR THE FRONT. OTHERWISE...ONE OR TWO ROUNDS OF SCTD SMALL
MULTICELL CLUSTERS APPEAR LIKELY. EMBEDDED BOWING SEGMENTS IN THESE
BANDS COULD YIELD DMGG WIND AND MARGINALLY SVR HAIL.
FARTHER SW...ANOTHER MCV APPEARS TO HAVE EVOLVED FROM OVERNIGHT MCS
IN N TX/SRN OK. THE MCV IS OVER FAR ERN OK ATTM AND COULD INFLUENCE
PATTERN/INTENSITY OF DIURNAL STORMS OVER AR/SRN MO AND THE LWR TN
VLY TODAY. WITH SFC HEATING...DOWNSTREAM AIR MASS OVER THE REGION
SHOULD BECOME MORE UNSTABLE THAN ON WEDNESDAY. COUPLED WITH FAIRLY
STEEP MID LVL LAPSE RATES...RICH LOW LVL MOISTURE... AND 30-35 KT
WSWLY MID LVL FLOW...SETUP MAY SUPPORT SMALL SCALE BOWS/BRIEF
SUPERCELL STRUCTURES WITH DMGG WIND AND HAIL.
...CNTRL/SRN PLNS...
UNCERTAINTY REMAINS REGARDING SVR WEATHER THREAT OVER KS...WRN
MO...OK...AND N TX. OVERALL LARGE SCALE PATTERN SUGGESTS THAT
PRIMARY SVR WEATHER AREA WILL ACCOMPANY THE STRONGER LLJ SEGMENTS
DIRECTED ENEWD WITH MCVS INTO THE OH VLY. HOWEVER...RICH LOW LVL
MOISTURE WILL PERSIST IN THE WAKE OF OVERNIGHT MCS IN N TX...AND
AMPLE MOISTURE FOR STRONG STORMS WILL EXTEND N TO ADVANCING COLD
FRONT IN KS/MO AND OK. IN ADDITION...STRONG SFC HEATING SHOULD
OCCUR...RESULTING IN STEEP LOW LVL LAPSE RATES BENEATH WELL-DEFINED
EML. AS A RESULT...VERY STRONG INSTABILITY WILL DEVELOP. SBCAPE
AOA 3000 J/KG APPEARS LIKELY FROM N TX THROUGH CNTRL OK INTO SRN
KS...WITH POCKETS ABOVE 4000 J/KG POSSIBLE IN CNTRL OK/NW TX.
FORCING FOR ASCENT WILL BE LIMITED OR SLIGHTLY NEGATIVE...AND WIND
PROFILES COMPARATIVELY WEAK /ALTHOUGH STILL SUFFICIENT FOR
SUPERCELLS/. BUT OUTFLOW BOUNDARIES AND SE-MOVING COLD FRONT WILL
BE PRESENT TO INITIATE STORMS. GIVEN THE ABOVE SETUP...IT APPEARS
THAT WHILE OVERALL COVERAGE OF STORMS MAY AT FIRST BE LIMITED...
THOSE THAT DO FORM COULD BE INTENSE...AND ACTIVITY COULD GROW
UPSCALE INTO ONE OR TWO CLUSTERS. VERY LARGE HAIL WILL BE THE MAIN
THREAT...ALTHOUGH ISOLD TORNADOES CANNOT BE RULED OUT DURING EARLY
STAGES OF STORM DEVELOPMENT...NEAR BOUNDARY INTERSECTIONS ...OR WITH
STORMS MOVING SSE ALONG BOUNDARIES. A THREAT FOR DMGG WIND COULD
ALSO DEVELOP IF STORMS ORGANIZE INTO FORWARD-PROPAGATING CLUSTERS.
WITH THE EXCEPTION OF ANY FORWARD-PROPAGATING CLUSTERS...MOST OF THE
STORMS SHOULD WEAKEN AFTER NIGHTFALL.
...CNTRL HI PLNS...
ISOLD TSTMS MAY FORM LATE THIS AFTN AND EVE OVER ERN WY...FAR WRN
NEB...AND NE CO...WHERE UPSLOPE FLOW WILL PREVAIL BENEATH EXIT
REGION OF NRN STREAM JET STREAK NOW OVER ORE/ID. MOISTURE WILL BE
LIMITED...BUT 60 KT DEEP WLY SHEAR MAY SUPPORT ROTATING STORMS WITH
HAIL. A SMALL MCS MAY EVOLVE FROM THIS ACTIVITY LATER IN THE EVE.
THE SYSTEM SHOULD MOVE MAINLY ESE ACROSS NEB AND POSSIBLY NRN KS
WITH ISOLD HAIL/HIGH WIND.
...UPR MS VLY/UPR GRT LKS...
A NARROW AXIS OF MID/UPR 50S SFC DEW POINTS WILL MOVE NE INTO ERN
IA...SE MN...AND WI THIS AFTN...JUST AHEAD OF SE-MOVING COLD
FRONT/NRN PLNS UPR TROUGH. TSTMS SHOULD FORM ALONG THE FRONT AS
HEIGHT FALLS WITH NRN STREAM VORT MAX GRAZE REGION BY LATE AFTN.
GIVEN 45-50 KT DEEP WSWLY SHEAR AND H7-H5 LAPSE RATES AOA 7
C/KM...SETUP COULD SUPPORT AT LEAST A FEW STORMS CAPABLE OF HIGH
WINDS/HAIL.
..CORFIDI.. 04/30/2009
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