SWODY1
SPC AC 290555
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1255 AM CDT SUN APR 29 2007
VALID 291200Z - 301200Z
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS MUCH OF SW TX AND THE
RIO GRANDE VALLEY...
..THERE IS A SLGT RISK OF SVR TSTMS OVER A SMALL PART OF THE UPPER
MS VALLEY...
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF
WRN...CNTRL...AND ERN MT...
..SYNOPSIS...
SRN STREAM MID/UPPER LEVEL LOW WILL TRACK GENERALLY EWD FROM NRN
MEXICO ACROSS THE RIO GRANDE VALLEY AND WEST TX THIS PERIOD WITH A
BAND OF 35-40KT 500MB FLOW AND 40-60M 12H HEIGHT FALLS SPREADING
FROM THE BIG BEND/TRANS-PECOS REGIONS TOWARD CNTRL TX THROUGH SUNDAY
NIGHT. PERSISTENT SELY LOW-LEVEL FLOW ASSOCIATED WITH THIS SYSTEM
WILL CONTINUE TO ADVECT ABUNDANT LOW-LEVEL MOISTURE NWWD UP THE RIO
GRANDE VALLEY AND INTO THE REGION OF LARGE SCALE ASCENT.
A BELT OF FAST WLY FLOW EXISTS WELL NORTH OF THE SRN STREAM
LOW...ALONG THE NRN BORDER STATES FROM THE PACIFIC TO THE EAST
COAST. A PAIR OF SHORT WAVE TROUGHS EMBEDDED WITHIN THIS FAST NRN
STREAM WILL PLAY A ROLE IN TSTM DEVELOPMENT THROUGH THE PERIOD. THE
LEADING IMPULSE IS FORECAST TO AMPLIFY WHILE DEVELOPING SEWD FROM
CNTRL CANADA ACROSS THE GREAT LAKES AND INTO THE NORTHEAST THROUGH
MONDAY MORNING. THE COLD FRONT TRAILING FROM THE ASSOCIATED
DEEPENING SURFACE LOW OVER ONTARIO/QUEBEC WILL SPREAD SEWD ACROSS
THE UPPER MS VALLEY THROUGH THIS AFTERNOON...INTO THE ERN GREAT
LAKES TONIGHT...AND THEN ACROSS NEW ENGLAND EARLY MONDAY.
A LOWER-AMPLITUDE UPSTREAM DISTURBANCE WILL MOVE QUICKLY FROM THE
PACIFIC NORTHWEST ACROSS THE NRN ROCKIES THROUGH LATE TODAY. MODEST
HEIGHT FALLS AND STRENGTHENING DEEP-LAYER WIND FIELDS WILL ACCOMPANY
THIS SYSTEM FROM THE INTERIOR NORTHWEST ACROSS MT THROUGH TONIGHT.
..RIO GRANDE VALLEY/WEST TX...
DESPITE THE POTENTIAL FOR CONVECTIVE DEBRIS AND PRECIPITATION
INHABITING GREATER DESTABILIZATION...STEEP MID LEVEL LAPSE RATES AND
POCKETS OF STRONGER HEATING WILL PROVE ADEQUATE FOR WIDESPREAD
CONVECTION ACROSS MUCH OF THE AREA TODAY. MOIST LOW LEVEL
SELY/UPSLOPE FLOW...AND MODEST TO STRONG LARGE SCALE LIFT WITH THE
MID/UPPER LOW WILL SUSTAIN THIS ACTIVITY...WHICH WILL LIKELY EXPAND
EWD ACROSS MUCH OF CNTRL/SRN TX THROUGH MONDAY. MOST SUPPORTIVE
CROSSOVER FLOW AND DEEP-LAYER SHEAR FOR ORGANIZED CONVECTION IS
FORECAST TO BE CONFINED TO AREAS FROM THE TRANS-PECOS AND BIG BEND
AREAS SEWD ALONG THE RIO GRANDE VALLEY WHERE BAND OF STRONGER MID
LEVEL FLOW WILL PASS OVER GREATER POTENTIAL INSTABILITY THROUGH
EVENING. SUPERCELLS APPEAR POSSIBLE IN THESE AREAS WHILE MORE
WIDESPREAD MULTICELLULAR STORMS OCCUR FARTHER NORTH...PERHAPS
EMBEDDED WITHIN LARGER CONVECTIVE CLOUD/RAIN SHIELD. LARGE HAIL AND
HEAVY RAIN APPEAR TO BE THE PRIMARY HAZARDS ACROSS THE AREA.
HOWEVER...TORNADO/WIND POTENTIAL WILL ALSO EXIST WITH ANY
SUPERCELL...ESPECIALLY CELLS ENCOUNTERING RESIDUAL DIFFERENTIAL
HEATING/OUTFLOW BOUNDARIES.
..NRN ROCKIES/MT...
AS LARGE SCALE ASCENT AND DEEP-LAYER WIND FIELDS INCREASE ACROSS THE
INTERIOR NORTHWEST AND CONTINENTAL DIVIDE...LEE-SIDE PRESSURE FALLS
AND HEATING OVER HIGHER TERRAIN WILL CONTRIBUTE TO 700-500MB LAPSE
RATES IN EXCESS OF 8C/KM ACROSS MUCH OF THE REGION DURING THE
AFTERNOON. LATEST WATER VAPOR IMAGERY AND GPS PW OBSERVATIONS
INDICATE A GRADUAL INCREASE TO MID/UPPER MOISTURE ACROSS THE NRN
GREAT BASIN AND NRN ROCKIES. LOW LEVEL MOISTURE PLUME WITH 40-45F
DEWPOINTS IS FORECAST TO SPREAD WWD TOWARD THE HIGHER TERRAIN AND
CONTRIBUTE TO THE DEVELOPMENT OF MODESTLY CAPPED MUCAPE OF 500-800
J/KG.
STRENGTHENING LEE-LOW/TROUGH AND DYNAMIC FORCING BENEATH ENTRANCE
REGION OF UPPER JET SHOULD OVERCOME CAPPING/INHIBITION AND AID
HIGH-BASED CONVECTIVE INITIATION IN THE 21-00Z TIME FRAME. GIVEN
STRONG VERTICAL SHEAR...STORMS SHOULD QUICKLY ORGANIZE AND POSE A
THREAT OF HAIL AND LOCALLY STRONGER WINDS. FAST-MOVING LINE
SEGMENTS...AND PERHAPS A SUPERCELL OR TWO...MAY CONTINUE TO POSE A
SEVERE THREAT WHILE TRACKING EWD ACROSS CNTRL MT THROUGH THE
EVENING...AND PERHAPS AS FAR AS ERN MT OVERNIGHT.
..UPPER MS VALLEY....
WEAK HEIGHT FALLS TRAILING THE AMPLIFYING SHORTWAVE TROUGH OVER
ONTARIO WILL JUST BRUSH THE UPPER MS VALLEY REGION WITH A COLD FRONT
FORECAST TO SETTLE SWD INTO WARM AND INCREASINGLY UNSTABLE AIR MASS
FROM SRN MN/IA EWD ACROSS SRN WI. WHILE LOW LEVEL AIR MASS WILL WARM
INTO THE 80S F...LIMITED BOUNDARY LAYER MOISTURE ACROSS THE REGION
WILL PROBABLY DETER GREATER DESTABILIZATION AND MAINTAIN CAPPING
UNTIL THE ARRIVAL OF THE FRONTAL CIRCULATION. STRONGEST SUPPORT FOR
TSTMS WILL BE FROM NRN IA ACROSS THE MS RIVER INTO WI THROUGH LATE
AFTERNOON AND INTO EARLY EVENING. DEEP LAYER SHEAR ACROSS THE
FRONTAL ZONE SHOULD BE MORE THAN SUFFICIENT FOR A FEW ROBUST
UPDRAFTS AND PERHAPS EVEN SUPERCELLS AND LARGE HAIL. GIVEN
RELATIVELY DRY BOUNDARY LAYER AIR MASS...STORMS SHOULD REMAIN
OUTFLOW-DOMINANT WITH SOME POTENTIAL FOR LOCALLY STRONG WINDS.
BACKBUILDING PROPAGATION APPEARS POSSIBLE ACROSS IA WHERE STRONGER
INSTABILITY FEEDING THIS CONVECTION COULD MAINTAIN A THREAT OF AT
LEAST ISOLATED HAIL/WIND INTO THE EARLY EVENING PRIOR TO DECREASE IN
STORM INTENSITY WITH DIURNAL STABILIZATION.
.CARBIN.. 04/29/2007
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