SWOD48
SPC AC 150831
DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0331 AM CDT WED AUG 15 2007
VALID 181200Z - 231200Z
WHILE THERE APPEARS TO BE GENERAL CONSISTENCY IN THE EVOLUTION OF
THE LARGE SCALE FLOW REGIME AND PATTERN ACROSS THE CONUS IN THE
MEDIUM RANGE...DETAILS REGARDING CONVECTIVE SYSTEM FORMATION AND
EVOLUTION RESULTING IN MORE WIDESPREAD SEVERE WEATHER EVENTS ARE NOT
AS CLEAR. UPPER LEVEL RIDGE AXIS OVER THE SRN STATES SHOULD CONTINUE
TO GRADUALLY DECREASE IN STRENGTH AS AMPLIFIED AND MODESTLY STRONGER
FLOW CONTINUES FROM ABOUT 35N LATITUDE...NORTH INTO CANADA. A
TROPICAL DISTURBANCE MAY BECOME ABSORBED WITHIN WEAK WLY FLOW ON THE
NWRN PERIPHERY OF THE SHRINKING ANTICYCLONE. THIS RESIDUAL IMPULSE
MAY TRACK SLOWLY FROM THE SRN PLAINS TO THE MS VALLEY THROUGH LATE
DAY 5/SUN-MON BASED ON LATEST ECMWF/GFS.
HEIGHTS ARE FORECAST TO RISE IN THE EAST THROUGH DAYS 4-5/SAT-MON IN
THE WAKE OF STRONG TROUGH AND FRONTAL INTRUSION OVER THIS REGION.
THE EXTENSIVE FRONTAL ZONE ASSOCIATED WITH THE TROUGH DEPARTING NEW
ENGLAND WILL LINGER FROM THE MID ATLANTIC/SOUTHEAST WNWWD ACROSS THE
MS VALLEY TO THE CNTRL/NRN PLAINS. THE POSITION OF THIS BOUNDARY
THROUGH DAY 4 IS WELL DEPICTED IN LOW LEVEL THERMAL FIELDS IN
GFS/ECMWF...AND GFS ENS MEAN. WEAK LOW-AMPLITUDE SHORT WAVE
IMPULSES...PERHAPS CONVECTIVELY INDUCED...WILL TRACK ALONG THE
BOUNDARY AND ENHANCE DEEP-LAYER LIFT AND CONVECTIVE DEVELOPMENT FROM
THE NRN PLAINS ESEWD ACROSS THE MIDWEST/OH VALLEY AREAS THROUGH DAY
6/MON-TUE. GIVEN UNCERTAINTIES IN TIMING AND EVOLUTION OF MCS
ACTIVITY ALONG THIS BOUNDARY..AS WELL AS STRENGTH OF WARM SECTOR
CAP...IT IS TOO SOON TO INTRODUCE AREAS THAT ACCURATELY DEPICT
HIGHER SEVERE WEATHER PROBABILITIES.
SIGNIFICANT INCREASE IN ZONAL JET ACROSS THE NERN PACIFIC IS
FORECAST TO CONTRIBUTE TO EVENTUAL EJECTION OF A STRONG UPPER TROUGH
FROM PACIFIC NORTHWEST TO NRN PLAINS AND SCNTRL CANADA DURING DAYS
5-7/SUN-TUE. GFS IS MORE PROGRESSIVE WITH THIS TROUGH WHEN COMPARED
TO ECMWF. SYSTEM IS FORECAST TO CLOSE OFF BY MIDWEEK WITH BELT OF
STRONGER WLY FLOW EXTENDING ACROSS THE NRN 1/3RD OF THE CONUS
THROUGH THE END OF THE WEEK. THE FORECAST EVOLUTION OF THE LARGE
SCALE PATTERN SUGGESTS A POTENTIALLY ACTIVE PERIOD OF SEVERE WEATHER
ANYWHERE FROM THE NRN/CNTRL HIGH PLAINS EWD ACROSS THE UPPER MS
VALLEY/GREAT LAKES AND NORTHEAST DURING DAYS 5-8. HOWEVER...TIMING
AND PLACEMENT DIFFERENCES WITH BOTH THE TROUGH/UPPER LOW...AND
DEVELOPING STRONGER FLOW IN ITS WAKE...INDICATE AN ACCURATE SEVERE
WEATHER FORECAST IS NOT POSSIBLE AT THIS TIME.
.CARBIN.. 08/15/2007
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