SWOD48
SPC AC 190749
DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0249 AM CDT MON SEP 19 2011
VALID 221200Z - 271200Z
...DISCUSSION...
MEDIUM RANGE MODEL GUIDANCE MAINTAINS AN AMPLIFIED UPPER FLOW
PATTERN DURING THE PERIOD WITH A DEEP TROUGH/LOW MOVING SLOWLY EWD
ACROSS THE ERN STATES AND AN UPPER RIDGE CENTERED OVER THE ROCKIES.
THE GFS TENDS TO BE SLIGHTLY MORE PROGRESSIVE WITH THE LONG WAVE
FEATURES COMPARED TO THE ECMWF AND ESPECIALLY THE GEFS ENSEMBLE
MEAN...WITH CONSIDERABLE VARIABILITY /STATISTICAL SPREAD/ IN THE
LOCATION OF THE UPPER LOW OVER THE ERN STATES. AT THE SURFACE...A
SECONDARY LOW IS FORECAST TO DEVELOP ALONG AN EWD MOVING COLD FRONT
OVER THE GENERAL MID ATLANTIC REGION BY DAY 5 OR 6 /FRIDAY-SATURDAY/
AND LIFT NEWD ACROSS NEW ENGLAND...WITH THE FRONT MOVING EWD OFF THE
ATLANTIC COAST THEREAFTER.
STRONG JET WINDS IN THE MID/UPPER LEVELS ARE FORECAST TO ROTATE
EWD/NEWD ACROSS THE MID ATLANTIC STATES ON DAYS 5-6
/FRIDAY-SATURDAY/ AND POTENTIALLY INTERACT WITH THE COLD FRONT AND
ADJACENT WARM SECTOR. THE SYNOPTIC PATTERN MAY BECOME FAVORABLE FOR
STRONG/SEVERE STORMS OVER THIS REGION...HOWEVER THIS WILL BE
DEPENDENT ON THE EWD PROGRESSION OF THE UPPER SYSTEM AND COLD
FRONT...AND THE EVOLUTION OF THERMODYNAMIC PROFILES AHEAD OF THE
COLD FRONT. CURRENT UNCERTAINTY ABOUT THE SYSTEM MOVEMENT AND
CONCERNS ABOUT LIMITED INSTABILITY /BASED ON CURRENT GFS FORECASTS/
PRECLUDE DELINEATION OF A 30% PROBABILITY SEVERE RISK AREA AT THIS
TIME...BUT TRENDS WILL NEED TO BE MONITORED IN SUBSEQUENT OUTLOOKS.
..WEISS.. 09/19/2011
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