Long Term Discussion

By: NWS
By: NWS

FRI NIGHT THROUGH WED. ALOFT...HIGHLY AMPLIFIED PATTERN COMMENCES EXTENDED PERIOD. THIS IS HIGHLIGHTED BY A RIDGE OVER EXTREME ERN PACIFIC...LONGWAVE TROUGHING OVER THE WRN 2/3RD OF CONUS WITH A LOW ON MONTANA/CANADA BORDER WITH AXIS SWWD TO BAJA CA...AND A RIDGE OVER ERN CONUS/WRN ATLC WITH AXIS FROM QUEBEC DOWN TO NE GULF OF MEX. THE UPPER LOW MOVES ENE INTO SW ONTARIO DURING THE EARLY WEEKEND DEAMPLIFYING THE TROUGH...WHILE STRONG SHORTWAVES CONTINUE TO MOVE THROUGH ITS BASE. THE BEST LIFT ASSOCIATED WITH THESE SHORTWAVES WILL REMAIN WELL N/NW OF LOCAL AREA. AT THE SURFACE...THE PERIOD BEGINS WITH A HIGH CENTER OFF THE GA/FL COAST WITH RIDGING EXTENDING WESTWARD TO ALONG FL-GA-AL BORDER. POTENT 988MB LOW ASSOCIATED WITH DEEP LYR TROUGH WILL BE LOCATED NE MN WITH ASSOCD COLD FRONT EXTEND SSE THRU MS RIVER VALLEY INTO TX. THE RESULTING INCREASING GRADIENT BETWEEN UPSTREAM LOW AND WRN ATLC HIGH WILL DEVELOP AN INCREASINGLY DEEP/TIGHT SOUTHERLY FLOW INTO THE NORTHERN GULF COAST. THIS WILL PROMOTE AN ACTIVE SEA BREEZE FRONT... ESPECIALLY OVER PANHANDLE/SE ALA/SW GA WITH SCT POPS EACH DAY. AS LOW LIFTS NEWD...TRAILING FRONTAL BOUNDARY EDGES EASTWARD INTO THE SOUTHEAST STATES THEN GRADUALLY MOVES EASTWARD TOWARDS NE GULF REGION SUNDAY INTO MONDAY. OF CONCERN IS THAT IF THIS SOUTHERLY FLOW IS SUFFICIENTLY STRONG... MAY NEED TO MONITOR THE POTENTIAL FOR HEAVY SURF AND MINOR COASTAL FLOODING...ESPECIALLY FOR WRN MOST BEACHES. EASTERN HALF OF CWA STILL REMAINS TOO FAR FROM FRONT AND UNDER DOMINANT WARMING INFLUENCE OF WRN PERIPHERY OF BUILDING DEEP HIGH PRESSURE RIDGE. ONSHORE LOW LEVEL FLOW SHOULD FAVOR WARM AND HUMID CONDITIONS. RAIN CHANCES ESPECIALLY ERN COUNTIES WILL BE ON THE LOW SIDE...AND MAINLY CONFINED SEA-BREEZE COLLISIONS EACH AFTERNOON. MODELS IN GOOD AGREEMENT DURING SHORT TERM BEGIN BUT BEGIN TO DIVERGE TO COMMENCE EXTENDED PERIOD...ALTHO SLIGHTLY CLOSER THAN 24 HRS AGO. THIS MAKES FORECAST TRICKY. FASTER GFS WHICH IS INITIALLY FURTHER NORTH WITH SURFACE LOW AND DEEPER WITH SHORTWAVE ROUNDING BASE OF AND DEEPENING THE PARENT UPPER LEVEL LOW. CONVERSELY SLOWER CANADIAN AND ECMWF MODELS IN BETTER AGREEMENT WITH WEAKER TROUGH/LOW AND STRONGER MORE WRN RIDGE. WHICH MODEL VERIFIES WOULD IMPACT WHERE SUBSEQUENT RIDGE AND RAINS SET UP OVER THE SOUTHEAST DURING LATE EXTENDED. THE ECMWF IS ALSO ABOUT 12 HOURS SLOWER WITH THIS EVOLUTION WHICH MAKES PINNING DOWN TIMING OF ANY CONVECTION DIFFICULT. FOR NOW BASED ON RECENT AND LONG TERM SUPERIORITY OF ECMWF ESPECIALLY FOR LATTER PART OF EXTENDED...WILL LEAN TOWARDS THIS MODEL AND ITS WARMER AND DRIER SIDE. BY LATE WEEKEND...GFS IS SHOWING A BUILDING DEEP LYR RIDGE TO OUR EAST OVER THE WRN ATLC AND BAHAMAS. CONVERSELY...THE ECMWF BUILDS A RIDGE FURTHER WEST INTO THE EASTERN GULF OF MEXICO. THIS WILL IMPACT HOW FAR SEWD FRONT WILL TRAVERSE. IF THE GFS VERIFIES...THIS WILL ALLOW THE POTENTIAL FOR A SOME IMPULSES TO MOVE OVERHEAD...AND KEEP MID/HI LVL CLOUDS AS WELL AS A MORE ACTIVE GULF SEABREEZE...THE FRONT CLOSER TO CWA WITH MORE CONVECTION AND HIGH HUMIDITY IN THE FORECAST. THE FAVORED ECMWF MEANS MORE LIKELY HOT AND DRIER CONDITIONS. BY SUNDAY AFTN...MODELS REALLY BEGIN TO DIVERGE. GFS SHOWS THAT ABOVE LOW HAS EJECTED OFF NE CANADA WITH RIDGE FLATTENING ALLOWING MORE IMPULSES TO RIDE EWD FROM UPSTREAM TROUGH AND ACROSS LOCAL REGION. AS SAME TIME UPSTREAM COLD FRONT HAS MOVED SUFFICIENTLY EWD TO BECOME QSTNRY ACROSS SRN ALA/CNTRL GA. THIS COMBINATION WILL INCREASE RAIN CHANCES MON EVE THRU TUES. CONVERSELY...ECMWF FAVORS RIDGING HOLDING STRONGER OVER LOCAL REGION LEADING TO INCREASED SUBSIDENCE AND WARMING MID-LEVEL TEMPERATURES WHICH WOULD LIMIT RAIN CHANCES. AGAIN WILL LEAN TOWARDS DRIER AND WARMER EURO. POPS WILL BE NIL TO WDLY SCT FRI NIGHT THEN WDLY SCT (E) TO SCT (W) POPS SAT THRU SUN FOLLOWED BY ISOLD (E) TO SCT (W) SUN NIGHT INTO TUES. UNDER SLY FLOW...MIN/MAX TEMPS WILL CONTINUE WELL ABOVE CLIMO THRU PERIOD (CLIMO IS MID-UPPER 50S/LOW 80S) INLAND MAX TEMPS WILL REACH OR EXCEED 90 DEGREES SAT-MON BEFORE INCREASING CLOUDS WITH APPROACHING FRONT DIP TEMPS INTO MID 80S.


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