lester - it did seem like there was some crazy weather down in the MD area the other day. The EF0 confirms that. Still
Discussion about the Philadelphia area lack of rainfall and potential coastal storm. Hopefully the rainfall pans out:
FXUS61 KPHI 211336
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
936 AM EDT SAT AUG 21 2010
.SYNOPSIS...
-- Changed Discussion --HIGH PRESSURE WILL SHIFT OFF THE NEW ENGLAND COAST TODAY. LOW
PRESSURE AND ITS ASSOCIATED COLD FRONT WITH SHOWERS IN THE OHIO
VALLEY WILL CROSS THE APPALACHIANS SUNDAY. THE LOW AND ITS
OCCASIONALLY UNSETTLED SHOWERY WEATHER FOR OUR REGION WILL REFORM
SOUTH OF LONG ISLAND MONDAY THEN DRIFT EAST OUT TO SEA WEDNESDAY.
HIGH PRESSURE WILL THEN SLOWLY BUILD INTO THE REGION FOR THE
LATTER PART OF THE WEEK.-- End Changed Discussion --
&&
.NEAR TERM /UNTIL 8 PM THIS EVENING/...
-- Changed Discussion --ANOTHER GOOD DAY IN PROGRESS ACROSS THE FORECAST AREA ALTHOUGH THERE
ARE MORE CLOUDS THAN EXPECTED THIS MORNING...ESP DEL WHERE CIGS
ARE THINNING BEFORE LOWS CIGS REFORM TO THE NORTHWEST AND NORTH
THIS EVENING.
IAD FULL SUN SOUNDING 93 TDY AND WALLOPS 97. MAY NEED TO RAISE
TEMPS 1-2DEGS IN THE 11AM UPDATE. AT 9AM... THE FORECAST TEMPS ARE
CLOSE TO FORECAST VALUES.
NOTING A VERY DRY PAST MONTH OR SO KPHL-KPNE ENE THROUGH MUCH OF
CENTRAL AND COASTAL NJ N OF KACY WHERE RFALL UNDER 2 INCHES WHICH
IS 25 PERCENT OF NORMAL OR GENERALLY 3 TO 4 INCHES DEFICIENT IN
THE LAST 30 DAYS.-- End Changed Discussion --
&&
.SHORT TERM /8 PM THIS EVENING THROUGH MONDAY/...
MAY NEED TO RAISE POPS 20 TO 30 PCT NW FRINGE OF THE FA IN THE 11 AM
UPDATE FOR LATE TONIGHT PER 06Z MODEL RUNS.
TONIGHT WILL BE WARMER THAN THE PAST NIGHT OR TWO AS THE CLOUDS WILL
HELP TO KEEP THE SURFACE HEAT FROM ESCAPING INTO THE ATMOSPHERE.
LOWS WILL BE IN THE UPPER 60S TO LOWER 70S ACROSS THE REGION.
WINDS SHOULD BE UP ENOUGH OVERNIGHT BUT WITH THE INCREASED
MOISTURE DUE TOT HE SOUTHEASTERLY FLOW, SOME PATCHY FOG MAY FORM.
THE BEAUTIFUL WEATHER COMES TO AN END ON SUNDAY AS INCREASED
CLOUD COVER AND MOISTURE SPREADS ACROSS OUR AREA. LOW PRESSURE
WILL MOVE ACROSS THE GREAT LAKES REGION AND PUSH A COLD FRONT
THROUGH CENTRAL PENNSYLVANIA ON SUNDAY. THIS FRONT WILL MAKE ITS
WAY INTO OUR AREA ON SUNDAY NIGHT AND MOVE OFFSHORE LATE SUNDAY
NIGHT INTO MONDAY MORNING. PRECIPITATION WILL SPREAD ACROSS THE
AREA FROM NORTHWEST TO SOUTHEAST AND BY SUNDAY EVENING MOST AREAS
SHOULD START TO SEE SOME RAIN SHOWERS AND/OR A THUNDERSTORM.
GREATEST CHANCES FOR THUNDER LOOK TO BE LATER IN THE DAY AND WITH
THE FRONTAL PASSAGE. PLENTY OF MOISTURE WILL BE IN PLACE AND THE
DIFFERENT MODELS ARE SHOWING DECENT PRECIPITATION AMOUNTS FOR OUR
AREA. RAIN MAY END UP BEING HEAVY AT TIMES IN SOME PLACES, AS
PRECIPITABLE WATERS ARE RUNNING PRETTY HIGH, BUT UNCERTAINTY WITH
RESPECT TO TIMING WE WILL HOLD OFF ON MENTIONING HEAVY RAIN IN THE
GRIDS. MEANWHILE, THE MODELS ALL INDICATE THAT THE UPPER LEVEL LOW
WILL CLOSE OFF AND IMPACT OUR AREA THROUGH AROUND MIDWEEK.
HOWEVER, THERE IS TOO MUCH DISPARITY IN THE MODELS TO GET A GOOD
GRIP ON TIMING/PLACEMENT OF THE LOW. HOPEFULLY THE MODELS CAN COME
TO A BETTER AGREEMENT OVER THE NEXT RUN OR TWO TO LEND BETTER
CONFIDENCE TO THE FORECAST.
TEMPERATURES ON SUNDAY WILL BE WARM AND AGAIN INTO THE 80S, ALTHOUGH
NOT AS WARM AS SATURDAY, MAINLY DUE TO LESS SOLAR INSOLATION. LOWS
SUNDAY NIGHT WILL ONCE AGAIN BE ON THE WARM SIDE, IN THE UPPER 60S
TO LOWER 70S ACROSS MUCH OF THE REGION.
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
WHILE THERE ARE DIFFERENCES IN THE MODEL SOLUTIONS FOR MONDAY
NIGHT INTO TUESDAY...THERE IS STILL THE POTENTIAL FOR HEAVY RAIN.
THE ECMWF WAS PREFERRED DURING THIS TIME PERIOD. THAT MODEL HAS A
CLOSED MID LEVEL SYSTEM OVER WESTERN VIRGINIA...WHILE THE 1200 UTC
GFS HAS OPENED IT SOLUTION IN THE MID LEVELS AGAIN (HAVING SHOWN A
CLOSED SYSTEM FOR THE 0600 UTC RUN).
THE CLOSED MID LEVEL SYSTEM TO THE SOUTHWEST PLACES THE FORECAST
AREA IN THE DEEP MID LEVEL SOUTH SOUTHWEST FLOW. THE SURFACE LOW
LOOKS TO ACT AS A FOCUS...WITH PRECIPITABLE WATER VALUES NEAR 1.50
INCHES. WILL NOT HIGHLIGHT THIS IN THE FORECAST JUST YET...AS MODELS
(AND FORECASTERS) OFTEN HAVE TROUBLE PLACING FEATURES WITH RESPECT
TO CLOSED MID LEVEL SYSTEM. IN ANY EVENT...WILL CARRY SHOWERS IN THE
FORECAST FOR MONDAY NIGHT...AND AT LEAST EARLY TUESDAY.
THE FORECAST FOR THE REMAINDER OF TUESDAY INTO EARLY WEDNESDAY WILL
HINGE ON JUST HOW FAST THE CLOSED MID LEVEL SYSTEM OPENS UP AND
MOVES OUT. THE DEEPEST MOISTURE SHOULD BE EAST OF THE AREA TUESDAY
AFTERNOON AND EVENING. COOL MID LEVEL TEMPERATURES COULD SPARK SOME
LOW TOPPED CONVECTION...BUT NOT CERTAIN OF THIS YET.
ALL MID RANGE MODELS SHOW A COLD FRONTAL PASSAGE LATE WEDNESDAY OR
WEDNESDAY NIGHT...AS A DECANT SHORT WAVE RIDES THROUGH THE NORTHERN
STREAM ACROSS EASTERN CANADA. WHILE MOISTURE WILL BE PRESENT...AND
AT LEAST MARGINAL INSTABILITY...WIND FIELD WILL PROBLEM REMAIN
FAIRLY LIGHT. ADD TO THIS FAIRLY WEAK SYNOPTIC LIFT...AND THIS
POINTS TO A LOW CHANCE OF SHOWERS AND THUNDERSTORMS AT THIS POINT.
AFTER THE FRONTAL PASSAGE...THE AIRMASS CHANGE LOOKS TO OCCUR LATE
WEDNESDAY NIGHT AND THURSDAY. DESPITE COOL MID LEVEL TEMPERATURES
WITH THE MAIN SHORT WAVE PASSING THURSDAY AFTERNOON...WILL KEEP THE
FORECAST DRY. THE MID LEVEL TROUGH LIFTS QUICKLY NORTHEAST
FRIDAY...AND MID LEVEL HEIGHTS RISE FAIRLY QUICKLY. WHILE ALL MID
RANGE MODELS SHOW THE MID LEVEL RIDGE TO THE SOUTH BUILDING BACK
NORTH INTO THE AREA...THE ECMWF SHOWS THE RIDGE GETTING IN AS EARLY
AS NEXT SATURDAY...WITH VERY HIGH MID LEVEL HEIGHTS. THIS APPEARS TO
BE A FAIRLY STRONG SIGNATURE THAT HOT TEMPERATURES MAY BE BACK FOR
THE END OF AUGUST.