Severe Thunderstorm Warning 151, NWS Wakefield, VA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WAKEFIELD VA
413 PM EDT WED OCT 27 2010

.SYNOPSIS...
STRONG LOW PRESSURE WILL TRACK NORTHEAST TOWARDS HUDSON BAY
TONIGHT INTO THURSDAY MORNING. A COLD FRONT GRADUALLY PUSHES
ACROSS THE MID ATLANTIC STATES ON THURSDAY...AND PUSHES OFF THE
COAST THURSDAY EVENING. HIGH PRESSURE BUILDS INTO THE REGION FROM
THE WEST LATE THURSDAY NIGHT INTO THE WEEKEND...BRINGING MUCH
COOLER AND DRY CONDITIONS TO THE REGION.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
TOR WATCH 733 REMAINS IN EFFECT FOR MUCH OF CNTRL AND ERN VA...AND
LWR MD ERN SHORE THRU 8 PM. SFC LVL WINDS GNLY 200-230 DIRECTION
AS OF 330 PM...BUT LATEST MSAS SHOWING PRES FALLS TO THE NW OF
RICHMOND. THIS MESOLOW MAY ALLOW THE WIND DIRECTIONS TO BACK A
FEW DEGREES FOR INCREASED SHEAR FOR POSSIBLE TORNADOES (TO MORE OF
A 170-200 DIRECTION). MAIN SVR THREAT LOOKS TO COME THIS
EVENG...PROBABLY BECMG MORE OF A HVY RAIN THREAT AFTER 00Z-02Z AS
SHEAR DIMINISHES AND DAYTIME HTG IS LOST. MAIN BATCH OF PRECIP
DOES NOT LOOK TO MAKE IT TO SE VA/NE NC UNTIL AFTER MIDNGT.

GIVEN PW/S BTWN 1.5 TO 2 IN AND DP TMPS 65-70...LCLLY HVY DOWNPOURS CUD
PRODUCE QPF'S AOA 1 INCH...AND WILL CONTINUE OVERNIGHT.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/...
MAIN CHANGE TO THIS PORTION OF THE FCST HAS BEEN TO SLOW DOWN THE
CLEARING/DRYING TREND. ON THU...MAIN SHORTWAVE ENERGY LAGS BEHIND THE
WIND SHIFT BNDRY BY SEVERAL HRS...NOT SURPRISING SINCE THE SFC LOW
IS ALL THE WAY UP NEAR HUDSON BAY AT THIS PT...AND MID LVL FLOW
STAYS WSW. FAVOR A BLEND BETWN THE SLOWER NAM/ECMWF SOLN AND THE
FASTER GFS (ALL MODELS ARE A LOT SLOWER THAN PRV RUNS HAD BEEN). THIS
ALLOWS FOR LIKELY POPS THROUGH MOST OF THE MRNG/ERLY AFTN HRS TWDS
THE COAST AND AT LEAST LOW END CHC FOR THE I-95 CORRIDOR. SKIES
LOOK TO CLR FROM NW TO SE DURING THE AFTN...BUT BKN/OVC CONDS MAY
LINGER ALL DAY FROM VA BCH TO NE NC. DESPITE VERY WARM HUMID
AIRMASS OVER THE EAST...TEMPS LIKELY ONLY RISE A FEW DEGREES FROM
AM LOWS DUE TO ALL THE CLOUDS/PRECIP. OVERALL MOST AREAS CAN
EXPECT HIGHS IN THE UPR 70S TO ARND 80 (LWR 80S IF CLEARING IS
FASTER).

UPR SHORTWAVE TRACKS ACRS SRN VA THU EVENG. BY THIS TIME THINK THE
MSTR WILL BE LMTD SO HAVE KEPT FCST DRY (ALTHOUGH LATEST ECMWF IS
EVEN SLOWER AND MORE AMPLIFIED SO THIS WILL BEAR WATCHING). SKIES
LOOK TO BECOME MCLR AFTER MIDNIGHT...WITH MUCH COOLER AIR MOVING
IN. LOWS IN THE 40S TO LWR 50S.

DRY/COOL FRI-SAT...HIGHS IN THE 60S AND LOWS FRI NGT/SAT AM INTO
THE 30S WELL INLAND...40S TWDS THE COAST.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
LONG TERM PERIOD LOOKS TO BE DOMINATED BY CANADIAN HIGH PRESSURE
WHICH WL DIVE SOUTH FROM SERN CANADA INTO NEW ENGLAND FOR THE LATTER
HALF OF THE WEEKEND INTO ERY NEXT WEEK. THIS FEATURE WILL PUSH A
(DRY) BACK DOOR BOUNDARY SOUTH INTO THE AREA ON SUNDAY...JUST AHEAD
OF A WEAK S/W TROUGH CROSSING INTO THE AREA FROM THE OH/TN VLYS.
KEPT SUNDAY/MONDAY DRY WITH GOOD MODEL AGREEMENT THAT FLAT/DRY
DOWNSLOPE FLOW CONTINUES THROUGH THE WEEKEND. WHILE DETAILS REMAIN A
BIT UNRESOLVED...BIG STORY FOR NEXT WEEK WL BE WITH AMPLIFICATION OF
THE LONGWAVE PATTERN FOR THE MIDDLE TO LATTER PORTION OF NEXT
WEEK...WITH STRONG UPR LVL TROUGH DROPPING FROM CENTRAL CANADA AND
DIGGING A DEEP UPR TROUGH INTO THE SERN CONUS. AS THIS
HAPPENS...HIGH PRESSURE OVER NEW ENGLAND WILL START TO RIDGE DOWN
THE EASTERN SEABOARD WITH LLVL ENE WNDS/HYBRID CAD-WEDGE PATTERN
SETTING UP. THIS TRANSLATES TO INCREASED FORECAST CONFIDENCE TOWARDS
INCREASING CLDS AND A TURN TWDS COOLER/WETTER CONDITIONS FOR THE
MIDWEEK PERIOD NEXT WEEK. HV ACCORDINGLY BUMPED UP POPS/CLD COVER
FOR THIS PERIOD AND LOWERED TEMPS ABT A CATEGORY.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
STRONG SW FLOW CONTS THIS AFTN AHEAD OF SLOW MOVING COLD FRONT
PUSHING IN FROM THE W...RADAR SHOWS PREFRONTAL ACTIVITY DVLPNG
ALONG A DCA TO DAN LINE. SATELLITE AND VISUAL OBS SHOWING SOME
BREAKS IN CLD COVER SO AFTN HEATING SHOULD ASSIST TSTM DVLPMT. HAVE NOT
TRIED TO TIME TSTM ARRIVAL BUT HAVE CB IN RIC SBY AND WE WILL SEE
SHWRS OVERSPREAD THE AREA FROM WEST TO E AS THE FRONT MOVES TO THE
COAST BY THUR AM. HAVE MVFR CONDS MOST LOCATIONS OVERNIGHT BUT
COULD SEE IFR/LIFR VSBYS WHERE HEAVIER BANDS OF PRECIP PERSIST.

CONDITIONS SLOWLY CLEAR OUT ON THU WITH VFR/DRY CONDITIONS EXPECTED
TO BEGIN LATE THU AND CONTINUE THROUGH THE WEEKEND.

&&

.MARINE...
SCA CONTINUES THROUGH TNGT OVER THE BAY/SND (THROUGH ERY THU AFTN
OVER NRN COASTAL WATERS) IN ASSN WITH STRONG SE FLOW AHEAD OF COLD
FRONT NW OF THE WATERS. STRONGEST WINDS REMAIN JUST OFF THE WATER
SFC...HOWEVER THINKING IS WE SHOULD CONTINUE TO SEE GUSTS TO LOW END
SCA CRITERIA THROUGH THIS EVENING (ESP ELEVATED SITES). WINDS/SEAS
GRADUALLY DIMINISH OVERNIGHT INTO ERY THU MORNING AS THE GRADIENT
CONTINUES TO RELAX.

ANOTHER ROUND OF SCA WL LKLY BE NEEDED IN ASSN WITH NW WNDS (CAA)
THU NGT INTO ERLY SAT...AS HIGH PRES BUILDS INTO THE REGION FM THE
W. THE HIGH MOVES OFF THE MID ATLC/SE CST LATE SAT...WITH A BACKDOOR
FRONT DROPPING ACRS THE AREA LATE SUN/SUN NGT.

&&

.CLIMATE...
RECORD HIGH TEMPERATURES FOR TODAY/WEDNESDAY...

FOR WED 10/27...
RIC 88 (1919)...DOUBTFUL.
ORF 84 (1919)...THIS HAS BEEN BROKEN.
SBY 83 (1984)...DOUBTFUL.
ECG 83 (1939)...THIS HAS BEEN BROKEN.

RECORD HIGH MINIMUM TEMPERATURES FOR TODAY/WEDNESDAY...

FOR TODAY/WED 10/27...
RIC 66 (1977)...THIS LIKELY WILL BE BROKEN (UNLESS TEMPS FALL
PRIOR TO 1 AM EDT).
ORF 67 (1939)...THIS LIKELY WILL BE BROKEN (UNLESS TEMPS FALL
PRIOR TO 1 AM EDT).

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
NC...NONE.
VA...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 7 AM EDT THURSDAY FOR ANZ630>633-
     654-656-658.
     SMALL CRAFT ADVISORY UNTIL 1 PM EDT THURSDAY FOR ANZ650-652.

&&

SYNOPSIS...LKB
NEAR TERM...LKB
SHORT TERM...LKB
LONG TERM...MAM
AVIATION...CY
MARINE...MAM
CLIMATE...AKQ

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