-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 141936
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
336 PM EDT TUE MAY 14 2013

.SYNOPSIS...
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HIGH PRESSURE WILL CONTINUE TO MOVE OFFSHORE TONIGHT AS A WARM FRONT
PASSES THROUGH THE MID-ATLANTIC REGION. A COLD FRONT WILL APPROACH
FROM PENNSYLVANIA LATE WEDNESDAY AND STALL OUT NEARBY THROUGH THE
END OF THE WEEK. ANOTHER UPPER LEVEL DISTURBANCE MAY BRING ANOTHER
ROUND OF INCLEMENT WEATHER OVER THE WEEKEND.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
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SFC WINDS STARTING TO BACK THIS AFTN AS HIPRES MOVES OFF THE
MID-ATLANTIC COAST. SIGNIFICANT WAA OCCURS IN MID-ATLANTIC REGION
OVER THE NEXT 24 HR IN RESPONSE TO DEVELOPING SLY RETURN FLOW AT THE
SFC AND WLY FLOW AT H8.

MID-LVL CLOUDS OVER THE OH VLY AND POTOMAC HIGHLANDS WILL LOWER AND
EXPAND EWD LATE IN THE DAY AND ESPECIALLY THIS EVE IN RESPONSE TO
INCREASING ISENTROPIC LIFT BETWEEN THE 800-600 MB LAYER. 12Z NAM/GFS
BOTH SHOW SFC REFLECTION OF A WARM FRONT REACHING THE POTOMAC
HIGHLANDS BY 00Z. THE FRONTAL BOUNDARY WILL LIFT NEWD THRU THE CWA
TNGT. LLVL CONVERGENCE/ISENTROPIC LIFT NEAR THE FRONT MAY SQUEEZE
OUT A FEW LGT SHOWERS OR SPRINKLES TNGT. CONFINED CHANCE POPS TO
NEAR THE M-D LINE BUT POPS WILL BE LOW SINCE MOISTURE IS VERY
LIMITED. LEANED TOWARD THE WARMER BIAS-CORRECTED MET FOR MIN TEMPS
WITH WAA AND INCREASING CLOUD COVER.
-- End Changed Discussion --

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
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WARM FRONT LIFTS NEWD THRU NERN MD AND NJ ON WED...PLACING THE
MID-ATLANTIC REGION IN WARM SECTOR. WITH H8 TEMPS IN THE UPPER
TEENS...STRONG SFC HEATING ONCE MRNG CLOUDS ERODE AND DOWNSLOPING
FLOW WITH YIELD HIGHS IN THE MID TO UPPER 80S. SLIGHTLY COOLER TEMPS
EXPECTED NEAR THE CHSPK BAY AND IN NORTH-CENTRAL MD.

A COLD FRONT WILL DROP SWD FROM PA LATE IN THE DAY. HIRES WRF MODELS
DEVELOP CONVECTION ALONG THE FRONT DURING THE PEAK HEATING HRS.
THESE STORMS MAY MOVE SOUTH OF THE M-D LINE EITHER DURING THE LATE
AFTN OR EVE. THERE IS STILL UNCERTAINTY WITH THE STRENGTH/COVERAGE
OF THESE STORMS BY THE TIME THEY REACH US. PART OF THAT UNCERTAINTY
IS RELATED TO STRENGTH OF THE H8-H7 CAPPING INVERSION. WE ARE IN
AGREEMENT WITH SPC THAT MODEL FCST DEWPOINTS...ESPECIALLY THE 12Z
NAM /WITH SFC DEWPOINTS IN THE MU60S/...ARE WAY TOO HIGH FOR WED
AFTN. THIS YIELDED UNREALISTICALLY HIGH FCST CAPE. WILL KEEP WORDING
IN HWO THAT MENTIONS SVR THREAT ON WED...BUT FOCUS IT MORE FOR THE
NRN CWA.

CONVECTION ALONG THE FRONT SHOULD WEAKEN DURING THE MID TO LATE EVE.
WITH THE LOSS OF DAYTIME HEATING...HAVE LIMITED SWD EXTENT OF CHANCE
POPS WED EVE TO ABOUT AS FAR SOUTH AS THE I-66 CORRIDOR. WED NGT
WILL BE MILD WITH LOWS GENERALLY IN 60S.
-- End Changed Discussion --

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
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SLOW MOVING UPPER LEVEL DISTURBANCE COMBINED WITH A FRONTAL
BOUNDARY WILL HELP TRIGGER PERIODS OF SCATTERED SHOWERS AND
THUNDERSTORMS THURSDAY THROUGH THE WEEKEND. THE GFS IS MORE
BULLISH WITH PROBABILITIES VS THE ECMWF. STILL SOME UNCERTAINTY
AND WILL CONTINUE TO GO WITH CHANCE TO HIGH CHANCE POPS AND NOT
LIKELIES ATTM. THREAT FOR SEVERE STORMS LOOKS MINIMAL. TEMPERATURES
THROUGHOUT THE PERIOD WILL RANGE FROM THE 70S TO THE 80S FOR HIGHS
AND 50S TO 60S FOR LOWS.
-- End Changed Discussion --

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
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VFR CONDITIONS THIS AFTN AND TNGT. MID-CLOUDS INCREASE AND LOWER
TNGT. STILL THINK SCT SPRINKLES DEVELOP PRIMARILY OVNGT BUT IMPACTS
WILL BE MINIMAL.

S-SW WINDS INCREASE WED WITH GUSTS NEAR 20 KT EXPECTED DURING THE
AFTN. A COLD FRONT WILL APPROACH FROM THE NORTH WED EVE. SCT SHOWERS
AND STORMS POSSIBLE MAINLY ACROSS THE NRN TERMINALS.

MOSTLY VFR THROUGH THE REST OF THE WEEK AND INTO THE WEEKEND.
SCATTERED SHOWERS/STORMS COULD DEVELOP EACH DAY WITH BRIEF
RESTRICTIONS IN VSBY AND CIGS BELOW VFR AND POSSIBLE PATCHY
OVERNIGHT FOG.
-- End Changed Discussion --

&&

.MARINE...
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NW WINDS AROUND 10 KT WILL BECOME SLY THIS EVE. SLY FLOW INCREASES
TNGT AS A WARM FRONT APPROACHES FROM THE WEST. HAVE ISSUED A SCA FOR
THE MD CHSPK BAY SOUTH OF POOLES ISLAND AND FOR THE MOUTH OF THE
TIDAL POTOMAC RVR...WHERE SLY CHANNELING ENHANCES WINDS TO NEAR 20
KT DURING THE OVNGT.

SLY WINDS INCREASE ON WED. SCA CONDITIONS EXPECTED ACROSS ALL OF THE
WATERS ONCE DAYTIME MIXING DEEPENS.

WILL NEED TO MONITOR ANY POTENTIAL STORMS DROPPING SOUTH OF PA WED
LATE AFTN AND EVE. STRONG WINDS WOULD BE POSSIBLE IF THESE STORMS
REMAIN ORGANIZED BY THE TIME IT REACHES THE NRN CHSPK BAY.

WINDS ARE EXPECTED TO REMAIN BELOW SCA LEVELS THROUGH THE REST OF
THE WEEK AND INTO NEXT WEEKEND.
-- End Changed Discussion --

&&

.CLIMATE...
LOWS THIS MORNING AT THE CLIMATE SITES...
42F AT DCA...
34F AT BWI...
32F AT IAD...

BOTH BWI AND IAD TIED THEIR PREVIOUS RECORD MIN TEMP FOR MAY 14 THAT
WAS PREVIOUSLY SET IN 1996.

THIS MRNG WAS ONLY THE 4TH TIME SINCE 1962 THAT IAD HAS RECORDED
A FREEZING TEMP THIS LATE IN THE SPRING. THE OTHER TIMES WERE 17
MAY 1984 (30F)...22 MAY 2002 (31F)...AND 14 MAY 1996 (32F).

THIS MRNG WAS ONLY THE 4TH TIME SINCE 1873 THAT BALTIMORE RECORDED A
MIN TEMP OF 34F OR COLDER THIS LATE IN THE SPRING. THE OTHER TIMES
WERE 17 MAY 1956 (33F)...21 MAY 2002 (34F)...AND 14 MAY 1996
(34F).

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO MIDNIGHT EDT
     WEDNESDAY NIGHT FOR ANZ531>534-537-539>541-543.
     SMALL CRAFT ADVISORY FROM NOON TO 8 PM EDT WEDNESDAY FOR
     ANZ530-535-536-538-542.
-- End Changed Discussion --

&&

$$
SYNOPSIS...JRK
NEAR TERM...JRK
SHORT TERM...JRK
LONG TERM...KRW
AVIATION...JRK/KRW
MARINE...JRK/KRW
CLIMATE...JRK