Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS61 KLWX 221518 AAA
AFDLWX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1118 AM EDT WED APR 22 2015

.SYNOPSIS...
LOW PRESSURE WILL SLOWLY PIVOT FROM THE GREAT LAKES TOWARD THE
SAINT LAWRENCE VALLEY THROUGH THE END OF THE WEEK. A COLD FRONT
TRAILING THE LOW WILL CROSS THE MID-ATLANTIC TODAY. HIGH PRESSURE
WILL BUILD IN FROM THE WEST FRIDAY...FOLLOWED BY ANOTHER LOW
PRESSURE SYSTEM THIS WEEKEND.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
HEADLINE UPDATE...THE WIND ADVISORY HAS BEEN EXPANDED FROM THE
LOWER SHEN VLY/BLUE RIDGE BACK NORTH/EAST UP ACROSS THE POTOMAC
HIGHLANDS AND THE REST OF THE BLUE RIDGE. THE EFFECTIVE TIMING IS
THRU LATE THIS EVE AND MAY NEED TO BE EXPANDED INTO THE METRO
AREAS FOR THE AFTN/EVE HRS AS WELL.

A FAST-MOVING COLD FRONT IS CROSSING THE APLCNS HERE IN THE LATE
MRNG HRS. THE AMBIENT WINDS OUT AHEAD OF BOUNDARY ARE STARTING TO
GUST WELL INTO THE 20-30KT RANGE. TEMPS AHEAD OF THE FRONT ARE
ALSO SURGING BACK INTO THE 60S AFTER A COOL OVERNIGHT PERIOD.
INSTABILITY WILL BE MARGINAL BUT ANY ELEVATED INSTABILITY WILL BE
ENOUGH TO TAP AN INTENSE JET MAX PASSING OVERHEAD. ISOLATED STRONG
GUSTY WINDS WILL BE MIXED-DOWN IN LIGHT/MODERATE SHOWER ACTIVITY.
THE NAM/RAP AND OTHER GUIDANCE SHOWING AN INTENSE 60-70KT JET ALL
THE WAY DOWN INTO THE MID-LEVELS...8-10KFT. THIS WILL BE WELL W/IN
THE INCOMING CLOUD DECK AND EVEN WEAK ELEVATED CAPE WILL DROP A
PORTION OF THESE WINDS DOWN THE STEEP SLOPE INDICATED ON THE 12Z
KIAD SNDG.

A FAIRLY WIDE SWATH OF SHOWERS COINCIDENT W/ THE INCOMING COLD
FRONT WILL MAKE ITS WAY OVER THE AREA. THE RAIN MAY NOT BE HEAVY
AS IT ARRIVES BUT IT WILL BE ENOUGH FOR INTERMITTENT GUSTS IN THE
30-40KT RANGE AND LOCALLY HIGHER. LIGHTNING MAY BE SOMEWHAT
SPARSE...STRONG WIND GUSTS WILL BE POSSIBLE. SMALL HAIL MAY ALSO
OCCUR WITH THE MORE ROBUST SHOWERS DUE TO LOW FREEZING LEVELS. THE
AREA IS IN A MARGINAL RISK FOR SEVERE WX AS A RESULT.

HIGHS TODAY MAY RISE INTO THE 70S AHEAD OF THE FRONT (SE AREA) BUT
MAY NOT TOP 60 IN THE WEST WHERE RAIN ARRIVES FIRST. CONCERNS ALSO
FOR THE POST-FRONTAL REGIME IN TERMS OF GUSTY WINDS. A RELATIVELY
BRIEF 2-3HR WINDOW FOR STRONG GUSTS OUT OF THE WEST MAY ALSO
AFFECT A BETTER PART OF THE CWA FOR THE LATE EVE HRS BEFORE THE
AREA STABILIZES.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...
THE UPPER LEVEL LOW WILL MOVE TOWARD THE ST LAWRENCE VALLEY
TONIGHT INTO THURSDAY. THE PERIOD IS EXPECTED TO BE DRY EXCEPT
PERHAPS IN THE UPSLOPE AREAS WHERE SOME POST-FRONTAL RAIN AND SNOW
SHOWERS MAY OCCUR EARLY TONIGHT...THEN AGAIN THURSDAY AS A VORT
MAX SWINGS THROUGH. EAST OF THE MOUNTAINS...THERE WILL ONLY BE AN
INCREASE IN CLOUDS THURSDAY. EXPECT BREEZY CONDITIONS ONCE AGAIN
ON THURSDAY...BUT MORE IN THE 25 KT RANGE. LOWS MAY FALL BELOW
FREEZING IN THE HIGHLANDS TONIGHT...WITH MID 30S-LOW 40S EAST. 850
MB TEMPS DROP BELOW 0C THURSDAY...RESULTING IN HIGHS ONLY IN THE
50S TO AROUND 60.

HIGH PRESSURE WILL BUILD ACROSS THE REGION THURSDAY NIGHT THROUGH
FRIDAY NIGHT. THERE IS A SLIGHT CHANCE FOR A BRIEF UPSLOPE SNOW
SHOWER OR TWO IN THE POTOMAC HIGHLANDS THURSDAY NIGHT AS LOW
TEMPERATURES BOTTOM OUT NEAR 30. TEMPERATURES ACROSS THE REGION WILL
BE BELOW NORMAL. PATCHY FROST IS ALSO A POSSIBILITY THURSDAY
NIGHT...THEN AGAIN FRIDAY NIGHT...AS TEMPERATURES FRIDAY NIGHT
BOTTOM OUT IN THE LOWER 30S AS WELL.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
A CHANCE OF RAIN RETURNS SATURDAY AND SATURDAY NIGHT AS A STORM
SYSTEM MOVES FROM THE TENNESSEE VALLEY TO THE CAROLINA COAST.
TEMPERATURES WILL REMAIN BELOW NORMAL.

HIGH PRESSURE WILL BUILD IN BEHIND AN ASSOCIATED COLD FRONT SUNDAY
THROUGH MONDAY NIGHT...BRINGING DRY CONDITIONS AND KEEPING
TEMPERATURES 5 TO 7 DEGREES BELOW NORMAL.

BY TUESDAY...A WARM FRONT WILL TRY TO WORKS ITS WAY NORTHWARD. A
CHANCE OF RAIN RETURNS TUESDAY INTO TUESDAY NIGHT AHEAD OF AND ALONG
THE WARM FRONT AS THE RIDGE OF HIGH PRESSURE BREAKS DOWN.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
FAST-MOVING FRONT INCOMING AND CONDS WILL CHANGE RAPIDLY. A SOLID
20-30KT SFC WIND NOW AFFECTING THE ENTIRE REGION BUT A LINE OF
SHOWERS COULD BRING A BRIEF VSBY REDUCTION AROUND MIDDAY INTO THE
EARLY AFTERNOON TODAY. THE SHOWERS MAY ALSO CONTAIN THUNDER AND
WILL LIKELY BRING HIGHER WIND GUSTS IN THE 30-40KT RANGE. WINDS
WILL SHIFT FROM SW TO W WITH FRONTAL PASSAGE. EXPECT ANOTHER
BREEZY DAY ON THURSDAY BUT WNW WINDS WILL BE CLOSER TO 20-25 KT.

VFR CONDITIONS THURSDAY NIGHT THROUGH FRIDAY NIGHT. MVFR OR IFR
CONDITIONS POSSIBLE SATURDAY AND SATURDAY NIGHT DUE TO THE CHANCE OF
LIGHT RAIN. VFR CONDITIONS SUNDAY.

&&

.MARINE...
GALE GUSTS MAY BE SPORADIC. SHOWERS/PERHAPS A THUNDERSTORM WILL
MOVE THROUGH THIS AFTERNOON AND BE MUCH MORE LIKELY TO BRING DOWN
GALE GUSTS. WINDS SHIFT TO THE WEST WITH THE COLD FRONTAL PASSAGE.
CONTINUE A SCA OVERNIGHT EXCEPT FOR THE UPPER POTOMAC SINCE AM NOT
SURE HOW WELL ATMOS WILL DECOUPLE. SCA CONTINUES FOR ALL WATERS
THURSDAY AS W WINDS GUST UP TO 25 KT.

NO MARINE HAZARDS THURSDAY NIGHT. SMALL CRAFT ADVISORIES POSSIBLE
FRIDAY. NO MARINE HAZARDS FRIDAY NIGHT THROUGH SUNDAY.

&&

.TIDES/COASTAL FLOODING...
TIDE LEVELS HAVE DROPPED ENOUGH THAT DO NOT THINK THERE WILL BE
PROBLEMS WITH MORNING HIGH TIDE CYCLE BUT WILL MONITOR. WITH SW
WINDS SHIFTING WEST TODAY...DO NOT EXPECT DRAMATIC DECREASES IN
WATER LEVEL. WILL HAVE TO MONITOR THIS FOR THE NEXT COUPLE OF
DAYS...AS WATER LEVELS WILL AT THE VERY LEAST REMAIN ELEVATED.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...WIND ADVISORY UNTIL 8 PM EDT THIS EVENING FOR MDZ003>005-501-
     502.
VA...WIND ADVISORY UNTIL 8 PM EDT THIS EVENING FOR VAZ025>031-040-
     501-503>505-507-508.
WV...WIND ADVISORY UNTIL 8 PM EDT THIS EVENING FOR WVZ050>053-055-
     501>506.
MARINE...SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 8 PM EDT
     THURSDAY FOR ANZ530>534-537>543.
     GALE WARNING UNTIL 8 PM EDT THIS EVENING FOR ANZ530>543.
     SMALL CRAFT ADVISORY FROM 10 AM TO 8 PM EDT THURSDAY FOR
     ANZ535-536.

&&

$$
UPDATE...GMS
PREV DISCUSSION...ADS/KLW



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.