Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 231846
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
246 PM EDT THU OCT 23 2014

.SYNOPSIS...
LOW PRESSURE EAST OF THE DELMARVA WILL SLOWLY TRACK EAST OF LONG
ISLAND TODAY. HIGH PRESSURE WILL RETURN TO THE MID ATLANTIC TONIGHT AND
REMAIN OVER THE AREA INTO THE FIRST PART OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
OFFSHORE LOW PRESSURE CONTINUES TO PULL AWAY FROM THE
AREA...WHILE HIGH PRESSURE BUILDS IN OVER THE OHIO VALLEY. STRONG
PRESSURE GRADIENT REMAINS OVER THE REGION...WITH NWLY WINDS
GUSTING 20-30KT. CLOUD SHIELD PERSISTS OVER ERN MD AND PORTIONS OF
NRN VA/WASHINGTON DC METRO...AND OVER THE POTOMAC HIGHLANDS WHERE
UPSLOPE CONDITIONS ARE PRESENT. SOME UPSLOPE SHOWERS ARE
POSSIBLE...BUT OTHERWISE DRY WEATHER EXPECTED THROUGH THE REST OF
THE AFTERNOON. HIGH TEMPS IN THE 60S OVER MOST LOCATIONS LATE THIS
AFTERNOON.

TIME OF PARTIAL ECLIPSE - 5:50 TO 6;15 PM. APPROX 1/4 OF SUN WL BE
COVERED IN THE SWRN SKY. CLDS SHOULD BE DIMINISHING DURG THIS
TIME...EXCEPT OVER NORTHERN AND EASTERN PORTIONS OF THE FORECAST
AREA. BEST CHCS FOR VIEWING WL MOST LKLY BE IN THE WRN PART OF
THE CWA AND CENTRAL SHEN VLLY.

LOW PRESSURE CONTINUES TO PULL AWAY TONIGHT WHILE HIGH PRESSURE
BUILDS EASTWARD...REACHING EASTERN WV BY EARLY MORNING. GUSTS
EXPECTED TO END AFTER SUNSET AS BOUNDARY LAYER DECOUPLES. HIGH
PRESSURE SHOULD BE CLOSE ENOUGH TO THE WESTERN COUNTIES OF THE CWA
TO ALLOW FOR A PERIOD OF GOOD RADIATIONAL COOLING. THIS WILL
RESULT IN LOWS NEAR FREEZING IN THE POTOMAC HIGHLANDS AND SOME
UPPER 30S IN THE SHELTERED VALLEYS. LOWS WILL BE IN THE 40S
ELSEWHERE.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
HIGH PRESSURE CONTINUES TO BUILD IN FROM THE WEST FRIDAY. THERE
WILL BE SOME LEFTOVER PRESSURE GRADIENT FROM THE COASTAL
LOW...WHICH WILL BE REACHING THE MARITIMES BY THE END OF THE
DAY...SO NW WINDS WILL GUST TO AROUND 20KT IN THE LATE MORNING AND
AFTERNOON. WITH MORE SUNSHINE...SLIGHTLY HIGHER 1000-500MB
THICKNESS AND A PARTIAL DOWNSLOPE WIND COMPONENT...HIGHS WILL BE A
FEW DEGREES WARMER THAN THURSDAY. MID TO UPPER 60S EXPECTED EAST
OF THE BLUE RIDGE AND IN THE SHENANDOAH VALLEY...AND MID 50S TO
LOW 60S AT HIGHER ELEVATIONS.

HIGH PRESSURE PERSISTS TO THE SOUTH AND WEST FRIDAY NIGHT THROUGH
SATURDAY. WEAK COLD FRONT MOVES THROUGH SATURDAY NIGHT...BUT WILL
HAVE LIMITED MOISTURE. DRY FRONTAL PASSAGE EXPECTED...EXCEPT
POSSIBLY SOME UPSLOPE RAIN OVER THE POTOMAC HIGHLANDS SATURDAY
NIGHT. HIGHS GENERALLY MID TO UPPER 60S FRIDAY...AND UPPER 60S TO
AROUND 70 IN SOME SPOTS SATURDAY. LOWS IN THE 40S FRIDAY NIGHT IN
THE METRO AREAS...AND IN THE MID TO UPPER 30S IN AREAS THAT
RADIATE WELL FRIDAY NIGHT. SATURDAY NIGHT LOWS GENERALLY IN THE 40S.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
MOST OF THE LONG TERM PERIOD WILL FEATURE A RATHER BENIGN
PATTERN...WITH DEEP-LAYER RIDGING ANCHORED ALONG THE EAST COAST FOR
THE FIRST HALF OF NEXT WEEK. THERE ARE A FEW FEATURES OF NOTE...1- A
PRESSURE SURGE/SECONDARY COLD FRONT SUNDAY ACCOMPANIED BY GUSTY
WINDS AND FALLING TEMPERATURES BUT NO PRECIPITATION ON SUNDAY...2- A
COLD FRONT ON WEDNESDAY...AND 3- A POTENTIAL APPROACHING TROUGH
LATER IN THE WEEK.

ALL GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH THE MIDDLE OF NEXT
WEEK...BUT THEN DIVERGES AFTER THAT.

DEEP-LAYER /DRY/ NORTHWESTERLY FLOW WILL PREVENT APPRECIABLE
MOISTURE FROM MOVING OVER THE REGION ON SUNDAY AS AN UPPER-LEVEL
TROUGH SWINGS BY TO THE NORTH OVER NEW ENGLAND. THUS THE REFLECTION
AT THE SURFACE IN THE FORM OF A COLD FRONT WILL NOT BE ACCOMPANIED
BY ANY PRECIPITATION. WINDS WILL INCREASE THROUGH THE DAY AFTER THE
FRONT MOVES THROUGH AND COULD BE GUSTY. THESE GUSTY WINDS WILL USHER
IN A COOLER AIRMASS SUNDAY NIGHT...WITH LOW TEMPERATURES DROPPING TO
FREEZING OVER PORTIONS OF THE WESTERN SLOPES. RIGHT NOW THE AREAS
THAT ARE MOST LIKELY TO FALL TO FREEZING HAVE ALREADY HAD THEIR
GROWING SEASON ENDED BY A FREEZE EARLIER THIS WEEK...BUT IF WINDS
DIE OFF QUICKER THAN CURRENTLY FORECAST DURING THE EVENING MORE
WIDESPREAD FROST/FREEZE CONDITIONS WILL BE POSSIBLE OVER THE
HIGHLANDS.

THE AIRMASS WILL REBOUND QUICKLY EARLY NEXT WEEK AS HIGH PRESSURE
SETS UP JUST OFF THE SOUTHEAST COAST...SETTING UP A SOUTHWESTERLY
RETURN FLOW. MODELS/ENSEMBLES ARE IN VERY GOOD AGREEMENT REGARDING
THE TIMING OF A COLD FRONT WEDNESDAY AFTERNOON...WHICH MAY BRING
RAIN SHOWERS TO THE AREA. HOWEVER THE BEST UPPER-LEVEL FORCING
PASSES OVER THE WESTERN GREAT LAKES SO AT THE MOMENT PRECIPITATION
WOULD LIKELY BE OF THE MORE SCATTERED VARIETY.

BEYOND THIS TIME IS WHEN THE MODELS DIVERGE...WITH NON-NCEP GUIDANCE
DEPICTING A FLAT SHORTWAVE APPROACHING THE EAST COAST...WHILE THE
GFS/SEVERAL GEFS MEMBERS HAVE A MUCH DEEPER TROUGH AND IMPENDING
CYCLOGENESIS NEAR THE MID-ATLANTIC BY THE END OF NEXT THURSDAY. THE
UNCERTAINTY STEMS FROM SPREAD IN HOW GUIDANCE HANDLES A LARGE
UPPER-LEVEL LOW MOVING OUT OF THE GULF OF ALASKA...WITH THE GFS
SLOWER/DEEPER RESULTING IN WEST COAST RIDGING/DEEPER EAST COAST
TROUGHING...AND THE NON-NCEP GUIDANCE A LITTLE QUICKER BRINGING THE
UPPER LOW CLOSER TO THE NORTHWEST COAST AND FLATTENING OUT THE
DOWNSTREAM FLOW RESULTING IN A LESS AMPLIFIED PATTERN IN OUR NECK OF
THE WOODS. THE MAJORITY OF THE GUIDANCE AND TELECONNECTIONS WOULD
TEND TO FAVOR A LESS AMPLIFIED PATTERN AT THE MOMENT BUT THAT STRAYS
FROM THE PATTERN WE HAVE SEEN OVER THE LAST SEVERAL WEEKS. TIME WILL
BE THE BEST INDICATOR AS TO WHETHER OR NOT THE PATTERN IS READY FOR
A CHANGE OR IF THE MID-ATLANTIC IS IN STORE FOR ANOTHER LARGE AND
SLOW-MOVING AREA OF LOW PRESSURE AND STORMINESS LATE NEXT WEEK.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
VFR THIS AFTERNOON WITH NW WINDS GUSTING 20-30KT. GUSTS END AFTER
SUNSET THIS EVENING...WITH NW FLOW AROUND 10KT...LIGHTER AT KCHO.
VFR CONTINUES FRIDAY WITH NW WINDS 10-15KT...GUSTING TO 20KT LATE
MORNING THROUGH AFTERNOON. VFR FRIDAY NIGHT THROUGH SATURDAY NIGHT
WITH LIGHTER WINDS.

VFR CONDITIONS EXPECTED SUN-MON NIGHT. GUSTY NW FLOW SUN UP TO 25
KTS POSSIBLE...DIMINISHING SUN NIGHT INTO MON AROUND 10 KTS OR LESS.


&&

.MARINE...
SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR ALL WATERS...WITH GUSTS
20 TO 30KT. MODELS ARE ALSO POINTING TO A POTENTIAL BRIEF
INCREASE IN GUSTS EARLY THIS EVENING...SO WILL CONTINUE TO MONITOR
THAT POSSIBILITY. SCA EXPIRES AT MIDNIGHT FOR NORTHERN TIDAL
POTOMAC AND CHESAPEAKE BAY ZONES...BUT RENEWS FRIDAY MORNING AS
GUSTS AROUND 20KT ARE EXPECTED MID MORNING THROUGH THE AFTERNOON.
LIGHTER WINDS FRI NIGHT THROUGH SAT NIGHT UNDER HIGH PRESSURE.

A PRESSURE SURGE BEHIND A DRY COLD FRONT WILL LIKELY LEAD TO SOLID
SMALL CRAFT ADVISORY CONDITIONS OVER THE WATERS DURING THE DAY ON
SUNDAY INTO SUNDAY EVENING. WINDS/SEAS SUBSIDE MONDAY INTO MONDAY
NIGHT...BEFORE SOUTHERLY CHANNELING BETWEEN OFFSHORE HIGH PRESSURE
AND A COLD FRONT APPROACHING FROM THE OHIO VALLEY COULD RESULT IN
SMALL CRAFT ADVISORY CONDITIONS TUESDAY INTO WEDNESDAY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ530-531-
     535-536-538>540-542.
     SMALL CRAFT ADVISORY FROM 9 AM TO 6 PM EDT FRIDAY FOR ANZ530-
     531-535-536-538>540-542.
     SMALL CRAFT ADVISORY UNTIL 6 PM EDT FRIDAY FOR ANZ532>534-537-
     541-543.

&&

$$
SYNOPSIS...KCS
NEAR TERM...KCS
SHORT TERM...KCS
LONG TERM...DFH
AVIATION...KCS/DFH
MARINE...KCS/DFH







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