Area Forecast Discussion
Issued by NWS Sterling, VA

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267
FXUS61 KLWX 070835
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
335 AM EST SUN FEB 7 2016

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN OVERHEAD THROUGH TONIGHT WHILE COASTAL
LOW PRESSURE PASSES BY WELL TO OUR SOUTH AND EAST. ANOTHER LOW
PRESSURE SYSTEM WILL DIVE SOUTH INTO THE OHIO VALLEY MONDAY BEFORE
PASSING THROUGH OUR AREA MONDAY NIGHT INTO TUESDAY. HIGH PRESSURE
WILL SLOWLY BUILD TOWARD OUR AREA DURING THE MIDDLE PORTION OF
NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
SURFACE HIGH PRESSURE WILL REMAIN OVERHEAD WHILE LOW PRESSURE
RAPIDLY INTENSIFIES OFF THE SOUTHEAST COAST. DRY CONDITIONS ARE
EXPECTED ALONG WITH SEASONABLE TEMPERATURES. HOWEVER...THERE WILL
BE SOME HIGH CLOUDS WELL NORTH OF THE LOW OFF THE SOUTHEAST COAST.
A PARTLY TO MOSTLY CLOUDY SKY IS EXPECTED...WITH THE THICKEST
CLOUD COVER MOST LIKELY ACROSS SOUTHERN MARYLAND.

THE LOW WILL MOVE OUT TO SEA TONIGHT WHILE HIGH PRESSURE REMAINS
OVERHEAD. DRY AND SEASONABLY CHILLY CONDITIONS ARE EXPECTED.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
A HIGH AMPLITUDE PATTERN SETS UP MONDAY THROUGH MONDAY NIGHT. AN
UPPER-LEVEL RIDGE WILL BUILD OVER THE WESTERN CONUS WHILE A POTENT
TROUGH AND UPPER-LEVEL LOW DIG SOUTH INTO THE OHIO AND TENNESSEE
VALLEYS. THE SURFACE LOW ASSOCIATED WITH THIS SYSTEM OVER THE
GREAT LAKES WILL TRANSFER ITS ENERGY INTO A COASTAL LOW LATER
MONDAY/MONDAY NIGHT AS SHORTWAVE ENERGY AROUND THE UPPER-LEVEL
LOW INTERACTS WITH THE BAROCLINIC ZONE ALONG THE MID-ATLANTIC
COAST. A SURFACE TROUGH/OCCLUDED FRONT WILL EXTEND FROM THE LOW
OVER THE GREAT LAKES SOUTHEAST THROUGH OUR AREA INTO THE LOW OVER
THE MID-ATLANTIC COAST. AT THE SAME TIME...SHORTWAVE ENERGY WILL
BE ROTATING AROUND THE UPPER-LEVEL LOW PASSING THROUGH OUR AREA.
THESE MECHANISMS WILL LIKELY CAUSE PRECIPITATION TO DEVELOP OVER
OUR AREA MONDAY AFTERNOON AND MONDAY NIGHT.

TEMPERATURES WILL BE WELL ABOVE FREEZING MONDAY IN THE VALLEYS SO
ANY PRECIPITATION MONDAY AFTERNOON INTO MONDAY EVENING WILL BE
RAIN OR RAIN/SNOW MIX WITH LITTLE OR NO ACCUMULATION.
HOWEVER...COLDER AIR IS EXPECTED TO WORK ITS WAY INTO THE AREA
LATER MONDAY NIGHT INTO TUESDAY.

GUIDANCE HAS COME INTO SOMEWHAT BETTER AGREEMENT AS TO WHERE THE
OCCLUDED FRONT/SURFACE TROUGH WILL SETUP MONDAY NIGHT AND TUESDAY.
THE BOUNDARY IS MOSTLY LIKELY TO SETUP FROM NEAR SOUTHERN MARYLAND
NORTH AND WEST OVER THE WASHINGTON METROPOLITAN AREA...THEN TOWARD
THE NORTHERN SHENANDOAH VALLEY BEFORE REACHING WESTERN MARYLAND.
AT THE SAME TIME...THE UPPER-LEVEL LOW WILL BE BUILDING OVERHEAD.
THE HEAVIEST PRECIPITATION WILL BE LOCATED ALONG AND TO THE
NORTH AND EAST OF THIS BOUNDARY. WITH COLDER AIR WORKING ITS WAY
IN...THIS MEANS THAT THE MAIN PTYPE WOULD BE SNOW EXCEPT PERHAPS
ACROSS SOUTHERN MARYLAND AND RIGHT ALONG THE BAY WHERE WARMER AIR
FROM THE WATERS MAY KEEP TEMPS UP A BIT. DESPITE THE BETTER
AGREEMENT AMONG GUIDANCE...THERE ARE STILL SUBTLE DIFFERENCES AND WITH
THE GRADIENT BETWEEN SIGNIFICANT SNOW ACCUMULATIONS VS. LITTLE OR
NO SNOW OVERHEAD...ANY SLIGHT CHANGE TO WHERE THIS BOUNDARY IS
LOCATED WILL HAVE SIGNIFICANT IMPACT ON THE FORECAST.

AS OF NOW...THE LATEST FORECAST LEANS TOWARD A CONSENSUS AMONG
THE GUIDANCE WHICH ALLOW FOR THE BEST CHANCE FOR SIGNIFICANT SNOW
ACCUMULATIONS TO BE IN THE MOUNTAINS AS WELL AS ACROSS NORTHERN
MARYLAND...NORTHERN VIRGINIA AND PERHAPS INTO THE WASHINGTON AND
BALTIMORE METROPOLITAN AREAS. FARTHER SOUTH ACROSS SOUTHERN
MARYLAND INTO CENTRAL VIRGINIA SNOW AMOUNTS WILL BE LIGHTER.
AGAIN...WANT TO EMPHASIZE THAT WITH THE GRADIENT OVERHEAD ANY
SLIGHT CHANGE WILL HAVE A SIGNIFICANT IMPACT ON THE
FORECAST...THEREFORE CONFIDENCE REMAINS LOW.

ANOTHER NOTE IS THAT 700MB-500MB MID-LEVEL LAPSE RATES WILL BE
FAIRLY STEEP...6-8 DEGREES C/KM ALONG AND NORTH/EAST OF THE
OCCLUDED BOUNDARY. THE CONVECTIVE ELEMENT MAY CAUSE HEAVIER BURSTS
OF SNOW WITH LOCALLY HIGHER AMOUNTS.

THE UPPER-LEVEL LOW WILL CONTINUE TO PASS THROUGH THE AREA TUESDAY
NIGHT. THE DRY SLOT SHOULD MOVE OVERHEAD...ALLOWING FOR ANY
LEFTOVER SNOW TO END FROM SOUTHWEST TO NORTHEAST. UPSLOPE SNOW
SHOWERS ARE STILL EXPECTED ALONG AND WEST OF THE ALLEGHENY FRONT.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
BY 12Z WED...00Z MODEL SUITE COMING INTO BETTER AGREEMENT ON THE
HANDLING OF DEPARTING SFC/COASTAL LOW AND DEPTH OF BROAD UPPER LVL
TROUGH. ATTENTION FOR THE LATTER HALF OF THE WEEK TURNS FROM PCPN
THREATS AND LOOKS MORE TO AN EXTENDED PERIOD OF BELOW NORMAL
TEMPS...WITH POTENTIAL WIND CHILL ADVISORY CONCERNS...ESP THE
WESTERN HALF OF THE CWA.

REGION REMAINS BETWEEN THE DEPARTING LOW AND APPROACHING SFC HIGH
WED AND THURS. AXIS OF THE UPPER LVL TROUGH REMAINS EXTENDED SOUTH
ACROSS THE MID-ATLANTIC...WITH THE BASE SETTLED OVER THE CAROLINAS.
THE POTENTIAL FOR SNOW SHOWERS (MIXED WITH RAIN SOUTHERN MD)
CONTINUES WED DESPITE DRYING AT THE SFC. HIGHER CONFIDENCE OF SEEING
UPSLOPE SNOW SHOWERS POTOMAC HIGHLANDS MID WEEK ON THE WNW
FLOW...AMOUNTING TO AN ADDITIONAL COUPLE OF INCHES. ANY SNOW TO THE
EAST WILL GENERALLY AMOUNT TO LESS THAN AN INCH. 850MB TEMPS DROP TO
BETWEEN -10 AND -15 DEGREES CELSIUS WED-THURS...RESULTING IN LOWS
REACHING THE SINGLE DIGITS/TEENS WED NIGHT AND HIGHS ON THURS IN THE
20S. THESE TEMPS COMBINED WITH WINDS GUSTING INTO THE 20S...ESP
HIGHER ELEVATIONS WEST OF THE BLUE RIDGE COULD SEE WIND CHILLS
DROPPING BELOW ZERO WED NIGHT AND STAYING BELOW THRU THURS NIGHT.
THIS IS HIGHLIGHTED IN THE HWO.

BRIEF INCREASE IN TEMPS FRIDAY AS THE UPPER LVL TROUGH PIVOTS
THROUGH THE REGION...LEADING TO BRIEF ZONAL FLOW ALOFT.
HOWEVER...CLOSED LOW REMAINS POSITIONED OVER SOUTHEASTERN CANADA
DURING THIS TIME PERIOD...RESULTING IN YET ANOTHER PLUNGE OF THE
FLOW AS THE NEXT TROUGH DEEPENS ACROSS THE EASTERN HALF OF THE US.
DEPENDING ON WHERE THE RIDGE AXIS ALIGNS OVER THE WESTERN HALF WILL
DETERMINE HOW DEEP THIS TROUGH GOES...AND AS SUCH...HOW EXACTLY COLD
IT GETS THIS COMING WEEKEND. ECMWF THE MUCH COLDER OF THE
SOLUTIONS...SHOWING 850MB TEMPS BELOW -20 DEGREES CELSIUS. USING THE
00Z SUPERBLEND FOR NOW...PLAYING A MORE CONSERVATIVE ROUTE WITH
TEMPS. EVEN SO...WIND CHILL ADVISORY LVL VALUES LOOK TO BE PSBL
AGAIN OVER THE WEEKEND.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
VFR CONDITIONS ARE EXPECTED THROUGH MIDDAY MONDAY. LOW PRESSURE
WILL MOVE INTO THE AREA LATER MONDAY AFTERNOON AND PERSIST THROUGH
TUESDAY. PRECIPITATION WILL LIKELY OVERSPREAD THE TERMINALS DURING
THIS TIME. THE STEADIEST PRECIPITATION IS MOST LIKELY ACROSS THE
NORTHERN AND EASTERN TERMINALS. PTYPE OF RAIN OR RAIN AND SNOW MIX
SHOULD CHANGE TO SNOW MONDAY NIGHT. IFR CONDITIONS ARE LIKELY
MONDAY NIGHT INTO MUCH OF TUESDAY. CONDITIONS WILL IMPROVE LATER
TUESDAY AND TUESDAY NIGHT AS DRIER AIR WORKS ITS WAY IN.

GENERALLY VFR CONDITIONS WED THRU THE END OF THE WEEK.
GUSTY NW WINDS WED AND THURS...WITH GUSTS BETWEEN 20-25 KTS. HIGH
PRESSURE BUILDING IN BY THE END OF THE WEEK WILL WEAKEN THE WINDS TO
LESS THAN 12 KTS.

&&

.MARINE...
LOW PRESSURE WILL PASS BY WELL TO THE SOUTH AND EAST OF THE WATERS
LATER TODAY AND TONIGHT. HOWEVER...THE GRADIENT WILL STRENGTHEN SO
A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE MIDDLE PORTIONS OF THE
BAY AND LOWER TIDAL POTOMAC RIVER LATE TODAY INTO MONDAY MORNING.
THE GRADIENT SHOULD SUBSIDE MONDAY BUT LOW PRESSURE WILL IMPACT
THE WATERS MONDAY NIGHT THROUGH TUESDAY NIGHT. A SMALL CRAFT
ADVISORY MAY BE NEEDED FOR PORTIONS OF THE WATERS DURING THIS
TIME.

SCA CONDITIONS LIKELY ON THE CHESAPEAKE BAY AND LOWER TIDAL
POTOMAC WED THRU THURS NIGHT. SCA ARE PSBL WED...BCMG MORE LIKELY
THURS ON THE UPPER TIDAL POTOMAC. ALL WATERS DROP BELOW SCA
CRITERIA FRI INTO THE WEEKEND.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 9 AM EST MONDAY
     FOR ANZ532-533-540-541.
     SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 9 AM EST
     MONDAY FOR ANZ534-537-543.

&&

$$
SYNOPSIS...BJL
NEAR TERM...BJL
SHORT TERM...BJL
LONG TERM...SEARS
AVIATION...BJL/SEARS
MARINE...BJL/SEARS



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