Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
119 PM EST THU NOV 27 2014

.SYNOPSIS...
AN UPPER-LEVEL DISTURBANCE WILL PASS THROUGH THE AREA TONIGHT AND
HIGH PRESSURE WILL BUILD OVERHEAD FRIDAY. THE HIGH WILL MOVE OFF
THE COAST DURING THE WEEKEND. A COLD FRONT IS EXPECTED TO MOVE
THROUGH MONDAY. 

&&

.NEAR TERM /THROUGH FRIDAY/...
AN UPPER-LEVEL DISTURBANCE WILL MOVE OFF TO OUR SOUTH AND EAST
THIS AFTERNOON WHILE A REINFORCING COLD FRONT MOVES THROUGH. THESE
SYSTEMS MAY BRING A FEW SPRINKLES/SHOWERS TO THE AREA DURING THIS
TIME. THE BEST CHANCE FOR SHOWERS WILL BE ACROSS SOUTHERN MARYLAND
AND THE VIRGINIA PIEDMONT...CLOSER TO THE UPPER-LEVEL DISTURBANCE.
MAX TEMPS WILL RANGE FROM THE UPPER 20S AND LOWER 30S IN THE
MOUNTAINS TO THE LOWER AND MIDDLE 40S NEAR WASHINGTON AND
BALTIMORE. A FEW SNOW SHOWERS ARE POSSIBLE IN THE MOUNTAINS...BUT
ANY ACCUMULATION WILL BE LIGHT AND CONFINED MAINLY TO LOCATIONS
ALONG AND WEST OF THE ALLEGHENY FRONT. 

SURFACE HIGH PRESSURE WILL BUILD TOWARD THE REGION TONIGHT BEHIND
THE COLD FRONT...BUT ANOTHER UPPER-LEVEL DISTURBANCE WILL SWING
THROUGH THE AREA DURING THIS TIME. A PRESSURE SURGE WILL CAUSE
BLUSTERY CONDITIONS AND IT WILL BE COLD DUE TO A NORTHWEST FLOW.
AN UPSLOPE NORTHWESTERLY FLOW WILL BRING ACCUMULATING SNOW TO
LOCATIONS ALONG AND WEST OF THE ALLEGHENY FRONT. MOISTURE WILL BE
PARTIALLY LINED UP WITH THE MAXIMUM DENDRITIC SNOWGROWTH ZONE
UNDERNEATH THE SUBSIDENCE INVERSION. THE SUBSIDENCE INVERSION WILL
ALSO REMAIN RELATIVELY HIGH AND THERE IS PLENTY OF MOISTURE AROUND
AS WELL. THEREFORE...A WINTER WEATHER ADVISORY HAS BEEN ISSUED FOR
THE RIDGE TOPS IN WEST VIRGINIA AND VIRGINIA ALONG AND WEST OF THE
ALLEGHENY FRONT. TWO TO FOUR INCHES OF SNOW IS EXPECTED ACROSS
THESE AREAS. A FEW SNOW SHOWERS MAY SPILL EAST OF THE MOUNTAINS
ACROSS NORTHERN MARYLAND...EXTREME NORTHERN VIRGINIA AND EASTERN
WEST VIRGINIA...BUT LITTLE OR NO SNOW ACCCUMULATION IS EXPECTED.
FCST MIN TEMPS WILL RANGE FROM THE TEENS ALONG THE ALLEGHENY FRONT
TO THE LOW 30S NEAR WASHINGTON AND BALTIMORE.

THE UPPER-LEVEL DISTURBANCE WILL MOVE OFF TO THE EAST FRIDAY WHILE
HIGH PRESSURE BUILDS OVERHEAD. ANY LEFTOVER SNOW SHOWERS ALONG THE
ALLEGHENY FRONT WILL DIMINISH AND SUNSHINE IS EXPECTED.
HOWEVER...IT WILL BE COLD DUE TO THE NORTHWEST FLOW AHEAD OF THE
BUILDING HIGH. MAX TEMPS WILL BE BELOW CLIMO...RANGING FROM THE
20S IN THE MOUNTAINS TO THE LOWER 40S IN THE VIRGINIA PIEDMONT AND
SOUTHERN MARYLAND. 

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
PATTERN SHIFT AS WRN CONUS RIDGE BREAKS DOWN AS AN UPR TROUGH SHIFTS 
SOUTH INTO THE PAC NW. AN ASSOCIATED WARM FRONT WILL MOVE EAST FROM 
THE MIDWEST STATES AND INTO THE NRN MID-ATLANTIC. 00Z ECMWF/12Z GFS 
SUGGEST LIFT FROM THIS FRONT WILL CAUSE PRECIP INTO THE CENTRAL 
APPALACHIANS FRIDAY NIGHT. IN SPITE OF WARM AIR ADVECTION...THERMAL 
PROFILES COOL ENOUGH FOR ALL SNOW. LIMITED POPS FOR NOW TO THE NWRN 
THREE ZONES (WEST OF THE ALLEGHENY FRONT). MID-LEVEL CLOUDS 
ELSEWHERE...THOUGH PLENTY OF COLD AIR AND LITTLE MIXING WILL ALLOW 
FOR MIN TEMPS IN THE LOW TO MID 20S INLAND...UPR 20S NEAR SHORE. 

WARM AIR ADVECTION CONTINUES THROUGH SATURDAY NIGHT IN SWLY FLOW 
WITH PLENTY OF CLOUD COVER. TEMPERATURES MODERATE THROUGH THE 
WEEKEND...REACHING NORMAL BY SUNDAY EVENING. TEMPS A BLEND OF 
MAV/MET AND SREF OVERNIGHT/MOSGUIDE DURING THE DAY. BY THE TIME 
PRECIP RETURNS TO WRN ZONES SATURDAY EVENING...IT SHOULD BE WARM 
ENOUGH FOR RAIN. NOT EXPECTING FREEZING RAIN AT THIS TIME DUE TO THE 
WARM NOSE DESCENDING...WILL HAVE TO LOOKOUT FOR THAT THOUGH. DRY 
EAST OF THE ALLEGHENY FRONT WITH SWLY/SLY FLOW 10 MPH OR SO 
MAINTAINED THROUGH SATURDAY NIGHT IN DECENT GRADIENT.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
HIGH PRESSURE SETS UP OFFSHORE FOR THE SECOND HALF OF THE WEEKEND 
INTO EARLY NEXT WEEK. THIS WILL SET UP A SOUTHERLY FLOW AND BRING IN 
WARMER TEMPERATURES...WITH HIGHS A FEW DEGREES ABOVE NORMAL EXPECTED 
SUNDAY AND MONDAY.

A COLD FRONT WILL APPROACH FROM THE WEST LATE MONDAY...AND CROSS THE 
AREA THROUGH TUESDAY. THIS WILL BRING THE REGION ITS NEXT CHANCE OF 
PRECIPITATION...BUT TEMPERATURES SHOULD BE WARM ENOUGH FOR ALL RAIN. 
SOME WET SNOWFLAKES MAY MIX IN ONCE THE COLD FRONT PASSES WITH ANY 
LEFTOVER SHOWERS MONDAY EVENING ALONG THE MASON-DIXON LINE AND WEST 
OF THE BLUE RIDGE MOUNTAINS MONDAY EVENING. NORTHWEST FLOW BEHIND 
THE FRONT WILL LIKELY RESULT IN UPSLOPE SNOW SHOWERS OVERNIGHT 
MONDAY NIGHT ALONG THE WESTERN RIDGES OF THE ALLEGHENY FRONT ONCE 
TEMPERATURES DROP...BUT AIRMASS WILL BE MARGINAL SO ANY ACCUMULATION 
POTENTIAL IS QUESTIONABLE.

A STRONG AREA OF HIGH PRESSURE /I.E. 1040 MB/ WILL BUILD TO THE 
NORTH TUESDAY INTO TUESDAY NIGHT. MEANWHILE...THE AFOREMENTIONED 
FRONT STALLS TO THE SOUTH...THEN SLOWLY RETURNS NORTH AS A WARM 
FRONT TUESDAY NIGHT. THERE IS A STRONG SIGNAL FOR COLD AIR DAMMING 
IN THE MODELS...WITH EVEN LOWER RESOLUTION GLOBAL MODELS SHOWING 
TEMPERATURES BELOW FREEZING AS PRECIPITATION BEGINS OVER MUCH OF THE 
SHENANDOAH VALLEY AND THE POTOMAC HIGHLANDS. ECMWF IS WARMER AT 850 
MB AND DEEPER WITH LOW PRESSURE TO THE WEST RESULTING IN MORE 
PRECIPITATION AND SUGGESTING A HIGHER ICE POTENTIAL ESPECIALLY WEST 
OF THE METRO. GFS IS COLDER AT 850 MB AND WEAKER WITH LOW PRESSURE 
TO THE WEST SUGGESTING LIGHTER QPF AND A MORE GENERIC WINTRY MIX OF 
SNOW AND RAIN. FOR NOW...STICKING WITH A CHANCE OF RAIN/SNOW...BUT 
WILL DEFINITELY NEED TO MONITOR AND FINE-TUNE OVER THE COMING DAYS 
AS POTENTIAL IS THERE FOR OVERRUNNING PRECIP. OVER COLD AIR TO 
RESULT IN WINTRY PRECIP OVER AT LEAST PART OF THE AREA TUESDAY NIGHT 
INTO WEDNESDAY. LEFT OUT OF HWO FOR NOW BECAUSE 30 PERCENT 
CONFIDENCE IS NOT THERE THAT WE WILL BE ISSUING HAZARDS GIVEN LARGE 
SPREAD IN TIMING/TEMPERATURES.

MODELS/ENSEMBLES BEGIN TO DIVERGE AFTER THIS TIME IN RESPONSE TO A 
PATTERN CHANGE ALOFT WITH MORE ZONAL FLOW OF PACIFIC ORIGIN TAKING 
HOLD.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
VFR CONDITIONS ARE EXPECTED THROUGH FRIDAY. A REINFORCING COLD
FRONT WILL MOVE THROUGH LATE THIS AFTERNOON AND EVENING. A
PRESSURE SURGE BEHIND THE BOUNDARY WILL CAUSE NORTHWEST TO GUST
AROUND 20 KNOTS TONIGHT THROUGH MUCH OF FRIDAY. WINDS WILL
DIMINISH TOWARD FRIDAY EVENING. 

VFR FRIDAY NIGHT THROUGH SATURDAY NIGHT. CALM FRIDAY NIGHT THEN 
SWLY/SLY FLOW INCREASES TO 10-15 KT SATURDAY...10 KT THROUGH 
SATURDAY NIGHT.

VFR EXPECTED SUNDAY W/ S FLOW 10-15 KTS. SUB-VFR POSSIBLE IN SCTD 
SHWRS MON EVE W/ FROPA. WINDS BECOME W AND DIMINISH TO LESS THAN 10 
KTS MON. FLOW BECOMES N THEN E BEHIND FROPA TUE W/ SUB-VFR POSSIBLE 
IN PRECIP LATE TUE. 

&&

.MARINE...
A REINFORCING COLD FRONT WILL MOVE THROUGH THE WATERS THIS
EVENING. A PRESSURE SURGE WILL CAUSE GUSTY NORTHWEST WINDS BEHIND
THIS SYSTEM THROUGH FRIDAY. A SMALL CRAFT ADVISORY IS IN EFFECT
FOR THE WATERS TONIGHT AND FRIDAY. 

HIGH PRES OVERHEAD FRIDAY EVENING...WITH RETURN FLOW INCREASING 
SATURDAY. SLY CHANNELING EXPECTED WITH SCA LIKELY BY LATE MORNING 
SATURDAY CONTINUING WELL INTO SATURDAY NIGHT.

SOUTHERLY FLOW WITH GUSTS EXCEEDING SMALL CRAFT ADVISORY CRITERIA IS 
LIKELY SUNDAY INTO SUNDAY EVENING AHEAD OF A COLD FRONT THAT WILL 
SLOWLY CROSS THE WATERS LATE MONDAY. WINDS DIMINISH AS THE FRONT 
PASSES...THEN STALLS NEAR THE WATERS THROUGH THE MIDDLE OF NEXT WEEK.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...WINTER WEATHER ADVISORY UNTIL 7 AM EST FRIDAY FOR VAZ503.
WV...WINTER WEATHER ADVISORY UNTIL 7 AM EST FRIDAY FOR WVZ501-505.
MARINE...SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 6 PM EST 
     FRIDAY FOR ANZ530-531-535-538-539-542.
     SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 6 PM EST FRIDAY 
     FOR ANZ532>534-536-537-540-541-543.

&&

$$
SYNOPSIS...BJL
NEAR TERM...BJL
SHORT TERM...BAJ
LONG TERM...DFH
AVIATION...BAJ/BJL/DFH
MARINE...BAJ/BJL/DFH

National Weather Service Glossary of Abbreviations