FXUS61 KAKQ 220349
AFDAKQ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WAKEFIELD VA
1049 PM EST MON DEC 21 2009
.SYNOPSIS...
WEAK HIGH PRESSURE RETURNS TO THE MID ATLANTIC REGION...AND WILL
DOMINATE OVER THE REGION THROUGH CHRISTMAS EVE. A WARM
FRONT...ASSOCIATED WITH A STRONG LOW PRESSURE OVER THE MID
MISSISSIPPI RIVER VALLEY...WILL SWING THROUGH THE MID ATLANTIC
REGION CHRISTMAS DAY...AND WILL BE FOLLOWED BY A COLD FRONT THAT
WILL MOVE THROUGH THE AREA BY SATURDAY MORNING. HIGH
PRESSURE BUILDS BACK INTO THE REGION FROM THE WEST SATURDAY
AFTERNOON INTO SUNDAY.
&&
.NEAR TERM /UNTIL 7 AM TUESDAY MORNING/...
TRAPPED LOW LEVEL MOISTURE AND WEAK COLD ADVECTION IS PRODUCING
SOME CLOUDS IN THE WESTERN PART OF THE FORECAST AREA. FURTHER
EAST...THE NW FLOW HAS KEPT THE CLOUDS AT BAY. MODELS INDICATE
THAT THE LOW LEVEL MOISTURE SHOULD THIN ALLOWING THE CLOUDS TO
BREAK AFTER MIDNIGHT. SO HAVE ALLOWED SOME CLEARING THERE
OVERNIGHT. ELSEWHERE SHOULD SEE MOSTLY CLEAR SKY. THE BIG CHANGE
IS THAT THE WINDS HAVE STAYED UP...WHICH HAS HELD TEMPERATURES UP.
BASED UP THIS...THE HIGHER DEW POINTS AND LATEST LAV
GUIDANCE...HAVE RAISED THE LOWS ABOUT 3 TO 5 DEGREES IN THE
WESTERN PART OF THE CWA WHICH ACTUALLY COOLING SOME SPOTS IN THE
EAST WHERE THE CLEARING HAS ALLOWED FOR MORE COOLING.
&&
.SHORT TERM /7 AM TUESDAY MORNING THROUGH THURSDAY/...
TUESDAY...THE SFC RIDGE BEGINS TO WEDGE DOWN THE LEE OF THE
APPALACHIANS. NW-SE RIBBON OF 850-500 MB MOISTURE S OF THE UPR LVL
JET STREAK (ALONG THE LOW-MID LVL CONFLUENT DEFORMATION ZONE) WILL
WORK ACROSS MUCH OF THE FCST AREA...MAINLY NW HALF OF THE CWA.
MOISTURE RIBBON IS ESSENTIALLY WARM-FRONTAL IN NATURE...WITH THE
N-S HORIZONTAL EXTENT LIMITED BY THE DEGREE OF MID/UPR LVL
CONFLUENCE (DEFORMATION). 850-500 MB RH'S DURING THE DAY PEAK ABV
75% OVER THE NW HALF...CLOSER TO 55-60% OVER THE FAR SE. WILL
THEREFORE HAVE SKIES BCMNG MOSTLY CLOUDY NW...PARTLY SUNNY SE. IN
TERMS OF POPS...DESPITE INCREASING 850-500 MB FGEN...DEEP LAYER
MOISTURE IS LACKING (ESPECIALLY IN THE LOWER LAYERS). THUS WILL
KEEP THE DRY FCST GOING. TEMPS WILL AGAIN BE ON THE CHILLY SIDE...
ESPECIALLY N AND W OF RIC CONSIDERING THE INCREASING CLOUDS AND
CONTINUED SNOW COVER. SFC WINDS VEERING MORE N AND EVENTUALLY NE
WILL ALSO LIMIT THE DOWNSLOPE WARMING POTENTIAL (FAVORING COOLER
TEMPS AS WELL)...WHILE THE WAA TAKING PLACE BTWN 850-700 MB
STRENGTHENS THE LLV INVERSION WITH TIME. MAV-MET MOS BLEND FOR
HIGH TEMPS IS CONSISTENT WITH THE CURRENT THINKING...AND WITH THE
PREVIOUS FCST...WITH ONCE AGAIN A FAIRLY GOOD GRADIENT FROM N/NW
AREAS (MID-UPR 30S) TO SE (MID 40S).
ANOTHER CHILLY NIGHT TUE NIGHT...AGAIN (LIKE A BROKEN RECORD)
ESPECIALLY IN AREAS WITH SNOW STILL ON THE GROUND...HOWEVER
CONTINUED 850-500 MB CONFLUENT DEFORMATION AND ASSCD NW-SE RIBBON OF
CLOUDINESS...AT LEAST EARLY ON...MAY LIMIT THE RADIATIONAL COOLING
AT LEAST TO SOME DEGREE. WILL CALL IT PARTLY CLOUDY NRN PTNS...MSTLY
CLEAR S. HAVE OPTED FOR THE COOLER MAV GUIDANCE WITH TEMPS...AGAIN
UNDERCUTTING READINGS BY AT LEAST 5F IN AREAS WITH SNOW PACK.
WEDNESDAY...1035+ MB SFC HIGH BECOMES CENTERED N OF LAKE SUPERIOR...
WITH RIDGE AXIS AND LLVL CAD FULLY WEDGED DOWN THE ATLC SEABOARD.
AGAIN...850-500 MB DEFORMATION ZONE WILL LIE ACROSS THE FCST AREA...
ALLOWING FOR PERIODIC MID/UPR LVL CLOUDINESS IN THE NW FLOW REGIME
ALOFT (MSTLY CLEAR TO PARTLY CLOUDY). TEMPS WED VERY SIMILAR TO TUE
BASED ON THE STRENGTHENING LLVL CAD WEDGE...NRLY LLVL FLOW...AND
THUS LIMITED VERTICAL MIXING. HIGHS AGAIN FROM THE MID-UPR 30S NRN
HALF...MID-UPR 40S S.
WEDNESDAY NIGHT AND THU...STRONG SFC HIGH SHIFTS SLOWLY E TO ST
JAMES BAY (ONTARIO/QUEBEC BORDER). STRENGTHENING LLVL STABILITY/CAD
WEDGE CONTINUES DOWN THE ERN SEABOARD...WITH INCREASING WAA MID
AND UPR LVL CLOUDINESS CHRISTMAS EVE AHEAD OF THE NEXT SYSTEM.
GFS/NAM CONSENSUS SUPPORTS A DRY FCST HWVR...AT LEAST INTO THE
EVENING HOURS ON CHRISTMAS EVE...GIVEN THE CURRENT PROJECTIONS OF
A DEEP DRY LAYER STILL IN PLACE BELOW 500-600 MB. TEMPS CONTINUE
ON THE CHILLY SIDE (SEASONABLE...THOUGH AROUND 5F BELOW
NORMAL)...WITH LOWS WED NIGHT FROM AROUND 20 FAR NW TO LWR 30S SE
AND HIGHS THU FROM MID-UPR 30S NRN PTNS TO UPPER 40S FAR SE.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
MODELS ARE CLOSE NOW IN SOLUTIONS WITH MAIN LOW MOVING UP WELL TO
THE W OF THE AREA ON CHRISTMAS DAY. TELECONNECTIONS SUPPORT THE LOW
MOVING WELL WEST OF THE APPALACHIANS. WITH HIGH PRESSURE RIDGING
SOUTH FROM NEW ENGLAND WILL HAVE SOME FORM OF COLD AIR DAMMING OVER
THE SNOW PACK ESPECIALLY ON CHRISTMAS DAY. NOT EXPECTING A LOT OF
PRECIP. MAIN ISSUE WILL BE PRECIP TYPE UNTIL ENOUGH WARM AIR ARRIVES
TO CHANGE ALL PRECIP TO RN. WILL GIVE SOME FREEZING RAIN ON
CHRISTMAS EVE NIGHT INTO CHRISTMAS MORNING STARTING OVER THE SNOW
PACK AREA AND GRADUALLY DIMINISHING TO THE NORTHWEST UNTIL ALL TEMPS
ABOVE FREEZING DURING CHRISTMAS MORNING. THIS LOOKS REASONABLE WITH
ECMWF AND GFS. WILL SEE SOME WARM UP AHEAD OF COLD FRONT WHICH
CROSSES THE AREA ON SATURDAY. THEN DRY AND COLD WITH TEMPS A LITTLE
BELOW NORMAL THROUGH MONDAY. THIS LOOKS SIMILAR ON ALL GUIDANCE.
&&
.AVIATION /04Z TUESDAY THROUGH SATURDAY/...
VFR CONDS OVER THE REGION. SOME SCT-BKN LOW/MID LVL CLOUDS MOVG THRU
THE AREA BUT NOT EXPECTED TO HAVE SIGNIFICANT IMPACT ON WX. WNDS
WILL BE W-NW OVERNIGHT LESS THAN 10 KT. VFR CONDS EXPECTED THRU THU.
NEXT WX SYS WILL IMPACT THE AREA LATE THU INTO FRI AS WIDESPREAD
RAIN MOVES IN. CHC OF A BRIEF PERIOD OF FRZ RAIN PSBL WEST OF RIC
THU NIGHT.
&&
.MARINE...
CONTINUED LOW PRESSURE WELL EAST OF THE CANADIAN MARITIMES WILL KEEP
SMALL CRAFT ADVISORY OVER NE PART OF THE WATERS UNTIL TUESDAY.
FINALLY WITH HIGH PRESSURE RIDGING IN FROM THE W WILL HAVE CONTINUED
NW FLOW BUT WINDS BECOMING LIGHTER. MOS GOING NEAR CALM AT NIGHT
OVER LAND WHICH LOOKS REASONABLE. WITH THE MAIN LOW PRESSURE GOING
INITIALLY W OF THE APPALACHIANS NOT EXPECTING MUCH SOUTHERLY PUSH
UNTIL THE COLD FRONT APPROACHES THIS WEEKEND. THEN WINDS WILL COME
BACK UP TO SMALL CRAFT CRITERIA AHEAD OF THE FRONT AND THEN AFTER
THE FRONT PASSES IN STRONG NW FLOW.
&&
.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
NC...NONE.
VA...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST TUESDAY FOR ANZ650-652.
&&
$$
SYNOPSIS...BKH/ESS
NEAR TERM...ESS
SHORT TERM...BKH
LONG TERM...JAB
AVIATION...JEF
MARINE...JAB
