Small Craft Advisory 8, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
911 PM EST MON JAN 9 2012

.SYNOPSIS...
HIGH PRESSURE WILL BUILD OVER THE REGION THROUGH TUESDAY. A STORM
SYSTEM WILL IMPACT THE MID- ATLANTIC REGION WEDNESDAY AND
WEDNESDAY NIGHT. A STRONG COLD FRONT IS EXPECTED TO CROSS THE
REGION ON THURSDAY...USHERING IN MUCH COLDER AIR TO THE REGION.

&&

.NEAR TERM /THROUGH TUESDAY/...
THE WAVE OF LOW PRESSURE ALONG WITH ITS ASSOCIATED UPPER-LEVEL
DISTURBANCE HAS MOVED OFFSHORE. SURFACE HIGH PRESSURE WILL SLOWLY
BUILD TOWARD THE REGION FROM THE OHIO VALLEY TONIGHT.

LOW-LEVEL MOISTURE REMAINS TRAPPED UNDERNEATH THE SUBSIDENCE
INVERSION MAINLY FOR LOCATIONS ALONG AND EAST OF THE BLUE RIDGE
MOUNTAINS. LOW CLOUDS ALONG WITH AREAS OF FOG WILL AFFECT THESE
AREAS LATE THIS EVENING INTO THE OVERNIGHT HOURS. THE BEST CHANCE
FOR FOG WILL BE ALONG THE BLUE RIDGE MOUNTAINS. A SPRINKLE OR
FLURRY CANNOT BE RULED OUT LATE THIS EVENING...BUT NO SNOW
ACCUMULATION IS EXPECTED.

AS THE WAVE OF LOW PRESSURE PUSHES OFF TO THE EAST...A LIGHT
WESTERLY FLOW MAY DEVELOP TOWARD MORNING CAUSING LOW CLOUDS AND
FOG TO DISSIPATE. RADIATIONAL COOLING WILL DEVELOP IF LOW CLOUDS
DO DISSIPATE...CAUSING TEMPERATURES TO DIP BELOW FREEZING ACROSS
MOST LOCATIONS. ANY WET OR SLUSHY ROADS MAY CONTAIN ICY SPOTS.

HIGH PRESSURE WILL CONTINUE TO BUILD TOWARD THE AREA TUESDAY. ANY
LEFTOVER LOW CLOUDS OR FOG WILL QUICKLY DISSIPATE EARLY IN THE
MORNING. A DOWNSLOPING WESTERLY FLOW WILL COMBINE WITH PLENTY OF
SUNSHINE FOR NOTICEABLY MILDER CONDITIONS TUESDAY AFTERNOON. MAX
TEMPS WILL RANGE FROM THE 40S IN THE MOUNTAINS...TO THE LOWER 50S
ACROSS WASHINGTON AND BALTIMORE...TO THE MID 50S ACROSS CENTRAL
VIRGINIA.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
H5 LOW OVER THE LWR MS VLY WL ROTATE TO MS/AL TUE NGT. SFC LOW NOT
FAR AHD OF THE UPR SYSTEM...NEAR TN BY 12Z WED. THERE/S A SPD DIFF
BTWN NAM/GFS /THE LATTER IS FASTER/...WITH THE ECMWF REPRESENTING A
COMPROMISE. ATTM...HV SHIED AWAY FM THE SLOWEST OF SOLNS...SPCLY IN
TERMS OF WAA INDUCED PCPN. EITHER WAY...TUE NGT WL BE DRY...W/ INCR
CLDS AHD OF THE LOW. THE EVNG HRS WL ONLY HV A FEW HIGH CLDS...SO
THERE WL BE AMPLE OPPORTUNITY FOR RADL COOLING. THAT LEADS TO A TEMP
CHALLENGE AS WAA SHUD HOLD TEMPS UP ON THE RDGTOPS...BUT THERE/S
POTENTIAL FOR SUBFREEZING MIN-T IN THE VLYS. AM TEMPTED TO GO WARMER
THAN MOS...BUT WONT GO THAT MUCH HIER DUE TO THE EVNG RADL COOLING
POTENTIAL.

PCPN WL OVERSPREAD AREA WED...MOST LKLY IN THE MRNG. THE TUE NGT
TEMP FCST WL IMPACT PTYPE AT ONSET. ASSUMING PCPN MOVES IN QUICK
ENUF...THERE/S A RISK OF NON-RAIN AT ONSET. GFS REPRESENTS THIS BEST
AS IT/S THE QUICKEST. THE GFS PTYPE OUTPUT SUGGESTS SNW...BUT THE
MDL SNDGS WUD HINT AT FZRA INSTEAD. SINCE TIMING ALSO IN DOUBT...WL
USE RASN AT ONSET AS A PLACEHOLDER. LATER SHIFTS WL NEED TO PIN THE
TIMING AND SUBSEQUENT TYPE FCST DOWN FURTHER.

WED AFTN-NGT WL BE THE WETTEST PD AS SFC LOW PASSES OFF THE
DELMARVA. THERE WL BE A 40 KT H8 LLJ TRANSPORTING MSTR FM THE
GLFMEX...PLUS GOOD MSTR INFLOW FM THE ATLC. QPF SHUD BE CLOSE TO AN
INCH. DUE TO CLDS/PCPN/ELY FLOW HV LOWER WED MAXT 5-8 DEGF INTO THE
40S. AM NOT AS COLD AS MAV...WHICH ISNT AN UNREALISTIC FCST...BUT
ITS A GOOD START. FURTHER...PCPN PLUS CAA LT AT NGT WUD MEAN MIN-T
CLOSE TO DEWPTS...WHICH WL BE IN THE 30S-LWR 40S. HV KEPT EVERYTHING
ABV FRZG...BUT IT/LL BE A DAMP...RAW NIGHT.

PCPN WL BE PULLING AWAY THU. POPS IN FCST REFLECTIVE MORE OF TIMING
UNCERTAINTY. TEMPS HV BEEN LWRD FOR ANOTHER PD.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
COLD AIR WL BE DRAINING SEWD THU NGT-FRI AS LOPRES DEPARTS UP THE
COAST. CAA CONTS INTO THE WKND...W/ THE CORE OF THE COLD AIR MAKING
IT HERE SAT. IN NW FLOW...XPCTG LOTSA UPSLP CLDS AND OCNL SNW
FLURRIES AND PREDOMINANTLY DWNSLP CLR SKIES. A S/WV PASSAGE FRI NGT
MAY INCR CLDS AT THAT TIME. THE BEST CHC AT ACCUM SHSN WL BE THU
NGT-FRI BEFORE INVERSION HGTS LWR. ALTHO TEMPS WL BE MUCH COOLER...
FCST MAXT/MIN-T -ONLY- DOWN CLOSE TO CLIMO.

BY SAT...A WK LOPRES SYSTEM WL BE DROPPING SEWD FM INVOF ALBERTA.
IT/LL BE CROSSING THE GRTLKS AND PASSING N OF THE CWFA SAT NGT-ELY
SUN. IT/LL BE COLD ENUF FOR SNW AT THAT TIME...ASSUMING QPF HOLDS
TOGETHER /WHICH IS A FAIRLY BIG ASSUMPTION THIS FAR OUT/. HV CHC
POPS IN THE GRIDS...SPCLY N/W. HIPRES WL BE BLDG THEREAFTER.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
LOW-LEVEL MOISTURE REMAINS TRAPPED UNDERNEATH THE SUBSIDENCE
INVERSION CAUSING LOW CLOUDS ALONG WITH AREAS OF BR. IFR
CIGS/VSBYS WILL PERSIST INTO THE OVERNIGHT HOURS BEFORE
DISSIPATING EARLY TUESDAY MORNING. DRIER AIR WILL SLOWLY MOVE IN
BETWEEN 6 AND 12Z...BUT RADIATIONAL COOLING MAY COUNTERACT DRY AIR
ADVECTION KEEPING LOW CIGS/VSBYS UNTIL APPROX 12Z. LATEST TAF
FORECAST SHOWS CIGS/VSBYS LIFTING BETWEEN 06 AND 09Z DUE TO THE
DRY AIR ADVECTION. THERE REMAINS A HIGH DEGREE OF UNCERTAINTY IN
THE FORECAST DURING THIS TIME.

HIGH PRESSURE WILL CONTINUE TO BUILD TOWARD THE TERMINALS TUESDAY.
ANY LEFTOVER LOW CLOUDS/BR WILL QUICKLY DISSIPATE. VFR CONDITIONS
ARE EXPECTED WITH WEST-NORTHWEST WINDS GUSTING AROUND 15 TO 20
KNOTS ACROSS MOST OF THE TERMINALS. WIND SPEEDS WILL BE LIGHTER
ACROSS KCHO.

VFR TUE NGT...BUT FLGT RESTRICTIONS RETURN WED AHD OF LOPRES.
XPCTG MOSTLY MVFR IN RA...BUT CUD HV A LTL SNW/FZRA AT START...
SPCLY CHO. RESTRICTIONS CONT INTO THU...W/ IFR CIGS MOST LKLY WED
NGT.

&&

.MARINE...
WINDS WILL REMAIN LIGHT THROUGH TONIGHT. WEST-NORTHWEST WINDS WILL
INCREASE AHEAD OF BUILDING HIGH PRESSURE TUESDAY. GUSTS AROUND 20
KNOTS ARE EXPECTED ACROSS THE NORTHERN PORTION OF THE BAY AND
UPPER TIDAL POTOMAC RIVER LATE TUESDAY MORNING AND AFTERNOON. A
SMALL CRAFT ADVISORY IS IN EFFECT FOR THESE AREAS.
ELSEWHERE...WIND SPEEDS WILL REMAIN BELOW SCA CRITERIA. HIGH
PRESSURE WILL BUILD OVER THE WATERS TUESDAY NIGHT CAUSING LIGHT
WINDS.

LOPRES APPROACHES WATER WED...PASSING JUST S WED NGT. SCA PSBL IN
E FLOW AT THAT TIME. BEST MIXING COMES ON THE BACK SIDE THU NGT-
FRI WHEN ANOTHER SCA OPPORTUNITY ARRIVES.

&&

.TIDES/COASTAL FLOODING...
LOW PRESSURE APPROACHES AREA WED...AND PASSES NE OF REGION EARLY
THU. THERE WL BE A PERIOD OF STRONG ELY FLOW WED NIGHT...WHEN
TIDAL DEPARTURES MAY INCREASE BY A FT OR MORE. WE/RE JUST PAST
FULL MOON...SO THERE WL BE A TIDAL CONTRIBUTION AS WELL. MAY GET
CLOSE TO MINOR THRESHOLDS.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 11 AM TO 6 PM EST TUESDAY FOR
     ANZ530>532-535-538>540.

&&

SYNOPSIS...MRK/BJL
NEAR TERM...BJL
SHORT TERM...HTS
LONG TERM...HTS
AVIATION...BJL/HTS
MARINE...BJL/HTS
TIDES/COASTAL FLOODING...HTS

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