Winter Weather in Maryland, March 17, 2002

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE/WASHINGTON
915 AM EST SUN MAR 17 2002

EVALUATION OF 12Z IAD SOUNDING SHOWS WET BULB ABV 0C RIGHT AROUND
835MB AND NEAR 0C RIGHT AROUND 900MB. OTHERWISE...WET BULB IS BELOW
FREEZING. BASED ON 12Z IAD SOUNDING AND A SKYWARN OBSERVER REPORT OF
PL IN RAPPAHANNOCK COUNTY...WILL BE EXPAND THE MENTION OF PE MIXED
WITH THE RA FURTHER S AND E.

BASED ON 06Z ETA BUFKIT SOUNDINGS...AND ASSUMING AN OBSERVED
SOUNDING FURTHER N WOULD BE A BIT COOLER THAN THE OBSERVED 12Z IAD
SOUDING...HAVE ADDED THE CHC OF RA/PL BEGINNING AS A BRIEF PD OF SN
FAR NRN COUNTIES.

MESO NETWORK OF OBS SHOWS SFC DEWPOINTS IN THE LOWER TO MID 20S IN
POCKETS FROM WASHINGTON CO TO CARROLL CO BUT WET BULBS CLOSE TO FRZG.
WILL MONITOR TEMP/DWPT/PCPN TRENDS CLOSELY NEXT FEW HOURS TO SEE IF
WE NEED TO STICK IN FZRA FAR NRN COUNTIES.

ZFP UPDATED WITH 1ST PD CHANGES. NO OTHER CHGS.

WALSTON

PREVIOUS AFD BELOW.
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NEAR TERM...
BASIC MDL AGREEMENT THAT ITS GONNA BE A WET STRETCH NEXT 36 HRS.
QSTNRY FNT ACRS NC W/ LOPRES OVR MS ATTM. PROLIFIC LTG ACRS TN IN
AREA OF STRNG UVV IN ASSOC W/ ISEN LIFT AT NOSE OF 40 KT H8 JET.
THIS AREA OF PCPN PROGGED TO SPREAD ACRS CWFA MIDDAY AS THE LOW
TRACKS INTO THE OHIO VLY.  UVV COMBINED W/ EVAP COOLING PRODUCES A
SUBZERO POCKET H9-H850...WHICH GETS REINFORCED BY NELY WNDS BLO THIS
LYR. OVERRUNNING FLW FM THE SW H850 AND ABV. MDL SNDGS POINT TO PL
PROFILE NW AND NC...W/ NEG ENERGY ABOUT DBL POS ENERGY PER ENERGY
METHOD AT TIME OF PCPN ONSET. ELSW...TEMPS A PINCH BLO FRZG AT 850
MB... BUT W/ BLYR TEMPS BTWN 3-6 DEG C...MAIN PTYPE SHUD BE RA. WL
KEEP NW QDRNT SEPARATE FOR PL REACHING GRND IN HVYR SPURTS. NOTHING
SHUD ACCUM AS MELTING WL RAPIDLY ENSUE W/ GRND TEMPS WARM DUE TO
RECENT NEAR-SUMMERLIKE BURST.

1ST ROUND WL DEPART TWD OR A LTL AFTR DUSK...W/ ROUND 2 MVG ALNG
CONVGC ZN REACHING CWFA AFTR MIDNGT...CONTG INTO MON MRNG. BY THIS
POINT...ENTIRE PROFILE ABV FRZG...SO OCNL RA WL DO. BTWN THE
TWO...ELY FLW...WET GRND...AND SAT ATM SHUD PROMOTE DZ/BR. A BIT OF
WND IN THE BNDRY LYR ONLY FCTR PREVENTING FG.

CAT POPS TDA-TMRW...XCPT LIKELY SW ON MON. MOS TEMPS CLS AND
ACCEPTED. LEANED TWD LTL DIURNAL RNG AS APPRO.

HTS

LONG TERM: COULD POSSIBLY SEE A LITTLE BIT OF CLEARING EARLY MONDAY
NIGHT AS FLOW OFF THE SURFACE TURNS TO THE NORTHWEST. WEAK SURFACE
PATTERN THOUGH.. AND ANY CLEARING COMBINED WITH RESIDUAL LOW LEVEL
MOISTURE SHOULD RESULT IN STRATUS/DRIZZLE/FOG DURING THE OVERNIGHT
HOURS. ETA EXTENSION AND AVN HAVE A SURGE OF WARM ADVECTION MOVING
ACROSS THE AREA DURING THE DAY ON TUESDAY... AND WILL RAISE POPS ON
TUESDAY INTO THE LIKELY RANGE.

SOME DIFFERENCES IN THE EXTENDED MODELS WITH THE EVOULTION OF THIS
WEATHER SYSTEM.  AVN TRIES TO TAKE THE ASSOCIATED SURFACE LOW OVER
US TUESDAY NIGHT AND EARLY WEDNESDAY. CANADIAN/NOGAPS TAKE THE
SURFACE LOW TO THE NORTH AND WEST OF US... AND DRAG A COLD FRONT
THROUGH THE AREA DURING THE DAY ON WEDNESDAY. UKMET AND EURO MODELS
LEANING TOWARD THIS TYPE OF SOLUTION AS WELL. WILL PROBABLY NOT MAKE
ANY CHANGES TO WEDNESDAY FORECAST AT TIME... AS TEXT MENTIONS RAIN
CHANCES DURING THE MORNING HOURS. WILL NEED TO KEEP AN EYE ON
EXTENDED MODELS NEXT COUPLE OF DAYS THOUGH TO SEE IF TIMING OF
PRECIP CHANGES.

AVN/MRF AND CANADIAN SHOWING COLD HIGH PRESSURE BUILDING INTO THE
PLAINS STATES FROM CENTRAL CANADA LATE IN THE WEEK. A DRY COLD FRONT
EXPECTED OVER THE AREA THURSDAY NIGHT OR FRIDAY... WITH TEMPS OVER
THE NEXT WEEKEND QUITE A BIT COOLER THAN NORMAL. 850 TEMPS DROPPING
DOWN TO THE -10 TO -12 RANGE... WITH RESULTING HIGHS LIKELY NOT
GETTING OUT OF THE 40S. WILL SCALE BACK HIGH TEMPS FOR DAY 6 AND 7
ACCORDINGLY.   MARGRAF

.LWX...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.