Winter Storm and Winter Weather in Virginia, January 19, 2002

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE/WASHINGTON
300 AM EST SAT JAN 19 2002

...A NAIL BITER FOR DC AND BALTIMORE...
...STAYING THE COURSE WITH ALL WARNINGS AND ADVISORIES...

NO MAJOR CHANGES FROM EXCELLENT PACKAGE LEFT BY YDAYS DAY SHIFT. 00Z
MODELS SHOW NO SURPRISES. MODELS ARE FAILY SIMILAR NOW WITH ONLY
MINOR DIFFERENCES. 00Z ETA CONTINUES TO BE A BIT STRONGER THAN THE
AVN WITH THE SFC LOW. IN ADDTN...THE ETA CONTINUES TO BE A BIT
WETTER THAN THE AVN/NGM AND CONTINUES TO THROW HIER QPF FURTHER N.
HOWEVER...THE ETA HAS BEEN SLOWLY GRAVITATING TOWARD THE AVN SOLN
DURING THE PAST FEW RUNS. THE AVN MODEL HAS PERFORMED BETTER THAN
THE ETA DURING THE PAST FEW EVENTS IN THIS REGION. WILL BE GOING ALG
WITH NCEP AND USE THE AVN QPF WITH THE IDEA THAT THERE COULD BE SOME
BANDS OF HEAVIER PCPN DUE TO CSI BANDING. THIS IS HINTED AT IN THE
VERTICAL CROSS SECTIONS.

VORT MAX OVR THE PLAINS WILL RACE EWD IN FAST ZONAL FLOW REACHING
THE MID ATLC STATES 06Z SUN THEN RACING OFFSHORE THEREAFTER. ASSOCD
SFC LOW WILL BE NEAR ORF AT 00Z SUN THEN DEEPEN AND MOVE ENE.

THIS WILL BE A FAST MOVER AND A QUICK EVENT. BOTH THE AVN AND ETA
SHOW A STRONG WAA PCPN EVENT FOR THE AREA. EXCELLENT UUVS AND
EXCELLENT ISENTROPIC LIFT OVR THE AREA TDA. BEST UVVS AND ISENTROPIC
LIFT EXIT THE AREA SHORTLY AFTER 00Z.  LGT PCPN SHUD MOVE INTO THE
AREA DURING THE MORNING HRS. BEST UUVS AND ISENTROPIC LIFT TRANSLATE
INTO A PERIOD OF MOD/HVY PCPN ACRS THE AREA THIS AFTRN AND SNOWFALL
RATES COULD EASILY EXCEED ONE INCH AN HOUR FOR A 3 TO 5 HR PERIOD.
ONCE THE BEST LIFT MOVES TO THE E AFTER 00Z...MOD/HVY PCPN WILL BE
OVR. HOWEVER...LINGERING MOISTURE AND STG VORT MAX COMING ACRS THE
AREA COULD RESULT IN SOME LINGERING LGT PCPN 00Z-06Z TNGT. BEHIND
VORT MAX...MODELS SHOW SOME CLRG LATE TNGT AND ZNS WILL REFLECT THIS.

WE STILL HAVE TWO BIG PROBLEMS WITH THIS SYSTEM...
THERE IS NO COLD SFC HIGH TO THE N OF THE AREA TO SUSTAIN TRANSPORT
OF COLD AIR INTO THE AREA. IN ADDITION...AVN/ETA BOTH SHOW THE 850MB
LOW PASSING OVR OR TO THE N OF THE DCA AREA.

WITHOUT A SFC HIGH TO THE N MAINTAINING A TRANSPORT OF COLD AIR INTO
THE AREA...AND WITH STRONG WAA ABV THE SFC...R/S LINE WILL BE
MARCHING NWD INTO OUR CWA THIS AFTRN. HOWEVER...DYNAMIC COOLING FROM
STG UVVS ALONG WITH HELP FROM EVAPORATIVE COOLING FROM PCPN FALLING
INTO DRY AIR MASS WILL BE FIGHTING OFF THAT NWD MOVE.

SPECIAL 06Z SOUNDING FOR IAD CAME IN JUST A TINY BIT COLDER THAN THE
00Z ETA FCST. SOUNDING SHOWS COLD AIR IS ENTRENCHED AND AIR MASS IS
VERY DRY(WHICH WILL AID IN EVAPORATIVE COOLING LATER).

ETA BUFKIT SOUNDINGS SUGGESTS PCPN WILL REMAIN ALL SNOW NW AREAS. IN
ADDTN...NGM AND AVN THERMAL STRUCTURES SUPPORT THIS SO WILL BE
REMOVING THE MENTION OF ZR/PL FM THE NW ZNS. FURTHER E...THINGS ARE
NOT AS SIMPLE.  THE ETA BUFKIT PCPN ALGORITHM FCSTS ABOUT 4 HRS OF
SNOW AT DCA AND BAL FOLLOWED BY A CHANGEOVER TO RA THEN BACK TO SN
AS IT ENDS AS COLDER AIR IS WRAPPED INTO THE AREA BHD THE DVLPG LOW.
HOWEVER...IF YOU LOOK AT THE FCST SOUNDING...THE SOUNDING IS
ISOTHERMAL WITH THE TEMP LINE BARELY MOVING ACRS 0C 850MB-825MB FOR
A BRIEF TIME. ONE NCEP PCPN ALGORITHM SUGGESTS NO CHANGEOVER AT DCA
AND BAL WHILE OTHER VARIOUS ALGORITHMS SUGGESTS SOME MIXING OR A
CHANGEOVER. BOTTOM LINE...THIS IS TOO CLOSE TO CALL FOR THE TWO
MAJOR CITIES AND WHEN AND IF IT CHANGES OVER WILL GREATLY AFFECT
ACCUMS. FURTHER W...THE ETA BUFKIT SOUNDING FOR IAD IS
ISOTHERMAL....BARELY STAYING BELOW 0C.  JUST A LOOK AT THE SOUNDING
WOULD SUGGEST SNOW BUT ODDLY ENOUGH...THE PCPN ALGORITHM SUGGESTS IT
WOULD CHANGEOVER TO PL/ZR AT IAD.

GIVEN THAT THERE IS NO COLD SFC HIGH TO MAINTAIN THE TRANSPORT OF
COLD AIR...WILL CONTINUE WITH THE CURRENT FCST OF MIXING WITH RA
FROM DC AND BAL EWD. HOWEVER...I DO SUSPECT THAT THE MIXING IN THE
CITIES WILL OCCUR AFTER 4 OR 5 HRS OF SN...SOME OF WHICH COULD BE
HEAVY. FURTHER W...BETWEEN THE BLUE RIDGE AND THE CITIES...WILL SAY
SN...POSSIBLY BECOMING MIXED WITH ZR/PL.

OVR MY FAR SE ZNS...THERMAL STRUCTURE SUGGESTS PCPN BEGINNING AS SN
BUT CHANGING OVR TO RA AFTER A COUPLE OF HRS OF SN.

WILL BE LEAVING THE ADVYS AND WARNINGS AS IS FOR NOW. WILL BE
TWEAKING THE WORDING OF THE ZNS A BIT HERE AND THERE. AFTER
COORDINATION WITH NCEP AND LOOKING AT THE MODEL QPFS...WILL BE
BACKING OFF TO 4 TO 8 INCHES NW ZNS.

WHERE MIXING OR A CHANGEOVER DOES OCCUR...IT COULD CHANGE BACK TO
LGT SN BFR ENDING AS CAA OCCURS ON THE BACKSIDE OF THE STORM.
HOWEVER...WILL NOT WORRY ABOUT THIS AT THIS JUNCTURE. DAY SHIFT CAN
TAKE A LOOK AT THAT POSSIBILITY.

THANKFULLY...SUNDAY LOOKS LIKE A NICE QUIET..TRANQUIL PLEASANT DAY.

NO SIGNIFICANT CHANGES TO THE EXTENDED. WEAK FNT OR TROF COMING THRU
MON. COULD SEE A SHRA OR TWO BUT WILL LEAVE IT DRY FOR NOW AND LET
DAY SHIFT RE-EVALUATE. THEN OTHER FNT THU.

FCSTID = 15 / WALSTON

.LWX...
DC...WINTER STORM WARNING TODAY FOR DCZ001.

MD...WINTER STORM WARNING TODAY MDZ002>003.
     WINTER STORM WARNING TODAY MDZ004>006-MDZ009>010.
     WINTER STORM WARNING TODAY MDZ007-MDZ011-MDZ013>014.
     WINTER WEATHER ADVISORY TODAY MDZ016>018.

VA...WINTER STORM WARNING TODAY VAZ027>031.
     WINTER STORM WARNING TODAY VAZ021-VAZ025>026-VAZ036>039-VAZ050.
     WINTER STORM WARNING TODAY VAZ040>042-VAZ051>053.
     WINTER STORM WARNING TODAY VAZ054>056.
     WINTER WEATHER ADVISORY TODAY VAZ057.

WV...WINTER STORM WARNING TODAY WVZ048>053...WVZ055.
     WINTER STORM WARNING TODAY WVZ054.