Heavy Snow in Pennsylvania, January 25 to 26, 2004

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE STATE COLLEGE PA
104 AM EST SUN JAN 25 2004

.UPDATE...
WIND CHILL READINGS RUNNING AROUND -15F OVER THE NORTHERN MOUNTAINS
THIS EVENING. AS HIGH PRES BUILDS IN LATER TONIGHT WINDS WILL DIE
DOWN. HOWEVER...RADIATIONAL COOLING WILL ALLOW TEMPS TO BECOME
FRIGID WITH LOWS ALONG THE NY BORDER -10 TO -20 BY DAWN (LOCAL OBS
NETWORK ALREADY SHOWING A COUPLE -12F READINGS OVER NORTHERN MCKEAN
COUNTY). WILL RUN WIND CHILL ADVISORY THROUGH 9 AM OVER THE
MOUNTAINS NORTH OF I-80. FURTHER SOUTH...INCREASING HIGH CLOUDS
SHOULD KEEP TEMPS FROM FALLING MUCH MORE OVER THE LAURELS.

FITZGERALD
&&

.PREV DISCUSSION...

MAINLY CLEAR SKIES ACROSS PRACTICALLY ALL OF THE REGION THIS EVENING
WERE ALLOWING TEMPS TO DIVE TO VERY COLD LEVELS. THE ONLY NOTABLE
AREA OF CLOUDS WAS ALONG A WEAK LVLL CONVERGENCE ZONE OVER SOUTHWEST
PENN...WHICH WAS HELPING TO CHANNEL MOISTURE ALL THE WAY FROM LAKES
SUPERIOR AND HURON. VSBYS FROM LIGHT SNOW SHOWERS WITHIN THIS WEAK
LAKE EFFECT BAND ARE PROBABLY NO LOWER THAN 2 MILES OVER THE SKI
AREA OF WESTERN SOMERSET COUNTY. STILL A FLUFFY HALF INCH OR SO OF
SNOW IS POSSIBLE DURING THE NEXT FEW HOURS.

18Z ETA NOT ABLE TO RESOLVE THIS MESO-B FEATURE...BUT 00Z RUC40 LLVL
WIND FIELDS SHOW SOME VERY WEAK STREAMLINE CONVERGENCE IN THE SAME
REGION AS THIS BAND. BOTH MODELS VEER THE MEAN LLVL FLOW BY ABOUT
20 DEG BETWEEN NOW AND 06Z...WITH A BROADLY DIVERGENT FLOW
DEVELOPING OVER THE SW ZONES. SO...I WOULD EXPECT THE CLOUDS AND
LIGHT SNOW EITHER TO ADVECT SOUTHWEST OF THE CURRENT AREA...AND/OR
BEGIN TO DISSIPATE.

A SIGNIFICANT CURRENT TEMP/DEWPOINT SPREAD AND DIMINISHING WIND WILL
ALLOW THE MERCURY TO BOTTOM OUT CLOSE TO 10 BELOW IN THE TYPICALLY
COLD VALLEY OF THE NORTHERN MOUNTAINS...NEAR ZERO ACROSS MUCH OF
CENTRAL PENN...AND EVEN IN THE SINGLE THROUGHOUT THE CITIES AND
TOWNS OF THE LOWER SUSQ REGION.

SIMILAR ETA/GFS TIMING ON THE ONSET OF SNOW SUNDAY AFTERNOON ACROSS
THE SW...AND A FEW HOURS AFTER DARK SUNDAY EVENING ACROSS THE
EXTREME NORTH AND EAST PARTS OF OUR CWA. WE REALIZE FROM EXPERIENCE
THAT STRONG L/M LVL WARM ADVECTION CASES SUCH AS THIS TYPICALLY
BEGIN AT LEAST A FEW HOURS AHEAD OF SCHEDULE. THE LEADING EDGE OF
THE PRECIP SHIELD MOVING SLOWLY NORTHEAST TOWARD THE LOWER OHIO AND
TENNESSEE VALLEYS APPEARS TO MATCH UP BETTER WITH THE INITIALLY
SLOWER/DRIER 18Z ETA.

A BIG FLIP FLOP WITH RESPECT TO MODEL QPF...AND ULTIMATELY
SNOWFALL...FOR OUR ENTIRE REGION SUNDAY NIGHT INTO MONDAY. ETA/GFS
AGREE QUITE WELL ON 24 HR AMOUNTS OF ONLY NEAR 2 INCHES ALONG THE
PA/NY BORDER BY 18Z MONDAY...WITH ABOUT 4 TO 7 INCHES CLOSE TO I-80.
SNOW AMOUNT DIFFER GREATEST OVER THE LAUREL HIGHLANDS WHERE THE
ETAS STRONGER AND MORE PERSISTENT 850 HPA FRONTOGENETIC FORCING
CREATES A BULLSEYE OF NEARLY 1 FOOT OF SNOW. COMPETING FACTORS IN
THIS EVENT WILL BE THE MAXIMUM UVVEL VIA THE ETA LOCATED JUST BELOW
(IN ELEVATION) THE PRIME SNOW GROWTH THERMAL RIBBON...BUT LIKELY
GREATER SNOW/WATER EQUIVALENTS THAN ARE FACTORED INTO THE MODEL SNOW
TOTALS.

IM NOT TOO IMPRESSED WITH THE OVERALL UPPER PATTERN OF A SHEARING
WAVE...INTO THE SLIGHTLY AMPLIFYING RIDGE AXIS RIGHT OVER PENN BY
LATE SUNDAY NIGHT. WAS DOES LOOK IMPRESSIVE THOUGH (AND HAS LED TO
RATHER RARE CASES OF HEAVY SNOW HERE) IS THE STRONG LVLL PRESSURE
GRADIENT/LLVL JET FUNNELING MOISTURE QUICKLY UP AND OVER THE
STATIONARY BAROCLINIC ZONE ALONG THE OHIO RIVER VALLEY INTO SWRN
PENN.

EMPLOYED EXTENSIVE COORDINATION WITH SURROUNDING OFFICES...AND
CAME UP WITH TRIMMING BACK THE TIMING OF STEADY SNOW BY 3-4 HRS LATE
SUNDAY/SUNDAY EVENING. WILL KEEP THE CURRENT WINTER STORM WATCH
GOING FOR NOW AND FINE TUNE THE WORDING TO INDICATE THE HIGHEST
THREAT FOR HEAVY SNOW ACROSS OUR SW (LAUREL HIGHLAND ZONES)...AND
POSSIBLY ONLY ADVIS CRITERIA ALONG THE NRN TIER (ESP ADJACENT TO
KBGM WHERE ISENT LIFT/UVVEL SHOULD BY THE LEAST WITHOUT A
STRONG/STATIONARY LVLL BOUNDARY AS SHOULD EXIST ACROSS THE SW
ZONES).

WILL MAKE SOME MINOR ADJUSTMENTS TO CLOUD/TEMP GRIDS
OVERNIGHT...BUT PREVIOUS FCST LOOKS IN GOOD SHAPE FOR THE SHORT
TERM.

A SIGNIFICANT WINTER EVENT HEADED FOR CENTRAL PA.  WINTER STORM
WATCH NOW POSTED FOR ENTIRE CWA.

BUT FIRST...HIGH PRESSURE REIGNS TONIGHT AS CLOUDS THIN OUT AND
TEMPS DROP TO WELL BELOW NORMAL LOWS AIDED BY FRESH SNOWPACK.  WINDS
WILL KEEP WIND CHILLS IN THE ZERO TO -10F RANGE YET AGAIN BEFORE
DIMINISHING LATE.

TOMORROW...CLOUDS BEGIN TO STREAM IN AHEAD OF DEVELOPING SYSTEM IN
THE CENTRAL US AS MOIST MID LEVEL FLOW OVERRUNS THE COLDER HIGH
PRESSURE AREA.  PRECIP WILL ARRIVE BY MID AFTERNOON AND SNOWS WILL
BEGIN TO ACCUMULATE BY SUNSET ACROSS THE S AND W.  THIS WILL ALSO
ENHANCE LOW LEVEL AGEOSTROPHIC FLOW AND RESULT IN SOME COLD AIR
DAMMING WHICH WILL HELP TIGHTEN THE BAROCLINIC BOUNDARY.  EXPECT A
DECENT SWATH OF 6+ INCHES ACROSS THE S MOUNTAINS AND LOWER/MID SUSQ
VALLEY.  THE NORTH IS A BIT MORE TRICKY.  THEY ARE EXPECTED TO END
UP JUST SHY OF WARNING CRITERIA...BUT A DRIER SNOW COULD RESULT IN
HIGHER ACCUMULATIONS IN THIS AREA AS WELL...UNLESS TOO MUCH DRIER
AIR IN THE LOW LEVEL AIR IS DRAGGED IN FROM THE NORTH AND CREATES A
SHARP EDGE TO THE PRECIP.  WITH MAIN EVENT STILL IN THE THIRD PERIOD
OF THE FORECAST...WILL CONTINUE THE WATCH (NOW FOR EVERYONE) AT THIS
TIME.

FIRST LOW EXITS MON MORNING...THEN SECONDARY LOW REACHES CENTRAL PA
LATER MONDAY BRINGING ADDITIONAL SNOW SHOWERS ALONG WITH THE
POTENTIAL FOR SOME SLEET AND FREEZING RAIN MON AFT/EVE.

RXR

LONG TERM

DESPITE NEARLY ZONAL FLOW MID TO LATE WEEK...COLD AIR TO REMAIN
ENTRENCHED ACROSS MOST OF FORECAST AREA AS ADDITIONAL STORMINESS
AFFECTS PENNSYLVANIA BY LATE WEEK.  MORE TRADITIONAL LAKE EFFECT
REGIME WEDNESDAY WILL GIVE WAY TO OVERRUNNING AND ANOTHER POTENTIAL
WINTER STORM LATE THURSDAY AND FRIDAY.  APPEARS THAT ENOUGH WARM AIR
MAY MIX IN FOR A SIGNIFICANT PERIOD OF MIXED PRECIPITATION LATE THU
NIGHT OR EARLY THURSDAY...AND THEN WERE BACK INTO THE FREEZER TO
FINISH OFF JANUARY. STORMY PATTERN PROGGED TO CONTINUE INTO THE NEW
MONTH WITH GFS ADVERTISING MORE POTENTIAL COASTAL DEVELOPMENT BY
LATE NEXT WEEKEND AND THE BEGINNING OF NEXT WEEK.

DEVOIR
&&

.CTP WATCHES/WARNINGS/ADVISORIES...
PA...WIND CHILL ADVISORY NORTHERN MOUNTAINS THROUGH 9 AM.
&&

HAZARDOUS WEATHER OUTLOOK...CORRECTED FOR DATE
NATIONAL WEATHER SERVICE STATE COLLEGE PA
138 AM EST SUN JAN 25 2004

PAZ004>006-010>012-017>019-024>028-033>037-041-042-045-046-049>053-
056>059-063>066-241215-
ADAMS PA-BEDFORD PA-BLAIR PA-CAMBRIA PA-CAMERON PA-CLEARFIELD PA-
COLUMBIA PA-CUMBERLAND PA-DAUPHIN PA-ELK PA-FRANKLIN PA-FULTON PA-
HUNTINGDON PA-JUNIATA PA-LANCASTER PA-LEBANON PA-MCKEAN PA-
MIFFLIN PA-MONTOUR PA-NORTHERN CENTRE PA-NORTHERN CLINTON PA-
NORTHERN LYCOMING PA-NORTHUMBERLAND PA-PERRY PA-POTTER PA-
SCHUYLKILL PA-SNYDER PA-SOMERSET PA-SOUTHERN CENTRE PA-
SOUTHERN CLINTON PA-SOUTHERN LYCOMING PA-SULLIVAN PA-TIOGA PA-
UNION PA-WARREN PA-YORK PA-
138 AM EST SUN JAN 25 2004

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL PENNSYLVANIA.

.DAY ONE...TONIGHT:

DANGEROUS WIND CHILL READINGS OF 15 TO 20 BELOW WILL AFFECT THE
NORTHERN MOUNTAINS THROUGH 9 AM SUNDAY.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY:

A WINTER STORM WATCH IS IN EFFECT FOR MOST OF CENTRAL PENNSYLVANIA
SUNDAY AFTERNOON THROUGH MONDAY MORNING. SIGNIFICANT ACCUMULATIONS OF
SNOW AND THEN SOME ICE ARE POSSIBLE. SEE THE LATEST WINTER WEATHER
MESSAGE (WSWCTP WWUS41 KCTP) FOR DETAILS.

SPOTTER CALL TO ACTION STATEMENT...

SPOTTER ACTIVATION IS LIKELY SUNDAY AND MONDAY.