FXUS61 KCTP 072041
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
341 PM EST MON DEC 7 2009
.SYNOPSIS...
A WEAK LOW PRESSURE SYSTEM WILL MOVE THROUGH THE EASTERN GREAT
LAKES REGION AND DOWN THE SAINT LAWRENCE RIVER VALLEY BY TONIGHT.
A MOISTURE-STARVED COLD FRONT TRAILING SOUTH FROM THE LOW WILL
SWEEP ACROSS THE REGION AND WILL BRING SOME SCATTERED SNOW SHOWERS
TO THE ALLEGHENIES LATE TODAY AND TONIGHT. HIGH PRESSURE WILL
RETURN FOR TUESDAY BRINGING LIGHT WIND AND CHILLY TEMPERATURES
BEFORE A SIGNIFICANT STORM SYSTEM LIFTS NORTHEASTWARD FROM THE
SOUTHERN PLAINS AND BRINGS A PERIOD OF SNOW FOLLOWED BY A WINTRY
MIX OF PRECIPITATION TUESDAY NIGHT INTO WEDNESDAY. MUCH COLDER AIR
WITH A GUSTY WEST WIND WILL FOLLOW FOR THE LATTER PART OF THE
WEEK.
&&
.NEAR TERM /THROUGH TUESDAY/...
INTERMITTENT LIGHT SNOW AND FLURRIES WILL OCCUR ACROSS MAINLY THE
WESTERN AND NRN MTNS OF PENN LATE TODAY AND TONIGHT AS A WEAK COLD
FRONT PUSHES EAST ACROSS THE REGION .
REGIONAL RADARS SHOWING THE ECHO BASES DOWN TO ABOUT 3 KFT AGL
ACROSS THE HIGHER TERRAIN OF WRN AND NRN PENN. SFC OBS ACROSS FAR
NWRN PENN AND NERN OHIO SHOW SOME VERY LIGHT SNOW FALLING IN AN
AREA OF WEAK ISENT LIFT AT THE NOSE OF A 40-45 KT SWRLY 850 MB
JET.
LLVL FLOW VEERING TO THE WEST WILL BRING LITTLE MORE THAN SOME
LIGHT SNOW SHOWERS ACROSS THE ALLEGHENIES TONIGHT...WITH A SHALLOW
BROKEN/OVC STRATO CU LAYER (AND PERHAPS SOME SNIZZLE) FURTHER
EAST.
THE EXTENSIVE CLOUD COVER WILL HOLD MIN TEMPS NEAR...TO JUST A
FEW DEG BELOW NORMAL - RANGING THROUGH THE 20S.
AN AREA OF HIGH PRESSURE WILL SLIDE NE ACROSS PENN TUESDAY...
BRINGING LIGHT WINDS AND SOME FILTERED SUNSHINE THROUGH VARYING
AMOUNT OF MID/HIGH CLOUDS. MAX TEMPS TUESDAY WILL BE 2-5F BELOW
NORMAL THANKS TO THE RATHER EXTENSIVE...ALBEIT SHALLOW SNOW COVER.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/...
WINTER STORM WATCH HAS BEEN POSTED FROM TUE EVE THRU MIDDAY WED.
CHALLENGING WINTER STORM CONTINUES TO DEVELOP...WITH A HIGH
CONFIDENCE BEST FORCING WILL PAST WELL TO OUR NW ACROSS NORTHCENTRAL
IN/SE LOWER MI LATE TUE. SFC RIDGE SLIDES WEAKENS MARGINALLY AND
SLIDES NE TOWARDS CANADIAN MARITIME ARND 00Z WED. THIS APPEARS TO
AMPLIFY 285-295K ISENTROPIC LIFT AND 850MB U-WIND ANOMS TO -3 TO -4
STD DEV BY 06Z WED. THERMAL PROFILES SUPPORT ONSET OF MOISTURE
ACROSS OUR SW CWFA TO BE SN...THEN AS WARM AIR ADVECTION INTO
MID-LVLS EXPECT A TRANSITION OVER TO FZRA BY ARND MIDNIGHT TUE NGT.
ENSEMBLES HAVE MAINTAINED HIGHEST ICE ACCRETION PROBS ACROSS THE
LAUREL HIGHLANDS OVERNIGHT TUE/EARLY WED PSBLY EXCEEDING A COUPLE
TENTHS OF AN INCH BEFORE CHANGING TO RA. FURTHER N/NE ICE
ACCRETION WILL BE LOWER AS PERIOD OF SN WILL PERSIST LONGER BEFORE
TURNING TO FZRA/SLEET/RA BEFORE 12Z WED. OVERNIGHT TEMPS WILL
GRADUALLY RISE FROM U20S TO L30S UNDER STRONG SOUTHERLY FLOW.
WARM AIR ADVECTION WILL CONTINUE WED AS A LLVL 850MB JET IS PROGGED
ARND 40-50KTS PUSHES TEMPS NEAR 40 DEG...WHICH WILL PUSH AN
REMAINING FZRA OVER TO RA ACROSS THE CWFA. CONFIDENCE REMAINS HIGH
THAT A DRY WEDGE LIFTS INTO CENTRAL PA MIDDAY WED...AND COULD CUTOFF
PRECIP FOR MUCH OF THE AFTN. 500MB TROUGH AXIS QUICKLY PIVOTS THRU
MIDDAY WED...HOWEVER IT DOESN/T APPEAR THERMAL RIDGE DEPARTS UNTIL
LATE WED. ISALLOBARIC SFC PRESSURE RISE COUPLET OF ARND 2MB/3-HR IS
PROGGED...WHICH MOST LIKELY WILL FEATURE GUSTY WINDS WED AFTN/EVE
AND STEADILY FALLING TEMPS. ATTM EXPECT UPSLOPE SN/LAKE EFFECT SN
NOT TO OCCUR UNTIL LATE WED...HOWEVER RESONANCE TIME OVER THE LAKES
WILL BE MINIMIZED AT ONSET PROVIDING A CELLULAR LOOK TO PRECIP FOR
NW MTNS.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
HIGH CONFIDENCE REMAINS FRONTAL BNDRY WILL DEPART THE REGION BY WED
EVE...WITH VERY INTENSE W/NWSTRLY FLOW PUSHING INTO THE MID-ATLANTIC
REGION THUR/FRI/SAT. FOR SEVERAL DAYS ENSEMBLES GUIDANCE HAS BEEN
POINTING AT 850MB WINDS OF 40-50KTS...UNDER A VERY AGGRESSIVE UPR
LVL JET OF 140-160KTS. THE AFOREMENTIONED ELEMENTS ARE GOING TO
BLEND WITH 850MB TEMPS PROGGED AT -14 TO -16 DEG C THUR/FRI AND
GENERATE COOL AND BLUSTERY CONDS. ATTM FEEL GIVEN CONSID CLOUD COVER
DURING DAYLIGHT HOURS TEMPS WILL HOLD IN THE 20S/30S FOR THE END OF
THE WEEK...HOWEVER IF SKIES CAN CLEAR TEMPS WILL EASILY COOL
OVERNIGHT.
SFC RIDGE IS PRESENTLY ADVERTISED BY ENSEMBLES FOR SAT/SUN...HOWEVER
CONFIDENCE IS LOW ATTM AS IT IS POSSIBLE RIDGE WILL BREAK DOWN
QUICKLY UNDER A PROGRESSIVE W-E FLOW AS A WEEKEND SHORTWAVE TRIES TO
DEVELOP ACROSS THE GULF OF MEXICO STATES. TEMPS REMAIN COOL THRU THE
UPCOMING WEEKEND.
&&
.AVIATION /21Z MONDAY THROUGH SATURDAY/...
VFR CIGS (BASES MAINLY BETWEEN 4-6 KFT AGL) WITH SOUTH TO SW WINDS
OF 4-8 KTS WILL PREVAIL THROUGH LATE THIS AFTERNOON AS A MOISTURE
STARVED WEATHER SYSTEM TRACKS EASTWARD FROM THE OHIO VALLEY.
ASSOCIATED WK SFC LOW LIFTING NEWD ACROSS THE GRT LKS AND UP THE
ST LAWRENCE VLY WILL PUSH A COLD/OCCLD FNTL SYS THRU THE REGION BY
TONIGHT.
CIGS WILL GRADUALLY LOWER LATE TODAY/EARLY TONIGHT TO MAINLY MVFR
ACROSS THE CENTRAL AND NW MTNS...WITH PERIODS OF IFR CIGS AND MVFR
VSBYS IN VERY LIGHT SNOW OR SNOW SHOWERS INVOF KBFD AND KJST
THROUGH ABOUT 12-13Z TUESDAY.
CONFIDENCE IS FAIRLY HIGH WITH RESPECT TO THE LOW CIG
RESTRICTIONS ACROSS THE ALLEGHENIES...ESP POST FROPA AS LLVL FLOW
BECOMES ALIGNED WITH THE LAKE AND ASCENDS THE HIGHER TERRAIN.
UNV/AOO/IPT SHUD STAY MVFR OR BETTER WHILE MDT WILL REMAIN VFR.
LOW CLOUDS (IFR TO MVFR) LKLY TO HANG TOUGH IN THE WEST THROUGH
THE MID MORNING HOURS. MAINLY VFR CIGS WITH PATCHY 5-6SM IN HAZE
EXPECTED FOR THE REMAINDER OF TUESDAY AS 1026-1028 MB SFC HIGH
SLIDES NE ACROSS THE STATE.
A SIGNIFICANT STORM SYSTEM IS FCST TO MOVE NE FROM THE SOUTHERN
PLAINS TUESDAY...AND THROUGH THE GRT LKS WEDNESDAY. STRONG
MOISTURE SURGE ALL THE WAY FROM THE GULF COAST REGION WILL OVERRUN
THE COLD AIR TRAPPED IN THE LOW/MID LVLS TO BRING A PERIOD OF
SNOW EARLY TUESDAY NIGHT...CHANGING TO A MIXED BAG OF WINTRY PCPN
DURING THE OVERNIGHT HOURS. THIS WILL CREATE WIDESPREAD IFR CIGS
AND VSBYS WITH A FEW PERIODS OF VLIFR CIGS AND VSBYS.
THE STRONG SE TO SOUTH WIND (40-50 KTS AROUND 2 KFT AGL) LATE TUE
NIGHT THROUGH WED MORNING WILL RESULT IN LLWS. AFTER A SEVERAL
HOUR LULL IN THE WIND WED AFTERNOON...A STRONG COLD FRONT WILL
PUSH EAST ACROSS THE COMMONWEALTH LATE WED/WED NIGHT FOLLOWED BY
AN INCREASING WESTERLY WIND OF 20-25 KT SUSTAINED...WITH GUSTS OF
35 TO 40 KTS POSSIBLE. THE MEAN...WESTERLY FLOW IN THE WAKE OF
THIS WILL LIKELY KEEP REDUCED CIGS AND VSBYS ACROSS THE WESTERN
AND NRN HIGH TERRAIN ALONG WITH SOME LAKE EFFECT SNOW SHOWERS.
OUTLOOK...
TUE...MVFR/IFR ACROSS THE NORTH AND WEST EARLY...BCMG MAINLY VFR
IN THE AFTERNOON. MVFR OVER MUCH OF THE CENTRAL AND EAST BCMG VFR
AFTER 13Z.
TUE NGT/WED...BCMG WDSPRD IFR IN SNOW/ICE. LLWS. AREAS OF VLIFR
CIGS AND VSBYS IN PERIODS OF +SN
WEDNGT/THUR...MVFR/IFR NORTH AND WEST IN SNOW SHOWERS. IMPRVG
CENTRAL/EAST. STRONG WESTERLY WNDS.
FRI/FRI NIGHT...MVFR WEST WITH SCATTERED SNOW SHOWERS. VFR EAST.
SAT...VFR...DECREASING TO IFR/MVFR LATE IN THE DAY/AT NIGHT IN SNOW
OR MIXED PRECIPITATION.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY
MORNING FOR PAZ004>006-010>012-017>019-024>028-033>036-045-056-
063-064.
&&
$$
SYNOPSIS...LAMBERT
NEAR TERM...LAMBERT
SHORT TERM...BEACHLER
LONG TERM...BEACHLER
AVIATION...LAMBERT
