HAMweather.com Area Forecast Discussion for County Warning Area CTP

Thu, 16 Feb 2012 07:38:22 GMT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
155 AM EST THU FEB 16 2012

.SYNOPSIS...
A FRONTAL SYSTEM MOVING FROM THE OHIO VALLEY THROUGH PENNSYLVANIA
WILL BRING WIDESPREAD LIGHT PRECIPITATION TO THE REGION TODAY. THE
LIGHT PRECIPITATION WILL START AS A WINTRY MIX IN SOME LOCATIONS
BEFORE TRANSITIONING TO RAIN BY THE LATE MORNING AND EARLY
AFTERNOON. HIGH PRESSURE WILL RETURN ON FRIDAY AND PROVIDE A DRY
START TO THE WEEKEND.

.NEAR TERM /UNTIL 8 AM THIS MORNING/...
REGIONAL RADAR SHOWS WARM ADV PCPN PUSHING EWD THRU THE UPPER OH
VLY AND APPROACHING NW PA AS OF 06Z. RUC SFC-850MB THERMAL
PROFILES INDICATE A MARGINALLY WARM +1-2C LAYER AT 925MB. P TYPES
COULD GO EITHER WAY DEPENDING ON PCPN RATES/WET BULB EFFECTS AND SUB-
FZG SFC TEMPS. THEREFORE WILL MENTION A MIXED BAG OF WINTRY PCPN
BEFORE SUNRISE MAINLY OVER THE N-CNTRL MTNS. WILL CONTINUE TO
MONITOR FOR POSSIBLE FZRA ADVY.

.SHORT TERM /8 AM THIS MORNING THROUGH 6 PM FRIDAY/...
A NRN STREAM TROF CROSSING THE UPPER GREAT LAKES SHOULD GRADUALLY
PHASE WITH THE LEAD WAVE IN THE SRN STREAM AS THEY ENTER THE NERN
QUAD OF THE COUNTRY ON THURS...RESULTING IN A PAIR OF WEAK SFC
LOWS INVOF THE GREAT LKS SLOWLY DEEPENING AND CONSOLIDATING INTO
ONE PRIMARY LOW CENTER IN SERN CANADA BY THURS NGT.
MEANWHILE...HEIGHT FALLS SPREADING ACRS THE MID-ATLANTIC REGION
SHOULD INDUCE A SECONDARY LOW NEAR THE CAROLINA COAST ALONG THE
ATTENDANT COLD FRONT TRAILING SWD FROM THE PRIMARY LOW. A SURGE OF
ABOVE NORMAL PWATS AND FAVORABLE JET DYNAMICS WILL ACCOMPANY THIS
SYSTEM AND SUPPORT WIDESPREAD PRECIPITATION ACRS CENTRAL PA THIS
PERIOD.

THE MAIN CONCERN AND GREATEST UNCERTAINTY IN THE SHORT TERM FCST
INVOLVES TRANSITIONING P TYPES...AS RELATIVELY WARM AIR ALOFT
/ABOVE 0C AIR AT 850MB/ IS COOLED FROM THE TOP DOWN DUE TO WET-
BULB EFFECTS AND LLVL MESOSCALE COLD AIR DAMMING PROCESSES KEEP
SFC TEMPS NEAR THE FREEZING MARK. FCST MODEL SOUNDINGS AND PLUME
DIAGRAMS STILL INDICATE THE POTENTIAL FOR A MIXED BAG OF WINTRY
PRECIP BEFORE GOING OVER TO MAINLY RAIN LATER THURS. DESPITE THE
P TYPE UNCERTAINTY...MARGINAL BLYR TEMPS AND TIME OF DAY WILL BE
LIMITING FACTORS FOR SNOW/ICE ACCUMULATIONS.

A SURGE OF COLDER AIR WILL INVADE THE REGION IN THE WAKE OF THE
COLD FROPA LATER THURS NIGHT INTO EARLY FRI...WITH PLENTY OF POST-
FRONTAL LOW CLOUDS/STRATOCU AND OCNL LAKE EFFECT/UPSLOPE SNOW
SHOWERS FOCUSED OVR THE HIGHER TERRAIN OF THE WESTERN ALLEGHENIES.

MAIN CHANGE FROM RECENT DAYS WILL BE THE AMT OF COLD AIR THAT
FOLLOWS THE MAIN SYSTEM LATE THU...WILL ADDITIONAL SYSTEMS
PULL IN A LOT OF COLD AIR AFTER THU...SEE SECTION BELOW.

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
WAVE EXITING TO THE EAST THU NIGHT WILL CHANGE LINGERING SHOWERS
OVER TO SNOW SHOWERS BEFORE ENDING AS MEAN FLOW AGAIN BECOMES
ZONAL. COLDER AIR...SEASONAL AIR...FILTERS IN BEHIND FOR
FRI AS HIGH PRESSURE SLIDES IN...WITH HIGHS ABOUT 10F LOWER THAN
THU - PUTTING THEM CLOSE TO NORMALS.

A RATHER FLAT...NRN STREAM SHORT WAVE SLIDES BY JUST TO THE NORTH
ON SATURDAY AND MAY TRIGGER A FEW RAIN OR WET SNOW SHOWERS OVR THE
NRN MTNS. THIS FEATURE WILL SHOULD PUSH A SECONDARY COLD FRONT
SEWD ACROSS THE COMMONWEALTH...ALLOWING A REINFORCING/SLIGHTLY
COLDER AIR MASS TO SPREAD INTO THE AREA FOR THE SECOND HALF OF THE
WEEKEND INTO EARLY NEXT WEEK. 

LOTS OF DIVERGENCE IN MODEL SOLUTIONS ON SUNDAY...WITH GFS MOST
INTERESTINGLY PRODUCING THE MOST PHASING WITH NORTHERN STREAM
ALONG WITH A DEEPENING LOW OFF THE MID ATLANTIC COAST. OTHER
MODELS AREN/T AS AGGRESSIVE...SHUNTING THE LOW FURTHER SOUTH AND
EAST AS RIDGE OF HIGH PRESSURE EDGES IN FROM THE NW. DID ADJUST
POPS UPWARD 10-20 PERCENT FOR SAT NIGHT/SUNDAY THOUGH...AND WILL
BE INTERESTING TO SEE IF ANY OTHER MODELS ADOPT THE GFS SOLUTION. 

RIDGE DOES BECOME THE DOMINANT FEATURE MON INTO TUE WITH COOL
MORNING AND MODERATING MAXES...AS RETURN FLOW KICKS IN ON TUE.
ANOTHER SYSTEM PROGGED FOR WED WITH A MIX OF RAIN/SNOW AS TEMPS
REMAIN ABOVE NORMAL.

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
LOW PRESSURE WILL TRACK EAST ACROSS THE OHIO VALLEY THIS
MORNING...SPREADING LOWERING CLOUDS ACROSS CENTRAL PA. LEADING
EDGE OF SPOTTY...LIGHT PRECIP JUST ENTERING WESTERN PA AT 06Z AND
SHOULD REACH MUCH OF CENTRAL PA BTWN 08Z-12Z. TEMPS WILL LIKELY BE
JUST COLD ENOUGH TO SUPPORT A LIGHT WINTRY MIX ACROSS THE NORTHERN
HALF OF THE STATE WITH THIS FIRST BATCH OF PRECIP...WHILE -SHRA
MOST LIKELY ACROSS THE SOUTH. A DRY LAYER IN THE ATMOSPHERE BLW
3KM /AS EVIDENCED BY 00Z PIT SOUNDING/ WILL LIKELY KEEP CIGS/VSBYS
IN THE VFR RANGE THRU AT LEAST DAWN.

AS LOW PRESSURE APPROACHES...DETERIORATING CIGS/VSBYS EXPECTED
DURING THE DAYLIGHT HOURS. ANY EARLY AM WINTRY MIX OVR NORTHERN PA
SHOULD TURN TO -RA BY MIDDAY...BUT WIDESPREAD IFR CONDS APPEAR
LIKELY BY AFTN OVR THE CENTRAL AND WESTERN MTNS AS STEADIER RAIN
ARRIVES. MARGINALLY HIGHER CIGS/VSBYS ARE POSSIBLE ACROSS THE
LOWER ELEVATIONS OF THE SUSQ VALLEY INCLUDING IPT/MDT/LNS.

RAIN WILL TAPER OFF THIS EVENING. HOWEVER...RESIDUAL LOW LVL
MOISTURE AND A LGT WIND WILL LIKELY RESULT IN AREAS OF FOG. A
DRIER WESTERLY FLOW WILL DEVELOP LATE TONIGHT...AS THE LOW PRES
SYS PASSES EAST OF PA. THIS WILL BRING A RETURN TO VFR CONDS EAST
OF THE MTNS. HOWEVER...UPSLOPING FLOW COULD PRODUCE LINGERING MVFR
CIGS AT BFD/JST. 

OUTLOOK...
FRI...AM LOW CIGS POSS W MTNS. 
SAT...NO SIG WX EXPECTED.
SUN...SNOW/LOW VSBYS POSSIBLE SOUTHERN PA.
MON...NO SIG WX EXPECTED.

.CTP WATCHES/WARNINGS/ADVISORIES...
NONE.