Snow Advisory 5, NWS Pittsburgh, PA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
345 PM EST WED FEB 21 2007

.SHORT TERM /TONIGHT THROUGH THURSDAY/...
LOW CLOUDS AND FOG HAVE FINALLY CLEARED OUT OVER ALL BUT OUR
SOUTHERNMOST EAST CENTRAL OHIO ZONES THIS AFTERNOON. TONIGHT SHOULD
REMAIN MAINLY DRY. ONLY CONCERN IS IMPACT OF MILDER TEMPERATURES
ON STREAM LEVELS DUE TO SNOW MELT AND ICE JAMMING AND MOVEMENTS. NEXT
LOW PRESSURE SYSTEM WILL TRACK SOUTHEAST ACROSS THE GREAT LAKES
LATE TONIGHT AND THURSDAY AND BRING A CHANCE OF RAIN AND SNOW
SHOWERS TO THE UPPER OHIO VALLEY REGION DURING THURSDAY.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
GFS AND ECMWF MODEL CONTINUE TO SHOW A MORE ZONAL UPPER LEVEL JET
STREAM FLOW INTO NEXT WEEK, WHICH MEANS GENERALLY A TREND TOWARD
MILDER TEMPERATURES THIS PERIOD. HOWEVER, AT THE START, THERE WILL
BE AN INFLUX OF COLDER AIR WITH THE PASSAGE OF THE CLIPPER-TYPE LOW
PRESSURE SYSTEM THROUGH THE GREAT LAKES THURSDAY AND THURSDAY NIGHT.
THIS WILL ALSO RESULT IN SOME SNOW SHOWERS BUT LITTLE SNOW
ACCUMULATION IS EXPECTED DUE TO THE SHALLOWNESS OF THE ASSOCIATED
UNSTABLE BOUNDARY LAYER. POSTFRONTAL WINDS WILL BECOME BRISK WITH
GUSTS INTO THE 30 MPH RANGE. HIGHS FRIDAY AND SATURDAY WILL BE NO
HIGHER THAN THE 30S.

GFS AND ECMWF MODEL RUNS CONTINUE TO SHOW A DEVELOPING LOW PRESSURE
SYSTEM MOVING NORTHWARD THROUGH THE MISSISSIPPI VALLEY THIS WEEKEND.
THIS WILL DRIVE AN OCCLUDING FRONT THROUGH THE UPPER OHIO VALLEY.
WITH GOOD GULF MOISTURE INFLUX AHEAD OF THIS FRONTAL LIFT,
PRECIPITATION AMOUNTS HAVE THE POTENTIAL TO REACH 0.50 TO 1.00
INCHES IN A 12H PERIOD. WITH SNOWMELT YIELDING 1-2 INCHES OF WATER
EQUIVALENT, THIS SITUATION WILL HAVE TO BE MONITORED FOR ITS IMPACT
ON AREA STREAMS AND RIVERS. THE OTHER CONCERN IS THE INITIAL
PRECIPITATION TYPE EARLY SUNDAY, AS TEMPERATURES CAN BE SUBFREEZING
AT LOWLEVELS. SO A MIX WAS MENTIONED.

MUCH OF NEXT WEEK WILL HAVE TEMPERATURES NEAR NORMAL AND
PRECIPITATION AMOUNTS SHOULD BE LIGHT, WHICH IS TYPICAL FOR A ZONAL
JET STREAM PATTERN.

&&

.AVIATION /21Z-18Z/...
LARGE AREA OF LOW STRATUS AND FOG CONTINUES TO ERODE SOUTHWARD. ONLY
TERMINAL STILL AFFECTED BY IFR CONDITIONS IS ZZV...AND EXPECT LOW
CLOUDS TO SCATTER OUT AT ZZV DURING NEXT HOUR OR TWO. VFR CONDITIONS
ARE FORECAST TO CONTINUE ACROSS THE REGION TONIGHT.

NEXT LOW PRESSURE SYSTEM WILL TRACK SOUTHEAST ACROSS THE GREAT LAKES
LATE TONIGHT AND THURSDAY. MID CLOUDS AHEAD OF SYSTEM SHOULD SLIDE
INTO THE UPPER OHIO VALLEY REGION TOWARD DAWN THURSDAY WITH CLOUD
BASES LOWERING TO AROUND 3000 FEET BY LATE MORNING. SCATTERED RAIN
AND SNOW SHOWERS WILL OCCASIONALLY REDUCE VISIBILITY TO MVFR MAINLY
DURING THE AFTERNOON THURSDAY. SURFACE WINDS WILL BECOME WEST WITH
GUSTS NEAR 25 KT AT TIMES.

&&

.MARINE...

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
OH...NONE.
PA...NONE.
WV...NONE.
&&

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