Frost Advisory 5, NWS State College, PA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
328 PM EDT SUN MAY 18 2008

.SYNOPSIS...
A DEEP UPPER LEVEL LOW OVER EASTERN CANADA AND THE NORTHEAST U.S.
WILL KEEP IT COOL AND UNSETTLED THROUGH MID WEEK. SHOWERS AND
ISOLATED THUNDERSTORMS WILL DISSIPATE THIS EVENING...BUT SOME
MIXED RAIN AND SNOW SHOWERS ARE EXPECTED TONIGHT ACROSS THE NORTHWEST.
MONDAY WILL BE QUITE CHILLY FOR MID MAY...AND SOME SNOW SHOWERS
AND FLURRIES WILL PERSIST INTO MID MORNING ACROSS THE NORTHWEST.
PARTLY TO MOSTLY SUNNY AND COOL CONDITIONS WILL PREVAIL ELSEWHERE.
ANOTHER STORM SYSTEM WILL PASS SOUTH OF THE REGION ON TUESDAY
BRINGING A CHANCE OF SHOWERS. TEMPERATURES SHOULD MODERATE TOWARD
NORMAL THURSDAY AND FRIDAY AS THE DEEP TROUGH FINALLY SLIDES TO
OUR EAST.

&&

.NEAR TERM /UNTIL 11 PM THIS EVENING/...
WATCHING SHOWERS CONTINUE TO PROPAGATE THROUGH NORTHWEST PA ON AN
EARLIER LAKE BREEZE BOUNDARY...CONTINUING TO PRODUCE SOME
LIGHTNING AND REPORTS OF PEA SIZED HAIL THANKS TO THE STEEP LAPSE
RATES AND WET BULB ZEROES BETWEEN 5-6K FEET. THIS ACTIVITY WILL
WANE BY MID EVENING AS THE HEATING IS LOST...BUT EXPECT FAVORABLE
FLOW OFF OF LAKE ERIE TO KEEP SHOWERS GOING NEAR THE LAKES WITH A
CHANGEOVER OR MIX TO SNOW AT KBFD LIKELY AFTER 00Z TONIGHT. CANNOT
RULE OUT A SHOWER OR THUNDERSTORM JUST ABOUT ANYWHERE LATE THIS
AFTERNOON OR EARLY EVENING GIVEN THE MAGNITUDE OF COLD AIR
SPILLING OVERHEAD...AND ANY CELL COULD PRODUCE PEA SIZED HAIL.

&&

.SHORT TERM /11 PM THIS EVENING THROUGH 6 PM MONDAY/...
A COLD SEASON LAKE EFFECT REGIME WILL CONTINUE INTO MONDAY MORNING WITH
SNOW OR RAIN AND SNOW SHOWERS EXPECTED DOWNWIND OF LAKE ERIE INTO
NORTHWEST AND NORTH CENTRAL PA. THE FLOW WILL VEER TO THE WEST BY
AFTERNOON WITH A DECREASING TREND IN SHOWER ACTIVITY BY THAT TIME.

PREVIOUS SHIFT INTRODUCED THE MENTION SOME SNOW IN THE NORTHERN
MOUNTAINS...AND THINK THIS IS STILL LOOKING REASONABLE DESPITE THE CALENDAR...
IT COULD EVEN BRIEFLY ACCUMULATE ON THE COLDER/GRASSY SURFACES
AGAIN DURING MONDAY MORNING IN THE NW. TEMPS ON MONDAY WILL BE
QUITE COOL WITH HIGHS ONLY IN THE 40S IN THE NORTH...TO NEAR 60
IN THE SE WHERE DOWNSLOPE AND MORE SUNSHINE WILL GIVE A BOOST. NW
WINDS WILL BE GUSTY AT TIMES ON MONDAY.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
MONDAY NIGHT LOOKS MAINLY DRY...BUT ANOTHER STORM SHOULD MOVE
SOUTH OF THE AREA BY EARLY TUES MORNING CLIPPING US WITH SHOWERS.
TIMING OF THESE SHORTWAVES IS PROBLEMATIC GIVEN THE STRENGTH OF
THE UPPER LEVEL JET IN BETWEEN THE EASTERN CANADA LOW AND
PERSISTENT AND HIGHLY AMPLIFIED RIDGE OVER THE CENTRAL UNITED
STATES. TUESDAY ALSO LOOKS JUST A LITTLE BIT MILDER THAN
MONDAY BUT STILL 15 DEGS COOLER THAN NORMAL FOR THIS TIME OF THE
YEAR. HIGHS WILL BE MAINLY IN THE 50S/L60S.

MODELS HAVE CONTINUED THE TREND OF DELAYING UPPER LEVEL RIDGING
FOR THE EASTERN U.S. UNTIL LATE NEXT WEEKEND. THUS...ANOMALOUSLY
DEEP UPPER LOW IS MOST LIKELY GOING TO STAY PARKED OVER EASTERN
CANADA AND NEW ENGLAND FOR THE BULK OF THE FORECAST PERIOD.

A HOPE FOR IMPROVEMENT IN TEMPS AND LESS RAIN WILL COME MAINLY
FROM A MODIFICATION OF OUR CURRENT AIRMASS AND LESS DIRECT
INTRUSIONS OF COLD AIR FROM CENT/NRN CANADA. THIS WOULD HELP OUR
TEMPS MODERATE...AND A PERSISTENT NW FLOW WOULD BE A MORE-DRY
FLOW PATTERN THAN THE FLOW WE ARE IN NOW...WHICH KEEPS
TRANSPORTING SHOTS OF MOISTURE FROM THE GOMEX EVERY 24-36 HRS. THE
LONG RANGE GUIDANCE IS POINTING TOWARD AN AMPLIFICATION OF THE
CURRENT FLOW -- WITH THE UPPER LOW OPENING UP TO A LONGWAVE TROF
OVER THE WESTERN ATLANTIC AND A RIDGE OVER CENTRAL NOAM. THE
NORTHERLY FLOW ALOFT WOULD HELP USHER A SFC HIGH DOWN FROM CENTRAL
CANADA INTO THE GREAT LAKES AT THE END OF THE WEEK. THIS - AGAIN -
SHOULD BE TAKEN WITH A GRAIN OF SALT. BUT IT IS ENOUGH TO KEEP THE
LATTER HALF OF THE FORECAST PERIOD /THURSDAY -SUNDAY/ DRY AT THIS
POINT.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
LOW TOPPED CONVECTION QUICKLY BECOMING THE MAIN AVIATION THREAT
THIS AFTERNOON WITH SCATTERED SHOWERS...ISOLATED THUNDER AND
REPORTS OF PEA SIZED HAIL AND GUSTY WINDS OVER NORTHWEST PA AS THE
COLD UPPER LOW DRIFTS OVER THE EASTERN LAKES. ACCOMPANYING THESE
SHOWERS ARE MVFR TO LCL IFR CIGS AND MVFR VSBYS...ALONG WITH SFC
WIND GUSTS TO 35-40KTS THROUGH 00Z MON. CONVECTIVE ACTIVITY SHOULD
DECREASE OVER ALL BUT AREAS DOWNWIND OF LAKE ERIE WHERE SHOWERS
WILL MIX WITH AND CHANGE TO SNOW SHOWERS AFTER DARK TONIGHT...
AND CONTINUE INTO MONDAY MORNING.

LAKE EFFECT ACTIVITY WILL WANE BY MIDDAY MONDAY...WITH A QUIET
STRETCH IN STORE MONDAY NIGHT INTO EARLY TUESDAY ACCOMPANIED BY
VFR CONDS. A WEAK SFC LOW DIVES SOUTH OF THE REGION ON TUESDAY
BRINGING A CHANCE OF SHOWERS TO ESPECIALLY CENTRAL AND SOUTHERN
ROUTES. WEAK SFC RIDGE TRIES TO POKE INTO SOUTHERN GRT LKS WED...BUT
MAY STAY WEST OF MID- ATLANTIC REGION ENUF TO KEEP WEAK NW FLOW
FOR CENTRAL PA INTO WED/THUR.

&&

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

&&

SYNOPSIS...DEVOIR
NEAR TERM...DEVOIR
SHORT TERM...DEVOIR
LONG TERM...DANGELO/GARTNER
AVIATION...DEVOIR