December 29, 2012 Forecast Discussion

000
FXUS61 KALY 262101
AFDALY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ALBANY NY
401 PM EST WED DEC 26 2012

.SYNOPSIS…
A SIGNIFICANT WINTER STORM WILL APPROACH FROM THE OHIO
VALLEY…AND THE MID ATLANTIC REGION TONIGHT…WITH A SECONDARY
COASTAL LOW BEING SOUTH OF LONG ISLAND TOMORROW MORNING…AND THEN
PASSING EAST OF CAPE COD TOMORROW AFTERNOON. THIS STORM WILL BRING
HEAVY SNOWFALL FROM THE CAPITAL REGION NORTH AND WEST…AND MIXED
PRECIPITATION TO THE SOUTH AND EAST. WEAK HIGH PRESSURE WILL BUILD
INTO THE NORTHEAST TO CLOSE WEEK WITH SEASONABLY COLD WEATHER FOR
LATE DECEMBER.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/…
…MAJOR WINTER STORM TO IMPACT EASTERN NEW YORK AND WESTERN NEW
ENGLAND TONIGHT THROUGH TOMORROW…

AS OF 355 PM EST…FOR THOSE THAT LOVE THE SNOW…HERE WE GO…WITH
THE FIRST WIDESPREAD WINTER STORM FOR THE YOUNG ASTRONOMICAL
WINTER SEASON OF 2012-13 !!!

ONLY HEADLINE CHANGE WAS TO ADD ERN GREENE AND WRN COLUMBIA
COUNTIES TO THE WINTER STORM WARNINGS. AN ADVISORY REMAINS UP FOR
THE MID HUDSON VALLEY…SRN TACONICS…AND NW CT.

THERE IS CONSIDERABLE AGREEMENT WITH THE 12Z GFS…ECMWF…GEFS…AND
THE CANADIAN GUIDANCE FOR A COLDER SOLUTION FOR MORE SNOW IN THE
ALY FCST AREA…ESPECIALLY NORTH AND WEST OF THE MID HUDSON RIVER
VALLEY. THE PRIMARY REASON IS THAT THE SECONDARY LOW FORMING OVER
NC IS EXPECTED TO TRACK SOUTH OF LONG ISLAND TOMORROW
MORNING…AND OVER MARTHA/S VINEYARD BY THE AFTERNOON. THIS WOULD
MEAN SOME MIXED PCPN WOULD ERUPT INTO THE MID HUDSON
VALLEY…SOUTHERN BERKSHIRES…TACONICS…AND ERN CATSKILLS. THE NAM
CAN NOT BE COMPLETELY DISCARDED WITH SOME PRONOUNCED DOWNSLOPING
TONIGHT…ESPECIALLY BTWN 03Z-09Z WHEN THE H925 LLJ IS THE
STRONGEST OUT OF THE E/SE AT 40-60 KTS. HOWEVER…THE WINDS SHOULD
SHIFT TO THE N/NE BTWN 09Z-12Z FOR ANY SHADOWING EFFECT TO
DIMINISH…AND THE PCPN TO CHANGE BACK OVER TO SNOW. WE HAVE SOME
GUSTS MENTIONED TO 40-50 MPH OVER NEAR THE WRN NEW ENGLAND
TERRAIN…AND CATSKILLS.

BACKING UP…SNOW IS ON THE DOOR STEP FOR THE SRN MOST ZONES RIGHT
NOW. THIS SNOW IS DUE TO THE STRONG ISENTROPIC LIFT ON THE 295K
SFC AHEAD OF A WARM FRONT TIED TO THE PRIMARY LOW OVER WV. THIS
PRIMARY LOW WILL QUICKLY DECAY…AS THE SECONDARY LOW CRANKS UP
OVER ERN VA/DELMARVA. THE H500 TROUGH IS TURNING NEGATIVE OVER THE
TN VALLEY…MIDWEST…AND SOUTHEAST WITH COPIOUS AMOUNTS OF
MOISTURE STREAMING IN FROM THE GULF AND ATLANTIC. THE CLOSED H500
CIRCULATION IS OVER THE KY/TN CORRIDOR AT THIS TIME. A BEAUTIFUL
BAROCLINIC LEAFLET IS EVIDENT OF THE SATELLITE/WV IMAGERY WITH A
DRY SLOT POKING INTO NC/VA. WHAT THIS ALL SPELLS IS EXPLOSIVE
SECONDARY CYCLOGENESIS.

THE CYCLONE TRACK WILL MAKES ITS WAY TO SOUTH OF LONG ISLAND BY
12Z TOMORROW. EXPECT SNOW RATES TO INCREASE TO 1 INCH AN HOUR
QUICKLY EARLY THIS EVENING FROM SOUTH TO NORTH. THE GUIDANCE HAS
UNDERDONE THE AMOUNT OF COLD AIR IN PLACE. THE MID HUDSON
VALLEY…SRN TACONICS…AND NW CT COULD RECEIVE 2 TO 6 INCHES OF
SNOW BEFORE A CHANGEOVER TO SLEET AND FREEZING RAIN AROUND
MIDNIGHT OR SO. THERE COULD BE SOME ISOLATED HIGHER AMOUNTS OVER
THE HIGHER POINTS OF THE LITCHFIELD HILLS. FURTHER NORTH…EXPECT
SNOW…HEAVY AT TIMES…WITH SOME GUSTY WINDS CLOSER TO THE WRN
NEW ENGLAND TERRAIN ASSOCIATED WITH THE STRONG E/SE LLJ. THE
LATEST PLUMES JUSTIFY A ONE INCH EQUIVALENT FOR ALY. THE GEFS ARE
SHOWING H850 LOW-LEVEL -U WIND ANOMALIES /EASTERLIES/ OF 4 TO 6
STANDARD DEVIATIONS ABOVE NORMAL 00Z-12Z…THIS MEANS SOME HEAVY
DUTY SNOW TOTALS COULD RACK UP OVER THE CATSKILLS…AND
ADIRONDACKS…GREENS AND BERKS ALONG THE ERN SLOPES. WE ARE
EXPECTING A QUICK 6-12" OF SNOW OVERNIGHT…ESPECIALLY ALONG THE
ERN CATSKILLS BEFORE A CHANGEOVER TO SOME SLEET/FREEZING RAIN.
BASED ON THE COOL SEASON CSTAR RESEARCH…THERE IS SOME EVIDENCE
OF A BAND FORM FROM THE CAPITAL REGION NORTH AND WEST BTWN 06Z-12Z
WHICH COULD INCREASE THE SNOW RATES FROM 1-2+ INCHES PER HOUR.
THIS BAND WAS BASED ON THE GFS. THE VALLEYS AREAS WILL LIKELY SEE
3 TO 6 INCHES OF SNOW OVERNIGHT IN THE WARNINGS.

MIN TEMPS WILL BE OF THE WET BULB VARIETY WITH GENERALLY TEENS
NORTH OF THE MOHAWK VALLEY…AND 20S TO THE SOUTH AND EAST.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/…
NEWER SHORT TERM COMING SOON…BEFORE 430 PM…

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/…
HPC GUIDANCE. A MOSTLY CLOUDY AND COLD PERIOD WITH A CHANCE OF
SNOW…THEN LAKE EFFECT SNOW SHOWERS DURING THE EARLY PART OF THE
WORK WEEK. LOW PRESSURE WILL INTENSIFY RAPIDLY ALONG THE SOUTHEAST
COAST ON SATURDAY…AND IT IS EXPECTED TO TRACK RAPIDLY NORTHEAST
WELL EAST OF CAPE COD AND SOUTH OF NOVA SCOTIA BY EARLY SUNDAY.

STILL MUCH IS IN QUESTION REGARDING HOW THIS SYSTEM EVOLVES…BUT
THE SYSTEM IS VERY LIKELY TO BRING ALL SNOW TO THE AREAS IT
AFFECTS. THINKING NOW IS THAT SNOW IS LIKELY SATURDAY AT LEAST
SOUTH AND WEST OF THE CAPITAL REGION…WITH A CHANCE ELSEWHERE GIVEN
THE HIGH DEGREE OF UNCERTAINTY.

BY SUNDAY NIGHT…WRAPAROUND AND LAKE ENHANCEMENT WILL HAVE BECOME
THE PREDOMINANT INFLUENCE ON THE BACKSIDE OF THE SYSTEM. HOWEVER…
THIS TOO LACKS CERTAINTY AS THE LOW LEVEL FLOW GIVES INDICATION IT
MAY BE TOO WEAK TO SUPPORT SIGNIFICANT LAKE EFFECT.

A WEAK IMPULSE CROSSING SOUTH OF LAKE ONTARIO COULD RESULT IN AN
EXPANDED AREA OF LIGHT SNOW ON WEDNESDAY. HIGH PRESSURE WILL NOSE
IN FROM THE NATION/S MID-SECTION TO FURTHER WEAKEN THE FLOW AND
LESSEN THE CHANCES FOR SNOW.

SATURDAY WILL BE THE LAST DAY ANYONE SEES TEMPERATURES ABOVE
FREEZING. HIGHS SUNDAY THROUGH WEDNESDAY WILL BE 32 DEGREES OR LESS
THROUGHOUT OUR FORECAST AREA. THANKS IN PART TO PARTIAL CLEARING
TUESDAY NIGHT…WEDNESDAY WILL BE THE COLDEST DAY AS HIGHS WILL
RANGE FROM ONLY THE LOWER TEENS IN THE ADIRONDACKS AND GREENS…TO
THE MID 20S IN THE MID HUDSON VALLEY.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/…
VFR CONDITIONS WILL QUICKLY ERODE AS A POTENT STORM SYSTEM
APPROACHES FROM THE SOUTH AND IMPACTS THE REGION FOR MUCH OF THE TAF
PERIOD.

THIS AFTERNOON…HIGH CLOUDS ASSOCIATED WITH A POTENT STORM SYSTEM
WILL QUICKLY OVERSPREAD THE REGION EARLY THIS AFTERNOON…BUT REMAIN
AT VFR LEVELS THROUGH THE EARLY EVENING. SNOW WILL QUICKLY
OVERSPREAD THE TAF SITES FROM SOUTH TO NORTH BETWEEN
21Z/00Z…DROPPING VISIBILITIES TO MVFR INITIALLY BEFORE DROPPING
FURTHER TO IFR AFTER 00Z. WINDS WILL BE LIGHT GENERALLY LESS THAN 10
KNOTS.

TONIGHT…MODERATE TO HEAVY SNOW WILL OVERSPREAD ALL TAF SITES
DURING THE OVERNIGHT HOURS…WHERE HEAVIER BANDING MAY OCCASIONALLY
REDUCE VISIBILITIES TO UNDER 1/2SM. AT THIS TIME…IT APPEARS THAT
KGFL WILL REMAIN ALL SNOW THROUGHOUT THE EVENT…WITH A TRANSITION
TO -SNPL AT KALB TOWARDS DAYBREAK…AND POSSIBLE SIGNIFICANT ICING
AT KPOU AND KPSF BEFORE A TRANSITION TO -RA AT KPOU AFTER 13Z.

THURSDAY…PRECIPITATION WILL SLOWLY BEGIN TO DECREASE IN COVERAGE
AND INTENSITY LATE IN THE TAF PERIOD…BUT STILL KEEP TAF SITES AT
IFR CEILINGS/VISIBILITIES. WINDS WILL GRADUALLY INCREASE AS THE
STORM SYSTEM APPROACHES…GENERALLY 10-15 KNOTS WITH OCCASIONAL
GUSTS TO 25 KNOTS. HAVE MENTIONED LLWS AT KPOU AND KPSF NEAR THE END
OF THE TAF PERIOD AS AN IMPRESSIVE 50-70 KNOT JET IN THE LOW-LEVELS.
HOWEVER…CONFIDENCE IS LOW AT THIS TIME THAT SIGNIFICANT MIXING TO
THE SURFACE WILL OCCUR…SO CONFINED STRONGEST WINDS JUST ABOVE THE
SURFACE.

OUTLOOK…
THU PM-NT…MVFR/IFR. -SHSN. -SHRA/-SHSN AT KPOU.
FRI-FRI NT…VFR. NO SIG WX.
SAT-MON…VFR/MVFR. CHC -SHSN.

&&

.HYDROLOGY…
A MAJOR WINTER STORM WILL IMPACT THE REGIONLATE THIS PM INTO THURSDAY
WITH MAINLY MODERATE TO HEAVY SNOW. SLEET…FREEZING RAIN AND RAIN
ARE EXPECTED MAINLY SOUTH AND EAST OF ALBANY…WHERE PRECIPITATION
TYPE WILL BE MOST VARIED. WITH THE BULK OF PRECIPITATION IN THE
FCA SNOW…OR FROZEN…THERE SHOULD BE MINIMAL HYDROLOGIC RESPONSE
EXCEPT SOME MODEST WITHIN BANK RISES IN SOUTHEAST NEW YORK AND
LITCHFIELD COUNTY CONNECTICUT. THE NERFC QPF WAS USED WITH 1-1.75
INCHES OF LIQUID EQUIVALENT.

WE WILL HAVE TO MONITOR IS THE FLOOD STAGE AT POUN6 IS NICKED WITH
THE E/SE LATE TOMORROW MORNING.

THURSDAY NIGHT INTO SATURDAY WILL HAVE SOME SCATTERED SNOW
SHOWERS MAINLY NORTH AND WEST OF THE CAPITAL REGION. SOME LIGHT
SNOW IS POSSIBLE LATE SATURDAY INTO SUNDAY. THE NEW WEEK WILL BE
MUCH COLDER…AND ICE MAY BEGIN TO FORM ON RIVERS AND LAKES OVER
THE HSA.

FOR DETAILS ON SPECIFIC AREA RIVERS AND LAKES…INCLUDING OBSERVED
AND FORECAST RIVER STAGES AND LAKE ELEVATIONS…PLEASE VISIT THE
ADVANCED HYDROLOGIC PREDICTION SERVICE /AHPS/ GRAPHS ON OUR WEBSITE.

&&

.ALY WATCHES/WARNINGS/ADVISORIES…
CT…WINTER WEATHER ADVISORY UNTIL 7 PM EST THURSDAY FOR CTZ001-013.
NY…WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 PM EST
THURSDAY FOR NYZ032-033-038>043-047>054-058>061-063-
082>084.
WINTER WEATHER ADVISORY UNTIL 7 PM EST THURSDAY FOR NYZ064>066.
MA…WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 PM EST
THURSDAY FOR MAZ001-025.
VT…WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 PM EST
THURSDAY FOR VTZ013>015.

&&

$$
SYNOPSIS…WASULA
NEAR TERM…WASULA
SHORT TERM…KL
LONG TERM…ELH
AVIATION…IRL
HYDROLOGY…KL/WASULA

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