March 19, 2013 Forecast Discussion

000
FXUS61 KALY 191442
AFDALY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ALBANY NY
1042 AM EDT TUE MAR 19 2013

.SYNOPSIS…
A DEVELOPING COASTAL STORM WILL TRACK ALONG THE NORTHEAST CORRIDOR
TODAY REDUCING ITS IMPACTS ACROSS THE REGION AS THE DAY
PROGRESSES. IN THE WAKE OF THIS STORM SYSTEM…WE WILL REMAIN IN
AN UNSETTLED WEATHER PATTERN WITH BRISK WESTERLY WINDS AND THE
CHANCE FOR ADDITIONAL WINTRY PRECIPITATION FOR THE REMAINDER OF
THIS WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/…
AS OF 1020 AM…NEXT BATCH OF PRECIPITATION HAS INCREASED IN
COVERAGE ACROSS FORECAST AREA…WITH ADDITIONAL SNOW AND SLEET.
AREAS SOUTH OF THE CAPITAL DISTRICT MAY ALSO SEE A BRIEF PERIOD OF
FREEZING RAIN MIXED IN AS WELL DURING THE MORNING HOURS…BEFORE
TRANSITIONING TO A SLEET/RAIN MIX DURING THE AFTERNOON. THIS BAND
OF PRECIPITATION WILL CONTINUE THROUGH THE AFTERNOON…BEFORE THE
DEFORMATION ZONE ROTATES EAST OF THE AREA.

EXPECT GENERALLY ANOTHER 2-4 INCHES OF ADDITIONAL ACCUMULATION
FROM THE CAPITAL REGION NORTHWARD…WITH LOCALLY HIGHER AMOUNTS IN
THE ADIRONDACKS AND SOUTHERN GREENS. THE QUESTIONS WILL BE EXACTLY
HOW MUCH OF THIS NEW SNOWFALL WILL BE MEASURABLE AS A MARCH SUN
ANGLE AIDS IN COMPACTING THE SNOW THIS AFTERNOON…AS WELL AS HOW
WARM BOUNDARY LAYER TEMPS GET IN THE MID HUDSON VALLEY. GIVEN
CURRENT BOUNDARY LAYER PROFILE…WILL CONTINUE TO LEAN TOWARDS A
COLDER SOLUTION WITH MAINLY SNOW FROM THE CAPITAL REGION
NORTHWARD…WITH SOME RAIN POSSIBLY MIXING IN ESPECIALLY IN THE
MID HUDSON VALLEY THIS AFTERNOON.

WILL CONTINUE WITH CURRENT HEADLINES AT THIS TIME AS OVERALL
FORECAST REMAINS IN GOOD SHAPE.

PREV DISC… COMPLEX STORM WAS UNDERWAY WITH REDEVELOPING OF THE
SURFACE LOW ALONG THE SOUTH SHORE OF LONG ISLAND WITH 3HR PRESSURE
FALLS OF NEAR 6MB/3HR. RADAR IMAGERY SUGGESTS THE PRECIPITATION
HAS BECOME INTERMITTENT AND DUAL POL DATA SUGGESTS MIX OF PRECIP
ACROSS THE SCHOHARIE VALLEY…CATSKILLS…MID HUDSON VALLEY AND NW
CT. BOUNDARY LAYER TEMPS WERE MAINLY INTO THE UPPER 20S SO THE
SNOW RATIO WAS AT OR BELOW 12:1. AS THIS COASTAL STORM
UNFOLDS…INVERTED TROUGH AXIS ALONG WITH THE TROWAL ADVECTING
WESTWARD SHOULD ALLOW FOR THE PRECIP TO REDEVELOP ACROSS MOST OF
THE REGION THIS MORNING AS SUGGESTED BY ALL AVAILABLE GUIDANCE.
THE COMPLICATED FACTOR TO THIS FORECAST WILL BE THE WARMING
BOUNDARY LAYER TEMPS AND THE HIGHER MARCH SUN ANGLE. IT APPEARS
OUR SOUTHERN COUNTIES MAY COME UP SHORT WITH WARNING CRITERIA AS
MOST OF THE ACCUMULATING SNOWFALL HAS ALREADY OCCURRED AND THE
ADDITIONAL PRECIPITATION TODAY WILL BE A WINTRY MIXTURE OR EVEN A
PERIOD OF RAINFALL CLOSE TO NOON HOUR. FURTHER NORTH…SEEMS MOST
OF THE PRECIP WILL FALL AS SNOW BUT ACCUMULATING WILL BECOME
PROBLEMATIC DUE TO THOSE WARMING BOUNDARY LAYER TEMPS AND SOME
POSSIBILITY OF A LITTLE SLEET MIXING IN FROM TIME TO TIME. THANKS
FOR THE EXCELLENT COORDINATION FROM NEIGHBORING WFOS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/…
BY SUNSET…THE COAST STORM IS EXPECTED TO BE INTO THE GULF OF
MAINE AS THE H850 LOW CLOSES OFF ACROSS EASTERN NEW ENGLAND. BY
THAT TIME…ACCUMULATIONS WILL BE DIMINISHING ACROSS MOST OF THE
REGION. LAKE EFFECT ACTIVITY WILL BE ON THE INCREASE DURING THE
NIGHT AS DELTA T/S INCREASE AN INVERSION HEIGHTS CLIMBING ABOVE 5K
FEET. QUESTION WILL BE HOW FAR THIS BAND PENETRATES INLAND AS
LOCAL CSTAR RESEARCH SUGGESTS NORTHERN HERKIMER COUNTY COULD
EXPERIENCE ADDITIONAL ACCUMULATING SNOWFALL. THERE IS A POTENTIAL
FOR ADDITIONAL HEADLINES AS LATER SHIFTS CAN ASCERTAIN THIS BETTER
ONCE THE MAIN SYNOPTIC EVENT HAS DIMINISHED.

BRISK WESTERLY WINDS WITHIN A COOL AND MOIST CYCLONIC FLOW WILL
KEEP THE CHANCE FOR PRECIPITATION THROUGH THE REMAINDER OF THE
SHORT TERM FORECAST. THE HIGHER POPS WILL BE RETAIN ACROSS
FAVORABLE UPSLOPE AREAS OF THE CATSKILLS…DACKS WHERE LAKE
CONTRIBUTIONS WILL BE MAXIMIZED. AS H850 TEMPS REMAINS BELOW
-10C…THIS WILL KEEP SURFACE TEMPERATURES BELOW NORMAL.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/…
TEMPERATURES WILL CONTINUE TO RUN BELOW NORMAL THROUGHOUT THE
PERIOD.

A NEGATIVE ARCTIC OSCILLATION (AO)/NEGATIVE NORTH ATLANTIC
OSCILLATION (NAO) WHICH HAS BEEN IN PLACE MOST OF THIS MONTH…LOOKS
TO CONTINUE. THESE BASICALLY INDICATE HIGHER THAN NORMAL PRESSURE AT
HIGHER LATITUDES WHICH ALLOWS ARCTIC AIR TO SLIP FURTHER SOUTH THAN
USUAL. THERE ARE SOME INDICATIONS FROM THE 00Z GFS ENSEMBLES THAT
AFTER PEAKING AT VERY ANOMALOUS LEVELS…BOTH INDICES WILL BEGIN TO
TREND TOWARD NEUTRAL CONDITIONS BUT PROBABLY NOT UNTIL EARLY NEXT
WEEK.

A LARGE UPPER AIR LOW DOMINATING THE CANADIAN MARITIMES…WESTWARD
INTO EASTERN CANADA…WILL UNABLE TO MOVE EAST DUE TO A LARGE
BLOCKING HIGH PARKED NEAR GREENLAND. THIS UPPER AIR LOW WILL
CONTINUE TO BRING CLOUDS AND SCATTERED SNOW SHOWERS…MAINLY TO THE
HIGHER TERRAIN…ESPECIALLY THE ADIRONDACKS INTO THE MOHAWK VALLEY
RIGHT INTO THE BEGINNING OF THE WEEKEND. SPOKES OF VORTICITY WILL
CONTINUE TO ENHANCE PERIODS OF UNSETTLED WEATHER…BUT THESE ARE
ALMOST IMPOSSIBLE TO PERFECTLY PREDICT THIS FAR OUT.

VALLEY AREAS…OUTSIDE THE MOHAWK VALLEY…SHOULD REMAIN MAINLY
DRY…BUT EVEN HERE…FLURRIES CANNOT BE RULED OUT AS THE STRONG
MARCH WILL ATTEMPT TO HEAT THE LOWEST LAYERS OF THE ATMOSPHERE
PRODUCING A STEEP LOW LEVEL LAPSE RATE…AND CUMULUS CLOUDS.

BY SUNDAY…AS THE AFOREMENTIONED UPPER AIR LOW FINALLY MOVES A
LITTLE FURTHER EAST…AND A PIECE OF A HUGE HIGH PRESSURE ANCHORED
OVER HUDSON/S BAY BUILD IN…DRYING SHOULD DIMINISH THE THREAT OF
SNOW SHOWERS…EVEN OVER THE MOUNTAINS. THERE WILL BE A LITTLE MORE
SUNSHINE…BUT IT WILL REMAIN WITH BELOW NORMAL TEMPERATURES.

MONDAY…A STORM LOOKS TO TRACK JUST SOUTH OF OUR REGION. IT WILL
HAVE TO BE WATCHED TO SEE IF WOULD BE ABLE TO PUSH NORTH ENOUGH TO
BRING PRECIPITATION TO PART OR ALL OF OUR REGION. FOR NOW…WE JUST
AVE SLIGHT POPS TO REFLECT THIS OUTSIDE POSSIBILITY. FROM THIS
VANTAGE POINT…IT LOOKS MARGINALLY COLD ENOUGH FOR ANY
PRECIPITATION TO FALL AS SNOW.

HIGH TEMPERATURES THROUGH THIS PERIOD WILL START OUT FROM THE UPPER
20S NORTHWEST TO NEAR 40 IN OUR SOUTHEAST ZONES. TEMPERATURES LOOK
TO MODERATE A LITTLE BIT BY THE WEEKEND…RANGING FROM THE MID 30S
IN OUR NORTHWEST ZONES TO MID 40S SOUTHEASTERN ZONES. OVERNIGHT LOWS
WILL RANGE IN THE TEENS NORTH…TO THE 20S SOUTH.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/…
A SIGNIFICANT LATE WINTER STORM WILL CONTINUE TO IMPACT THE AREA
THROUGH TODAY WITH MVFR…OCCASIONALLY IFR CONDITIONS…EXCEPT
MAINLY IFR AT KGFL.

PRECIPITATION WILL INITIALLY BE PATCHY AND INTERMITTENT THROUGH
13Z…BEFORE BECOMING STEADIER ONCE AGAIN BETWEEN 13Z-15Z…AND
PERSISTING THROUGH EARLY AFTERNOON. P-TYPE MAY INITIALLY BE A MIX
OF SNOW AND SLEET AT KGFL/KALB/KPSF…BEFORE BECOMING ALL SNOW
WITH MAINLY IFR CONDITIONS. AT KPOU…PRECIPITATION SHOULD BEGIN
AS RAIN AND/OR SLEET…BEFORE GRADUALLY MIXING WITH AND/OR
CHANGING BACK TO SNOW BEFORE ENDING AROUND MIDDAY…WITH
ASSOCIATED MVFR TO IFR CONDITIONS.

BY 18Z-20Z…PRECIPITATION WILL BEGIN TO DIMINISH AT EARNEST AT
KPOU…AS WE ASSIGN ONLY A VCSH THERE. IT WILL TAKE A LITTLE
WHILE LONGER FOR SNOW TO TAPER OFF AT THE OTHER TAFS…PROBABLY
NOT UNTIL WE ARE DONE WITH THE EVENING PEAK. AT KALB…THERE IS A
CHANCE THAT MOHAWK HUDSON CONVERGENCE COULD PRODUCE A THIRD
FLAREUP OF SNOW (DROPPING CONDITIONS BACK TO IFR FROM LOW MVFR
LATE IN THE AFTERNOON). HOWEVER…DID NOT INCLUDE THAT POSSIBLE
SCENARIO IN THE TAF AT THIS TIME.

SURFACE WIND WILL GENERALLY BE FROM THE NORTH OR NORTHEAST AROUND
5KTS…EXCEPT EASTERLY 10KTS GUSTING TO 20KTS AT KPSF. THE WIND
THERE WILL EVENTUALLY BACK MORE TO A NORTHEAST TO NORTH DIRECTION
LATER TODAY AND WEAKEN A LITTLE.

LOW LEVEL WIND SHEAR WILL BE PROBLEMATIC OVER THE NEXT 1-3
HOURS…AS EAST TO SOUTHEAST WINDS AROUND 2000 FT AGL INCREASE TO
30-40 KT…WHILE SFC WINDS REMAIN MAINLY N TO NE AT LESS THAN 10
KT. THE E/SE WINDS ABOVE THE SFC WILL GRADUALLY DECREASE LATER
THIS MORNING…REDUCING THE LOW LEVEL WIND SHEAR.

OUTLOOK…
TUE NIGHT-SAT…MAINLY VFR. CIG. BREEZY. CHC SUB-VFR -SHSN.

&&

.FIRE WEATHER…
NO CRITICAL FIRE WEATHER CONCERNS FOR THE NEXT FIVE DAYS.

A SIGNIFICANT STORM SYSTEM WILL TRACK ACROSS THE REGION TODAY. IN
THE WAKE OF THIS STORM SYSTEM…WE WILL REMAIN IN AN UNSETTLED
WEATHER PATTERN WITH BRISK WESTERLY WINDS AND THE CHANCE FOR
ADDITIONAL WINTRY PRECIPITATION FOR THE REMAINDER OF THE WEEK.

THE GROUND WILL BE SNOW COVERED IN ALL PLACES TODAY. THE SNOW PACK
WILL SLOWLY MELT IN THE VALLEYS THROUGH THE REMAINDER OF THE WEEK
BUT LIKELY REMAIN OVER THE MOUNTAINS.

&&

.HYDROLOGY…
NO HYDROLOGICAL PROBLEMS EXPECTED THROUGH THE WEEK.

A SIGNIFICANT PRECIPITATION WILL BEGIN TO DIMINISH THROUGH THE
DAY. IMPACTS ON AREA STREAMS AND RIVERS WILL BE MINIMAL AT THIS
TIME.

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 8 PM EDT THIS EVENING FOR CTZ001-
013.
NY…WINTER STORM WARNING UNTIL 8 PM EDT THIS EVENING FOR NYZ032-
033-038>043-047>054-058>061-063-064-082>084.
WINTER WEATHER ADVISORY UNTIL 8 PM EDT THIS EVENING FOR NYZ065-
066.
MA…WINTER STORM WARNING UNTIL 8 PM EDT THIS EVENING FOR MAZ001-
025.
VT…WINTER STORM WARNING UNTIL 8 PM EDT THIS EVENING FOR
VTZ013>015.

&&

$$
SYNOPSIS…BGM
NEAR TERM…IRL/BGM
SHORT TERM…BGM
LONG TERM…HWJIV
AVIATION…HWJIV/KL
FIRE WEATHER…HWJIV
HYDROLOGY…GJM/BGM

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