March 7, 2013 Forecast Discussion

000
FXUS61 KALY 071825
AFDALY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ALBANY NY
125 PM EST THU MAR 7 2013

.SYNOPSIS…
A POWERFUL STORM IS SITUATED OFF THE MIDDLE ATLANTIC
COASTLINE. MEANWHILE…ANOTHER UPPER LEVEL DISTURBANCE WAS TRACKING
ACROSS THE UPPER GREAT LAKES. THESE SYSTEMS WILL INTERACT AND BRING
ANOTHER ROUND OF WINTER WEATHER TO EASTERN NEW YORK AND ADJACENT
WESTERN NEW ENGLAND INTO TONIGHT. PRECIPITATION WILL END FROM NORTH
TO SOUTH FRIDAY MORNING INTO THE EARLY AFTERNOON…AS HIGH PRESSURE
SETTLES INTO THE AREA FOR THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/…
AS OF 1245 PM EST…THIS UPDATE INVOLVES PUTTING THE TACONICS INTO
A WINTER WEATHER ADVISORY FOR 3-6 INCHES OF SNOW. ALL THE TACONICS
HAVE BEEN INCLUDED INCLUDING ERN RENSSELAER…ERN COLUMBIA…AND
ERN DUTCHESS COUNTIES. THE ADVISORY STARTS AT 1 PM. ALSO…THE
ADVISORY START TIME HAS BEEN CHANGED TO 1 PM FOR WRN NEW
ENGLAND…THE ERN CATSKILLS…THE HELDERBERGS…AND THE
SCHOHARIE/WRN MOHAWK VALLEYS. THE MAIN COASTAL LOW IS WELL
SOUTHEAST OF LONG ISLAND…SOME THE DEFORMATION SNOWFALL IS BEING
CAPTURED BY THE UPSTREAM UPPER LEVEL LOW OVER THE CNTRL AND ERN
GREAT LAKES REGION.

THE BOUNDARY LAYER REMAINS DRY…AND WARM IN THE VALLEYS. WE
CONTINUE TO FORECAST 2-4" THIS AFTERNOON INTO TOMORROW MORNING.
THE LATEST VWP AT KENX SHOWS NORTHERLY FLOW IN THE VALLEY…AND
E/NE FLOW JUST ABOVE THE BOUNDARY LAYER. THIS HAS CAUSED SOME
DOWNSLOPING OFF THE WRN NEW ENGLAND TERRAIN…AND VIRGA TO OCCUR.
PERIODS OF LIGHT SNOW AND FLURRIES HAVE OCCURRED…BUT THE
STEADIEST ECHOES ARE OVER THE CATSKILLS…AND WRN NEW ENGLAND
/SOUTH OF SRN VT/.

TEMPS WERE ADJUSTED DOWN A LITTLE BASED ON TRENDS AND THE
EVAPORATIVE COOLING. MAX TEMPS WILL STRUGGLE TO GET TO 40F IN THE
VALLEYS. EXPECT MAXES IN THE MID TO U30S IN THE VALLEYS…AND 20S
TO M30S OVER THE HILLS AND MTNS.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/…
DISCOUNTING THE NAM /WAY TOO HIGH WITH QPF AND OVERALL
DYNAMICS/…GLOBAL MODELS AND THE CONSISTENT ECMWF SUGGEST TONIGHT
SNOW WILL OVERSPREAD MOST OF THE REGION. AS THE UPPER LOW OVER THE
GREAT LAKES REGION TRACKS ACROSS WESTERN NY AND INTO CENTRAL
PA…THIS PLACES OUR REGION IN AN ENHANCED REGION OF DIVERGENCE.
THIS CAN ALSO BE SEEN IN THE CROSS SECTIONS WITH A RAPID INCREASE
IN THE OMEGA FIELD AND AGEOSTROPHIC VERTICAL CIRCULATION.
FURTHERMORE…QG FIELDS FROM THE GFS/ECMWF POINT TOWARD MAX
VERTICAL VELOCITIES AROUND 06Z FRIDAY WHICH COINCIDES WITHIN THE
BEST DENDRITIC SNOW GROWTH REGION. SO THERE COULD BE AN ENHANCED
PERIOD OF SNOW LATER TONIGHT. THE QUESTION IS THE BOUNDARY LAYER
TEMPERATURES. FOLLOWING THE GFS-MOS AND ECMWF- MOS…TEMPERATURES
WILL BE NEAR OR JUST BELOW FREEZING IN THE VALLEY LOCATIONS WITH
UPPER 20S ACROSS THE HIGHER TERRAIN. THIS MAY CUT BACK SOMEWHAT
THE SNOWFALL AMOUNT ACCUMULATIONS. HOWEVER…WHERE FAVORED UPSLOPE
CONDITIONS ARE MAXIMIZED SUCH AS THE CATSKILLS…AND OUR ADJACENT
WESTERN NEW ENGLAND COUNTIES…WILL STAND THE BEST CHANCE FOR
HIGHER ACCUMULATING SNOWFALLS. THEREFORE…IN CLOSE COORDINATION
WITH NEIGHBORING OFFICES…WE WILL ISSUE A WINTER WEATHER ADVISORY
FOR THESE REGIONS. THE EXCEPTION TO THIS WILL BE THE VALLEY
LOCATIONS AND THE ADIRONDACKS WHERE THE AFOREMENTIONED VALLEY
TEMPERATURES AND THE BEST LIFT TO REMAIN SOUTH OF THE DACKS WHICH
WILL MINIMIZE THE EXPECTED QPF. AVERAGE QPF FROM THE HPC/WPC AND
GLOBAL MODELS ARE BETWEEN ONE QUARTER TO ONE HALF OF AN INCH.
USING A 10:1 RATIO WOULD SUGGEST 2-6 INCHES. THE FRIDAY MORNING
COMMUTE COULD BE TRICKY.

THE UPPER LOW IS EXPECTED TO QUICKLY BECOME ABSORBED WITH THE
LARGER STORM IN THE ATLANTIC WHICH WILL BRING ABOUT A RATHER QUICK
END TO THE SNOWFALL FROM NORTH TO SOUTH DURING FRIDAY MORNING. THE
SURFACE PRESSURE GRADIENT WILL BE RATHER TIGHT ACROSS THE REGION
SO A RATHER BRISK DAY IS EXPECTED WITH INCREASING AMOUNTS OF
SUNSHINE FROM NORTH TO SOUTH.

SURFACE HIGH FROM THE UPPER PLAINS AND MISSISSIPPI RIVER VALLEY
WILL CREST OVER THE GREAT LAKES REGION AND INTO THE EASTERN CONUS
LATE FRIDAY NIGHT. THIS WILL SET THE STAGE FOR DIMINISHING WINDS
AND CLEARING SKIES. DEPENDING ON RESIDUAL SNOW COVER WILL DICTATE
THE OVERNIGHT LOWS. WE WILL SHADE A LITTLE COLDER WITH THE
EXPECTATION OF SOME SNOW COVER.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/…
THE LONG TERM PERIOD WILL BE CHARACTERIZED BY A WARM UP IN
TEMPERATURES…AND THE ARRIVAL OF ANOTHER STORM SYSTEM EARLY NEXT
WEEK.

SATURDAY THROUGH SUNDAY…THE WEEKEND WILL BE DOMINATED BY HIGH
PRESSURE SPRAWLING ACROSS THE FORECAST AREA AND DRY CONDITIONS.
MEDIUM RANGE MODEL GUIDANCE IS IN GOOD AGREEMENT WITH A PERIOD OF
DRIER AIR USHERING IN MOSTLY CLEAR SKIES…ACCOMPANIED BY A
SOUTHWESTERLY RETURN FLOW…WHICH…COUPLED WITH THE INCREASING
MARCH SUN ANGLE…WILL ALLOW TEMPERATURES TO RISE INTO THE MID/UPPER
40S IN VALLEY AREAS SATURDAY…WITH LOWER 40S ACROSS HIGHER
ELEVATIONS…AND EVEN WARMER…UPPER 40S TO SOME LOWER 50S IN
VALLEYS FOR SUNDAY…WITH MID 40S ELSEWHERE. OVERNIGHT MINS WILL
FALL INTO THE 20S FOR SAT NT/SUN AM. THIS HIGH PRESSURE WILL BEGIN
TO SLIDE OFFSHORE SUNDAY AS ANOTHER STORM SYSTEM APPROACHES FROM THE
MIDWEST.

MONDAY THROUGH WEDNESDAY…MODEL GUIDANCE SUGGESTS ANOTHER STORM
SYSTEM WILL DEVELOP ACROSS THE CENTRAL PLAINS AND MOVE OUT ACROSS
THE MIDWEST MONDAY. ONCE AGAIN THE UPPER-LEVEL FLOW TRIES TO CUTOFF
FROM THE BROADER FLOW REGIME…ALTHOUGH THE 00Z/ECMWF AND GFS ARE
FAIRLY SIMILAR IN BRINGING LOW PRESSURE INTO THE REGION TUESDAY.
HAVE INTRODUCED SLIGHT CHANCE TO LOWE CHC POPS ACROSS THE FORECAST
AREA BEGINNING SUNDAY NIGHT TO ACCOUNT FOR ANY MODEL TIMING
DIFFERENCES.

REGARDLESS OF THE INITIAL TIMING OF PRECIPITATION…THE LONG RANGE
MODEL SUITE CONTINUES TO FAVOR A TRACK OF THE STORM SYSTEM WEST OF
THE FORECAST AREA…WHICH GIVEN WARM BOUNDARY LAYER TEMPERATURES
ACROSS MOST OF THE REGION…WILL FAVOR MAINLY A RAIN EVENT…PERHAPS
WITH SOME HIGHER ELEVATION LOCATIONS EXPERIENCING A WINTRY MIX. HAVE
INCLUDED HIGH CHANCE POPS LATE MONDAY THROUGH TUESDAY AS A FRONTAL
BOUNDARY APPROACHES THE AREA…AND A POTENTIAL LOW PRESSURE SYSTEM
PASSES ALONG THE BOUNDARY ACROSS THE REGION.

OF INTERESTING NOTE HOWEVER IS THE JET ORIENTATION ASSOCIATED WITH
THIS STORM SYSTEM…AS GUIDANCE CONTINUES TO SUGGEST COUPLING OF THE
NORTHERN AND SOUTHERN STREAMS. THIS WOULD PLACE MUCH OF THE FORECAST
AREA UNDER BOTH THE RIGHT ENTRANCE REGION OF THE NORTHERN STREAM AND
LEFT EXIT REGION OF THE SOUTHERN STREAM…ALLOWING FOR RAPID
MOISTURE TRANSPORT INTO THE AREA WITHIN A REGION OF FAVORABLE
DYNAMIC ASCENT. GIVEN ANTECEDENT WARM CONDITIONS AND CURRENT
SNOWPACK ESPECIALLY ACROSS THE ADIRONDACKS…LATEST HYDROLOGICAL
ENSEMBLE FORECASTS SHOW BANK RISES APPROACHING ACTION STAGE…SO
WILL NEED TO CONTINUE TO MONITOR THE LATEST GUIDANCE. THE SYSTEM IS
FORECAST TO MOVE OUT OF THE AREA BY WEDNESDAY…AND FOLLOWED BY A
SURGE OF PROGRESSIVELY COLDER AIR ALONG WITH WINDY CONDITIONS. SNOW
SHOWERS WILL LIKELY OCCUR ACROSS NORTHERN AREAS DUE TO A COMBINATION
OF CYCLONIC FLOW…AND OROGRAPHIC EFFECTS.

TEMPERATURES WILL BE ABOVE NORMAL FOR MUCH OF THE LONG TERM
PERIOD…WITH HIGHS REACHING INTO THE 40S TO LOWER 50S IN VALLEY
LOCATIONS AND LOWER TO MID 40S ELSEWHERE. LOWS WILL GENERALLY BE IN
THE UPPER 20S ACROSS THE ADIRONDACKS TO MID 30S IN VALLEY LOCATIONS.
AS THE STORM SYSTEM EXITS THE REGION BY MIDWEEK…TEMPERATURES LOOK
TO LOWER TO NEAR NORMAL…WITH WED MAXES REACHING THE LOWER/MID 40S
IN VALLEY AND UPPER 20S TO MID 30S ACROSS HIGHER ELEVATIONS…AND
MORNING MIN TEMPS IN THE 20S ACROSS NORTHERN AREAS…AND LOWER TO
MID 30S ELSEWHERE.

&&

.AVIATION /18Z THURSDAY THROUGH MONDAY/…
LIGHT SNOW OR FLURRIES HAS OVERSPREAD MOST OF THE REGION. EXPECT
MAINLY VFR/MVFR LIGHT SNOW AT KALB/KGFL DUE TO NORTHERLY WINDS
BRINGING DRIER AIR INTO THE REGION. AT KPOU/KPSF EXPECT MVFR LIGHT
SNOW TO OCCASIONALLY IFR SNOW FOR THE REST OF THE AFTERNOON. AS THE
UPPER LOW OVER THE GREAT LAKES REGION TRACKS TO THE SOUTHWEST OF THE
REGION TONIGHT…THE SNOW WILL BECOME MORE WIDESPREAD TONIGHT. AFTER
00Z THIS EVENING HAVE GENERALLY FORECAST IFR CONDITIONS AT ALL THE
TAF SITES THROUGH EARLY FRIDAY MORNING…WITH A SLOW IMPROVEMENT
FROM NORTH TO SOUTH TO MVFR AND THEN VFR CONDITIONS.

NORTH TO NORTHEAST WINDS WILL PERSIST AT 8-12 KT THROUGH
TODAY…WITH OCCASIONAL GUSTS OF 15-25 KT POSSIBLE…ESP AT KPOU AND
KALB. WINDS WILL GRADUALLY BACK MORE INTO THE NORTH AT AROUND 10 KT
AFTER SUNSET…THEN PICK UP FROM THE NORTH TO NORTHWEST ON FRIDAY AT
10 TO 15 KTS WITH GUSTS OF 20 TO 25 KTS.

OUTLOOK…
FRI AFTN…MAINLY VFR…POSSIBLE MVFR/IFR IN -SN LIKELY AT KPOU AND
KPSF.
FRI NT-SUN NT…VFR. NO SIG WX.
MON…VFR/MVFR. CHC RAIN SHOWERS.

&&

.HYDROLOGY…
LITTLE TO NO HYDRO PROBLEMS ARE EXPECTED THE NEXT FEW DAYS. A
POWERFUL STORM IN THE WESTERN ATLANTIC AND THE APPROACH OF THE
UPPER LEVEL STORM OVER THE GREAT LAKES ARE EXPECTED TO PRODUCE
PRECIPITATION ACROSS THE REGION LATE THURSDAY INTO EARLY FRIDAY.
AT THIS TIME…STORM TOTAL QPF AMOUNTS THROUGH FRIDAY MORNING ARE
EXPECTED TO RANGE FROM ABOUT A QUARTER TO AROUND A HALF AN
INCH…WHICH SHOULD FALL MAINLY AS SNOW. SOME TIDAL IMPACTS MAY
BRING WATER LEVELS UP ACROSS THE HUDSON RIVER…ESPECIALLY INTO
POUGHKEEPSIE. AT THIS TIME…WITH THE FORECAST LOW LEVEL WIND
FIELD FROM THE NORTH…EXPECTATIONS ARE FOR THE WATER LEVELS TO
REMAIN JUST BELOW FLOOD STAGE TONIGHT.

LOOKING OUT FURTHER IN TIME…HIGH PRESSURE IS EXPECTED TO BUILD
INTO THE REGION FOR THE WEEKEND. TEMPERATURES ARE EXPECTED TO
MODERATE TO ABOVE NORMAL…WITH TEMPERATURES FALLING BELOW FREEZING
AT NIGHT…SO THERE WILL BE DIURNAL SNOWMELT.

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 NOON EST FRIDAY FOR CTZ001-013.
NY…WINTER WEATHER ADVISORY UNTIL NOON EST FRIDAY FOR NYZ040-047-
048-051-054-058-061-063-066.
MA…WINTER WEATHER ADVISORY UNTIL NOON EST FRIDAY FOR MAZ001-025.
VT…WINTER WEATHER ADVISORY UNTIL NOON EST FRIDAY FOR VTZ013>015.

&&

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

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