March 7, 2013 Forecast Discussion

000
FXUS61 KALY 071132
AFDALY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ALBANY NY
632 AM 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 AS HIGH PRESSURE SETTLES INTO THE
AREA FOR THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/…
AS OF 6 AM…RADAR WAS QUICKLY EXPANDING WITH REFLECTIVITIES ACROSS
LITCHFIELD AND BERKSHIRE COUNTIES BUT HOW MUCH IS REACHING THE
GROUND REMAINS TO BE SEEN. NEVERTHELESS…LATEST HRRR/RAP POINT
TOWARD AN INCREASE IN COVERAGE OF THE PRECIPITATION TOWARD NOON.
THE 06Z NAM REMAINS AN OUTLIER WITH THE GFS REMAINING MORE
CONSISTENT WITH PREVIOUS FORECAST AND HPC/WPC INPUTS.

AS OF 3 AM…REGIONAL RADAR REVEALS PRECIPITATION ASSOCIATED WITH
THE COASTAL STORM WAS ACROSS LONG ISLAND…THE EASTERN 2/3RDS OF
CONNECTICUT AND SOUTHEAST MASSACHUSETTS. BOUNDARY LAYER
TEMPERATURES WHERE THE PRECIPITATION WAS OCCURRING WERE MAINLY
ABOVE FREEZING…HOWEVER…SNOW WAS BEING OBSERVED. THIS WILL BE
THE CHALLENGE PART OF THE FORECAST AS TOO THE IMPACT THESE
TEMPERATURES WILL HAVE WITH THE EXPECTED SNOWFALL ACCUMULATIONS
HEADING INTO TONIGHT. OTHERWISE…DURING TODAY…OVERNIGHT LOWS
DID NOT DROP TOO MUCH ACROSS THE REGION AS WE WILL FAVOR THE
WARMER SIDE OF THE GUIDANCE /MAV AND ECMWF MOS/ WITH NEAR 40F IN
THE VALLEYS AND MIDDLE 30S ELSEWHERE. AS FOR PRECIPITATION…PER
THE LATEST RAP/HRRR…OVERALL LIFT WILL BE ON THE INCREASE LATE
THIS MORNING AND ESPECIALLY THIS AFTERNOON AS THE UPPER LOW OVER
THE GREAT LAKES REGION APPROACHES WITH A RAIN/SNOW MIXTURE
EVOLVING. IN ADDITION…THIS WILL INTERACT AND ASSIST WITH MOISTURE
ENTRAINMENT FROM THE EAST AS OMEGA…QG FORCING AND DEFORMATION
WILL BE ON THE INCREASE.

&&

.SHORT TERM /FRIDAY 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 WEDNESDAY/…
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 /12Z THURSDAY THROUGH MONDAY/…
FOR THIS MORNING…WE ARE CLOSELY WATCHING A BAND OF SNOW SHOWERS
APPROACHING FROM THE SOUTHEAST. THIS BAND IS EXPECTED TO AFFECT KPOU
AND KPSF OVER THE NEXT 1-2 HOURS…WITH A FEW BRIEF REDUCTIONS OF
VSBY INTO THE MVFR/IFR RANGE EXPECTED. THIS BAND SHOULD WEAKEN UPON
HEADING FURTHER N AND W…SO HAVE ONLY INCLUDED MENTION OF MVFR
VSBYS AT KALB BETWEEN 12Z-15Z…AND VCSH AT KGFL. OTHERWISE…EXPECT
MAINLY VFR CIGS/VSBYS AT KGFL/KALB/KPOU THROUGH MIDDAY…AND MVFR
CIGS AT KPSF THROUGH AROUND NOONTIME.

FOR THIS AFTERNOON…PRECIPITATION WILL EXPAND WESTWARD FROM NEW
ENGLAND AND BECOME ENHANCED ACROSS THE REGION. TEMPERATURES
INITIALLY SHOULD BE WARM ENOUGH TO SUPPORT SOME RAIN AND SNOW MIXED
AT KGFL/KALB/KPOU…WITH MAINLY SNOW AT KPSF. TOWARD AND AFTER
SUNSET…THE PRECIPITATION SHOULD BECOME MAINLY SNOW…OF LIGHT TO
MODERATE INTENSITY. EXPECT IFR VSBYS AND CIGS TO DEVELOP ONCE THE
PRECIPITATION CHANGES TO ALL SNOW THIS EVENING…AND SHOULD LAST
THROUGH 10Z-11Z/FRI AT KGFL/KPSF/KALB…AND THROUGH 12Z/FRI AT KPOU.

NORTH TO NORTHEAST WINDS WILL PERSIST AT 8-12 KT THROUGH
TODAY…WITH OCCASIONAL GUSTS OF 15-25 KT POSSIBLE…ESP AT KPOU AND
KPSF. WINDS WILL GRADUALLY BACK MORE INTO THE NORTH AT AROUND 10 KT
AFTER SUNSET.

OUTLOOK…
FRI MRNG…MVFR/IFR. -SN LIKELY AT KPOU AND CHC -SN AT
KGFL/KALB/KPSF.
FRI AFTN-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 FROM 5 PM THIS AFTERNOON TO NOON EST
FRIDAY FOR CTZ001-013.
NY…WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO NOON EST
FRIDAY FOR NYZ040-047-048-051-058-063.
MA…WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO NOON EST
FRIDAY FOR MAZ001-025.
VT…WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO NOON EST
FRIDAY FOR VTZ013>015.

&&

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

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