December 17, 2013 Forecast Discussion

000
FXUS61 KALY 171138
AFDALY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ALBANY NY
638 AM EST TUE DEC 17 2013

.SYNOPSIS…
A LOW PRESSURE SYSTEM PASSING SOUTH OF THE REGION WILL BRING A
WIDESPREAD LIGHT TO MODERATE SNOWFALL TO THE AREA TODAY. THE SNOW
WILL SPREAD NORTHWARD ACROSS THE AREA DURING THIS MORNING AND IS
EXPECTED TO TAPER OFF THIS EVENING. SCATTERED SNOW SHOWERS ARE
THEN EXPECTED TONIGHT AND WEDNESDAY…ESPECIALLY ACROSS THE HIGHER
TERRAIN. A GRADUAL WARMING TREND IS THEN EXPECTED FOR THE END OF
THE WORKWEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/…
AS OF 615 AM EST…BITTER COLD REIGNS ACROSS THE REGION…WITH
WIDESPREAD TEMPS OF -10F TO -20F ACROSS THE NORTH COUNTRY…AND -5F
TO +5F ELSEWHERE.

CLOUDS ARE RAPIDLY INCREASING ACROSS CENTRAL AND SOUTHERN
AREAS…WITH A RATHER LOW DECK…WITH CIGS GENERALLY BETWEEN
3500-5000 FT AGL. LIGHT SNOW IS CURRENTLY DEVELOPING THE SE
CATSKILLS/MID HUDSON VALLEY REGION…AND WILL SPREAD ACROSS THE
CAPITAL REGION…SCHOHARIE VALLEY…NW CT AND BERKSHIRES BETWEEN
ROUGHLY 7 AM-10 AM…AND INTO THE MOHAWK VALLEY…THE LAKE
GEORGE/SARATOGA REGION AND SOUTHERN VT BETWEEN 10 AM AND NOON.

ONCE THE SNOW STARTS…WE EXPECT PERIODS OF LIGHT TO MODERATE SNOW
TO CONTINUE THROUGH EARLY THIS EVENING…WITH TOTAL ACCUMS
GENERALLY 2-4 INCHES…EXCEPT FOR 3-6 INCHES ACROSS PORTIONS OF
THE MID HUDSON VALLEY…NW CT…BERKSHIRES…SOUTHERN VT AND SE
CATSKILLS WHERE SOME OROGRAPHIC ENHANCEMENT IS LIKELY…AND 1-3
INCHES ACROSS THE SOUTHERN ADIRONDACKS.

IT APPEARS THAT THERE WILL BE 2 MAIN BURSTS OF SNOW THROUGH
TODAY…THE FIRST ONE BEING DRIVEN MAINLY BY LOW/MID LEVEL WARM
ADVECTION…WHICH WILL BE MAINLY THIS MORNING…THEN PERHAPS THE
BEST BURST OF SNOW LATE THIS AFTERNOON INTO EARLY THIS
EVENING…DUE TO ENHANCED 850-700 FRONTOGENESIS TO THE N/NW OF AN
EMBEDDED SHORTWAVE TRANSLATING JUST S/E OF THE
REGION…INTERACTING WITH AN INCREASING INFLUX OF LOW LEVEL
MOISTURE BEING ENTRAINED INTO THE DEVELOPING STORM SYSTEM. THIS
SECOND BURST SHOULD BE GREATEST ACROSS THE GREATER CAPITAL REGION
AND SARATOGA REGION…BERKSHIRES AND SOUTHERN VT…MOST LIKELY
BETWEEN 4 PM AND 7 PM…THEREBY POTENTIALLY ADVERSELY IMPACTING
THE EVENING COMMUTE. WE WILL HAVE TO CLOSELY MONITOR RADAR TRENDS
DURING THIS PERIOD…AS THE ENHANCED F-GEN NOTED ON THE RUC13 FROM
THE CAPITAL REGION EAST INTO THE BERKSHIRES AND SOUTHERN VT
COINCIDES WITH INCREASING MOISTURE/TO NEAR SATURATION/FROM THE
ATLANTIC WITHIN THE 850-700 LAYER…POTENTIALLY ENHANCING BANDING
POTENTIAL AND PERHAPS LEADING TO LOCALLY GREATER SNOWFALL AMTS
THAN CURRENTLY INDICATED.

SINCE NEAR TERM MODELS SUCH AS THE RUC13 AND HRRR HINT AT THIS
SECOND BURST OF SNOW BETWEEN 4 PM AND 7 PM…HAVE EXTENDED THE
WINTER WEATHER ADVISORIES UNTIL 7 PM.

TEMPS TODAY WILL STRUGGLE TO CLIMB INTO AND THROUGH THE TEENS TO
LOWER 20S IN VALLEY AREAS…AND LOWER TO MID TEENS ACROSS HIGHER
ELEVATIONS…WITH MAX TEMPS LIKELY NOT OCCURRING UNTIL BETWEEN 5-7
PM. GIVEN THAT THE CLOUDS WILL BE RATHER LOW…AND THAT MUCH OF
THE PRECIP WILL BE FALLING FROM A LOWER CLOUD DECK INITIALLY THEN
WHAT OCCURRED ON SATURDAY…THE POTENTIAL AND DEPTH OF WET BULB
COOLING WILL BE LESS THAN WHAT OCCURRED THIS PAST SAT. SO…WE
HAVE SIDED WITH THE COOLER SIDE OF A MAV/MET MOS BLEND…BUT DID
NOT STRAY TOO MUCH.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/…
TONIGHT…ANY STEADIER SNOW SHOULD TAPER OFF ACROSS SE VT EARLY.
OTHERWISE…EXPECT SCATTERED SNOW SHOWERS TO OCCUR OVERNIGHT AS
THE MID/UPPER LEVEL TROPOSPHERIC TROUGH AND COLD POOL PASS
THROUGH…WITH 500 MB TEMPS DIPPING INTO THE -35C TO -40C RANGE.
925-700 LAPSE RATES STEEPEN…AND SHOULD ENOUGH MOISTURE BE
PRESENT WITHIN THIS LAYER…COULD LEAD TO SOME EMBEDDED HEAVIER SNOW
SHOWERS AND/OR SQUALLS…LEAVING ADDITIONAL COATINGS…TO PERHAPS
UP TO AN INCH OF SNOWFALL OVERNIGHT. TEMPS SHOULD FALL INTO THE
TEENS IN MOST AREAS.

WED-WED NT…THE AFOREMENTIONED MID LEVEL TROUGH/COLD POOL MOVES E
OF THE REGION IN THE AFTERNOON. HOWEVER…A FAIRLY WELL ALIGNED
WESTERLY FLOW MAY ALLOW FOR LAKE EFFECT SNOWBANDS TO DEVELOP
ACROSS NORTHERN HERKIMER CO IN THE AFTERNOON…AND MAY EXTEND WELL
INTO HAMILTON CO OR EVEN NW WARREN CO FOR A BRIEF TIME LATE IN THE
AFTERNOON INTO EARLY WED NT…AS SUGGESTED PER THE CSTAR FUNDED
INLAND LAKE EXTENT PROGRAM. THIS COULD LEAD TO AT LEAST 1-3 INCHES
OF SNOWFALL…WITH SOME POTENTIAL FOR GREATER AMTS…PERHAPS INTO
THE ADVISORY RANGE. WILL ADDRESS THIS POTENTIAL IN THE HWOALY.
ELSEWHERE…SCATTERED SNOW SHOWERS AND FLURRIES WILL BE POSSIBLE
ACROSS HIGHER ELEVATIONS…WHERE ADDITIONAL MINOR ACCUMS COULD
OCCUR…WITH SOME SNOW SHOWERS/FLURRIES OCCASIONALLY MIGRATING
INTO VALLEY AREAS…ESP NEAR AND N OF THE MOHAWK RIVER. FOR
TEMPS…EXPECT SLIGHTLY MILDER MAX TEMPS WED…REACHING THE 20S TO
LOWER 30S IN VALLEYS…WITH TEENS TO MID 20S ACROSS HIGHER
ELEVATIONS…AND OVERNIGHT MINS WED NT/THU AM FALLING MAINLY INTO
THE TEENS…WITH SOME SINGLE DIGITS POSSIBLE ACROSS NORTHERN AREAS
AND HIGHER ELEVATIONS ACROSS WESTERN NEW ENGLAND.

THU-THU NT…A SOUTHWEST LOW LEVEL FLOW WILL DEVELOP DURING THIS
TIME…ALLOWING FOR GRADUAL MODERATION IN TEMPS. SOME LINGERING
LAKE EFFECT SNOW MAY OCCUR THU ACROSS EXTREME NORTHERN
HERKIMER/HAMILTON COS…BEFORE THE INVERSION LEVEL FALLS.
THEN…SOME WARM ADVECTION PRECIP COULD DEVELOP ACROSS THE WESTERN
DACKS LATE THU NT…IN THE FORM OF LIGHT SNOW…OR EVEN A LIGHT
WINTRY MIX. THU MAX TEMPS SHOULD REACH THE LOWER/MID 30S IN
VALLEYS…AND 20S ACROSS HIGHER ELEVATIONS…WITH OVERNIGHT MINS
THU NT/FRI AM ONLY FALLING INTO THE 20S IN MOST AREAS…WITH TEMPS
POSSIBLY RISING IN SOME AREAS LATE AT NIGHT.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/…
INCREASING AGREEMENT IN THE MODEL AND ENSEMBLE GUIDANCE THROUGH THE
PERIOD. ONE UPPER IMPULSE AND ASSOCIATED FORCING SUPPORTS
PRECIPITATION FRIDAY AND FRIDAY NIGHT. THEN ANOTHER UPPER IMPULSE
AND ASSOCIATED FORCING AFFECTS OUR REGION SATURDAY NIGHT THROUGH
SUNDAY NIGHT. THE TIMING OF THESE SYSTEMS WILL LIKELY GET ADJUSTED
WITH TIME AS THEY ARE WITHIN QUICK WEST SOUTHWEST UPPER CONFLUENT
STEERING FLOW. ALSO…WORDING RAIN AND SNOW THROUGH THE PERIOD SINCE
THERE IS SUCH HIGH UNCERTAINTY IN THE POTENTIAL AREAS OF SLEET
AND/OR FREEZING RAIN.

THE PRECIPITATION TYPES AND THE POSITION OF A POTENTIALLY BROAD
PRECIPITATION TRANSITION ZONE ARE STILL IN QUESTION. HOWEVER…
THERE IS MORE AGREEMENT FOR ANY MIXED PRECIPITATION EARLY FRIDAY
MORNING TO CHANGE TO MAINLY LIQUID PRECIPITATION OVER CENTRAL AND
SOUTHERN AREAS BEFORE COVERAGE OF PRECIPITATION DECREASES FRIDAY
NIGHT. MIXED PRECIPITATION COULD REMAIN MIXED OVER NORTHERN AREAS.
HIGHS FRIDAY IN THE LOWER TO MID 40S IN MANY AREAS WITH MID TO UPPER
30S IN THE HIGHER ELEVATIONS.

LOW LEVEL FORCING WEAKENS FRIDAY NIGHT AND SATURDAY WITH WEAK LOW
LEVEL RIDGING OVER THE REGION. LINGERING MOISTURE AND PROXIMITY TO
THE LOW LEVEL THERMAL GRADIENT AND WIND CONVERGENCE PROXIMATE TO THE
LOW LEVEL BOUNDARY COULD SUPPORT SCATTERED SHOWERS…WITH SOME
FLURRIES OR SNOW SHOWERS. THE BRIEF LOW LEVEL RIDGING COULD ALLOW
TEMPERATURES TO FALL TO NEAR FREEZING IN MANY AREAS FRIDAY NIGHT AND
MID TO UPPER 20S IN THE HIGHER ELEVATIONS… AGAIN SUPPORTING
SCATTERED SHOWERS AND SNOW SHOWERS.

CURRENT GUIDANCE SUGGESTS THE NEXT SYSTEM ARRIVES THROUGH THE DAY
SATURDAY AN CONTINUES SATURDAY NIGHT THROUGH SUNDAY…EXITING SUNDAY
NIGHT. THE WARM ADVECTION AND FORCING LOOK STRONGER WITH THIS
SYSTEM…DRIVING THE WARM AIR FURTHER NORTH…SUPPORTING A
PRECIPITATION TRANSITION TO RAIN IN MOST AREAS. QUITE A STRONG
SOUTHWEST TO WEST SOUTHWEST BOUNDARY LAYER JET TRACKS THROUGH THE
REGION AND THE BOUNDARY LAYER THERMAL GRADIENT IS QUITE TIGHT AS IT
TRACKS EAST AND SOUTH SUNDAY AND SUNDAY NIGHT. SO…WILL HAVE TO
KEEP AN EYE ON WINDS AND POTENTIAL FOR LOCALLY HEAVY RAIN ON THE
MELTING SNOW PACK. HIGHS SATURDAY IN THE LOWER TO MID 40S…LOWER
TO MID 30S HIGHER ELEVATIONS. HIGHS SUNDAY IN THE UPPER 40S TO LOWER
50S…WITH UPPER 30S TO LOWER 40S IN HIGHER ELEVATIONS.

STRONG COLD ADVECTION SPREADS ACROSS THE REGION BY MONDAY MORNING
AND CONTINUES THROUGH THE DAY. SOME LAKE EFFECT SNOW BANDS SHOULD
FORM BUT INLAND EXTENT IS IN QUESTION. HIGHS MONDAY IN THE 20S TO
LOWER 30S.

THERE COULD STILL BE A LOT OF CHANGES TO HOW THESE SYSTEMS DEVELOP
AND IMPACT THE REGION. THERE ARE INDICATIONS OF A POTENTIAL BROAD
MIXED PRECIPITATION TRANSITION ZONE…BUT THE POSITION AND AREAL
EXTENT OF THE PRECIPITATION TRANSITION ZONE KEEPS CHANGING IN
SUCCESSIVE SETS OF GUIDANCE. THERE IS STILL A CHANCE THAT THE
CURRENT INDICATIONS OF MORE RAIN AND LESS WINTERY PRECIPITATION OVER
MUCH OF OUR REGION COULD CHANGE BACK TO COLDER AND MORE MIXED
PRECIPITATION DEPENDING ON HOW THE SYSTEMS DEVELOP IN THE NEXT 3+
DAYS. HOWEVER…THE INCREASING CONSENSUS FROM GUIDANCE OF MORE
LIQUID AND LESS MIXED PRECIPITATION SEEMS THE MOST LIKELY SCENARIO
AT THIS TIME.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/…
A LOW PRESSURE SYSTEM WILL BRING A WIDESPREAD LIGHT TO MODERATE
SNOWFALL TO THE AREA TODAY. THE SNOW WILL SPREAD NORTHWARD ACROSS
THE AREA DURING THE MORNING AND IS EXPECTED TO TAPER OFF TOWARD THIS
EVENING.

SNOW IS BEGINNING AT KPOU AND WILL SPREAD NORTHWARD TO KALB AND KPSF
BY 13Z-14Z AND BY KGFL BY 14Z. INITIALLY MVFR CONDITIONS ARE
EXPECTED WITH IFR DEVELOPING AS THE SNOW BECOMES STEADIER AS THE
MORNING PROGRESSES. AROUND 5 HOURS OF IFR SNOWS ARE EXPECTED WITH AN
IMPROVE BACK TO MVFR MID TO LATE AFTERNOON. KEEPING VCSH THROUGH
ABOUT 05Z AT ALL TAF SITES WITH LINGERING MOISTURE. AFTER
05Z-06Z…VFR CEILINGS AND VISIBILITIES SHOULD PREVAIL AT ALL TAF
SITES.

WINDS WILL BE NEARLY CALM THROUGH THE MORNING HOURS WITH A LIGHT
SOUTHEASTERLY FLOW DEVELOPING LATER IN THE MORNING AND BECOMING
VARIABLE AGAIN BY LATE AFTERNOON AND EVENING.

OUTLOOK…

WEDNESDAY NIGHT: NO OPERATIONAL IMPACT. NO SIG WX.
THURSDAY: NO OPERATIONAL IMPACT. NO SIG WX.
THURSDAY NIGHT: LOW OPERATIONAL IMPACT. SLIGHT CHANCE OF SHSN.
FRIDAY: MODERATE OPERATIONAL IMPACT. CHANCE OF RA…SN.
FRIDAY NIGHT: MODERATE OPERATIONAL IMPACT. SCATTERED SHRA…SHSN.
SATURDAY: MODERATE OPERATIONAL IMPACT. CHANCE OF RA…SN.

&&

.HYDROLOGY…
A CLIPPER TYPE SYSTEM WILL AFFECT THE REGION TODAY INTO THIS
EVENING. THE PRECIPITATION IS EXPECTED TO BE ALL SNOW WITH THIS
SYSTEM. TOTAL LIQUID EQUIVALENT WITH THIS SYSTEM IS EXPECTED TO
RANGE FROM ONE TO THREE TENTHS OF AN INCH WITH THE HIGHEST AMOUNTS
OVER THE ERN CATSKILLS…W-CNTRL MOHAWK VALLEY…AND WRN NEW
ENGLAND. THIS SYSTEM WILL REDEVELOP SOUTH OF LONG ISLAND…AND
QUICKLY MOVE NORTHEAST OF CAPE COD TOMORROW NIGHT.

SOME LAKE EFFECT SNOW IS POSSIBLE WED-THU WITH LIGHT SNOW
AMOUNTS…AND LIQUID EQUIVALENTS GENERALLY LESS THAN A TENTH OF AN
INCH FOR THE WRN DACKS REGION…AND NRN TIER OF THE HSA.

FOR THE MID WEEK…TEMPS WILL CONTINUE TO BE BELOW NORMAL AND ICE
WILL CONTINUE TO FORM AND THICKEN ON AREA RIVERS…STREAMS AND
PARTICULARLY LAKES.

A MODERATING TREND IN TEMPS IS LIKELY THU INTO FRI…WITH A
FRONTAL BOUNDARY BRINGING SOME SHOWERS TO CLOSE THE WORK WEEK.
SOME SNOW MELT IS LIKELY THIS WEEKEND. ALSO…A STORM SYSTEM
MOVING ALONG A FRONTAL BOUNDARY NEAR THE HSA MAY BRING SIGNIFICANT
PCPN TO THE FORECAST AREA SAT NIGHT INTO SUNDAY WITH EVEN MILDER
TEMPS. THIS WILL CONTINUE TO BE MONITORED FOR THE UPCOMING
WEEKEND.

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 THIS EVENING FOR CTZ001-
013.
NY…WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR NYZ054-
058>061-063>066.
MA…WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR MAZ001-
025.
VT…WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR
VTZ013>015.

&&

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

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