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Area forecast discussion 
National Weather Service Albany New York
643 PM EST sun Dec 21 2014

Synopsis...
high pressure over the northeast and Quebec will keep a moist low
level flow over the region...with lots of clouds into middle week.
There will be some spotty precipitation tonight and a better chance
for light mixed precipitation Monday night and Tuesday. Wednesday
a storm will organize in the Tennessee Valley and intensify rapidly
as it moves north to the Ottawa Valley. It will bring a period of
locally heavy rain and strong winds Wednesday into Wednesday
night.

&&

Near term /until 6 am Monday morning/...
massive inversion from 925hpa to 850hpa combined with low level easterly
flow and weak uvm with 500hpa trough over region will insure its mostly
cloudy with lowering clouds overnight. Some spotty precipitation particular
on the east facing slopes of the Litchfield Hills/Berks and
Taconics overnight is expected also. The remainder of the forecast area will
be dry with mainly cloudy skies overnight and lows in the middle
teens to middle 20s.

&&

Short term /6 am Monday morning through Tuesday night/...
on Monday...mostly cloudy conditions will continue as moisture
starts to lift northward from the middle Atlantic region on Monday
ahead of a surface low lifting northeastward along the eastern
Seaboard. While it will be dry...clouds will be fairly widespread
with highs on Monday in the 30s.

On Monday night moisture starts to overspread the forecast area as
the low pressure system is located off the Delaware-Maryland-Virginia peninsula with
a trough of low pressure along the southern New England coast.
Weak isentropic lift is expected across the forecast area with a plethora of
precipitation types Monday night across the southern half of the forecast area with
mainly snow across the northern half of the forecast area. Precipitation should start
as snow in all areas before the transition occurs during the
second half of the night across the southern half of the forecast area and
eventually the northern half of the forecast area by morning. Partial thickness
values and model soundings support some light freezing rain and
sleet mixing in. Lows Monday night will be tricky with not much
of a drop from daytime highs on Monday. Expect lows Monday night
to be in the middle 20s to lower 30s.

On Tuesday...freezing rain will linger into early Tuesday morning
across the northern half of the area with all rain from middle
morning Tuesday on across the forecast area. Highs on Tuesday are expected to
be in the upper 30s to middle 40s.

Tuesday night a storm system will move into the eastern Great
Lakes with an increasing southerly flow ahead of it. As the low
approaches it will lift a warm front into southern Pennsylvania
and the middle Atlantic region. It will be warm enough Tuesday night
such that all of the precipitation which will be mainly light will
fall in the form of rain. Expect lows Tuesday night to be in the
30s to lower 40s.

&&

Long term /Wednesday through Sunday/...
the extended forecast looks wet and mild to start for Christmas
evening...and then blustery and colder conditions return for Christmas
into the weekend with perhaps some unsettled weather to close the
Holiday weekend.

As previous discussions have mentioned the past several days...a
potential multi-hazard event is possible Wednesday into Thursday with a strong
low pressure system moving well west of the region from the Tennessee
Valley into the Great Lakes region and southeast Canada. This system will
bring milder weather across eastern New York and western New England with above normal
temperatures...and a surge of Gulf moisture. Also strong S to SW winds
ahead of the deepening and intensifying surface cyclone are expected Wednesday
into Wednesday PM...and a band of very heavy rainfall will occur with the
passage of the cold front. The above normal temperatures coupled with 1 to
2 inches of rainfall in 24 hours or less...and snow melt could produce
some minor Hydro issues. Also the strong gusty winds ahead of the
cyclone and its associated cold front...and in the wake of the front
with the cyclone deepening to 970 hpa or lower over western Quebec could
allow for some strong west/northwest winds across the region on Christmas.

Wednesday-Wednesday night...initial burst of rainfall during the day on Wednesday will
be with the isentropic lift on the 285/290k surface. The warm front
should lift quickly north during the afternoon. An anomalous
southerly low level jet jet of 40-60 kts at h850 will advect in anomalous precipitable water
values of 3 to 5 Standard devs above normal according to the latest
gefs. The +v-wind anomalies /southerlies/ are 2 to 3 Standard devs above
normal. The heaviest rainfall looks like it will be in the late
afternoon into the overnight period. H850 temperatures rise to +10c to
+12c in the warm sector. The narrow cold front rainband looks like
it will swing through on the GFS/ECMWF/can ggem between
06z-12z/Thu...as the cyclone deepens and intensifies as it moves
north/NE towards James Bay. High temperatures on Christmas evening will be in the
middle to u50s from the capital region south and east /nearly 20
degrees above normal/...and m40s to l50s to the north and west. As
colder air filters in Wednesday night...expect some of the rain to
transition to snow over the high peaks of the southern dacks. Perhaps an
inch or so of wet snow is possible. Lows Christmas morning will be
in the middle to u30s west of the Hudson River valley...and lower to
middle 40s from the Hudson River valley east.

Christmas-Christmas night...low pressure continues to deepen over
western Quebec near James Bay. Significant mslp pressure rises will be
occurring over the forecast area with the passage of a secondary cold
front and the upper trough axis. Blustery west/northwest winds of 15 to 30
miles per hour with some gusts to 35-45 miles per hour will be possible due to the deeper
mixing and a strong low-level pressure gradient. A wind headline
may be needed here for parts of the forecast area. Some westerly
upslope snow showers will be common over the western dacks...and western
greens. Highs will range from the m30s to u40s from northwest to southeast over
the forecast area. The snow showers will taper off Christmas night with
slight to low chance probability of precipitation west of the Tri Cities. Light snow accums
are possible over the western dacks and southern greens. Lows will be in the
middle 20s to l30s.

Fri-Sat...high pressure briefly ridges in from the south with the
middle level flow west/SW aloft. A clipper type low approaches from the
Great Lakes region and southern Ontario on Friday. This system lifts
north/NE into Quebec with some scattered snow showers ahead of the boundary
mainly north and west of the capital district Friday night into
Saturday. Some isolated rain/snow showers may get into the capital
region and Berkshires during the day on Saturday. High will be in
the m30s to m40s with lows in the middle 20s to l30s. Highs on
Saturday will be a little colder with the cold frontal passage with
highs in the l30s to u30s over the higher terrain...and u30s to l40s
in the valleys.

Saturday night into Sunday...a mean upper level trough set up over
the Great Lakes region...northeast and East Coast. The GFS has weak
impulses in the west/northwest cyclonic flow focusing lake effect and west/northwest
upslope snowfall. The European model (ecmwf) has the low-level baroclinic zone
hanging close to the coast. A coastal wave moves along it Sunday
for some snowfall for most of the region. A lot of uncertainty
still exists...so a low chance of snowfall was used for the entire forecast
area on Sunday. Temperatures look seasonable for late December.

&&

Aviation /00z Monday through Friday/...
stratus deck remains trapped under massive inversions over fca
with little change likely throhgh the taf period. Mainly MVFR
ceilings and visibility with widespread hir terrain obscured. Gradually lowering
ceilings overnight with areas of IFR conds developing. Weak uvm associated with
weak 500 hpa cut off over region...and low level Atlantic moisture inflow
will result in scattered -shsn/isolated zl over west new eng and southern most
areas of New York state. Conds in these areas could become widespread IFR
overnight.

On Monday...lingering patchy -sn and or zl will diminish early.
Otherwise IFR/MVFR conditions may improve slightly during the day

Winds will remain light...from the north to NE at less than 8 knots through
the period.

Outlook...

Monday night: moderate operational impact. Chance of rain...sn...fzra.
Tuesday: moderate operational impact. Chance of rain...sn.
Tuesday night: high operational impact. Likely rain.
Wednesday: high operational impact. Definite rain.
Wednesday night: high operational impact.Breezy definite rain showers...ra.
Christmas day: moderate operational impact.Windy with gusts to 34.0 chance of rain showers.
Thursday night: low operational impact.Breezy no sig weather.
Friday: no operational impact. No sig weather.

&&

Hydrology...
no hydrologic issues are anticipated through Tuesday night. A
widespread rainfall is expected Wednesday into Wednesday night as
a large low pressure system moves across the region. Rainfall
amounts of 1 to 2 inches are likely along with significant
snowmelt which raises the potential for minor flooding and
significant within bank rises of larger Stem rivers. Mmefs
guidance suggests the best chances for minor flooding would be
from the Hudson Valley through western New England. It is too
early to issue any flood watches...however will mention in the severe weather potential statement
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...none.
New York...none.
Massachusetts...none.
Vermont...none.

&&

$$
Synopsis...Snyder
near term...11
short term...11/Snyder
long term...wasula
aviation...Snyder
hydrology...11/NAS

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