Area Forecast Discussion
Issued by NWS Albany, NY

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FXUS61 KALY 251150
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
650 AM EST Sat Feb 25 2017

.SYNOPSIS...
An anomalously warm and humid air mass will be over eastern New
York and western New England into this afternoon. A strong cold
front will bring heavy rain showers, scattered thunderstorms
and gusty winds to the region this afternoon into early this
evening. Much colder air will filter into the area with some
light accumulating snowfall especially over the higher terrain
tonight, as blustery and cold conditions finish the weekend with
temperatures more typical of late February.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A Flood Watch remains in effect for the western Mohawk Valley,
the upper Hudson, the southern Adirondacks, Lake George Saratoga
region and southern Vermont from today through Sunday. See
the Hydrology section for details...

The entire forecast area is in a Slight Risk for the possibility
of severe thunderstorms this afternoon into early this evening
with damaging winds the main threat.

As of 648 AM EST...The sfc map this morning looks similar to
May 25th rather than Feb 25th for a large portion of the
forecast area with temps in the 50s to lower 60s, except for a
portion of the southern Adirondacks, and Lake George Region,
where the warm front back southward as a cold front and became
stationary with temps in the the 30s to lower 40s this morning.
For example, KGFL is 39F at 633 am, and KDDH is 62F! Sfc dewpts
are in the 40s and the 50s for a large portion of the forecast
area with a southerly flow advecting in the milder temps and
dewpts due to the ridge downstream and the strong flow ahead of
the upstream upper level trough that will be turning negatively
tilted as it moves across the Great Lakes Region and Midwest
into southeastern Canada. The sfc cyclone associated with the
negatively tilted upper trough will pass well north and west of
the region towards James Bay this afternoon. However, a strongly
forced cold front supported by impressive upper level dynamics
/for example, the right entrance region of the H250 northern jet
stream will interact with the left front quadrant of the
subtropical branch of the jet stream over the mid-Atlantic
States/ will swing across the region with chances of
thunderstorms, some of which could be severe.

The morning will start out with a cluttered warm sector with
lots of stratus around. The stratus has been most evident across
western New England and parts of the Hudson River Valley and
into the Taconics. Some isolated showers or pockets of drizzle
are possible this morning, but it looks likes the leading edge
of the showers and scattered thunderstorms get close to the
western portion of the ALY forecast area based on the latest
3-km HRRR and NAM at 20Z.

The pre-convective environment is a classic cool season high
shear-low CAPE set-up. 0-6 km bulk shear values of 50-75 kts,
and 0-1 km values of 30-40 kts ahead of the front with low
amounts of sfc based instability generally less than 100 J/kg
based on the NAM/GFS. However, the MUCAPE values are 100-350
J/kg on the GFS with DCAPE values of 200-700 J/kg. Mid level
lapse rates on both the GFS/NAM are in the 6.5C-7C/km range
with a very strong sfc-H850 theta-e gradient from west to east
with the front. PWATS will be in the two thirds of an inch to 1
inch range, as these values are 1 to 3 standard deviations above
normal based on the latest GEFS. A strongly forced low topped
line of convection is likely with perhaps some QLCS segments
early on before fusing into a narrow cold front rainband between
20Z-01Z/SUN across the region. The latest 3-km HRRR has the
QLCS elements getting into the western Adirondacks between 20Z-
21Z.The low-level helicity values are also high and SPC did
include a 2% contour for tornadoes, however, we agree that
damaging winds will be the main threat, and we foresee several
special weather statements /SPSs/ focusing on the winds and
heavy rainfall, and potentially some SVR`s. In the gridded
forecasts we included the wording heavy rainfall and gusty winds
with the thunderstorms. The GEFS does have a strong +v
component of the wind anomaly /strong southerlies/ over the
region between 18Z to 00Z. The h925 winds do increase to 30-40
kts ahead of the front. We have some southerly wind gusts of
30-40 mph ahead of the boundary. These fell short of the
advisory level.

Temps will not have far to go in many locations once the stratus
burns off in the late morning into the early afternoon ahead of
the front. We have highs in the lower to mid 60s in the valley
areas with some upper 60s near the mid Hudson valley and mid 50s
to lower 60s over the hills and mountains. Some locally heavy
downpours are possible, but FFG values remain high outside of
the Flood Watch for snowmelt and runoff in our area, so we did
not expand the watch at this time.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/...
Tonight...We are looking at a 10C difference in H850 temps over
a narrow east to west corridor across the front with temps
falling below 0C over the western Adirondacks at 21Z, and temps
close to +8C over the Hudson River Valley into western New
England. By 03Z, H850 temps on the GFS/NAM are below 0C across
most of western New England and -8C to -9C over the
Adirondacks/eastern Catskills, and the western Mohawk Valley.
The scattered thunderstorms should diminish around 7-8 pm, but
in the strong cold advection in the wake of the front, expect a
quick transition to snowfall especially over the higher terrain,
and then the lower elevations. 1-3 inches is possible over the
western Adirondacks, portions of the eastern Catskills, and the
southern Greens, and possibly the northern Berkshires. Valley
areas north of the mid-Hudson Valley will likely have an inch or
less. The western Mohawk Valley may get around an inch.

The colder temps will try to slow down the runoff from the rain,
but we believe the Flood Watch for rain and snowmelt still looks
good for the northern half of the hydro service area where two
thirds of an inch to and inch and a quarter is possible. We are
expecting a half inch or less further south and east from the
Capital Region and into the mid-Hudson Valley and NW CT. WPC
placed the eastern Catskills and portions of the Capital Region
north and west into a Marginal Risk of exceeding the FFG
guidance, but with little QPF the past 10-12 days and higher
zonal FFG values compared to BGM`s area upstream, we believe
our current Flood Watch looks fine. Low temps tumble back to
the 20s to lower 30s with a few teens over the southern Dacks by
day break. The west winds will increase to 10 to 20 mph with
some gusts in the 30-40 mph range.

Sunday...A blustery and cold day is expected with the best
mixing anticipated late in the morning into the afternoon. West
to northwest winds of 15 to 25 mph will be possible with some
gusts in the 35 to 45 mph range in the Capital
Region...Mohawk Valley...Taconics...Berkshires...and the
eastern Catskills. Our confidence was not high enough for a 3rd
period wind advisory, and based on collaboration with
neighboring WFO`s, we feel the gusts fall short at this time. A
brief lake connection with the mixed layer winds veering to the
northwest will keep some multibands snow showers/flurries going
for the western Adirondacks/western Mohawk Valley/Schoharie
Valley/eastern Catskills going through the morning into the
afternoon with light accums of an inch or less. Much colder
temps with mid 30s to lower 40s in the valley areas, and 20s to
lower 30s over the hills and mountains. It will feel more like
late FEB.

Sunday night into Monday...High pressure builds in from the Mid
Atlantic Region late Sunday into Sunday night...and then drifts
offshore. Mid and upper level heights rise, and some low to mid
level warm advection kicks in. Some scattered snow showers are
possible over the western Adirondacks Sunday night into Monday.
Lows Sunday night will be in the teens and 20s. Sunshine mixes
with clouds well in advance of the next cold front on Monday
with temps rising about 5-10 degrees above normal again with
mid 40s to lower 50s in the valleys, and upper 30s to mid 40s
over the mountains.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Active weather will persist through much of the long term period,
with a transition from zonal flow at upper levels to a broad trough
over the northeastern CONUS and below normal temperatures by next
weekend.

The period starts out with high pressure over the region Monday
evening, gradually shifting eastward off the east coast by late
Monday night. With a zonal flow aloft, the next low pressure system
will quickly approach from the central plains and mid Atlantic
regions on Tuesday. The surface warm front associated with this
system will lift through Tuesday afternoon/evening, spreading
precipitation across the area, but will mention slight chance pops
Monday night to account for wider time window if the system movement
speeds up. Thermal profiles indicate potential for some mixed
snow/rain at the onset, especially for areas north of Albany and
over the higher terrain. Temps should warm enough for plain rain by
late Tuesday morning or early afternoon. As the surface low lifts
across the Great Lakes, precipitation will remain possible from
Tuesday afternoon through Wednesday afternoon.

A stronger system is then forecast to track from the Upper Great
Lakes northeastward into southeast Canada by Wednesday. Our region
will be on the warm side of cyclone initially, with the potential
for warming into at least the upper 40s to lower 50s despite
rainfall. If breaks of sunshine can occur, temperatures would be
even warmer. The system`s cold front will push through in the
Wednesday night time frame, with a chilly air mass filtering in
behind the front. Rain looks to transition over to snow on the
backside of the system, with chances for snow across the high
terrain Wednesday night/Thursday. As the core of the upper trough
moves over New York on Friday, another low pressure system will pass
through the forecast area, bringing a chance for snow showers area-
wide. Strong cold advection ensues Friday night, with lows
potentially dropping into the single digits across the Adirondacks
and into the teens elsewhere.

Winter isn`t over yet. After a period of significant warmth this
week, expect below normal temperatures for the first full week of
March and the potential for snow on the ground in many
locations.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
A strong cold front will sweep east across the TAF sites late this
afternoon. A period of moderate to heavy rain showers, strong gusty
winds, and even a few rumbles of thunder will be possible as the
leading edge of the front moves through, with light to moderate rain
likely lingering in its wake. So expect conditions to drop to IFR or
lower within the stronger thunderstorms. There is also potential for
rain to change over to snow behind the front but this depends on how
quickly the cold air can invade the region. Shower chances should
gradually diminish after about 06Z/Sun but fog and low level
moisture will likely keep conditions at MVFR/IFR through the end of
the forecast period.

Winds will be southerly increasing to 10-15 kt by late this morning
with higher gusts around 25-30 kt at KALB. Some low level wind shear
may develop toward afternoon where surface winds are relatively
light and a southerly low level jet moves overhead. LLWS may need to
be mentioned in subsequent TAF issuances.

Winds will shift into the west with the cold front and increase to
10-20 KT with gusts of 25-35 KT possible, perhaps even stronger in
any embedded thunderstorms.

Outlook...

Sunday Night: No Operational Impact. NO SIG WX.
Monday: No Operational Impact. NO SIG WX.
Monday Night: No Operational Impact. NO SIG WX.
Tuesday: Moderate Operational Impact. Chance of RA...SN.
Tuesday Night: Moderate Operational Impact. Chance of RA.
Wednesday: High Operational Impact. Likely RA.

&&

.HYDROLOGY...
Flood Watch in effect for the western Mohawk Valley, the upper
Hudson, the southern Adirondacks, Lake George Saratoga region and
southern Vermont from today through Sunday. Runoff will result
from a combination of snow melt over the past couple days and
heavy rainfall this afternoon into this evening.

At this time minor flooding of some main stem rivers is expected,
including the upper Mohawk, smaller rivers/streams in areas with
significant snow depth in the southern Adirondacks and southern
Green Mountains of Vermont, and possibly even portions of the upper
Hudson basin. There remains the potential for flooding for areas
south of the watch, but confidence is much lower with less
rainfall and snowmelt expected.  So will continue to mention
the threat in the HWO for possible expansion of the watch if
conditions warrant.

A warm and and moist air will be over the region into this
afternoon. A quick moving, strong cold front is expected to
bring a period of moderate to heavy rainfall this afternoon and
early this evening. Total rainfall forecast of around a half an
inch to around 1.25 inches is forecast through tonight, with
the lowest amounts in the Mid- Hudson Valley and Northwest
Connecticut, and the highest amounts over the western/southern
Adirondacks. The time frame for greatest potential for flooding
is during and after the cold front passage due to heavy
rain/snow melt combination and subsequent runoff. The
precipitation will change to snow quickly behind the front
especially over the mountains, which will slow down the run-off
tonight.

Drier and colder air will filter in behind the cold front for
Sunday, with some lake effect snow possible across the western
Adirondacks and western Mohawk Valley. Strong west to northwest
winds of 15 to 25 mph with strong gusts will also slow down the
runoff later in the 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.

&&

.CLIMATE...
All-time February high temperature records set yesterday at
Albany and Poughkeepsie.

Albany reached 74 degrees, which broke the old all-time
February record of 69 set yesterday. Poughkeepsie reached 73
degrees, which broke the all time February record of 72 set
back in 1954.

Also, Glens Falls set a daily record high yesterday of  59
degrees breaking the old record of 55 degrees set in 1985.

&&

.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...Flood Watch through Sunday evening for NYZ032-033-038>043-
     082>084.
MA...None.
VT...Flood Watch through Sunday evening for VTZ013>015.

&&

$$
SYNOPSIS...Wasula
NEAR TERM...Wasula
SHORT TERM...Wasula
LONG TERM...JPV/JVM
AVIATION...KL/JVM
HYDROLOGY...NAS/Wasula
CLIMATE...WFO ALY


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