Area Forecast Discussion
Issued by NWS Albany, NY

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FXUS61 KALY 050226
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
926 PM EST Sun Dec 4 2016

.SYNOPSIS...
A warm front will lift northward tonight and spread light snow
across the region overnight into Monday morning. This system will
lift away from the region Monday night as high pressure returns
briefly for Tuesday. Then another warm front approaches Tuesday
night into Wednesday with another round of light snow for most of
the region.

&&

.NEAR TERM /THROUGH MONDAY/...
Leading edge of solid clouds spreading north ands east and areas
along and north of the Mohawk Valley into southern VT have cooled
into the lowwer to mid 20s already. Once the cloud cover spreads
over the entire region, temperatures will hold steady and maybe
rise a degree or two toward daybreak. The snow is reaching the
ground around the PA/OH border as area 00Z soundings show the dry
layer aloft that is evaporating snow aloft over central/western
NY/PA. The dry layer should saturate through the night as the
leading edge of the snow heads east. So, snow should begin over
most areas before and by daybreak. Some minor adjustments to the
cloud cover, timing of the onset of snow and temperatures based on
current data and trends.

Prev Disc...A rather large swath of precipitation per the
national radar mosaic extending from the central Great Lakes
Region, Mid West down into the southeast CONUS. There is a notable
break across the Ohio River Valley at this time. H2O vapor imagery
does show a rather deep moisture entrainment around the cut-off
upper low over northern Mexico advancing northeast. Meanwhile,
upper trough progressing through the mid and upper Mississippi
River Valley is beginning to show signs of becoming negatively
tilted. As the evening progresses, good ageostrophic vertical
response along with strong isentropic lift on the 280-285K surface
should fill in the radar gap over the Ohio Valley and spread
northeast overnight. Per the RAP13/HRRR, the onset of the light
snow will hit our southwest portion of the CWA around 06Z then
spread into the heart of the region between 08-10z then quickly
across western New England counties shortly thereafter. This will
make for a tricky morning commute across the entire region.
Referring back to the isentropic analysis, still advecting up to 3
g/kg on the surface with low CPD/s with strong lift and
ageostrophic response. Could a brief period of moderate snow
between 09-15Z timeframe with total accumulations of generally 1-2
inches with near 3 inches for the Adirondacks. Then later Monday
morning, we begin to lose some of the mid and higher level
moisture as we transition toward very light rain/snow showers as
boundary temperatures moderate at or above freezing. So additional
accumulations will be light at best. Overnight lows will generally
be in the 20s and highs Monday range from the lower 30s across the
Dacks and higher terrain of the southern Greens to near 45F for
the Mid Hudson Valley.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
Minor lake response Monday evening with marginal delta t/s per
BUFKIT profiles with lowering inversion heights as building
heights and anticyclone at the surface quickly build into the
region. So clouds will slowly dissipate from southwest to
Northeast Monday night and depending on how quickly these clouds
dissipate will determine just how cold we get with fresh snow
coverage. At this time, we will shade just below MOS guidance.

Tuesday, high confidence of a quiet period of weather between
waves as the ridge aloft and surface reflection transverses the
region from southwest to northeast. However, clouds will be in the
increase as the aforementioned upper low over northern Mexico
becomes entrained with the digging upstream trough and tracks
northeastward toward the area. Highs Tuesday mainly into the 30s.

Those clouds will thicken and lower once again Tuesday night with
additional light snow expected. Smilier to the event tonight into
Monday morning, overrunning situation is expected as thermal
column looks to support mainly light snow. The isentropic analysis
is not as strong and the upper support is a bit weaker as the flow
is rather confluent across the Mid West and Northeast. Additional
accumulations of 1-3 inches are expected at this time with a start
time late in the evening southwest of Albany to across the
remainder of the region overnight.

Wednesday this system quickly departs and mid levels quickly dry
off, yet, upper levels remain quite moist. We will diminish PoPs
through the daylight hours and slow down any clearing. With
additional snow pack, we will keep temperatures a little cooler
and closer to the blended approach.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Much colder temperatures will be making its way into the region
during the extended period, with several additional opportunities
for precipitation as well.

In the wake of the departing surface wave on Wednesday, weak high
pressure will pass over the region on Wednesday night.  This should
allow for mainly dry conditions. Lows will fall into the mid 20s to
lower 30s.

Surface cold front, which will be the leading edge of the much
colder air mass, will be passing across the region on Thursday. The
models continue to show differences, as the 12Z ECMWF and a few 12Z
GEFS members continue to show a wave along this boundary bringing a
period of more steady precipitation. Otherwise, just some rain and
snow showers (becoming predominately snow showers as colder air
works into the region) is expected along the frontal boundary on
Thursday.  If the wave does develop along the boundary, then a few
additional inches of snowfall would be possible across the
region.  Highs will generally be in the 30s for Thursday.

Behind the front, much colder and windy weather will move in for the
remainder of the extended period.  Lake-effect snow bands will
organize off the eastern Great Lakes, with some accumulation
possible for the western Adirondacks, western Mohawk Valley,
Schoharie County and eastern Catskills, depending on the exact band
orientation for Friday into Saturday. Additional snow showers and
flurries will be possible further east as well.  High temps will
only reach the mid 20s to mid 30s for Friday through Sunday with
blustery conditions. Lows will fall into the teens and 20s across
the whole area.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Some high clouds beginning to spread across the region this evening
but the deeper cloud cover and moisture is close, into PA and
central/western NY.  Precipitation is lagging quite a bit behind,
with the leading edge of snow into far western NY and
western/central PA.  Based on radar trends and mesoscale guidance
the leading edge of the snow will reach the TAF sites between 08Z-
10Z, so indicating 09Z until probabilities can be assessed for any
development of snow overhead prior to the arrival of the leading
edge of the current area of snow.

Once the snow arrives, ceilings will drop to MVFR levels and
predominant visibilities around 2-3 SM.  There will be some
intervals of bursts of heavier snow between 12Z-16Z with IFR
visibilities and ceilings, and a possible mix with rain at KALB and
KPOU. The snow and/or mix is expected to taper off between 16Z-19Z,
then visibilities become VFR but ceilings will be slow to lift
through MVFR trending just into VFR at KALB and KPOU but likely
holding in the MVFR range at KGFL and KPSF.

Light winds through much of tonight will become southeast to south
at less than 5 Kt.  South winds at less than 10 kt Monday morning
become west at less that 10 Kt Monday afternoon.

Outlook...

Monday Night: No Operational Impact. NO SIG WX.
Tuesday: Low Operational Impact. Slight Chance of RA...SN.
Tuesday Night: High Operational Impact. Likely RA...SN.
Wednesday: Moderate Operational Impact. Chance of
SHRA...SHSN...RA...SN.
Wednesday Night: Moderate Operational Impact. Chance of SHSN.
Thursday: Moderate Operational Impact. Chance of RA...SN.

&&

.HYDROLOGY...
River levels will remain nearly steady or continue to slowly
recede through the next several days.

This will be an active week with a few waves impacting the region.
Most of the precipitation will fall as the form of snow with QPF
values one tenth to one quarter of an inch Sunday night into
Monday then again Tuesday night into Wednesday with slightly
higher values up too one half inch QPF. Thursday into Friday more
chances for wintry precipitation.

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.
NY...None.
MA...None.
VT...None.

&&

$$
SYNOPSIS...BGM
NEAR TERM...BGM/NAS
SHORT TERM...BGM
LONG TERM...Frugis
AVIATION...NAS
HYDROLOGY...BGM/11



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