Area Forecast Discussion
Issued by NWS Albany, NY

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000
FXUS61 KALY 230039
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
739 PM EST Thu Feb 22 2018

.SYNOPSIS...
Snowfall will end this evening with partial clearing tonight.
Another system will bring valley rain and higher elevation
wintry mixed precipitation Friday. Milder and mainly dry on
Saturday, but another round of mixed precipitation is likely
Saturday night into Sunday.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
As of 6 pm, have allowed the winter weather advisory to expire
as snowfall has exited the area. May see some partial clearing
from north to south tonight as high pressure briefly expands
across the area, though there may end up being some lower- level
moisture that doesn`t get scoured out. Lows expected to be in
the mid- teens to mid- 20s, still a bit above normal.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY/...
Winter Weather Advisory for wintry mixed precipitation in
effect for the eastern Catskills and southern Adirondacks Friday
morning into Friday evening, and for the southern Greens from
Friday afternoon into Friday evening...

Friday, the high shifts eastward over Nova Scotia while the low
level jet magnitudes increase. This will result in a renewed round
of moisture transport and isentropic lift, with precipitation
becoming likely by the afternoon. We`ll start out the day cold
with early morning temps in the teens and 20s, so some mixed
precipitation is likely especially at the onset. The high is not
in an ideal location to keep cold air locked in place, at least
in the north/south valleys below 1000 feet, so currently do not
expect much in the way of wintry accumulation there, as temps
aloft and at the surface warm enough to support mainly rain as
the p-type. Over the higher elevations of the Catskills and
Adirondacks, thermal profiles support more in the way of a
mixture of sleet and freezing rain for a good portion of the
day. This will especially be true over the Adirondacks where a
fairly deep snow pack still exists, and it has proven very
difficult to scour out the cold air in similar circumstances.
Still considerable uncertainty with respect to how much
precipitation falls as sleet vs freezing rain, with NAM forecast
soundings showing a cold layer between 925 and 975 mb, but
there is enough confidence in freezing rain to support the
issuance of winter weather advisories for the terrain above 1000
feet. This is supported by the 12Z HREF, which has mainly
RA/FZRA across our forecast area Friday into Friday night.

Low-level winds veer Friday night spelling a gradual end to the
isentropic lift, with weak high pressure expanding in late. A
good deal of low-level moisture will still be around, so could
see a continuation of light spotty showers or drizzle.
Temperatures Friday night will remain fairly steady or perhaps
rise somewhat, remaining mainly in the 30s.

Saturday, low-level winds will become west-northwesterly and
usher in slightly drier air as weak high pressure expands into
the area. We`ll start the day fairly mild, and depending on the
amount of clearing that occurs, we could be looking at a fairly
mild day. Clouds increase late in the day ahead of the next
system, and we could even see light precipitation beginning in
the evening over southern zones as yet another round of
isentropic lift begins.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
We start the long term period with a complex wintry mix event
Saturday night into Sunday followed by large scale ridging for a
period during the upcoming work week before the pattern turns active
late in the week.

There is good model consensus on the overall pattern leading into
the wintry mix event for Saturday night/Sunday with a 1030-1035mb
high positioned in eastern Quebec, an amplifying shortwave embedded
in a longwave trough across the Central Plains and high pressure
placed off the Florida coast. High pressure in Quebec ahead of our
developing winter storm means south/southeast flow should yield
seasonable to slightly above normal temperatures for eastern
NY/western New England Saturday night. As our shortwave trough
traverses the Midwest and enters the northern Great Lakes, it looks
to become negatively titled allowing the low at the surface to
strengthen. In addition, we will be monitoring a strengthening 160kt
jet over the Ohio Valley that will lead to plenty of upper level
divergence in southern Canada that should provide additional
intensification of our low. In fact, by 12z Sunday, there is good
model agreement that our system will reach its mature stage as it
becomes nearly vertically stacked and closed off at nearly all
levels.

Due to the strength of our low, there will be a good amount of warm
air advection associated with the system`s warm front that will lead
to precipitation from southwest to northeast overnight Saturday into
Sunday here in eastern NY/western New England. The antecedent high
could make precipitation struggle to reach the surface initially as
dew points at the start may be in the 20s through the area. Once the
column saturates, initial precipitation may fall as rain outside of
the higher terrain but cold air damming and evaporative cooling from
widespread precipitation should quickly cool the column and allow
precipitation to transition to a wintry mix by Sunday morning. There
will be plenty of moisture associated with this disturbance thanks
to high pressure positioned off the Florida coast and 160kt jet
pumping tropical moisture into the Northeast. Thus, dynamically
cooling should be quick and should keep the column cool through
at least the morning hours.

Current SREF and GEFS plumes show probability of nearly all precip
types through the daytime Sunday and although rain has the high
probability, experience tells us cold air is hard to scour out in
these situations and warm fronts are very slow to progress through
our area. Thus, have kept the potential for wintry mix in our
current forecast through 18z Sunday. After 18z, the 850mb jet should
strength up to 50kts which could help mix the warmer air aloft down
through the boundary layer. While we show mainly rain in the current
update for Sunday afternoon, this is a low confidence forecast and I
would not be surprised if we trend cooling in future updates. The
latest model suite also shows a secondary low developing in southern
New England Sunday afternoon which would keep the warm front
suppressed south and east of our CWA and the cold air wedge
firmly in place through the daytime. The system`s cold front
should finally move through Sunday evening, ending the
precipitation from west to east.

High pressure noses into the Northeast from the Ohio Valley in the
wake of this system which would lead to breezy conditions Monday
with temperatures slightly above normal in the upper 30s to mid 40s.
A secondary cold front associated with the 500mb trough axis should
then arrive by 00z Tuesday with colder air following for Monday
night. Large scale ridging associated with high pressure over the
Gulf Coast States should lead to quiet conditions for the mid-week
with temperatures remaining near to slightly above normal.

However, the pattern turns active for the second half of the work
week as shortwave troughs from the Great Lakes usher in additional
storm threats into the Northeast.

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
Snow has moved east of the TAF sites and expect some clearing
overnight with VFR conditions and light winds. Clouds will
increase and lower ahead of the next system on Friday with rain
showers arriving at POU / ALB / PSF during the early afternoon.
At GFL enough cold air may be in place so that the precipitation
starts as a light sleet or freezing rain, before transitioning
to rain Friday evening. Winds will become south-southeast at 5
to 10 kts Friday afternoon.

Outlook...

Friday Night: Moderate Operational Impact. Chance of SHRA.
Saturday: No Operational Impact. NO SIG WX.
Saturday Night: High Operational Impact. Likely SHRA...SHSN.
Sunday: High Operational Impact. Definite SHRA...SHSN.
Sunday Night: Low Operational Impact. Slight Chance of SHRA...SHSN.
Monday: No Operational Impact. NO SIG WX.
Monday Night: No Operational Impact. NO SIG WX.
Tuesday: No Operational Impact. NO SIG WX.

&&

.HYDROLOGY...
Main hydrologic concern continues to be flooding due to ice jams
along the Mohawk River in central Schenectady, southern Saratoga and
northeast Albany counties, as well as the Hudson River in a small
area of central Warren county. Flood warnings or Flood Advisories
are in place for these areas. Refer to the flood statements for
additional details. The main larger ice jam has broken into
small pieces on the Mohawk River, but are scattered between Lock
9 and Cohoes Falls. Ice jams appear to be settling in place,
but sudden movement will still be possible tonight into Friday
which could cause fluctuations in water levels.

Outside of ice jam areas, snow will end this evening, with a quarter
to half inch of QPF across the southern 2/3 of the area. Additional
wintry precipitation is expected Friday into the weekend, with rain
as well. Wintry precip including freezing rain, is expected for
mainly high elevations areas. Current forecasts call for around a
three quarters of an inch to over an inch of liquid equivalent
precipitation during this time, with the greatest amounts west of
the Hudson Valley. Runoff from this precipitation may result in
additional river rises. Temperatures are expected to remain above
normal during this time, but not as warm as earlier this week.

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...Winter Weather Advisory from 9 AM to 10 PM EST Friday for
     NYZ033-041-042-047-058-063-082-083.
MA...None.
VT...Winter Weather Advisory from noon to 10 PM EST Friday for
     VTZ013-014.

&&

$$
SYNOPSIS...Thompson
NEAR TERM...Thompson
SHORT TERM...Thompson
LONG TERM...Speciale
AVIATION...MSE/JPV
HYDROLOGY...JPV


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