Area Forecast Discussion
Issued by NWS Albany, NY

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FXUS61 KALY 102340
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
640 PM EST Sun Dec 10 2017

.SYNOPSIS...
Lake effect snow will impact portions of the western
Adirondacks tonight. Fair weather is expected for Monday with a
widespread snowfall expected for Monday night and Tuesday as
another storm system approaches from the west.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
As of 640 PM EST...Winter Weather Advisory for lake effect snow
remains in effect tonight for northern Herkimer and western
Hamilton counties.

Broad upper level through continue to be situated over the Great
Lakes and Northeast US. With w-sw flow coming parallel over the
long axis of Lake Ontario, a single concentrated band of lake
effect snow is ongoing. The core of this band is just west and
north of northern Herkimer County. However, 3km HRRR and NAM
suggests this band will oscillate back and forth across northern
Herkimer County this evening into tonight, especially from Route
28 on northward. Looking for an additional 2 to 4 inches of
snow before all is said and done in that area. This will bring
total accumulations to 3 to 6 inches for the lake-effect area.

Elsewhere, skies are partly to mostly cloudy. A few additional
lake enhanced light snow showers and flurries are ongoing across
the western Mohawk Valley, but little to no accumulation is
occurring with this activity. It should remain fairly quiet
through the overnight hours, with some batches of leftover
lake-effect clouds moving across the region.

Temperatures will be near normal overnight with teens higher
elevations to 20s lower elsewhere.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
...Winter Storm Watch posted for northern half of forecast
area...

Weak high pressure will build in for Monday. There could be
some light snow showers across the northwest portion of the area
as a weak cold front settles south. Otherwise, expect some
sunshine particularly in the afternoon. Temperatures will be a
few degrees below normal.

Clouds will increase later Monday into Monday night ahead of the
next storm system. Models are in good agreement that low
pressure will track across into the northern portion of the
forecast area on Tuesday. Secondary development will occur off
the Long Island coast with the primary low tracking into Maine.
NAM and GFS in good agreement on QPF with upwards of 0.75 inch
total forecast in the max zone running along a Herkimer-Fulton-
Saratoga- Windham line. The Euro comes in somewhat lighter in
this region. Ascent from this storm looks to be driven by warm
advection with particularly impressive omega noted on the
280K/285K surfaces. Other parameters such as dendritic growth
zone and FGEN forcing are not overly impressive. That being
said, the isentropic lift is supportive of the QPF totals.
Recent research here at the office has focused on using our GIS
tool GAZPACHO to offer guidance on QPF biased forecasting in
various flow regimes. For the upcoming storm, we are looking at
925mb winds southeast around 30 knots. Research shows that in
this regime we have typically underestimated snowfall in favored
upslope regions of the Adirondacks and Greens. Putting it all
together we are looking for 8 to 12 inches in the watch area
with amounts trending lower away from watch zones. This would
imply advisory criteria snowfall for much of the remainder of
the area. Across the mid Hudson valley temperatures may warm
enough to bring some rain into the picture holding down totals.
High temperatures will range from mid 20s north to upper 30s
south.

In the wake of the system cold and blustery conditions set in
for Tuesday night and Wednesday. Lows on Tuesday night are in
the single digits to mid 20s. Highs on Wednesday will barely
budge from morning lows. These temperatures combined with gusty
winds of 15 to 25 mph will yield wind chill values from minus
10 degrees to the teens.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Our active and wintry pattern continues into the extend forecast as
a longwave trough persist over the Eastern Conus. While we will be
monitoring numerous shortwave rotating into the Northeast which will
present a number of snow threats, model agreement remains poor on
exact timing, placement and intensity of each shortwave. However, we
have higher confidence in a period of below normal temperatures
impacting eastern NY/western New England Thursday - Friday.

We start off the extended Wednesday night with the potent, closed
upper level trough responsible for the snow event Tuesday positioned
east of our area. Northwest flow behind this trough should lead to
cold air advection and the start of cold temperatures in our region.
H850 isotherms fall to -15C to 18C and low temperatures are expected
to fall into the teens in the valley and single digits elsewhere.
Such cold air flowing over the relatively warm lakes could lead to
continued lake effect snow, especially in the Adirondacks and Mohawk
Valley.

High pressure tries to nose in from Canada during the day Thursday
and the change in flow regime plus subsidence should suppress the
lake effect snow bands. The incoming high could lead to a slight
pressure gradient leading to somewhat breezy winds. Thus, wind
chills Wed night into Thursday could fall below zero, especially in
the hill towns/elevations. Wind Chills in the Adirondacks could even
fall into the negative teens so we`ll be keeping a close eye if any
wind chill advisory headlines will be needed.

Chilly temperatures remain in placement Thursday - Friday with high
temperatures likely only rising into the 20s and lows in the
teens/single digits which is about 10 - 15 degrees below normal for
mid - December. Our next shortwave exits the Great Lakes and heads
into our area bringing the next threat for snow Friday - Saturday.
While some moisture is associated with this disturbance, poor model
agreement remains on placement, timing and intensity giving us a low
confidence forecast on snow potential. However, we increased POPs to
slight chance and even chance to reflect this threat.

Height rising are possible in the wake of this trough leading to the
flow regime shifting to W or even SW with temperatures rebounding
closer to normal heading into the weekend. However, additional
shortwaves are expected to traverse the Northeast late in the
weekend into early next week which will once again bring additional
threats for snow. Moisture look lackluster at this time so any
threats should be of the lighter variety.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
VFR conditions are expected overnight and into the day on
Monday. With an upper level trough overhead and lake-effect snow
upstream of the area, there will continue to bkn-ovc cigs around
5-8 kft, esp for KGFL/KALB. Otherwise, light s-sw winds of
around 5 kts is expected through the overnight hours with no
precipitation.

On Monday, there will be sct-bkn cigs around 4-6 kft with no
precip through the day. Westerly winds will be around 10 kts.
Some mid level clouds may increase towards evening as the next
storm system approaches from the west.

Outlook...

Monday Night: High Operational Impact. Definite SN.
Tuesday: High Operational Impact. Definite SN.
Tuesday Night: Low Operational Impact. Slight Chance of SHSN.
Wednesday: Moderate Operational Impact. Breezy Chance of SHSN.
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 SHSN.

&&

.HYDROLOGY...
No hydrologic problems are expected through the week ahead.

Cold weather with periods of snow and snow showers are forecast.
Ice will form and thicken on area lakes and rivers and some
river gauges may start to show erroneous readings due to ice by
the end of the 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 Storm Watch from late Monday night through late Tuesday
     night for NYZ032-033-038-039-041>043-050-082>084.
     Winter Weather Advisory until 7 AM EST Monday for NYZ032-033.
MA...None.
VT...Winter Storm Watch from late Monday night through late Tuesday
     night for VTZ013>015.

&&

$$
SYNOPSIS...OKeefe
NEAR TERM...Frugis/OKeefe
SHORT TERM...OKeefe
LONG TERM...Speciale
AVIATION...Frugis
HYDROLOGY...OKeefe


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