Area Forecast Discussion
Issued by NWS Albany, NY

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000
FXUS61 KALY 181556
AFDALY

AREA FORECAST DISCUSSION
National Weather Service Albany NY
1056 AM EST Tue Dec 18 2018

.SYNOPSIS...
Expect partly to mostly sunny skies, cold, and windy
conditions with a few snow showers and flurries in the hill towns
west of the Hudson River for today. Tonight will be mainly clear and
cold with diminishing winds. High pressure will continue to allow
for dry weather Wednesday into Thursday with milder temperatures,
before a storm system brings a widespread rain to the region for
Thursday night into Friday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
As of 1055 AM EST...A few snow showers and flurries continue
this morning west of the Hudson River Valley, especially over
the eastern Catskills. These should diminish by the afternoon
with the lowering subsidence inversion in the north to northwest
flow. Latest satellite picture shows mostly sunny conditions in
the valleys, with a few intervals of sun over the higher
terrain outside of the Hudson and Mohawk Valleys, as the higher
terrain areas will trend to partly/mostly sunny conditions by
the afternoon. Brisk northwest winds of 10-20 mph with a few
gusts in the 25 to 35 mph will continue into the early
afternoon, before diminishing with the sfc high building in.

Previous near term...

Upper level shortwave trough continues to push eastward, as it is
now located over eastern New England and into Atlantic Canada.
Our region continue to be dominated by cold northwest flow on
the backside of this departing upper level disturbance, as 850
hpa temps have dropped down to -15 degrees C thanks to strong
cold advection.

Cyclonic flow, picking up a little bit of lake moisture, has
allowed for some lake-enhanced and upslope snow showers and
flurries this morning, especially across the western
Adirondacks, eastern Catskills and southern Greens. The heavier
lake activity is located over central NY, where the lake fetch
is better with this northwesterly wind direction. As the upper
level trough departs, these lake enhanced and upslope snow
showers will end this morning and clouds will start to break for
some sunshine. Outside of a fresh dusting across the highest
terrain, little to no additional accumulation is expected this
morning.

It will continue to breezy through the morning hours, as good
mixing and a decent pressure gradient continues to allow for
northwest winds gusting over 25 mph at times. These winds will
start to diminish this afternoon, as surface pressure starts
nosing into the area from the Midwest.

With the cold temps aloft, max temps today will be well below
normal and much colder than recent days. Highs will only reach
into the 20s for most spots (teens in the Adirondacks and
southern Greens), and the wind will make it feel even colder.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/...
Dry and quiet weather is expected through the entire short term
period.

High pressure will move from the Ohio Valley towards the mid
Atlantic states for tonight into Wednesday. This will allow for
mainly clear skies and light to calm winds. Good radiational
cooling will allow temps to fall into the teens for much of the
area for tonight (single digits in the Adirondacks). Temps will
be a little milder for Wednesday with 30s for most areas with a
few more clouds around.

As the high pressure area departs off the eastern seaboard, our
region will get into a southwest flow, both at the surface and
aloft. Building heights and warming temps aloft will allow
temperatures to become much milder. Temps will be in the 20s for
Wed night and reach mid 30s to mid 40s for Thursday. Although
Thursday will start off with some sun, clouds will be increasing
through the day, as a large storm system over the Mississippi
Valley and Deep South starts to move towards the area.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Upper level ridge axis along with departing surface high will result
in likely the only dry period in this long term portion of the
forecast, early Thursday evening.  Under an increase in cloud
coverage through the night, temperatures will initially be
seasonable cool, yet, moderation is expected as warm advection gets
underway toward morning in advance of our storm system.

Unsettled weather is then expected to arrive overnight Thursday into
Friday , as the upper low pushes eastward across the Gulf Coast
states, with the large amplitude trough results in considerable
strengthening of S-SE flow aloft along the east coast and I95
corridor into our region. Strong diffluence aloft and low-level
moisture flux will likely result in widespread precipitation to
develop and affect the entire region. Surface temps may start out
around or slightly below freezing in some of the typical sheltered
higher elevation valleys, which could result in a brief period of
freezing rain and sleet at the onset. However, the bulk of the
precip type for most of the area should be plain rain as temps warm
through the 30s by sunrise Friday.

Two main concerns remain with the system are the potential for heavy
rainfall and also strong S-SE winds. The time frame for moderate to
heavy rainfall looks to be late Thursday night through much of
Friday (especially in the morning), as the closed low tracks
northward along or just west of the southern/central Appalachians
and the system`s occluded front only gradually pushes eastward
during this time. The 00Z GEFS is forecast a surge of at least +3 to
+4 STDEV moisture flux at 850 mb (+6 approaching Litchfield County),
with PWAT of around +3 to +4 STDEV and easterly/southerly wind
anomalies of between +3 to +5 STDEV which is an anomaly increase
from the previous run. This points to not only a heavy rain threat,
but also potential for flooding given temps expected to warm into
the 40s to perhaps 50s in some areas, with QPF and snowmelt possibly
both contributing factors to runoff. This will have to be watched,
as some guidance is suggesting 1-2 inches of rainfall with this
system. MMEFS from the GEFS and NAEFS point toward several points
potentially getting to flood stage. The strong S-SE winds may
require wind headline for favored areas that typically mix down
strong wind in this type of flow regime, such as the Taconics,
southern Greens and Berkshires.

The upper low is forecast to move through Friday night into
Saturday, with a trailing cold front associated with the surface low
tracking NE across southern Quebec. GFS/ECMWF are in fairly good
agreement with regards to the synoptic scale features, but differ
with smaller scale details, including QPF (deformation placement).
Once the cold front moves through Saturday morning, ptype will
transition to snow showers in the mountains and rain/snow showers in
valleys based on diurnal trends Saturday through Sunday. Best
chances for additional precip will be across the higher terrain of
the western Adirondacks and southern Greens.  Within the cold
advection, Lake Ontario may become increasingly enhanced with Lake
Effect Snow bands.  Although, difficult to say where and how far
inland these bands will get (climatological favored area of the
western Dacks, western Mohawk Valley and Schoharie Valley).

Zonal flow within a broad upper level trough is expected to set up
for Sunday night into Monday, with possible short wave passage on
Monday may result in some light snow or snow showers.  Additional
lake response is possible as well with marginal instability
parameters.

&&

.AVIATION /16Z TUESDAY THROUGH SATURDAY/...
VFR conditions should prevail through this TAF forecast cycle.
Satellite imagery and surface observations reveal TAF locations are
mostly in the partly cloudy to clear skies.  Lake effect snow and
lower clouds remain to the west-southwest with another batch of
upslope stratus into the southern Greens.  So just diurnally driven
VFR clouds and good visibilities.

The winds will be northwest around 13-18 kt with gusts of 20-30 kt
through much of the next 12 hours, winds will relax toward sunset
at speeds less than 10kts.

Outlook...

Wednesday Night: No Operational Impact. NO SIG WX.
Thursday: No Operational Impact. NO SIG WX.
Thursday Night: High Operational Impact. Definite RA.
Friday: High Operational Impact. Ocnl RA.
Friday Night: High Operational Impact. Likely SHRA.
Saturday: Moderate Operational Impact. Breezy Chance of SHRA.
Saturday Night: No Operational Impact. NO SIG WX.
Sunday: No Operational Impact. NO SIG WX.

&&

.HYDROLOGY...
Dry weather is expected through Thursday. Temperatures will be
very cold for today and tonight, allowing ice to form and
strengthen on area rivers, lakes and ponds. Temperatures will
start to moderate for Wednesday and Thursday, although overnight
lows on Wednesday night will continue to be fairly cold.

A storm system will bring a widespread steady, soaking rainfall
to the region for Thursday night through Friday. There is still
some uncertainty regarding exact amounts, but current guidance
forecasts show an inch or more of rain is possible, with some
enhanced higher amounts across the mountains. This would allow
for at least within bank rises on rivers and streams,
especially considering there may be some snow melt due to mild
temperatures, and strong southeast winds as well. It`s still
unclear if this runoff would be enough to cause any flooding, as
it will ultimately depend on just how much rainfall occurs. The
latest MMEFS guidance shows about a 10% chance of a few river
points reaching flood stage based on GEFS guidance.

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...Frugis/Wasula
NEAR TERM...SND/Frugis/Wasula
SHORT TERM...Frugis
LONG TERM...BGM/JPV
AVIATION...BGM
HYDROLOGY...Frugis


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