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FXUS61 KALY 180528
AFDALY

AREA FORECAST DISCUSSION
National Weather Service Albany NY
1228 AM EST Mon Feb 18 2019

.SYNOPSIS...
Low pressure will approach from the Ohio Valley tonight bringing
snow to eastern New York and western New England. The storm
system will redevelop east of New Jersey and pass south of Long
Island tomorrow morning into the afternoon bringing a light to
moderate snow accumulation across the area. The snow will taper
to scattered snow showers and flurries by the late afternoon
into the early evening, as high pressure will bring mainly dry
and seasonably cold temperatures Monday night through Tuesday
before another storm system arrives late Wednesday into
Thursday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Winter Weather Advisory remains in effect through 4 pm EST
Monday for the Mohawk Valley, Greater Capital Region,
Helderbergs, mid Hudson Valley, Taconics, eastern Catskills,
Berkshires and Litchfield County, Connecticut...

As of 1230 AM EST, bands of light to moderate snow have expanded
north and east well into the Mohawk Valley, Saratoga region and
southern VT, and points south and west. Coverage remains
somewhat patchy, with distinct breaks in the snowfall between
bands. Snowfall rates approached 1 inch/hour across some
southern areas, from the SE Catskills east into the Litchfield
Hills, while generally remaining between 0.5-1 inch/hour within
heavier bandlets elsewhere.

We expect the snow to continue expanding northward into the
southern Adirondacks over the next 1-3 hours, with periods of
light to moderate snow expected elsewhere through daybreak.

Otherwise, much of the Great Lakes and Northeast Region is
located near a mid and upper level jet confluent region. A
strong mid and upper level trough is centered over the central
CONUS with a closed northern stream H500 circulation weakening
and opening up, while a southern stream short-wave lifts
northeast from the TN Valley. This disturbance shears out, but
some good over running snowfall sets up with plenty of low-
level cold air in place and the isentropic lift increasing on
the 285K sfc with a modest low- level jet ahead of the primary
sfc low and its warm front/inverted sfc trough.

The forecast area will be located near the left exit region of
nearly a 125 kt H500 jet streak. Some warm advection pcpn
should be commencing between 9 pm and midnight initially south
and west of the Capital Region, and then overspreading the
entire area. It will take a little time for column to saturate.
The low-level H850-700 FGEN strengthens overnight (especially on
the NAM) as the primary low moves toward western/central PA/NY,
and then redevelops east/southeast of NJ. Snowfall rates could
reach a half to three quarters of an inch an hour between
roughly midnight and 6 am based on the latest 12 HREFs. We
increased the POPs to categorical values at this time. We
followed the 12Z HREFS on the increased rates during this time
frame. Overall, a couple of inches of snowfall should be on the
ground in most locations (the one exception may be portions of
the southern Adirondacks, and portions of the Lake George
Region) by daybreak with 2 to 4 inches from the Capital
Region/Mohawk Valley southward. We leaned fairly close to the
WPC QPF, which was in line more with the 12Z NAM/ECMWF/GFS. The
GFS tended to be the lightest.

PWATS are not highly anomalous with this system with the latest
GEFS grazing southern areas with slighter greater than normal
values. The H850 low-level jet is not highly anomalous with the
+v-component wind anomalies /southerlies/ increasing to +1 to
+2 STD DEVs above normal transporting some gulf or Atlantic
moisture into the region. The 12Z GFS/NAM indicate a
southwesterly LLJ of 25-30 kts overnight. The pcpn efficiency is
not expected to be dramatic as the dendritic growth zone in the
remains high up, not intersecting the upward vertical motion or
omega well. Lows tonight will likely be due to wet bulbing with
lows in the teens north and west of the Capital Region, and
lower to mid 20s to the south and east.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH TUESDAY NIGHT/...
Winter Weather Advisory until 4 pm EST MON from the Mohawk
Valley, Greater Capital Region, Helderbergs, mid Hudson Valley,
Taconics, eastern Catskills, Berkshires and Litchfield County,
Connecticut...

Tomorrow...The snow will be continuing through the limited
holiday morning commute with some snow covered slick roads, and
reduced visibilities. There are some indications from the
guidance, that a dry slot may get close to the southeast
Catskills, and the mid- Hudson Valley after daybreak, as the
pcpn intensity may let up. Also, the NAM BUFKIT model soundings
are indicating that we could lose the ice nuclei in the clouds
after 12Z near KPOU. The best isentropic lift and low-level
FGEN shifts east to northeast of the region. There could be a
brief period of snow mixing with or changing to freezing rain
near the I-84 corridor, so we have a light glaze of ice of a
coating to a hundredth in the forecast for southern Dutchess,
Ulster, and Litchfield Counties.

Periods of light snow should continue further north due to an
inverted sfc trough northwest of the secondary coastal wave
forming near southern NJ and passing south of Long Island. The
mid and upper level jet dynamics will also remain favorable for
the snow persisting into the early afternoon coupled with some
vorticity advection associated with the northern stream short-
wave. Total QPF came up slightly into the 0.20-0.40" range and
we increased snow amounts a couple of inches. We are expecting 3
to 6 inches of snow in the advisory area. The highest totals
will likely be around 6 inches in the eastern Catskills,
Helderbergs, and a few locations in the Berkshires. Not
widespread enough for a warning. Further north, we have 2 to 4"
in the southern Adirondacks, Lake George/Northern Saratoga
Region, and southern VT. A few locations in the southern Greens
could get around 4", but it was not widespread enough for an
advisory. We used snow to liquid ratios a little above climo in
the 12-17:1 range. If amounts edge up further north, then the
advisory may have to be expanded later. The 12Z HREFS mean 24-hr
snowfall went kind of high in the 6-8" or so range in parts of
the Helderbergs, eastern Catskills, Schoharie Valley, and the
western Mohawk Valley. We think the low end of the range could
be hit, but based on the track of the secondary low and the
limited moisture this seemed kind of high. We also extended the
end time for the advisory to 4 pm as snow in the the mid/upper
deformation zone could linger a bit between 1-4 pm especially
from the Capital Region/Taconics eastward. If the snow ends
sooner, then it can be canceled. High temps will range from the
mid and upper 20s north and west of the Capital Region to the
lower to mid 30s mainly from the Tri Cities south and east.

Monday night...Low pressure moves further into the North
Atlantic south and east of Nova Scotia. The H500 trough axis
moves down stream, as well as a sfc trough. Cold advection
occurs overnight with H850 temps falling to -13C to -17C from
the Capital Region northwest, and -9C to -13C south and east.
The skies should become partly cloudy to mostly clear. Some
narrow multibands of lake effect snow may graze the western
Mohawk Valley, northern Catskills, and western Adirondacks in
the northwest flow. Lows will be in the single digits to lower
teens, though some below zero readings are possible over the
southern Adirondacks. The northwest winds coupled with the cold
temps may produce wind chills below zero over the higher
terrain.

Tuesday-Tuesday Night...A broad sfc anticyclone builds eastward
from the northern Plains and the Upper Midwest eastward across
the Great Lakes Region into the Northeast. Some lingering lake
effect snow showers or flurries may persist near the western
fringe of the forecast area, near the southern Herkimer county
in the western Mohawk Valley. Any snow accumulation would be
very light. The lowering subsidence inversion should end the
activity by the afternoon, as it will be partly to mostly sunny
and cold as highs will be in the teens to lower 20s over the
mtns, and mainly 20s in the valleys though a few lower 30s are
possible over the mid Hudson Valley. Tue night, ideal
radiational cooling may occur with clear/mostly clear skies,
light to calm winds, and fresh snow cover with the sfc ridge
building in. Lows may fall to zero to 5 below over the southern
Adirondacks, and southern Greens, single digits over the rest of
the forecast area, except the mid Hudson Valley, southern
Taconics, and NW CT where some lower teens are possible.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
This period will be front and back-loaded with wintry conditions,
with a period of dry weather in between. Wednesday will start
off chilly, as high pressure gives way to a low pressure complex
from the Deep South. This system works its way rapidly up into
the northeast, quickly spreading cloudiness across the region on
Wednesday, with snow likely by Wednesday evening. The exact
evolution of this system will decide how much snow our forecast
area gets, and whether it will end as rain showers on Thursday.
For the past 48 hours, the GFS has been fairly consistent, and
highs on Thursday should reach well into the 40s from the Lake
George- Saratoga Region on south. Right now, 2 to 4 inches of
total snow looks to be what we can expect out of this system
before any daytime changeover to showers on Thursday.

Things dry out and skies brighten to end the work week, but
temperatures should be decent, with highs running from around 30
degrees in the northern high peaks...to the mid 40s across the
Mid- Hudson Valley. The weekend will be even warmer as the next
system also lifts out of the Deep South. Snow or mixed
precipitation overspreads our entire area Saturday night, with
most locations going over to rain on Sunday.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
Periods of light snow will affect all TAF sites through this morning
as a weak area of low pressure tracks south of the region. There is
not much deep moisture with this system, so the snow will be light
with intermittent periods of near moderate snow.

Ceilings and visibilities will be predominantly MVFR but
visibilities will lower to IFR in the bursts of near moderate snow
and brief periods of ceilings just under 1000 feet are likely. Snow
will end by 19Z and ceilings will lift to VFR at KALB and KPOU later
Monday afternoon while lifting to around 3000 feet at KGFL and KPSF.

Light winds will become north to northwest between daybreak and noon
and then increase to 10-15 Kt with gusts 20-25 Kt through Monday
afternoon.

Outlook...

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

&&

.HYDROLOGY...
A storm system will bring accumulating light to moderate snowfall
tonight into tomorrow with total liquid equivalents of two to
four tenths of an inch.

Another seasonably cold and dry stretch is likely Monday night
through most of the day Wednesday. Some thickening of ice is
possible on the main stem rivers, lakes and streams.

Another storm system is expected late Wednesday into Thursday
and this storm will bring snow changing to a wintry mix and/or
rain to the region. As of right now, about a quarter to half
inch of liquid equivalent is expected.

Drier weather looks to return late in the week into next weekend
with slightly above normal temps, but overnight lows should
fall below freezing with any snow melt refreezing. No
significant warm-ups or heavy precipitation events are expected
into next weekend.

As a result, river and stream levels will generally hold steady
through at least the end of next week and widespread snow melt,
ice movement or flooding is not expected at this time.

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...Winter Weather Advisory until 4 PM EST this afternoon for
CTZ001-013.
NY...Winter Weather Advisory until 4 PM EST this afternoon for
NYZ038>040-047>054-058>061-063>066-082.
MA...Winter Weather Advisory until 4 PM EST this afternoon for
MAZ001-025.
VT...None.

&&

$$
SYNOPSIS...Wasula
NEAR TERM...KL/JPV/Wasula
SHORT TERM...Wasula
LONG TERM...ELH
AVIATION...NAS/JPV
HYDROLOGY...Frugis/Wasula
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