Area Forecast Discussion
Issued by NWS Albany, NY

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FXUS61 KALY 191010
AFDALY

AREA FORECAST DISCUSSION
National Weather Service Albany NY
510 AM EST Sat Jan 19 2019

.SYNOPSIS...
High pressure will briefly build in this morning but
clouds will thicken and lower with initially light snow over
spreading the region by the afternoon.  The snow will increase in
intensity and become heavy tonight in advance of a warm front to a
storm system moving out of the Tennessee Valley and then
redeveloping and reaching the Jersey Coast Sunday morning.  Some
mixed precipitation of sleet and freezing rain is possible south of
the Capital Region, as the low pressure system moves towards Long
Island.  The snow and mixed precipitation will diminish Sunday
afternoon, as the cyclone moves into the Gulf of Maine. Dangerously
cold wind chills are expected Sunday night into Monday with frigid
temperatures and blustery winds.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
As of 510 AM EST...

...Winter Storm Warning for Eastern NY and western New England
4 pm today until 4 pm Sunday...

A major winter storm is still on track to impact the forecast
area this afternoon into Sunday. There are some slight
differences in the track of the system with the guidance and the
thermal profiles that we had to expand the mixed pcpn zone
slightly further north, but overall a widespread heavy snowfall
for most of the region is still expected.

A cold front has moved through most of the forecast area this
morning with cold advection still ongoing as temps fall into the
teens and 20s. Some single digit and below zero readings
are possible well to the north. High pressure is building south
of James Bay funneling plenty of cold air into the region
setting the stage for the winter storm. The mid and upper level
flow is relatively flat or zonal over the Northeast, but will
become southwesterly ahead of the potent southern stream trough
ejecting out of the southern Plains and heading towards the
lower MS River Valley. Another northern stream upper level
trough will be digging south/southeast across southern Canada, the
Upper Midwest and northern Great Lakes Region. These two
disturbances will interact and phase Sunday morning for a potent
storm to impact the region.

A weak mid level disturbance in the northern stream coupled
with warm advection ahead of the old cold frontal boundary
will quickly allow clouds to thicken and lower with some light
snow breaking out northwest of the Capital Region initially, and
then expanding across the rest of the region by the late
afternoon into the early evening. Snow amounts will be on the
light side with 1 to 2 inches by nightfall across the western
Adirondacks, western Mohawk Valley, Lake George Region and
northern Catskills. Expect a few tenths of an inch to an inch
from the Capital District south and east. Temps will only be in
the teens north of the Capital Region with 20s from Albany
south and east. A few readings close to 30F are possible over
the mid Hudson Valley and NW CT.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/...
Winter Storm Warning for eastern NY and western New England 4
pm today until 4 pm Sunday

Tonight...the low-level baroclinic zone is very impressive over
the forecast area with strong isentropic lift on the 280-285k
surfaces quickly increases from the south/southwest ahead of
the warm front to low pressure that will move from the TN
Valley towards the OH Valley, and then redevelops east of the
central Appalachians over central and eastern VA between 06Z-
12Z. Strong mid and upper level dynamics will be in place, as
the right entrance region of a H250 150-160 kt jet streak will
be near eastern NY and western New England with strong upper
level divergence. A low-level southeasterly jet of 40-60 kts
will advect in Gulf and Atlantic Moisture. PWATS increase to
1-2+ STD DEVs above normal based on the 00Z GEFS with an H850
low-level +v-anomaly /southerlies/ of 1-2+ STD DEVS above
normal, and the -u-component /easterlies/ anomaly is -2 to -4
STD DEVS above normal. There will likely be orographic
enhancement off the eastern Catskills and the eastern
Adirondacks with this strong anomaly. The low to mid level FGEN
is very impressive with the strong QG lift generated by the
differential thickness advection. We expect the snow to increase
in intensity between 9 pm and midnight south of the Capital
Region, and then quickly expanding northward with snow rates of
1 to 3 inches an hour. CSTAR work indicates that some lateral
translating bands ahead of the warm front are possible. A heavy
snowfall is possible across the entire forecast with 4-8 inches
possible over the Mid-Hudson Valley, and NW CT before some
mixing occurs. Further north, locations could get 8-12+" of
snow overnight. We do think the Capital Region will get into the
heavy snow bands.

We tended to use a blend of thermal profiles from the NAM and
ECMWF. The GFS was the furthest north with the warmer air in the
H850 to H700 layer as it tracks the sfc low further inland to
ern PA by 12Z. We followed the 00Z NAM and EC with the sfc low
getting close the Delmarva Region. Nonetheless, with H850 temps
getting close to 0C to +5C with H925 temps being well below
freezing, we did expand the sleet and freezing rain slightly
further north into the southern Berkshires, Columbia County and
the southeast Catskills. The model soundings profiles fit more
sleet initially with the warm nose less than +3C at over above
H850, but then it lowers in height especially for eastern
Ulster, Dutchess and Litchfield Counties between 09Z-12Z. We
placed 1 to 2 tenths of an inch of ice in these areas. The sleet
and ice will cut down on the snow accums some, but the 00Z
HREFS, NAM and WPC guidance continue to show support up to 12Z
for the 4-8" or 5-10" of snow in these spots.

We can not emphasize how strong the thermal gradient and QG
lift is with this system, as the dendritic growth zone is up
high initially, but the QG omega is so strong with the upper jet
support to reach it, and the secondary jet streak moving up
along the East Coast later in the morning on Sunday. Snow to
liquid ratios will likely be above the climo average from the
Capital Region north in the 15-20:1 range, and 10-15:1 south
before the mixed pcpn transition. Some expect a dry fluffy snow
for most of the region.

Temps will likely only drop into the teens and 20s, with
single digits north of the of the Mohawk Valley and west of the
Capital Region.

Sunday...Low pressure begins to strengthen and organize near
coastal NJ, and we followed a track just south of Long Island
which the EC/NAM showed. The snow will continue to be heavy over
most of the region, and then it appears especially on the NAM
additional mesoscale banding forms in the north/northwest
quadrant of the cyclone in the mid and upper level deformation.
It looks like quasi-stationary bands that eventually pivot are
possible. 1-2+ inch snow rates are possible. The mixed pcpn of
sleet and freezing rain will transition back to snow over the
region in the late morning. The NAM BUFKIT profiles show the
dendritic growth lowering intersecting the strong lift with snow
ratios in the 13-16:1 range. Additional snowfall is possible
through the late morning of 5-10" in some locations. Storm
totals look on track with 10-20" with perhaps 2 feet over the
southern Greens and the northern/easter Catskills. We did favor
locations from the Capital Region/Mohawk Valley northward to be
in the 15-20" range. The Berkshires still look to get 10-18"
with the icy mix lowering totals south of the MA Pike. Also,
some downsloping early on could lower totals over west of the
southern Greens, but the low-level flow will be north to
northeasterly.

The system is a fast mover, since it is an open wave and most
of the snow should be over between noon and 3 pm. The winds will
increase as the cyclone deepens. Expect northwest winds to
increase to 10 to 20 mph with some gusts in the 30-35 mph range
producing some blowing and drifting snow. Temps will fall during
the day as colder air is drawn into the system, and the northern
stream disturbance dives southward across the region. Temps will
fall during the late morning and the afternoon from highs in the
teens and 20s to the single digits and 20s with some below zero
readings over the southern Adirondacks.

The northern stream upper level disturbance dives across the
region with frigid air Sunday night, as H850 temps fall into
the 1 to 2+ STD DEV range colder than normal with H850 temps of
-22C to -30C. The low temps will fall below zero across most of
 the region with zero to 10 below zero readings in many
 locations, and 10 to 15 below or colder over the southern
 Greens, southern Adirondacks, and the eastern Catskills. Wind
 chill readings will start to get dangerous to life
 threateningly cold, especially for the high terrain. Wind chill
 values will be -15 to -40F below zero are possible late Sunday
 night into Monday morning, as wind chill advisories/warnings
 will be needed later in time.

Monday...A frigid day is expected with still nasty winds chills
as the H500 upper level circulation moves across the region. A
strong sfc pressure gradient continues to be over the region
between high pressure over the OH Valley, and low pressure
moving into the Canadian maritimes. Some scattered lake enhanced
snow showers and upslope snow showers are possible. Highs will
only be in the single digits in the valley areas with below zero
readings over the mtns. Wind Chills head lines may be needed for
part of the day.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
The long term period will be quite active with multiple chances for
precipitation, preceded by bitterly cold temperatures.

To start, Monday night will be frigid as low temperatures plummet to
zero degrees in the  mid-Hudson valley to 20 below zero in the
Dacks. This airmass is at least 1 to 2 standard deviations below
normal and is associated with a deep upper trough that is progged to
pull away from the region at the start of this period. Tuesday
should remain dry as ridging both at the surface and upper levels
build into the forecast area. Southerly low level flow will also aid
in moderation of temperatures by Wednesday.

Precipitation chances return on Wednesday as energy both in the
northern and southern streams approach the northeast. In fact, it
looks like multiple pieces of energy in the southern stream will
continue to move along the upper ridge axis towards our area
Wednesday into Thursday. This would result in chances for mainly
snow and perhaps a wintry mix through this time frame. A strong cold
front is then progged to pass through Thursday night, leading to
colder temperatures to end the work week. Behind this frontal
passage, the upper trough deepens, which would lead to another shot
of dangerously cold air by next weekend.

It is worth noting that there are model differences regarding the
southern stream energy and timing of precipitation so stay tuned to
the forecast as models come into better focus.

&&

.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
Light snow showers from earlier this evening have diminished,
resulting in mainly VFR conditions across all TAF sites. MVFR
CIGS will linger at KPSF for a few more hours but should lift to
VFR prior to daybreak. VFR conditions will then prevail through
this morning as mid and high level clouds thicken. A major storm
system then moves into the area, spreading snow across all TAF
sites from west to east. Heaviest snow will likely occur between
22Z/Sat through the end of the forecast period and beyond. This
will lead to flying conditions quickly diminishing to LIFR by
around 00Z-04Z/Sun across the entire region. Expect both low
CIGS and reduced visibilities during this time. At the end of
the forecast period, some sleet and freezing rain may mix into
KPOU with snow continuing at all remaining sites.

Winds will remain from the north to northwest at 5 to 10 kts
through the TAF forecast period.

Outlook...

Sunday Night: Low Operational Impact. Breezy Areas BS.
Martin Luther King Jr Day: Low Operational Impact. Breezy Slight Chance of SHSN.
Monday Night: No Operational Impact. NO SIG WX.
Tuesday: No Operational Impact. NO SIG WX.
Tuesday Night: Moderate Operational Impact. Chance of SN.
Wednesday: Moderate Operational Impact. Likely RA...SN...SLEET.
Wednesday Night: Moderate Operational Impact. Likely SN...SLEET.
Thursday: Moderate Operational Impact. Likely SN.

&&

.HYDROLOGY...
A potent winter storm will impact the region today into Sunday
afternoon. The precipitation type is expected to be mainly
snow, with a wintry mix possible across the southern Berkshires,
southeast Catskills, mid Hudson Valley, southern Taconics, and
northwest Connecticut. Total QPF will generally be in the 1 to
1.5 inch range with some slightly higher amounts over the
southern most basins. This precipitation will not have an
immediate impact on area rivers and streams as it will be
frozen/freezing precipitation.

With the strong southeast flow, the tidal gauge at Poughkeepsie
may hit the caution stage late Sunday morning into the early
afternoon.

Very cold and mainly dry weather is expected Monday into
Tuesday. Another storm with snow or a wintry mix changing to
rain is expected late Tuesday night through Wednesday, although
precip amounts and precip types are still uncertain 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 Storm Warning from 4 PM this afternoon to 4 PM EST
     Sunday for CTZ001-013.
NY...Winter Storm Warning from 4 PM this afternoon to 4 PM EST
     Sunday for NYZ032-033-038>043-047>054-058>061-063>066-
     082>084.
MA...Winter Storm Warning from 4 PM this afternoon to 4 PM EST
     Sunday for MAZ001-025.
VT...Winter Storm Warning from 4 PM this afternoon to 4 PM EST
     Sunday for VTZ013>015.

&&

$$

SYNOPSIS...Wasula
NEAR TERM...Wasula
SHORT TERM...Wasula
LONG TERM...JLV
AVIATION...JLV
HYDROLOGY...Frugis/Wasula


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