Albany Office Forecast Discussion

008
FXUS61 KALY 160103
AFDALY

AREA FORECAST DISCUSSION
National Weather Service Albany NY
803 PM EST Tue Jan 15 2019

.SYNOPSIS...
A strong cold front will sweep across the area Wednesday
bringing chances for snow showers, mainly across the higher
terrain. A light snowfall is expected Thursday night into
Friday and a potent winter storm is expected to impact the
region over the holiday weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 400 PM EST...Weak mid level impulse was tracking off the
New England coastline this evening. Ample cloud coverage was in
place across most of the region with breaks into the mid-Hudson
Valley and portions of NW CT. Some minor lake moisture
contributions were underway downwind of Lake Ontario where some
flurries/light- snow/freezing drizzle. A closer look at area
soundings and enhanced IR Satellite imagery reveals the top of
the moisture layer does not touch favorable ice nuclei formation
hence the freezing drizzle potential into the Dacks. The
remainder of the region should be dry with variable cloud
coverage with lows ranging from the teens to lower-mid 20s.

Wednesday, potent upper jet and surface low across Canada will
bring a strong cold front into the region Wednesday. Overall
depth of moisture remains less than ideal for deeper convective
potential for snow squalls, but can not ignore the steep low
level lapse rates and some surface based CAPE where an isolated
squall could occur (mainly to the west and north of Albany).
Otherwise, considerable cloud coverage will once again be
problematic along with increasing winds through the afternoon
hours, especially with frontal passage. Momentum transfer
suggest wind gusts of 30-40 MPH.  Highs will range from 35-40F
for valley locations to 25-30F for the higher terrain.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As surface high builds in the wake of the strong cold front, a
very chilly air mass will settle across the region under mainly
clear skies and diminishing winds Wednesday night. Seems near
ideal radiational cooling as overnight lows should range from
below 0 across the Dacks to near 15F for the mid-Hudson Valley
and NW CT.

Surface high slides across and east of the region Thursday through
Thursday evening. A tranquil period of weather with light winds
and chilly temperatures as H850 temperatures remain below -10C.
Highs Thursday afternoon range from mid teens to mid 20s.

A short wave breaks free from the system moving ashore across
Southern California and quickly tracks east-northeast between
I70/I80 corridors. Broad isentropic lift commences during the
overnight hours Thursday with thickening clouds and light snow
evolving from southwest to northeast. Some question with the
southwest flow regime and how far north the snow moves into the
region as mesoscale impacts from downsloping may limit snowfall
potential into the Capital Region with the higher terrain the
most susceptible to accumulating snow. The ECMWF seems to be in
the middle ground as we will forecast around 3" of snow leading
into the morning commute Friday. This too is supported with
specific humidity values of 1-2 g/kg advecting northward on the
isentropic surface for a better part of 12-hrs. Snow is expected
to end from west to east with some residual snow showers across
the terrain. Highs Friday range from the mid-upr 20s across the
terrain to low-mid 30s for valley locations, could approach 40F
for the mid-Hudson Valley and portions of Litchfield County.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Main story for the upcoming weekend is a potentially significant
multi-hazard winter storm with impacts including heavy snowfall
accumulations and wintry mix/ice accumulations for some followed by
strong winds and possibly dangerous winds chills.

We start the long term period Friday night with a rather moisture
starved arctic front moving into the Northeast. Decent cold air
advection sets up behind the front ushering in 850hPa isotherms
between -11C and -16C over Lake Ontario which could lead to a strong
enough delta-T between the air and lake water temperatures that snow
showers get an extra boost of lake moisture. Therefore, increased
POPs to slight chance over the Adirondacks to account for a few snow
showers that reach into the region behind the frontal passage Friday
night.

Canadian high pressure in Quebec then builds southward into the
Northeast for Saturday, spreading a chilly airmass into eastern NY
and western New England with high temperatures expected to stay
below freezing throughout the area. Downstream in the Tennessee
Valley/Ohio Valley, our winter storm will becoming more organized as
a southern stream wave in the southern Plains phases with a northern
stream wave that is part of a larger upper level low over the Hudson
Bay containing very cold air. Our southern stream wave will need to
be closely monitored this week as its strength will be vital in
predicating the eventual storm track. It looks to originate in the
Pacific Ocean and does not reach the West Coast until Thursday. This
tells us two things. First, it likely will be moisture rich bringing
potential for heavy precipitation and secondly, weather balloons
will not be able to sample it until the second half of the week
which is a key source of data for our weather models. Until then, we
will rely on satellite data.

There remain some discrepancies among the latest global guidance on
where and when our northern stream and southern stream waves phase
which will be very important in where our storm tracks and thus what
type of precipitation falls over eastern NY and western New England.
The 12z/15 ECMWF and CMC-NH are in decent agreement in our southern
stream wave strengthening over the southern Plains and digging into
the Gulf States where it picks up additional moisture from the Gulf
of Mexico before phasing with our northern stream wave over the Ohio
Valley Saturday night. As the two phase, we will be left with a full
latitude positively tilted trough that becomes neutrally tilted over
the Eastern Conus on Sunday. This set-up would allow our surface low
to strengthen as it heads northeastward up the Appalachian Mountains
across PA Saturday night entering the mid-Hudson Valley on Sunday.
This scenario would give mostly snow to the Capital District and
areas north/west but potentially a period of wintry mix for the
Catskills, mid-Hudson Valley and western New England Saturday night
into Sunday morning. The 12z/15 GFS keeps the southern stream wave
weaker over the southern Plains resulting in a storm track that is a
bit further west than the ECMWF/CMC-NH solution and thus brings the
potential for wintry mix further north and west into the Greater
Capital Region.

At this point, we favor the ECMWF/CMC-NH track and updated our
latest forecast to reflect this thinking. It is important to point
out that while the slight differences in storm track will have
implication on far north up the Hudson Valley and into western New
England the wintry mix of sleet/freezing rain/plain rain extends
Saturday night into Sunday morning, all three continue to be in good
agreement that this storm will contain a high amount of
precipitation. In fact, all show similar amounts averaging between
1.00 and 2.00 inches of precipitation which is very impressive.
Areas north and west of the Capital Region which are more favored to
see primarily snow, could end up with a significant snowfall event
with higher confidence that we reach warning-criteria. Areas in the
mid-Hudson Valley, Catskills and Litchfield County, CT will be a
trickier forecast as we iron out the rain/snow line details and
potential for sleet and freezing rain accumulations which could cut
down on snowfall amounts.

The main impact time from this winter storm looks to be Saturday
afternoon into part of the day Sunday and most areas should start
off as all snow before the warm sector and thus wintry mix potential
arrives overnight Saturday. Very cold air wraps in quickly behind
our winter storm Sunday afternoon/night and with high pressure in
the Great Lakes building eastward, strong winds could lead to
dangerous wind chills Sunday night into Monday. In fact, the air
mass following our winter could be the coldest of the season with
potential for temperatures to remain in the single digits on Monday
and only teens on Tuesday.

&&

.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
A broken-ovc mostly VFR deck of stratocumulus clouds covers much
of eastern NY and western New England this evening with cloud
heighs mostly from 3000 to 4000 feet. These clouds will persist
overnight at GFL/ALB/PSF. Farther south, mainly clear skies are
expected to persist at POU through the night although patches
of strato cumulus clouds may show up at times. Winds will be
light and variable.

A cold front will approach the area from the northwest on
Wednesday. BKN cloud cover will likely persist at GFL/ALB/PSF
through the afternoon with southwest winds increasing to 10 to
20 kts during the afternoon. Expect more sunshine at POU with
mainly sct clouds.

Outlook...

Wednesday Night: Low Operational Impact. Breezy NO SIG WX.
Thursday: No Operational Impact. NO SIG WX.
Thursday Night: High Operational Impact. Likely SN.
Friday: Moderate Operational Impact. Chance of SHSN.
Friday Night: No Operational Impact. NO SIG WX.
Saturday: Moderate Operational Impact. Chance of SN.
Saturday Night: High Operational Impact. Definite SN.
Sunday: High Operational Impact. Definite SN.

&&

.HYDROLOGY...
Light precipitation amounts this week in the form of snow,
mainly Thursday night into Friday morning. However, over the
holiday weekend a widespread precipitation is expected. At this
time mainly snow is expected with a wintry mix possible south
and east of the Capital District.

Temperatures will favor continued ice formation/thickening on
area waterways.

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...BGM
NEAR TERM...BGM
SHORT TERM...BGM
LONG TERM...Speciale
AVIATION...MSE/JPV
HYDROLOGY...BGM

NWS ALY Office Area Forecast Discussion