Area Forecast Discussion
Issued by NWS Albany, NY

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000
FXUS61 KALY 240914
AFDALY

AREA FORECAST DISCUSSION
National Weather Service Albany NY
414 AM EST Thu Jan 24 2019

.SYNOPSIS...
Mild temperatures and rain are expected today. The rain will be
moderate to briefly heavy and could result in some flooding
especially south and east of the Capital Region. Colder air will
cause the rain to turn to snow this afternoon and evening
before it ends. It will turn much cooler Friday into Saturday
with some mainly light snow showers possible through the
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
...Flash Flood Watch in effect through 6 pm for western New
England, the Taconics, and the Mid-Hudson Valley...

As of 400 am, steady rainfall continues over southwest flow
upslope-favored locations such as the southern Adirondacks,
southern Greens, and northern Berkshires, as well as the Lake
George Saratoga region. Mesonet obs show that anywhere from 0.75
to 2.00 inches of rainfall has occurred in these areas already.
This is a fairly impressive system from a moisture standpoint
with PWATs forecast to reach 1-1.25 inches over much of the
forecast area today, which is +3 to +4 SD per the NAEFS. Equally
impressive are the 850 mb V-anomalies which are forecast to
reach +2 to +3 SD. 850 mb wind speeds may be as high as 85 kt
per the NAM over southern parts of the forecast area. Where
rainfall is spottier early this morning, it will fill in from
west to east as an elongated area of strong 850 to 700 mb
frontogenesis spreads into the region, along with an
increasingly favorably positioned right entrance region of a
strong upper level jet. This will allow a period of moderate
rainfall to occur throughout the forecast area during the
morning into the early afternoon. CAMs such as the latest couple
runs of the 3km NAM and the HRRR are indicating a narrow cold
frontal rain band crossing the region from west to east roughly
15-19Z. Enhanced rainfall rates can be expected if this band
materializes, but the prospects for enhanced wind appear low
given the strong inversion and lack of instability. Expecting a
basin average additional 0.50-1.50 inches of rain today,
bringing storm totals to 1-2 inches. Amounts up to 3 inches are
possible in the favored upslope areas of the southern
Adirondacks and southern Greens. See the hydro section below for
discussion on flood potential. With strong southerly flow, high
temperatures will be boosted into the 40s to low 50s in many
areas, except staying around 40 or below in the southern
Adirondacks.

Colder air begins to spread in from west to east in the
afternoon hours behind the frontal boundary, which will change
rain to snow before ending. The deeper moisture and better
forcing for ascent will depart before temperature profiles are
cold enough to support snow, but minimal accumulation is
possible, generally around an inch or less, possibly a couple of
inches above 1500 feet elevation. Westerly winds will become
strong and gusty behind the front this afternoon and evening.
Any lingering snow showers should diminish after 00Z, except for
some lingering activity over the high terrain of the
Adirondacks/Greens. Lake effect parameters become marginally
favorable late tonight with southwesterly flow, and a surface
trough may focus a band over northern Herkimer County, with
additional light accumulation possible. Cold advection will send
low temperatures back down into the mid teens to mid-20s, which
could result in wet spots freezing back up again.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
Anomalously strong 500 mb closed upper low will stretch from
Hudson Bay to southern Ontario during the short term, while
broad troughing will dominate the flow pattern east of the
Rockies. A shortwave trough will rotate around the base of the
upper low Friday, with a weak surface low/trough parallel and
just north of the St. Lawrence Valley. This trough will likely
focus a band of lake effect snow over northern Herkimer and
Hamilton Counties into Friday night and early Saturday as
moderate lake-induced instability develops. The band may
oscillate during this time period, possibly shifting back south
Friday night and back north again Saturday morning, which should
limit accumulations in any given spot, but winter weather
advisories may be needed in future forecast cycles. Elsewhere,
deep mixing is forecast as H850 cold advection occurs coincident
with peak diurnal heating. This could result in some convective
snow showers or squalls spreading downstream of the lake effect
areas into the valleys by the afternoon with potential
highlighted by positive values of the snow squall parameter. A
limiting factor is the lack of a sharp surface boundary upon
which to focus the snow showers. It will be breezy as well.
Seasonably chilly Friday night, although partial cloud coverage
and a respectable pressure gradient should keep temperatures
from falling too much.

Lake effect activity may be ongoing Saturday morning before
shifting north as winds back toward southerly by the afternoon.
This will be the result of a strong PV anomaly shifting
southward across Ontario toward Lake Superior into Saturday
night. Temperatures won`t be impacted to much during the day
Saturday as a cold airmass remains in place with below-normal
highs in the mid-teens to mid-20s. The southerly flow will
increase Saturday night along with cloud cover, so low
temperatures won`t fall off too much from Saturday`s highs. Some
upslope snow showers will become possible over the southern
Adirondacks late.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Large upper level trough will dominate across the Great Lakes and
into the Northeast during the long term period.  As a result,
shortwave troughs rotating around the main upper level low over
Canada will swing across the region from time to time, allowing for
some snow showers and helping to enhance lake effect precipitation.

At the start of the long term, upper level energy will be moving
across Ontario and Quebec and a surface cold front will move across
the region for Sunday into Sunday night. This will allow for some
scattered snow showers, with the best chance across northwestern
parts of the region, where some lake moisture will aid in the
development of snow showers. Temps look fairly seasonable for
Sunday, although much colder temps will arrive behind the front for
Monday, when temps will only reach into the teens and 20s.

Most of Monday looks fairly quiet, although the break will be brief,
as the next system will be quickly heading towards the area from the
Great Lakes for Tuesday into Tuesday night.  There are some
differences within the model and ensemble guidance on just how far
south this next system digs.  This will determine if temps warm up
for Tuesday or if they remain fairly cold.  Some models suggest
there could be a steadier period of snow, others suggest just
passing snow showers (and possible even rain showers for southern
areas).  For now, will play the forecast in the middle until models
start to come into better focus.

Behind this system, very cold weather is expected for the middle to
latter part of the week.  Although it will be dry for most areas,
some bands of lake effect snow will develop off the eastern Great
Lakes.  Considering the very cold temperatures and persistent flow
in place, some significant accumulation is possible for the western
Adirondacks.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
Approaching storm system will continue to bring periods of rain
through the remainder of the overnight hours.  Although flying
conditions have generally been VFR/high end MVFR, they will become
solidly MVFR and eventually IFR for all sites by daybreak for both
visibility and ceilings.  Surface winds will be variable, with light
or calm conditions at KGFL/KPOU/KPSF, while KALB will see southerly
winds around 10-15 kts.  At 2 kft, southerly winds will be 40-45
kts, so will include LLWS for all sites.

A period of moderate to heavy rainfall is expected for Thursday
morning for all sites.  The lowest visibility is expected to be at
KPSF/KPOU, although all sites look IFR through the morning hours.
Surface winds will generally be around 10 kts, although some higher
winds are possible at KALB, with LLWS continuing in place.

The heaviest rain will start to taper off after midday, but light
rain will continue into the afternoon with MVFR conditions. As temps
fall, precip could even changeover to snow at KPSF, although it
appears that temps won`t cool down fast enough for this to occur at
the valley sites. Winds will switch to the west for the afternoon
and be around 10-15 kts with some higher gusts.

Once precip tapers off by late afternoon or early evening, flying
conditions should return back to VFR for all sites.  Skies will
start to clear out for Thursday night and westerly winds will
continue to be gusty for all sites.

Outlook...

Friday: Moderate Operational Impact. Chance of SHSN.Friday
Night: No Operational Impact. NO SIG WX. Saturday: No
Operational Impact. NO SIG WX. Saturday Night: Low Operational
Impact. Slight Chance of SHSN. Sunday: Low Operational Impact.
Slight Chance of SHSN. Sunday Night: Moderate Operational
Impact. Chance of SHSN. Monday: Low Operational Impact. Slight
Chance of SHSN. Monday Night: Moderate Operational Impact.
Chance of SN. Tuesday: High Operational Impact. Likely SN.

&&

.HYDROLOGY...
Flash Flood Watch has been expanded to include southern Vermont
and the northern Taconics while remaining in effect for western
Massachusetts, northwest Connecticut, the Mid Hudson Valley, and
the central/southern Taconics this morning through this evening.

Moderate rain will continue today, becoming steadier in areas
where it has been light overnight, as it becomes more focused on
a low- level front. An additional 0.50 to 1.50 inches of
rainfall is expected today, with storm total amounts generally
from 1-2 inches. Higher amounts around 3 inches are possible in
the southern Adirondacks and southern Green Mountains. The rain
could be briefly heavy along a narrow cold frontal rain band
from the late morning into the mid-afternoon. The rainfall will
diminish from west to east this afternoon into the evening,
changing to snow before ending. This rainfall, along with the
melting snow, will allow for some rises on rivers and streams.
Much of the precipitation will likely be absorbed by the
snowpack, especially over the southern Adirondacks and Lake
George Saratoga Region where temperatures will only rise into
the upper 30s to low 40s. However, south and east of Albany
(where snow pack is more limited) more of the precipitation will
be converted to runoff. With a frozen ground in place, some
minor flooding is possible, including along the Housatonic
River. Some of the snowpack over the northern Taconics and
southern Greens could begin to melt as dewpoints reach the mid-
40s this morning, so minor flooding will also be possible along
the Walloomsac and the Hoosic.

In addition, urban/small stream/poor drainage flooding is
possible across the area, especially since drains are covered by
snow banks in many areas. Some isolated flash flooding also
cannot be ruled out.

With river rises and ice movement on some rivers, ice jams can
not be ruled out. However the limited amounts of total runoff
should prevent this from being a major concern and this will be
more of an isolated issue.

Behind this storm system, colder weather will return to the
region for Thursday night into the weekend. Any additional
precip will be in the form of snow and fairly light.

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...Flash Flood Watch from 6 AM EST this morning through this
     afternoon for CTZ001-013.
NY...Flash Flood Watch from 6 AM EST this morning through this
     afternoon for NYZ060-061-064>066.
MA...Flash Flood Watch from 6 AM EST this morning through this
     afternoon for MAZ001-025.
VT...None.

&&

$$
SYNOPSIS...Thompson
NEAR TERM...Thompson
SHORT TERM...Thompson
LONG TERM...Frugis
AVIATION...Frugis
HYDROLOGY...MSE/Thompson


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