Area Forecast Discussion
Issued by NWS Albany, NY

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437
FXUS61 KALY 210521
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
121 AM EDT Sat Jul 21 2018

.SYNOPSIS...
Fair and dry weather will continue through most of Saturday as
high pressure remains dominant across the northeast. A wave of
low pressure is forecast to develop and track northward Saturday
night into Sunday with a period of rain and perhaps a
thunderstorm. A warm and more humid air mass arrives for the
second half of the weekend and lingering into most of next week
with periods of showers and a chance of thunderstorms.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
As of 100 AM EDT...Per the GOES-16 Nighttime Microphysics
channel, a sct-bkn canopy of CI/CS was slowly advecting
northeastward this early Saturday morning. Otherwise, a tranquil
overnight is expected as ridge axis slides slowly east-
northeast. Minor tweaks to the temperatures and dewpoints per
observational trends.

Prev Disc...High pressure has built east and light south winds
are occurring over the region. The should remain clear through
the night. Light south winds could keep temperatures up through
the night in parts of the Hudson Valley including the Capital
District. There could be some localized fog as well. Just minor
adjustments to temperatures and sky cover through the night.
Previous AFD below...

Clear calm weather once again tonight with high pressure over
the area. Dew points and temperatures are a bit higher than
yesterday so we expect lows tonight to be a few degrees warmer
than last night, although still perhaps just a bit below
guidance blends given good radiational cooling conditions. We
are expecting lows down to near 50 over normally cooler
locations in the north country, with mid 50s to lower 60s
elsewhere. Patchy fog will once again form in cooler areas and
near water sources.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/...
High pressure moves off the east coast on Saturday. Based on
current expected timing of low pressure approaching from the
midwest and south we are expecting Saturday to remain dry over
eastern NY and western New England through late afternoon,
however will rain will likely overspread the lower Hudson Valley
toward evening as low pressure approaches.

A strong mid-level cyclonic system associated with yesterday`s
and today`s midwest severe weather will approach our area on
Saturday. Surface low pressure will develop along the mid-
Atlantic coast Saturday and track north up the coast toward
central NY by early Sunday. There has been some model
disagreement on the exact track of this system for the past few
days, however the latest runs of the operational models
including the 12z ECMWF are in excellent agreement with the
track of this system to the west of eastern NY. Timing for the
onset of rain with this system for our area should be during
Saturday evening for the mid-Hudson valley and Catskills, then
spreading north across the Capital District to the Adirondacks
by late Saturday night.

East-southeasterly flow at 850 mb of 3-4 standard deviations
above normal will bring a plume of 2-3 standard deviation above
normal precipitable water values near to just above 2.00 inches
across our area with the passage of this system late Saturday
night. It appears that the most likely location for heaviest
rains will be near to just west of the low-level cyclone track
across central to western NY, however locally heavy rains could
still occur in our area especially in areas where the east-
southeast flow is upslope such as the Catskills or southern
Adirondacks. Dry antecedent conditions for most areas plus the
fact that this system will be a fast-mover should keep the
flooding threat relatively low across our area, but localized
problems can`t be ruled out, especially in the aforementioned
higher terrain areas susceptible to upslope precipitation
enhancement.

Winds in the Hudson valley should be near to below 15 kts on
Saturday night with a stable temperature profile keeping strong
winds confined above the boundary layer. However higher
elevations could see wind gusts to 30 or 40 mph given the strong
low-level southeasterly jet expected above 2000 feet ASL.

The steady rain should end early Sunday as the low-level cyclone
moves north to north central NY and weakens. However ample
moisture along with some instability will likely trigger a few
showers and thunderstorms during the afternoon Sunday. Any
convective storms Sunday will contain locally heavy rainfall
given the very moist conditions. 850-700 mb flow from the
south-southwest to 30 kts could even provide enough shear to
allow for scattered storms to briefly organize into some
organized clusters, enhancing the localized flash flood
potential.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Still a good consensus in sources of guidance/ensembles for upper
ridging to build into the eastern U.S. off the Atlantic as the upper
feature in the OH Valley weakens and retrogrades south and west.
Zone of deep tropical airmass extends over our region and as
northern stream upper energy gradually approaches from southern
Canada, an increasing low level pressure gradient will support
stronger than normal south to southwest boundary layer flow. Any
upper dynamics will be weak and there is little to no low level
thermal forcing but the deep tropical moisture with PWAT values
around 2 inches along with the forcing in and near the stronger
boundary layer wind flow will support good coverage of showers and
thunderstorms.

The better coverage should be in the afternoon and evening with the
daytime heating and also in areas of terrain due to upslope winds.
There could be a few breaks in the clouds from daybreak through part
of each morning to help temperatures rise solidly into the 80s
destabilizing the atmosphere across the region. Highs will be a
little cooler, upper 70s to around 80. However, lows will be in the
uncomfortable upper 60s to lower 70s but some mid 60s higher
terrain.

There are hints at the upper energy in southern Canada could track
far enough east and upper troughing amplifying in the eastern U.S.
that a cold front could track through as early as Thursday night but
there are timing differences in sources of guidance with some
guidance suggesting more toward Friday with a potential frontal
passage. With the tropical airmass in place next week, any
thunderstorms could have quite a bit of locally heavy rain and
localized flash flood potential has to be watched, even with the
dry long term conditions over much of our region.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
Upper level ridge is shifting offshore, but surface high pressure
remains close enough to keep it rain-free through the day today.  IR
satellite imagery shows bands of high clouds start to approach from
the south and west.  Although the TAF period starts off fairly clear
for most sites, high clouds will quickly increase in coverage this
morning.  Before that occurs, a brief period of IFR fog is possible
at KGFL just prior to sunrise and perhaps some MVFR BR at KPSF as
well. Otherwise, it will remain VFR with calm or light southerly
winds in place.

It will continue to be VFR through the day today.  High and mid
level clouds will increase through the day.  South to southeast
winds will be 5 to 10 kts for all sites.

By evening, rain will be moving up from south to north, as low.
pressure travels up the mid-Atlantic coast.   KPOU could see a
shower as early as 00z, but it probably won`t be a steady rain until
at least 02z. Rain will reach KPSF/KALB/KGFL by 03z-06z. Within the
steady rain, flying conditions will likely lower to MVFR and IFR for
the rest of Saturday night as well, as some locally heavy downpours
will be possible. Winds will switch to the E-NE and start to become
gusty, especially at KPSF/KPOU, where wind gusts of 20 knots are
possible.

Outlook...

Saturday Night: High Operational Impact. Likely RA.
Sunday: High Operational Impact. Likely SHRA...TSRA.
Sunday Night: High Operational Impact. Likely SHRA...TSRA.
Monday: High Operational Impact. Likely SHRA...TSRA.
Monday Night: Moderate Operational Impact. Chance of SHRA...TSRA.
Tuesday: High Operational Impact. Likely SHRA...TSRA.
Tuesday Night: Moderate Operational Impact. Chance of SHRA...TSRA.
Wednesday: High Operational Impact. Likely SHRA...TSRA.

&&

.FIRE WEATHER...
Dry weather will persist through the start of the weekend.
Unsettled conditions return Saturday night and into the second
half of the weekend as a frontal system slowly approaches from
the west.

RH will fall to 30-50 percent this afternoon and recover to
80-100 percent late tonight, with areas of dew formation
possible.

Winds will be mainly from the southerly direction at 5-10 mph
today into tonight.

&&

.HYDROLOGY...
Dry weather is expected through at least Saturday.

A wave of low pressure is expected to develop across the
southeast United States and track northward this weekend. This
is expected to spread a period of rain with perhaps a
thunderstorm Saturday night into Sunday. Forecast rainfall
amounts up to an inch are expected with a few isolated higher
amounts where deeper convection is possible. These values
should have minimal impact to area river and streams as levels
are quite low and our recent dry conditions as noted in the
latest drought monitor of D0-D1 levels.

Then a slow moving frontal system approaching from the west,
along with a several waves of low pressure tracking northward
within a very moist airmass in place, could lead to frequent
showers and thunderstorms, some with locally heavy downpours for
Sunday through at least the middle of next week. Potential
exists for training elements that would result in water level
rises. Stay tuned for further updates through the weekend.

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/Wasula
NEAR TERM...MSE/BGM/NAS
SHORT TERM...MSE
LONG TERM...NAS
AVIATION...Frugis/NAS
FIRE WEATHER...BGM
HYDROLOGY...BGM



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