Area Forecast Discussion
Issued by NWS Albany, NY

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FXUS61 KALY 230125
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
925 PM EDT Sun Oct 22 2017

.SYNOPSIS...
High pressure will continue to move east of northern New
England and Nova Scotia tonight.  A southerly flow between the
departing surface high and a slow moving cold front approaching from
the west will allow some clouds to increase with a slight chance of
showers south and east of the Capital Region tomorrow.  The slow
moving cold front will bring some heavy rain, a chance of
thunderstorms and windy conditions to region late Monday Night into
Wednesday.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
As of 925 PM EDT...High pressure was across the Canadian
maritimes this evening. Some cirrus spilling over the top of
the ridge of high pressure should thin some this evening.

The low-level return flow from the sfc high will allow
for the south/southwest winds to increase the low-level
moisture for some stratus and patchy fog to move into the mid-
Hudson Valley/NW CT and locations south and east of the Capital
Region. The low-level moisture advection may allow the stratus
to reach the Capital Region by daybreak. Further north the skies
will be clear/mostly clear with the decoupling of the winds and
some patchy fog may form once again in the Upper Hudson
Valley/Glens Falls area and to the east of the southern Greens
in the CT River Valley. Some patchy fog is also possible near
the western New England higher terrain.

Temps tonight should be milder than the previous few evenings
with mid 40s to lower 50s. The warmer readings will be in the
Capital Region where the southerly winds albeit light may
continue most of the night due to funneling up the Hudson River
Valley.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
Tomorrow...A strong upper level trough will be approaching the
Midwest and Oh Valley as it becomes negatively tilted as some
northern stream energy from a poleward trough begins to phase
with it late in the day, as the cold front to the system slowly
pushes eastward from the Great Lakes Region, Ohio Valley,
extending southward into the Southeast.

The impact tomorrow for our forecast area is for that gradual
shift of the mid and upper level ridges axis downstream. Low-
level moisture and theta-e advection increases. The low-level
pressure gradient tightens between the departing sfc high east
of the Nova Scotia and the cyclone that forms and deepens, as
it moves into the central Great Lakes Region. Low-level clouds
will increase from the south during the morning into the
afternoon. There continues to be a subtle weak impulse/short-
wave in the S/SW flow that may focus some light rain showers or
drizzle from the the southern reaches of the Capital Region
south and east. We kept a slight to low chance of showers in
late in the day based on the NAM/GFS/CMC/ECMWF. The H925 winds
begin to increase by late in the day to 25-35 kts and it will
become breezy. Some sunshine is possible across the northern
zones during the day. The mild southerly flow coupled with H850
temps still about 1 to 2 standard deviations above normal will
allow for highs to be in 60s to lower 70s across most of the
region with the cooler readings over the southern
Adirondacks/southern Greens in the upper 50s to lower 60s.

Monday night...The air mass becomes more humid, as the low and
mid level low flow strengthens. The 12Z ECMWF and CMC continue
to be on the faster end of the envelope of solutions with the
movement of the cold front towards the region. The NAM and GFS
are a little slower. All model indicate the low-level jet to
increase at H925 to about 30 to 45 kts and the H850 winds 45-60
kts. The 12Z GEFS has the H925 +v-component of the wind
/southerlies or meridional component winds/ increase to +2 to
+3 standard deviations above normal, and the H850 +v-component
increase to +3 to +4 STD DEVS above normal, which will help
transport Atlantic and Gulf moisture towards the region. It will
become breezy/windy, but we are not confident we will mix these
stronger winds to the sfc at night, and with the rain filling
in to the west it may hard to achieve the stronger gusts at this
time frame. We are expecting south to southeast winds of 10 to
20+ mph with some gusts in the 30-35 mph range at night, and the
wind should be blowing strong on the ridge tops. We will
continue to monitor for a possible Wind Advisory.

Tue-Tue night...The weather becomes very active with the slow-
moving cold front impacting eastern NY and western New England
with perhaps a weak wave or two moving along it. The latest
indications from all the guidance is for a slow-moving rain
band with embedded thunderstorms /a narrow cold frontal
rainband/ potentially impacting the region from west to east.
The air mass becomes very moist with sfc dewpts rising into the
mid 50s to perhaps mid 60s. There are timing and QPF
differences, but all indications are for deep moisture transport
riding all the front, as the flow becomes parallel from the sfc
to aloft. The deep southerly flow allows PWATS to rise well over
an inch, and the latest GEFS has PWATS 2 to 4 standard
deviations above normal during with the anomalous low-level jet
focusing showers with heavy rainfall, and potentially shallow or
low-topped convection. The latest GFS/NAM has some weak
instability at 100-300 J/kg over parts of the forecast area. The
0-6 km bulk shear is high in the 45-60+ kt range. SPC has the
entire forecast area in a Marginal Risk. We included gusty winds
with the chance of thunderstorms. We will also have to see if
any synoptic gradient winds mix to the surface for a potential
Wind Advisory too. Some gusts of 40 to 45 mph are possible. In
the south to southeast flow some orographic enhancement is
possible along the east facing slopes of the southern Greens,
Adirondacks and Catskills. The flow may back to the southeast
with a weak ripple or two of low pressure moving along it. PoPs
were continued in the categorical range and gradually the
rainband is moved from west to east Tue night. A widespread 1 to
3 inches is possible with locally higher amounts.

WPC has placed most of eastern NY and western New England in a
Slight Risk of exceeding the Flash Flood Guidance in Day 3 /Tue
Tue night/. The antecedent conditions are dry, and the placement
of the heaviest rain is still uncertain. If the heavy rain
showers train or repeatedly move over the same area, there could
be some urban and poor drainage flood issues, and perhaps
isolated flash flooding. We will mention the possibility of a
flood or flash flood watch if this becomes more certain in the
HWO. Widespread flooding is not expected yet on the main stem
rivers.

Highs on TUE will still be in the 60s to lower 70s in the muggy
air mass ahead of the front, and slowly cool down to the
mid/upper 40s to mid/upper 50s from west to east.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
By mid-week, a strong upper level trough will be in place over
the Great Lakes and will continue to strengthen as an additional
shortwave enters into the base of the trough. This upper trough
is expected to shift east and then northeast into New England
by Friday, allowing for another upper trough to develop and
deepen over the Great Lakes for next weekend.

At the surface, a strong southerly jet will still be in place across
western New England ahead of a cold frontal boundary. The latest 12Z
GEFS guidance indicates the v-wind anomaly exceeds 3 STD early
Wednesday, along with a PWAT anomaly 2 to 4 STD above normal.
However, this anomalous moisture and strong winds quickly shift east
into New England throughout the day as the cold front pushes through
the remainder of the area. Some showers and potentially heavy rain
will still be possible along and ahead of the front but should shift
east/exit the region by Wednesday evening.

Rainfall totals Monday night through Wednesday evening range from an
inch across western areas to over 3 inches across western New
England. Even with these higher amounts, widespread river flooding
isn`t expected due to recent dry weather and lower flows, but minor
flooding of urban, poor drainage and low lying areas is certainly
possible, especially during the periods of heaviest rainfall and in
areas where leaves and other debris block drainage.

As the upper level trough passes overhead, some showers will be
possible through Thursday night. High pressure builds in at the
surface, leading to a break in rain and more sunshine Friday and
Saturday. The next potential storm system, similar to the one at the
start of the period, approaches the region Saturday evening into
Sunday, bringing more rainfall.

Temperatures throughout the period will generally range from the 40s
at night to the 60s during the day, which is still slightly above
normal for late October.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
With high pressure remaining nearby this evening, VFR
conditions are expected to continue for all sites with light
southerly winds. Just few-sct passing cirrus clouds are expected
throughout the evening.

Winds will decrease for this evening with the loss of daytime
heating and winds should become very light or calm once again
for tonight. Although it looks mainly VFR for much of the
overnight hours with some additional passing high cirrus,
cannot rule out some mist/fog for late tonight at KGFL, KPOU and
KPSF thanks to good radiational cooling once again. Also,
thanks to the persistent southerly flow, some low stratus may
advect northward from the coastal areas and impact KPOU/KPSF
towards 09z-10z with MVFR/IFR conditions.

As the next low pressure system approaches the region tomorrow,
clouds and low level moisture will begin increasing from the
south, with potential MVFR CIGS at KPOU/KPSF after 13Z.

Outlook...

Monday Night: High Operational Impact. Windy With Gusts To 30.0 Likely SHRA...FG.
Tuesday: High Operational Impact. Windy With Gusts To 36.0 Definite SHRA...TSRA.
Tuesday Night: High Operational Impact. Definite SHRA...TSRA.
Wednesday: High Operational Impact. Likely SHRA.
Wednesday Night: Moderate Operational Impact. Chance of SHRA.
Thursday: Moderate Operational Impact. Chance of SHRA.
Thursday Night: Low Operational Impact. Slight Chance of SHRA.
Friday: No Operational Impact. NO SIG WX.

&&

.FIRE WEATHER...
High pressure will continue to move east of northern New
England and Nova Scotia tonight. Clouds begin to increase on
Monday. A slow moving cold front impacts the area late Monday
night through Tuesday night with periods of showers and windy
conditions.

The RH values will increase to 85 to 100 percent tonight. They
will only lower to 60 to 80 percent tomorrow afternoon...and
increase close to 100 percent Tuesday morning.

The winds will be light to calm tonight, and increase from the
south at 10 to 15 mph tomorrow with a few higher gusts in the 20
to 25 mph range. The winds will be southerly Monday night at 10
to 20 mph with some gusts in the 30 to 40 mph range especially
in the Capital Region and on the mountain or hill tops.

The next widespread soaking rainfall will be Monday night into
Tuesday night.

&&

.HYDROLOGY...
Heavy rainfall is expected to impact the Hydro Service Area
Tuesday morning into the Wednesday.

A widespread rainfall arrives late Monday night into Wednesday
morning associated with a slow moving cold front. Rainfall
amounts may range from 1 to 3 inches from this system with
locally higher amounts up to 4 inches. The heaviest totals may
be along or east of the Hudson River Valley to western New
England. Some ponding of water on roadways is possible as well
as clogged drains from fallen leaves. Some training of the heavy
showers and possible thunderstorms may produce isolated flash
flooding.

Currently, the MMEFS guidance does not show any main stem river
flooding, but a few points such as Eagle Bridge and Williamstown
get the Caution or Alert Stage. We will continue to monitor if a
Flash Flood or Flood Watch is needed Tuesday into Wednesday. The
antecedent conditions are dry which should allow the ground to
absorb the rainfall if it is not too heavy.

Additional rainfall of a half an inch to an inch is possible
mainly across western New England Wednesday night into
Thursday,if a wave of low pressure moves along the front near
eastern New England.

Overall, a trend to drier weather is expected Friday into
Saturday.

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...Wasula
NEAR TERM...11/Wasula
SHORT TERM...Wasula
LONG TERM...JVM
AVIATION...Frugis/11/JVM
FIRE WEATHER...BGM/Wasula
HYDROLOGY...BGM/Wasula



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