Area Forecast Discussion
Issued by NWS Albany, NY

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FXUS61 KALY 171027
AFDALY

AREA FORECAST DISCUSSION
National Weather Service Albany NY
627 AM EDT Wed Jul 17 2019

.SYNOPSIS...
Showers and thunderstorms will increase in coverage today, as a
cold front approaches from the north, and remnant moisture from
Barry tracks across the area. Locally heavy rainfall will be
possible. The front should settle south of the region Thursday,
bringing slightly cooler temperatures and decreasing chances for
showers. The front will then return during Friday as a warm
front, bringing oppressive heat and humidity through this
upcoming weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
As of 630 AM EDT, showers and isolated thunderstorms continue
for areas mainly within and north of the Mohawk River, across
the southern Adirondacks into portions of southern VT. Locally
heavy downpours have been occurring, with rainfall amounts as
high as 1.03 inches occurring at Old Forge according to NYS
Mesonet. Rainfall rates have generally been 0.25-0.5"/hour, with
some locally higher rates noted.

These showers/thunderstorms will continue drifting
east/northeast through 10 AM, affecting areas mainly north of
I-90. Locally heavy rain will be possible which could lead to
some ponding of water in low lying, poor drainage areas (and
urban areas such as Glens Falls). Somewhat more spotty
showers/isolated thunderstorms may affect areas as far south as
the I-90 corridor during this time, and will have to watch in
case some backbuilding and ensuing training of cells develops
across the Mohawk Valley, Saratoga region and Capital Region.

This initial surge of rain appears to be tied to the leading
edge of a low level jet approaching from the southwest, as well
as ahead of an embedded shortwave across Lake Ontario. There may
then be a decrease in areal coverage of showers/storms across
northern areas between mid morning and noontime, although at
least some showers/isolated thunderstorms will remain possible.

During this time (through noon), most areas south of I-90 should
remain dry outside of isolated showers/thunderstorms. However,
as forcing from the north and west increases this afternoon,
showers and thunderstorms should begin to develop and/or build
south and east. In addition, shortwave currently located across
IL/IN will continue tracking east today, and will provide
increased forcing for southern areas by late afternoon. So,
showers/storms will become more numerous later this afternoon
for areas near and especially south of the I-90 corridor. This
same region will also experience the best instability, as some
small pockets of clearing may develop, allowing for ML CAPES of
1000-1500 J/kg in some areas. 0-6 km bulk shear will generally
be 25-30 KT, although mid level lapse rates appear weak,
generally 5-5.5 C/km. SPC has placed southern areas within a
slight risk for severe thunderstorms, with isolated damaging
wind gusts possible. However, bigger threat continues to be the
heavy rain potential given PWAT`s approaching 2", and also some
possibility for brief backbuilding/training of cells across
central and southern areas, where WPC has maintained an area of
slight risk for excessive rainfall (mainly south of I-90 in
NY/MA). Recent dryness should mitigate overall flash flood
potential, but can not rule out isolated instances of flash
flooding of poor drainage/urban and low lying areas.

As for temperatures, will side closer to the warmer National
Blend of Models numerical output and EC MOS, which suggests
lower/mid 80s in most valley areas, except 85-90 across the mid
Hudson Valley, where some heat indices could briefly approach
the mid 90s. There is enough uncertainty in these areas as to
how long, and if, apparent temperatures (heat indices) reach the
mid 90s, therefore no heat advisories at this time. For the
remainder of the area, mainly mid 70s to lower 80s are
indicated.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...
Tonight, the main shortwave will be approaching southern areas
overnight, while a cold front slowly settles southward. Best
forcing looks to be across southern areas, where widespread
showers and embedded thunderstorms should be ongoing through
midnight, before decreasing in coverage from west to east. The
threat for heavy rain will continue in these areas through
midnight, and additional isolated instances of damaging winds
within any more robust convection will remain possible during
this time as well. Farther north, isolated/scattered showers
and thunderstorms may be ongoing closer to the actual cold front
across the southern Adirondacks, upper Hudson Valley and
southern VT this evening, before decreasing in coverage toward
or after midnight as the front reaches the I-90 corridor.
Otherwise, warm and humid with areas of fog possible, with lows
mainly in the 60s to lower 70s.

Thursday, the front should continue settling south of the
region, as a moist but cooler air mass overspreads the region
from the northeast and east. Enough moisture may linger for some
spotty showers or drizzle across the region, with plenty of low
clouds persisting. Highs may reach 75-80 in valley areas,
perhaps warmer across the western Mohawk Valley and SW
Adirondacks where breaks of sun could develop, while eastern
areas may hold only in the lower 70s.

Thursday night-Friday night, low clouds and some spotty drizzle
could linger in some areas through Friday morning. Otherwise,
the frontal system should begin retreating north and east during
Friday. It remains uncertain how much mixing and heating occurs
in the wake of the warm front Friday afternoon, especially for
areas east of the Hudson River and across the upper Hudson
Valley. For now, have indicated lower 90s within valley areas,
with 80s elsewhere, although there is some possibility for even
higher temperatures should the warm front pass through more
quickly. Combined with dewpoints in the upper 60s to lower 70s,
heat indices could reach the upper 90s to lower 100s for many
valley areas, so heat advisories will likely be needed, at least
for valley areas. Although mid level capping may prevent much
convection from occurring Friday afternoon, can not rule out
isolated/scattered late day thunderstorms across the southern
Adirondacks where elevated terrain sources may yield enough
lifting mechanism to trigger convection. There may be a better
chance for convection late Friday night, especially across
northern areas, as upstream convection from the Great Lakes
region could spill into these areas toward daybreak Saturday.
This will have to be watched very closely, as there should be
considerable elevated instability lingering through the night
along with steepening mid level lapse rates with an approaching
Elevated Mixed Layer (EML). Lows Friday night may be hard
pressed to fall below 75 in many valley areas, with upper
60s/lower 70s across higher terrain.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Heat headlines will likely be necessary Saturday and possibly Sunday
as well. There is an increasing consensus from sources of
guidance/ensembles for upper troughing to build south out of SE
Canada and a cold front to cool off our region some time between
Sunday evening and Monday afternoon.  The timing is uncertain but
strong thunderstorms are likely ahead of the cold front as there are
indications of considerable instability due to the heat ahead of the
front.  There may be some steep midlevel lapse rates enhancing
instability as well and quite a sharp thermal and moisture boundary
for good low level forcing.

Highs Saturday solidly in the 90s with heat indices over 100 in some
areas.  Highs in the 80s in higher terrain Saturday. Highs Sunday a
few degrees cooler than Saturday but still upper 80s to lower 90s
many areas with some mid 90s southern areas and 80s higher
elevations. Heat indices in the Hudson Valley from around the
Capital Region to mid Hudson Valley and NW CT could be in the mid to
upper 90s Sunday.

Including some isolated to scattered thunderstorms in the southern
Adirondacks and areas bordering the eastern Catskills in case there
is some terrain induced scattered activity within our unstable and
humid airmass. Better coverage of scattered thunderstorms Sunday
afternoon through Monday afternoon, depending on the timing of the
cold front. Then cooler and drier air Tuesday.

Highs Monday in the 80s but some 70s in higher elevations. Highs
Tuesday in the upper 70s to lower 80s but a few mid 80s southern
areas and lower to mid 70s higher terrain.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
Area of showers in western/central NY tracking east while some
isolated showers extend east near KALB. Showers will affect KALB and
KGFL through daybreak, then showers will build east and south to
KPSF and KPOU from daybreak through midday. Showers should be light
enough so that VFR conditions are expected until lower layers are
saturated around daybreak and through midday.

Intervals of showers expected between daybreak and early afternoon
with intervals of MVFR ceilings and visibilities. Then with some
instability in the afternoon, there are chances for thunderstorms.
Including PROB30 for KALB, KGFL, KPSF. There should be some better
coverage of thunderstorms around KPOU later in the afternoon, so
including an hour of TEMPO wit thunder from 20Z-21Z but indicating
PROB30 for thunder there the rest of the afternoon through 24Z. The
timing of any thunder will be adjusted once thunderstorms develop
later today.

Coverage of showers and thunderstorms will decrease through the
evening and diminish to just showers. Including just VCSH at all TAF
sites during the evening with mainly VFR ceilings and visibilities.
There could be some MVFR ceilings and visibilities this evening
depending on how much rain fall around the TAF sites during the day
but that is unknown.

Winds will be light south at less than 10 Kt through this afternoon,
then just variable at less than 6 Kt this evening.

Outlook...

Thursday Night: Low Operational Impact. Isolated SHRA.
Friday: No Operational Impact. NO SIG WX.
Friday Night: Low Operational Impact. Isolated SHRA...TSRA.
Saturday: No Operational Impact. NO SIG WX.
Saturday Night: No Operational Impact. NO SIG WX.
Sunday: Moderate Operational Impact. Scattered SHRA...TSRA.

&&

.FIRE WEATHER...
Showers and thunderstorms will become widespread this afternoon
and evening, as a frontal system approaches from the north, and
remnant moisture from Barry tracks across the area. Given the
tropical nature of the moisture, heavy rainfall in showers and
thunderstorms is likely as the precipitation shield slides south
through today and tonight. The front should settle south of the
region Thursday, bringing slightly cooler temperatures, before
surging back northward Friday, setting the stage for heat and
humidity into the upcoming weekend.

RH will drop to 50-70 percent this afternoon, then climb to dropping
to 90-100 percent tonight. RH should only fall to 65-75 percent
Thursday afternoon.

Winds will be south to southwest at 5-15 mph today, shifting
into the north to northeast at similar speeds tonight into
Thursday.

&&

.HYDROLOGY...
Increasing chances for showers and thunderstorms will occur across
the area today into tonight. This will be mainly due to the
remnants of Barry lifting through the region, along with a cold
front approaching from the north. Showers could contain
localized heavy rainfall.

However, a mitigating factor for heavy rain is that most of the
region has been drier than normal during the past 30 days. WPC
continues areas south of the I-90 corridor in NY and western
New England within a slight risk for excessive rainfall, with
the remainder of eastern New York/western New England in a
marginal risk due to anomalous high PWATs and some potential for
training of deeper convective cells. Any flooding concerns
through this period would likely be localized in urban/poor
drainage and low lying areas.

Please visit our Advanced Hydrologic Prediction Service /AHPS/ web
page for specific area rivers and lakes observations and
forecasts.

&&

.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
MA...None.
VT...None.

&&

$$
SYNOPSIS...KL
NEAR TERM...KL
SHORT TERM...KL
LONG TERM...NAS
AVIATION...NAS
FIRE WEATHER...KL/OKeefe
HYDROLOGY...KL/OKeefe


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