Severe Thunderstorm Warning 123, NWS Albany, NY

Area Forecast Discussion
National Weather Service Albany NY
439 PM EDT Fri Aug 4 2017

.SYNOPSIS...
Warm and humid conditions will remain in place through
tonight.  This will keep the threat for additional showers and
thunderstorms in the forecast. Showers and thunderstorms increase
tonight into early Saturday along and ahead of a cold front. A
cooler and drier air mass is expected for the remainder of the
weekend before more wet weather arrives for early next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 4 pm, scattered convection continues in the prefrontal
airmass. Weak organization to the storms with deep layer shear
around 20 kt as the strongest midlevel flow remains off to the
west. One or two of the deepest cores have produced hail and
damaging winds. CAMs suggest this activity will persist through
the rest of the diurnal heating before diminishing around 00Z. A
few strong to marginally severe storms can continue to be
expected into the evening. Storms have around 1500-2000 J/kg
SBCAPE to work with per SPC Mesoanalysis. Coverage should
remain scattered at most given the weak forcing.

Tonight, the deep upper low now moving across the central Great
Lakes will continue to eject northeastward and become negatively
tilted. One or more bands of showers and thunderstorms are
forecast to cross the region tonight, likely an extension of
the activity ongoing from southern Ontario into Ohio along a
cold front. After the afternoon and evening convection weakens,
it appears we could have a lull in activity before the front
approaches. Have worked this idea into hourly PoPs. CAMs suggest
the frontal band will work into the western Adirondacks and
Mohawk Valley around midnight or just before. The instability
will be waning even as the wind field increases, likely
resulting in a weakening trend to the convection. Cannot rule
out some gusty winds especially over western parts of our
forecast area with any lingering instability given fairly strong
low-level wind fields, but overall the trend should be a
weakening one with eastward extent. Locally heavy rainfall will
be a possibility given storm motions somewhat parallel to the
boundary, but overall the system will be progressive enough to
limit the flooding threat. Rainfall may not reach the Hudson
Valley until closer to 09-12Z. It will be a mild night with a
southerly gradient in place. Areas around the Capital District
may not fall below 70F with gusty southerly winds up the valley.

At 12Z, model consensus supports a frontal position roughly
along or just west of the Hudson Valley. Main question will be
if any destabilization can occur to the east of the front to
support an additional convective threat. Given the likely
presence of prefrontal clouds and precipitation and early
frontal passage, this potential is questionable. However, NAM
still generates MLCAPE of 1000-1500 J/kg east of the Hudson by
18Z, with deep- layer shear around 40 kt. SPC marginal risk from
the Hudson eastward appears to handle this situation properly.
Best potential for thunderstorms and severe weather is over our
western New England counties. Otherwise, a drying and clearing
trend will occur behind the front from west to east. Dewpoints
drop into the mid- 50s to lower 60s by the afternoon hours, with
a moderate westerly breeze. H850 temps drop to around +7C over
Lake Ontario, whose average surface temp is around 22C, so could
be looking at some lake-effect clouds and showers over the
western Adirondacks by late in the day.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
Quiet weather Saturday night into Sunday as upper flow becomes
zonal upstream of the passing trough. Lows finally back into the
50s under mostly clear skies Saturday night, with some upper 40s
in the higher terrain. A bit breezy again on Sunday with highs a
few degrees below normal in the upper 60s to upper 70s.

Sunday night into Monday, a broad trough will deepen over the
Western Great Lakes, sharpening as it tracks toward the
Northeastern US. A surface low is expected to develop downstream
of the trough over the eastern seaboard. Still various solutions
on the track and strength of the low, with the ECMWF on the
stronger, northern end of the envelope (developing a seasonably
strong low within a coupled upper jet structure), and the GFS on
the weaker, southern end. Enough consensus for likely PoPs for
the northern half for Monday and categorical for the southern
half. Should the ECMWF verify, we could be looking at a
widespread, steady, moderate rainfall event. Regardless, it
looks to be cool with temperatures struggling to reach 70 in the
warmest spots. While most of the rainfall looks to occur Monday,
it could start in spots late Sunday night.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Those seeking relief from the heat are in luck as the extended
period will feature temperatures running slightly below normal for
early August (normal highs low 80s) accompanied with lower humidity
levels. Besides seasonably cool temperatures, we can also expect a
mix of pleasant days with high pressure in control along with
unsettled days that bring threats of showers and possible
thunderstorms.

Based on current guidance, the start of the extended outlook looks
wet as our rather robust low pressure system from Monday could
linger pasted sunset. While there is still uncertainty on exact
timing, given the impressive dynamics including an intensifying
shortwave in the Great Lakes and 95-105kt 300mb jet over the
Northeast, rain could continue into the evening. For now, have high
end chance POPS N/W of the Capital District and likely POPS in
southeastern zones (western MA, NW CT and lower Hudson Valley)
Monday evening as the system exits into New England. Due to the
dynamics, south/eastern areas could even see periods of steady rain
during this time with both the Euro and Canadian in agreement on
this solution.

Most of the rain should be out by daytime Tuesday but the associated
upper level trough swings into the Northeast during the day which
could lead to returning isolated to scattered showers. Guidance does
show a H850 cold pool of 7-8C moving into the northern CWA so may
even have to monitor potential hail/graupel, especially if enough
sun peaks through during the afternoon hours. Temperatures Tuesday
should be warmer than Monday but still below normal reaching only
into the low - mid 70s. In addition, northerly surface winds could
be a bit breezy Tuesday as well as a 1020-1025mb high from the Ohio
Valley nosing into the region behind out departing low.

High pressure takes control Wednesday giving us a very pleasant day
with temperatures near to slightly below normal in the mid - upper
70s. The high shifts into New England Thursday and returned
southwesterly flow sets up over the area so we should reach around
80 with dew points rising a bit as well.

Friday and Saturday turn more unsettled as our next shortwave exits
the Midwest and with southwesterly flow in place, instability could
lead to threats of showers and thunderstorms. Temperatures should
increase to around normal with dew points on the rise as well.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
Prefrontal showers and thunderstorms will continue this
afternoon across eastern NY and western New England. The cold
front will move slowly across the region tonight into tomorrow
morning.

VFR conditions are expected outside of any thunderstorms this
afternoon into early this evening. Brief reductions to MVFR/IFR
levels are possible in any thunderstorms. KPOU/KPSF have the
best chance between 18Z-22Z, where KALB/KGFL also have TEMP0
groups out from 20Z to 00Z/FRI.

The cold front approaches this evening, and PROB30 groups were
used in the 05Z to 12Z time frame to address additional
thunderstorms. Lowering cigs/vsbys are possible in the bands of
showers and embedded thunderstorms with widespread MVFR
conditions developing. Some IFR conditions are possible in terms
of cigs at KPSF. The band of showers and thunderstorms should
move east of the terminals in the late morning.

Southerly winds of 8 to 15 kts with gusts to 20 to 25 kts
especially at KALB will continue this afternoon. The winds will
be from the south at 5 to 10 kts tonight, and veer to the
southwest at 10 to 15 kts in the late morning with some gusts in
the 20 to 25 kt range possible.

Outlook...

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

&&

.FIRE WEATHER...
A cold front will pass through the region tonight into early
Saturday, bringing widespread showers and thunderstorms to the
area. Rainfall is expected to linger into Saturday from the
Hudson Vally eastward, with a drying trend from west to east
during the day. A cooler and drier airmass will continue to
filter in on Sunday, with RH values falling into the mid-40s to
mid-50s. Westerly winds may gust to 20-25 mph behind the front
Saturday and during Sunday afternoon. Another widespread
rainfall event is expected for Monday.

&&

.HYDROLOGY...
Widespread showers and thunderstorms, some containing heavy
rainfall, are expected tonight into Saturday morning as a cold
front moves east across the region. Localized ponding of water
in low lying/poor drainage and urban areas will be possible, but
progressive nature of the system will limit the flooding
threat. Additional showers and thunderstorms are likely for
areas east of the Hudson Valley Saturday morning into early
afternoon.

Dry weather will build in for later Saturday afternoon and
Sunday.

Another widespread rainfall event is expected late Sunday night
into Monday.

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/Thompson
NEAR TERM...Thompson
SHORT TERM...Thompson
LONG TERM...Speciale
AVIATION...Wasula
FIRE WEATHER...Thompson
HYDROLOGY...BGM/Thompson

Hazardous Weather Outlook
National Weather Service Albany NY
447 PM EDT Fri Aug 4 2017

CTZ001-013-MAZ001-025-NYZ032-033-038>043-047>054-058>061-063>066-
082>084-VTZ013>015-052100-
Northern Litchfield-Southern Litchfield-Northern Berkshire-
Southern Berkshire-Northern Herkimer-Hamilton-Southern Herkimer-
Southern Fulton-Montgomery-Northern Saratoga-Northern Warren-
Northern Washington-Schoharie-Western Schenectady-
Eastern Schenectady-Southern Saratoga-Western Albany-Eastern Albany-
Western Rensselaer-Eastern Rensselaer-Western Greene-Eastern Greene-
Western Columbia-Eastern Columbia-Western Ulster-Eastern Ulster-
Western Dutchess-Eastern Dutchess-Northern Fulton-Southeast Warren-
Southern Washington-Bennington-Western Windham-Eastern Windham-
447 PM EDT Fri Aug 4 2017

This Hazardous Weather Outlook is for northwestern Connecticut,
western Massachusetts, eastern New York and southern Vermont.

.DAY ONE...Tonight.

There is a chance of thunderstorms this evening into tonight. There
is a marginal risk for severe thunderstorms as a cold front
approaches the region. Isolated damaging wind gusts would be the
greatest potential hazard from these thunderstorms, along with
frequent cloud to ground lightning strikes. Brief heavy rainfall will
accompany any thunderstorm that could lead to ponding of water in
low lying, poor drainage and urban areas.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

The marginal risk for severe thunderstorms continues through early
Saturday afternoon, as a cold front moves across the region. Isolated
damaging wind gusts would be the greatest potential hazard from
these thunderstorms, along with frequent cloud to ground lightning
strikes. The best potential for severe thunderstorms is east of the
Hudson Valley.

In addition, locally heavy rainfall could lead to ponding of
water in low lying, poor drainage and urban areas into Saturday
morning.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

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