Area Forecast Discussion
Issued by NWS Albany, NY

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FXUS61 KALY 190000
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
800 PM EDT Sat Aug 18 2018

.SYNOPSIS...
A cold front will move southward through the southern New York
and southern New England this evening. A drier airmass will move
in behind the front this evening. Sunday and Monday are
expected to be mainly dry and much less humid, although a few
showers are possible from time to time over far southern areas.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 745 PM EDT, cooler and drier air continues to filter into
the region from the north, resulting in lower dew points and
breezy conditions. Clouds continue to linger, however, with
some low to mid level moisture evident in the GOES-16 layered WV
imagery. Temperatures are currently in the 60s but are expected
to dip into the upper 50s to mid 60s overnight. This is on track
with the current forecast so have freshened up the hourly temps
and sent the update to NDFD and web servers. Further details
regarding the forecast follow...

As of 145 PM EDT, showers and thunderstorms are ongoing ahead
of a cold front from the Berkshires southwestward to northeast
Pennsylvania. The cold front will continue to push southeast
through the remainder of the forecast area later this afternoon
and this evening. The front will be intersecting a still-moist
airmass characterized by PWATs of 1.75 to 2.00 inches, so it
will be accompanied by scattered showers and thunderstorms. Some
of the storms still have the potential to produce locally heavy
rainfall, especially along and south of a line from the southern
Berkshires to western Ulster County where more favorable
frontal timing may allow for some respectable surface-based
instability of 1000-2500 J/kg to develop given dewpoints in the
low 70s and temperatures heating up into the upper 70s/low 80s.
The front should be fairly progressive which will limit a more
substantial flash flooding threat, but will have to especially
watch areas that saw heavy rain on Friday for localized flooding
concerns. Deep-layer shear values forecast to be 25 to 30 kts
presents a marginal opportunity for storms to be organized, with
several CAMs showing a broken line of convection occurring
along the front. Isolated gusty winds cannot be ruled out. Main
threat period for gusty winds and heavy rain appears to be
roughly through 22Z.

For the areas north of the frontal boundary, a drying trend is
expected with breaks of sunshine towards evening in the wake of
the front. High temps are a little tricky, but have sided away
from the MET MOS guidance which appears to be a cool outlier.
Highs are expected to range from the upper 60s to lower 80s.

Tonight, we`ll be in a low-level northeasterly flow regime in
the wake of the front as the deeper moisture shifts south of the
region. A couple of lingering showers are possible across the
extreme southeast portion of the forecast area. To the north, it
is a tricky call with respect to sky cover as some guidance
indicates a midlevel cloud deck developing in the cold
advection. Outside of this area, some patches of fog are
possible across northern zones as high pressure builds from the
north. It will be noticeably less humid with dewpoints in the
mid 50s to mid 60s with lows in the mid 50s to mid 60s.

The frontal boundary is expected to stall somewhere in the
vicinity of the Delmarva Sunday, while a weak mid-level trough
exists over the mid-Atlantic into the Northeast. Will retain
low chance PoPs over southern portions of Ulster/Dutchess/Litchfield
Sunday to account for possible further shifts northward of a
wave of low pressure along the frontal boundary. For the
remainder of the forecast area, dry east to northeast flow at
low/mid levels should keep things dry, although we may see some
high clouds. Highs Sunday mainly in the upper 60s to upper 70s.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
Sunday night, departing upper low near the I84 corridor will
exit off the New England coast as ridge of high pressure at the
surface will likely build in from the north-northeast. This may
bring some additional moisture off the Atlantic into our New
England counties, other the remainder of the region this high
should allow for good radiational cooling conditions under
partly cloudy to mostly clear skies. Have blended with guidance
and previous forecast with near seasonal normals. Dewpoints
settle back into the 50s.

Higher confidence in a dry forecast and more clearing skies for
the entire forecast area Monday into Monday night. Both the
ridge at the surface and aloft increase so tranquil and near
seasonable temperatures for the later half of August.

Tuesday, global models are a little slower with the approach of
the next upstream storm system set to impact the central and
northern Mississippi River Valley. So we will reduce the onset
of PoPs/Wx in the morning hours and continue with PoPs into the
afternoon hours with the higher values to the west of the Hudson
River. Clouds will increase through the day as temperatures
should climb toward 80F for valley locations and low-mid 70s
elsewhere.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
An impressive low pressure for late August moves up the Saint
Lawrence River Valley Tuesday night into Wednesday. Initially,
precipitation associated with the system`s warm front may struggle
to reach into eastern NY/western New England as high pressure
maintains control over eastern New England. However, by 06z
Wednesday, enough warm air advection associated with the system`s 35-
45kts 850mb jet should push northeastward into our region leading to
widespread precipitation. We should be within in the warm sector
during the overnight hours and with dewpoints very mild in the mid
- upper 60s, it should be a humid night. PWATS look to be over 1.5 -
2 inches with the Hudson Valley potentially over 2".

It`s worth noting that the GFS and Canadian suggest a stronger 500mb
height and wind field associated with this low Tuesday night into
Wednesday over the EURO. These models suggest that the initial
neutrally titled 500mb trough strengths, forms a closed low over
southern Canada and turns negatively titled heading into 12z
Wednesday as the trough axis moves through eastern NY/western New
England. Should this occur, we may have some strong to even severe
weather to contend with Wednesday morning. While instability is
lacking with under 1000J/kg of MLCAPE showing on most pieces of
guidance, this could be a high shear low CAPE environment as 0-6km
shear looks to be 40-45kts thanks to the impressive 500mb wind field
of 50-55kts. Mid-level lapse rates are decent as well ranging 5.5-
6C/km. Therefore, the period from 12z-18z Wednesday will need to be
monitored for a potential line of strong to severe storms as the
trough axis/surface cold front progresses through eastern NY/western
New England. Given the high humidity, any storm will be capable of
heavy downpours.

By Wednesday afternoon and night, it looks to turn breezy as the
impressive surface low (which its 990-995mb MSLP 3-4 standard
deviations below normal for this time of year according to the GFES)
moves through northern New England/southern Canada leading to a
decent pressure rise/fall couplet and isallobaric wind field.
Increased wind gusts to 20-30mph for Wednesday afternoon to reflect
this threat, especially in the Dacks and southern VT where the
isallobaric winds looks to be strongest. Cold advection will lead to
gradually falling temperatures Wednesday afternoon as well and we
should see a drastic drop in humidity heading into Wednesday night.
Overnight lows should be comfortable falling into the 50s.

Pleasant conditions remain in place Thursday and Friday as large
scale high pressure and weak ridging moves in from the Midwest.
Temperatures should be closer to normal for late August only
reaching into the upper 70s both days. Humidity level remain low as
well thanks to the northerly flow.

The weak ridge axis should move into eastern New England heading
into Saturday which should lead to to west-southwesterly flow aloft.
This in turn should allow temperatures to warm up a few degrees
Saturday reaching into the low 80s. For now left a dry forecast but
a few shortwave embedded in the overall flow aloft will need to be
watched.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Drier and cooler air, along with breezy conditions, will
continue to filter into the region from the north overnight in
the wake of a cold front. These breezy conditions, along with
lingering low to mid level clouds/moisture should inhibit fog
formation. Outside of MVFR/IFR CIGS at KPSF/KPOU overnight,
conditions will be VFR through the forecast period. All sites
should improve to VFR after 12Z/Sun.

Outlook...

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

&&

.FIRE WEATHER...
After a wet day Friday and southern portions on Saturday,
a drying trend will occur from north to south in the evening,
setting the stage for a cooler and mainly dry period Sunday and
should last into Tuesday morning. High temperatures will be
near to slightly below normal Sunday and Monday with a light
east to northeast wind. RH values will bottom out mainly in the
50 percentile.

&&

.HYDROLOGY...
Much of the region saw rainfall on Friday and southern areas
during Saturday, with several spots receiving in excess of an
inch and some areas across Columbia and Berkshire Counties
seeing two to five inches of rainfall. Showers and thunderstorms
will exit and weaken our southern zones by early evening.

Waters will continue to recede into the remainder of the weekend
and into Tuesday morning.

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...11/Thompson
NEAR TERM...11/Thompson/JVM
SHORT TERM...BGM
LONG TERM...Speciale
AVIATION...JVM
FIRE WEATHER...BGM/Thompson
HYDROLOGY...BGM/Thompson


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