Area Forecast Discussion
Issued by NWS Albany, NY

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272
FXUS61 KALY 262329
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
729 PM EDT Fri May 26 2017

.SYNOPSIS...
Rain showers north and east of the Capital District will slowly
diminish into this evening as low pressure departs, setting up a
milder and mainly dry Saturday. It will be slightly warmer still
on Sunday with a mixture of sun and clouds. Showers and possibly
a few thunderstorms are likely Sunday night into Memorial Day.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Rain is on the diminishing trend and will continue through this
evening. Some weak cold advection will occur through the night
with dew points falling. The weak cold advection will help
temperatures fall near forecasted lows. So, some minor
adjustments to rain chances and temperatures through this
evening. Previous AFD has a few more details and is below...

Stacked upper low still churning over the Gulf of Maine. Narrow
deformation zone within enhanced midlevel theta-e corridor
wrapping back into the system from the north and west is leading
to the continuation of showers mainly from the Western
Adirondacks to the Capital District to the Berkshires and points
north and east. Just a few showers to the south and west where
shallow convection and also a few cloud breaks are occurring.
Hi-res models indicate the steadier activity breaking up after
22Z or so, so have tapered PoPs back to chance afterward. A good
deal of cloud cover should continue overnight for much of the
area as there is plentiful cloud cover upstream and not a real
good drying signal, though have worked in a very gradual partial
clearing trend from southwest to northeast. With the cloud
cover, lows tonight in the mid-40s to low 50s will be slightly
above seasonal normals.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
Mean upper ridging builds in Saturday into Sunday, which should
result in mainly quiet weather for the first part of the holiday
weekend. Only fly in the ointment appears to be tied to the MCV
now tracking across Illinois. Model consensus is for the MCV to
dampen out as it tracks into the mean ridging. GFS, which had
been the most amplified with the MCV, has now trended less-
amplified. The upshot is that most areas will remain dry on
Saturday; however, have continued slight chance PoPs over our
southern tier of counties Saturday afternoon/evening as the
northern fringe of the precip associated with the MCV may just
brush the region. Otherwise, at least partial sunshine is
expected, though upstream cloud cover and only weak high
pressure/subsidence suggests a healthy cloud fraction will
remain. High temps will be several degrees warmer than recent
days, though likely still coming up a bit short of normal. Quiet
once again Saturday night under subsident northwesterly flow.
Some fog is not out of the question depending on the degree of
clearing as the boundary layer will remain somewhat moist.

Upper ridging will crest over the region Sunday, giving way to
weak height falls Sunday night as the first in a series of
impulses emanating from a deep and expansive upper low near Lake
Superior approaches. Sunday is expected to be a tad warmer than
Saturday as 925 mb temps warm by around 4C under partial cloud
cover. However, clouds will be increasing late in the day ahead
of the impulse. Increasing low-level jet/moisture transport
ahead of the impulse will bring a chance of showers to the
forecast area Sunday night, with likely PoPs after 06Z west of
the Hudson Valley. However, models have trended slower with this
system as of late, so latest forecast slows down the arrival of
PoPs. Some elevated instability works into areas west of the
Hudson Valley, so have kept slight chance thunder in the
forecast Sunday night.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
The extended portion of the forecast continues to look unsettled for
much of next week with a mean longwave trough over south/southeast
Canada, the Upper Midwest, Great Lakes Region into the Northeast.
Several disturbances will impact the forecast area until late in the
work week.

Memorial Day... A short-wave in the southwesterly flow aloft quickly
approaches the region Monday morning.  After a warm frontal passage,
a weak cold/occluded front will focus showers and a slight chc of
thunderstorms during the late morning into the afternoon based on
the latest GEFS/GFS/ECMWF/CAN GGEM. The Showalter stability indices
briefly become negative with some elevated instability coupled with
MUCAPE values generally 500 J/kg or less especially west of the
Hudson River Valley.  Pops were raised to likely values from west to
east across the entire forecast area, as well as an area of
categorical values was used north and east of the Capital Region
during the day. H850 temps are in the +8C to +10C range, but lots of
clouds and the rain cooled air should keep max temps cooler than
normal with highs generally in the upper 60s to around 70F in the
valleys, and upper 50s to mid 60s over the hills and mountains.

Monday night into Tuesday...A surface low may form along the front
and pass south of New England Monday night for some scattered
showers to linger especially south and east of the Capital Region.
The upper level trough amplifies and the GEFS has H500 height over
the upper Midwest/Great Lakes region 1 to 2 standard deviations
below normal. Another short-wave rounds the base of the trough from
the OH Valley and eastern Great Lakes Region with another round of
showers and slight chance of thunderstorms ahead of a cold front.
The 12Z GFS has a bit more instability /MUCAPES in the 500-1000+
J/kg range/and 0-6 km bulk shear values of 50 kts, so some of the
thunderstorms could be on the strong side if enough heating occurs.
There are some signals of steepening mid level lapse rates to 6.5-
7C/km. We kept the thunderstorm threat at a slight chance for now,
but this may have to be raised later if the thunderstorm threat
becomes clearer.  After lows in the upper 40s to mid 50s, max temps
will be seasonable in the mid 60s to mid 70s across the forecast
area.

Tuesday night into Thursday...The broad upper level trough drifts
over southeast Canada, the Great lakes Region and Northeast. A
series of sfc troughs and mid level short-waves move across the
region in the cyclonic flow.  Scattered showers tied to the diurnal
heating will be possible Wed and Thu afternoons.  There could be
some small hail, as the cold pool moves near the region. The showers
coverage should dissipate each evening, although the better cyclonic
vorticity advection initially will set-up north and west of the
Capital Region on WED. Lows will range from the mid/upper 40s over
the mtns to lower to mid 50s in the valleys each night with upper
60s to mid 70s for highs in the lower elevations, and upper 50s to
mid 60s over the hills and mountains, as these temps are a shade
below normal for late May into early June.

Thu night into Friday, there are some signals in the medium range
guidance that the longwave trough axis moves downstream as well as
the core of the coldest air aloft with some ridging building
eastward from the Great Lakes Region. A slight chc of showers was
kept in the grids, but this looks like the best chance of a dry day
based on the latest EC/GFS.  Temps still look slightly below normal
for early June.

&&

.AVIATION /23Z FRIDAY THROUGH WEDNESDAY/...
The upper level trough to the system and moist cyclonic flow
will continue to impact the TAF sites with scattered showers
especially from KALB-KSPF north and east into this evening. Low-
level moisture will linger most of the overnight period into
tomorrow morning, as some weak ridging begins to build in across
the region for Saturday.

Ceilings will vary from MVFR to VFR this evening before
becoming predominantly MVFR by midnight. Ceilings at KPOU may be
VFR all night. Ceilings will then rise into the VFR range after
13Z-14Z at all TAF sites. Visibilities will be VFR at all TAF
sites outside the scattered showers this evening, with
visibilities possible dropping to as low as 3SM in scattered
showers.

Ceilings and visibilities are expected to be VFR Saturday
morning and afternoon. KPSF will linger the longest with high
MVFR cigs until the late morning/early afternoon.

The winds will be generally light from the north to northwest
at 6 Kt or less tonight. Light and variable direction winds of
5 kts or less are likely late Saturday morning into the early
afternoon.

Outlook...

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

&&

.FIRE WEATHER...
Slightly warmer and drier Saturday with light northwesterly
winds. A bit warmer still on Sunday with light southerly winds.
RH values will bottom out in the 50s both days. Showers and a
few thunderstorms become likely Sunday night into Memorial Day.

&&

.HYDROLOGY...
Mainly dry weather is expected Saturday and Sunday. An
approaching system will bring the likelihood of showers and a
few thunderstorms Sunday night into Memorial Day, with total QPF
ranging from 0.25-0.75" expected. Additional periods of showers
and thunderstorms are likely Tuesday and Wednesday.

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.

&&

.EQUIPMENT...
The ASOS in Glens Falls at the Floyd Bennett Memorial Airport
continues to experience outages with hourly METARS occasionally
missing. This will continue until communications are fully
restored.

&&

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

&&

$$
SYNOPSIS...Thompson
NEAR TERM...NAS/Thompson
SHORT TERM...Thompson
LONG TERM...Wasula
AVIATION...NAS
FIRE WEATHER...Thompson
HYDROLOGY...Thompson
EQUIPMENT...



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