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fxus61 kaly 271035 
afdaly

Area forecast discussion
National Weather Service Albany New York
635 am EDT Thu Apr 27 2017

Synopsis...
early cloud cover today will give way to clearing skies and warm
temperatures. A weakening cold front will provide the opportunity
for scattered showers and thunderstorms tonight. Skies clear again
on Friday with another warm day expected. Warm temperatures continue
Saturday, though a few showers or storms are possible. Sunday will
be not quite as warm, but still mild for this time of year.

&&

Near term /through tonight/...
as of 620 am, stratus still covering much of the region. A look
at some webcams shows a few patches of fog toward the Schoharie
valley, Catskills, and Adirondacks. Minor changes to going
forecast.

Previous discussion...stacked low pressure just south of Cape
Cod is readily visible on water vapor imagery. Meanwhile to our
west, a deep upper trough has become negatively tilted and is
ejecting northeastward into the lower Ohio Valley. Shortwave
ridging exists in between these two features and will translate
into the local area today, leading to quiescent weather.
However, a good deal of low-level moisture exists, and with a
lack of flow at low levels, an extensive stratus deck is in
place across most of the forecast area. Fog has yet to
materialize due to this stratus limiting surface cooling, but
could still form in patches if any clearing occurs. Model
forecast soundings suggest the moisture will thin out today with
more clearing today than yesterday. Still a tricky high temp
forecast though. Very warm 850 mb temps increase to the lower
teens c. Yesterday at Albany, temps shot up to the lower 70s
with 850 temps around 9c where a few cloud breaks occurred.
Meanwhile at Poughkeepsie, temperatures only reached 61 where a
solid overcast was in place all day. Despite the clearing
forecasted, model soundings suggest mixing will come up short of
850 mb; however we have seen multiple times so far this Spring
that models have drastically underestimated mixing depths. Given
these sources of uncertainty have stuck close to MOS guidance
for highs, going a little above outside south/east portions of
the forecast area where clouds should hang on the longest. Highs
today expected to reach the upper 60s to near 80, still well
above climo even in the cooler spots.

Tonight, as surface low pressure tracks north toward James Bay,
its weakening cold front will approach the local area. Some weak
height falls will occur as the leading edge of the deep trough
enveloping much of the country eases toward our area. The best
height falls/forcing for ascent will remain well west of our
region. Still, enough evidence exists to support at least scattered
coverage of showers and a few thunderstorms overnight. Best
coverage is expected to be over the western Adirondacks/Mohawk
Valley closer to the best synoptic-scale forcing. A few hundred
j/kg of MUCAPE as well as the weakening instability plume
washes into our area supports the chance for thunder. High
values of deep-layer shear with fast 500 mb flow overhead, but
limited instability is expected to keep any convection garden-
variety. Another very mild night with southerly flow ahead of
the front, with lows in the mid-50s to near 60.

&&

Short term /Friday through Saturday night/...
the front should be clear of the local area by the mid-morning
hours Friday, with Post-frontal subsidence leading to a
clearing trend. Another very warm day is expected, as there is
really not any cold air advection behind the front.

Upper-level ridging will attempt to expand into the
northeastern US beginning Friday night as the pattern becomes
very amplified. However, the upper jet/lower-level baroclinic
zone will remain in close proximity to the local area. Midlevel
moisture will increase late Friday night into Saturday, and high
pressure over south-central Canada will try to expand eastward,
pushing the lower-level frontal boundary across the region on
Saturday. There is not a lot of synoptic-scale forcing for
ascent with the upper ridge in place, but cannot rule out a few
showers or maybe a thunderstorm from late Friday night into
Saturday as the front crosses the region. A notable solution is
the NAM, which appears to generate an mesoscale convective system and pushes it across
our northern zones Friday night. Don't think this is totally
probable but it's something to watch for. Model forecast
soundings suggest a respectable amount of instability Saturday
with dewpoints in the upper 50s and steep midlevel lapse rates
from the capital district south, suggesting a conditional threat
for some stronger storms should they develop. Uncertainty with
respect to coverage precludes mentioning this threat in the severe weather potential statement
for now, and Storm Prediction Center just has general thunder over the southern
portions of the County Warning Area. It will also be quite breezy Saturday as
mixing into a strong low-level wind field will occur.

After another very mild night Friday night, another very warm
day is on tap for Saturday, with highs ranging from the mid-60s
over the Adirondacks to the lower 80s in the Mid-Hudson valley.
Considerably cooler Saturday night, though still well above
seasonal normals in most areas.

&&

Long term /Sunday through Wednesday/...
the extended forecast period continues to be unsettled into the
middle of next week, as a mean upper level trough will set up over
the northeast and southeastern Canada Tuesday into Wednesday.

Sunday...high pressure will be in control to start the long term
building in from south of James Bay. An h500 ridge will be situated
east of the mid-Atlantic coast. Clouds will be on the increase
during the day, as a warm front lifts northward from the Ohio Valley
and mid Atlantic states. Low pressure associated with the warm
front will be moving northward into the central MS River Valley, as
an upstream mid and upper level trough turns negatively tilted.
Clouds will continue to thicken and lower from the south and west
with the increasing isentropic lift ahead of the warm front. Some
isolated to scattered showers will begin to impact the forecast area
during the afternoon. The better chance of showers will tend to be
west of the Hudson River valley. H850 temps increase to about +8c
to +12c from northeast to southwest across eastern New York and western
New England for high temps to be in the mid and upper 60s in the
valleys, and upper 50s to lower 60s over the mtns.

Sunday night into Monday...the isentropic lift continues to enhance
ahead of the front with good low-level moisture convergence for a
better chance of showers Sunday evening. The warm front will likely
not make its way across the forecast area until later Monday, so
high chc and likely pops were carried into Monday morning. The
forecast area will likely get into a warm sector on Monday. The GFS
does not have a lot of SBCAPE over the region with generally less
than 500 j/kg, but the showalter stability indices fall to -1c to -
3c with a notable south to southwest low-level jet of 40-50 kts
between 18z to 00z Tuesday. A chance of thunderstorms was included
across the entire area on Monday. The air mass will become more
humid with sfc dewpts getting into the 50s to lower 60s. After lows
in the 40s to lower 50s, expect highs to be above normal in the
humid air mass with generally lower 70s in the valleys and 60s over
the higher terrain and across most of western New England.

Monday night into Tuesday...a strong low pressure system closes off
over the western and central Great Lakes region. The cold front on
the leading edge of the upper trough impacts eastern New York and western
New England with a band of showers and some isolated to scattered
thunderstorms Monday night into Tuesday morning. The 0-6 km bulk
shear increases to 50+ knots Monday night ahead of the front with
MUCAPE values of 100-400 j/kg off the latest GFS. Layered precipitable waters rise
to 1-1.50+ inches for a brief period. Some bursts of moderate to
heavy rainfall area are likely with the cold front. Lows Monday
night with be on the mild side with mainly upper 40s to upper 50s
across the region. The cold front moves through by daybreak based
on the GFS/ECMWF/can ggem. Post cold frontal advection and cyclonic
flow aloft will impact the area on Tuesday. Scattered showers north of
the Mid-Hudson valley and breezy conditions are likely as a short-
wave moves across the region associated with the upper low. H850
temps tumble to -3c to +1c from northwest to southeast across the
region by 00z Wednesday based on the latest GFS.

Tuesday night to Wednesday...in the cyclonic flow at the sfc and
aloft, cool and chilly conditions will dominate for the mid-week. A
slight to low chance of showers is possible from the capital
region/Berkshires north and west. Lows will be on the cool side
with mid/upper 30s to around 40f over the mountains and lower to mid
40s in the valleys. Temps may dip a shade below normal on Wednesday with
some isolated showers in the cool cyclonic flow. Lower to mid 60s
are possible from the capital district and Mid-Hudson valley south
and east into northwest CT with generally 50s north and west, though some
upper 40s are possible over the southern dacks and southern
greens.

&&

Aviation /12z Thursday through Monday/...
low pressure near Nantucket will continue to move eastward this
morning. The stacked sfc cyclone will be well east to southeast
of Cape Cod by the late afternoon into the early evening. A
cold front will approach from the west tonight with scattered
showers and isolated thunderstorms.

Low MVFR conditions prevail this morning for kgfl/kalb/kpou and
IFR cigs and vsbys at kpsf with plenty of low-level moisture
trapped under an inversion well north and west of the stacked
cyclone. Ceilings are generally in the 1.5-2.5 kft above ground level range with
reductions to IFR levels at kpsf in the 500-800 feet above ground level range
with vsbys in the 1.5-2.5 sm range at kpsf. These conditions
will gradually improve at kpsf into the MVFR range between 14z-
16z.

The trend will be for the cigs to slowly rise back to high MVFR
levels in the late morning into the early PM with some drier
air/subsidence on the northwest side of the cyclone and with a
short-wave ridge building in for kgfl/kalb/kpou and possibly
kpsf. A brief period of clearing is possible in the mid to late
afternoon with VFR conditions at all the taf sites. However, a
cold front will be approaching from the west with a chance of
showers once again. Cigs will fall back into the MVFR range
especially between 01z-04z/Fri. The greatest threat for showers
will be btwn 07z-12z. There is also a slight to low chc of
thunderstorms, but our confidence was not high enough to
include in the tafs. Expect widespread MVFR conditions, with IFR
conditions once again at kpsf.

The winds will increase from the south to southeast at 5-10 kt
late this morning into the afternoon, and lighten from the S/southeast
at 4 to 7 kts tonight.

Outlook...

Friday night: no operational impact. No sig weather.
Saturday: moderate operational impact. Breezy chance of rain showers...tsra.
Saturday night: no operational impact. No sig weather.
Sunday: low operational impact. Slight chance of rain showers.
Sunday night: moderate operational impact. Chance of rain showers.
Monday: moderate operational impact. Chance of rain showers...tsra.
Monday night: high operational impact. Likely rain showers...tsra.
Tuesday: moderate operational impact. Chance of rain showers.

&&

Fire weather...
partial to nearly total clearing is expected by this afternoon
with a warm day in store. The warmest temps and quickest
clearing will be found the farther north and west one GOES. Relative humidity
values will fall into the 40 to 65 percent range, with southeast
winds increasing to 10 to 15 mph. Scattered showers and
thunderstorms are possible tonight along a weakening cold front.
It should clear and dry out quickly on Friday with another very
warm day expected. Relative humidity values will drop into the 30 to 40
percent range, with westerly winds at 5 to 10 mph. Very warm and
a bit more humid Saturday, with a few showers or storms
possible. It will be quite breezy with southwest winds of 10 to 20
mph with some gusts to 30 mph possible. Relative humidity values will fall to
around 40 to 50 percent.

&&

Hydrology...
scattered showers and a few thunderstorms are expected tonight
along a weakening cold front. Basin-average quantitative precipitation forecast amounts are
expected to be under a tenth of an inch, but locally higher in
thunderstorms. Though periods of showers could occur at times
this weekend, amounts should be hydrologically insignificant.

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.
New York...none.
Massachusetts...none.
Vermont...none.

&&

$$
Synopsis...Thompson
near term...Thompson
short term...Thompson

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