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Area forecast discussion
National Weather Service Albany New York
428 PM EDT sun Apr 30 2017

a warm front will increase the threat of isolated to scattered
showers tonight into early Monday as it slowly lifts north of
the region. A warm and more humid air mass will be over the
region on Monday, but a cold front will bring widespread showers
and a chance of thunderstorms late in the afternoon into
Tuesday morning.


Near term /until 6 am Monday morning/...
rain and clouds along and north of the warm front in our region
prevented any warming of temperatures today, and clouds should
prevent temperatures from falling much tonight. Isolated
showers exiting but cloud cover persisting. Satellite trends
show the western edge of the cloud cover retreating east and
north slowly through central NY/PA. However, more scattered
showers and thunderstorms in western New York/PA developing in slowly
increasing low level convergence where the boundary layer wind
flow is increasing proximate to the boundary layer thermal

The cooler dryer airmass over eastern New York and New England is
still fairly well anchored and until the low level ridging moves
farther east, the clearing line to the west may get hung up in
the Catskills and Adirondacks overnight and into the early
morning hours of Monday. The scattered showers and thunderstorms
will likely track east through the night within the zone of
elevated instability over our region, which would contribute to
more cloud cover and mention of isolated to scattered showers
and storms between midnight and daybreak in some areas.

Lows tonight within a few degrees of current temperatures, which
are in the 40s to mid 50s.


Short term /6 am Monday morning through Wednesday/...
the proximity of the warm front not only at the surface but the
boundary layer is wreaking havoc with temperature forecasts as
the difference in temperatures on either side of the warm front
vary 20 degrees or more from eastern New York to central NY/PA.
Sources of guidance have been far from perfect forecasting where
the warm front and temperature gradient sets up. So, will have
to rely on some near term trends to see what areas have the best
chances for the warm front to push north through the day Monday.

Sources of guidance have been consistent and relatively accurate
with the boundary layer winds forecasts and are consistent in
showing steadily increasing southwest boundary layer winds
tonight and Monday. Since the clearing line is already slowly
building east, as long as the current convection in western
areas does not expand and anchor the cooler drier air over our
region into Monday morning, some breaks of sun and temperatures
in the 70s should be reachable Monday afternoon. The boundary
layer thermal gradient surges north and loosens, which also
suggests some downsloping wind flow should finally have some
benefits in terms of warming US into the 70s. However, northern
areas into southern Vermont and the northern Berkshires may just get
to 70 if the warm front is slow to push north and east.

Even if the low clouds and cooler airmass is dislodged, quite a
bit of mid and high clouds will be over the area as convective
debris from upstream convection spills east. Some scattered
prefrontal convection could form and affect western areas Monday

There is a general consensus for the cold front to track through
our region Monday night and the early morning hours of Tuesday.
There will be considerable instability late Monday afternoon and
evening, moderating later Monday night. The low level flow will
be relatively strong, so some thunderstorms could approach
severe criteria, especially along and west of the Hudson

Cold advection spreads across the region Tuesday and the upper
dynamics advance through the Great Lakes toward our region.
Cooling aloft and the proximity of the boundary layer thermal
gradient building east and south will support scattered showers
in many areas through the day Tuesday. There should be some
break in the clouds in between showers. So, highs Tuesday in
the 60s to lower 70s but some upper 50s northern areas.

Upper dynamics tracking across northern areas will continue the
isolated to scattered showers Wednesday with the best chances in
the western Mohawk Valley through the southern Adirondacks. Some
snow shower activity is possible in the higher elevations of the
southern Adirondacks Tuesday night. Highs Wednesday in the 50s
to lower 60s but upper 40s northern areas.


Long term /Wednesday night through Sunday/...
the long term period will be active with multiple upper-level
shortwaves and cool temperatures. 12z GFS and European model (ecmwf) model runs
coming into better consensus regarding the evolution of the cut off
low over the NE US throughout the upcoming weekend. There will be
increasing precipitation chances and sky cover as we head towards
the weekend.

On Wednesday evening, some trailing upper level energy will allow
for a chance of showers mainly north and west of the greater capital
region as the main upper level low continues to lift further
northeast. Very brief and weak surface ridging migrates through the
region Wednesday night through early Thursday providing a break in
precipitation before the next low pressure system develops in the
mid-Mississippi Valley. Temperatures Wednesday night will be quite
chilly depending on the cloud cover as the 850mb temps are -1 to -3
c across most of the area, with resulting surface temperatures in
the upper 30s/low 40s in valley regions and low to mid 30s in the
higher terrain.

The 12z GFS and European model (ecmwf) seem to be in a bit more of agreement with
respect to the cut-off low development and its interaction with
shortwave energy diving southward out of Canada during the thurs-sun
time frame. Both models develop a surface low over the Tennessee
Valley Thursday afternoon, spreading rainfall northeastward ahead of
and along a warm front that extends into our region. There is
increasing confidence for rain chances Thursday through Friday and
then significant model discrepancy persists on Saturday. The GFS has
precipitable water anomalies of 2-3 Standard deviations suggesting the potential
for a moderate amount of rainfall over the weekend. Ultimately, the
location and amount of precipitation will be dependent on where the
upper-level low develops. Sunday looks to be cloudy with some
leftover showers at this point as the surface low departs to our
northeast. 850hpa temperatures of -2 to -7 c dive southward into
eastern New York Sunday into Sunday night so there could be a chance for
some snow mixing in with the lingering rain showers.

Below normal temperatures should continue Thursday through Sunday,
with daytime highs mainly in the mid/upper 50s in valley locations
and low 50s over the higher terrain. Overnight lows in the mid 40s
in valley locations with upper 30s across higher elevations. A
seasonably cold airmass may move into the region late Sunday into
Monday so we may not have seen the end of winter quite yet!


Aviation /20z Sunday through Friday/...
scattered showers over the region north of a warm front are
exiting and will affect the taf sites through about 20z. No
other rain seen upstream and mesoscale models suggest little if
any additional development through late afternoon and much of

Clouds are persistent north of the warm front but ceilings are
above 3000 feet. Keeping conditions VFR through most of tonight
with ceilings slowly lowering with the slow approach of the warm
front from the south. There could be additional shower and
isolated thunderstorm development between midnight and daybreak
Monday that may track into our region as increasing low level
winds aloft increase the convergence along the warm front. So,
as the ceilings lower, adding vcsh to all taf sites after about
08z and through 13z- 14z.

Ceilings could lower around or into the IFR range at all taf
sites between midnight and daybreak, then rise back to just to
VFR, just over 3000 feet after about 14z. Although ceilings may
take longer to rise above 3000 feet at kpsf.

Winds will be light north to east this afternoon at less than 10
kt. Winds turn to southeast this evening at 10 kt or less and
then south Monday morning at around 10 kt.


Monday night: high operational impact. Breezy definite rain showers...tsra.
Tuesday: moderate operational impact. Breezy chance of rain showers.
Tuesday night: low operational impact. Slight chance of rain showers.
Wednesday: moderate operational impact. Breezy chance of rain.
Wednesday night: low operational impact. Slight chance of rain.
Thursday: moderate operational impact. Chance of rain.
Thursday night: high operational impact. Definite rain.
Friday: high operational impact. Likely rain.


Fire weather...
a warm front will increase the threat of isolated to scattered
showers tonight into early Monday as it slowly lifts north of
the region. A warm and more humid air mass will be over the
region on Monday, but a cold front will bring widespread showers
and a chance of thunderstorms late in the afternoon into
Tuesday morning.

The relative humidity values recover to 85 to 100 percent tonight and fall
only to 55 to 70 percent Monday with scattered showers and
thunderstorms late Monday afternoon. Relative humidity values will be 70 to 90
percent Monday night and drop to 40 to 60 percent Tuesday. Winds
will become southeast to south tonight into Monday at 10 to 15
mph. Winds shift to west late Monday night at around 15 mph and
become northwest at 10 to 20 mph Tuesday.


isolated to scattered showers and thunderstorms are expected
tonight with local rainfall amounts up to a quarter inch. A
strong cold front will cross through the region late Monday
afternoon into Tuesday morning. This front may allow for some
locally higher rainfall totals due to more widespread showers
and a chance of thunderstorms in a more humid air mass. No
problems are anticipated on the main Stem rivers. Rainfall
amounts will range from a quarter to three quarters of an inch
over the Hydro service area with some locally higher amounts in
thunderstorms. Ponding of water on roadways or low lying areas
and poor drainage within urban areas will be possible.

Showery and unsettled weather continues Tuesday into Wednesday
with additional light rainfall amounts of a few hundredths to a
quarter of an inch.

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...
New York...none.


near term...NAS
short term...NAS

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