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fxus61 kaly 301043 
afdaly

Area forecast discussion
National Weather Service Albany New York
643 am EDT sun Apr 30 2017

Synopsis...
high pressure will continue to ridge in from southwest Quebec this
morning with cool late April weather, as a weak disturbance may
focus some isolated to scattered showers, as well as a few rumbles
of thunder especially west of the Hudson River valley this
afternoon. 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 PM this evening/...
as of 633 am EDT...a cool/cold start to the last day of April,
as a chilly Canadian air mass continues to build into the region
from near James Bay, as it will drift southeast across
west/southwest Quebec by the afternoon. Lows this morning were
in the 30s and 40s, with some upper 20s across the dacks and
southern green mtns.

The cold front that moved through yesterday has become
stationary near the Ohio Valley and mid Atlantic states. A short-
wave moving over the western periphery of the h500 closed
anticyclone centered east of the Carolinas this morning on the
GOES-16 water vapor channels will drift into western-central New York.
The short-wave and a sfc trough will focus some isolated-
scattered showers with the better forcing due to the isentropic
lift roughly from the capital region/northern Catskills north
and west. The 00z European model (ecmwf)/NAM/can ggem are the most aggressive
with this feature in the late morning into the afternoon. The
00z GFS has a secondary sfc anticyclone building from east of
the Gulf of Maine. We have placed isolated to scattered showers
in the forecast with the higher pops west of the Hudson River
valley and from the Tri Cities north. The showalter stability
indices looked more stable with less MUCAPE on the GFS compared
to the NAM. Our confidence was greatest for isolated
thunderstorm or a few rumbles of thunder again west of the
capital region. The latest hrrr hints at the capital region
north for the more robust showers/isolated thunderstorms from
the late morning into the early PM, which fits with the latest
radar and satellite trends upstream over southeast Ontario/western New York
and PA.

Temps continue to trend down cooler today due to the shallow
cold air funneled into the region from the sfc anticyclone to
the north, and the possibility of the showers producing rain
cooled air. As the wind veer from the north/northwest in the sfc
and boundary layer to the east southeast enough warming may
occur for highs to get closer to the an European model (ecmwf)/gfsmos blend over
the cooler NAM MOS highs. Highs will generally be in the upper
40s to mid 50s over the hills/mountains and upper 50s to lower
60s in the valley areas.

&&

Short term /6 PM this evening through Tuesday night/...
tonight...the warm front starts to make progress northward, as
the better lift and synoptic forcing continues to be with the
thermal trough earlier in the day well north of the region along
the rim of the h500 ridge off the coast. Nonetheless, some
isold-scattered showers and patchy drizzle will likely occur
form the Hudson River Valley North and east ahead of the warm
front with the low-level boundary layer flow being from the
southeast. Some low-level stratus will likely blanket most of
the region. A gray and cool overnight period is expected with
lows predominately in the 40s.

Monday...a potent closed upper low continues to churn north to
northeast into the upper Midwest and western Great Lakes region.
Meanwhile, downstream over the northeast the the mid and upper
level flow amplifies from the southwest with the sfc ridge
shifting slightly further offshore. It will take a little time
for the low stratus to burn off in the morning, but there are
hints in the guidance of some sunshine by the early afternoon as
we bust into the warm sector. H850 temps of +12c to +14c would
support even higher temps that we are forecasting, but the
clouds may be tough to erode especially east of the Hudson River
valley. Also, some showers and thunderstorms will likely flare
up quickly in the afternoon with a potential prefrontal sfc
trough ahead of the cold front. We have mainly a chance of
showers and thunderstorms in the late afternoon with the better
coverage at night. Highs will generally be in the mid 60s to mid
70s across the region with the cooler temps across western New
England and over the mountains.

Monday night...the low-level jet ahead of the cold front
increases with a deeper fetch of moisture out of the Gulf. The
south to southwest h850 low-level jet increases to around 50
kts. The convergence and synoptic lift increases with the front
coupled with good upper jet dynamics. Locations north and west
of the capital region will likely be near the rear entrance
region of an h250 jet streak of 100-110 kts per the latest
nam40. The front comes through at night with waning instability.
Some strong thunderstorms may be possible with gusty winds
especially near the western Mohawk Valley and southern
Adirondacks. The latest Storm Prediction Center day 2 graphic has the marginal risk
barely clip Herkimer County. The better chance for severe
thunderstorms looks to be west with the better heating, shear
and instability set up. We will continue to monitor any
potentially severe threat, but for now will call it widespread
showers with a chance of thunderstorms. With sfc dwpts surging
into the 50s to around 60f and precipitable waters a couple of Standard
deviations above normal...in the 1-1.50"+ inch range, as a
decent burst of rain is possible with around three quarters of
an inch over the northwest zones /southern dacks/ to quarter
inch over northwest CT/Mid Hudson valley. Lows will be milder in the
upper 40s to upper 50s.

Tue-Tue night...the closed cyclone upstream over the northern
Great Lakes region, and southern Ontario will continue to impact
the area with breezy and cool conditions with scattered showers
as several short-wave impulses swing through the cyclone across
the region. The most widespread showers will likely be north and
west of the capital region in the cyclonic flow with some west-
southwest orographic enhancement off the western Adirondacks and
southern greens. Plenty of Great Lake moisture will be tapped in
the cyclonic flow. Highs will be mainly in the 50s to lower 60s
west of the Hudson River valley...and mid 60s to around 70f from
the Hudson River valley eastward except some cooler readings in
the upper 50s to lower 60s over the southern greens. Lows fall
back to the mid 30s to mid 40s over the region Tue night, as the
stronger cold advection sweeps across the region.

&&

Long term /Wednesday through Saturday/...
the long term period will be dominated by general upper level
troughiness and below normal temperatures. And although the models
continue to struggle with the evolution of the cut off low during
the latter part of the week, there seems to be increasing confidence
for daily rain chances and plenty of cloudiness.

On Wednesday, 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 shortwave ridging passes through the
region Wednesday night as the next low pressure system takes shape
in the mid-Mississippi Valley. Temperatures Wednesday night could be
quite chilly depending on the cloud cover as the 850mb temps are -1
to -4 c across most of the area, with 700 mb temps ranging from -6
to -10 c.

The 00z/30 GFS and European model (ecmwf) continue to struggle with the evolution of
a cut off low 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 into our region. Even though there
continues to be discontinuity in the model solutions beyond Thursday
afternoon, there is increasing confidence for rain chances through
at least Friday. Potential for additional rain over the weekend will
depend on the position of the upper low and trough.

Below normal temperatures should continue Thursday through Saturday,
with daytime highs mainly in the 50s, and overnight lows in the 40s,
although some 30s could occur across higher elevations.

&&

Aviation /12z Sunday through Thursday/...
VFR conditions will prevail through at least this afternoon,
with mainly mid level clouds. There is the potential for some
showers/thunderstorms to develop during the afternoon hours but
due to lower confidence, decided to only include vcsh at this
time. Model soundings also indicate that ceilings build down during
the late evening and overnight hours so have trended ceilings to
IFR after 06z/Mon.

Winds will be out of the north/northeast at 5-10 mph most of
today then shift back to the southeast towards the end of the
period. Some low level wind shear is also possible at kpsf late
in the period.

Outlook...

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...
high pressure will continue to ridge in from southwest Quebec this
morning with cool late April weather, as a weak disturbance may
focus some isolated to scattered showers, as well as a few
rumbles of thunder especially west of the Hudson River valley
this afternoon. 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 cold front will bring
widespread showers and a chance of thunderstorms late in the
afternoon into Tuesday morning.

The relative humidity values will lower to 35 to 55 percent today with
isolated light showers as the winds will shift to east to the
southeast at 5 to 15 mph. 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. Winds
will become southeast to south tonight into Monday at 10 to 15
mph.

&&

Hydrology...
a warm front will lift north through tonight. Rainfall amounts
will be fairly light once again, with a few hundredths to a
tenth of an inch or so.

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

&&

$$
Synopsis...wasula
near term...wasula
short term...wasula

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