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Area forecast discussion 
National Weather Service Albany New York
652 am EDT Wednesday may 27 2015

Synopsis...
a warm and humid air mass will continue to be over
eastern New York and western New England today. An upper level
disturbance well ahead of a cold front will focus some strong to
severe thunderstorms with locally heavy rainfall this afternoon into
early this evening. The cold front will move through the region on
Thursday with more scattered showers and thunderstorms. High
pressure will build in from the north and west Thursday night into
Friday with drier and less humid conditions.

&&

Near term /until 6 PM this evening/...
..strong to severe thunderstorms possible this afternoon into
early this evening across eastern New York and western New England.

As of 650 am EDT...some isolated showers have popped up over the Tug
Hill plateau and the southern dacks. Some changes have been made to the
probability of precipitation and weather this morning there. Also removed the patchy fog
over the middle Hudson Valley and southern CT. It continues to be
variably cloudy across the forecast area. Severe weather threat continues
for the afternoon.

A very warm and humid air mass is over the forecast area this morning
with temperatures in the 60s to l70s. A subtropical ridge anchored along
the East Coast continues to funnel in the humid air. Upstream on
the water vapor loop an upper level trough is moving across the
upper Midwest and the western Great Lakes region. This feature will
arrive on Thursday...a short-wave moving through the Ohio Valley into the
eastern Great Lakes...western New York and PA this morning...and a prefrontal
surface trough will be the lifting mechanisms for shower and
thunderstorm development. Some local cstar work with sunya has
shown that prefrontal surface troughs can yield some significant
severe weather events across New York and New England.

Storm Prediction Center has the entire area in a slight risk...actually it is a very
large area that extends from northern ME to District of Columbia with the latest day 1
graphic. There is plenty of low-level moisture in place with surface
dewpoints in the lower to m60s...and some spotty u60s. Precipitable waters will
rise to the 1.25-1.75 inch range with some isolated values closer
to 2"...especially where it rains based on the BUFKIT and model
profiles. The 0-6 km bulk shear values increase to 30-40 kts by
the late morning into the early afternoon with the greater shear
from roughly the I-90 corridor northward...and lesser amounts to
the south. Instability continues to be variable on the guidance
due to the varying amounts of cloud cover...and some of the
guidance showing surface dewpoints in the lower 70s. Can not really find
any 70f dewpt air unless one GOES into the Lower Middle Atlantic
region. Therefore...leaning closer to the GFS SBCAPE profiles with
1000-2000 j/kg of instability...with some slightly lower amounts
and possible some higher amounts. It appears that the best
intersection of the shear and cape profiles will be in the noon to
6 PM time frame. The middle-level lapse rates are not very steep
based on the NAM/GFS/ec guidance. However...there are some high
dcape values prognosticated around the 1000 j/kg range. The soundings are
very unidirectional...and the organized convection would likely
favor multicells evolving into a few clusters or lines of strong
to severe thunderstorms with bowing segments and damaging winds
the main threats. We have phrased the zones as chance of
thunderstorms...and some may be severe.

The latest hrrr layer comp reference product favors the convection
development between noon and 3 PM from the Hudson River Valley
West. Multicells forming into clusters and lines are the Mode
depicted. The anomalous precipitable water values and moisture in the boundary
layer will favor heavy rainfall. The cells should be moving
along...but the parched ground may not allow absorption quickly
and runoff could be an issue for an isolated flash flood. The Hydro
service area desperately needs the rain...since most areas are in
d1 or a moderate drought.

The main potential inhibitors for a major/widespread severe event
for the County Warning Area would be clouds limiting the instability and the weak
middle level lapse rates. Also...the better jet dynamics lag upstream
tied to the upper trough and approaching cold front for Thursday
morning. The right entrance region of the a h250 jet streak does
get close to west-central New York between 18z- 00z. Overall...we do feel
confident that the forecast area will get some active or severe
weather...just not clear if it will be a minor or major event. High
temperatures will generally be in the lower to m80s in the valley
areas...and 70s to l80s over the hills and mountains

&&

Short term /6 PM this evening through Friday/...
tonight...the surface trough moves through with the scattered showers and
thunderstorms ending in the early evening. There will likely be a
lull in the activity...but the cold front and upper trough will be
approaching the eastern Great Lakes region and western New York. Some slight and
low chance probability of precipitation were kept in west of the Hudson River valley between
09z-12z showers and possibly thunderstorms ahead of the front.
Lows will still be mild in the middle and u60s in the valley
areas...and u50s to l60s over the mountains

Thursday...the NAM/GFS/ECMWF continues to be in agreement with a faster
progression of the surface cold front and associated upper trough. If
it lags a little...then the southeast extreme of the forecast area /Mid
Hudson valley...southern Berks...and northwest CT/ will have to be monitored
for some strong to severe thunderstorms. Right now...all of our
forecast area is in a general thunderstorm outlook. The instability
looks much less than todays...and the better dynamics with the
upper jet GOES north/NE into southern Quebec...northern New York...and northern New
England. A slight to low chance of thunderstorms was kept in
everywhere into the early to middle PM...then quickly diminished from
the west/northwest to S/se. Maximum temperatures will be tricky with the cold advection
in the wake of the front...and strong mixing or downsloping
occurring. Expect brisk west/northwest winds during the PM. H850 temperatures fall
to +8c to +13c by the 00z/Friday from northwest to southeast over the area. Highs
will range from the u60s to l70s over the southern dacks/W-cntrl Mohawk
Valley to m70s to l80s over the rest of the region...except some
u60s/l70s over the Catskills/southern greens...and m80s over the middle
Hudson Valley/northwest CT.

Thursday night...the upper trough axis moves downstream...and brisk
west/northwest winds will diminish as surface anticyclone ridges in from the
north and west early on...and settles over New York and New England by
Friday morning. Humidity levels will decrease compared to the previous
night with lows in the m40s to l50s over the mountains...and middle and
u50s over the valley areas.

Friday...the synoptic subsidence with the upper level ridge...and
the surface high will continue to close the week. The subtropical
ridge will be in control again. A dry and less humid day is
expected...but the S/SW flow aloft will increase ahead of the next
trough and cold front upstream. Expect mostly sunny conditions
with highs in the lower to m80s in the valleys...and 70s to near
80f over the hills and mountains humidity levels should be fairly nice
still with surface dewpoints in the 50s.

&&

Long term /Friday night through Tuesday/...
well above normal temperatures Friday night-Sat should trend back to
near or below normal sun-Tue...as the East Coast upper level ridge
deamplifies with the approach of shortwave energy from southern
Canada. As it deamplifies...a cold front will cross the region
sometime late Sat or early sun. This should bring showers and
thunderstorms to the region. Depending on additional shortwave
energy rounding the base of the incoming upper level trough
approaching the Great Lakes/southeast Canada...it is possible that the cold
front slows down and/or a wave develops along it and tracks south of
the region. Should this occur...showers could linger in the wake of
the front for sun into Tuesday...but mainly across southern areas.

Warm and somewhat humid Friday night across the region with lows in
the upper 50s to middle 60s. As the cold front approaches on
Saturday...the southerly flow ahead of it will boost temperatures to highs
in the 80s across the region...but somewhat cooler air off the
Atlantic will result in the coolest temperatures occurring over southern
areas. Scattered showers and thunderstorms will also increase across the
region...and have forecast probability of precipitation to rise to low chance across the
southeast by late afternoon...ranging up to likely probability of precipitation over the
Adirondacks. Saturday night probability of precipitation continue to rise...reaching likely
levels across most of the region...with high chance probability of precipitation over the
southern fourth of the forecast area. Lows Saturday night will range
from the upper 40s over the Adirondacks...to the lower 60s over the
far southern part of the forecast area.

Due to the possibility of a wave along the front...probability of precipitation for Sunday
remain fairly high...between 40 and 50 percent during the morning...
and 30 to 45 percent during the afternoon...with the highest probability of precipitation
over the south. Highs Sunday in the 60s to middle 70s.

Still the potential for the front to become stationary far enough
north to result in some showers across parts of the region Sunday
night through Tuesday. Have forecast either dry conditions or slight
chance probability of precipitation from the Adirondacks to the Lake George area during this
period. Slight chance probability of precipitation most other areas...and low chance probability of precipitation
over the extreme south. Lows Sunday night will be in the middle 40s to
lower 50s. Highs Monday in the 60s to lower 70s. Lows Monday night
in the middle 40s to lower 50s once again...and highs Tuesday in the
upper 60s to middle 70s.

&&

Aviation /12z Wednesday through Sunday/...
high pressure anchored off the eastern Seaboard will maintain a warm
and humid southwest flow across the region through Wednesday. An upper
level disturbance will trigger scattered showers and thunderstorms
for Wednesday afternoon.

Mainly VFR conditions expected at the kgfl/kalb/kpou/kpsf taf
sites through 18z on Wednesday. The exception will be a period of
fog and stratus at kpsf between 08z and 13z early this morning.
After 18z...expect a band of at least scattered showers/thunderstorms to
develop and move across the region. Have included vcsh in the
forecast after 18z at all the taf sites...and a prob30 group for
the possibility of thunderstorms with strong gusty winds (wind
gusts up to 35 mph) between 18z and 22z at kgfl/kalb/kpou...and
19z to 23z at kpsf.

Winds will remain southerly at 5-10 knots at kalb...and light and
variable elsewhere through a few hours after sunrise. After 13z
Wednesday...winds will increase from the south or southwest to
8-12 knots...with gusts of 15-20 knots by late morning/early afternoon.



Outlook...

Wednesday night: moderate operational impact. Chance of rain showers...tsra.
Thursday: moderate operational impact. Chance of rain showers...tsra.
Thursday night: low operational impact. Breezy no sig weather.
Friday: no operational impact. No sig weather.
Friday night: no operational impact. No sig weather.
Saturday: moderate operational impact. Chance of rain showers...tsra.
Saturday night: high operational impact. Likely rain showers...tsra.
Sunday: moderate operational impact. Chance of rain showers.

&&

Fire weather...
a warm and humid air mass will continue to be over
eastern New York and western New England today. An upper level
disturbance well ahead of a cold front will focus some showers and
thunderstorms with locally heavy rainfall this afternoon into
early this evening. The cold front will move through the region on
Thursday with more scattered showers and thunderstorms. High
pressure will build in from the north and west Thursday night into
Friday with drier and less humid conditions.

The relative humidity values will lower to 45 to 60 percent this afternoon...then
increase to 70 to 100 percent tonight...and the decrease to 35 to
55 percent on Thursday.

The winds will be from the south to southwest at 10 to 15 miles per hour
today with gusts to 25 miles per hour...then 5 to 15 miles per hour tonight. The winds
will shift to the west to northwest at 10 to 20 miles per hour with some
gusts to 30 miles per hour on Thursday with the cold frontal passage.

&&

Hydrology...
no widespread Hydro problems expected this week...however
thunderstorms will be capable of producing locally heavy downpours
today into tonight.

The U.S. Drought monitor has much of eastern New York and western
New England in the d1 category...which is considered moderate
drought at this time.

Warm and humid conditions with chances for showers and
thunderstorms...mainly during the afternoon into the early
evening are expected today. There is a chance of showers and
thunderstorms ahead of the cold front on Thursday.

Precipitable water values of 1.25-1.75 inches with locally higher
values are expected today...so storms will be capable of
producing heavy downpours. An isolated flash flood may be possible
if storms repeatedly move over the same area...or the dry/parched
ground does not absorb the rainfall quickly.

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
long term...gjm
aviation...gjm
fire weather...bgm/wasula
hydrology...bgm/wasula

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