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Area forecast discussion 
National Weather Service Albany New York
649 am EDT Monday Aug 3 2015

Synopsis...
a cold front will approach from the eastern Great Lakes
region today. There is a chance of strong to severe thunderstorms
ahead of the cold front this afternoon into tonight. The cold front
will be east of the region Tuesday morning...but an upper level
disturbance will continue the threat for scattered showers and
thunderstorms Tuesday afternoon...as cooler and drier air will
arrive for Wednesday.

&&

Near term /until 6 PM this evening/...
..some severe thunderstorms are possible this afternoon into
tonight...

As of 648 am EDT...an h500 closed upper level low continues to be
near northern Ontario and James Bay this morning. Several short-waves
rotating around the upper level low will continue to impact the
forecast area the next few days. One short-wave moving through the
base of the long-wave trough will impact the region later
today...as it moves through the lower Great Lakes region and Ohio
Valley.

At the surface...a weak surface cyclone over the central/eastern Great Lakes
region is moving towards southeast Ontario this morning. The forecast area
will be in a warm sector today with surface dewpoints rising into the
u50s to perhaps m60s. A prefrontal surface trough ahead of the main
cold front will move across western-central New York late this morning into
the afternoon. Convection is expected to fire just ahead or in the
prefrontal surface trough zone between the surface trough and the cold front.

The guidance continues to indicate a threat will increase for
some strong to severe thunderstorms this afternoon into tonight.
Some scattered strong to severe thunderstorms may reach the southern
dacks/W-cntrl Mohawk Valley between 2-5 PM...then much of eastern New York between
5-8 PM including the capital region...and then potentially
spreading into western New England between 8-11 PM. The latest hireswrf
reference product continues this trend...though the hrrr is a little
faster. The 4-km wpc Storm Prediction Center WRF actually has some convection fire
with an outflow boundary near the Lake George region around 2-4
PM. We are going to stick closer to the hireswrf for the timing at
this point.

The best middle level lapse rates will be over the forecast area in the
early to middle PM based on the GFS/NAM. These lapse rates will be in
the 6.5-7+c/km range. There are significant differences in the
instability profiles between the NAM/GFS. The NAM is on the higher
end with sbcapes of roughly 1000-2000 j/kg with slightly higher
surface dewpoints. The GFS has only sbcapes of 500-1000 j/kg with
slightly higher pockets. The surface dewpoints are lower on the GFS. The
surface to boundary layer winds are from the S/SW during the day. The
0-6 km bulk vertical wind shear values increase to 35-45 kts
during the PM. Some deep organized convection is anticipated with
large hail and damaging winds possible. Multicells or multicell
lines look possible especially with the unidirectional wind
profiles in the BUFKIT sounds. Some bowing elements/wet microbursts
may occur...as inverted-v profiles are also evident in the
soundings. Damaging winds look like the primary threat with some
potential for large hail as the secondary threat. Actually h850
temperatures increase to +15c to +19c over the forecast area. Highs are
expected to reach the m80s to lower 90s in the valley areas...and
m70s to l80s over the higher terrain.

The better upper jet dynamics arrive towards nightfall...but
decent upper level divergence occurs over eastern New York prior to then.
Precipitable waters do increase to 1.25-1.50+ inches over most of the
region...so some locally heavy downpours are possible. We will
continue the trend from the previous forecast in the zones/grids
to phrase that some storms maybe severe in the middle PM to late PM.

&&

Short term /6 PM this evening through Wednesday night/...
tonight...the degree of how widespread the severe weather may
potentially be will depend on how fast the upper impulse and cold
front move across the region...since the instability may possibly
be waning. As mentioned above...the better upper level dynamics
arrive towards sunset...an impressive cyclonically curved jet
streak at h250 of 85-95 kts will pass west of the Hudson River
valley. Eastern New York and western New England will be near the right entrance
region of the jet streak. Some enhancement to the convection may
occur...and some of the multicells may get into western England. There
maybe an isolated supercell or two closer to the better deep
shear...which looks like it would be north of the I-90 corridor at
this point. High chance and likely probability of precipitation were maintained ahead of the
cold front...as it sags east/southeast across the forecast area. Some heavy
downpours will be possible...but the precipitable waters do not look highly
anomalous at this point /around a Standard dev above normal/. The
thunderstorms should start around midnight or shortly thereafter.
At this point it is hard to tell if a widespread or major event
will occur for the region....but we agree with Storm Prediction Center and have at
least moderate confidence for some severe in the forecast area. Lows
Monday night will be on the mild side with middle and u60s from the
eastern Mohawk Valley...southern reaches of the Lake George region
south and east...and u50s and l60s north and west.

Tuesday...the cold front will be near western New England by
daybreak. The surface dewpt boundary will still be progressing east
across eastern New York. The NAM is advertising alot of instability for Tuesday
with a deeply sheared environment. The GFS has less again...but
there is a small area of high instability from the the Mass Pike
south and east into northwest CT. Storm Prediction Center does have Litchfield city clipped by
the marginal risk. Middle level lapse rates will be around 6.5c/km
with another short-wave rotating around the upper level low. Will
have to monitor for some strong storms with gusty winds and small
hail /no enhanced wording yet/...especially from the capital
district south and east. Low-level cold advection will be ongoing
during the late morning into the PM. Downsloping effects off the
eastern Catskills/eastern dacks may allow maximum temperatures to get into the middle
and u80s in the Hudson River valley/capital region. Expect m70s to
l80s in most other locations...except over the southern dacks/southern
greens where some u60s to l70s are possible in the cold advection
regime...as h850 temperatures lower to +10c to +16c from northwest to southeast over
the forecast area by the late PM. A slight to low chance of thunderstorms
will continue until sunset.

Tuesday night...with the loss of the diurnal heating the scattered
showers and thunderstorms will diminish quickly. The isolated-scattered
showers may linger the longest over the southern dacks. Lows will
generally be in the middle 50s to around 60f with some u40s to l50s
over the southern dacks/southern greens. Humidity levels will be quite
comfortable.

Wednesday-Wednesday night...the forecast area will still be under the influence of
the upper level low centered over S-central Quebec. In the cyclonic
flow another piece of short-wave energy will swing across upstate
New York and New England. The best chance of isolated-scattered showers due to the
cyclonic vorticity advection will be north and west of the
capital region. H500 temperatures will be around -15c to -18c from aly
north and west. The h500 heights are about 2-3 Standard devs below
normal based on the latest gefs for Wednesday. H850 temperatures will be 1-2
Standard devs below normal. Highs on Wednesday will be in the m60s to l70s
over the mountains...and middle and u70s in the valleys...with a few 80f
readings near kpou. Clearing skies and light to calm winds will
allow for cool night for the first week of Aug...with high
pressure building in. Lows will range from the u40s to m50s over
the forecast area.

&&

Long term /Thursday through Sunday/...
below normal temperatures expected with highs mainly in the 70s.

Guidance is in general agreement that a cold front should stall to our
south late in the week somewhere across the middle Atlantic region. The exact
location is very much in question at this time. Guidance is also in
general agreement that a large upper level low will move north of the
Canadian Maritimes late in the week leaving the Great Lakes region and
northeast under a longwave trough though the weekend.

The differences in the models are on how they handle short wave energy
moving through the longwave trough and its impacts the position of the
stalled boundary and the strengthen of an area of low pressure that is
expected to form and move eastward along the boundary. Guidance have not
been showing any consistency. At this time...the operational run of the GFS
keeps the boundary...low and precipitation shield to our south while the
European model (ecmwf) brings a soaking rainfall to the area late Thursday night and Friday
to mainly to areas south of Interstate 90.

Have favored guidance from the weather prediction center to maintain
forecast consistency and have chance probability of precipitation for areas south of I-90 late
Thursday night and Friday. As for the weekend...have mainly slight chances
probability of precipitation since the timing of additional short waves in highly uncertain.

&&

Aviation /12z Monday through Friday/...
a period of showers and thunderstorms is expected to impact the
taf sites as a cold front approaches the region late this afternoon
and evening. Conditions will be favorable for the possibility for
some strong to severe thunderstorms.

VFR conditions are expected well into the afternoon hours with
conditions lowering to MVFR with the convection late this afternoon
and evening. IFR conditions will be possible but have not been include
in the tafs at this time. Have addressed the threat of the storms with
a prob30 group including thunderstorms. Fog is expected to develop late
tonight as the cloud cover decreases and winds lighten up.

At kalb...southerly winds will continue and are expected to become gusty.
At the other taf sites...a south to south-southwest wind will develop
which will become gusty ahead of the cold front during the day. A lighter
southerly flow is expected in the wake of the storms as we head into the
overnight hours.

Outlook...
Tuesday night-Thu: no operational impact. No sig weather.
Thursday night-Fri: low operational impact. Slight chance of rain showers.

&&

Fire weather...
a cold front will approach from the eastern Great Lakes
region today with a chance of showers and thunderstorms. The cold
front will be east of the region Tuesday morning...but an upper
level disturbance will continue the threat for scattered showers
and thunderstorms Tuesday afternoon...as cooler and drier air will
arrive for Wednesday.

The relative humidity values will lower to 40 to 60 percent this afternoon...and
increase to 75 to 100 percent tonight. The relative humidity values will lower to
35 to 55 percent Tuesday afternoon.

The winds will be from the south to southwest at 10 to 20 miles per hour
today...and south to southwest at 5 to 15 miles per hour tonight. The winds
will be form the west to northwest at 10 to 20 miles per hour on Tuesday with
the front moving across the region.

&&

Hydrology...
mainly dry weather is expected this morning with showers and
thunderstorms expected this afternoon and evening as a cold front
approaches and crosses the region. The storms will be capable of
producing locally heavy downpours as precipitable waters rise up to around 1.5
inches ahead of the boundary. The heavy rainfall could lead to
some minor flooding in poor drainage and low lying areas. Also
some sharp within bank rises would be expected on streams...creeks
and some small rivers.

Isolated to scattered showers and thunderstorms are expected on
Tuesday especially during the afternoon as the upper level trough
axis approaches and passes over the region. Rainfall amounts may
range from a tenth to a third of an inch with locally higher
amounts.

A trend towards drier weather will occur on Wednesday...and
continue until Friday morning.

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...iaa
aviation...iaa
fire weather...bgm/wasula
hydrology...bgm/wasula

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