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Area forecast discussion 
National Weather Service Albany New York
629 am EDT Sat Jul 12 2014

Synopsis...
high pressure will slide off the New England coastline today. This
will allow for the return flow of more humid air back into the
region for the region this weekend. Along with the increase in
moisture...the chance for showers and thunderstorms will be
on the rise. The threat for severe weather is in the forecast
Sunday.

&&

Near term /until 6 PM this evening/...
as of 600 am EDT...some altocumulus castellanus seen outside our forecast office
window with sunrise indicating at least middle level instability. Per
the rap13 the middle level lapse rates remain at or above 6.5 c/km
later today. So no changes to the forecast at this time...just
minor adjustments to hourly grid observations.

Previous disc...an elongated ridge of high pressure along the i95 corridor
will continue to slide off the Atlantic coast today.
Meanwhile...upstream on the infrared satellite imagery there is already
evidence of the warm air advection with high and middle level cloud
cover on the increase. Surface dewpoint analysis /isodrosotherms/
reveals the low level moisture transport was underway across the
Ohio Valley...Southern Lower Michigan and just south of Mason-
Dixon line. Current NCEP model short term guidance suggest this
low level moisture transport will commence with the passage of the
surface ridge. Meanwhile...in the upper levels as seen in the water
vapor Loop...A short wave was moving across Lake Huron. This short
wave will pass across upstate New York from the noon hour and through
the middle afternoon hours. In addition...middle level lapse /h850-h500/
are prognosticated to climb at or above 6.5 c/km but surface instability
varies with a little drier forecast on the ruc13/GFS as opposed to
the NAM. A compromise suggest sbcapes climb into the 100s j/kg. So
combining all these parameters warrants the continuation of the
slight chance probability of precipitation mainly along and west of the Hudson River with
the terrain under the initial threat first.

Under an increase canopy of cloud cover...and h850 temperatures climbing
into the middle teens...surface high temperatures should yield middle 80s for
valley locations and upper 70s for the terrain.

&&

Short term /6 PM this evening through Monday/...
... Weather potential increasing for Sunday...

Tonight...warm front will be approaching from the west as an mesoscale convective system
over the central-northern plains quickly tracks east along and
north of i80. Meanwhile the vortex near western Hudson Bay is
forecast to migrate further south toward Lake Winnipeg. The
ageostrophic response will be an increasing low level jet with
speed convergence over upstate New York. This will keep the threat for
additional convection along the Theta-E ridge axis over the
western portions of the region later tonight. We will continue
with the previous excellent forecast with increasing probability of precipitation from
west to east overnight. This overnight convection will remain
elevated so severe weather is not expected at this time.

Sunday...that potentially changes on Sunday as per close
coordination with Storm Prediction Center...most of eastern New York is now in a slight risk
for severe thunderstorms. While considerable cloud cover is
expected...it will not take too much for sunny breaks to occur
in-between convection. Several parameters are adding up for a
potentially active day. A close proximity of a warm front...high
precipitable waters close to 2 inches...MUCAPES close to 2k j/kg per the
NAM/GFS...low level hodographs exhibiting low level curvature with
helicities at or above 200 m2/s2 and lowering LCL/S...damaging
wind threat and an isolated tornado threat is in the forecast. Per
Storm Prediction Center discussion...higher severe probabilities may be warranted in later
outlooks depending on timing and greater confidence in degree of
destabilization. Highs should average into the lower 80s for
valley locations and 70s elsewhere...surface dewpoints climb to
between 65f-70f.

Sunday night into Monday...plenty of model discrepancy as either a
cold front will slide slowly across the region or become quasi-
stationary as suggested by the GFS. A compromise of the available
guidance suggests this front will become quasi-stationary south of
i90 and return back as a warm front on Monday. This will continue
the threat for showers and thunderstorms mainly for the southern
portions of our County warning forecast area. With nocturnal aspect Sunday
night...expectations are for the severe weather potential to
diminish as we lose the surface based parcels. That changes on
Monday with the return of the warm front an rooting the surface
parcels as a potentially another active day may be unfolding. Per
swody3 outlook...our southern regions are just outside of the
slight rise with the entire region into a general outlook. As for
temperatures through the period...guidance numbers are fairly
close with a blended approach utilized.

&&

Long term /Monday night through Friday/...
active weather will be continuing at the beginning portion of the
extended period.

On Monday night into Tuesday...a deep cutoff upper level low will be
moving from the Great Lakes towards southern Canada...with a surface
cold front slowly approaching from the west. There are significant
differences in the placement of the cutoff low at 500 hpa when
comparing the latest 00z GFS...ggem and European model (ecmwf). The European model (ecmwf) is the
slowest of all three models...and lags the cutoff behind the
longest...which would keep a threat of showers/thunderstorms in the
forecast through at least middle week.

As a result of the deep meridional flow ahead of the cutoff
low...there will be a strong southerly component ahead of this
system across our area for Monday night into Tuesday. This will
allow precipitable water values to reach around 2.00 inches...which is close to 2
Standard above normal according to climatology. With daytime temperatures in the 70s
to near 80 and dewpoints reaching the upper 60s to low 70s...there
will be plenty of moisture available for periods of heavy showers
and thunderstorms. We will have to watch the potential for locally
heavy rainfall...as local studies have shown these types of setups
to be conducive for widespread flash flooding across our area.

In addition...there will be the potential for strong to severe
T-storms...as the upper level dynamics shift closer to our
area...and puts our area in the right rear quadrant /right entrance
region/ of a cyclonically curved 130 knots jet at 250 hpa. The degree
of severe weather will ultimately depend on just how much instability is
available. It may be limited due to extensive cloud cover...and
flash flooding may wind up being a bigger threat than severe storms for
Monday night/Tuesday.

Depending on which model is correct...the cold front will cross our
area sometime between Tuesday and Wednesday morning. Once it
crosses our area...much less humid air will work into our region
from the west. With the upper low slowly filling in and weakening to
our north...cyclonic flow will start keep the threat of a shower in
the forecast through Wednesday...and possibly even for Thursday for far
northern areas. If the European model (ecmwf) is correct though...there still be some
heavy showers for eastern areas for Tuesday night into Wednesday
morning...as the front will be crossing through around that time.

Otherwise...the remainder of the week looks quiet with a mostly to
partly sunny sky...as surface high pressure builds into the area from
the west. The upper low looks to continue to weaken and lift across
Quebec...with drier... cooler and less humid air in our area during
the late week. Daytime temperatures will be in the 70s to low 80s...and
overnight lows in the 50s to low 60s.

&&

Aviation /12z Saturday through Wednesday/...
high pressure is situated east of the area just off eastern New
England. As this high pressure area starts to move away...broken high
clouds over central New York and eastern Ontario will start to spread over
the terminals during the morning hours. In addition to the broken high
level clouds...some diurnal cumulus will develop today...but an inversion
around 700 hpa will prevent any cumulus from growing very tall. As a
result...it looks to remain rain free at the terminals today with
continued VFR conditions. Southerly winds will be around 4-8 kts.

Winds look to decrease to 5 kts or less for this evening with
continued scattered high clouds around. There may be some overnight fog at
kgfl once again...mainly late after midnight. Otherwise...VFR
conditions look to continue for all sites through the overnight
hours. Middle and high level clouds will increase late at night as a
warm front starts to approach from the west.

Outlook...

Sunday night through Tuesday night: moderate operational impact.
Chance of rain showers...tsra.
Wednesday: low operational impact. Slight chance of rain showers.
Wednesday night through thursday: no operational impact. No sig weather.

&&

Fire weather...
as high pressure slides offshore...the return flow will increase
low level moisture through the remainder of the weekend. This in
turn will also increase the potential for showers and
thunderstorms...some containing heavy rainfall.

Minimum relative humidity values this afternoon with generally fall between 40
and 50 percent...an recover to values at or above 90 percent.
Those values remain elevated on Sunday with values at or above 60
percent.

Light winds will become southerly at 10 miles per hour or less today into
tonight. The magnitudes increase through Sunday with 10 to 15 miles per hour.

&&

Hydrology...
no widespread Hydro problems are expected into tonight...but
then a series of cold fronts could bring several rounds of showers
and thunderstorms possibly containing heavy rainfall Sunday into
the middle week.

Generally...dry conditions are expected through at least early
today. However...a warm front and higher moisture content will
bring some scattered showers and thunderstorms overnight into Sunday
and lasting through Tuesday.

These frontal boundaries associated with a strong upper level
trough west of the region could bring intermittent showers and
thunderstorms Sunday into the middle week period. Locally heavy
rainfall in the humid air mass could increase the threat for the
potential of isolated flash flooding with some impacts on the main
Stem rivers...small streams and creeks. At this point it is
difficult to pinpoint where the heavy rainfall will occur...but
some locations could receive several inches of rainfall from any
convection that repeatedly moves over the same areas.

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...bgm
near term...bgm
short term...bgm
long term...frugis
aviation...frugis
fire weather...bgm/wasula
hydrology...bgm/wasula

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www.Weather.Gov/Albany

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