Area Forecast Discussion
Issued by NWS Albany, NY

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FXUS61 KALY 231051
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
651 AM EDT Fri Jun 23 2017

.SYNOPSIS...
Warm and humid weather is in store today into tonight along
with periodic showers and thunderstorms, some of which could
produce locally heavy rainfall. Saturday will see a drying trend
behind a cold frontal passage. Seasonable temperatures on Sunday
with perhaps a few showers or a thunderstorm over northern
portions of the forecast area.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 630 am, training convection with heavy rainfall rates
continues to track across far northern portions of Herkimer and
Hamilton Counties. MRMS and KTYX radar estimates up to 2 inches
has fallen over the past 3 hours. Regional radar suggests a
northward trend to the western portion of this activity over
Lake Ontario, so expect the heavy rainfall to shift north of the
forecast area after 12Z. IR imagery suggests cloud tops are
warming as well. Fortunately this is a very sparsely populated
area that is not prone to flooding, so have handled it with SPS.
Elsewhere, a few showers are bubbling up from high-based cloud
deck over the Capital District, Taconics, Berkshires, and
Litchfield Hills.

Previous discussion...As of 330 am, current radar composite
shows an extensive area of showers and thunderstorms along a
cold front extending from near Omaha into lower Michigan. This
activity is also downstream of a deep upper trough rotating into
the western Great Lakes as seen on water vapor imagery. Further
east, another area of showers and thunderstorms that had
developed earlier around western Lake Erie along a low-level
warm front is pushing across Lake Ontario and into the Southern
Adirondacks. Otherwise, flat upper ridging is in place over the
local forecast area. Moisture associated with TC Cindy is
streaming northward and being entrained into the upper-level
flow per water vapor imagery. At the surface, moister air
characterized by dewpoints in the mid-60s to lower 70s is
located across central New York and points south within the warm
sector. The diffuse surface warm front is currently pushing
across the local forecast area, but with the upper ridging and
still a fair amount of low-level dry air evident on the 00Z KALY
sounding, much of the forecast area remains dry at this hour.

As we go on through the day, a progressively warmer and moister
airmass will creep into the region behind the warm front. PWATs
increasing to 1.75-2.00 inches, freezing levels at 15-16 kft,
and 700/850 mb dewpoints around 5/15C respectively, are all
toward the top end of the sounding climatology for this time of
year. This points to the threat of heavy rainfall within any
thunderstorms that can develop. The problem, though, appears to
be with a lack of forcing within the warm sector, which could
limit the coverage of showers and thunderstorms. There does
appear to be a low-amplitude disturbance lifting through during
the late morning into early afternoon hours that could set off
some activity. Activity may be more widespread across the
Southern Adirondacks as well, closer to the front/low-level
theta-e gradient. Will have to watch for potential of storms to
train near this boundary, although current indications are that
it will push far enough north for this not to be a big problem.

The other aspect to discuss is the severe weather potential.
Moderately strong midlevel flow will contribute to bulk shear
values of 25 to 40 kt. Midlevel lapse rates are poor, but with
surface dewpoints approaching 70F and temperatures warming into
the low to mid-80s, could see pockets of MLCAPE AOA 1 J/g.
These parameters could result in marginally severe cells with
the main threat being damaging winds. The limiting factor will
be coverage of storms given the lack of forcing, as well as a
good amount of cloud cover possibly inhibiting instability. SPC
marginal risk for severe weather looks good.

Forcing for ascent increases tonight with slightly better upper
height falls approaching along with the surface cold front. PWAT
values remain high with some moisture pooling along the front -
GFS and NAM depicting 2-2.25 inches around 03Z. Severe weather
threat would seem to wane with the loss of diurnally generated
instability, but heavy rainfall will still be a threat given the
increase in forcing and the moist atmosphere. Still, not enough
signal to go with a flash flood watch, but will continue to
mention heavy rainfall potential in the HWO. Coverage of showers
and storms will decrease late from northwest to southeast behind
the cold front. A very mild night in store especially from the
Capital District southward.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Some showers and thunderstorms may linger into Saturday morning
especially across portions of the Catskills, Mid-Hudson Valley,
and NW CT as the front will still be passing through those
areas. A drying trend will occur with PWATs dropping to below
0.75 by 18Z, and dewpoints falling into the 50s to lower 60s.
Highs will be near seasonal normals. A mainly clear to partly
cloudy and dry night is in store Saturday night.

Sunday, a rather strong shortwave trough will approach the
forecast area, rotating through the longwave trough that sets
up over much of the eastern US. This forcing could be enough to
touch off a few showers despite the dry airmass. Forecast
soundings show some shallow instability, so could hear a rumble
of thunder or two. Best chance for showers is north of I-90.
Another disturbance could generate a few showers at night as
well, though coverage should be somewhat limited with the lack
of the diurnal contribution to instability. Low temps will be
cooler than recent days, likely a bit below seasonal normals.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
A mean longwave mid and upper level trough will be over the
eastern CONUS for early in the week. Guidance is in general
agreement the trough sharpens as a short wave moves about the
base of the trough Tuesday and it becomes neutrally tilted as
it exits and moves off the coast by mid week. As a result our
weather will be unsettled. Do have the mention of thunder during
the afternoon into the evening hours as instability develops
with the heating of the day. The better chances for storms
are expected on Tuesday. Temperatures are expected to run
5 to about 10 degrees below normal with highs generally from
the lower 60s to upper 70s Monday and Tuesday with lows in
upper 40s to mid 50s.

Models indicates some ridging should begin to build in Wednesday.
However, it should be brief as the flow flattens as short waves
approach and pass to our north Thursday. The longwave pattern
is expected to amplify again as a trough develops over the
Northern Plains into the Great Lakes region. Temperatures are
should moderate back to near normal by Thursday.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
A warm front has lifted through and humid and warm airmass is
being ushered in. With the area in the warm sector and short
waves moving through flow there will be rounds of convection
through the TAF period. It is a tough forecast to determine the
timing at the individual TAF sites. Have addressed chances with
TEMPO and PROB30 groups in TAFs. Mainly VFR conditions are
expected through much of the day; MVFR conditions will occur
with convection as well as IFR. Storms are capable of very heavy
downpours. Widespread MVFR conditions are expected to develop
by late in the day and persist through the night as heights
begin to fall as the approaching trough deepens to our west.

Southerly flow develops and will increase to 10 to 15 knots
with gusts in the teens to about 25 knots. The flow is expected
to shift more to the southwest and decrease some in the evening.

Winds stronger in and near thunderstorms.

Outlook...

Saturday Night: No Operational Impact. NO SIG WX.
Sunday: Moderate Operational Impact. Chance of SHRA...TSRA.
Sunday Night:  Slight Chance of SHRA.
Monday: Moderate Operational Impact. Chance of SHRA...TSRA.
Monday Night: Low Operational Impact. Slight Chance of SHRA.
Tuesday: Moderate Operational Impact. Chance of SHRA...TSRA.

&&

.FIRE WEATHER...
Warmer and more humid conditions will return today, along with
increasing chances for showers and thunderstorms, some of which
may produce locally heavy rainfall. The showers and
thunderstorms should continue tonight, before gradually
tapering off Saturday as a cold front moves through and south of
the region. Another upper level disturbance could trigger a
passing shower or thunderstorm Sunday.

Minimum RH values today will be around 60 to 70 percent. A drier
airmass will allow RH values to drop to 40 to 50 percent on
Saturday.

Winds today will be south to southwest and increase to around
10 to 15 mph, with gusts up to 25 mph possible. Winds Saturday
will be from the west at 10 to mph kt with gusts to 25 mph.

Winds will be stronger, and variable in direction in and near
any thunderstorms.

&&

.HYDROLOGY...
Showers and thunderstorms will become more widespread today into
tonight as a frontal system gradually moves across the area. It
will become more humid, so there is the potential for locally
heavy rainfall today into tonight. Some urban/poor drainage
flooding and isolated flash flooding will be possible with
thunderstorms. Basin average rainfall forecast to be around a
half to three quarters of an inch, but locally higher amounts
will occur in thunderstorms. Showers and thunderstorms with
locally heavy downpours may linger into Saturday morning from
the Capital Region and points south and east.

Mainly dry weather then expected for Saturday afternoon with
isolated to scattered showers and thunderstorms possible Sunday
into Monday.

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.

&&

.EQUIPMENT...
KGFL airport observation has been intermittently missing again
as technicians continue to troubleshoot. We will continue to
monitor and update this statement as needed.

&&

.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
MA...None.
VT...None.

&&

$$
SYNOPSIS...Thompson
NEAR TERM...Thompson
SHORT TERM...Thompson
LONG TERM...IAA
AVIATION...IAA
FIRE WEATHER...KL/Thompson
HYDROLOGY...KL/Thompson
EQUIPMENT...


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