Scientific Forecaster Discussion
fxus61 kaly 290501
Area forecast discussion
National Weather Service Albany New York
101 am EDT Mon may 29 2017
the first in a series of quick-moving disturbances will
approach the region tonight, spreading showers and possibly a
few thunderstorms across the forecast area late tonight into
Memorial Day. Temperatures will be several degrees cooler than
normal on Memorial Day. More clouds and showers are likely
Tuesday and Wednesday, with thunderstorms also possible Tuesday.
Near term /through today/...
as of 1 am EDT, some breaks in the mid level clouds have
developed across portions of the upper Hudson Valley into
southern Vermont and western Massachusetts. Combined with light winds, temps in
these areas have dropped into the lower 50s. Elsewhere, skies
remain mostly cloudy, with temps holding into the mid 50s to
lower 60s. A steady south/southeast wind continues within some
north/south oriented valleys.
Latest regional radars suggest deeper convection aligning in an
east-west orientation across PA near and just south of I-80, with
lighter showers to the north. Latest hrrr/3km NAM would suggest
heavier rain should be advancing farther north by now. It is
possible that the deeper convection farther south may be robbing
moisture transport further north into nys, thus delaying the
steadier precip. For now, based on these trends, have slowed
timing of rain onset across the region by at least 1-3 hours,
and may need to adjust even later with subsequent updates.
Otherwise, recent water vapor imagery shows expansive upper low
centered over far western Ontario, with shortwave ridging
centered across and just east of New England. More widespread
precipitation will hold off until the stronger Illinois
disturbance arrives late tonight. Low-level jet magnitudes
increase to 30-35 kt late tonight as precipitation is produced
within a fairly narrow Theta-E axis. Still some disagreement in
the timing of the upper wave and low level jet forcing, but a general
trend toward slower arrival of precipitation is in the grids for
this forecast package. Latest model consensus puts the peak
time for precipitation over the majority of the forecast area
from 12-18z Memorial Day. Elevated instability appears confined
to western portions of the forecast area, so have gone with
slight chance of thunder mainly west of the Hudson Valley.
Rainfall should diminish somewhat after 18z as weak subsidence
spreads into the region in the wake of the upper wave. Even so,
forecast soundings suggest plenty of moisture remaining, so a
good deal of clouds should remain with perhaps a few lingering
showers. With the expected rainfall, cloud cover, and
southeasterly surface winds, temps will struggle to reach the
low 60s in the warmest valleys. Some gusty winds are possible in
the favored southeast flow spots of The
Greens/Taconics/Berkshires, but the core of the strongest
southeast winds tracks to the west, so headlines are not
anticipated at this time.
Short term /tonight through Tuesday night/...
short term period will remain unsettled as the expansive upper
low center drifts into central Ontario and several low-amplitude
disturbances slide across the forecast area along the periphery
of the low. Mainly dry Monday night as subtle ridging builds in
the wake of the leading Memorial Day disturbance. However,
leading edge of additional height falls is not far behind so a
few showers may develop late across northern/western portions of
the forecast area. Convective potential is the main focus for
Tuesday as fast midlevel southwesterly flow will lead to
impressive deep-layer shear of 50-60 kt. Weak lift will spread
into the region as upper heights edge lower along the periphery
of the upper trough. A weak surface boundary or confluence zone
will track into the forecast area with a corridor of upper 50s
to lower 60s dewpoints ahead of the boundary. The question is
whether we can achieve any surface-based instability to generate
updrafts. The NAM is not very bullish on this potential, with
instability limited over northwestern portions of the forecast
area due to the expected ongoing clouds and showers, and also
depicts a Stout cap around 850 mb over southeastern portions of
the forecast area. The GFS looks a bit better with around
400-700 j/kg of MLCAPE. If this instability were to occur, it
would lead to the potential of organized, marginally severe
convection given the strong deep layer shear. Storm Prediction Center marginal risk
looks good given the uncertainty. Highs Tuesday will be
dependent on any insolation, but look to be mainly in the 60s to
around 70. Showers may persist into Tuesday night as the weak
boundary moves across the forecast area, though the potential
for convection should diminish with the loss of diurnal heating.
Long term /Wednesday through Sunday/...
this will be a period of marginally inclement weather with near
seasonable temperatures. Early day showers will gradually diminish
as a weak ridge of high pressure build across our region. This
will provide US with about 36 hours of dry weather before a cold
front impacts our region from the northwest...bringing US a
good chance for showers...and our best chance for thunderstorms
during the period. The activity winds down as the front dips
south Friday night...and the weekend will start off dry; but a
wave will develop along the front, lifting it back north as it
approaches from the Midwest, though there is still great
uncertainty how the weekend will evolve. There is a possibility
Sunday will be sunny and dry.
Aviation /06z Monday through Friday/...
overcast mid-level cloud deck in place across the region, well
ahead of an approaching frontal boundary over the lower Great
Lakes and Ohio Valley. Conditions will likely remain VFR through
much of the night, although widespread showers will develop
from southwest to northeast around or shortly after sunrise,
with conditions expected to deteriorate to MVFR once showers
commence. MVFR conditions with associated showers will persist
through the morning and into the afternoon, with cigs possibly
lowering to IFR at kpsf. Later in the day, coverage of showers
will become more scattered but with continued MVFR conditions.
MVFR cigs are expected to continue into Monday evening, and may
lower to IFR levels later at night, esp at kpsf.
Winds tonight through Monday will be southeast around 5-10 kt.
However, slightly stronger south/southeast winds are expected at
kalb through at least daybreak, with speeds averaging closer to
10 kt, and occasional gusts of 15-20 knots possible.
Low level wind shear has been included in tafs for kgfl and
kpou through around daybreak, as surface winds remain light
from the southeast at less than 8 kt, while winds around 2000 feet
above ground level increase from the south/southeast to 30-35 knots.
Monday night: low operational impact. Slight chance of rain showers.
Tuesday: high operational impact. Likely rain showers...tsra.
Tuesday night: moderate operational impact. Likely rain showers...tsra.
Wednesday: moderate operational impact. Chance of rain showers...tsra.
Wednesday night: no operational impact. No sig weather.
Thursday: no operational impact. No sig weather.
Thursday night: no operational impact. No sig weather.
Friday: moderate operational impact. Chance of rain showers...tsra.
an approaching system will bring rainfall to the region tonight
into Memorial Day, along with cooler temperatures. Showers and
thunderstorms will be likely again on Tuesday with seasonable
temperatures. A bit warmer Wednesday with yet another chance of
an approaching system will bring showers and a few
thunderstorms tonight into Memorial Day, with total quantitative precipitation forecast ranging
from 0.50-1.00" expected. Highest amounts are expected to be
over the Mohawk Valley and western Adirondacks. Additional
periods of showers and thunderstorms are likely Tuesday and
Wednesday, with basin average quantitative precipitation forecast likely remaining less than an
additional half inch Tuesday, and less than a quarter 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.
the ASOS at the Floyd Bennett Memorial Airport in Glens Falls,
NY, Pittsfield Municipal Airport, MA, and Harriman-and-West
Airport in North Adams, Massachusetts continue to experience outages with
hourly metars occasionally or continuously missing. This will
persist until communications are fully restored.