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Area forecast discussion
National Weather Service Buffalo New York
444 PM EDT Thu Oct 17 2019

Synopsis...
low pressure across Maine will weaken and slide eastward with
rain slowly tapering off to scattered showers before ending by
early Friday. Dry weather will then return by Friday afternoon as
high pressure builds back into the region, with fair weather and
steadily warming temperatures then following for the weekend as
the high slides off the East Coast.

&&

Near term /through Friday/...
radar imagery showing widespread light rain with a few pockets of
moderate rain across the majority of the area this afternoon,
with the only drier locations across the far southwest corner of
the state removed from the deeper moisture. The widespread rain
is being driven by the remnants of an inverted trough, which is
rotating southward across New York. Associated deep moisture,
low level convergence, and a well defined axis of deformation to
the west of the strong coastal low are supporting this
rainfall. In addition to the synoptic scale forcing, moderate to
Strong Lake instability and northwest upslope flow are
enhancing the rainfall to the southeast of the lakes. By late
afternoon the deeper moisture and best forcing will begin to
move away from the area, which will allow for a gradual decrease
in coverage and intensity of the rain.

The strong coastal low will accelerate east from the Maine coast
this evening to the Gulf of Saint Lawrence Friday. The moist
cyclonic flow will diminish from west to east across our region as
this system moves away, allowing for a continued decrease in
coverage and intensity of showers. Nonetheless, enough lake induced
instability will persist tonight through early Friday morning to
support some lake effect rain showers southeast of the lakes,
supported by orographic enhancement across the higher terrain. High
resolution model guidance suggests a Georgian Bay connection may
bring an uptick in coverage of showers late this evening and early
overnight for the Rochester area. With this in mind, kept probability of precipitation in
the likely range through most of the night southeast of Lake
Ontario. Rainfall amounts will be light however, with additional
amounts of a tenth to quarter inch at most in the persistent bands
after 6pm this evening.

Abundant moisture trapped beneath the subsidence inversion will keep
skies overcast across the region tonight. This will keep
temperatures from dropping much, with lows in the lower 40s on the
lake plains and upper 30s across higher terrain.

Friday any remaining light lake effect showers or sprinkles
southeast of the lakes will end by mid to late morning as inversion
heights continue to lower, and moisture becomes too shallow to
support rain. Clouds will be very stubborn to break however with
ongoing Shallow Lake instability and northwest upslope flow beneath
the steepening subsidence inversion. If there is any clearing across
western NY, it will likely not develop until late afternoon. The
clouds and cool airmass will only support highs in the lower 50s on
the lake plans and mid to upper 40s across higher terrain.

&&

Short term /Friday night through Sunday night/...
the upper level ridge currently east of The Rockies with a
corresponding surface high pressure ridge will be directly overhead
Friday night. With strong subsidence, any remaining inland stratocu
should quickly dissipate with mostly clear or clear skies overnight.
This should result in valley fog and areas of frost forecast over
areas where the growing season is still considered active. Sheltered
areas in lower terrain may reach the 32f mark, while other locations
should hover in the lower to mid 30s. In higher terrain, many areas
should be able to drop below 32f.

Despite the cool start, Saturday should turn out to be a nice day
with weak warm air advection on the back side of the ridge which
should be moving toward and off the East Coast by the evening. Skies
should remain mostly clear throughout the day and well into the
evening. The slight warm advection together with abundant sunshine
should allow temperatures to generally reach the 60f mark, with the
usual variations by terrain and proximity to the lakes.

Saturday night shouldn't be as cold as the previous night,
but still expect some temperatures to dip into the 30s in
sheltered/higher terrain, with ~40f readings elsewhere.

The next system is currently traceable back to the Pacific
northwest. This system is forecast to remain fairly weak as it
moves into the plains and then barely make it into the Great Lakes
region by Sunday. This system will probably go unnoticed as it
moves through. Can envision a mid/upper level cloud deck, but right
now will continue to stay on the drier side with low (~15%) chance
for measurable rain for Sunday. Otherwise, the region should see
another day with temperatures creeping into the lower 60s, followed
by another dry night with lows mostly in the 40s.

&&

Long term /Monday through Thursday/...
warm air advection will increase Monday as a 40kt low-level jet
moves north along The Spine of the Appalachians. A southeast wind
will increase across the region while surface high pressure retreats
to the northeast. While a cold front will be approaching from the
west, mostly dry and warm are expected Monday with highs in the
upper 60s to near 70. A slowly deepening surface low will move north
of Lake Superior Monday night-Tuesday morning. The associated cold
front will track east across the eastern Great Lakes late Monday
night through Tuesday. The 10/17 12z GFS is a smidge faster
than the European model (ecmwf) with the timing of the cold front. Showers,
possibly heavy at times will track east ahead and along the
front. The strong low-level jet will mainly be on the stable
side of the front as it moves by but gusty winds are possible
when the front passes.

The large scale trough will become negatively tilted by Wednesday
and strong cold air advection is expected to move across the Great
Lakes behind the cold front. Forecast guidance is depicting 850mb
temperatures dropping to -3 to 0c. Lake induced instability will be
present while the combination of westerly flow and upstream moisture
will allow a lake response to form Tuesday night and end by Thursday
east of Lake Erie and Lake Ontario. There may be a period Wednesday
night where the boundary layer gets cold enough for snow showers
across the higher terrain east of Lake Ontario and the western
southern tier. They will be short-lived as high pressure moves into
the region during this time.

&&

Aviation /21z Thursday through Tuesday/...
extensive wrap around moisture from a strong coastal low over New
England continues to combine with lake effect instability and
upslope flow to produce widespread light rain or showers across
the region late this afternoon. These lake effect showers
will slowly diminish tonight before ending Friday morning. Visibility
will be mostly VFR from this point forward, although a few
pockets of MVFR will still be found in the more persistent areas
of rain.

Widespread low stratus/stratocumulus will continue late this
afternoon through at least early afternoon Friday. Ceilings will be
mainly MVFR through the time period, with some areas of IFR this
afternoon and tonight across higher terrain. Ceilings will begin to
slowly improve to VFR later Friday afternoon.

Outlook...

Saturday through Monday...mainly VFR.
Tuesday...areas of MVFR with a chance of showers.

&&

Marine...
deep low pressure over New England will begin to accelerate east
along the Maine coast tonight before reaching the Gulf of Saint
Lawrence on Friday. Moderate to strong northwest winds will continue
through this evening before gradually diminishing later tonight and
Friday. Small Craft Advisory conditions will persist through late
tonight on Lake Erie, and through much of Friday on Lake Ontario.

High pressure will then build into the eastern Great Lakes Friday
night and Saturday before drifting off the East Coast Sunday. This
will bring a period of lighter winds to the eastern Great Lakes for
the weekend.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...Small Craft Advisory until 5 am EDT Friday for lez040-041.
Small Craft Advisory until 8 PM EDT this evening for
lez020.
Small Craft Advisory until 5 am EDT Friday for loz030.
Small Craft Advisory until 5 PM EDT Friday for loz043-044.
Small Craft Advisory until 2 PM EDT Friday for loz042.
Small Craft Advisory until 11 am EDT Friday for loz045.

&&

$$

Synopsis...Hitchcock/apffel
near term...Hitchcock/apffel

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