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Area forecast discussion 
National Weather Service Buffalo New York
344 am EDT Monday Apr 27 2015

Synopsis...
a cool...moist northerly flow will continue across the eastern Great
Lakes region today with scattered rain showers. This shower activity
will diminish through the overnight hours tonight as an upper level
low pressure drifts farther out to sea. Dry weather and clearing
skies will return Tuesday and will last through Wednesday before a
weak system brings the next chance of showers by Thursday.

&&

Near term /through tonight/...
water vapor imagery this early morning displays an upper level low
continuing to spiral off the Atlantic Canada coastline. A vorticity
maxima is seen dropping across Lake Huron this morning...creating a
westward upper level trough of low pressure that will drop across
our region this morning.

Regional radars show sparse shower activity of sprinkles/light
showers across The Finger lakes region and east of Lake Ontario this
early morning. To the west and closer to the vorticity maxima
scattered showers are developing and dropping southward across the
northern Niagara Frontier.

As this upper level trough passes...low level moisture convergence
on a northerly flow will increase. This moisture will produce light
rain showers through the day...with activity highlighted over the
upslope regions south of Buffalo and Rochester...as well as east of
Lake Ontario. Coverage should remain fairly spotty with plenty of
rain free time...and amounts should be kept to less than a tenth of
an inch in most locations.

High resolution models and the NAM/GFS are consistent with
developing this low cloud deck this morning. This deck of clouds
will lower such that areas of drizzle...and low clouds/fog is
possible across the hills of SW New York state and also across the Tug Hill and
western foothills of the Adirondacks. Surface dewpoints...which will
mainly remain below the lake water temperatures...are not getting
quite high enough to support any advection fog from the lakes off
the Cold Lakes.

Though temperatures at 925 hpa will be a degree warmer than
yesterday...additional cloud cover today will likely hold afternoon
temperatures a degree or so colder than Sunday. This will place many
areas in the middle 40s to around 50...which is a solid 10 degrees
below normal.

Tonight as the upper level low drifts farther out to sea a weak
ridge of high pressure will press eastward across the Great Lakes
region. Rain shower activity will end through the evening and
overnight hours...though skies may remain fairly cloudy through the
night. If clearing does develop patchy areas of fog will develop.
Likeliest areas for this would be far western New York and the higher
terrain of the Tug Hill region. Lows tonight will range from the middle
30s across the inland southern tier...to lower 40s near the lake
plains.

&&

Short term /Tuesday through Wednesday/...
a closed upper low in the Canadian Maritimes will gradually yield to
a narrow 500 mb ridge which will build into our region. This will
allow surface high pressure across the upper lakes on Tuesday to
spread westward into our region by Wednesday.

Tuesday should start off with at least partial cloud cover and
perhaps some patchy fog. However...drier air will work in
across the region from the top down...and should eventually result
in clearing of any remaining low clouds/stratus Tuesday. Partly to
mostly sunny skies combined with 850mb temperatures of around +2c should
result in warmer temperatures. Expect highs on Tuesday to be in the
lower 60s across interior sections...with cooler temperatures in the
upper 40s to lower 50s south of Lake Ontario and Lake Erie. The northwest
flow should keep most of the Buffalo metropolitan area on the warm side of
the lake breeze. By Tuesday night expect mostly clear skies with
decent radiational cooling allowing temperatures to drop into the
middle 30s to lower 40s. There may be some patchy fog in the southern
tier valleys.

Wednesday looks to be a warm day...as the shortwave ridging and
thermal ridge axis shift across the forecast area. Model consensus
850 mb temperatures rise to around +5c with the GFS a notable cooler
outlier. This consensus combined with mostly sunny skies should
result in highs in the middle to upper 60s on the warm side of the lake
breeze...with highs in the 50s along the immediate lakeshores. This
combined with fairly light winds should result should be a fantastic
Spring day.

&&

Long term /Wednesday night through Sunday/...
there continues to be a significant difference in model guidance
through much of the long term period. This difference mainly stems
from how much energy will break off from a shortwave near Hudson Bay
on Tuesday night. The operational GFS has consistently broken off
more energy which drops across the Great Lakes on Wednesday night
and then results in a cut-off low near the middle Atlantic which takes
over from the Canadian maritime low. The 00z ggem/European model (ecmwf) (and the
nam) break off considerably less energy which takes the same
track...but is not enough to cut-off so instead it pivots off
the middle Atlantic and feeds into the Canadian maritime low. It is
also Worth noting the majority of GFS ensemble members side with the
ggem/ECMWF...with ensemble MOS reflecting low forecast confidence
for this timeframe. The differences between these two solutions (and
it will probably be one or the other) is significant. The GFS
solution would result in showers Thursday and Friday and much cooler
temperatures into the weekend while the European model (ecmwf)/ggem solutions would
result in only a small chance for showers and warmer temperatures.

Based on the model consensus...we still view the GFS solution as
less likely...and given the relatively binary options (cut-off low
or not) the forecast will lean toward the European model (ecmwf)/ggem solutions. This
said...there still is a chance the GFS will verify which would
require significant adjustments to the current forecast.

Which ever solution verifies...it appears a broad ridge of high
pressure will build across much of the Continental U.S. On Sunday...with a zonal flow
near the Canadian border. This will bring seasonably warm
temperatures as colder air will be suppressed well to the north.

&&

Aviation /08z Monday through Friday/...
at 06z VFR flight conditions were found across the region with just
a few sprinkles passing through the Genesee Valley and Finger Lakes
region. As a cool northerly flow increases low level moisture across
the region this morning expect an expansion of light showers towards
dawn across all taf sites. Activity will be light and scattered and
will carry a vcsh in the prevailing category...and a tempo for the
best opportunity for light rain showers. Shower activity may have
the longest duration over the southern tier...including the kjhw
terminal where IFR ceilings are possible this morning with areas of
drizzle. Elsewhere ceilings will likely lower to MVFR flight category.

Showers will increase this afternoon east of Lake Ontario where an
upslope flow near the closed upper level low will likely bring rain
showers to the Tug Hill region. All shower activity will slowly
diminish through the overnight hours with a return to VFR. That said
any clearing of the skies may allow for some patchy fog to form that
will reduce visibilities. The best chance for this to happen will be
across the hills south of Buffalo where some localized IFR visibilities are
possible the second half of the night.

Outlook...
Tuesday...any MVFR/IFR ceilings improving to VFR.
Wednesday...mainly VFR.
Thursday and Friday ... of MVFR possible with a chance of
showers.

&&

Marine...
northwest winds will average 10 to 15 knots on the eastern Great
Lakes today through tomorrow. These winds will back some to westerly
on Wednesday as the upper level low exits eastward and weak surface
high pressure builds eastward towards the eastern Great Lakes. Winds
will continue to remain light on Wednesday with wave heights over
the next 72 to 96 hours 3 feet or less.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...none.

&&

$$

Synopsis...Thomas
near term...Thomas
short term...apffel
long term...apffel/church
aviation...Thomas
marine...Thomas

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