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Area forecast discussion 
National Weather Service Buffalo New York
445 am EDT Tuesday Mar 31 2015

Synopsis...
a fast moving clipper low will bring a period of snow across the
southern tier today...before high pressure and dry weather returns
tonight through Wednesday. Temperatures will remain below normal
Wednesday...but Thursday could bring temperatures well above normal.
A cold front Thursday night should bring rain and gusty winds across
the area. The potential for unsettled weather remains through the
weekend.

&&

Near term /through tonight/...
WV imagery shows a distinctive shortwave in the northwesterly flow
over Michigan this morning. This wave will continue to slide quickly
southeastward across PA by this afternoon and off the Atlantic coast
by this evening. This trajectory will send precipitation
overspreading the southern tier today...and with a cool airmass in
place across the area on the north side of the weak surface low
tracking across PA...this should be an all snow event. Farther north
across the southern shore of Lake Ontario from Buffalo to Rochester
and into the north country...there will be little sensible impact to
weather today...other than a mainly cloudy and cool day as the
northern shield of middle-high level cloud cover slides across the
state.

The 00z model runs trended the track of the wave slightly back to
the north again. Comparing the 00z model suite forecast to this
mornings radar/satellite/surface observation...it appears the precipitation
shield is actually even slightly farther north than the models
forecast as of 08z. Forecast quantitative precipitation forecast is from a consensus of the 00z
ec/GFS/Gem/NAM/(21z)sref which were in fairly good agreement...then
adjusted northward slightly by blending in some 05z hrrr...which
seems to be better capturing the current position of the wave and
associated precipitation shield. The best forcing and moisture associated
with the wave will pass just south of the forecast area...across
northern PA...this will result in the highest quantitative precipitation forecast amounts in western
New York of around a third of an inch closest to Jamestown and the
southwest corner of the state.

Across the southern tier...surface temperatures in the upper 20s
with dew points in the low to middle 20s are primed to support all snow
at the onset with the warm layer aloft suppressed well to the south
across PA. The greatest snowfall amounts are expected around the
Jamestown area into the southwest corner of Chautauqua County. The
combination of the highest quantitative precipitation forecast amounts and early day timing will
support snow accumulations of 2 to 3 inches...and would not rule out
an isolated 4 inch report in the far southwest corner...but forecast
confidence in that happening is very low and not enough to warrant
an advisory. The rest of the southern tier / including Cattaraugus
and Allegany counties / should see 1 to 3 inches of snow
accumulation with the highest amounts closest to the PA border.
These locations will also increasing have to contend with daytime
heating and solar insolation through the cloud cover working against
snow accumulations...especially on paved surfaces. Thus accumulating
snow will become more limited to grassy and elevated surfaces. As
snow rates decrease into the afternoon...and eventually the snow
ends from west to east across the southern tier...temperatures
should manage to climb a couple to a few degrees above freezing. Any
accumulated snow remaining on paved surfaces at that point should
quickly melt off by middle to late afternoon.

Elsewhere / including Buffalo...Rochester and the north country /
locations along and south of the thruway could see some light snow
showers from late morning through early afternoon...but should be of
little consequence. Locations north of the thruway should see an
entirely dry day. Without any precipitation to content
with...temperatures will climb into the upper 30s this
afternoon...with the cloud cover likely keeping most locations from
touching 40.

Tonight...the shortwave and snow across the southern tier will be
long gone and dry air will work in from the north across the
forecast area. This will allow for cloud cover to clear out quickly
from north to south across the area. With the north country clearing
out early and light winds in place...radiational cooling should
allow temperatures to drop into low to middle teens overnight.
Elsewhere...some thin lingering cloud cover should help keep
temperatures in the low 20s. A weak shortwave in the northwesterly
flow may bring a few light snow showers back into the western
southern tier late tonight...but these should not last long and will
result in little additional snow accumulations.

&&

Short term /Wednesday through Thursday night/...
Wednesday morning another much weaker clipper will move across Lake
Erie and the upper Ohio Valley. Any light precipitation with this should
remain west of our region...but it will bring some cloud cover to
the area during the morning especially from the Genesee Valley and
western Finger Lakes into western New York. The morning clouds should
quickly diminish for the afternoon as the clipper washes out and
high pressure builds into the Great Lakes region with increasing
drying and subsidence. Despite the increasing sunshine temperatures
will remain below normal...with upper 30s to around 40 across the
lower elevations of western New York and low to middle 30s across the north
country.

High pressure settles overhead Wednesday evening before drifting to
the eastern Seaboard overnight. This will bring mainly clear skies
and light winds initially...which will allow for some early
radiational cooling. Overnight southerly return flow will develop in
the wake of the departing high and force rising temperatures. A warm
frontal segment will move quickly from southwest to northeast across
the area late Wednesday night...reaching the north country by early
Thursday morning. The deepest moisture and strongest isentropic
upglide with the warm front will Cross Lake Ontario and the Eastern
Lake Ontario region...where a few rain and snow showers are possible
late Wednesday night and early Thursday. For the rest of the
area...dry low levels should keep any precipitation from reaching the
ground with just a period of middle level cloud cover.

The warm front will exit the north country early Thursday...leaving
the entire County Warning Area in the warm sector for the day. Deep south-southwest flow within
the warm sector will allow 850mb temperatures to soar to near +10c. The
combination of a much warmer airmass and south-southwest downslope flow will
boost temperatures into the middle 60s on the lake plains of western
New York...with middle to upper 50s across the interior southern tier and
Eastern Lake Ontario region. The last time we saw a high temperature of 60f
or higher was November 30th at Buffalo and Rochester. The south-southwest wind
direction will keep most of the lake cooling on the Canadian side of
the border...except for areas along the Niagara River off Lake Erie
and near Cape Vincent off Lake Ontario where highs will be
considerably cooler.

Most of Thursday will be rain free...but ongoing warm advection and
isentropic upglide combined with the approach of the initial middle
level height falls and DPVA could produce a few widely scattered
showers during the afternoon with a mix of sun and clouds.

A fairly strong cold front will cross the area Thursday night along
with a convectively augmented middle level shortwave and low level jet
maximum. This will produce several hours of showers...reaching western
New York during the middle evening then spreading east to the Eastern Lake
Ontario region by around midnight. Forcing will be fairly strong...
with convergence enhanced by a 60+ knot low level jet. A plume of
deeper moisture will be captured by this system...with precipitable water rising
to around 1.25 inches along the front. The combination of quality
moisture and dynamics will produce rainfall amounts of a quarter to
third of an inch over a few hours. Both the NAM and GFS also show
some lingering marginal instability along the advancing front with
around 100j/kg of elevated cape and showalter index near 0c. While
these instability values are extremely marginal...in the presence of
a strongly forced environment it may be enough for a few isolated to
scattered thunderstorms along the front. Given the strength of the
low level wind field...any convective showers /with or without
thunder/ along the front may produce very gusty winds.

The rain will quickly end from west to east overnight as the cold
front moves east of the area and a strong push of drying moves into
the lower lakes.

&&

Long term /Friday through Monday/...
Friday will start off dry...but later Friday and Friday night most
medium range guidance continues to suggest a secondary frontal wave
will move through the Ohio Valley and into the northeast forced by a
strong middle level shortwave moving along the advancing baroclinic
zone. This will bring increasing chances of precipitation again later
Friday afternoon and especially Friday night. The European model (ecmwf) remains
stronger and farther north with this feature than the GFS...and has
support from the 00z Canadian Gem with a similar track and
intensity. As this system passes by to our south...colder air will
be filtering into the region and allow rain to change to snow Friday
night. If the timing and track are just right there could even be
some accumulation.

This system will quickly move away from the area Saturday morning
with just a few leftover snow showers in cold northwest flow during
the first half of the day. Temperatures will again drop to well
below normal with highs only in the 30s. Another cold front will
cross the area Saturday night with a chance of more snow showers.
This will keep cold air in place for Easter Sunday with highs again
only in the 30s. High pressure and drying aloft should keep Sunday
dry with a decent amount of sunshine.

By Monday both the GFS and ecwmf bring a sharp baroclinic zone
slowly northward across the area...with a chance of some rain and
wet snow. Looking a little farther ahead...behind this slowly moving
boundary another push of much warmer air should arrive for at least
a day or two around the middle of next week.

&&

Aviation /09z Tuesday through Saturday/...
a clipper low will bring widespread snow across the New York southern tier
/ PA northern tier today. Conditions at kjhw will quickly
deteriorate to IFR or lower this morning as snow could be heavy at
times through late morning. Snow will taper off from west to east
across the southern tier this afternoon. Initially IFR ceilings will
linger at jhw with upslope flow in place...but drier air will
eventually work in from the north tonight to break up the low cloud
deck.

Elsewhere...kiag/kbuf/kroc/kart will see little to no impact from
the clipper low outside of middle-high level clouds across the area
today...and thus VFR conditions will prevail. Would not rule out
some isolated/scattered snow showers near kbuf from middle morning to
early afternoon...but these should remain south of the terminal.

Outlook...
Wednesday...VFR.
Thursday and Thursday night...VFR/MVFR with rain showers becoming
likely later in the day.
Friday...VFR/MVFR with a chance of rain showers.
Saturday...VFR/MVFR with a chance of snow showers.

&&

Marine...
expect a period of light to modest northeasterlies and northerlies
today and tonight as a clipper system passes across the Ohio
Valley... before high pressure and light winds build back across the
Great Lakes on Wednesday.

&&

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

&&

$$

Synopsis...church
near term...church
short term...Hitchcock
long term...Hitchcock
aviation...church
marine...church

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