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188
FXUS61 KBUF 190243
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
943 PM EST Mon Feb 18 2019

.SYNOPSIS...
Scattered weak lake effect showers southeast of Lake Ontario will
end early Tuesday as strong surface high pressure moves east across
the state.  The next system will approach the region by late
Wednesday and bring a wintry mix to the region Wednesday night
followed by a period of rain.  This system may briefly end as snow
on Thursday before another area of surface high pressure moves in for
the end of the week.

&&

.NEAR TERM /THROUGH TUESDAY/...
Mesoscale processes will continue overnight south and southeast of
Lake Ontario. The airmass above 4000` will quickly dry out. Lapse
rates below this will be steep enough to support lake effect
processes though, mainly from Wayne to Oswego County, although
portions of Orleans and Monroe counties may see some scattered snow
showers. Most of this will be light and hard to detect via KTYX or
KBUF 88Ds, but we`ll have good coverage from GOES16 with no upper
level cloud cover. Accumulations, if any, should be an inch or less.

The remainder of the region should see slowly decreasing cloud cover
but with upslope flow may hinder the ability to complete clear
out with some flurries possible. Temperatures east of Lake
Ontario however may plummet with fresh snow cover, light winds
and clear skies, with overnight lows near (or lower) than 10F
below zero. The remainder of the region should see temperatures
mostly in the single digits or into the teens where cloud cover
lingers the longest.

Strong surface high pressure will then move east into the region for
Tuesday.  Localized lake effect right along southern Lake Ontario
shoreline early Tuesday will try to keep going even under a strong
cap near between about 3500-4000`, but eventually this will be
pushed ENE and probably offshore, ending altogether in the
afternoon.   The remainder of the area should see variable clouds to
mostly or sunny skies east of Lake Ontario.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
High pressure will be anchored directly overhead Tuesday evening and
gradually begins an eastward ooze toward New England by Wednesday
morning. This will allow for return flow from the south on the west
side of the high to start to draw warmer air northward toward the
CWA by Wednesday morning. As this occurs, the mid-level ridge axis
will shift east of the area on Wednesday morning, and allow the area
to start to be susceptible to mid-level moisture streaming in from
the southwest ahead of the next sprawling upper low in the mid-
latitude flow.

The mid-level vort maxima will shift toward the Great Lakes rapidly
on Wednesday, largely phasing into the anomalously strong upper jet
streak that has become semi-resident in the northeastern U.S. The
right entrance region of this feature will be anchored somewhere
near the area, so with an upward catapult in layer moisture, upper
divergence, and differential thermal advection, precipitation should
blossom across the area as the wave translates in. With warm
advection well underway, particularly off the deck on model
soundings, a short period of inefficient snow will be likely before
a transition to sleet/freezing rain and eventually rain will be
common across the area. Given a very high dendritic growth layer and
warm advection processes, snow growth will be inefficient, so 1-2"
would seem to be the maximum for snowfall potential before a
changeover. The length of time for freezing precipitation will
largely be modulated by how difficult mixing out of cold air in the
lowest elevations will be. That said, the Lake Erie shoreline and
Buffalo area summarily have the shortest window for icing.

Drier conditions return for a spell behind this system, as mid-level
ridging returns to the area.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
High pressure will move from west to east and across the area on
Friday, which will provide dry weather which will last well into
Saturday. Highs on Friday will range from the mid 30s to around 40
with lingering cloud cover eventually giving way to a partial
clearing by Friday night. Saturday looks to be quite a nice day with
warmer conditions and temperatures climbing into the 40s. The
warmest areas will be the lake plains due to a developing southerly
downslope flow when the surface high exits to our east. Cloud cover
will increase from southwest to northeast with the approach of the
next system, but any showers should hold off until late in the day
or Saturday night.

Things get much more active for the latter half of the weekend and
into next week. A closed 500 mb low is forecast to move across
mid-western states Saturday night, with the majority of model
guidance then tracking a strong corresponding surface low across
the Great Lakes region in the Sunday timeframe. Model agreement
provides confidence in the general pattern even if there remains
uncertainty in the exact strength, timing, and track. Latest
model runs suggest the most likely track is across the central
Great Lakes and then across southern Ontario province Sunday
night. This would potentially bring strong to damaging winds
behind the cold or occluded front with this system. A more
westward track or weaker system would lower this risk, but given
the latest consensus the wind potential is a least worth a
mention in the HWO.

This track would also bring rain and warm temperatures to most of
the region, with upper 40s and lower 50s likely south of Lake
Ontario. It`s a closer call across the North Country which will be
closer to the track of the low. Depending on the track,
precipitation may be mixed with snow there. The bulk of the
precipitation will be Saturday night and Sunday, with model
consensus suggesting a half inch to an inch of QPF with this system.

Colder air will build into the region Sunday night, with lingering
rain showers changing over to snow. By Monday, it may be cold enough
aloft to support a limited lake response east of Lake Ontario which
will be enhanced by upsloping in a a strong westerly flow behind the
system.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
Surface high pressure will move into the region by Tuesday but with
continued localized lake effect SE of Lake Ontario.  Therefore
expect MVFR in most areas to gradually improve to VFR with mainly a
stratocu deck in weak upslope flow.

Outlook...
Tuesday and Tuesday night...improvement to VFR areawide.
Wednesday...Deterioration to MVFR/IFR with light mixed precipitation
becoming likely overnight.
Thursday...VFR/MVFR with a chance of snow and rain showers.
Friday and Saturday...VFR.

&&

.MARINE...
Surface high pressure will build into the region for Tuesday with
light winds lasting through Tuesday night. Advisory level winds will
return by Thursday following the passage of another surface low and
its trailing cold front.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...Zaff
NEAR TERM...TMA/Zaff
SHORT TERM...Fries
LONG TERM...Apffel
AVIATION...Zaff
MARINE...Zaff