Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 150910

Area Forecast Discussion
National Weather Service Buffalo NY
410 AM EST Sat Dec 15 2018

Low pressure will move along the East Coast through Sunday, but high
pressure extending from the lower Great Lakes to northern New
England will keep our region mainly dry over the weekend. Otherwise
there will be patchy fog today and possibly some light rain across
the Southern Tier tonight and Sunday. Following the passage of this
system, colder weather will then return early next week and bring
the potential for some lake effect snow southeast of the lakes.


High pressure across Michigan will slide east into southern Ontario
province today, and into northern New England by late tonight. This
will keep our region dry through at least today, and most areas dry
tonight as well. The main forecast challenge is the potential for
fog and low clouds to move into the region. This is shown in BUFKIT
forecast soundings using NAM and most mesoscale guidance, and to a
lesser extent by the GFS. Often, shallow low level moisture is
overdone by model guidance, and instead it mixes out resulting in
mostly clear skies (and much warmer temperatures) instead. In this
case, there is a considerable amount of fog and stratus upstream
across Michigan and southern Ontario which provides support for NAM
and other model guidance. It is possible this fog may be dense in
some areas. Based on this, the forecast will carry more fog and
stratus today and into tonight. However, with a developing northerly
component surface flow expect this low moisture will be south of the
lakes due to upsloping and essentially get blocked by the higher
terrain. If this plays out, then high temperatures today will only
be in the mid to upper 30s across most of the area, except in the
lower 40s across the Western Southern Tier.

For tonight, stacked low pressure will move northward and slightly
closer to our region. The majority of model guidance keeps any
precipitation with this system to our south, but RGEM/GGEM and some
SREF ensemble members bring some light precipitation into the western
Southern Tier tonight. This could be problematic since surface
temperatures will be near or slightly below freezing, resulting in
the potential for freezing rain. Since there is low confidence that
any precipitation will occur, winter headlines will not be issued.
Elsewhere will be dry, with lingering fog and stratus still possible.


Upper level cutoff and associated surface low near the Delmarva
region Sunday morning. Most model guidance suggesting that the
northern edge of the precipitation shield will be across the western
Southern Tier and southern Finger Lakes, perhaps a bit farther
Sunday morning. Surface temperatures may still be at or just below
freezing, keeping the potential for some pockets of freezing rain in
the forecast through Sunday morning.

Precipitation will diminish from west to east Sunday afternoon into
Sunday night as the upper system and associated surface low push
well off the east coast.

Monday, a sharp cold front plows through the region. The cold front
will only produce some minor synoptic snow, but cold air will deepen
quickly behind the front transitioning to northwest flow lake effect
snow showers. Overall lake parameters become increasingly favorable
for a period of accumulating snow, but marginal temperatures near or
slightly above freezing will limit accumulation efficiency, perhaps
1-3" accumulations during the day Monday.

Temperatures initially above freezing early in the day Monday will
drop through the day, with most locations in the 20s by Monday
evening with wind chills in the teens. Any snowfall may initially
melt before the temperature drop off which may cause a freeze-up on
roadways by the Monday evening commute.

Temperatures will continue to fall off Monday night dropping into
the teens and 20s, with wind chills down into the single digits and
teens. Incoming drier air and lowering inversion heights will help
to lessen any lake effect snow showers southeast of the lakes.

Upper level ridging building eastward into the lower Great Lakes
Tuesday. We should see increasing amounts of sunshine through the
day with any lingering snow showers ending. High temperatures only
in the 20s with brisk northwest winds.


The deep upper level trough which briefly digs into New England and
Tuesday night will exit by Wednesday morning, to be replaced by a
ridge surface and aloft building into the eastern third of the
nation. The building ridge and warm advection will bring
temperatures above average again for Wednesday and Thursday, with
highs in the low to mid 40s at lower elevations. Wednesday will be
dry with surface high pressure centered over the Mid Atlantic states
and a ridge extending northward into the eastern Great Lakes and New
England. Model guidance begins to diverge by Thursday. The GFS is
fastest with the next system, spreading rain into our area. The
Canadian GEM and ECMWF are slower, with rain not arriving until
Thursday night. With this in mind, kept POPS low chance for Thursday
before ramping up Thursday night.

Model uncertainty continues Friday. The GFS, GEM, and ECMWF all have
a trough moving through the Great Lakes and New England with
associated precipitation chances. The faster evolving GFS has enough
cold air moving into our region to possibly bring a rain/snow mix or
change to wet snow late Thursday night and Friday, while the slower
ECMWF and GEM would be warm enough for mainly rain. Given the
inherent uncertainty at day 7, went with a rain/snow mix and
temperatures in the upper 30s to lower 40s.

Looking a little further ahead, it does appear likely cold air will
return by next weekend. Model guidance shows typical variance in the
synoptic scale details, but in a broad sense a deep trough will
begin to carve out over central and eastern North America, allowing
colder air to move back into the Great Lakes and New England. GEFS
and CMCE ensembles over the past few days show good support for
troughing and cold air becoming established most of the time for the
week between Christmas and New Years. Thus, it appears the warmup
this weekend and again later next week will be transitory with more
consistent winter weather on the horizon.


There is a risk for LIFR cigs and dense fog with visibility below a
half mile today. However, there is a lot of forecast uncertainty.
There will be a lot of low level moisture today, and this still may
mix out with VFR flight conditions. However given the latest model
guidance and fog and stratus to our north it now appears more likely
that there will be an extended period of IFR conditions from 09Z to
18Z today at most of our TAF sites including KBUF/KROC. This low
moisture will be enhanced by upsloping as a northerly flow develops
and encounters higher terrain south of the lakes. As a result, the
best flight conditions are likely to be at KJHW, where the low
moisture will be thin and may mix out.

For this afternoon and evening, it is possible that stratus and fog
will linger in some areas. It is likely that there will be a modest
improvement in visibility with daytime heating, but with low sun
angles it is possible that if stratus does move in that it may hold
in through the 06Z TAF cycle. This said, there probably will be some
breaks, making the aviation forecast particularly difficult.

Saturday night and Sunday...Mainly VFR. A chance of rain with
mixed precipitation possible Saturday night/early Sunday across
the Southern Tier.
Monday and Tuesday...VFR/MVFR with a chance of snow showers.
Lake effect snow possible southeast of the lakes.
Wednesday...Mainly VFR.


Northeast winds will freshen on the lakes today and tonight as low
pressure works through the Mid Atlantic states and high pressure
becomes centered over the lower Great Lakes. A period of wind/waves
nearing small craft advisory criteria may develop during this time
period from Dunkirk to Ripley on Lake Erie.

The graident will relax on Sunday, before a cold front moves
across the lower Great Lakes late Sunday night or Monday morning
turning winds west then northwest with gusts potentially
reaching 30 knots. This period will likely require small craft
advisories Monday into Tuesday.





NEAR TERM...Apffel
LONG TERM...Hitchcock
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