Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 230532
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
132 AM EDT Thu Mar 23 2017

.SYNOPSIS...
High pressure across the lower Great Lakes will result in fair
weather today with temperatures rebounding a bit. A frontal
boundary will stall across the region this weekend, with several
disturbances moving along the front and bringing periods of
rain over the weekend and into the first half of next week.

&&

.NEAR TERM /THROUGH TODAY/...
Sprawling arctic high pressure will continue to build in across the
Great Lakes overnight. A few scattered narrow bands of lake
effect clouds will persist southeast of Lake Ontario supported
by the cold airmass, but the very shallow inversion and dry
synoptic scale environment will only permit partly cloudy skies
at most. Otherwise for the rest of the area expect clear skies
overnight.

High pressure will move over the forecast area overnight setting the
stage for optimal radiational cooling with light to calm winds and
clear skies. Locations with lingering snowpack, such as the North
Country and interior portions of the western Southern Tier will see
temperatures plummet overnight, with lows bottoming out in the
single digits to near zero. Meanwhile, lake plains locations, those
with limited snow pack, and urban areas will see temperatures mainly
in the low to mid teens.

The large high pressure system will slide to our east after
daybreak, with some limited return flow developing by mid- day
and the afternoon. This will allow for some moderation in
temperatures as the core of the cold airmass exits the region.
High temperatures will run a fair bit warmer than Wednesday, as
temperatures reach the low 30s in the North Country to within a
few degrees of 40 in Western NY. Full sunshine in the morning
will give way to a gradual increase in mid/high clouds later in
the afternoon as mid level warm advection increases from west to
east.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...
After a midweek dry spell, the region will enter a prolonged
unsettled and relatively mild period that will last at least through
the weekend as a slow moving upper level low meanders across the
nation`s mid-section. Southerly return flow around high pressure
stationed off the Eastern Seaboard, enhanced by a strengthening low-
level jet will pump moisture and mild air northwards across the
Great Lakes. Meanwhile, a northerly flow of cooler and drier
Canadian air be found just to our north, sharpening a frontal
boundary across the lower Great Lakes. This front will then serve as
the focus for a band of precipitation across the forecast area that
will develop starting late Thursday night as the warm front lifts
across the region. With warm air initially overrunning the initially
sub-freezing surface air, we may see a brief period of mixed
precipitation, particularly across the Southern Tier and North
Country, late Thursday night into Friday morning before the arrival
of much warmer air on southwesterly flow changes precipitation over
to rain. Temperatures Thursday will then warm into the 50s across
Western NY, with low 40s in the North Country.

Currently, the model consensus places the frontal precipitation band
along and north of the Thruway, with around a half to three quarters
of an inch of precipitation possible, heaviest across the north
Country. Temperatures across the forecast area should hold above
freezing Friday night, allowing for ongoing frontal precipitation to
persist as rain, with the possible exception of the St. Lawrence
valley, where a possible backing northerly flow may bring in some
sub-freezing air and result in mixed precipitation early Saturday
morning.

As we move into Saturday, diurnal effect should keep precipitation
mostly rain, however, as the broad surface low wandering across the
Mississippi valley draws closer to the region, increasing
northeasterly flow into this low may draw colder surface air over
Canada back across the forecast area, potentially undercutting the
warm air aloft.  This may result in more substantial sleet and/or
freezing rain across the North Country, and possible as far south as
the Lake Ontario plain. Model guidance differs somewhat in how far
north the warm front travels into Canada Friday, and hence how far
south it will retreat Saturday, so all mixed precip grids are being
left as a chance for the time being.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
An active wet pattern will continue Sunday into at least the middle
of next week as western and north-central NY will remain within the
track of at least two mid-level troughs. Each of these troughs will
provide synoptic lift over and moist southerly flow into our region
that will interact with a low frontal boundary. The first will shift
over our region in the Sunday-Monday time frame while the second
looks to shift over our region Tuesday. It appears now that this
boundary from Sunday into Monday will lie further to the north
towards or across the Saint Lawrence River Valley then should be
shoved even further northeast by the second trough/surface low. For
western NY into the Finger Lakes, the position of this front will
allow for plenty of low level warm air to support high confidence
for a soaking plain rain. Looking across the North Country into the
Saint Lawrence Valley, the position of the front will be more
sensitive to p-type and a risk for some freezing rain Sunday night
and Monday night with cold northeasterly flow down the SLV. Have
kept any wording for freezing rain at chance POPs due to the
uncertainty in frontal position this far out.

In terms of surface temperatures, areas to the south of the front
will mainly feature warmer temps upper 40s into the 50s while areas
north of the boundary will see cooler temperatures 30s and lower 40s
with some 20s possible in the North Country during the overnights.

In terms of QPF, a rough average accumulated total among the models
Sunday through Tuesday ranges from around a half inch on the ECMWF
to around 2 inches on the GFS. While the long duration of this event
should not bring any flash flooding concerns, river and stream rises
and areal flooding of low-lying areas may be possible. If sub-
freezing air remains locked at the surface on the north side of the
front there could also be a threat of some significant ice
accumulations but the lowest confidence is found in that scenario.
Overall, confidence on the specific placement of any weather hazards
during this period is fairly low at this range which has precluded a
mention in the Hazardous Weather Outlook.

On Wednesday, the second surface low will shift off into New England
with a cooler and perhaps very dry northwest flow in its wake. The
12z ECMWF shows very dry air with just a cool northwest flow on
Wednesday while the GFS shows some lingering wrap around moisture
may lead to some upslope/lake enhanced showers. Have gone with
slight/low chance POPS for Wednesday under a more clear signal shows
up in the guidance.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
High pressure will remain across the region overnight with SKC
in most areas. A few scattered lake effect clouds will persist
in a small area southeast of Lake Ontario with bases around 4K
feet. The surface high will drift to the Mid Atlantic later
today. VFR will continue with a modest increase in mid/high
clouds from west to east later in the afternoon.

Clouds will thicken and lower tonight, but it should generally
remain dry and in the VFR category until just before 12Z Friday.
There is also a potential for LLWS after 06Z Friday.

Outlook...

Friday...Deterioration to MVFR/IFR with rain. The rain may begin as
a brief period of freezing rain or snow in some areas.
Saturday thru Monday...MVFR/IFR with rain likely at times.

&&

.MARINE...
Winds have diminished with high pressure building across the
lower Great Lakes so the small craft headlines will be allowed
to expire. This high will will remain across the waters through
this evening with light winds and negligible waves.

S or SW winds will increase Friday, and may approach small craft
criteria. After this, a boundary will stall across the region,
with a northeasterly flow likely on Lake Ontario and variable
winds on Lake Erie. This may require small craft headlines on
Lake Ontario for portions of the weekend.

&&

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

&&

$$

SYNOPSIS...APFFEL
NEAR TERM...APFFEL/CHURCH/HITCHCOCK
SHORT TERM...WOOD
LONG TERM...SMITH
AVIATION...APFFEL
MARINE...APFFEL



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