Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 300524
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
124 AM EDT Thu Mar 30 2017

.SYNOPSIS...
High pressure north of the region will move east tonight while a
low pressure system over the Mississippi Valley draws moisture
northward toward the New York on Thursday. Chances for rain
will increase over far Western New York Thursday afternoon, with
precipitation spreading across all of Western and Central New
York Thursday night. This complex system may bring some thunder
to far Western New York while a brief period of snow will be
possible east of Lake Ontario. The system will change to all
rain by Friday and move east of the region for the weekend.

&&

.NEAR TERM /THROUGH TODAY/...
Overnight...high pressure will build east into Quebec with a ridge
extending down into NY. Increasing mid/upper level warm advection
will bring a gradual increase in high clouds from west to east
overnight. The high clouds will be thin enough to allow for some
radiational cooling, but will hinder the process a bit. Low
temperatures will drop below freezing for most locations, with the
coldest readings in the mid 20s in the North Country.

Model consensus has trended faster with the onset of precipitation
on Thursday. The 18Z and 00Z NAM in particular are faster, with the
HRRR and current radar trends also supporting the faster trend.
Expect rain to enter the Western Southern Tier around noon,
spreading into Buffalo by mid-afternoon and to Rochester late
afternoon. Latest model consensus supports a start time about 3
hours faster than 12Z based guidance.

This faster timing has other impacts to the forecast, with
cooler high temperatures expected, especially across western
portions. It`s also interesting to note that BUFKIT thermal
profiles support a brief period of rain and snow mix across the
lower Genesee Valley and Finger Lakes regions late Thursday
afternoon. Given the March sun, this is not likely to produce
any accumulation, but it is possible a few snow flakes will be
mixed in at the onset.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...
Let there be no doubt...it is going to be wet and unsettled for much
of this period as another soaking rain will be in the offing. The
good news is that the rain will pull away from the region just in
time to give us a fairly nice weekend.

A storm system...currently spawning severe weather across the Lower
Mississippi Valley...will approach our region from the Ohio Valley
Thursday night. A 40kt low level jet ahead of this stacked low will
pump abundant GOMEX moisture up and over a tight H925-70 baroclinic
zone that will be in place over the Lower Great Lakes. A weakly
coupled H25 jet will accompany the isentropic lift...so plenty of
forcing will be in place to interact with a moisture rich (PWAT arnd
1") environment. This will encourage some locally moderate to heavy
rain...and as mentioned in a previous discussion...could support the
potential for elevated convection. Pattern recognition...including
the strength of the warm frontal boundary...has looked impressive
for several days. FINALLY...forecast soundings are suggesting steep
enough lapse rates aloft for elevated CAPE values in excess of 100
j/kg. Will add the chance for thunderstorms to the western zones...
with some enhanced wording for some heavy rain. These should be
focused along an axis of mid-level warm air advection which will
spread from SW-NE Thursday evening. Rain may briefly taper off
behind this across the Western Southern Tier Thursday evening
before the next round of steady rain moves in later in the
night.

For sites east of Lake Ontario...the pcpn could start off as a
wintry mix...so will maintain that wording. Snow should struggle
to accumulate in most areas, but precipitation rates should be
ample for some accumulation across higher terrain. Several
inches are possible across higher terrain before warmer mid-
level air changes precipitation over to rain late in the night.
This is a difficult snow forecast since temperatures will be
very marginal.

The stacked low will drift across the Upper Ohio Valley on Friday...
while its associated warm frontal boundary will push north across
Lake Ontario and the North Country. This will encourage the
steadiest and `heaviest` rain to move across the eastern Lake
Ontario region in the vcnty of the strongest isentropic lift...while
mainly hgt falls and a divergent upper level flow will drive lesser
rains (including some drizzle) over the western counties...and in
particular across the Southern Tier. Will use cat pops across all of
the forecast area. Any mixed pcpn at the start of the day over the
North Country will change to just rain by late morning. Afternoon
temperatures will range form the upper 40s near the Pennsylvania
border to the upper 30s across the eastern Lake Ontario region.

As the upper level support for the complex storm system drifts east
across Pennsylvania Friday night...the initial sfc reflection will
weaken then `jump` (redevelop) off the New Jersey coast. While the
bulk of the moisture will remain in place over the region during the
storms transition to the coast...only limited low level forcing will
persist. This will allow the widespread rain to taper off as a bit
of light rain and/or drizzle...again mainly over the Southern Tier.
Given the light sfc gradient and near saturated conditions...there
will likely be some fog as well...with dense fog possible over the
higher terrain.

While mid level ridging will make its way across the Lower Great
Lakes on Saturday...guidance is suggesting that a weakness in the
sfc pressure field will remain in place over our forecast area. This
will promote enough of a cyclonic flow in the low levels to combine
with leftover low level moisture (trapped beneath a subsidence
inversion) to keep much of the day shrouded under clouds. Temps
Saturday afternoon will be in the mid to upper 40s.

A shortwave in the northern branch will sweep across the St Lawrence
Valley Saturday night...glancing by our forecast area in the
process. While there will still be a fair amount of low level
moisture in place...high pressure nosing south from Hudson Bay
should supply us with fair dry weather. Temps Saturday night will
generally settle into the low to mid 30s.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Ridging moving across the Lower Great lakes should supply us with a
nice ending to the weekend...as at least partial sunshine and H85
temps near zero C will enable afternoon temperatures to get into the
50s (up 40s Ern Lake Ont Region).

Another southern stream closed low over the southern Plains and
Lower Mississippi Valley will amplify a downstream ridge over the
Ohio Valley Sunday night and Monday. This will keep fair dry weather
in place with temperatures remaining a few degrees above early April
norms.

The various medium range guidance packages diverge with their
solutions at this point...as one forecast `camp` opens up the
southern stream closed low and drifts it across our forecast area
late Monday night and Tuesday. The other `camp` keeps the bulk of
the system to our south...with notably lower POPS and QPF. Will
maintain the likely pops over our region on Tuesday to avoid flip
flopping.

While there is low confidence in the guidance for Wednesday...there
is general consensus that our forecast area will be in a lull as far
as pcpn is concerned. Will refrain from the details due to the large
variance among the various ensemble members of the GEFS and ECMWF.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
High pressure will build east across Quebec overnight into Thursday
morning with a ridge extending down into NY. This will support a
continuation of VFR conditions with high clouds gradually increasing
from west to east and lowering into a mid level deck Thursday
morning. Increasing warm advection ahead of a warm front will allow
rain to develop across Western NY during the afternoon, with rain
then spreading east into Central NY by evening. Expect CIGS/VSBY to
remain VFR for the first few hours of rain as the low levels remain
unsaturated. By Thursday evening the low levels will saturate, and a
low level frontal inversion will steepen, further trapping low level
moisture and increasing the likelihood of IFR CIGS and MVFR to IFR
VSBY across Western NY with low stratus and ongoing light rain.

Across the North Country the airmass will be colder, and likely
support wet snow at the onset Thursday evening including KART with
IFR VSBY.

Outlook...
Friday into Saturday...MVFR/IFR with rain. A chance of
thunderstorms Friday night.
Sunday and Monday...VFR.

&&

.MARINE...
Winds will turn easterly by Thursday and southeasterly Friday
as our next storm system passes south of the Great Lakes. Winds
will reach 15-20 knots with the highest waves in Canadian
waters. However, low-end small craft criteria should still be
reached across the Western half of Lake Ontario late Thursday
through Friday. Winds should be out of the northwest following
the passage of the low for the weekend.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory from 5 PM this afternoon to 5 PM EDT
         Friday for LOZ043.
         Small Craft Advisory from 2 PM this afternoon to 5 PM EDT
         Friday for LOZ042.

&&

$$

SYNOPSIS...ZAFF
NEAR TERM...APFFEL/HITCHCOCK/ZAFF
SHORT TERM...APFFEL/RSH
LONG TERM...RSH
AVIATION...HITCHCOCK
MARINE...APFFEL/ZAFF



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