Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 181014

Area Forecast Discussion
National Weather Service Buffalo NY
614 AM EDT Thu Apr 18 2019

Breezy and much warmer conditions will be common across the area
today as a warm front surges northward into Canada. Low pressure
will then slowly cross the region Friday through Friday night with
showers and a chance of a few thunderstorms and locally heavy
rainfall. Unsettled weather will continue over the weekend.


Surface low pressure is pushing northeastward across the
Leelanau Peninsula of Michigan and should advance through the
Soo this morning. A snaking warm front ahead of this low is
currently lifting rapidly to the northeast from southern Ontario
through central New York. General ascent ahead of this front is
generating precipitation aloft, however saturation below the
lifting layer is fairly weak. This has resulted in fairly poor
coverage of rainfall ahead of the front to this point, however
radar depictions indicate a general uptick in areal coverage
early this morning. That said, the front will push to the
northeast of the area progressively, which will allow for much
of the area to be post-frontal shortly after sunrise.

Behind the warm front, the area moves into the warm sector, as
the trailing cold front still resides back along the
longitudinal axis of Lake Michigan. With additional waves moving
up this front, its eastward progress looks to be painfully slow.
In fact, overnight guidance suggests a substantially slower
frontal progression seems quite likely. As a result, the chances
of rainfall have been reduced across the board from this
afternoon into tonight, as in all likelihood, deeper moisture
will remain to our west with a slower moving front than was
previously advertised.

With all of this in mind, as warm air advances into the area
today, low level profiles should steepen a bit with abundant
insolation. This will allow for gusty southerly winds to develop
and for strong vertical mixing to adiabatically bring the +14C
or so at 850 mb to the ground. The net result looks to be
widespread 70s in the forecast, which puts us about 20 degrees
above average for the afternoon.

With a slower frontal progression, we remain in the warm sector
overnight. This will keep temperatures above normal yet again.


On Friday, a sharp upper level trough extending down the
Mississippi River Valley will close off and drift across
Tennessee on Friday night. A strong frontal boundary will extend
roughly from western Lake Erie to the Saint Lawrence Valley on
Friday morning. As the upper level low closes off, a weaker flow
will allow this boundary to meander slightly southward late
Friday into Friday night. Meanwhile a deep southerly flow of
moist air will flow across the mid-level thermal gradient with
widespread rain developing across the lower Great Lakes and
nearby lake plains. Further inland will remain in the warm
sector, with a cyclonic flow aloft supporting showers with
enough instability to support a few thunderstorms. Steadier rain
showers will push a bit southward Friday evening before the
boundary stalls out late in the night. Given the sharp boundary,
significant adjustments were made to sharpen model consensus
forecast while maintaining the consensus frontal position.
Interior sections will remain in the warm sector with highs in
the lower 70s on Friday. However, closer to the lakes expect
highs in the 60s and only in the 50s near the immediate
lakeshore. Any shift in the position of the front will result in
drastically different temperatures for the Buffalo and
Rochester metro areas on Friday.

There remains a limited risk for flooding, with model consensus
QPF for this timeframe between 0.75" to 1.50." Current river
levels are high, but it probably would take amounts near or
greater than the high end of that range. Uncertainty stems from
the position of the sharp frontal boundary, but most guidance
keeps the greatest amounts just to the north of the area. Based
on MMEFS ensembles, the risk is greatest in the Black River
basin, but even there, the risk is generally in the chance
category. Based on this, will continue to to highlight potential
flood concerns in the Hazardous Weather Outlook product.

Saturday and Saturday night the closed upper low will lift
northeastward into our region and begin to get sheared apart as
it gets partially recaptured by the northern stream. This will
encourage the weakening frontal boundary to move northward on
Saturday. With the axis of the richest moisture and heaviest
rain likely getting shunted to the east of our region by
Saturday morning, this should result in some lighter showers on
Saturday as our region comes under the increasing influence of
the advancing upper low. These will become considerably more
scattered Saturday night as forcing and moisture both turn much
weaker and more diffuse. High temperatures on Saturday will be
mainly in the 60s, with 50s along the immediate lakeshores.


Large scale pattern features an Omega block which over the course of
time during this period will transition to a Rex block over the
north Atlantic.

The cut off low, on the western portion of the Omega block, will
slowly open up and then merge with an upstream trough tracking east
across Canada. As the upper low tracks northeast across the lower
lakes it will bring a chance of showers to our region on Sunday.
With its passage a weakening frontal boundary will sag south of the
lower lakes and then stall becoming east-west oriented across
Ohio/Pennsylvania on Monday. Strong surface high behind the
front over Ontario Canada and upper Great Lakes will take hold
with mainly dry weather through Tuesday. Model Guidance diverge
after Tuesday regarding the eventual return of the east-west
oriented frontal boundary. Have kept chance POPs in the forecast
for showers Wednesday and beyond for its potential return. High
temperatures will also be highly depended on the east-west
oriented frontal boundary speed of the return to the lower
lakes. Latest guidance still suggests a warm-up Monday, cooler
temperatures Tuesday as the boundary slips south of NY then a
big warm up Wednesday with its return.


Warm frontal rainfall will exit the area to the NE within the
next hour or two. Otherwise, strong SW wind off the deck will
result in some LLWS until daytime ensues and stronger wind can
mix down. A slow-moving cold front will take until Saturday
morning to really get into the picture, which should allow for
VFR conditions to continue.


Friday...VFR/MVFR in showers and scattered thunderstorms.
Friday night...IFR in low clouds and fog.
Saturday...MVFR with showers likely.
Sunday...VFR/MVFR with a chance of showers.
Monday...Mainly VFR with a chance of showers.


South winds will increase today behind a warm front that will
advance northeastward through the St. Lawrence Valley.
Sustained winds will increase to 20 knots or better along the
Lake Erie shore, aided by downslope winds, and also on the
eastern portion of Lake Ontario. While the greater wave action
will focus mainly in Canadian waters, the wind speeds are still
high enough to necessitate Small Craft Advisories. South winds
will slowly diminish Thursday evening.

A period of moderate to strong northeast winds will then develop
Friday night through Saturday as low pressure moves NNE along the
Appalachians. These winds will relax by Sunday as the low weakens.


MARINE...Small Craft Advisory until 8 PM EDT this evening for LEZ040-
         Small Craft Advisory until 11 PM EDT this evening for
         Small Craft Advisory until 2 AM EDT Friday for LOZ045.



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