Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 190037

Area Forecast Discussion
National Weather Service Buffalo NY
737 PM EST Sun Feb 18 2018

High pressure will pass to the south of the area tonight, then
low pressure will track into the Upper Great Lakes Tuesday and
into Quebec Wednesday. This will result in fair weather tonight,
followed by periods of rain and a dramatic warm up for the
first half of the week. Temperatures will soar into the 60s or
warmer which would be the warmest weather since last October.


High pressure will move off the New England coast tonight. The
surface high will briefly ridge into the region this evening before
southerly winds increase later tonight as the high moves to the
east. This will result in gusty downslope winds off the Chautauqua
Ridge starting after midnight tonight. Forecast cross sections show
favorable mechanisms for mountain wave development off the ridge,
with about 45 knots of south-southeast winds near ridge top level,
along with a tight vertical potential temperature gradient. Thus
these winds near ridge top level should duct to the surface along
the Lake Erie shoreline, with gusts to around 50 mph expected. Have
issued a Wind Advisory for this area. Outside of this area, expect
generally windy conditions for all areas north of the higher
elevations, including the Buffalo southtowns, the Northern Finger
Lakes and the Black River Valley to Fort Drum, with gusts 35-45 mph
at times late tonight through Monday morning.

Low temperatures tonight will mainly be during the evening hours
(near the freezing mark) with rising temperatures due to
downsloping and increasing warm advection later tonight. Expect
temperatures near the 40 degree mark by commute time Monday
across western NY, while some freezing temperatures linger in
the North Country. Skies should clear briefly this evening
before mid and high clouds spread in advance of the next system
late tonight.

On Monday a 50 kt LLJ advect warm and moist air into the region from
the south. This will bring period of steady rain to nearly all areas
with model consensus starting the rain from SW-NE during the morning
hours. Rainfall amounts will generally be from a quarter to half
inch. Temperatures will warm throughout the day with temperatures
expected to be in the lower 50s south of I-90 by Monday evening.
Patchy fog may develop Monday afternoon as dew points increase and
move across patchy snow cover and ice.


Widespread rain will be ongoing across Western and North-central
NY Monday night. Low pressure over the Midwest states will be
shifting northeast following a warm front stretched across
Michigan into Quebec. Warm air advection supported by a 50+ kt
low level jet ahead of the low and south of the warm front will
continue to supply anomalously moist air tied to the Gulf of
Mexico north over New York producing some soaking rains along
the warm front Monday night through Tuesday. A +3/+4
standardized anomaly is associated with PWATs in excess of one
inch. This is near or above the daily max moving average for mid
February. The warm air advection and southerly flow across the
forecast area will keep mild temperatures in place overnight.
Temps should actually rise through the overnight as warm air
continues to advect across the region.

Through Tuesday, the surface low is forecast to shift north across
Michigan, then push into Quebec Tuesday night. Through this time,
the warm front should push farther north of New York with the axis
of heaviest rain pushing north and west of the forecast area along
the northern edge of the strong 50-60kt low level jet and tightest
gradient of 850mb temps aloft. This should allow for much of Western
and North-central NY to see some dry time with likely a tight
gradient between rain and no rain.

The surface low will shift across Quebec through Wednesday then off
the coast of Newfoundland Wednesday night. This should drag the
associated cold front across Western and North-central Wednesday
with widespread rain again shifting southeast across our region. As
the cold front presses southeast there is a chance that any
lingering showers on the backside could mixing with and changing to
some snow showers.

An anomalous ridge with 500mb heights potentially rising in
excess of 575dm will promote well above normal temperatures
ahead of the cold frontal passage on Wednesday. Temperatures
will rise through the 50s in Western NY and 40s east of Lake
Ontario Monday night. Dewpoints pushing above 50 across the
still frozen Lake Erie should produce Areas of fog which will
likely advect into portions of the Niagara Frontier. Expect
temperatures to continue to rise well above normal on Tuesday
with Highs well into the 60s across most locations with 70+ in
the Genesee Valley not out of the question. Coolest temps will
be along the Lake Erie shoreline and eastern Lake Ontario
shorelines with southwest winds crossing the cool lake waters.
Temps will again remain very mild Tuesday night with the frontal
zone to our northwest. The cold front will bring a return of
near normal temperatures in the wake of the front Wednesday.
Temperatures behind the front could exhibit a non-diurnal trend
under cold air advection. Temps continue to slip back to near
freezing Wednesday night.

Total QPF Monday through Wednesday yields closer to one half an inch
of rainfall over the Finger Lakes increasing toward an inch close to
the Lake Ontario shore. Highest QPF is still expected toward the
Saint Lawrence River Valley where and inch and a half could fall.
A Flood Watch remains issued from Monday night through Wednesday
east of Lake Ontario with the increased confidence in the warm
temperature and resultant large-scale snowmelt and river rises.
This flood potential will include the Black River. See the
Hydrology section below for more details.


Strong dry high pressure is forecast to build over the Great Lakes
Thursday then across New York and New England Thursday night. There
remains a low chance of some lingering rain and snow showers toward
the western Southern Tier on Thursday depending on the speed of the
front but dry weather should be expected elsewhere with some
sunshine also returning. Temperatures will run much closer to normal
with highs only reaching into the mid 30s to perhaps 40 toward the
PA border. Lows will slip into the 20s Thursday night.

12z models continue to show at least two surface waves/frontal zones
crossing our region between later Friday into next weekend. The
closest model agreement seems to point toward Friday night for one
wave where likely POPs have been placed. Otherwise, chance POPs for
rain and at times rain/snow or snow showers run through the weekend
with p-type dependent on diurnal fluctuations in surface temps.
Southerly flow will promote temps around 10 degrees above mid-late
Feb normals.


VFR conditions will last through 12Z, then steady rain will spread
into the region from SW-NE. This will result in lowering cigs, which
will be somewhat offset by downsloping at BUF/IAG/ROC. At JHW expect
IFR conditions to develop late Monday morning due to increasing low
moisture in the southerly flow. Also, increasing winds aloft will
result in LLWS at most locations Monday morning.


Monday afternoon...Deteriorating to IFR in rain and patchy fog.
Monday night...Mainly IFR in rain and low cigs.
Tuesday...Generally VFR to MVFR in showers but IFR across the
North Country in more widespread rain.
Wednesday...MVFR in moderately heavy showers.
Friday...VFR/MVFR. A chance of rain or snow showers.


Winds and waves will subside early tonight with an area of high
pressure passing to the south. Southerly winds will then increase
early Monday morning, with sustained winds reaching near 30 knots
along the Lake Erie near shores, and 20 to 25 knots on the eastern
end of Lake Ontario. While the greatest wave action will be directed
into Canadian waters, have issued small craft advisories through
Monday afternoon due to the strong offshore winds alone.


There remains a significant risk for flooding in the Black River
Basin. A prolonged period of warm temperatures in the 50s and 60s
will result in significant snow melt, and the Black River basin
still has a significant amount of snow water equivalent in place
despite the brief warm up a few days ago. Although model guidance
has shifted the axis of heaviest rain a bit north and into southern
Ontario province, an inch or more of rain is likely in the Black
River basin through mid-week.

The greatest risk for flooding is as the Watertown forecast point
where ensembles show that there is a risk of moderate flooding due
to the widespread (but prolonged) nature of the rain and snow melt.
Latest RFC forecast show the Watertown forecast point still rising
at the end of the forecast, with an increasing risk of flooding
starting on Wednesday. Flooding may be prolonged with the forecast
potentially remaining above or near flood stage for several days.
Boonville and McKeever will respond a bit more quickly, and may
reach flood stage on Wednesday but if they do should crest quickly
and fall within a day or so. Ice jams also may be an issue with
some ice still in place in and along some waterways in the
basin. Meanwhile, snowmelt and rain may result in general
flooding of smaller tributaries in the region.

Elsewhere, there is much less snow pack in place due to recent warm
temperatures. Rainfall amounts in excess of an inch may cause some
creeks in the Buffalo area and lower Genesee basin to approach flood
stage, but model consensus keeps the steadier rains to the north of
these basins with basin averaged between a half inch and an inch.


NY...Flood Watch from late Monday night through Wednesday evening
     for NYZ006>008.
     Wind Advisory from 1 AM to 10 AM EST Monday for NYZ019.
MARINE...Small Craft Advisory from 1 AM to 4 PM EST Monday for LEZ040-
         Small Craft Advisory from 1 AM to 4 PM EST Monday for



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