Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 181950
AFDBUF

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

.SYNOPSIS...
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.

&&

.NEAR TERM /THROUGH MONDAY/...
High pressure centered across the mid-Atlantic states this afternoon
will move off the New England coast tonight. Radar shows just a
few flurries east of Lake Ontario which will end by sunset.
Otherwise stratus clouds will continue to erode through this
evening, but this will be a slow process with moisture still
trapped beneath an inversion.

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 moderate downsloping
off the Chautauqua Ridge with a few hours of wind gusts over 40
mph in the favorable downslope regions after midnight tonight.
Low temperatures will mainly be during the evening hours with
rising temperatures due to upsloping later tonight. 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.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
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.

A 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.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
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.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
Cloud cover will linger into this afternoon, with bases above
3k feet in all locations except the higher terrain of the
Southern Tier which includes the JHW terminal. Stratus will
scatter out this afternoon, resulting in widespread VFR
conditions by late afternoon as high pressure passing to the
south ridges into the region. 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.

Outlook...

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.
Thursday...VFR.
Friday...VFR/MVFR. A chance of rain or snow showers.

&&

.MARINE...
Winds will briefly meet small craft criteria this afternoon
across eastern portions of Lake Ontario. Winds and waves will
subside tonight with an area of high pressure passing to the
south. Southerly winds will then increase Monday, but this
direction is not favorable for building waves in the nearshores
so no small craft headlines will be issued at this time.

&&

.HYDROLOGY...
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.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Flood Watch from late Monday night through Wednesday evening
     for NYZ006>008.
MARINE...None.

&&

$$

SYNOPSIS...APFFEL
NEAR TERM...APFFEL
SHORT TERM...SMITH
LONG TERM...SMITH
AVIATION...APFFEL
MARINE...APFFEL
HYDROLOGY...APFFEL



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