Area Forecast Discussion
Issued by NWS Buffalo, NY

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790
FXUS61 KBUF 191923
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
223 PM EST Mon Feb 19 2018

.SYNOPSIS...
Low pressure will track into the Upper Great Lakes Tuesday and into
Quebec Wednesday. This will result in 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 TUESDAY/...
A deep upper level trough is over the Rockies while a strong
ridge is off the Southeast US, resulting in a long and similarly
strong upper level jet oriented from the plains NE toward the
Canadian Maritimes. This is allowing low level southerly flow to
surge NNE into much of the Eastern US. A baroclinic leaf is
forming over the midwest from the flow aloft with surface low
near IA. Fairly impressive warm air advection continues east of
the low with a ribbon of rain along a warm front poised to move
NNE into the region this afternoon. This will result in a
period of rain, heaviest just NE of the Niagara Frontier into
the evening.

Later tonight, the wide rain band should continue to slowly
move north, and may eventually be completely north of at least
WNY by Tuesday morning (but still over central NY). Areas south
of the rain shield will start to see temperatures rise well into
the 50s, with some areas gracing the 60F mark by Tuesday
morning.

Tuesday, with most of the rain north of the region, expect the
anomalously warm airmass underneath the relatively strong low
level 40-50kt jet to produce record temperatures, with many
areas reaching the mid to upper 60s, and a few ~70F readings in
the Genesee Valley. Despite the strong jet just off the surface,
the airmass should still have some stratification resulting in
winds having a hard time mixing to the surface, with some gusts
near 30mph.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
On Tuesday night the region will be firmly in the warm sector, with
low pressure across southern Ontario maintaining a deep southerly
flow of warm air. Winds will prevent any cooling at all Tuesday
night with temperatures remaining within a few degrees of 60 for
most of the night. The warmest conditions will be across the
lake plains due to downsloping. Otherwise, a warm front will be
located north of the Eastern Lake Ontario region and a cold
front just to the west of the Niagara Frontier. There is a
chance of a shower from either of these boundaries but the vast
majority of the night will be simply dry and unseasonably warm.

A cold front will then move across the area with the front
expected to cross western New York Wednesday morning and the
Eastern Lake Ontario region early in the afternoon. Model
consensus is in fairly good agreement in terms of timing,
however even small differences will impact high temperatures
considerably on Wednesday. Given this timing, expect
temperatures to rise well into the 60s east of Rochester with
slightly cooler conditions to the west. Highs should come early
in the day with temperatures falling into the 40s Wednesday
afternoon. A period of rain will accompany the front, though
amounts should be modest (a tenth to quarter inch). Abundant low
moisture along the boundary will result in areas of low clouds
and fog, especially northeast of the lakes where moist air will
be mixed with relatively cool lake waters and ice.

Temperatures will almost return to normal behind the front Wednesday
night and Thursday with lows Wednesday night mainly in the 20s and
highs on Thursday in the 30s. High pressure will build across the
Upper Great Lakes region, with some guidance extending this ridge
into the North Country which would support colder temperatures
there. There is some uncertainty how far south of the area the
boundary will push Wednesday night, and whether a wave of low
pressure along this boundary will clip southern portions of the
area late Wednesday night into Thursday. Model consensus
supports at least a chance of precipitation across the Southern
Tier with diminishing chances to the north. Forecast thermal
profiles are marginal with rain, snow, or mixed precipitation
possible. High pressure will pass just to the north of the
region Thursday night, supporting mainly dry weather with lows
mainly in the 20s.

&&

.LONG TERM /FRIDAY THROUGH SUNDAY/...
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 /19Z MONDAY THROUGH SATURDAY/...
VFR conditions will slowly deteriorate this afternoon as steady
rain spread into the region from SW-NE. Steady rain continues
through at least the evening before becoming showery overnight
or ending altogether over interior sections near NY/PA state
border. LLWS will be an issue, particularly overnight with a SW
wind near 40-50kts just off the surface.

Outlook...

Tuesday...Generally VFR to MVFR in showers but IFR across the
North Country in more widespread rain.
Wednesday...MVFR and  IFR in moderately heavy showers.
Thursday...VFR.
Friday and Saturday...VFR/MVFR. A chance of rain or snow
showers.

&&

.MARINE...
Southerly winds will then increase this 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, small craft
advisories are in effect through the afternoon due to the strong
offshore winds alone.

&&

.HYDROLOGY...
There remains a significant risk for flooding in the Black River
Basin. The combination of rain and a prolonged period of warm
temperatures will result in significant run-off in the basin. There
is still a basin average of 4-5 inches (water equivalent) with up to
10 inches across higher terrain. The majority of this will melt over
the next two days.

Although there is high confidence in warm temperatures and
associated snow melt, it is uncertain exactly how much rain will
fall. Model consensus has the axis of heaviest rainfall along the
Saint Lawrence Valley, with less rain expected south of Watertown.
Total rainfall amounts of 1-2 inches are likely in the Black River
Basin through Wednesday. There is a chance there will be more if
this axis shifts slightly south.

The greatest risk for flooding is as the Watertown forecast point
due to the widespread nature of the event and higher rainfall
amounts across the Black River basin north of Lowville. MMEFS
ensembles continue to show a likelihood of at least minor flooding
at Watertown, with significant chances of moderate and possibly even
major flooding. This depends on how much rain falls with the
ensembles capturing some model runs which place this axis across the
Black River basin. The risk for flooding is slightly lower at the
Boonville and McKeever forecast points since less rain will fall in
these portions of the basin. Even so, snowmelt and even some rain
may cause at least minor flooding.

In addition to river flooding, the combination of rain and snow melt
may cause localized flooding in the Watertown area. Ponding of water
may close roadways and cause basement flooding, especially if the
axis of heaviest rainfall shifts even slightly south. Also smaller
creeks and rivers are at risk across Northern Jefferson county where
rainfall amounts will be the greatest. Ice jams also may be an issue
with some ice still in place in and along some waterways in the
basin.

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 rainfall amounts of an inch or less expected in
these basins. High flows can still be expected, with some locations
likely to reach action stage.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Flood Watch from 1 AM EST Tuesday through Wednesday evening
     for NYZ006>008.
MARINE...Small Craft Advisory until 4 PM EST this afternoon for LEZ040-
         041.
         Small Craft Advisory until 4 PM EST this afternoon
         for LOZ043>045.

&&

$$

SYNOPSIS...HSK
NEAR TERM...ZAFF
SHORT TERM...APFFEL
LONG TERM...SMITH
AVIATION...HSK/ZAFF
MARINE...CHURCH/HSK
HYDROLOGY...APFFEL/HSK



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