Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 200018
AFDBUF

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

.SYNOPSIS...
Low pressure will move into the Upper Great Lakes Tuesday and into
Quebec Wednesday. This will result in periods of rain along with a
dramatic warm up for the first half of the week as temperatures soar
into the 60s and low 70s in parts of the Genesee Valley.  This will
be the warmest weather across the region since last October. A cold
front will move through on Wednesday, but temperatures will still
remain a little above February normals during the end of the week.

&&

.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 while carrying anomalous
moisture from the Gulf of Mexico. A poorly defined baroclinic leaf
has formed over the midwest from the flow aloft with surface low
near northern IL. Fairly impressive warm air advection continues
east of the low with a ribbon of rain along a warm front slowly
moving NNE though NY. The result will be continuing rain through the
evening hours.

Overnight this boundary will continue moving northward across the
region, while widespread rainfall will continue to track from west
to east along the boundary. This will result in a drying trend
across the Southern Tier counties late tonight into early Tuesday
morning. Meanwhile the North Country will get into the more
moderate, to heavy at times, rainfall overnight and into Tuesday
morning. The southern Tug Hill region will do fairly well with
rainfall accumulations overnight, given the strong southwesterly
upslope component there, with locally around an inch and half
tonight through Tuesday. Temperatures will follow the non-diurnal
trend overnight, with continued warm advection as the boundary
slides northward. Temperatures the time most people are heading out
the door Tuesday morning will be in the upper 40s in the North
Country to near 60 across western NY. Rain showers will likely
remain across the Niagara Frontier to the North Country Tuesday
morning, before ending across the Niagara Frontier by midday
Tuesday. Rain will linger longest in the North Country, likely not
moving northward into Canada until Tuesday evening/night.

Tuesday, with most of the rain north of the region by the afternoon,
expect the anomalously warm airmass underneath the relatively strong
low level 40-50kt jet to produce record temperatures, with many
areas reaching the upper 60s, with low 70s readings in the Genesee
Valley. Record highs should be smashed for KBUF (64) and KROC (62).
KART will be closer to the baroclinic boundary and in/out of rain,
and may have a tough time breaking their record high of 62F, but it
will be close. Some afternoon clearing is possible across western NY
and the Genesee Valley which will both help bolster temperatures,
and help steepen low-level lapse rates. Expect some strong wind
gusts to mix down during the mid to late afternoon, especially where
some sunshine can break through. Gusts would likely be strongest
across the Niagara Frontier inland from the lake shores, were gusts
35 to 45 mph are possible. Inland locations may see gusts around 30
mph.

&&

.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 with the warmest conditions across the lake plains
due to downsloping. Otherwise, it should be mainly dry with a warm
front 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 move across the area with the front expected to
reach 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. Expect high
temperatures will be well into the 60s east of Rochester, with
slightly cooler highs likely 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 in the tenth to quarter inch range. 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 which develops 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 which will be
closer to surface high pressure. Temperatures are marginally cold
enough to support snow, with rain, snow, or mixed precipitation
possible.

High pressure will pass just to the north of the region Thursday
night, supporting mainly dry weather. Lows will be mainly in the
20s. There is a small chance for rain or snow late across the
Western Southern Tier depending on the speed of the next system.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Active weather pattern to continue during this period with several
chances for precipitation.

Low pressure over the Central Plains will be in the process of
moving into the Mississippi and Ohio River Valley on Friday.
Meanwhile, high pressure over New England will slowly exit to the
Northeast. A warm front associated with this approaching system will
cross the Lower Great lakes early Friday. Initially, it will be cold
enough for a mixture of a little snow mixed with rain before turning
over to all rain as southwesterly flow brings in a much warmer air
mass to the region. The surface low will then track just to the west
of the lower lakes late during the day Friday and then push its cold
front through the region. Latest Guidance packages suggest that the
cold front will stall over Pennsylvania Friday night. Several weak
waves of low pressure will then ride along this boundary bringing a
chance of showers to the region on Saturday.

The last in a series of low pressures will quickly develop over the
Central Plains which will bring the best chance for widespread rain
Sunday. The low pressure system will depart the region late Sunday
with precipitation ending from west to east. Quiet and drier weather
returns Monday with surface high pressure building over the Ohio
Valley. Otherwise, highs will remain above climo (+5F - +10F) with
the daytime highs in the mid and upper 40s likely for most
locations.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
Widespread MVFR conditions with widespread rain will continue
overnight, with local IFR conditions across the higher terrain of
the Southern Tier. This area of rain will move slowly northward
tonight and Tuesday, with rain ending and flight conditions
improving from south to north. Rain will likely end after midnight
across the Southern Tier, by mid to late morning across western NY,
and by Tuesday evening in the North Country. Low level wind shear
will remain an issue through much of the TAF period, with a 45 knot
low level jet at about 2kft. Gusty southwest winds are expected
Tuesday afternoon across the Niagara Frontier, with gusts 35 to 40
knots possible.

Outlook...

Tuesday night... Mainly VFR...SHRA with MVFR developing late.
Wednesday...MVFR with -SHRA.
Thursday...VFR.
Friday and Saturday...VFR/MVFR. A chance of rain or snow showers.

&&

.MARINE...
Southerly, mostly offshore winds will continue tonight through
Tuesday as a low pressure system track by to our northwest, but
still mainly in the 15-25kt range on Lake Erie. Thus have pushed the
SCA out through  This pattern will continue through Tuesday night.
Wednesday morning. A cold front will then move through Wednesday
with WNW flow behind the front, with likely SCA conditions
developing on Lake Ontario.

&&

.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 10 AM EST Wednesday for LEZ020-040-
         041.

&&

$$

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


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