Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 191817
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
117 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 WEDNESDAY NIGHT/...
Anomalous upper level ridge just off the Southeast coast will
continue to strengthen up to 3 standard deviations above normal
through Tuesday night. This will hold the trough in place over
the Southwest CONUS, resulting in a southwesterly mean flow
nearly parallel to frontal boundary extending just to the north
of New York state. Continued surge of moisture along the front
will keep the axis of heaviest rain north and west of the
forecast area along the northern edge of the strong 50 knot plus
low level jet. South of the boundary, much of the area will see
plenty of dry time Tuesday night.

The frontal boundary north of the area will get dragged across the
area as a cold front 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 Wednesday night.

The cold front will bring a return of near normal temperatures in
the wake of the front Wednesday. Temperatures behind the front will
exhibit a non-diurnal trend under cold air advection. Temperatures
will continue to slip back to near freezing Wednesday night.

Total rainfall 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 totals are still expected toward the
Saint Lawrence River Valley where and inch and a half could fall.
A Flood Watch remains in effect through Wednesday east of Lake
Ontario with the combination of significant snowmelt and river
rises. This flood potential will include the Black River. See the
Hydrology section below for more details.

&&

.LONG TERM /THURSDAY 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 /18Z 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. 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, generally an inch to inch and a half of rain
is likely in the Black River basin with higher amounts possible
on the Tug Hill 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 tonight 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...HSK/ZAFF
SHORT TERM...TMA
LONG TERM...SMITH
AVIATION...HSK/ZAFF
MARINE...APFFEL/CHURCH/HSK
HYDROLOGY...APFFEL/HSK



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