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Area forecast discussion
National Weather Service Buffalo New York
805 PM EDT Mon may 21 2018

Synopsis...
a warm front will move east across western New York overnight,
followed by a cold front on Tuesday. Both fronts will bring some
rain along with the chance for thunderstorms. Dry weather will
follow for the rest of the week.

&&

Near term /through Tuesday/...
convection over Ohio continues to move east-northeast slowly towards our region
late this evening. This convection is associated with abundant
moisture that resides just south of the region, as seen by a tight
gradient of precipitable water with only about 0.5" over New York but up
to 1.5 over Ohio. Upper level satellite water vapor imagery shows
the steering flow both convergent and heading north toward wny. The
main plume is sourced from the Gulf of Mexico and is feeding a
shortwave trough aloft over the upper Mississippi Valley. A weaker
plume is moving north from FL and into the Appalachians.

A surface low pressure system underneath the Midwest trough will
develop a weak warm and trailing cold front, the first of which will
cross the region overnight. This should have no problem overcoming
the current relatively dry airmass. Timing for the start of
rainfall is currently forecast to be near or a few hours before
midnight at the far western New York/PA border. The leading edge of rain
should then move east across wny overnight, and be near or over the
Eastern Lake Ontario region by daybreak Tuesday. Quantitative precipitation forecast is currently
set at about 0.5" south of Lake Ontario to possibly over an inch
near the interior southern tier, with about 0.25" east of Lake
Ontario. This will result in some periods of locally heavy
rainfall, but without any flood threat.

On Tuesday, much of wny will be in a subtle but fairly saturated
warm sector as the surface low pressure system moves east across the
region. It's trailing cold front should be able to touch of a line
of convection originating on lake breeze boundaries southeast/south
of either/both Lake Erie/Ontario. Otherwise expect abundant cloud
cover for much of the day. There won't be much of a change in
airmass ahead or behind the cold front other than a subtle wind
shift, so expect abundant clouds on both sides of the front.

&&

Short term /Tuesday night through Friday night/...
after a wet and unsettled day on Tuesday...we can anticipate
significant improvement in our weather as we work through Tuesday
night into Wednesday.

A ridge centered over the middle of the country Tuesday night will
amplify and drift east Wednesday and Thursday. After a few leftover
showers Tuesday evening...this scenario will lead to clearing skies
during the overnight with absolutely beautiful weather to follow for
Wednesday and Thursday. Temperatures both days will average above
normal as Max temps will end up between 75 and 80. The gradual day
to day warming will be accompanied by low humidity levels...so it
should feel quite comfortable.

As a large surface high drifts east of our region Thursday night and
Friday...the return flow around the backside of the system will
circulate warmer and somewhat more humid air into our forecast area.
When full mixed...850 mb temps climbing to around 16c within this
environment will fully support Friday afternoon Mercury readings of
80 to 85f. Most guidance packages though are under playing forecast
highs by as much as 5 degrees f. The mid Summer warmth will be
accompanied by continued fair dry weather.

&&

Long term /Saturday through Monday/...
the forecast remains quite uncertain for next weekend into early
next week with significant model differences and run to run flips in
models. Abundant tropical moisture will continue to stream into the
southeast states through the period, but how much of that moisture
makes it all the way north into the eastern Great Lakes remains in
question. The latest 12z GFS brings a rather strong backdoor cold
front south across our region Saturday night, with a seasonably
strong and dry high pressure building into New England which would
keep US dry Sunday through Monday. This is a major change from the
past few runs of the GFS, which kept any frontal boundary well north
of our region.

The 12z European model (ecmwf) is much more consistent with previous European model (ecmwf) runs, and
the previous GFS runs in keeping any drier air well north of our
region through early next week. This solution is the model of
choice, and will keep our area warm and rather muggy Saturday
through Monday. Expect highs in the lower 80s away from lake
influences and lows in the lower 60s through the period. There will
be a chance of a few showers and thunderstorms each day, but forcing
appears weak so expect the showers to remain scattered in nature
with rain free time each day as well. The deepest of the tropical
moisture and stronger forcing looks to remain well south of our area
through Monday.

&&

Aviation /00z Tuesday through Saturday/...
VFR conditions will hold through the first half of tonight. Later
tonight, a warm front will move east-northeast across New York state which will
bring lowering ceilings and reduced visibilities with rain showers and
possibly a few embedded rumbles of thunder with a little
elevated instability. Otherwise, a subtle cold front will cross
the region Tuesday with another round of showers and a chance of
a thunderstorm well south and east of the lakes.

Tuesday night, high pressure will slowly build into the region
behind the front with slow but improving conditions overnight.

Outlook...

Wednesday through Friday...VFR.
Saturday...chance of showers with some MVFR.

&&

Marine...
a surface low will move east-northeast across the lower Great Lakes by Tuesday
with a warm front overnight, followed by a cold front Tuesday
afternoon. Wind speeds will be under Small Craft Advisory but with varying wind
direction, eventually becoming northwest behind the cold front late
Tuesday. Light winds and local circulations are expected for the
remainder of the week.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...none.

&&

$$

Synopsis...AR/zaff

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