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Area forecast discussion
National Weather Service Buffalo New York
431 PM EDT Mon Jun 24 2019

Synopsis...
a weak warm front and then a cold front will move across the area
resulting in showers and a few thunderstorms tonight. Most of the
showers will end Tuesday morning as the cold front exits east of the
area. A weak disturbance may spark a few showers and
thunderstorms on Wednesday and this will be followed by high
pressure and dry weather on Thursday.

&&

Near term /through Tuesday/...
an upper level ridge axis extends from the mid-Atlantic states
to central New York this afternoon. Just behind this ridge axis
is a line of mid-level warm air advection. Thick mid level
clouds have developed long this warm frontal boundary, along
with a few light showers. Outside of these light showers, the
rest of this afternoon will be mainly dry and seasonably warm
with high temperatures in the upper 70s to lower 80s.

An upper level trough axis will approach this evening, and this
along with a pre-frontal surface trough which will provide the
focus for showers tonight. Latest model guidance is a bit slower
with steady precipitation, and this is not expected to reach
western New York until around sunset. There still will be some
instability in place across far western New York, with some
embedded thunderstorms possible. Precipitable water values will increase to
nearly 2 inches, so there is a risk of locally heavy rainfall
with some of these storms. This said, these storms will be
moving which will mitigate the risk for flooding.

It still appears the heaviest rain and greatest severe weather
potential will be to the south and west of our area. However
some model guidance (the NAM is the most noteworthy) does track
convection further north across our area. If this happens, wind
fields will be stronger and there would be a limited severe
weather risk. This said, instability will be diminishing when it
arrives this evening, so the window is a narrow one. Storm Prediction Center shows a
marginal risk for severe weather across far western portions of
the southern tier.

Showers will taper off from west to east early Tuesday morning,
and the vast majority of the day will be dry as drier air builds
in behind the cold front. Mesoscale guidance shows some
scattered showers developing across the western southern tier
and along the lake breeze in Niagara County. These should at
best be scattered, and with limited instability may not develop
at all. Otherwise, clouds will linger through the morning hours
before clouds scatter out in the afternoon. It will be a breezy
day with winds gusting 30 to 35 mph northeast of the lakes.

Temperatures will remain mild overnight with lows in the mid to
upper 60s. Highs on Tuesday will be in the mid to upper 70s.

&&

Short term /Tuesday night through Friday/...
Tuesday night high pressure will build eastward across the Ohio
Valley, with a ridge extending into the eastern Great Lakes. Any
showers with the departing cold front will be well east of the area
by evening, with high pressure supporting a mainly dry night. Lows
will be in the low to mid 60s in most areas, with some upper 50s in
the cooler southern tier valleys and Lewis County.

Wednesday a weak mid level shortwave will move east across the Great
Lakes, with an associated weak surface cold front reaching western
New York by the late afternoon or evening. Moderate instability will
develop ahead of this system with surface temperatures in the 80s
and dewpoints in the 60s. As is often the case in the Summer, most
of the potential convection will likely focus along the pre-frontal
trough and lake breeze boundaries from midday through early evening.
Given the weak nature of the forcing, coverage may remain scattered
in nature. The best coverage will be along and inland of lake breeze
boundaries from the western southern tier to central NY, with the
lowest coverage northeast of lakes Erie and Ontario as stable lake
shadows develop.

Any showers and storms will end from west to east Wednesday evening
with the passage of the cold front. Weak high pressure will then
build back into the Ohio Valley and eastern Great Lakes Thursday and
Thursday night with a return to mainly dry weather. Temperatures
will remain typical of early Summer, with highs in the lower half of
the 80s and lows in the 60s in most locations.

Friday another relatively weak mid level shortwave and associated
cold front will move across the Great Lakes. The weak forcing will
combine with moderate instability to produce another chance of a few
scattered showers and thunderstorms, especially in the afternoon.
Warm advection ahead of the system will boost 850mb temps to around
+16c, which will likely support highs in the mid 80s away from lake
influences along with moderate humidity. It will turn fairly breezy
ahead of the cold front Friday, especially northeast of Lake Erie
where gusts may reach 30 mph.

&&

Long term /Friday night through Monday/...
most active part of long term will be Friday night through Saturday
night with multiple chances of showers and thunderstorms driven
by different forcing mechanisms. Northwest flow aloft downstream
of Sharp Ridge over central North America keeps stronger jet
energy/cooler temps aloft across Quebec, the lower Great Lakes
and New England. Strongest shortwave and jet energy drops across
later Saturday into Saturday night along with associated cold
front. Some hints now showing up there could be stronger
thunderstorms as early as Friday night into Saturday morning
well ahead of main forcing as instability in form of steeper mid
level lapse rates (elevated mixed layer) advects in downstream
of the plains ridge. Lower Great Lakes into New York and
Pennsylvania would be on gradient of higher MUCAPES building
closer to the ridge axis. Any weaker shortwave heading into the
region and/or surge of focused warm air advection could allow
some convection to break out over our forecast area. Currently
the Canadian model is most emphatic with that idea showing what
looks like mesoscale convective system in its qpf output, but it is an idea that has
some merit based on the pattern outlined above. Increased pops
compared to previous forecast more toward model consensus. Looks
muggy Friday night in warm sector with lows in the 60s, perhaps
even upper 60s with some wind and dwpnts pushing into the mid
60s.

No matter whether convection does or does not develop Friday night,
likely looking at another period of convection on Saturday, this
time surface based, with build up of instability (mlcapes over 1000
j/kg) during peak heating and approaching cold front. Highs on
Saturday shoud easily hit low 80s, but if cold front is slower may
even reach upper 80s given such warm 850 mb temps. With expected
instabilty and stronger wind fields aloft, there is a certainly a
non zero risk of severe storms in the later Friday night (probably
more marginal) through Saturday afternoon and evening time frame.
Would say right now the greatest chance for severe storms would
be Saturday afternoon into Saturday evening with 0-6km deep
layer shear values progged from 30-40 kts and ample instability
present ahead of the cold front.

Good agreement that main shortwave and associated cold front clears
entire forecast area later Saturday night/early Sunday morning
leaving cooler and less humid conditions on Sunday. Maybe lingering
isold or scattered convection inland toward Finger Lakes, but most
areas probably end up dry behind the cold front. High pressure
arriving Sunday night and Monday will keep the dry weather going
into next Monday. High temps both Sunday and Monday should stay in
the mid to upper 70s.

&&

Aviation /21z Monday through Saturday/...
scattered showers will move across western New York this afternoon,
but these will be light with mainly VFR flight conditions
through 00z

A cold front will approach the region this evening showers and a
few thunderstorms will develop ahead of this along a pre-frontal
trough or wave of convection. These will be heavy at times,
lowering visibility to 2-3sm at times. Ceilings will also lower,
especially with the passage of the cold front which will be
later tonight.

Conditions will gradually improve Tuesday morning as drier air
builds in to the region behind the cold front. It also will be
windy, especially northeast of the lakes during the day
Tuesday.

Outlook...

Tuesday night...VFR.
Wednesday...mainly VFR with a chance of a few widely scattered
showers and thunderstorms.
Thursday...VFR.
Friday and Saturday...mainly VFR with a chance of a few widely
scattered showers and thunderstorms.

&&

Marine...
a cold front will move across the lower Great Lakes tonight.
Southwesterly winds will increase behind this front, especially
on Lake Erie. A Small Craft Advisory was issued for Lake Erie
for late tonight and Tuesday. It will be choppy on Lake Ontario,
but winds will not be as strong. Winds will diminish Tuesday
night.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...Small Craft Advisory from 4 am to 6 PM EDT Tuesday for lez040-
041.

&&

$$

Synopsis...apffel
near term...apffel

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