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Area forecast discussion 
National Weather Service Wilmington Ohio
740 PM EDT Thursday Jul 24 2014

Synopsis...
high pressure responsible for dry and cool weather over the Ohio
Valley will slide southeast across Ohio into the Appalachians
tonight and Friday...providing a very comfortable night with lows
in the 50s. A few record lows will be possible. Returning
southerly flow Friday night and Saturday on the backside of the
high Friday night and Saturday will allow for increased warmth and
moisture...and with that will come the potential for several
clusters of showers and thunderstorms later Friday night through
the entire weekend. Severe weather will be possible as the next in
a series of very strong cold fronts approaches from the northwest.
This next frontal passage will bring yet another cool week with
much of next week expected to remain well below normal in terms of
temperature.

&&

Near term /until 6 am Friday morning/...
diurnal cumulus will dissipate this evening bringing mostly clear
skies and a strong radiational cooling event to the area. With
dewpoints currently in the low-middle 50s...a rapid evening temperature drop
is expected. Record low temperatures at the three climate sites
are as follows...

Columbus /cmh/...52f in 1911
Cincinnati /cvg/...56f in 1931
Dayton /day/...50f in 1906

The Cincinnati record is in jeopardy...will be very close based on
tight statistical guidance clustering in the middle 50s. Some typical
cool spots may drop into the upper 40s. With the high moving right
overhead around sunrise think potential is certainly there.

&&

Short term /6 am Friday morning through Saturday night/...
this period will be characterized by a large swing/change in
airmasses and quiescent weather on Friday morning to potential
severe storms and heavy rainfall by Saturday night.

At 25... 500mb anticyclone will remain situated over New
Mexico with a very dynamic and anomalous closed low cresting the
ridge over sask/Alberta...flattening the ridge somewhat. The
persistent eastern Continental U.S. Longwave trough will still exist in a
positive tilt fashion from la/Alabama northeast through the upper Ohio
Valley where a cyclone will exist east of Hudson Bay.

Through the day Friday...the closed low will move slowly eastward
while the ridge in the west flattens...which deamplifies the eastern
Continental U.S. Longwave trough further and shunts it east. As such...surface
high pressure and cool/dry weather will build eastward with return
flow beginning to our west. The bulk of Friday will be
gorgeous...low humidity...mix of sun and clouds and temperatures
rebounding into the upper 70s.

That is where more significant changes begin and the Entry Point
into what will likely be an active weekend. By Saturday morning
the potent closed low will be approaching Lake Winnipeg while a
more subtle shortwave trough is ejected atop the flattening northestern
quadrant of the western ridge...down the slide of increasingly fast
west-northwesterly middle level flow into the Great Lakes. On the nose of a low
level moisture transport maximum...and at the edge of an strong
plains-based elevated mixed layer /warm...dry...steep lapse rate
environment/...convective instability will be advected in from the
west later Friday night with MUCAPE significantly increasing above
the eml later in the night. An mesoscale convective system or two is likely to be manifested
on the leading edge of these entities...and will be approaching
the area Friday night/Sat morning with timing/location very much in
doubt. Precipitable water will double /0.60" to 1.20"/ in less than 12 hours as
this destabilization aloft takes place. Confidence on where this
activity moves is not high...but did increase the shower/storm
chances Friday night into Saturday morning over a large portion of
the area to account for this potential. Per 25.12z
ECMWF/GFS/NAM...somewhere in Indiana/Northern Ohio seems the best
bet at 12z Sat morning.

As the remnants or what remains of any storm activity moves across
the area Saturday morning...heights will continue to slowly rise in the
wake of the lead shortwave trough and ahead of the potent closed
low now digging into Minnesota. The eml will become entrenched
over the area with point forecast /bufr/ soundings from 25.12z NAM and
GFS both showing strong inhibition from late morning
through the bulk of the afternoon. Thus...attempted to show a
reduction in rain chances during this time...as mlcinh on many
soundings exceeds 200 j/kg and in some data exceeds 300
j/kg. This should promote a warm...increasingly humid day with
decreasing elevated storm threats...with dewpoints rising toward
70f and air temperatures in the middle/upper 80s.

Saturday evening/overnight...confidence is low on the details but
a renewed low level jet/moisture transport signal will develop
ahead of the digging Minnesota/WI closed low...pointed into IL/in/OH.
There may be outflow/differential heating boundaries from Sat
morning convection...but either way forcing becomes good enough
and a signal crops up in the data for nocturnal mesoscale convective system
potential...which could be anywhere from Ohio back into Illinois.
This may be initially rooted above the cap but given Reservoir of
strong instability amidst the eml...and impressive shear...there is
concern for an organized severe weather event Sat night into
Sunday morning with primary focus of damaging wind via forward
propagating convective system. In fact...cips analogs indicates
that the synoptic pattern ingredients as being predicted by the
25.12z NAM has produced a number of wind-producing mesoscale convective system systems
across the corn belt/Ohio Valley. A closer look at the details
/events within the pattern match -- top 15 analogs on various
domains/ shows a couple higher-end events of either in terms of
area affected or number of reports...and these signals were
present on 25.00z GFS pattern matches...so feel confident in
beginning to raise awareness of this potential in hazard weather outlook
product for Sat into Sunday. Degree of instability and 0-3km shear are
favorable.

Lurking in the tall grass is heavy rain potential with gefs
reforecast probabilities suggesting that rain amounts being
suggested by ensemble mean /already decent/ may actually be underdone in
this multi-mesoscale convective system scenario over Saturday/Sunday. Wpc already running
slight risks for excessive rainfall on day 3 /Sat and Sat night/
which seems reasonable based on reforecast data and 25.12z
deterministic runs showing mesoscale convective system potential. 25.00z naefs
probabilities also centered on Ohio. Westerly low level jet ahead of a
digging upper trough /which is the pattern on Sunday morning/ may
promote backbuilding and training on the southern fringe of any forward
propagating mesoscale convective system.

&&

Long term /Sunday through Thursday/...
active weather pattern will be in place for the beginning of the
long term period. Models are in good agreement on a mesoscale convective system moving
across the forecast area Sunday morning. This feature will bring widespread
thunderstorm activity across the area. With model agreement
increased precipitation chances significantly during this time.
There is a decent chance of severe weather with this feature with
damaging winds the primary threat. An isolated tornado cannot be
ruled out however. Will add mention of this threat to the severe weather potential statement. In
addition to the severe threat this feature will bring moderate to
heavy rain to the area which may lead to some flooding issues as
well.

Additional thunderstorm activity will be likely during the afternoon
and evening hours on Sunday as a cold front approaches and works
into the region. There is quite a bit of instability across the
area for Sunday. There is the additional chance for severe weather
Sunday afternoon into the evening hours. Damaging winds and large
hail will be possible. In addition a tornado threat will also be
possible. Some questions remain on the strength of this second
event as this will be dependent on the first round of
thunderstorms. Will also highlight this severe threat in the severe weather potential statement.
With multiple rounds of showers and thunderstorms there will again
be the threat of flooding.

Thunderstorms move out of the forecast area Sunday night and cooler air will be
ushered into the forecast area. An upper level disturbance on Monday will
allow for decent cloud cover and some shower activity. This will
keep temperatures cool and well below normal. High temperatures
are only expected to be in the low to middle 70s on Monday. High
pressure then works into the area for the remainder of the long term
allowing for dry conditions. High temperatures will gradually warm
each day after Tuesday. Tuesday looks to have to coolest high
temperatures of the long term period.

&&

Aviation /00z Friday through Tuesday/...
few-scattered cumulus at 5kft will continue to exhibit a quick dissipation
this evening in favor of clear skies. Winds will lighten and go
somewhat variable but primarily be north under 4kt. Some sunrise
surprise fog is possible but should be confined to lower lying
areas...potentially hitting kluk hard through about daybreak as
min temperatures are forecast below expected dewpoint values per MOS
guidance.

Another nice day with fair weather cumulus is expected tomorrow although the
lighter north winds will keep a little less cold air advection in
place which will let the cloud cover be a bit more scattered than
it was today...and clear out quickly tomorrow in the late
afternoon.

Outlook...thunderstorms possible Saturday and Sunday.

&&

Iln watches/warnings/advisories...
Ohio...none.
Kentucky...none.
In...none.

&&

$$
Synopsis...binau
near term...binau
short term...binau
long term...Novak
aviation...franks

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