ILN issues Area Forecast Discussion (AFD) at Jul 19, 1:27 AM EDT171
FXUS61 KILN 190527
AFDILN
AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
127 AM EDT Fri Jul 19 2024
.SYNOPSIS...
Dominant high pressure centered over Iowa this evening will
influence the weather over the Ohio Valley into and through the
weekend with dry conditions, and below normal temperatures as it
shifts slowly across the Great Lakes. Increasing warmth and
moisture is on tap late in the weekend into most of next week
with warm and humid days returning, and increasing chances for
showers and storms as a moist southwesterly flow sets up and
persists on the backside of the departing high pressure system.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Skies already mostly clear, with temperatures falling a little
faster than expected. Still thinking that mid/upper 50s for
overnight low looks good, just tweaked hourly temperatures.
Still expecting some valley fog, with clear skies and light
winds increasing the potential.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
Strong 1020mb high pressure will elongate and sprawl from the
Mid Mississippi River Valley into and across the Great Lakes on
Friday. Light north/east winds will continue, and widespread
subsidence will guarantee ample sunshine outside of more fair
weather cumulus which will develop in few/scattered fashion.
PWAT anomalies will remain 1.5 to 2.0 sigma below climatology as
surface dewpoints remain the 50s. Winds overall will decrease
considerably in the lower troposphere as the high exerts its
influence as the day wears on. Under clear skies Friday night,
overnight lows will drop back down into the 50s to around 60.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
This period will be characterized by a warming, moistening, and
destabilizing airmass over the Ohio Valley that will end up
becoming quite unsettled from late in the weekend through all of
next week.
From a hazard assessment standpoint - despite temperatures
largely remaining below normal - instability will be on the
increase owing to increased moisture and relatively cool temps
aloft. Experimental machine learning probabilities of severe
storms based on the 18.00 GEFS pattern from both CSU and NSSL
show slowly increasing /albeit still quite low and perhaps
climatologically normal/ probabilities of severe storm and
heavy rain hazards in this pattern. The signal is broad/muted,
which is interpreted right now as a pretty typical mid-summer
pattern where most storms contain low end threats of pulse
downburst wind and/or localized torrential rain. So no
significant concerns of anything looking atypical from what we
normally see during a normal late July week, but certainly could
be several days where low end threats of strong storms /wind/
or heavy rain could develop.
In the details...beginning on Saturday morning...an amplified
height pattern aloft is present over the CONUS with anomalous
western US ridging, and deep troughs anchored in the northeast
Pacific and across eastern North America...an omega-like
blocking pattern. Shortwave energy will be dropping down the
backside of this ridge into the Mid Mississippi River Valley on
Saturday and into Sunday, and this will further re-develop /
re-center the upper trough axis in the eastern half of the
CONUS back over Iowa/Missouri/Arkansas. By Sunday evening, this
trough to our southwest will continue to deepen owing to
amplification/retrogression of the Bermuda/subtropical
anticyclone off the southeast coast. The net effect of this
process - in combination with the strong surface high from
Friday/Saturday slipping southeast of the area - will be a
uniform increase in low-mid level southwesterly flow into the
Ohio Valley which begins Saturday night and just continues to
increase slowly Sunday into Monday. This will continue in
steady-state / stagnant continuation through
Tuesday/Wednesday/Thursday as the once-Omega-block construction
of the upper air pattern becomes somewhat Rex-blockish with
very strong western Canada height anomalies trying to overtop
retrograding negative anomalies now moving westward into the
Southern Plains as the subtropical ridge to our southeast tries
to build north/west.
Sensibly speaking - all of this means increasing dewpoints/deep
moisture on southwesterly flow which manifests with slowly
increasing rain/storm chances from south to north with
time. Initially focused over northern Kentucky (weekend), the
rain chances become more widespread Monday as southwesterly flow
and PWAT anomalies increase. Forcing Monday/Tuesday will be
weak, but deterministic soundings from most ensemble members
suggest an uncapped airmass as dewpoints press toward 70F. Just
enough deep layer southwesterly flow /30kts at H5 within the
PWAT ribbon/ suggests this environment may able to wring out a
few organized storms each afternoon with tall skinny CAPE
profiles seen amidst PWATs pushing past 1.75".
A more appreciable shortwave trough is evident in the ensemble
members sometime (poor timing agreement) Wednesday or Thursday,
which may help focus higher rain chances, and a little higher
hazard chance via traditional late July thunderstorm clusters.
&&
.AVIATION /05Z FRIDAY THROUGH TUESDAY/...
VFR with light northeast winds throughout, except at KLUK where
there could be some brief visibility reductions early in the
period. MAybe a few cumulus during peak heating as well as some
thin cirrus spreading across the region.
OUTLOOK...No significant weather is expected at this
time.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.
&&
$$
SYNOPSIS...Binau/JDR
NEAR TERM...JDR
SHORT TERM...Binau
LONG TERM...Binau
AVIATION...
Source:
ILN issues Area Forecast Discussion (AFD) at Jul 19, 1:27 AM EDT---------------
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