Area Forecast Discussion
Issued by NWS Wilmington, OH

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874
FXUS61 KILN 261041
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
641 AM EDT Fri Apr 26 2019

.SYNOPSIS...
Rain is expected to continue this morning, until low pressure
moves northeast out of the Ohio Valley. A brief period of high
pressure will bring dry conditions late Friday into Saturday
morning, before a fast-moving low pressure system progresses
through the Ohio Valley and southern Great Lakes from Saturday
afternoon through early Sunday morning.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
An ill-behaved surface low is now centered near the Lake Erie
shoreline in northern Ohio, with a frontal boundary currently
crossing through the ILN CWA behind it. Once this front has
passed, winds have been switching to the northwest -- though as
of this writing, much of the ILN CWA is still in southwesterly
flow to the south of the low. The widespread precipitation
currently over the ILN CWA is largely the result of a shortwave
that has moved eastward from the middle Mississippi Valley. Just
upstream, a second distinct shortwave -- now in phase with the
lead wave -- has moved into the area from the northern plains.
This second wave is responsible for the band of precipitation
currently entering western Indiana.

With the combination of these two waves, rain -- which may be
moderate to heavy at times -- is expected to continue for
another several hours. A gradual diminishing in intensity is
expected after 12Z, but at this point it would be fair to call
antecedent conditions rather wet, and additional rainfall over
the next 4-6 hours could lead to flooding. Neither the shear or
thermodynamics support any continued threat of severe weather,
so hydrologic concerns are the main focus through the morning.

One slight concern going into the afternoon is that a few models
(HRRR / WRF-NMM) have indicated the potential for some
convective development in the eastern half of Ohio at around
21Z. Looking at soundings during this time frame, lapse rates
are expected to be very steep, but with poor low-level moisture
leading to very narrow CAPE with equilibrium levels below 20kft.
It is not even clear if that will be deep enough to produce
lightning, but nonetheless, some convective showers are possible
in the far eastern sections of the ILN CWA -- particularly in
the Columbus area after 4PM. PoPs were kept in place a little
longer than previously forecast to account for this.

No real changes were made to the wind gust forecast, with a
tight pressure gradient and the aforementioned steep lapse rates
allowing for gusts into the 30-40 MPH range this afternoon.

To no surprise, Friday will be cooler than Thursday, on the back
side of the cold front in a notably cooler air mass. Highs are
expected to be in the upper 50s to lower 60s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
By this evening, the surface low will be moving into Quebec, and
the phasing mid-level troughs will both be exiting eastern Ohio.
This will place the ILN CWA within a regime of deep-layer
northwesterly flow, which will persist through the first half of
Saturday. This cold advection pattern will bring temperatures
into the upper 30s to middle 40s by early Saturday morning, but
the winds will keep frost from becoming likely.

An extremely narrow wedge of high pressure will be passing
through the area on the first half of Saturday, providing not
even a full day of quiet conditions over the ILN forecast area.
Attention will turn upstream to a compact surface low, which is
expected to be moving through the Quad Cities area by Saturday
evening. Along an elevated warm front, precipitation should
already be developing and moving into the northwestern sections
of the forecast area by Saturday afternoon.

No expectations for a big jump in temperatures from Friday to
Saturday, as flow will remain westerly through much of the day,
only switching to the south in the late afternoon after the axis
of the high has moved to the east. However, this switch in wind
direction may occur a little sooner in the southern sections of
the forecast area, which may bring temperatures slightly warmer
there -- into the lower to mid 60s. Elsewhere, mid 50s to near
60 can be expected.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
For Saturday night into Sunday morning, a low pressure system
will quickly move east across the Great Lakes, weakening some as
it does. The chances for rain will be highest north near the
low track, with low chances of rain along the cold front across
the far south. Precipitation will taper off from west to east
late and into sunrise Sunday morning. Clouds and gusty winds
will linger in the morning, then sunshine can be expected by the
afternoon hours as surface high pressure builds into the Great
Lakes. Lows will range from the lower 40s northwest to the lower
50s southeast. There will be some recovery to the temperatures
on Sunday, but it will be cooler with highs ranging from the
lower 50s north to the lower 60s south.

Mostly clear skies are forecast for Sunday night as the high
moves to our northeast. There is some potential for patchy frost
across central Ohio if winds decrease for a long enough period
of time. Will continue to monitor. Lows will range from the
upper 30s to the lower 40s.

The dry weather for Sunday night will be short lived as
precipitation chances move back into the region for Monday and
remain in place through the week as several short waves and
frontal systems traverse the region. Warmer temperatures will be
in place during this time with highs generally in the 60s and
70s. A few 80 degree temperatures will also be possible near and
south of the Ohio River on Wednesday and Thursday. There is at
least some instability each day and therefore have some thunder
mentioned in the forecast as well.

&&

.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
Showers will continue to impact the TAF sites through the
morning hours. While most of the rain should occur with VFR
visibilities, some brief MVFR visibilities may be possible in
the heavier showers. Of greater concern is low-end MVFR to IFR
ceilings that will persist through the rest of the morning.
Periods of IFR ceilings will be most likely at KDAY/KCMH/KLCK.

Rain should begin to scatter out and lighten up during the
late morning, eventually clearing from west to east. As this
occurs, winds will switch to the NW and become quite gusty, with
gusts of around 30 knots expected at all TAF sites. There is
also a chance of some additional shower and thunderstorm
development during the afternoon, which could possibly affect
KCMH/KLCK. For now, a VCSH will be used to note this
possibility, as the activity should remain fairly scattered.
Outside of this possibility, VFR conditions are expected at all
TAF sites by early to mid afternoon. Winds will diminish and
lose their gusts overnight, then become light and variable on
Saturday morning.

OUTLOOK...MVFR conditions will be possible on Saturday night
into Sunday.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.

&&

$$
SYNOPSIS...Hatzos
NEAR TERM...Hatzos
SHORT TERM...Hatzos
LONG TERM...Hickman
AVIATION...Hatzos



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