460
FXUS61 KILN 181902
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
302 PM EDT Wed Sep 18 2024

.SYNOPSIS...
Slow moving upper level low pressure system over the Carolinas
will continue to move slowly northeastward and redevelops off
the Eastern Seaboard. Weak axis of high pressure from
southeastern Canada into the Mississippi Valley will continue
the warm dry weather over the Ohio Valley through Friday. A weak
system pushing through the Great Lakes over the weekend may
bring some limited or scattered rain showers particularly on
Friday night or Saturday, but most areas will remain dry. A
little more active and unsettled pattern will develop over the
Ohio Valley from the early into middle portions of next week,
with slightly better chances of showers and storms. It will
remain warm through the period with highs well into the 80s.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Primary concern now through sunrise on Thursday are whether 1)
any isolated showers can develop through early evening and 2)
coverage/intensity of any fog areas overnight.

Elongated mid/upper trough axis which is the remnants of the
tropical low from over the weekend has shifted east from PA to
SC, with the primary circulation center over SC. Shallow
boundary layer moisture has pushed westward on weak easterly
winds through much of the ILN CWA as of 18Z with dewpoints from
the middle 50s to lower 60s. Cumulus (out the window and on
visible satellite) does not have much vertical growth (yet),
but with several hours of sunshine/heating still to come, we may
see a shower or two still pop up given several hundred joules
of CAPE with temperatures warming into the middle and upper 80s.
Not enough to formally mention in the forecast - but would not
be surprised to see one or two.

Tonight - the diurnal cumulus should rapidly dissipate and with
the residual low level moisture that remains over the area, the
background setup/support for at least a little fog formation is
there. Light winds /easterly/, mostly clear skies, weak high
pressure axis near the area, and longer September nights suggest
valley fog should develop rather easily, and there are some
signals /HREF probabilities of visibility <1SM/ of potential
overland/areal fog to boot (see what happened this morning in NW
Ohio and northern IN). For right now - given some uncertainty of
coverage of this radiational event - have opted to mention
patchy fog for now - but the potential exists for one or two
areas of thicker/denser fog - and the likelihood of that
seemingly centered in west-central or central Ohio.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
The mid/upper level low and trough axis will continue to open
up and elongate as it shifts off the Eastern Seaboard on
Thursday, leaving a rather nondescript/baggy/ill-defined surface
pressure pattern over the local area. Underneath increasing
upper ridging, a general axis of very weak high pressure and
subsidence will remain over the area. The moisture pool in the
boundary layer which pushed west into the ILN forecast area
today, will begin mixing out amidst continued easterly flow,
getting worked with plenty of sunshine and very dry soils.
Dewpoints should once again mix down into the 50s during the
afternoon as temperatures warm again in earnest into the middle
and upper 80s in the afternoon. Clear skies will continue into
Thursday. While a diminishing band of cirrus will cross the
forecast area in the morning, more fair weather cumulus are
again expected in the afternoon. Winds will remain light.

Clear skies expected again Thursday night will likely again
support valley fog formation, and lows will pull back toward
60F.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
This period will be characterized by an increasingly unsettled
flow pattern that at least supports some chance of rain - better
than what we`ve seen for a little while.

Days 2 and 3 - An initial shortwave near Lake Winnipeg, with a
southward-extending trough axis into the western Great Lakes on
Friday morning, will largely pass northwest of the local area
on Friday night into Saturday as it glances off mid level
ridging centered over the Southern Plains. There is - and has
been - a very low rain chance signal with this system for areas
of west central Ohio in the 10%-20% range, but admittedly
forecast soundings and background forcing signals are rather
paltry, and will keep a dry forecast for now on Friday and night
and Saturday as the remnants of this trough axis pass across
the area. Some of the stronger solutions with this feature would
drop a weak frontal boundary into the area on Saturday and
renew a chance of showers developing in peak heating along the
low level moisture axis, but in the presence of drought
conditions and low level moisture being overforecast of late,
will keep rain chances out of the forecast at this time period
for right now, as the bulk of the ensemble membership remains
dry under subtle height rises. Once again temperatures on both
days will soar well into the 80s, with dewpoints mixing back
each day into the 50s.


Days 4-7 - Think Sunday remains largely warm and dry again as
well, downstream of a rather potent shortwave trough moving
through the Central Plains. This trough will be lifting
northeast atop the persistent Southern Plains mid/upper level
ridge, and may be in the process of being absorbed into larger
scale northern stream troughing (GFS-based ensemble solutions)
crossing central and southern Canada, or remaining separate and
lagging behind on a slower/stronger solution (ECMWF-based
ensemble solution). There is a rather decent forcing (and thus
QPF) signal that develops as a result of these processes to our
west on Sunday that become disparate between the forecast
systems as the system shifts east Sunday night and into
Monday/Tuesday. While the bulk of QPF should remain far enough
west to guarantee yet another dry and warm day on Sunday,
confidence breaks down on the specifics of the geometry, timing,
moisture, and forcing quality as this mid/upper level trough
sweeps through the Great Lakes Sunday night, Monday, and even
into Tuesday as per the above. Moisture will definitely be on
the increase as PWAT anomalies surge well above late September
normals, and the presence of the shortwave trough and attendant
frontal boundaries should be adequate for shower/storm chances
Sunday night- Tuesday, but the timing and flow field differences
right now amidst the ensemble members don`t allow for anything
more than 25-40% chances during at particular time period. Will
just need to wait for a better signal to emerge in the days
ahead. Adding uncertainty during this time period is what looks
to be a pattern in the Gulf of Mexico that may support potential
of tropical / low pressure development, and if/when that occurs
could have considerable impacts on ridge geometry over the
south/east United States. Much uncertainty - the takeaway right
now there are increasing signals for better rain chances - and
the warmth will certainly continue.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
Scattered to locally broken VFR cumulus continues to develop
early this afternoon, but expect cloud bases to lift a little
more through the day due to heating so no MVFR potential with
these clouds even if they go broken/ceiling for a brief
period. Most will be scattered in coverage. Light northeast
winds will sometimes go variable in direction due to weak
pressure gradient.

Winds should go calm or light/variable before sunset with vast
majority of cumulus dissipating. With clear/mostly clear skies
tonight, think valley fog will develop and affect LUK as it
usually does on clear/calm autumn nights, and have TEMPO for IFR
visibility there. A separate signal for more widespread / areal
fog is showing up across the area. Confidence is low in how this
may manifest, but felt confident enough to bring some MVFR
visibilities via TEMPO groups into all TAF sites between 08-12Z.
Coverage and favored location is not high, and future forecasts
may need to consider lower visibility based on observational
trends. Background setup (clear skies, longer nights, light
northeast wind, shallow moisture recently having moved into the
area) makes areas of fog (or perhaps low clouds) more probable
later tonight.

Any remaining fog should lift/mix out on Thursday morning with
more scattered cumulus by 18Z, and continued light northeast or
easterly winds.

OUTLOOK...No significant weather expected.

&&

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

&&

$$
SYNOPSIS...Binau
NEAR TERM...Binau
SHORT TERM...Binau
LONG TERM...Binau
AVIATION...Binau