ILN issues Area Forecast Discussion (AFD) at Aug 6, 1:53 PM EDT999
FXUS61 KILN 061753
AFDILN
AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
153 PM EDT Tue Aug 6 2024
.SYNOPSIS...
A cold front will move south through the area late today into
tonight, with a chance of storms. Slightly cooler and less humid
air will then move into the region for Wednesday and through the
end of the week. Another cold front will likely bring some
additional cooling and drying for the weekend.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Morning update...
No major changes for the update this morning as thunderstorms
north of the area continued to be monitored. Temperatures have
warmed quickly into the low to mid 80s under sunny skies with
the boundary layer quite humid. Despite the humidity, no cumulus
are observed with the atmosphere capped (12Z ILN RAOB). This
greatly limits the potential for thunderstorm initiation over
the area ahead of the front. The special RAOB for Debby will
help confirm the strength of the capping inversion moving into
the early afternoon. A pre-frontal trough is attempting to
initiate a few elevated showers across northern Indiana, but it
is unclear how these will evolve as the move into northwestern
Ohio.
At this time, it is still expected that all thunderstorm
activity and potential severe weather will require the front to
descend closer to west-central/central Ohio late this afternoon,
if not the evening.
Previous discussion...
Will discuss the overall pattern and heat potential in the Near
Term AFD section, and convective potential this afternoon and
evening in the Short Term AFD section.
A surface low pressure center is currently located over Iowa. To
the east of this low, a stationary frontal boundary extends into
the southern Great Lakes. Although this front is somewhat poorly
defined as of 3AM, it is forecast to become much better defined
(in terms of both a theta-e gradient and a wind shift) by this
afternoon. The air mass to the south of this front remains warm
and humid. The KILN 06Z special sounding recorded a precipitable
water value of 1.66 inches, and dewpoints remain generally
around 70 degrees.
Forcing is expected to remain north of the ILN CWA for much of
the day, and recent model runs have suggested the overall
southward progression of the front will be a little slower than
previously forecast. This will keep most (if not all) of the
ILN CWA in the warm sector through peak heating. With high
temperatures in the upper 80s to mid 90s, and dewpoints
generally in the lower 70s, heat indices will reach the mid 90s
(north) to upper 90s (south). It would only take a small
deviation from current forecast T/Td values to get into Heat
Advisory criteria for some of the southern ILN counties. This
concern will be mentioned in the HWO and a Special Weather
Statement.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
As of this writing (3AM), an elevated cluster of thunderstorms
is located just west of Milwaukee. These storms are associated
with a 500mb shortwave and a southwesterly LLJ at 850mb, but the
convection is well on the cool side of the surface boundary.
This overall scenario should remain somewhat the same as the
shortwave progresses to the ESE today, with a convective complex
riding along or just on the cool side of the surface front. At
some point this afternoon, the convection may end up becoming
more surface-based, with a severe threat developing across
northern Ohio (referencing the SPC D1 outlook). This initial
round of storms is likely to miss the ILN forecast area to the
north.
After 18Z, storm chances will gradually increase in the ILN CWA
from north to south, although confidence remains low in how
exactly this will play out. It is generally assumed that the
strongest deep-layer forcing will remain north of the area, but
some convergence associated with the southward-moving surface
front will likely be a focus for convective development by late
afternoon or early evening. CAMs are providing a wide range of
solutions on when exactly this will occur, with the HRRR being
one of the drier models until evening. Have trended PoPs
drier through 18Z, with a measured southward progression of
precipitation chances after that point. Will keep the likely
PoPs to just the far northern and northeastern sections of the
forecast area around 00Z. As the front continues southward later
in the evening, it would be hard to call for a totally dry
forecast at any point, so the forecast will keep precipitation
chances going (in a gradually-diminishing state) through
morning.
The severe potential for the ILN CWA remains unclear. The more
appreciable overlap of shear and instability will stay just
outside of the area, with a pattern that may favor one or more
clusters / MCSs propagating ESE roughly parallel to the surface
boundary. As development occurs in the ILN CWA in the late
afternoon and early evening, instability and deep-layer shear
both appear sufficient (if not overly so) for a few strong to
severe storms. The low-level wind fields are quite hard to
diagnose, with a rather significant wind shift in the vicinity
of the boundary. It is unclear if there will be much of a
contribution from 0-1km or 0-3km shear. Thus, storm mode may
favor multicell clusters and perhaps a supercell or two, but
with more of an isolated than long-lived or organized threat.
Wednesday appears likely to be mostly dry, though some showers
could still occur in the southeastern ILN CWA. Some slight
relief from the heat appears likely, with highs on Wednesday in
the upper 70s (north) to mid 80s (southeast).
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
For Wednesday night, high pressure will build into the Great
Lakes and New England. Meanwhile, eyes will be on Debby as it
churns slowly northward toward the South Carolina coast. Skies
will become mostly clear with lows in the 60s.
For Thursday into Thursday night, Debby will continue to slowly
meander northward into the Carolinas. Meanwhile, we should
remain dry. Models are showing a developing inverted trough
across the east. It remains yet to be seen if this could trigger
an isolated shower/storm in the afternoon/evening. Highs will
range from the lower 80s northwest to the lower 90s southeast.
For Friday into Friday night, it looks like the remnants of
Debby will get lifted to the northeast across the mid Atlantic
region as a large scale mid level trough digs southeast into the
Great Lakes and parts of southeast Canada. This process will
also push a cold front east through our region. There could be
enough forcing and instability for a low chance for afternoon
and evening showers/storms for our eastern zones before
diminishing Friday night as the front exits. After lows of 65 to
70, highs on Friday will range from the lower 80s northwest to
the upper 80s southeast.
For the upcoming weekend, the mid level trough will continue to
slowly move east into the eastern Great Lakes, southeast
Canada, and the New England region. We should remain dry as
surface high pressure wedges into the Ohio Valley from the west.
It will be cooler and less humid. Highs Saturday will range
from the mid 70s north to the lower 80s south. Lows will range
from the 50s to the lower 60s Saturday morning, and in the 50s
for Sunday morning.
Aforementioned surface high pressure will settle across the
Ohio Valley Sunday nigh into Monday. After cool lows in the 50s,
temperatures will begin to moderate some with highs in the
upper 70s to perhaps the mid 80s. Humidity levels will remain
comfortable.
&&
.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Winds have increased this afternoon to around 10 or so knots
from the south or southwest (210-240).
Continue to monitor shower and thunderstorm activity north of
area TAF sites. Maintained mention of VCSH for central Ohio
sites (CMH/LCK) and added a mention for ILN. For DAY, there is
enough confidence that thunderstorm activity developing along
the OH/IN border will gradually work southward this evening
to add mention of thunder later this evening into the early
overnight. Additional changes are possible to these four
locations as trends are monitored this afternoon. Remain
confident that coverage will remain limited to none around
CVG/LUK.
A wind shift is still expected overnight as the front passes
from north to south through area TAF sites. Winds will be around
10 knots.
MVFR ceiling mentions are maintained from the 12Z forecast with
increasing ceilings to perhaps VFR thresholds is some locations
by early afternoon. Still can't rule out some IFR at CMH/LCK,
but confidence remains low with this aspect of the forecast.
Confidence is higher around DAY so a TEMPO period was added for
IFR ceilings from 09 to 13Z.
OUTLOOK...No significant weather expected.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.
&&
$$
SYNOPSIS...Hatzos
NEAR TERM...Hatzos/McGinnis
SHORT TERM...Hatzos
LONG TERM...Hickman
AVIATION...McGinnis
Source:
ILN issues Area Forecast Discussion (AFD) at Aug 6, 1:53 PM EDT---------------
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