ILN issues Area Forecast Discussion (AFD) at Jul 4, 1:36 PM EDT091
FXUS61 KILN 041736
AFDILN
AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
136 PM EDT Thu Jul 4 2024
.SYNOPSIS...
Multiple rounds of showers and thunderstorms remain in the
forecast through Friday. The area looks to dry out over the
weekend as high pressure builds across the Ohio Valley.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Update (Severe Thunderstorm Watch)...
A Severe Thunderstorm Watch was recently issued for portions of
northern Kentucky. Although thunderstorms extend northward into
southwest and west-central Ohio, the best instability remains
consolidated along the southern border of the ILN CWA. The
Kentucky Mesonet shows a 10 to 15 degree temperature difference
is present across only 1 or 2 counties from north to south. With
increasing southwesterly flow, the better heating/moisture will
likely nudge northward into the watch area ahead of the
thunderstorm line. Damaging winds remain the greatest threat
with these storms with an isolated spin-up tornado possible.
Otherwise, behind the line, the atmosphere is beginning to
recover as mostly clear skies are allowing for efficient
heating. The amount of recovery will be critical for the
potential second round severe threat later on this evening.
This would be handled through a completely different watch, if
necessary at all.
Previous discussion...
Regional radar mosaic is quite active this morning as
thunderstorms continue to develop and persist across much of
southern/south-central Indiana. A pseudo-warm front wing is
also developing thunderstorms into portions of northern Kentucky
and soon, southeast Indiana. PoPs have been adjusted to the
latest radar trends and mesoscale factors through the early
afternoon.
The latest 12Z HRRR is likely too quick with the erosion of the
thunderstorm activity, so this increases uncertainty for the
overall CAM projections for the next, more concerning round of
development later this afternoon and early evening. With the 13Z
update, SPC introduced a Level 2 of 5 risk (Slight Risk
including 5% tornado) into southeast Indiana, northern
Kentucky, and portions of southwest Ohio. This scenario becomes
more plausible the faster the ongoing thunderstorm activity
clears, allowing for mass support northward ahead of an
approaching MCV. If enough clearing can occur, the potential
exists for discrete storms to persist within an environment of
strengthening deep- layer flow and backed low- level flow. The
magnitude of the backed flow may be largely dependent on the
remnant cold-pool air mass left behind modifies with afternoon
heating and moisture transport.
To the north of this morning's thunderstorm activity, a broad
shield of light-moderate rain with embedded thunder is expected
through the rest of the morning. This should gradually decrease
in coverage as the thunderstorm activity to the south shifts
east. Additional, scattered thunderstorm activity will be
possible late this afternoon into the evening hours, but the
overall severe threat is limited.
While much of the previous discussion was focused on the severe
weather threat, the east to west corridor of thunderstorms this
morning may bring cause for locally heavy rainfall depending on
how quickly it propagates eastward. Southeast Indiana and
portions of northern Kentucky currently stand the best chance of
observing the locally heavy rainfall. This could lead to high
water in a few spots.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Mid level shortwave and thunderstorm complex to be moving thru
the area thru the evening. Some additional fog development will
be possible in the moist environment overnight. Mild lows are
expected generally in the lower 70s.
More significant mid level low to track thru the Great Lakes
Friday. Associated surface cold front to sweep thru the area
during the afternoon. Some uncertainty remains regarding the
degree of instability Friday with residual cloud cover from
Thursday night's pcpn. Given that effective shear increases to
around 40 kts, even low end moderate instability will support
a threat for severe storms mainly in the east. The main threat
will be damaging winds. Expect highs to range from the mid to
upper 80s.
&&
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
A cold front will be progressing east of the Ohio Valley on
Friday night. Cooler, drier air moves in behind the front for
the weekend as high pressure builds in from the west through
Sunday. This will signal an end to the hot, humid, and unsettled
weather setup from this past week. Forecast highs on Saturday
remain in the lower 80s and lows Saturday night will be in the
lower 60s. Highs on Sunday reach back into the middle 80s.
Surface high pressure shifts east of the area by Monday.
Southwesterly flow redevelops west of the high which will allow
heat, humidity, and afternoon rain chances to return midweek. A weak
surface boundary and upper level shortwave may increase rain chances
on Tuesday before diurnal shower/storm chances return to lower
probabilities by Wednesday and Thursday.
&&
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
Scattered, disorganized thunderstorms continue to form and
dissipate across the area this afternoon. This has made timing
challenging. To the south, a more organized line of
thunderstorms will pass to the south of the area. Behind the
line, temperatures are beginning to warm following this
morning's thunderstorms/stratiform rain. Therefore, left VCTS
mention in through the rest of the afternoon and into the
evening (00Z-02Z) as additional thunderstorms are forecast.
Confidence on timing and coverage are low so no TEMPO groups
were added.
Following the thunderstorm/shower activity this evening, another
period of MVFR/IFR CIGs is expected through the overnight into
Friday morning. Some VIS restrictions are also forecast.
Improvement is expected through the mid-morning with VFR
expected by the afternoon. The front will still not have passed
through until after 00Z Saturday so some thunderstorms will once
again be possible.
Surface flow will be less than 10 knots except for influences
from thunderstorms. Westerly winds increase to above 10 knots
Saturday afternoon.
OUTLOOK...Thunderstorms possible on Friday.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.
&&
$$
SYNOPSIS...AR
NEAR TERM...McGinnis
SHORT TERM...AR
LONG TERM...Campbell
AVIATION...McGinnis
Source:
ILN issues Area Forecast Discussion (AFD) at Jul 4, 1:36 PM EDT---------------
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