Forecast Discussion for ILN NWS Office
297
FXUS61 KILN 030146
AFDILN
AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
946 PM EDT Thu May 2 2024
.SYNOPSIS...
The unseasonably warm pattern will persist across the region for
the foreseeable future, with periodic episodes of rain and
storms nearly every day through the end of next week. Although
not all spots will receive rain each day, there likely will be
at least a few showers or storms around fairly frequently, with
the most unsettled stretch likely to evolve near the middle of
next week.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Showers in the northern ILN CWA have mostly dissipated this
evening, though an isolated shower or two will remain possible
for the next few hours. A greater chance for precipitation will
begin to move into the area after 08Z, as 925mb-850mb theta-e
advection continues, and a weak shortwave (more evident on
models at 700mb than 500mb) moves into the area. Have slightly
sped up the eastward progression of PoPs during the early
morning hours, but otherwise the going forecast appears
reasonable.
Previous discussion >
Some diurnally-driven Cu have sprouted about the area,
coincident with an axis of slightly better LL moisture
availability (shown via sfc DPs in the upper 50s and lower 60s).
This axis of slightly higher LL moisture is advecting back to
the N, with some mixing out of sfc DPs on the southern flank
(near the OH Rvr) as we progress into late afternoon. By early
this evening, the highest DPs (upper 50s) may be close to I-70
and near/W of I-75, suggesting a relatively small temporal and
spatial window for a spotty SHRA or TSRA or two to develop in EC
IN and WC OH this evening. Even with this being said, the
overall potential for spotty activity is somewhat low, with the
best coverage centered in the 22z-02z time frame near a corridor
from Fayette/Union Cos IN to Shelby/Auglaize Cos OH. Gusty
winds in a favorable DCAPE environment will be the primary
threat with any stronger cores, but there are notable
uncertainties regarding both the coverage and intensity of
storms that develop (if any at all). Do think that the potential
for gusty/damaging winds with storms is low enough to continue a
null HWO for now.
The main item of interest for the remainder of the daytime will
be the unseasonably warm temps in the mid to even upper 80s.
This, combined with sfc DPs ranging from the mid 50s to around
60 degrees will certainly lend itself to a "summerlike" feel
about the area this afternoon/evening. Although these values are
not "hot" by traditional summertime standards, the occurrence of
these temps/humidity this early in the season is fairly anomalous
for the area. For example, if the high at KCVG or KDAY reaches
the fcst of 86F, it would be the first time reaching such a temp
this early in the season (on/prior to May 2) at each respective
site since 2012.
The diurnally-driven Cu should wane in coverage toward/beyond
sunset, lingering the longest in WC OH where those spotty
SHRA/TSRA (if there are any at all) could percolate a bit into
the late evening hours. Lows tonight dip into the lower/mid 60s
area-wide amidst calm/light winds and thickening mid/upper
level cloud cover late in the night.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
The short term period will be somewhat unsettled, although not
particularly concerning from a hazardous-weather perspective. A
midlevel S/W will eject NE through the TN/OH Vlys through the
morning, with a very diffuse LL flow pattern in its wake
stretching SW to NE squarely through the region. While there
will be some very subtle LL convergence near the LL trof axis,
a remnant weak low/MCV will likely provide a focus for the most
persistent coverage/development of activity as we progress into
the afternoon/evening. A few SHRA will move into the far wrn
parts of the ILN FA shortly after daybreak before /slowly/
expanding E into the rest of the area through the course of the
daytime. Recent guidance has trended slightly slower with the
progression of this feature into the local area, so have
adjusted PoPs accordingly.
By the afternoon into the evening, there should be an expansion
in coverage of SHRA/TSRA activity locally, albeit in a very
disorganized manner. SCT to numerous SHRA, with some ISO
embedded TSRA, will be the primary item of interest mid
afternoon through the evening hours along/immediately ahead of
the weakly-convergent LL flow axis and MCV remnant, which
should migrate into N KY by Friday evening. The weak convergence
associated with these two separate, but related, features
amidst an amply-saturated (high PWAT) environment will keep
SHRA/iso TSRA activity going for a fairly extended stretch from
late Friday morning through late Friday night. However,
activity should decrease from W to E past midnight into Saturday
morning, with at least a few SHRA likely still lingering in
central OH to NE KY by daybreak Saturday.
The overall potential for TSRA vs. SHRA on Friday is fairly low
considering the somewhat meager instby in the profile. In fact,
the weak steering-layer flow likely points to brief heavy rain
as being the only /low-end/ concern, and even this looks too
negligible to even add to the HWO at this juncture.
Highs on Friday will be very-much convectively-modulated, with
temps reaching into the lower 80s from NE KY through central OH
before the better SHRA/iso TSRA activity moves in later in the
day. Elsewhere, highs should top out in the mid 70s, although
certainly temps may only top out around 70 in EC/SE IN where
thicker cloud cover/more persistent pcpn coverage will evolve
earlier in the day than will be the case for points further E.
Lows Friday night dip into lower 60s amidst extensive LL cloud
cover (a soupy setup).
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
An unsettled...warm...somewhat humid...and potentially active period
for early May is in the offing during this period. There may be
hazards including severe storms and locally heavy rain/flooding
given the large scale / synoptic setup at some point during the
middle of next week, but timing/area is highly uncertain.
At 12Z Saturday, a closed mid/upper level low pressure over Hudson
Bay will be meandering slowly east across southeast Canada
through/atop ridging to its east into Sunday. Some weakness in the
height field /weak 700mb trough/ across the Ohio Valley and
embedded/strung out vorticity - almost somewhat removed from
stronger flow to the north - will plod along slowly through the
weekend and keep things unsettled Saturday, while a secondary weak
wave ripples through the Great Lakes on Sunday maintaining some
degree of rain chance. Rain chances Saturday should remain highest
east of I-75 along a diffuse surface trough moving ever so slowly
east underneath the strung out vorticity aloft and mid-level
troughing. On Sunday...while the weak 700mb trough will have exited
to the east, more energy moving through the Great Lakes and also
through KY/TN Sunday night will maintain rain chances. Just an
unsettled...non-washout-but-still-showery weekend with highs in the
70s.
On Monday...the residual impacts of the southern stream wave moving
through KY/TN will likely foster diurnal shower/storms especially
south, before that system pushes east as well.
A progressive...deep upper trough will be pushing steadily east
across the western CONUS on Monday, forcing replacement height rises
over the Ohio Valley in the wake of weekend unsettled weather. This
system will slow and continue to deepen as it centers over the
Dakotas by Tuesday, which places the Ohio Valley in broadly
diffluent/southwesterly flow aloft with a wide open Gulf of Mexico-
sourced low level jet transporting plenty of warmth/moisture for the
middle of next week. While the magnitude of the negative height
anomalies trends downward through the week, the trough axis remains
intact and maintains a feed of moderate/fast southwesterly flow atop
a southerly low level jet well into Thursday. As a result of all of
this, ejecting waves out of the trough should focus/funnel through
the Ohio Valley along an oscillating frontal boundary draped
somewhere nearby. These waves are common in all
deterministic/ensemble member runs, but with widely varying latitude
and depth.
It is noted that CIPS analogs running on the mean GEFS pattern
highlights a broad area of potentially daily severe convective
threat from the central and lower Mississippi River Valley, into the
Ohio Valley Tue-Thur that is mirrored by 02.00Z CSU MLP guidance.
GEFS/EPS instability matrices are strongly aligned in this time
period offering moderate instability, and plenty of precip chances
via waves moving through the area. 02.00Z EPS EFI/SOT graphics paint
a corridor of anomalous CAPE/shear overlap for early May through the
Ohio Valley, peaking on Wednesday, but timing should taken
cautiously at this time range as daily threats will be modulated
heavily by low amplitude shortwave tracks and convective overturning
in previous days. The pattern - when taken cumulatively - suggest
rainfall/flooding issues could be present either with individual MCS
episodes, or from repeated rounds of convection as the ridge slowly
flattens and low-mid level flow begins to align in a WSW orientation
by the end of next week, when an effective frontal should begin to
settle south of the area and we cool/dry out perhaps into next
weekend. But until then...Tues night-Thursday bears some potential
for several rounds of organized storms, some of which could be
strong to severe, with locally heavy rain/flooding.
&&
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
VFR conditions are expected for most of the TAF period. Tonight,
most locations will remain dry, with showers and storms likely
to remain a bit away from the KDAY/KCMH/KLCK airports, and
nowhere near the others.
Some valley fog is possible at KLUK overnight.
A greater chance for showers, and possibly thunderstorms, will
move into the area tomorrow afternoon. Some VCSH and -SHRA
periods have been included in the TAFs. Model data suggests that
these entire periods may not be wash-outs, and there could
actually be some breaks in the rain, so later TAF issuances may
be able to refine the timing of the rain and storms in a more
detailed way. As this occurs, some MVFR ceilings will also move
into the area. These appear most likely to impact KCVG/KLUK, but
could also get into KDAY/KILN.
OUTLOOK...Thunderstorms are possible at times from Saturday
through Tuesday. MVFR ceilings are likely Friday night into
Saturday, with IFR ceilings and MVFR VSBYs possible Friday night
into Saturday morning. MVFR conditions are possible again Sunday
morning.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.
&&
$$
SYNOPSIS...KC
NEAR TERM...KC/Hatzos
SHORT TERM...KC
LONG TERM...Binau
AVIATION...Hatzos
NWS ILN Office Area Forecast Discussion
