IWX issues Area Forecast Discussion (AFD) at Jul 29, 1:39 PM EDT787
FXUS63 KIWX 291739
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
139 PM EDT Mon Jul 29 2024
.KEY MESSAGES...
- Showers and storms will continue to develop this afternoon. Widespread
severe weather not expected, but a few storms may produce
gusty winds and brief heavy rainfall.
- Several additional chances of showers and thunderstorms
tonight through Thursday. Confidence in details regarding
timing, coverage, severity still on low side due to the
influence of each round of convection on favorable ingredients
of storms for the next day's potential.
- If severe weather occurs, greatest potential appears to be
Wednesday afternoon into Thursday.
- Peak afternoon heat indices may top out near 100 for much of
the area for Wednesday and Thursday, but this potential will
be affected by extent of showers and thunderstorms.
&&
.DISCUSSION...
Issued at 350 AM EDT Mon Jul 29 2024
Today will mark the beginning of an active weather pattern that
will continue into Thursday and potentially Friday.
Some light rain showers persist early this morning east of I-69 in
closer proximity to narrow axis of best deep moisture that aided in
yesterday's scattered showers. Looking upstream, a convectively
enhanced short wave is associated with an area of showers and
thunderstorms across eastern Iowa/northwest Illinois. Some
enhanced low level west-southwest flow on southern periphery of
this feature will allow for some renewed low-mid level theta-e
advection back across the southern Great Lakes and Ohio River
Valley today. This advective forcing and compact nature of this
vort max should allow for maintenance of showers and scattered
thunderstorms in western portions of the forecast area after 15Z
this morning. Some diminishment in intensity is possible late
morning/early afternoon but with this convectively enhanced vort
max or MCV type feature slowly making its way across the region
today, some diurnal enhancement is expected this afternoon.
Severe weather threat is somewhat challenging to assess today.
Background shear is overall on the weak side, but stronger
westerlies on southern side of convectively enhanced short wave
should locally augment shear profiles. This enhancement to
shear profiles should tend to maximize south and southwest of
the local area however. Despite renewed low level moisture
advection this afternoon via westerly low level flow,
instability progs do not look overly impressive today as plume
of steeper mid level lapse rates should lag back from the Corn
Belt into western TN. An isolated wind threat does appear
possible late morning through late afternoon across
approximately western half of the area where more favorable
timing may exist with upstream vort max. Some isolated severe
wind threat could evolve, but overall expectation would be for
generally sub-severe storms. One possible consideration today,
much of the shear will be based in low/mid levels with 0-1km
shear vectors possibly as high as the 15 to 20 knot range in
vicinity of this vort max. With a vorticity-rich short wave,
always some concern for shallow mesovortex/mini-supercell type
structures given low level shear, but lack of impressive deep
layer shear profiles should temper extent of severe risk today.
This short wave may be slow to exit this evening but passage of this
vort max should allow effective frontal position to shift south of
the area from southern Iowa into central Indiana by Tuesday morning.
Lingering showers and thunderstorms are expected into this evening,
but better potential of any convection growing upscale may tend to
remain south of the local area in closer proximity to earlier
outflows. With effective frontal boundary south of the area early
Tuesday, a lull in greater convective potential is expected for
first part of Tuesday, but a good deal of uncertainty persists
regarding the late Tuesday/Tuesday night period. Another fast moving
ridge-riding upper wave is expected to race across the Dakotas this
evening before diving south and likely triggering another convective
cluster across the Upper Midwest/Cornbelt Tuesday afternoon.
Depending on exact orientation of instability gradient, local area
may be affected by potential MCS Tuesday night, but as mentioned,
confidence in finer details will be tough to attain at this forecast
distance. Primary threats would be for locally heavy rainfall and
some wind potential if upscale growth occurs.
Wednesday and Thursday will feature the return of more oppressive
heat and humidity as boundary retreats back to the north. Highs in
upper 80s to around 90 for these days combined with dew points in
the low to mid 70s could produce peak afternoon heat indices nearing
the 100 degree mark.
Confidence in convective details becomes even harder to attain
for Wednesday and Thursday. Wednesday should feature very
unstable conditions with some dependence on instability
magnitudes on evolution of any late Tuesday night convection.
Steep mid level lapse rates and decent amounts of deep layer
shear should be in place by Wednesday raising some concern for
better chance of strong/severe storms Wednesday/Wednesday night.
The main item of uncertainty Wednesday is a trigger or focusing
mechanism that might be needed to overcome any weak capping
concerns. By Thursday, large scale synoptic support becomes more
defined as guidance continues to suggest larger scale upper
trough beginning to approach the area. Shear parameters could
become a bit more marginal by Thursday however.
Details regarding midweek severe potential will take some
time to fine tune, but will need to watch these periods for perhaps
greatest severe potential of this forecast period. Chances of
showers and thunderstorms linger into Friday with main upper
trough/low, but this should be in a weaker sheared environment with
loss of elevated mixed layer and weaker instability.
First part of the weekend should feature a break from rain chances
as more stable conditions develop across the Great Lakes and Ohio
Valley. However, longwave pattern does not appear to change much
heading into the first part of next week with mean upper ridge
western CONUS and mean upper trough southeast Canada. This could
make local area vulnerable to additional NW flow disturbances toward
end and beyond this forecast valid period as moisture recovery would
be likely in this synoptic pattern.
&&
.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 134 PM EDT Mon Jul 29 2024
South winds 10-12kt with higher gusts will continue this
afternoon before gradually veering more southwesterly as the day
progresses. Have added a tempo group for thunderstorms at SBN
during 22z-02z time frame given latest guidance; MVFR/IFR
conditions possible in heavier storms. Confidence remains lower
further east so have left VCTS at FWA for now. Overnight,
MVR/IFR cielings are likely to roll back into the area but a
weak westerly flow around 5-7kts should keep stuff just off the
surface, thus precluding the addition of lower visibilities into
the forecast.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Marsili
AVIATION...Norman
Source:
IWX issues Area Forecast Discussion (AFD) at Jul 29, 1:39 PM EDT---------------
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