IWX issues Area Forecast Discussion (AFD) at Jul 30, 4:26 AM EDT643
FXUS63 KIWX 300826
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
426 AM EDT Tue Jul 30 2024
.KEY MESSAGES...
- Confidence continues on the lower side regarding the potential
of impacts from 1 or more thunderstorm complexes, mainly
tonight through Wednesday night.
- Better chances for showers and thunderstorms Thursday through
Saturday. Thursday may end up the best chance for strong to
severe storms.
- Heat indices should be in the 90s through Thursday with some potential
for near 100 degrees Wednesday/Thursday.
&&
.DISCUSSION...
Issued at 332 AM EDT Tue Jul 30 2024
Line of showers and thunderstorms that was associated with a weak
trough have dissipated across far eastern areas. Subsidence behind
the trough should limit any new development through at least
late afternoon. The lack of convection should allow for a decent
amount of sun, resulting in highs well into the 80s which
combined with dewpoints in the low to 70s will bring heat
indices in the mid to maybe upper 90s.
2 upstream features will likely play a large factor in
additional thunderstorm development later this afternoon into
tonight as they track SE out of Iowa and Minnesota. Theta-e
gradient will likely reside SW of the area through tonight with
majority of the CAMs pointing towards renewed convective
development late this afternoon into early evening from Iowa
into central IL and IN, corresponding nicely with latest updates
to DY1 outlook. A few CAMs suggest lesser development into this
evening with the theta-e gradient shifting further NE and
possibly lighting up as LLJ increases. This scenario seems much
less likely, but cannot be fully ruled out. Consensus from
surrounding offices was to keep pops limited to chc into tonight
and await evolution of the next round of storms. Main threats
would be damaging winds and very heavy rainfall.
Thunderstorm chances Wednesday into Wednesday night once again
will be determined by impacts of overnight convection, location
of best instability gradient and timing of any upstream MCVs
that may drift into the area during peak heating. Main genesis
area for storms Wed/Wed night seems to be back in NE/SD in
association with a mid level trough that will be dropping slowly
SE. SPC has expanded the marginal risk for DY2 to cover the
entire area for a combination of development with any remnant
MCV or outflows from the morning convection as well as
aformentioned NE/SD convection. Once again threats would be both
damaging winds and heavy rain.
Current thinking is greatest strong to severe storm threat could
occur Thursday into Thursday night as the trough mentioned
causing storms Wed upstream approaches and deepens somewhat.
Plenty of instability will be in place to provide a decent shot
of convection. DY3 outlook has introduced a slight risk in the
SW half or so, which seem reasonable at this point.
The trough will close off and linger into Saturday with
periodic mainly afternoon/evening chances for showers and some
thunderstorms. Best chances seem to exist Friday afternoon and
evening with lingering higher dewpoints still in the area,
especially east. NBM attempted to introduce categorical pops,
but consensus was to cap at likely for now. A trend to more
tranquil weather should arrive Sunday into Tuesday.
With regards to temperatures and heat indicies, dewpoints in the
upper 60s to mid 70s (locally higher?) will linger across the
area with highest levels near the theta-e gradient that should
edge closer for both Wednesday and Thursday. Heat indices should
generally be in the 90s, but some areas could touch 100 degree
or slightly higher IF storms hold off. No need for headlines at
this point, but will need to monitor.
&&
.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 152 AM EDT Tue Jul 30 2024
A strong convectively enhanced upper vort max will continue to
depart the region to the east for the remainder of the
overnight. Loss of diurnal instability has led to a diminishment
of showers and isolated thunderstorms, and potential of
additional showers and thunderstorms at the terminals has waned.
Lingering low level moisture and weak anticyclone building in
across the western Great Lakes could be sufficient for some
patchy fog formation into early Tuesday morning along with
patches of MVFR cigs around 2k ft. Passage of this short wave
and associated sfc reflection should take low level boundary
south of the terminals through the day today, keeping bulk of
daytime shower/storm chances south and west of terminals. By
late this period, some indications that return low level theta-e
advection and strong instability gradient across the western
Great Lakes could be focal point for renewed convective
activity, but confidence in location is low. Instability
gradient may be just far enough west to keep most of showers and
storms west of terminals, but will need to reassess Tuesday
night period with later TAF issuances, particularly for KSBN
which could have more of a potential for additional
showers/storms tonight.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Fisher
AVIATION...Marsili
Source:
IWX issues Area Forecast Discussion (AFD) at Jul 30, 4:26 AM EDT---------------
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