IWX issues Area Forecast Discussion (AFD) at May 20, 2:21 PM EDT743
FXUS63 KIWX 201821
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
221 PM EDT Mon May 20 2024
.KEY MESSAGES...
- A strong to locally severe thunderstorm is possible between 6
and 10 pm in NW Indiana/SW Lower MI as well as locally heavy
rain.
- Strong to severe thunderstorms are possible late Tuesday
night, mainly west of IN-15 and then again along and east of
I-69 Wednesday afternoon and evening.
- Warm and muggy conditions to be replaced by somewhat cooler
and less humid air late this week into the Memorial Day
weekend with some chances for showers and storms.
&&
.DISCUSSION...
Issued at 214 PM EDT Mon May 20 2024
Very summer-like pattern comes with summer like challenges for
convection over the next couple of days in a rather moist and
diurnally unstable environment. Highs the next several days will
soar well into the 80s
Initial focus, with greatest (albeit still somewhat reserved)
confidence being with impacts of a MCV set to move across SE
Wisconsin later this afternoon. While the best dynamics remain
northwest of the area, a spoke of the wave does clip far NW areas,
resulting in some weak convergence that may be sufficient to
develop scattered showers and storms in the 22-00Z time frame.
NAM suite overly unimpressed with the development with other
CAMs a bit more confident on some development (HRRR the
greatest). Much like yesterday, shear profiles are rather paltry
(20 kts or less) resulting in more pulse type convection that
could drop a good deal of rain in a short time along with some
threat for locally gusty winds/small hail. Confidence in
eastward extent in the 00Z-04Z period decreases with loss of
diurnal heating and continued NE track of the MCV removing the
already limited convergence. Concerned that likely pops this
evening may be overdone, but if it is going to occur, location
is about right. Have made some adjustments to pops to reflect a
bit more inland extent to the storms but continue with a
weakening trend into the overnight hours.
Between 9Z Tue and quite possibly through 4-6Z Wed the best
forcing will likely remain well north into MI with the warm
front and well west with the cold front, resulting in a dry
forecast despite increasing instability and shear during the
afternoon and evening hours. 700 mb temps of +11 to +12 C edge
in as well, further capping off any development. While a stray
shower or storm could form across northern parts of the area
during the morning and maybe late afternoon in the far W, by far
the best chances look to wait to closer to 6Z Wed and beyond as
a line of strong to severe storms will likely have moved across
IL and be edging into western areas. A few CAMs show some
possible additional development ahead of the line on more of a
pre-frontal trough late evening with the main line then catching
up. Several models show a fair amount of SFC based CIN taking
shape overnight and the 50 kts of 0-6 km shear actually
decreases just ahead of the approaching convection (still
maintained along and behind). If the line holds together into
the overnight hours, pockets of damaging winds and some large
hail would be the main concerns. Slight risk in NW areas appears
reasonable still for Tuesday night with greatest chances
remaining well west of the area across E IA/W IL where a
moderate risk for severe storms now exists.
Cold front will ease its way through Wednesday with the potential
for some lingering cloud cover early. CAMs vary greatly on potential
for development along and ahead of the front with stronger signals
maybe residing just SE of our area during the afternoon/eve hours as
better upper level dynamics take time to catch up with the front.
DY3 slight risk is warranted at this point, but may change over the
next 24 to 36 hours as the mesoscale impacts of Tuesday night's
convection becomes more apparent. New blend of models expands the
likely pops well NW to match where the better chance for storms
may exist (SE third or so-roughly I-69 east) and lingers into
Wednesday evening. This could very well be overdone, but given
the proximity of the front can't entirely dismiss.
Frontal boundary will settle south of the area, with models
continuing to indicate a weak disturbance edging north from TX
Thursday evening towards the Ohio Valley for Friday. Additional
waves move in from the northern Plains the rest of the weekend into
early next week resulting in several period of slgt chc to chc pops
over the holiday weekend. Don't think by any means it will be a
washout, but something to monitor in the coming days. The cloud
cover will help keep it somewhat cooler during the day (70s).
&&
.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 124 PM EDT Mon May 20 2024
Mid level ridging and capping with 700 mb temperatures above normal
across the area is expected to keep pop shower and thunderstorm
activity at bay until around 00z or so. As a vorticity maximum heads
into the Western Great Lakes and Lower Michigan area, left over
instability may be able to maintain some level of strong
thunderstorm activity into SBN terminals, but less of a chance to
reach FWA. Can't rule out at least an MVFR VISBY restriction, but
confidence is low on that. Additional flight restrictions will be
possible Tuesday morning as Lake MI marine air filters in, but
confidence on the extent of that is also low. Will address with a
tempo group for now. Also, expect gusty winds this afternoon to die
down this evening.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Fisher
AVIATION...Roller
Source:
IWX issues Area Forecast Discussion (AFD) at May 20, 2:21 PM EDT---------------
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