IWX issues Area Forecast Discussion (AFD) at Jul 3, 5:12 AM EDT684
FXUS63 KIWX 030912
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
512 AM EDT Wed Jul 3 2024
.KEY MESSAGES...
-There is a marginal risk for strong to severe storms today
between 2 and 8 pm EDT. The best chance will be south of US
24. Damaging winds and heavy rain are the main threats. Highs
will be in the 80s, with locations south of US 24 seeing heat
indices in the low 90s.
-There are chances for showers and thunderstorms most days into
early next week, but especially Thursday night into Friday and
then again Tuesday. Highs will be in the 80s. Lows will be in
the 60s. Severe weather is not expected at this time.
&&
.DISCUSSION...
Issued at 511 AM EDT Wed Jul 3 2024
There is a marginal risk for strong to severe storms today for
locations south of US 24, especially along/east of I 69. As of this
writing we're sitting in the warm sector of a surface low centered
over Central Wisconsin, with the warm front extending into Lower
Michigan from roughly Ludington to Detroit. Further west in IL/WI is
the cold front, slightly slower than anticipated in previous
forecasts. Still, light rain and isolated thunderstorms exist out
ahead of it thanks to a pre-frontal trough, with lightning/thunder
more likely as you head further south where a convective complex in
NE Missouri/SW IL is trucking eastward. This complex may end up
hogging some of our moisture transport this morning, which will
limit pop coverage initially as the trough enters our area. Have
roughly 20-30 percent chances this morning, weakening with limited
moisture transport and washed out forcing (better west with main
front). It's possible we see just sprinkles or light rain showers
between 12-17z, then a reinvigoration as the actual cold front moves
into the forecast area from 18z-00z. Expect the cold front to be
entering our west around 15-18z timeframe, reaching the central CW
around 20z and then exiting by around 00z-03z. Expect rain and storm
coverage to be pretty isolated-scattered at first, then consolidate
and become more numerous as we get into the late afternoon/evening.
It's possible the storms become more organized just south and east
of our forecast area, which is why SPC did trim the Slight out of
our area, and the marginal back to south of US 24 (mainly east of I
69). That being said, most of the guidance still shows decent
destabilization this afternoon (500-1200 J/kg of surface based
CAPE...the GFS has 1500-2000 in our marginal risk area), and we have
potentially up to 20-30 knots of 0-6 km shear to work with. Still,
mid level lapse rates are fairly paltry, so don't expect severe
storm coverage to be more than isolated (2-5 pm EDT) to maybe
scattered (5-8 pm EDT). Once we lose our daytime heating and the
front exits the area, expect mostly dry conditions (save for some
low chance pops in the far south where the front could linger a
little longer than forecast). Confidence is low in severe weather
potential, but if it does occur, expect damaging winds and heavy
rain to be the primary threats.
Thursday (Independence Day) is a tricky forecast-and models have
struggled with this the past few days bouncing between dry and then
chances for showers/storms, likely because there is uncertainty as
to how far south the cold front from today will make it before
stalling, then if/when/how far it will shift back northward as a
warm front Thursday into Thursday night. Much of the guidance has
the warm front lifting north into Lower MI (From roughly Holland to
Detroit)b by 12-15z Friday morning, and the cold front extending
down from Central WI To IL (much like this morning, actually).
Aloft, flow is fairly zonal for Thursday, and most of the questions
regarding precipitation development revolve around the timing of the
surface warm front lifting north and the passing of mid level
shortwaves. Right now, it looks like the focus is after 2 pm,
especially along and south of US 30 associated with a short wave.
After 8 pm EDT the chances drop off before the main warm front lifts
north, reinvigorating chances into the 30-50 percent range from
2 am into Friday morning. Otherwise, expect variable cloud
cover and highs in the low to mid 80s, with lows falling into
the 60s.
Friday the cold front passes through the CWA from west to east. I
have likely pops in the morning with the warm front lifting north,
then as the cold front drifts eastward focused the highest
chances along it. Expect the front to exit the CWA by 00-03z
Saturday, with a couple of weak troughs moving in overnight as
the main surface low drifts across Lake MI and into Northern
Lower/Eastern Upper MI) through 12z Saturday. With regards to
intensity on Friday afternoon/evening it looks like the better
forcing and instability for severe weather will be just east of
our area, with SPC keeping the Day 3 Marginal risk out of our
area this issuance. Still something to monitor, but I suspect
much is conditional on how the morning evolves with morning
convection. Highs will be in the 80s.
The surface and upper level low centered over Michigan will lift
northeastward into southern Ontario by Saturday afternoon/evening,
with a few trailing shortwaves left behind to contend with. Kept
conditions dry for Saturday at the moment, with most models keeping
precipitation with these waves further north (just north of our
CWA). However, with the shortwave passing during peak heating of the
afternoon/evening, wouldn't be surprised to see a few showers and
storms pop up east of I 69. Highs will be in the upper 70s.
A ridge of high pressure builds in for Sat night-Sunday, with dry
conditions expected until late Sun aft/evening (mainly far west).
Highs will be in the mid 80s. Chances for showers and thunderstorms
persist Mon-Wed as an upper level trough and surface system cross
the Great Lakes. Highs will be in the low to mid 80s. Lows will be
in the 60s.
&&
.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 123 AM EDT Wed Jul 3 2024
A weak cold front will wash out across the area this morning.
Scattered showers and isolated thunderstorms are possible but
confidence in timing and coverage remain too low to include in
the TAF. Better chance for rain at KSBN will be this morning and
models continue to suggest a brief period of MVFR ceilings
behind the front. Better chance for rain at KFWA will be during
the late afternoon but by then better moisture/instability is
shunted to the south and confidence is low that KFWA will see
any rain let alone thunder. Will hold KFWA dry for now and re-
assess with the 12Z TAF's.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...MCD
AVIATION...AGD
Source:
IWX issues Area Forecast Discussion (AFD) at Jul 3, 5:12 AM EDT---------------
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