IWX issues Area Forecast Discussion (AFD) at Jul 21, 7:03 AM EDT514
FXUS63 KIWX 211103
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
703 AM EDT Mon Jul 21 2025
.KEY MESSAGES...
- Hot and humid conditions will develop Wednesday and persist
through Friday with highs in the lower 90s and heat indices
from 100 to 105.
- Shower and thunderstorm chances return for the upcoming
weekend.
- There is a moderate swim risk for Lake Michigan beaches in
Berrien County, MI and La Porte County, IN for this morning.
Breaking waves and currents are expected. If visiting the
beach, pay attention to beach flags and heed the advice of
lifeguards or beach patrol. Conditions will improve by late
morning.
&&
.DISCUSSION...
Issued at 341 AM EDT Mon Jul 21 2025
Axis of showers and storms has pushed well south of the area
along a stationary boundary, with another diffuse boundary
pushing south through the CWA with decreasing dewpoints. Some
patchy, shallow ground fog has been noted from time to time at a
few locations, mainly in portions of lower MI and NW Ohio. Have
added a mention of patchy fog in the grids through sunrise and
will watch if the fog becomes more widespread or persistent for
any possible headlines.
500 mb heights will slowly increase over the next couple of
days, peaking late Wed into Thursday (594-596 dm). This will
usher in a brief return to high heat indices with the worst
conditions expected Thursday. The fine balance of temperature
and dewpoints will be key in just how high we can get for heat
indices, as dewpoints in the mid 70s or higher can limit air
temperatures somewhat (around 90 to low 90s vs low to mid 90s).
Those few degrees can make all the difference wrt advisory vs
warning level values. Coordination took place with offices to
our west and south on possible headlines. Appears that criteria
should be met Thursday everywhere for an advisory, possibly in
the W and N on Wednesday. Will continue to message in HWO and
social media.
As for precipitation chances, the increasing ridging will usher
in very warm 700 mb temps (11 to 13 C), effectively capping the
atmosphere and preventing any convection into Thursday. Model
blend has some slgt chc to chc pops NW Thursday night, then
increasing to likely in some areas Friday as the ridging breaks
down somewhat and the first in a series of disturbances ridge
the periphery of the ridge. Likely pops may be a touch high, but
will leave alone for now. Pops will linger through the remainder
of the period, mainly diurnally driven. The upper level ridge
will build across the Plains, with heights even higher that the
upcoming heat waves (596 to 599 dm). Our area will be oriented
in a NW to SE gradient on the edge of the ridge, which could set
the stage for thunderstorm complexes to develop upstream and
track into the area. Something to watch later on down the road.
&&
.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 653 AM EDT Mon Jul 21 2025
Predominantly VFR conditions at the TAF sites outside of early
this morning where KFWA is currently VLIFR (1/4SM, OVC003).
Expect this to clear up within the next hour or two, so beyond
15z expect some mid-high level clouds associated with a system
along the stationary front to the south.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Fisher
AVIATION...MCD
Source:
IWX issues Area Forecast Discussion (AFD) at Jul 21, 7:03 AM EDT---------------
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