Evanston, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

677
FXUS63 KLOT 130530
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1230 AM CDT Fri Jun 13 2025

.KEY MESSAGES...

- Scattered showers and possibly a couple of thunderstorms
  Friday into Saturday, especially south of I-80.

- Very warm and humid with occasional chances for showers and
  thunderstorms early to mid next week.

&&

.DISCUSSION...
Issued at 255 PM CDT Thu Jun 12 2025

Through Friday night:

Weakening surface boundary is draped across northern IL, but
outside of areas influenced by the marine layer, there is very
little theta-e difference across the boundary. We are seeing
a modest, albeit rather mushy, cumulus field developing near and
south of this weak boundary beneath the cirrus canopy. Aided by
little more than some weak low level convergence, the chances
for any showers developing late this afternoon appears low.
Opted to hang onto slight chance pops late this afternoon until
around sunset on the off chance a couple of showers manage to
develop.

Upper low over the southern Plains is still progged to devolve
into an open wave as it moves slowly northeast toward the mid
Mississippi Valley. Scattered showers could encroach on our
far southern late tonight with the shower chances spreading
slowly northward Friday morning. Still appears the best chances
of rain will be south of I-80, though some showers can`t be
ruled out farther north.

Any filtered sunshine through the cirrus shield Friday
afternoon could theoretically allow for some weak boundary
layer destabilization. Nearly moist adiabatic mid level lapse
rates will further limit destabilization, but cannot rule out
some isolated thunderstorms Friday afternoon, with chances
increasing the farther south. Some scattered showers could
continue into Friday night as the slow moving system continues
to meander ever so slowly east-northeastward across the region.

- Izzi

Saturday through Thursday:

On Saturday, the open wave (remnant closed low) to our south and
its associated weak surface low pressure reflection will track
toward the central Ohio Valley. With this farther south low path
and stabilizing influence of high pressure over the Great Lakes
region, shower chances have trended markedly southward over the
past few model cycles. There should still be some shower activity
south of I-80, but probably more isolated to widely scattered in
nature, with highest coverage (55-60% PoPs) generally south of
US-24. Better mid-level moisture being focused down near the
surface low (and 700-500 mb RH will be trending drier PM hours)
and already sub-marginal (5.5C/km or less) mid-level lapse rates,
there`s only a slight chance for a few isolated embedded
thunderstorms where measurable precip may occur. High
temperatures inland of Lake Michigan will range from the upper
70s to mid 80s inland, warmest west/northwest due to increasing
sunshine and "coolest" southeast due to thicker clouds. Dew points
generally in the 60s will translate to moderate humidity levels,
common for mid June.

Following a quiet and seasonable Saturday night into Sunday
morning, a convectively modified impulse (possible MCV) may move
toward the mid MS Valley by early evening. This could conceivably
bring some threat for showers and isolated thunderstorms to
far interior sections in the afternoon, particularly near/west of
I-39 in north central/NW Illinois. With a sharp west-northwest to
east-southeast instability gradient resulting in limited
instability locally, suspect that the 12z ECMWF/EPS (ECMWF
Ensemble) cycle was too bullish with the convectively driven QPF
footprint. The 20-30% PoPs well away from the lake, highest
northwest, in our official forecast, appear appropriate for now in
light of the rest of the guidance being less bullish/farther west
with their QPF output than the EC. Expecting high temperatures a
couple degrees warmer on Sunday vs. Saturday, in the mid to upper
80s away from the lake, along with muggy conditions, especially
south of I-80 (near 70F dew points). Temps may be able to climb
a couple degrees lakeside as well, but still notably cooler.

Looking ahead to next work week, we`ll enter into a classic
summer-time pattern with very warm (aside from any lake cooling)
and humid conditions and occasional shower and thunder chances.
Modest forcing and weak flow aloft Monday-Tuesday should translate
toward largely diurnally driven convection (peak coverage in the
afternoon-evening) and the main thunderstorm threats being
lightning, downpours, and localized gusty winds. Despite the day 6
lead time, there`s a decent signal in the ensemble guidance for a
stronger synoptic system and associated cold frontal approach
into the region in the Wednesday-Wednesday night timeframe. This
may be a period to watch for organized convection and a threat for
strong to severe thunderstorms in the region. If the Wednesday-
Wednesday night timing comes to fruition, then Thursday would
likely end up mainly dry and slightly cooler/less humid in the
wake of the cold front passage.

Castro

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 1230 AM CDT Fri Jun 13 2025

Key Aviation Messages for the current TAF period:

- 30 percent chance for showers during the afternoon and early
  evening

- Potential for MVFR cigs after 00Z

This evening`s shower chances have petered out. High clouds
are still seen on satellite, but VFR conditions will prevail
through Friday. Winds remain out of the northeast and are
weakening, potentially becoming light enough to be variable at
select sites around the region.

No major changes to the shower chances in the forecast for
Friday. As an upper level wave moves over the area, it brings
the chance for showers. But weaker forcing lowers confidence in
exact coverage which could range from isolated to widely
scattered. Best chances look to be around KGYY and to the south
during the afternoon, but could linger into the evening and
spread northward depending on the movement of the wave. An
eventual VCSH or TEMPO for -SHRA mention may be needed with
later updates.

Through much of the day, winds are expected to be at or less
than 10 knots. Guidance is suggesting southeasterly winds in the
morning ahead of the wave, then slowly becoming more easterly
and eventually northeast Friday night.

Guidance is in slight disagreement with cig trends overnight
into Saturday morning. As that wave weakens in the evening,
there was enough confidence to introduce MVFR cigs into the TAF
(though lower confidence in timing of the cigs). Some of the
guidance is being very aggressive in the potential for IFR
cigs. But without a lot of agreement, it was only introduced as
a FEW group at this time.

DK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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