Marine Weather and Tide Forecast for Zion, IL

DISCUSSION
Issued at 256 PM CDT Thu Oct 10 2024

Through Friday Night:

With dew points in the 30s and lower 40s this afternoon and clear skies and light winds tonight, undercut raw model guidance for forecast lows and leaned toward MOS guidance.
Expecting mid to upper 40s (localized lower 40s) outside of Chicago and mid to upper 50s in and near the city.

Friday will be the peak of the warmth in our latest stretch of dry conditions with well above normal temperatures. After a clear and cool start to the day, summer-like warmth is in store for the afternoon. Forecast high temperatures in the 80-86F range coinciding with breezy southwest winds gusting up to 25-30 mph and dew points mixing out to ~45-50F should translate to an elevated risk for a more rapid spread of brush and grass fires.
Consider postponing any planned outdoor burning and use plenty of caution when disposing of smoking materials.

A fairly stout backdoor cold front will shift south across most of the area Friday night, the first sign of the impending notable cool-down coming later in the weekend. Breezy north- northeast winds north of I-80 behind the front will be strongest near the lake, with gusts up to 25-35 mph.

Saturday through Thursday:

The front will become quasi-stationary across our far southern CWA on Saturday, separating seasonably mild conditions (60s and 70s) I-80 and north/coolest closer to the lake from one more day of summer-like upper 70s to lower 80s well south of I-80.

Recent model guidance cycles have varied run to run regarding column moisture availability mid day Saturday through the evening. A robust short-wave trough over the northern Great Lakes will spread mid-level height falls across the lingering elevated frontal zone north of the quasi-stationary front. In the 12z cycle, there was a trend back toward sufficient moisture for scattered showers developing, with possibly even a few isolated embedded thunderstorms in the evening, for the northeast half or third or so of the CWA Also contributing in this setup should sufficient moisture materialize will be the tightening thermal gradient aloft (frontogenesis) and fairly steep mid-level lapse rates. For this afternoon's issuance, PoPs peaked in the 30-40% range Saturday evening.

A stronger reinforcing cold front will force the original stalled frontal zone southward on Sunday, knocking temperatures down inland about 5-10 degrees vs. Saturday. Breezy northwest winds behind the front will gust up to 30-35 mph. Looking at a favorable thermodynamic setup for lake effect showers downwind of Lake Michigan Sunday night, primarily for northeast Porter County and points east. Aside from the lake effect potential, Sunday night will be chilly with lows in the 30s and 40s and gradually subsiding northwesterly breezes adding to the chill.

A final even more pronounced push of cool air will arrive on Monday behind yet another reinforcing cold front. Mid-level impulses pivoting around the western periphery of deep troughing over northeast North America may support the development of isolated to scattered showers Monday afternoon. Forecast highs are only in the mid to upper 50s! An even more favorable thermodynamic setup for lake effect showers is probable Monday night, with a prevailing 340-350 deg wind direction favoring Lake and Porter Counties down to near or just south of the Kankakee River.

The bigger story for the rest of the area (outside of Chicago)
is the likelihood of the first good frost and localized freeze setup, as low temperatures dip into the lower to mid 30s both Monday and Tuesday nights. Barring a big change in the setup, or more cloud cover, frost/freeze headlines are a decent bet.
Tuesday's highs will only be in the lower to mid 50s, albeit with plenty of sunshine underneath surface high pressure. Medium range indicators favor a return to above normal temperatures and dry conditions mid to late next week and beyond.

Castro

AVIATION /00Z TAFS THROUGH 06Z SATURDAY/
Issued at 642 PM CDT Thu Oct 10 2024

Key messages:

- Southwesterly gusts to 20-25 kts during the daytime Friday

- Northeasterly wind shift behind cold front Friday night

Initially easterly winds under 10 kts will veer to a southwesterly direction over the course of the night. These southwesterly winds should pick up and start gusting to around 20-25 kts by the late morning before subsiding again by Friday evening. Towards the very end of the current 30-hour TAF period for ORD and MDW, a cold front is then expected to produce a northeasterly wind shift.

Otherwise, VFR conditions are expected to prevail with increasing high-level cloud cover during the latter half of the TAF cycle.

Ogorek

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