Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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236 FXUS63 KLOT 170530 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1230 AM CDT Tue Sep 17 2024 .KEY MESSAGES... - Hot and dry conditions continue this week. - Long-range models advertise a pattern shift during the last week of the month with a return of chances for rain. Time will tell if such a pattern change occurs. && .DISCUSSION... Issued at 221 PM CDT Mon Sep 16 2024 A stretch of incredibly quiet and dry conditions continues, with expanding drought conditions across the area. Regional low-level water vapor imagery this afternoon shows the extent of an incoming plume of exceptionally dry lower- tropospheric air, with brightness temperatures nearing 0 C. Model guidance indicates dewpoints at 700 mb nearing -40 C, and this appears to be corroborated by recent AMDAR soundings. This wedge of dry air is forecast to linger overhead through about Thursday as it will become caught between the tropical circulation in the vicinity of the Carolinas and a digging/amplifying upper low across the Great Basin. Based on how surface dewpoints are responding across northern Indiana within the core of the driest part of this airmass, have undercut blended guidance dewpoints through Thursday afternoon, although not quite to the values advertised by the HRRR/GFS which continue to show general low PM dewpoint biases. Thankfully, light winds will preclude more appreciable fire weather concerns. High temperatures will be a degree or three "cooler" tomorrow compared to today as thickness values decrease a bit. Global/coarse-resolution guidance remains in good agreement towards the end of the week, suggesting that increasing west and southwesterly low and mid-level flow will begin to "fold over" the higher theta-e airmass that`s been collecting across Iowa into our area during the Thursday-Friday time frame. A modest increase in low-level warm advection is forecast to develop across eastern Iowa and far northwest Illinois Thursday night into Friday, and with this, some signal for light QPF across our I-39 locales is evident in today`s 12z runs. That said, forecast soundings across our area suggests any activity that does develop during this time frame will probably tend to fizzle with eastward extent, and have capped any PoPs to slight chances across our northwest locales with this in mind. Beyond this into the weekend and next week, prospects for widespread, soaking rains continue to look pretty slim as the deepest moisture and more active southwesterly flow looks to remain just to our west. Carlaw && .AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 1230 AM CDT Tue Sep 17 2024 No significant forecast concerns through the period. Light east winds will likely become calm for many locations early this morning then increase into the 5-8kt range mid/late morning. A lake breeze will move through the Chicago terminals this afternoon with speeds likely around 10kts. Easterly winds will diminish to 5kts or less this evening, possibly becoming light and variable by early Wednesday morning. Some shallow ground fog or patchy fog may develop early this morning and again late Tuesday night into Wednesday morning. Favored areas for early this morning appear to be across far northeast IL into southeast WI. Not expecting anything widespread nor at the terminals. cms && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago