Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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686 FXUS63 KLOT 160713 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 213 AM CDT Mon Sep 16 2024 .KEY MESSAGES... - Hot and dry conditions will prevail through the weekend. - 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 213 AM CDT Mon Sep 16 2024 Through Sunday: We remain locked in a doldrums between aggregate upper-level troughing across the western United States and expansive Rex blocking over the Ohio River Valley. Persistence is the way to go in this regime, favoring highs today through Wednesday in the upper 80s to around 90 and overnight lows in the upper 50s to lower 60s. Daily lake breezes will keep shoreline locations some 5 to 10 degrees cooler during the afternoon and evening hours. Lobes of dry air originating from the Ohio River Valley will propagate into our region today through Wednesday, leading to very low humidity levels (relative humidity of only 20 to 30% each afternoon). The exception will be in the wake of the aforementioned lake breezes, where locally higher humidity levels will prevail (dew points over Lake Michigan are in the low to mid 60s). Toward the end of the week, an upper-level trough currently propagating over Aleutian Islands of Alaska will dive into southern California while "kicking" the current western US trough northeastward into the northern Plains. At the same time, the Rex block (and associated broad surface cyclonic flow) across the Ohio River Valley will get nudged toward the Atlantic Coast. The net result will be an eastward drift of upper-level ridging toward the Great Lakes and the reestablishment of a feed of low-level moisture from the Gulf of Mexico toward the Upper Mississippi River Vally. For this reason, will advertise rising humidity levels by this weekend with a continuation of above- average temperatures in the mid to upper 80s. Prospects for widespread, soaking rainfall currently look slim to none through the weekend as upper-level forcing remains focused to our west. So, when will it rain again? Conceptually, would have to think that the elongated upper-level jet streak currently stretching over central Russia will intensify and shift eastward over the Pacific Ocean toward the end of the week, causing the upper-level pattern across the US to become more progressive thereafter. It is for this reason that multi-run ensemble meteograms of QPF have been showing a return of precipitation chances, as well as a gradual stair-step downward in temperatures, to our area during the last week of September. Time will tell if such a pattern change will take place. Borchardt && .AVIATION /06Z TAFS THROUGH 12Z TUESDAY/... Issued at 1210 AM CDT Mon Sep 16 2024 No forecast concerns through the period. Light east/southeast winds early this morning may become light and variable or calm at times. Speeds will increase back into the 6-9 kt range by mid/late morning. A lake breeze is expected to move inland this afternoon turning winds more east/northeast for the Chicago terminals with speeds perhaps around 10kts for a few hours. cms && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago