Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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222 FXUS63 KLOT 190528 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1228 AM CDT Thu Sep 19 2024 .KEY MESSAGES... - Summer-like daytime warmth continues through Saturday (last day of astronomical summer!) - Potential for isolated to widely scattered showers and thunderstorms late Thursday night into Friday with a cold front. - Chances for more widespread rain return Sunday into early next week, though extent of drought relief is uncertain. && .DISCUSSION... Issued at 200 PM CDT Wed Sep 18 2024 Through Friday: The broad area of high pressure over the eastern Great Lakes will continue to promote dry and summer-like conditions through Thursday. Therefore, expect high temperatures to once again top out in the mid to upper 80s Thursday afternoon with overnight lows in the mid-50s to lower 60s. Additionally, the combination of dry conditions and warm temperatures will also allow dew points to mix down into the lower 50s on Thursday resulting in afternoon humidity values in the 25 to 35 percent range. Given that winds are expected to be light (speeds generally under 10 mph) the threat for fire weather concerns appears to be low, but caution should be exercised with any burning due to dry fuels which could yield quick fire starts. Heading into Thursday night, rain chances will gradually begin to increase from west to east as a cold front, currently over the central Plains, moves in. However, the antecedent dry conditions and aforementioned dew points do look to limit the coverage of showers, especially with eastward extent, as the drier air will be working against the limited moisture along the front. That said, there could be some locations that don`t pick up much in the way of rainfall. Though, rainfall totals are only expected to be in the 0.10 to 0.20 inch range for those that do see rain; which will do little for our worsening drought. Additionally, the limited moisture also looks to hamper the destabilization Friday afternoon which means that thunder coverage will likely be very isolated but did maintain a slight chance (around 20%) mention for thunder in the off chance a more robust core can materialize. Nevertheless, showers and any storms are expected to conclude by Friday evening as the front exits to the east. Yack Friday Night through Wednesday: In the wake of Friday`s front, a slightly drier air mass is expected to filter into the area Friday night into Saturday. That, in combination with modest height rises in the wake of Friday`s weak shortwave will keep rain chances low and mainly sub-mentionable Friday night through Saturday evening. By Saturday night and Sunday, a longwave trough will emerge east of the Rockies across the Plains states. A weaker, more subtle shortwave trough may precede this larger trough and could bring with it a threat of some showers and possibly isolated storms later Saturday night into Sunday, but there is spread in guidance in the handling of this more subtle feature leading to lower than average confidence. While there is some threat for beneficial rainfall this weekend, it is also plausible that many areas squeak out a mostly rain-free weekend. The Plains trough is progged to phase with northern stream trough as they both progress east into the Mississippi Valley Sunday night into Monday. While by no means a slam dunk with timing and magnitude of phasing still uncertain, this system could be the area`s best chance of some much needed rainfall across most of the area through Monday night (40%+ chance PoPs). Friday night will be relatively cool with lows in the mid-upper 50s outside of Chicago (low-mid 60s in the city). Daytime high temperatures will remain unseasonably warm this weekend with highs in the 80s away from the lake on Saturday (with low humidity due to dew points mixing out into the 50s), and mid 70s to lower 80s on Sunday (with higher humidity/dew points in the 60s). In the wake of Sunday night/Monday trough, somewhat cooler/more seasonable temperatures (highs in the 70s) are expected during the early to middle part of next week for the first work week of astronomical fall (autumn equinox is at 7:43 AM CDT Sunday). Castro/Izzi && .AVIATION /06Z TAFS THROUGH 12Z FRIDAY/... Issued at 1228 AM CDT Thu Sep 19 2024 Forecast concerns include... Lake breeze/southeast wind shift mid/late afternoon. Chance of showers early Friday morning with thunder possible. Light/calm winds overnight will become south/southwest after daybreak with speeds into the 6-10kt range. A lake breeze will develop by early afternoon and there is uncertainty for how far inland the lake breeze will move, likely reaching both ORD/MDW though only medium confidence for timing, which could be late afternoon at ORD. Even if the lake breeze doesn`t make it to ORD or MDW, winds will shift back to southeast by early this evening across the entire area. Winds are then expected to slowly turn back to the south/southwest early Friday morning. There will be a chance of showers early Friday morning, likely just after 06z at RFD and in the predawn hours for ORD/MDW. Opted to add prob mention for the 30 hour ORD/MDW tafs though whatever precipitation does develop may be dissipating as it moves across northeast IL. There is also a small chance for an isolated thunderstorm, with the best chance, though still low, across northwest IL and at RFD. Fog potential early this morning looks rather low with perhaps the best chance across far northeast IL and into southeast WI. Not planning any fog mention for the terminals at this time. cms && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago