Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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630 FXUS63 KLOT 040602 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 102 AM CDT Tue Jun 4 2024 .KEY MESSAGES... - Isolated showers and storms across northern Illinois into this evening. - Unsettled weather pattern continues through mid-week as showers and storms are expected Tuesday into Wednesday morning. - Warm, moist air continues to bring the warmer temperatures across northern Illinois Tuesday, but cooler temperatures are expected Thursday and Friday behind frontal passage. && .DISCUSSION... Issued at 309 PM CDT Mon Jun 3 2024 Showers and storms have developed this afternoon across northwestern Illinois, as a north-south oriented boundary sits along the mid and upper Mississippi River Valley. Additional development is expected to occur this afternoon through the evening, however it is expected to remain near and west of the I-39 corridor over the next hour or 2, before beginning to shift ne across northern counties of the LOT CWA...north of roughly the I-88 corridor and then I-90 corridor heading into the overnight. Isolated strong to severe storms are possible, however most of the activity is forecast to remain general showers and storms. Heading into the overnight and Tuesday, a low pressure system will deepen across the southern Plains before moving into the Ohio River Valley late Tuesday into early Wednesday. This will lift moisture from the Gulf into the area Tuesday morning into the afternoon, bringing another chance for shower and storm development as instability once again increases across the Midwest. With warm southerly air flowing into the region ahead of this system, expecting showers and storms to rapidly develop Tuesday afternoon (20-22z) and track eastward through evening. A larger upper-level low pressure core situated across central Canada will track eastward Tuesday, trailing an elongated frontal boundary into the central Plains and deep south. As this boundary tracks to the east Tuesday night into Wednesday morning, the chance for a second round of showers and storms will move through the region. The question at hand today was timing of this frontal system, as well as the early convection Tuesday afternoon, this is expected to keep the potential of strong to severe storms at bay overnight Tuesday into Wednesday. Drier weather is forecast to return across the Midwest, as the unsettled weather pattern is finally shifted out of the region during Wednesday. Along with the dry weather arriving Thursday and Friday, models are indicating a break in the summer-like temperatures with highs back in the 70s. The 70s then look to linger into and through the upcoming weekend across much of the area, with some cooler temperatures expected near and along the lakeshore. Chances this weekend for isolated to scattered showers and storms at times could be possible this weekend, however the overall probability remains less than 25% at this time. Baker && .AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 102 AM CDT Tue Jun 4 2024 Main Concerns: - Scattered TS probable near the terminals in the late afternoon. - SHRA with another round or two of TS possible in the evening and overnight. - Wind direction in the late afternoon and early evening. - Lower CIGs likely overnight/early Wednesday. Another challenging convective forecast through this TAF cycle, though confidence is higher in at least one round of TS causing some impacts. Quiet VFR conditions with southerly winds (15-20+ kt gusts by the early afternoon) will persist until 19-20z. Instability will build out ahead of a subtle upper level disturbance lifting northward, which should be enough to kick off widely scattered TS in the late afternoon (~20-24z) in the vicinity of the terminals. While on station impacts can`t be ruled out, TS coverage with this first round appears likely to be sparse enough to warrant current VCTS mention. A stronger upper disturbance will pivot northeastward this evening and early overnight. Expecting TS to be fairly widespread with this in a portion of the ZAU airspace, with the main question being if the higher coverage ends up a bit south of the TAF sites. Went with a PROB30 for this possible second TS window. Finally, a cold front will approach overnight, likely preceded by SHRA and isolated TS (confidence too low for another PROB30 mention). CIG guidance indicates low MVFR to patchy IFR CIGs should develop during this time. Regarding wind direction uncertainty, it`s a bit unclear if south-southeast or south-southwest will be favored at ORD and MDW during the strongest winds this afternoon, so the TAF split the difference. In addition, some guidance indicates a close approach of the lake breeze toward 00z this evening, which will need monitoring. Castro && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago