Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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123 FXUS63 KLOT 271815 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 115 PM CDT Thu Jun 27 2024 .KEY MESSAGES... - Today will be beautiful with highs in the low to mid 70s, low humidity levels, periods of sunshine, and a northeasterly breeze. Cooler conditions can be expected along the lakeshore. - Dangerous swimming conditions will prevail at all Lake Michigan beaches throughout the day. - Thunderstorms are expected Friday night into Saturday, with a conditional severe weather threat areawide late Friday night and generally southeast of I-55 Saturday afternoon. && .DISCUSSION... Issued at 253 AM CDT Thu Jun 27 2024 Through Friday: A surface high pressure system will continue slowly meandering through the Great Lakes and deliver a spectacular late June day. Mostly sunny skies, low humidity levels, a northeasterly breeze, and seasonably cool highs in the mid to upper 70s will prevail. Closer to the lakeshore, onshore flow will hold highs in the mid to upper 60s. The only forecast element today worthy of additional explanation today is waves at lakeshore beaches. This afternoon, the center of the surface high pressure system is expected to be located in Lower Michigan. Meanwhile, the difference between the marine and land airmasses will grow to around 10 or 15 degrees. As a result, the low-level pressure gradient along the southern tip of Lake Michigan should become locally packed and support a continuous feed of sustained 15 kt winds. Waves thus appear poised to remain between 3 and 4 feet through much of the afternoon across the southwestern section of Lake Michigan. For this reason, felt it would be prudent to extend the Beach Hazards Statement through 10 pm tonight from northern Cook to Porter counties. Tonight, winds will turn southwesterly in response to the development of and eastward movement of aggregate lee pressure troughing in the Plains. Clouds will thicken as upper-level vort maxes approach from the west. Overnight lows should range from the upper 50s to lower 60s (which would make for the coolest nighttime temperatures since around June 14th or 15th). Tomorrow, several upper-level shortwaves will pass through the Great Lakes ahead of a more substantial upper-level trough propagating through the northern US. With forecast soundings depicting a deep (10kft+) layer of dry air through the morning hours, any approaching radar echoes should be largely virga with perhaps a 10-20% for a few sprinkles making it down from time to time. By early afternoon, top- down saturation should allow for occasional scattered showers. With that in mind, tomorrow afternoon does not look like a washout. In fact some areas may remain completely dry. Meager mid-level lapse rates will preclude a mention of thunder in our forecast through at least Friday evening. Borchardt Friday Night through Wednesday: Strong low-level moisture transport below a plume of modest mid- level lapse rates across the mid and Upper-Mississippi River Valley will advect toward the area Friday night. Low-level WAA/isentropic ascent and strong effective shear suggests a threat for a few strong to severe elevated storms with large hail late Friday night through daybreak Saturday. A cold front approaching on Saturday will gradually end thunderstorm chances from northwest to southeast through the day. Impressive mid- level flow for late June will yield a kinematic environment favorable for discrete supercell structures with large hail congealing into multicell clusters with damaging wind across primarily the southeast half of the CWA Saturday afternoon. This scenario will be conditional upon the absence of any upstream convective debris Friday night as well as any further slowing of the frontal speed. Finally, 2"+ PWATs advecting into the area Friday night into Saturday will support a localized flash flood risk, though recent forecast trends showing a more progressive pattern during this window have limited a more expansive flood risk as this time. A mid-level ridge and broad surface high will drift eastward across the Great Lakes region Sunday and Monday, promoting dry and seasonably cool conditions under mostly clear skies. Modest mid-level lapse rates and higher low-level moisture will advect toward the mid-Mississippi River Valley on Tuesday ahead of a couple fast-moving mid-level waves within the western flank of the departing ridge. While current expectations are that forcing will out-run a more favorable low-level moisture environment Tuesday afternoon and evening, a severe thunderstorm risk exists into at least the northwest half of the CWA if low- level moisture arrives earlier than currently forecast. A trailing cold front may then stall somewhere between the forecast area and Ohio River Wednesday into Independence Day, supporting generally chance PoPs for showers and storms in this period. Kluber && .AVIATION /18Z TAFS THROUGH 00Z SATURDAY/... Issued at 1255 PM CDT Thu Jun 27 2024 VFR conditions are expected to continue into tonight as clear skies give way to BKN250 cloud cover generally after 00z this evening. High cloud cover should remain into tomorrow morning, slight decreasing in height to around BKN090 to BKN100 by the morning hours on Friday. Toward the afternoon hours, 30% chances for showers and perhaps a rumble of thunder or two will spread in from west to east, generally reaching the Chicagoland area in the late afternoon to early evening tomorrow. Winds will generally by northeasterly this afternoon and will gradually come around to southeast by dawn, and then south southwest by Friday afternoon. Winds willl increase in the late morning and remain elevated into the evening with gusts to around 20 knots. NWS Chicago && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Beach Hazards Statement until 4 PM CDT this afternoon for ILZ006-ILZ103-ILZ104. IN...Beach Hazards Statement until 4 PM CDT this afternoon for INZ001-INZ002. LM...Small Craft Advisory until 3 PM CDT this afternoon for the IL and IN nearshore waters. && $$ Visit us at weather.gov/chicago