Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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498 FXUS63 KLOT 110513 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1213 AM CDT Sat May 11 2024 .KEY MESSAGES... - Quick (an hour or 2) hit of showers, and a few embedded thunderstorms, tonight. - Drying out for Saturday with breezy northwesterly winds gusting up to 30 mph during the day. - Warm with low humidity on Mother`s Day, mainly dry until the evening when a few showers will be possible. - Widespread rain (potential for locally heavy totals) likely on Monday-early Tuesday...Coolest conditions next week on Tuesday. && .DISCUSSION... Issued at 300 PM CDT Fri May 10 2024 Through Saturday night: A quick hitting band of showers will shift southeastward across the area with a cold front later this evening into the overnight hours as a compact and fast moving mid/upper level impulse digs southeastward out of the Arrowhead of MN. The fast movement of this feature will result in only an hour or two period of precipitation at any given location tonight. The best window for this period of rain looks to come in the 9pm to midnight timeframe for northwestern portions of the area (including the Rockford area), 10pm to 1 am timeframe for much of the Chicago metro area, and in the 11pm to 3am time period for southern/southeastern sections of the area. Steepening lapse rates could support a few embedded gusty thunderstorms with this activity tonight, though no severe weather is anticipated. The cold front, and any showers and cloud cover associated with it, will clear the area prior to daybreak Saturday morning. In its wake, northwesterly winds will become gusty (up around 30 mph) for a period on Saturday, though speeds should abate through the afternoon as an afternoon lake breeze push turns the winds onshore across northeastern parts of IL. Partly cloudy conditions during the day will allow temperatures to top out in the upper 60s to around 70, especially for inland areas. However, onshore flow during the afternoon will result in cooler afternoon conditions near Lake Michigan. The forecast for Saturday largely looks to remain precipitation free for much of the area. While this is the case, there is a non-zero threat (up to about a 10% chance) for a few isolated afternoon showers, primarily near the area of enhanced low-level convergence along the lake breeze boundary in northeastern IL. While I would not be surprised to see a couple of these, it appears they would be short lived, and cloud depths would be far to shallow to support charge separation and hence thunder. For these reasons, I have opted to maintain a dry forecast for the time being. Otherwise, expect quiet and mainly clear weather Saturday night. KJB Sunday through Friday: Breezy southwest winds, warm advection, dew points mixing out to the upper 40s to around 50F, and plenty of sunshine will set the stage for a warm Mother`s Day Sunday. Look for highs to reach the upper 70s to lower 80s, albeit with low humidity levels. A weak cold front will approach the area Sunday night. With neutral height tendencies and diurnally unfavorable timing, a few showers and maybe a weakening thunderstorm or two developing over Wisconsin and northeast IA late in the day may be able to drift into far northern Illinois in the evening. 30-40% PoPs are focused north of I-80 in the evening and then generally in the 20-30% range overnight when it may very well be primarily dry. It`s unclear if MUCIN will be overcome to support any lightning, though maintained some low thunder chances. Monday into Tuesday, the upper-level wave currently in the process of becoming "cut-off" in the southwestern United States is expected to become "re-absorbed" into the upper-level flow while drifting eastward toward the mid Mississippi River Valley. As the surface low reflection associated with the upper wave drifts northeast, the cold front approaching Sunday night will drift south and take on back-door characteristics on Monday. With forcing from the approaching wave and perhaps the backdoor front, showers and a few thunderstorms may break out Monday morning through midday. Over the last few model cycles, operational and ensemble guidance has come into better agreement in a period of inclement weather with widespread rain/thunderstorms Monday afternoon into Monday evening and overnight. With this increased signal, collaboratively adjusted PoPs into the 75-80% range centered on Monday afternoon, though envision likely (60-70%+) PoPs Monday evening will also trend higher. Seasonably high PWATs of up to 1.5" (150-200% of normal) and slow motion of showers and any embedded thunderstorms may support some locally "hefty" rainfall totals in the 1-2.5" range. The system TROWAL should gradually pivot southeast into Tuesday, drying things out from north to south. It appears the appreciable rain into the daytime hours on Tuesday should primarily be south of I-88 or south of I-80 and likely exiting south by or during the afternoon. High temperatures near normal (low 70s) on Monday, except cooling off near the lake as winds flip onshore in the afternoon, will be decidedly cooler on Tuesday. Looking at low- mid 60s if that inland and likely only mid 50s lakeside with breezy north-northeast winds gusting up to 25-30 mph, strongest near the lake. Wednesday will trend back closer to normal inland but stay cool near the lake with continued onshore flow. The next (uncertain) shower and thunderstorm chances will return Thursday-Friday amidst near seasonable temps (highs in 70s). Castro/Borchardt && .AVIATION /06Z TAFS THROUGH 12Z SUNDAY/... Issued at 1213 AM CDT Sat May 11 2024 A band of showers with embedded thunderstorms and northwesterly wind gusts of 25 to 30 kt will continue moving across the terminals within the first 1 to 1.5 hours of the TAF. Thereafter, winds will settle northwesterly and mid-level clouds will clear. After daybreak, northwesterly winds are expected to quickly increase in magnitude with sustained speeds of 15-20kt and gusts of 25-30kt. A few mid-level clouds (based between 5kft and 10kft) may develop during the afternoon. A dry airmass will facilitate efficient decoupling an hour or two after sunset, leading to light and variable winds. Toward daybreak Sunday, winds will settle on a southwesterly direction and gradually increase to the 5-10kt range. Borchardt && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago