Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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192 FXUS63 KLOT 261936 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 236 PM CDT Sun May 26 2024 .KEY MESSAGES... - Scattered thunderstorms late this afternoon through mid- evening, some of which could be strong to severe with large hail, gusty winds and possibly a brief tornado. - Threat for a few strong to locally damaging wind gusts with scattered thunderstorms tomorrow afternoon, after about 3 PM. && .DISCUSSION... Issued at 236 PM CDT Sun May 26 2024 Through Tonight: Precip from this morning`s convection has cleared the CWA, with the associated cirrus shield trailing by an hour or two. Low- level temps have quickly responded where clearing has occurred in the southwest CWA. Temps there have risen solidly into the mid 70s while dew points have held steady in the mid 60s. MLCIN has correspondingly completely eroded for roughly the southwest third of the CWA. With pockets of cumulus continuing to grow in this area, convective initiation is probable within the next hour. An initial area of convergence, likely from a small trough axis pinwheeling around an upper-low to the west, appears to be most favorable for initial development from I-39 SSW through the IL River Valley. Additional axes of convergence are lined up into eastern Iowa to along a cold front. Deep-layer shear profiles will be supportive of organized convection across the vast majority of the forecast area, but especially roughly along and east of the I-55 corridor very late this afternoon through early evening. While it is becoming quite likely that storms will develop, potential coverage of convection is less clear given the delayed destabilization this afternoon. At this time, scattered coverage appears to be the most likely scenario versus a solid line of storms. Severe convection with large hail and gusty winds are possible. A gradually veering near-surface wind profile will slowly lower the tornado threat, but with existing axes of convergence (including a lake-enhanced outflow through the Chicago metro) and a slightly slower veering trend farther east could offer localized areas supportive of a brief tornado from the southern Chicago metro and roughly east of I-55. Convection potential should end from west to east late this evening, with dry conditions expected for much of the area overnight. Kluber Monday and Monday night Monday looks to start out on a generally cloudy note. Steep low- level lapse rates will yield west to northwesterly breezes (gusts to around 30 mph) within a well-mixed PBL. The main focus is on the likelihood for scattered afternoon and evening low (ish) topped showers and thunderstorms. While clouds looks to remain fairly expansive through the day, instability is expected to nonetheless build through the day as mid-level temperatures cool in advance of an approach vort max (500 mb temps will be near the 10th percentile for this time of year). MLCAPE values won`t be particularly high, perhaps 500-750 J/kg, but this should be sufficient for shower and storm development as MLCIN erodes. The upstream vort max looks quite impressive across Montana, and this feature will impinge on the region late in the afternoon with attendant height falls and DCVA maximizing after 3 pm. Have boosted PoPs a bit late in the afternoon and in particular across our west (closer to the vort max). Deep layer shear will modestly step up through the day as westerly 500 mb flow increases and looks supportive of some degree of updraft organization. Given the presence of steep low-level lapse rates, this looks like a decent setup for a few strong to perhaps locally damaging wind gusts out of swiftly-moving convective elements. With how cold temperatures will be aloft, suspect thunderstorms will be somewhat slow to diminish through the evening and have held onto chance PoPs through the late evening hours. Carlaw Tuesday through Sunday This discussion remains unchanged from the overnight shift. An upper level ridge axis building across the Rockies early in the week will drive an active belt of enhanced northwesterly flow aloft across the Great Lakes region through Tuesday. Following quickly the heels of Monday`s weather maker, a stronger impulse (currently seen spinning in the water vapor imagery across central Manitoba) will eject southeastward into the western Great Lakes on Tuesday along the eastern periphery of the building upper ridge axis. A chilly late May airmass accompanying this impulse is likely to make Tuesday one of the coolest days of the week. In fact, breezy northwesterly winds through the day, combined with increased afternoon cloud cover could keep temperatures in some parts of northern IL from climbing out of the 60s! There will also be another good shot for scattered afternoon showers and even a few storms as lapse rates steepen under the cold mid-level trough (temps at 500 mb around -20C). Following the eastward passage of this second impulse on Tuesday, the ridge axis over the Rockies will shift eastward, likely becoming centered over the western Great Lakes later in the week. As this occurs, we are looking to see at least a few day period of dry (and rather pleasant) weather from Wednesday through the later part of the week as surface high pressure sets up shop over the Great Lakes region. Mostly sunny skies are expected, and while temperatures will remain in the low to mid 70s for Wednesday and Thursday, readings are expected to rebound back to near 80 for the end of the week into next weekend. KJB && .AVIATION /18Z TAFS THROUGH 00Z TUESDAY/... Issued at 1250 PM CDT Sun May 26 2024 Key aviation messages: - First round of RA ending by 19Z - Increasing scattered TSRA potential late afternoon into the evening, some could be severe - Westerly wind shift late this evening along with MVFR cigs - 30-40% chance for scattered TSRA again Monday afternoon The area of rain will begin to lift north of the terminals over the next hour or so. A lull in the precipitation may occur for an hour or two but signs are pointing toward renewed thunderstorm development later this afternoon and continuing into the evening hours. Accordingly have introduced VCTS for a broader time window for the Chicago area terminals from 22-03Z with targeted shorter TEMPO groups for TSRA. Any storms that develop will have the potential to become severe. Wind directions will favor an easterly direction this afternoon then southeast by late afternoon/early evening. A cold front will then swing through the area this evening, earliest at RFD, latest at GYY turning winds west northwest. The timing of this wind shift will be refined with later updates and may arrive a bit earlier than currently advertised in the TAFs depending on how quickly thunderstorms exit to the southeast. MVFR stratus is expected to fill in behind the front and persist overnight into Monday morning. Periods of IFR can`t be ruled out. Lastly, toward the end of the 30-hr TAF period there is a 30-40% chance for scattered gusty showers and thunderstorms again Monday afternoon into the evening. Petr && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago