Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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828 FXUS63 KLOT 141730 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1230 PM CDT Fri Jun 14 2024 .KEY MESSAGES... - Hot and humid conditions next week along with periodic chances for showers and thunderstorms. && .DISCUSSION... Issued at 214 AM CDT Fri Jun 14 2024 Through Saturday: No notable weather is expected in the area through Saturday as surface high pressure will rule over the Great Lakes going into this weekend. Expect seasonably warm temperatures today, along with abundant sunshine and comfortable humidity levels once the residual moisture from last night`s storms is mixed out and shunted southward this morning. A lake breeze will also march inland today and cause high temperatures near the lakeshore to end up being about 10-15 degrees cooler (in the low to mid 70s) than at locations farther inland (low to mid 80s). Saturday looks similarly quiet as we remain on the southwest periphery of the Great Lakes surface high pressure bubble and an upper-level ridge axis begins to slide over the area. High temperatures should be nearly a carbon copy of what they`ll be today, though southeasterly return flow will keep lake cooling efforts focused into Illinois and allow for locales near the northwest Indiana lakeshore to see similar temperature readings to locations that are farther inland. There should be more high-level cloud cover on Saturday compared to today as a result of a subtle shortwave trough cresting the upper-level ridge. Actually wouldn`t entirely be surprised if this cloud deck thickened up enough to support some virga over our northwestern CWA late in the day, but dry air in the low and middle levels of the troposphere should preclude any hydrometeors from actually reaching the ground. Ogorek Saturday Night through Thursday: For Sunday, have held onto some slight chances for showers and storms mainly through midday and north of I-80. Several mid-level disturbances and even a larger-scale shortwave are slated to be in our vicinity, and in the presence of appreciably steep mid-level lapse rates, this could support some shower/storm chances. The main story in the extended remains on the likelihood of building heat and humidity as an anomalously deep upper ridge builds off to our east. There seems to be decent agreement in the general placement of the core of the high at this point, centering across the Mid Atlantic and eventually the Northeast towards the middle and end of next week. This puts us on the western fringes of the primary zone of large scale subsidence and certainly opens the door up for perturbations embedded within the southwesterly flow aloft to be carried across the forecast area. As a result, isolated to scattered storms can`t be ruled out, and these would obviously have an impact on temperatures and dewpoints, at least to some degree. Sunday and Monday may end up being the most uncomfortable days of the stretch as the core of the building high makes its closest approach to the area. There are some significant differences in how guidance is handling afternoon mixing trends within the deepening PBL, however, which is resulting in quite a bit of spread in the high temperature and dewpoint departments. The GFS looks much more like the extended NAM on Sunday with a less mixed boundary layer and much higher dewpoints and lower air temperatures compared to the more deeply-mixing ECMWF, UKMET, and CMC. The differences aren`t necessarily trivial either, with dewpoint and air temperature differences near 10 degrees at times. From a heat index perspective though, this may not result in much of a material difference as heat indices would still even out in the mid to upper 90s on Sunday, and then a few degrees higher than that on Monday with a smattering of 100 degree readings in play. For now, elected to maintain warmer air temperatures and lower dewpoints, in line with the blended offering and the ECMWF, UKMET, and CMC output. This results in uncomfortable conditions, but heat indices largely staying under advisory criteria (105 degrees) on Monday. Muggy and warm conditions will continue through the middle of the week, although likely not quite to Monday`s levels as the the core of the high builds further east into the Northeast US. As mentioned previously, diurnally-driven, isolated pulse convection will be possible given the heat/humidity Monday and Tuesday afternoons. By Wednesday/Thursday a synoptic front will approach from the northwest, which may help to focus a bit more in the way of shower and storm coverage. Carlaw && .AVIATION /18Z TAFS THROUGH 00Z SUNDAY/... Issued at 1230 PM CDT Fri Jun 14 2024 A lake breeze has flipped winds to the northeast at KORD, KMDW, and KGYY and will get to KDPA between 19Z to 20Z. There remains a chance for northeast winds at KRFD this afternoon, but confidence is lower with the uncertainty if the boundary can hold itself together that far inland. Gusts have already been observed 15 to 20 knots, but they are fairly sporadic so while they may continue occasionally, it was kept out of the TAF. Other than some light cumulus development both this and tomorrow afternoon, VFR skies are expected through the TAF period. Winds will turn to the southeast Saturday morning. Once again it will not be ruled out for occasional gusts up to 20 knots in the late afternoon Saturday, but confidence in persistence was too low to add to the TAF. DK && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago