Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/07/19

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
623 PM CDT Tue Aug 6 2019 .SHORT TERM... 310 PM CDT Through Wednesday night... Through Tonight: Pesky low clouds are finally scattering this afternoon, allowing for temps to warm. However, despite lingering moisture dew points in the middle to upper 60s, there are still very weak mid-level lapse rates over the area, as seen on latest aircraft soundings from MDW. Thus, suspect the weak to moderate uncapped SB/ML CAPE shown on SPC mesoanalysis remains a bit overdone. Latest visible satellite suggests this to be the case, with any towering Cu in the Cu field well northwest of the CWA. With the main forcing for convection well east of the area, little/no low-level convergence inland, and weak lapse rate environment not expected to improve much through early evening, it continues to appear coverage of any showers through early evening will be quite low/isolated to perhaps widely scattered. Weak short-wave(s) moving overhead would be the source of larger scale forcing, which did kick off a few showers well north of us over southwest Wisconsin in the better Cu field. One possible area of focused convergence and perhaps a few showers would be on the synoptically enhanced lake breeze moving inland through early evening, from roughly just south of latitude of downtown Chicago to points south. For areas well inland, best chance for isolated development looks to be mainly I-80 and south though can`t completely rule it out north. Thunder wise, given aforementioned weak forcing and convergence (aside from near lake breeze) and weak mid-level lapse rates limiting destabilization, think chances are isolated/slight chance at most. Turning to later tonight, clear to partly cloudy skies and light to calm winds should enable low temperatures outside of Chicago to cool to at or below current dew point temperatures. Low dew point depressions could support patchy fog development, so added patchy fog mention in the grids after midnight through early Wednesday outside of Chicago. Doesn`t appear fog would become widespread, but some patchy visibility under 1 mile can`t be ruled out in favored low-lying areas. Wednesday-Wednesday Night: The rest of the daytime hours Wednesday should be primarily dry and warm. Forecast soundings indicate good mixing potential with steady west-southwest to westerly winds. As has been the case in the drier pattern we`ve been in lately, suspect the afternoon dew points shown on the NAM and GFS will be well overdone and likely closer to the better verifying ECMWF, so expectation is mixing out to the upper 50s over the city and lower to perhaps mid 60s elsewhere. Progged 925 mb temps in anticipated well mixed air mass should support highs in the mid to upper 80s (85-89), with upper 80s potentially widespread. With no low-level/surface convergence, and maybe a weak wave moving over the area in the afternoon, would expect mostly developing Cu and little chance of shower/t-storm development (except maybe far N/NW CWA late afternoon). Convective trends Wednesday evening-night are uncertain. A cold front will be approaching at an unfavorable diurnal time and instability should be fairly minimal with continued weak mid-level lapse rates. It looks like slightly better chance for widely scattered showers and storms will be north of I-80 closer to glancing blow from short-wave forcing over Wisconsin. Confidence on any strong-severe storms is low and if any risk, would most likely be for gusty/strong winds in parts of far north/north central IL where SPC has a level 1 (Marginal) risk. Low chances for showers and perhaps storms may then swing southeast after midnight. Castro && .LONG TERM... 310 PM CDT Thursday through Tuesday... Drier and slightly cooler air will filter in behind the front on Thursday, so should be a pleasant day for this time of year with highs in the lower to mid 80s inland and upper 70s to around 80 lakeside. Only slight chance PoPs PM hours are well south of IL and Kankakee Rivers closer to better moisture and instability near the front. After a comfortable Thursday night, Friday will be similar to Thursday if maybe a degree or two cooler and again feature a bit cooler temps lakeside. Relatively benign northwest flow aloft expected over the region through the upcoming weekend with continued comfortable dewpoints will spell little threat of organized rain. Some of the 12z guidance, namely the ECMWF and Canadian, introduced the potential for building heat by Sunday, so mid 80s in official forecast would be underdone if this occurs. Indications in the medium range guidance point toward a warm and humid and more active stretch early next week as disturbances ride over northern periphery of mid-upper ridge centered over the southern Plains and mid South. Castro/Izzi && .AVIATION... For the 00Z TAFs... VFR conditions are expected through the period. At 00Z TAF issuance, a few -SHRA near RFD will dissipate over the next couple hours. Meanwhile, a lake breeze boundary has stalled near ORD and may oscillate over the terminal for the next hour before pushing farther inland and weakening after sunset. Light and sometimes variable winds are then expected tonight ahead of steady W winds on Wednesday. There is a low chance that an isolated TS could affect ORD/MDW near the very end of the period (03-06Z Thursday), but decided to keep the TAF dry for now given the high uncertainty. Kluber && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. 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