Area Forecast Discussion
Issued by NWS Chicago, IL

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000 FXUS63 KLOT 241139 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 639 AM CDT Mon Oct 24 2016 .SHORT TERM... 306 AM CDT Through tonight... Not much to talk about in the short term. Bank of stratus over WI has been steadily moving SSE toward N IL early this morning, but the area is eroding on all flanks and would anticipate this trend continuing with just a period of some SCT-BKN cloudiness this morning, especially eastern CWA. Otherwise, look for diminishing north winds this morning with a lake breeze probable this afternoon but with no significant cooling as area-wide temps should be in the 50s today. Clear skies initially and calm winds should allow for a quick drop in temps this evening before leveling off a bit overnight as mid-high cloudiness increases late. Izzi && .LONG TERM... 306 AM CDT Tuesday through Sunday... In the longer term, first forecast concern is with shortwave trough forecast to traverse the region mid-week. The 00Z GFS and ECMWF are in pretty good agreement in tracking sfc low across our CWA, largely following the I-80 corridor. There is still spread in the models, with NAM farther north (though with little ensemble support), and GEM a bit farther north. If GFS/ECMWF verify then stiff east winds, low cloudiness, and steady rain would likely result in temps holding in the 40s roughly from I-88 northward (though probably a bit warmer near the lake). A fairly large temp gradient is expected near the track of the low, with GFS/ECMWF favoring 60s in our far southern counties. Should the farther north solutions pan out, then highs would be warmer farther north with rain more spotty. Didn`t make any changes to the model blend that we initialize the gridded database with, however, if the GFS/ECMWF remain steady with their track then later forecasts would need to sharped up the temp gradient across the CWA cooling highs north and warming them a bit far south. No significant push of cold air in the wake of this system with dry conditions and temps near seasonal norms Thursday. Late in the week we continue to see substantial run-to-run volatility in the medium range models. Earlier runs, particularly of the ECMWF, took shortwave energy5 off the west coast and phased it some with northern stream. Latest run hang the west coast shortwave back and now feature a dominant northern stream shortwave, with resultant sfc much farther north. Assuming this latest trend in the models were to verify, then Friday would likely be a breezy/windy and unseasonably warm day with just a small chance of scattered showers/T-storms along the cold front Friday night. Given the volatility of the models in this time range, opted to just leave the blended model cocktail alone in the grids. Latest guidance would support highs similar to what we saw Sunday (mostly low 70s), followed by a quick chance of sctd convection along a front, then dry conditions the remainder of the weekend with more seasonal temps. Once guidance locks onto a solution, some respectable changes to the forecast we`re putting out this morning are quite possible. Izzi && .AVIATION...
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For the 12Z TAFs... Expect VFR conditions for much of the forecast period as high pressure builds across the region. There is a small window when MVFR ceilings could occur this morning, but this should remain brief. Winds will likely continue to vary around due north this morning, starting just slightly west of north. Speeds may approach the 10-12 KT range closer to mid morning but this will likely be a short duration window of a couple of hours. Also expect the winds to become more north northeast by mid to late morning. Rodriguez
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&& .MARINE... 259 AM CDT Stronger northerly winds still in place early this morning as deep low pressure is situated over southeast Canada and as high pressure builds east from the Northern Plains. This will likely keep winds elevated slightly longer today and have adjusted the forecast to reflect the likelihood of 30 KT persisting for a time today. This will impact the nearshore waters as well, with longer duration of elevated waves today. Did adjust the small craft advisory with these changes, with hazardous conditions for small craft continuing longer today. High pressure will then move across the lake later today into tonight, with speeds diminishing. Next forecast concern still remains with expected low pressure to move across the region by midweek. This still looks to provide a period of gales across the lake during this time. Will need to continue to monitor this period for the potential for these higher winds, and especially as there is some variability with the exact track of the low that could impact highest winds. Rodriguez && .LOT WATCHES/WARNINGS/ADVISORIES...
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