Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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548 FXUS63 KLOT 080955 CCA AFDLOT Area Forecast Discussion...CORRECTED National Weather Service Chicago/Romeoville, IL 355 AM CST Fri Nov 8 2024 .KEY MESSAGES... - Patchy fog possible this morning, mainly in areas outside of the Chicago metro. - Brief period of showers Saturday evening into early Sunday morning followed by breezy winds Sunday afternoon. - Another storm system may result in another period rain around mid-week. && .DISCUSSION... Issued at 239 AM CST Fri Nov 8 2024 Through Saturday: Clear skies overnight have allowed surface temperatures to cool to or near the surface dew points at most of our ASOS/AWOS sites away from the heart of the Chicago metro early this morning. Considering this and the fact that we still have several hours of darkness to go, we will probably see some fog develop before sunrise. That said, low-level flow appears that it may remain elevated just enough in this relatively dry air mass to prevent widespread dense fog from developing, and forecast guidance on the whole is not particularly excited about that possibility as well, so thinking that we`ll likely be able to get by without a Dense Fog Advisory. Still, at least patchy dense fog development cannot be ruled out, so we`ll have to continue to monitor observational trends over the next few hours. Tranquil weather conditions are otherwise expected today with surface high pressure in the region. High temperatures overperformed model guidance by a few degrees yesterday, and would expect a similar story to play out today in the same air mass with the passing cirrus not likely to inhibit solar insolation as much as the HRRR and RAP, among other models, would suggest. Thus, have nudged forecast high temperatures upwards a smidge with most of our forecast area likely to see highs reach or eclipse the 60 degree mark. The mostly clear skies should then afford us another seasonably cool night with low temperatures in the low-mid 40s favored across much of the Chicago metro and mid-upper 30s favored elsewhere. Upper-level cloud cover will be on the increase going into Saturday as a closed-off upper-level low slides eastward across the central Plains. These clouds should thicken up enough to keep Saturday`s daytime temperatures a few degrees cooler than what they should be today. While the cloud deck may grow deep enough for attempts at hydrometeor production to get going as the leading flank of mid-level vorticity glides overhead Saturday afternoon, a sub-500 mb wedge of dry air will likely prevent any raindrops from reaching the ground until after sunset. Ogorek Saturday Night through Thursday: Overall, the long term period remains seasonably mild, with only a couple brief chances for primarily light rain. The first shot of rain will be right at the start of the period, namely Saturday night into at least early Sunday morning. The main feature of interest supporting this period of rain is the slow moving mid/upper low that is expected to shift out across the front range of the Colorado Rockies into this evening. As it does, surface low pressure is expected to quickly consolidate and become occluded under the main upper low across the Central Plains into Saturday. An accompanying occluded frontal boundary will then sweep eastward across our area Saturday night as the vertically stacked system tracks into the Upper Midwest. Our best shot of rain comes with the arrival of the frontal boundary Saturday evening/night. This looks to be a fairly short period of rain (~6 hours), however, as a mid-level dry slot is expected to quickly punch northeastward into the area following the surface frontal passage. This should thus result in a quick west to east ending of the rain either late Saturday night or early Sunday morning. Some additional low chances (15-35%) for light showers will continue Sunday afternoon, with the best chances being near the WI state line and points northward as the main system tracks into the western Great Lakes. With no real push of colder air into the area on the back side of this system conditions on Sunday will remain mild (highs in the upper 50s/low 60s), albeit with breezy west winds. Dry and quiet weather is expected in the wake of this system for Monday and Tuesday before our next shot of rain comes with another approaching weather system during the mid-week period (Wednesday into Thursday). However, model and ensemble guidance still continue to display a large amount of spread with the actual timing and overall evolution of this mid-week system. With this in mind, I did not make any changes to the NBM chance POPS (30-50%), though they are admittedly likely too broad brushed from Wednesday into Thursday. KJB && .AVIATION /06Z TAFS THROUGH 12Z SATURDAY/... Issued at 1055 PM CST Thu Nov 7 2024 No significant aviation forecast concerns for the 06Z TAFs. Light west winds are expected to turn northwest Friday morning behind a weak surface trough, then eventually shift to the northeast by Friday evening. Winds will then likely turn more easterly after midnight Friday night and become breezy in the 10-15 kt range. Otherwise, VFR conditions are forecast through the period, with mainly some patchy high clouds increasing Friday and Friday evening. Once winds turn east off the lake late Friday night, some patchy MVFR cloud bases can`t be ruled our. Ratzer && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago