Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 10/28/17


Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
853 PM CDT Fri Oct 27 2017 .UPDATE... 843 PM CDT No real big changes this evening, however, did make some slight adjustment to the pop/wx mainly for locations north of I-80 where there may be a slight increased chance of sprinkles or flurries tonight through early Saturday morning. Overall, conditions still appear marginal for precip development tonight, given initial light ascent overhead and with lacking deep moisture. Nonetheless, have seen reports of both sprinkles or flurries already this evening. With a slight increase in forcing through the night with the arrival of a vort lobe just to the northwest, could see some slight increase in coverage. Deeper moisture and lacking crystals have been in question this evening but some indications this evening are leading to believe there could be more flurries observed than sprinkles. Latest AMDAR soundings showing moisture present in the -8 to -10 C layer and although crystals are more than likely to be lacking in this temp range, it is not out of the question. This presence of crystals is also noted on latest GOES R imagery, and all supportive of latest short term guidance trends of the slightly higher chance of flurries tonight. However, still not expecting any accumulation tonight. Rodriguez && .SHORT TERM... 224 PM CDT Through Saturday... Blustery and colder weather will persist through the near term, with the potential for a few sprinkles or flurries late tonight into early Saturday morning, mainly over far northern IL. Surface low pressure was analyzed over the Upper Peninsula of Michigan early this afternoon, in association with a closed upper low over WI. A secondary surface trough/cold front extended from the low through western WI and into eastern IA, beneath the main upper trough axis. This secondary cold front will push east across the forecast area overnight into early Saturday, with a little deeper wrap-around moisture spreading a few sprinkles or flurries into the area mainly after midnight tonight. Forecast soundings depict moisture up to about 750 mb, with the coldest temps at the top of the layer approaching -10C. This suggests a lack of ice nucleation for producing snow, though any deeper cloud layer would likely support ice crystals and a potential mix of light rain/snow. Precip is expected to be light, with no accumulation, but a few wet flakes could be in the air over parts of far northern IL toward morning. Otherwise, cloudy skies and blustery westerly winds will persist in the tight cyclonic surface pressure gradient with the slowly departing low. Clouds/winds will keep temps from dropping off too much overnight, generally in the lower and middle 30s. Similar conditions favor undercutting MOS numbers for max temps Saturday as well, with afternoon highs about 40-42 rather than low-mid 40`s from MET/MAV guidance. Ratzer && .LONG TERM... 320 PM CDT Saturday night through Friday... No significant changes to the long term forecast with trends for much below normal temperatures for much of the period, with some warming expected toward the end of next week. The upper level long wave pattern continues to trend toward a broad upper trough covering all of the CONUS except for the west and east coasts. Between the lowering heights from the broad upper trough and flow trending to nwly aloft, expect temperatures through mid week to be well below normal, with highs in the 40s in the 30s. The coldest night should be Saturday night when temperatures across much of the area west of the Indiana state line will be in the upper twenties to low 30s. However, the urbanized areas of the Chicago Metro area will likely remain above freezing, but will include Cook County in the Freeze Warning since the outer neighborhoods should drop to or below freezing. Toward the end of next week, the longer range guidance is indicating a trend to rising heights aloft and more zonal, wly flow aloft. This should allow for some moderation to temperatures, trending back to seasonal normals of upper 50s to arnd 60 F and lows in the upper 30s to low 40s. There will be periodic chances for some light pcpn through the extended forecast period with shortwaves dropping southeast out of the nrn plains and scntrl Canada. Timing of individual waves has some uncertainty due to timing differences among the models, so have carried generally low chance to slight chance PoPs. There could be some light rain showers or light snow showers or a mix, depending on how timing of the short waves lines up with diurnal temperature trends. Regardless of p-type, QPF amounts will be low. && .AVIATION... For the 00Z TAFs... Did not make big changes to the TAFs as west southwest wind expected to continue, while the current VFR ceilings lower to MVFR overnight. Am monitoring the possibility for a slightly earlier time frame of this transition, and have already moved up the timing by an hour. Low end MVFR still appearing more likely across the RFD area, with a brief window of IFR ceilings not out of the question. Continued a dry forecast for late tonight into early Saturday morning. However, could see some locations seeing a small window of either sprinkles or flurries mainly during early Saturday morning. Ceilings expected to slowly lift through the day, with VFR returning by Saturday afternoon. Rodriguez && .MARINE... 320 PM CDT Low pressure is lifting northeast from northern Wisconsin and the central upper Great Lakes region. A secondary surge of cold air will push across the lake late tonight and early tomorrow, setting up an extended period of brisk winds shifting from swly this evening to nwly by tomorrow morning. Winds and waves hazardous to small craft will likely persist through the day tomorrow for the Illinois nearshore waters and into tomorrow night for the Indiana nearshore waters. A weak ridge of high pressure moving across the lake will allow winds to diminish over the lake Saturday night and Sunday. Another low will track across the upper Great Lakes Sunday and then become absorbed into a larger low over sern Canada Sunday night. early Monday. The cold front associated with this low will move across the lake early Monday morning. Another surge of cold air following this front may bring some westerly gales Monday afternoon and evening. && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Freeze Warning...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010- ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022- ILZ023-ILZ032-ILZ033-ILZ039...11 PM Saturday to 9 AM Sunday. IN...None. LM...Small Craft Advisory...Winthrop Harbor to Gary IN until 7 PM Saturday. Small Craft Advisory...Gary to Michigan City IN until 4 AM Sunday. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO