906 FXUS63 KILX 281504 AFDILX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LINCOLN IL 1004 AM CDT MON SEP 28 2015 .UPDATE... ISSUED AT 1000 AM CDT MON SEP 28 2015 Earlier fog has lifted, but a large expanse of lower clouds remains present west of I-55. This has shown some signs of contracting on the last few visible satellite images. There is a fair amount of sunshine over the eastern CWA at present, but this will become more filtered as high clouds move up from the south this afternoon. Moisture continues to stream northward with a weak upper feature moving into far southeast Missouri, with isolated showers still expected in our area. We're already seeing a few of these tracking northeast from the St. Louis metro, so some westward adjustments were made to the existing 20% PoP's, as well as to speed up the timing. && .SHORT TERM...(TODAY) ISSUED AT 329 AM CDT MON SEP 28 2015 The latest surface map indicates a narrow band of mid 60s dew points stretching from the Gulf Coast northward through a good portion of Illinois. Satellite and surface data showing a band of mid clouds from northeast Missouri thru central Illinois with a break in the clouds over southeast Illinois. With the clear skies in the southeast and the high moisture content in the air areas of fog have developed with a few locations reporting visibilities of a quarter of a mile. As the band of mid clouds shifts further north, we may see the fog expand north as well as many areas may see a brief period of clearing early this morning which will allow at least some patchy fog to form. May need a dense fog advisory for parts of south central and southeast IL for a few hours early this morning before the fog quickly dissipates between 8 and 9 am. The water vapor loop indicates a weak shortwave over far northern Arkansas drifting north away from a much large upper low over the Gulf Coast states. This feature is progged to push into our area today bringing the threat for isolated showers again to parts of the forecast area. RAP-13 forecast soundings showing once we start to warm up the lower levels of the atmosphere we should see a fairly decent cumulus field develop, however, most of the forecast soundings were showing a decent subsidence inversion around 700 mb which should limit any instability from the 850-700 mb layer, so mainly an isolated shower threat with convective temperatures at or just above 80 degrees today. With a little better mixing expected today, afternoon temperatures should warm a few degrees from yesterday with most areas expecting highs in the 80 to 85 degree range, with the warmest readings in the west and south this afternoon. .LONG TERM...(TONIGHT THROUGH Sunday) ISSUED AT 329 AM CDT MON SEP 28 2015 Central IL will be in a squeeze play tonight as southern stream short waves push northward from mid MS river valley into southeast IL with 20-30% chances of showers by overnight. Meanwhile a cold front over central MN/NE to track SE toward the IL river by 12Z/Tue. Showers appear to be post frontal/behind the front and have 20-30% chances of showers overnight especially late nw of Peoria. Lows tonight in the low to mid 60s again. Tuesday appears to be our best chances of showers with even isolated thunderstorms in southeast IL Tue afternoon as the cold front pushes through rest of CWA during the day Tue. Have chances of showers diminishing to slight chance over northern counties Tue afternoon while 40-50% southeast of I-70 with better instability present and giving isolated thunderstorms. A temperature gradient sets up on Tue with highs near 70F nw of IL river, to lower 80s southeast of I-70. Dewpoints in the low to mid 60s to start the day to slip into the low to mid 50s behind the front over northern counties Tue afternoon. Have isolated showers in southeast IL southeast of I-70 Tue evening as front exists south of area. Then dry and cooler weather expected with decreasing clouds from north to south during Tue night, with clouds lingering longer in southeast IL. Lows Tue night range from upper 40s nw of IL river to mid 50s in southeast IL. High pressure settling into the Great Lakes Region on Wed to bring dry and less humid weather with ne breezes and mostly sunny skies. Highs Wed mostly in the lower 70s, with a few upper 60s north of Peoria by Galesburg and Lacon. Lows Wed night in the mid to upper 40s with Lawrenceville near 50F. A weak upper level trof digs southward into the ohio river valley on Thu and ne winds to keep temps cooler. Highs Thu in the upper 60s and lower 70s with coolest readings ne CWA. Extended models diverge with upper level pattern late this week into early next week, but generally show upper level trof controlling our weather with temps a bit cooler than normal with highs in the mid to upper 60s. GEM model is more aggressive with qpf into eastern IL Thu night and across IL Fri but sided toward the drier ECMWF and GFS models which are more consistent from previous runs. These two models generally are dry over central/SE IL from Wed through Sat and trended forecast in that direction. Have slight chances of showers Sat night and Sunday with more cloud cover. && .AVIATION...(FOR THE 12Z TAFS THROUGH 12Z Tuesday MORNING) ISSUED AT 600 AM CDT MON SEP 28 2015 LIFR/VLIFR conditions have developed just south of the TAF sites and the lower cigs and vsbys were slowly drifting north and may affect at least SPI, DEC and CMI for a couple of hours early this morning. Otherwise, once the fog dissipates we expect any lingering low cigs or vsbys to improve rapidly after 14z, with mainly SCT-BKN VFR cigs late this morning into the afternoon hours. A weak weather disturbance will move up from the south this afternoon bringing a slight chance for a shower to parts of the area, but coverage too limited to include in the 12z TAF issuance. Any lingering shower activity should dissipate early this evening with sct-bkn cigs at 4000-5000 feet with a layer above 20000 feet indicated on the latest forecast soundings. If we do see any clearing later tonight, fog and low cigs will become a threat after 06z, similar to what happened late last night. Surface winds will be out of the south to southwest at 8 to 13 kts today and southerly tonight at 4 to 8 kts. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Geelhart SHORT TERM...Smith LONG TERM...07 AVIATION...Smith