222 FXUS63 KILX 111645 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 1145 AM CDT THU AUG 11 2016 .UPDATE... Issued at 1143 AM CDT Thu Aug 11 2016 Have gone ahead and issued a Heat Advisory for about the western half of the forecast area (Lacon-Lincoln-Taylorville westward). Late morning dew points remaining in the 76-78 degree range and some heat index values already above 100. Parts of the eastern half of the forecast area will probably reach near 105 heat index as well, but currently thinking this will not be as widespread as temperatures remain a bit cooler in that area. UPDATE Issued at 949 AM CDT Thu Aug 11 2016 Main concern for the update is with the heat index. 9 am observations showing widespread dew points of 75-78 degrees over the forecast area, with heat index in some cases already in the mid 90s. Am expecting these to lower a tad as a decent amount of sunshine should allow for some mixing, but latest tweaks to the temp/dew point grids still producing mainly 100-105 heat index today. Will hold off on an advisory at this point, and go with a Special Weather Statement to address the borderline conditions. Decaying MCS tracking across eastern Iowa is starting to bring some cloudiness to the far northern CWA. Gust front is starting to get out ahead of the convection over southern/southeast Iowa and this should lead to a decreasing trend of the associated showers before they reach the northwest CWA, so will keep the forecast dry in that area for now. Across the southeast, have maintained some 20-30% PoP's for this afternoon with the HRRR continuing to show some popcorn-type development. && .SHORT TERM...(Today and tonight) ISSUED AT 334 AM CDT Thu Aug 11 2016 Surface high pressure has finally edged further off to our east early this morning allowing a light southeast flow across the forecast area. Satellite data indicates a band of clouds and a few showers over southwest Indiana that occasionally has snuck into far east central/southeast Illinois this morning. Hard to find much support for the precip except for the high precipitable water values of +2 inches extending from southern IL northeast thru most of Indiana coupled with a weak area of low level convergence over southeast IL. Further north and west, a clear sky combined with light winds has led to some patchy fog and expect that to dissipate quickly just after sunrise this morning. Then our attention will turn to the heat this afternoon and coverage of any convection over southeast IL and the possibility of the storms over Iowa edging into far northwest Illinois later today as well. Coverage of convection over southeast IL will be scattered at best and mainly this afternoon into early this evening with most of the hi-res convective allowing models suggesting the activity to our northwest should dissipate before entering our northwest counties this afternoon. Forecast soundings showing mixed layer capes increasing to around 2500 J/KG but with little to no forcing approaching our area, will keep any mentionable POPs over southeast Illinois, closer to the deeper tropical moisture. Soundings indicate highs around 90 again this afternoon coupled with dew points in the mid 70s will yield heat index values of 100-105 degrees for a few hours this afternoon. Any isolated to widely scattered convection over east central or southeast Illinois should quickly dissipate this evening. As the cold front well off to our northwest edges closer to our area late tonight, shower and thunderstorm chances will increase, especially west of I-55 during the early morning hours of Friday. With a bit better southerly flow tonight coupled with a more cloud cover, its going to be a warm and muggy night with early morning lows only dropping off in to the mid 70s. .LONG TERM...(Friday through Wednesday) ISSUED AT 334 AM CDT Thu Aug 11 2016 A subtropical mid/upper level ridge with 596 dm 500 mb low off the NC coast to continue to ridge westward into the mid MS river Valley on Friday. This to provided another very warm and humid day over central/southeast IL with highs 85-89F north of I-72 and near 90F from I-72 south. Dewpoints in the mid to upper 70s to give heat indices peaking Friday afternoon from 98-104F from IL river southeast with highest readings in southeast IL. A 565 dm 500 mb low over southern Saskatchewan to track eastward to the Manitoba/Ontario province line by sunset Friday. Its associated upper level trof moving into the Midwest and interacting with deep tropical moisture with precipitable water values of 2-2.4 inches to support scattered showers and thunderstorms especially over the IL river valley where likely pops are, while lower pops of 30-40% in southeast IL. A 1006 mb surface low pressure moves east across northern MI Friday night and drives a cool front southeast over the IL river valley, and then into central IL on Saturday, and southeast IL Saturday night. This will likely have a band of showers/thunderstorms with it as it slowly progresses southeastward. Areas nw of the IL river will trend drier on Saturday and then just slight pops along I-55 Sat night while likely pops continue over southeast IL. Will see a few weak surface low pressure system eject northeast long the frontal boundary that will become quasi-stationary near the Ohio river Sun/Mon while also bringing up more tropical moisture as precipitable water values could rise as high as 2.4-2.6 inches in southeast IL this weekend. This is 200% above normal levels for mid August and about has high as precipitable water values get in IL. It appears more likely that heavy rains of 2-3 inches and locally 3-4 amounts will occur in southeast IL mainly from I-70 south this weekend. Highs Saturday in the mid 80s, while still humid with dewpoints ranging from near 70F over IL river valley and mid to upper 70s in southeast IL where heat indices peak in the mid 90s Sat afternoon. Highs Sunday mostly in the lower 80s with dewpoints easing down to 65-72F, highest in southeast IL. Extended models still have differences with frontal position and more low pressure system lifting back northeast along it and question as to how far back north front gets early next work week. GFS is most aggressive with qpf spreading ne across CWA later Monday into Tue evening while GEM and ECMWF models focus qpf in southeast IL. Will lean toward the GEM/ECMWF models with higher pops in southeast IL while just slight pops over northern/nw CWA Mon/Tue. Though still have areas from Peoria north dry on Monday before slight pops return Monday night. Precipitable water values elevate back to near or above 2 inches later Monday into Tue especially southern areas so this could bring more heavy rain chances to southeast IL. Highs generally in the lower 80s Mon/Tue. Isolated convection still appears possible on Wednesday with highs in the mid 80s and still rather muggy with dewpoints in the upper 60s to around 70F. && .AVIATION...(For the 12Z TAFS through 12Z Friday morning) Issued at 605 AM CDT Thu Aug 11 2016 LIFR TO VLIFR conditions possible for TAF sites especially along and east of I-55 for the next couple of hours, otherwise, VFR conditions are expected thru this evening. Patchy dense fog should dissipate rather quickly after sunrise leading to sct-bkn cumulus after 15z with the primary concern for bkn cigs around CMI and just east of DEC this afternoon. TSRA chances limited enough to keep out of the 12z TAFs with the primary threat for widespread showers and storms not arriving until after 06z northwest of PIA. If cloud cover and rain holds off longer than currently expected tonight, we may see at least some MVFR vsbys in fog again after 06z. Surface winds will be southerly today at 7 to 12 kts today and from 5 to 10 kts tonight. && .ILX Watches/Warnings/Advisories... Heat Advisory until 6 PM CDT this evening for ILZ027>031-036-037- 040>042-047>052. && $$ UPDATE...Geelhart SHORT TERM...Smith LONG TERM...07 AVIATION...Smith