159 FXUS63 KILX 190453 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 1153 PM CDT Tue Mar 18 2014 .DISCUSSION... ISSUED 930 PM CDT Tue Mar 18 2014 Low pressure at the surface will move from west central Missouri at 02z to south central Wisconsin by 12z. Rain showers will develop ahead of the low as the warm sector passes across Illinois. A few thunderstorms will be possible closer to the triple point as the dry mid-level air punches into Illinois. showers are already approaching far western IL as of 0215z. We will keep chance PoPs will be this evening with likely PoPs across the north from 03z to 09z during the best omega. Any thunder chances will end with the cold fropa between 09z and 12z, with lingering light rain showers changing to snow showers in the cold advection. The precipitation after 12z will be mainly trace amounts, behind the departing low pressure. Brisk northwest winds will gust to 25-30 mph on Wed, adding a wintry chill to the air. Updates this evening were to cloud, PoPs, and weather to match the current trends. Also some minor adjustments to the temps and dewpoints. Updated forecast info will be available shortly. Shimon && .AVIATION... ISSUED 1153 PM CDT Tue Mar 18 2014 Low pressure will track across northern IL overnight, bringing a quick push of moisture and lift across C IL. Instability parameters show favorable conditions for a few thunderstorms as the warm sector passes over the terminals. Thunderstorms are already in progress in east-central Missouri, moving northeast toward SPI. The best window of opportunity for thunder should be in the hours between 06z and 11z from SW to NE. The rain chances should diminish after 12z from the west as the cold front passes across the terminals. Lingering spotty showers may continue after sunrise as rain mixes with or changes to snow. No snow accumulation is expected. We ended VCSH at 15z as additional dry air arrives above the cloud layer on very strong NW winds. Southeast winds at 10 to 20 kt late this evening will generally continue in that range the rest of the night as the low pressure reaches the IL/WI border by 12z. Winds will sustain in the 14-17kt range behind the low and cold front as winds shift to south between 12-15z and then become northwest Wed morning. NW winds will increase to 20g30kt by Wed afternoon in the strong cold advection. Cloud heights will most likely dip to MVFR as the rainfall develops, then remain MVFR through much of the day Wed in the cold low level air. Shimon && .PREV DISCUSSION... ISSUED 255 PM CDT Tue Mar 18 2014 The main focus through the period is with the deep low pressure system which will move across the area tonight, with the potential for showers and a few thunderstorms which will exit the area early Wednesday. Farther out, another low will track north of the forecast area Thursday night into Friday with a warm up ahead of it, then a chance of showers and a trend toward colder temperatures especially late in the weekend into early next week. Surface low pressure was over eastern Kansas this afternoon. This low is progged to lift northeast across far northern Illinois after midnight tonight, and northeast of the state after sunrise Wednesday in response to a strong mid-level short wave propagating out of the plains. Low level moisture return with this system is initially blocked by the southern extent of high pressure over the Gulf Coast states, though moisture was beginning to surge north across east Texas at 19z. Strong dynamics associated with the approaching short wave and surface low will spread across the forecast area this evening, though moisture will be slow to catch up with this deeper forcing. Guidance continues to depict blossoming of precipitation over the region during the late evening/overnight hours however, though with relatively low qpf given late moisture arrival. Some potential for isolated to scattered thunder exists, with a pocket of steep mid-level lapse rates arriving with the main short wave trough axis overnight. Breezy south-southeast winds should help keep temperatures from falling off too tonight, with mos numbers looking a bit too cool given warm advection and winds. System exits to the northeast Wednesday morning with a few spotty showers lingering into mid-day. Cool pocket aloft swings across mainly northern IL where rain may mix with some wet snow, though low level thickness progs and surface temps warming back into the mid 40s to near 50 by afternoon suggest little potential for any persistent rain/snow mix across central IL. Gusty west winds up to 30 mph linger into the afternoon as pressure gradient only slowly relaxes as low pulls away to the northeast. Winds will diminish Wednesday night and Thursday as surface high pressure ridge builds in from the west. Warm advection redevelops Thursday afternoon/night as the ridge moves off to the east...and broad upper ridging develops with 90+ meter height rises behind departing eastern CONUS trough. Models indicate another short wave trough propagating along the US/Canadian border Thursday, with an area of low pressure and troughing extending south across the plains. Winds become south again by Friday as the low passes over Northern IL, with temps expected to warm into the 60s in most areas before the trailing cold front pushes through later in the afternoon. Some potential for showers ahead and along the cold front Friday and Friday evening, though moisture again remains somewhat limited and thus only low chance pops mentioned. Column cools enough for a mention of a rain/snow mix north of SPI area overnight...though mainly as precip ends. Cool Canadian high pressure will build southeast across the Midwest over the weekend, with a secondary push of colder air keeping temps in the 30s/lower 40s by Sunday. Another upper trough will bring the potential for some light snow and a reinforcing push of cold air late Monday into Tuesday. Ratzer && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$