Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
986 FXUS63 KILX 281353 AFDILX Area Forecast Discussion...Updated National Weather Service Lincoln IL 853 AM CDT Fri Jun 28 2024 .KEY MESSAGES... - Widespread rain returns to the area today and tonight, though the risk for severe weather and flash flooding has decreased. - Drier, cooler and less humid conditions evolve Saturday night through Monday; ideal for outdoor activities. - Seasonably hot and humid weather returns by the middle of next week, extending through the holiday weekend, with near daily chances for showers and storms. && .UPDATE... Issued at 852 AM CDT Fri Jun 28 2024 Showers, some dropping some sprinkles to the ground through a semi- dry sub-LCL layer, continue drifting just north of east across central Illinois this morning with warm advection ahead of a mid- level shortwave that`s producing a bit more in the way of shower/storm activity upstream across northern MO and IA. That activity will slowly meander our way today, though fortunately the sfc high pressure that`s now slowly departing to the east has maintained seasonably dry low levels, suppressing instability and hence limiting the vigor of precip in our neck of the woods tonight. The 12z HRRR suggests dewpoints, currently in the low to mid 60s across central Illinois, will climb to around 70 by this evening to foster a narrow plume of 700-1300 J/kg MUCAPE as a weak LLJ overspreads the region, but by and large scattered to widespread convection and associated clouds will prevent sufficient instability for much in the way of a severe threat. Temps, in the upper 60s (north) to mid 70s (southeast), are still (in accordance with fresh highres guidance) forecast to climb into the mid to upper 80s this afternoon since it wouldn`t take much in the way of sunshine for a quick spike, however upstream clouds are a bit thick so we might (though time will tell) fall a degree or two shy of those forecast highs; confidence is too low to make much in the way of changes at this time. Bumgardner && .DISCUSSION... Issued at 141 AM CDT Fri Jun 28 2024 A quick peek at radar this morning reveals an area of showers pushing into far western Illinois. This activity is high-based and struggling to reach the ground, with quite a bit of dry air to overcome in the lowest 10 kft (see 00z ILX sounding). The better opportunity for measurable rain arrives this afternoon as a compact mid-level shortwave lifts across the Mid- Mississippi Valley and provides life-support to a decaying MCS/MCV. By that time, thunderstorm potential appears low with the decaying MCS/MCV outpacing the axis of instability. Leaning on the latest hi-res guidance, this first round of measurable rainfall looks to stay north of I-72 -- perhaps well north. The best opportunity for measurable rain arrives late tonight as strong shortwave energy pivots across the Upper Mississippi Valley and helps drive a surface cold front into portions of the Upper Midwest and Central Plains. A 30-40 kt LLJ will veer ahead of the front and provide the focus for nocturnal convection to blossom overnight. Most of the 00z CAMs suggest storms initializing over central Missouri overnight as the LLJ moves atop some sort of west-east surface boundary. As the cold pool matures with eastward extent, the MCS will stake a greater claim of the LLJ -- effectively robbing central Illinois of its share of rich theta-e air needed for strong convection. The net effect, if this narrative comes to fruition, will be a diminished threat for severe weather and flash flooding for central Illinois as storm coverage will be more sparse with higher inflow bases. One final note about the setup for today/tonight is that we appear to have a column moisture and instability problem. And, it`s quite possible that the culprit is the cut-off low positioned along the Gulf coast. Without a good fetch of western-Gulf air surging northward into Illinois, we are left with recycled moisture and what is looking more-and-more like a disjointed LLJ. This most likely adds up to a very non-uniform QPF field across central and southeast Illinois through Saturday afternoon. For what it`s worth, the 10th-90th percentile 24-hr QPF from the 00z HREF offers something like 0.05" - 1.25" as a reasonable range of expected rainfall -- most of which is expected north of I-70. We will need to keep an eye on model trends for Saturday with the cold front pushing across the forecast area. The current thinking is that convective debris from Friday night will mitigate boundary layer recovery Saturday afternoon -- every 00z CAM omitted convective initiation over our forecast area. After a dry, secondary cold front makes its passage Saturday, temperatures will cool down in a big way. Afternoon highs on Sunday and Monday are forecast to be in the upper 70s, with overnight lows cooling into the 50s Sunday night, per deterministic NBM guidance. This modified Canadian air mass will not stick around long, though. By the middle of next week, typical summertime heat and humidity will return across the region. Mid-range global guidance is in fair agreement that another cold front sinks south into central Illinois sometime Tuesday night or Wednesday, with it stalling-out over or just south of the forecast area. This could put us in a position for daily thunderstorm chances Tuesday-Friday depending mostly on where the 594mb heat dome sets up. The NBM continues to hedge this time period with daily 40% PoPs. MJA && .AVIATION... (For the 12z TAFs through 12z Saturday Morning) Issued at 516 AM CDT Fri Jun 28 2024 Overcast mid-level clouds will be accompanied by scattered showers through this TAF period. Mention of VCTS has been retained for tonight, with both confidence and coverage still too uncertain to upgrade to prevailing TSRA. While cigs are forecast to remain VFR through the period, some guidance suggests a reduction to MVFR is possible near the end of the period as a cold front draws closer to the regional terminals. MJA && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$