Marine Weather and Tide Forecast for Kane, IL

SHORT TERM
(Through Late Friday Afternoon)
Issued at 221 PM CDT Thu May 15 2025

The Pacific cold front continues its eastward march across the CWA early this afternoon. As of 1900 UTC, it was located just west of a KVIH>>KPPQ line. The boundary is most evident looking at dewpoint values, as there is very little wind shift and not much of a temperature gradient associated with this front. The limiting factors discussed the past few days are all in play, with fairly strong capping evident between 800 and 900 hPa on ACARS soundings. Temperatures however toward the top of the inversion aloft are beginning to cool from west to east, so the strength of the cap should be weakening over the next few hours. The bigger problem from a convective initiation standpoint is forcing.
Surface convergence along the boundary in our neck of the woods is nearly non existent, with maybe 20-40 degrees of veer as you travel from east to west across the boundary. The main thrust for mid/upper level forcing for ascent is also well to the north of the area. There is some convection across northern Arkansas and far southeast Missouri where surface convergence along the boundary is a bit stronger. Perhaps this is associated by a weak, but subtle midlevel impulse as well but neither short-term guidance nor water vapor imagery is really picking up on much of anything.
The trajectory of these storms however should keep them southeast of our CWA Some CAMs have suggested a brief isolated supercell or two out ahead of this area in southwest/south central Illinois between ~23 and 02Z. Maybe this is due to a subtle midlevel impulse and some cooling advecting in aloft. This is a long way of saying that any severe threat this evening remains highly conditional. The threat is also still very confined both temporally and spatially as detailed above.

The Pacific cold front finishes moving through the area around 0300 or 0400 UTC, with dry weather favored for the remainder of the night. Cannot totally rule out a stray shower or weak thunderstorm overnight in far southeast Missouri, but chances appear to be at or below 10%.

Confidence has continued to increase with respect to convective trends on Friday ahead of a stronger cold front that will move through the CWA Southerly winds should increase quickly Friday morning, allowing for warmer and unstable air to surge back northward.
There remains some degree of uncertainty on exactly how far north the richer dewpoints (and ergo, instability) advects by Friday afternoon, but it appears to be a slam dunk for southeast Missouri and southwest Illinois. Parts of east-central Missouri and western Illinois are more on the northwestern edge of where convection is likely to develop or where left moving supercells (after splits) may move into. The convective mode should be predominantly supercells, given a strong orthogonal component of the deep-layer shear vector to the orientation of the cold front.
Hodographs show either straight hodographs or veer-back-veer profiles, both of which tend to favor at least some splitting of supercells. Left movers are typically shorter lived and almost exclusively a large hail threat while right movers are both hail and tornadic threats. Because of these splits, there also may be some mergers. These can be destructive or constructive in nature, but these mergers may also lead to some small bowing segments.
This is where damaging winds would be most favored, as the current thinking is that any formation of a well-defined QLCS will not occur until after it exits the CWA Overall, the main concerns continue to be on the potential for very large hail (2.75+") given supercells as a primary convective mode and very large CAPE within the -10 to -30C layer/hail growth zone. Any long-tracked supercell would have the capability of producing a swath of very large hail as well. There certainly is tornado potential, especially with more southern extent. Low-level shear/helicity increases as you go more into southeast Missouri and southwest Illinois. Storms will also not exit this area until closer to 23-0Z, which means some increase potentially in low-level cyclonic curvature of hodographs as the nocturnal low-level jet begins to increase. In terms of timing, there is more confidence on the end of the window for severe thunderstorms than the beginning. Storms should exit the area roughly between 23 and 0Z, but the onset could be as early as ~17Z or as late as ~20Z. The large difference on the front end is simply due to differences in exactly when convective initialization occurs tomorrow.

Gosselin

LONG TERM
(Friday Night through Next Thursday)
Issued at 221 PM CDT Thu May 15 2025

(Friday Night - Saturday Night)

After the passage of the cold front early Friday evening, a brief period of cooler and drier weather is likely to start off the weekend. Temperature trends with respect to Saturday continue to cool as guidance has trended more toward the cooler GFS/GEFS solution of the past couple of days. Highs on Saturday are forecast to be mainly in the mid to upper 70s, or right around normal for this time of year. Lows each night are expected to drop back into the 50s, which would also be near seasonal normals.

(Sunday - Next Thursday)

A return to a more active pattern remains in the offing late this weekend and into early next week. Not much has changed over the past couple of days, with an MCS expected both Sunday night and Monday night along/north of a retreating warm front. This boundary should progress northward in time, which means it is unlikely that the subsequent nocturnal MCS moves over the same region each night. Trying to pinpoint where each of these MCSs will track this far out is a fool's errand, but it does appear likely that widespread rainfall will accompany at least portions of the CWA with each round, the question is exactly where. Heavy rainfall (and possible flash flooding) could become more of a concern if Monday night's round tracks over the same areas as Sunday night's, but as all spelled out above, that does not seem likely at this point in time. Total precipitation probabilities for 2+" on the latest LREF peak out at about 40-50%, but drops to less than 10% for 4+". While April was very wet, soil moisture has largely reset back closer to normal levels due to mostly near or slightly below normal rainfall so far during the month of May. In fact, a good portion of northeast Missouri and west-central Illinois has been drier than normal and can really use 2-3" of rainfall.

There also remains quite a bit of uncertainty with how Tuesday/Tuesday night will evolve as clusters of the 500-hPa height pattern diverge quite a bit with respect to the timing, track, and strength of the mid/upper level low coming out of the desert southwest. There may be a conditional threat for severe weather, but this will likely be dependent upon availability of sufficient instability. Given that an MCS is expected Monday night, ongoing showers/thunderstorms and cloud debris could really help limit daytime instability on Tuesday.

While the exact timing is still unclear, ensemble guidance is in good agreement at a pretty significant pattern change for mid/late next week. A slow-moving mid/upper level closed low is likely going to be to our northeast, with well-below normal temperatures advecting in behind it. Both the EPS/GEFS show strong 850-hPa temperature anomalies (-5 to -8C). That is notable for late spring/almost early summer. Highs in the 60s to near 70 degrees are likely with lows dropping into the 40s to low 50s.

Gosselin

AVIATION
(For the 06z TAFs through 06z Friday Night)
Issued at 1128 PM CDT Thu May 15 2025

Mainly dry and VFR conditions are expected through late morning and Friday afternoon when thunderstorms will develop across parts of central and eastern Missouri into southwest Illinois. Have included PROB30 groups from 16-19Z at COU/JEF and from 20-23Z at STL/SUS/CPS. Any of the thunderstorms will have the potential to produce MVFR or IFR ceilings and visibilities and the storms over STL/SUS/CPS on Friday afternoon may produce hail and wind gusts over 35 knots. Wind gusts outside of thunderstorms will diminish this evening only to increase again into the 20 to 30 knot range.
Winds will turn out of the west and decrease on Friday evening.

Britt

LSX WATCHES/WARNINGS/ADVISORIES
MO...None.
IL...None.