Marine Weather and Tide Forecast for Ashland, IL

UPDATE
Issued at 901 PM CDT Thu Apr 17 2025

Severe convection continues to bubble over far western Iowa late this evening. The majority of the CAMs show this activity tracking east-northeast along the nose of the LLJ into northern IL late tonight and staying just north of the county warning area. There is a low chance activity could graze Knox/Stark/Marshall counties late tonight, but the only model still indicating that is the 18Z NAM Nest.

Winds will remain elevated overnight with gustiness picking up once again by mid to late morning. Forecast soundings still suggest strong capping in place most of the day, which is already noted on our 00Z sounding with a 10 degree C temperature profile at 700 mb.
The 00Z HRRR still implies there may be a few robust updrafts late Friday afternoon as the front approaches and the CAP begins to erode. However, coverage doesn't begin to expand until later Friday night as a broad ~50 kt LLJ spreads over the area. Although confidence isn't high in the exact start time of convection on Friday, storms could begin initiating as early as 5-7 pm.

NMA

DISCUSSION
Issued at 214 PM CDT Thu Apr 17 2025

Afternoon water vapor imagery shows a very dry mid level air mass and elevated mixed layer lifting northeast across OK/KS which guidance depicts overspreading central Illinois overnight into Friday morning. Soundings show very steep lapse rates that are nearly dry-adiabatic especially within the 800-600mb layer. This is atop an incredibly strong capping inversion. MLCIN in excess of 600 J/kg will be in place to start the day Friday and is expected to persist most of the day across central Illinois very effectively capping the warm sector and preventing deep convection. It's not until the arrival of a cold front Friday evening that guidance begins to erode the cap. Scattered storms should eventually be able to form Friday evening, and parameter space is supportive of severe weather once the cap breaks.
Moderate instability around 1000-1500 J/kg MLCAPE and strong deep layer shear of 45-50 kt will allow for rotating updrafts with initially discrete storms. Forcing along the front appears weak Friday evening with the surface low pulling away across the Great Lakes and a col area moving into central Illinois late in the evening. Given the modest synoptic scale forcing and antecedent cap, it appears that upscale growth will be slow if much at all.
CAMs generally depict scattered clusters of storms over the area.
Storm coverage will increase late in the evening and overnight, especially south of I-72, in response to a low level jet along the lower to mid Mississippi Valley overspreading southern Illinois.

Frontal boundary is expected to meander over the southern half of the state over the weekend and will serve as the focus for additional rounds of showers and storms. The heaviest period of rain is expected to be Friday night into Saturday morning associated with the aforementioned LLJ. Cloud bearing flow (850-300mb) and deep layer shear vectors are both parallel to the quasi-stationary surface front indicating that training storms will be possible. HRRR LPMM through Saturday morning shows some localized swaths of 1.5-2.0 inches with additional rain expected later Saturday and Sunday.

NBM 72-hour mean QPF from Friday through Monday morning ranges from around 1.25 along the I-74 corridor to 1.50-2.00 inches along our southern CWA boundary (Beardstown to Lawrenceville).
90th Percentile indicates that there is some potential for some higher end rainfall amounts of over 3.00 inches of rain through the weekend. RFC 6-hour flash flood guidance generally ranges between 2.5-3.0 inches.

Early next week, departing low pressure over the Great Lakes will usher in colder air across the Upper Midwest and into central Illinois while, at the surface, high pressure builds across the region. This will allow for a dry but slightly cooler start to the upcoming week. Highs will top out around 60 degrees Monday, but should begin to warm back up Tuesday and Wednesday as the ridge axis shifts to our east allowing southwest flow to overspread the area. Models begin to diverge by the middle of next week, but another area of low pressure and attendant cold front is expected sometime in the Wed/Thu timeframe bringing the next chance for precip to the area.

Deubelbeiss

AVIATION
(For the 06z TAFs through 06z Friday Night)
Issued at 1206 AM CDT Fri Apr 18 2025

While south wind gusts have begun to drop off, sustained speeds of 10-20 knots will remain common through the night. Gusts approaching 30 knots should resume toward mid to late morning, with winds gradually trending southwest during the day. Late in the period, the arrival of a cold front will shift the winds to the west or northwest, but this is most likely from KBMI-KSPI west.

Convection remains a concern later in the period, with latest model guidance suggesting the period from about 22-23Z into early evening as most favorable for any thunderstorms.

Most of the time, VFR conditions will prevail with ceilings around 7000 feet. As the front approaches, ceilings begin to lower late in the period, with probabilities of MVFR conditions increasing to around 40%. Some of this may be due to storm activity, with a more more widespread risk of sub-3000 foot ceilings after the current TAF period.

Geelhart

ILX WATCHES/WARNINGS/ADVISORIES
None.