Marine Weather and Tide Forecast for Ashland, IL

DISCUSSION
Issued at 136 AM CDT Wed Apr 30 2025

Water vapor satellite early Wednesday morning shows broad zonal flow extending from the Central Plains into the Great Lakes, while a southern stream trough is centered over the Four Corners Region.
Deterministic guidance is in agreement mid-upper level flow will veer to southwesterly from the Mississippi River Valley into the Midwest as that trough shifts eastward into the Southern Plains today. The associated moisture transport will thus spark showers and a few thunderstorms across the Prairie State today into tomorrow when that trough finally lifts into the region.

Friday, another trough diving southeast out of the Canadian Prairies will dig into the Great Lakes, with a vort max on its southern flank sparking some additional - though more isolated - afternoon and evening showers across much of the Midwest, including central IL.
Cool advection behind that trough will push temperatures to below normal for both Friday and Saturday, but ridging is slated to build back into the region early next week to bring a return to above normal temperatures. With the strengthening omega block across the eastern half of the U.S., moisture return should stay confined to our west and hence dry conditions are forecast from Saturday through at least mid next week.

***** Severe Weather Risk Today *****

Ahead of the main trough in the Southern/Central Plains, deterministic guidance depicts a mid level disturbance lifting into the area this evening into tonight. As a result, the frontal boundary stalled over the southern portion of the state will translate north as a warm front. Isentropic upglide north of the front will spark some stratiform rain mid-late morning across central IL, with some showers during the afternoon. Our attention, however, will be on the front itself this afternoon, where convergence will spark thunderstorms fed by 2000-3000 J/kg SBCAPE to its immediate south. 0-6km shear vectors oriented nearly parallel to the front should keep storms anchored to it this afternoon and evening, and with 200-350 m^2/s^2 of 0-3km SRH we're concerned about all severe hazards with supercells the favored storm mode. Hail would be the most probable severe hazard, though if/when storms become surface based the low LCLs and aforementioned directional wind shear would favor a tornado threat as well. Now, precisely where the front sets up is not agreed upon by the CAMs, but looking at mean composite reflectivities from the HRRR it seems near or south of the I-72 corridor will be the spot to watch especially between roughly 5-11pm.

***** Heavy Rain/Localized Flooding Potential Tonight? *****

The rather ill-defined surface low is progged to lift right through central IL tonight. An FGEN band collocated with a couple hundred MUCAPE on its northwest side may promote a band of heavier showers, with HRRR LPMM suggesting localized 6h rain totals over 2 inches (which is approaching FFG) most likely near or west of roughly I-55. If there are any impacts, we don't expect more than nuisance flooding characterized by ponding of water in urban or otherwise flood-prone areas, and perhaps some swelling of area creeks and streams. Fittingly, WPC has us outlooked in a level 1 of 4 (marginal) risk for excessive rainfall.

Due to the convective nature of precip and mesoscale forcing mechanisms, rain totals will vary considerably from one location to the other across the county warning area (CWA). The 10th-90th range from HRRR, which still doesn't capture the localized highest and lowest totals, suggests most locations will fall between roughly 0.3 and 2 inches west of I-55, and between a tenth and 1 inch further east. Our forecast, which splits the difference of the extremes and leans close to NBM mean, ranges from little more than an inch along the IL River to around a half inch along the I-57 corridor.

As a superfluous aside: East of the low's track, southwest winds will pick up and may (HRRR probs are 40-70%) gust upwards of 30 mph tomorrow morning mainly north/east of a Lacon to Decatur to Paris line.

***** Severe Risk Tomorrow Too? *****

With the lack of an obvious push of cold advection behind that first low, and given the long-awaited approach of the main upper trough from the Southern Plains, we'll need to keep our our peepers peeled for severe weather tomorrow. All but one of the CAMs are hinting that a very weak cold front trailing south of the first low may serve as the focus for organized convection which would initiate near or east of the IL/IN state line, while the NAMNest, being a little further west, clips areas south of I-70 with those storms.
However, HRRR mean brings afternoon surface dewpoints into the low 60s east of roughly the IL River, which, combined with cooling temps aloft beneath the main upper trough, would result in 1000-2000 J/kg of SBCAPE to fuel storms in the weakly sheared environment. This absence of notable deep layer shear will result in pulsey, garden- variety storms area-wide during the afternoon and evening, though we won't completely write off the chance the strongest storm/two could produce localized hail or a strong wind gust as it collapses. These will also be capable of brief heavy rains due to the seasonably high theta-E environment, though the cells should be so small that even with their slow movement hydro issues are unlikely (5% chance).

***** Turning Dry for the Weekend *****

The next upper trough arriving from the northwest tomorrow night into Friday will drag a cold front through central and southeast IL Friday morning, and then another Friday night evening-night. The push of cool and dry advection from the northwest will favor steep low level lapse rates and some shallow instability Friday afternoon and evening, which should be enough to spark a few showers. Forecast soundings from the NAM and GFS suggest the inverted V and high cloud bases could support some gusty winds with those showers - something we'll keep on eye on as higher-res guidance starts to capture that period of the forecast.

As surface high pressure builds into the region Saturday, conditions should turn dry - making for a pleasant, albeit seasonably cool, weekend with Saturday's highs in the mid 60s and Sunday's in the upper 60s to low 70s. As the surface high shifts east and ridging expands into the Ohio Valley and Great Lakes Regions, conditions will turn warmer going into next work week with NBM giving a 40-50% chance for 80+ degF highs by Tuesday.

Bumgardner

AVIATION
(For the 12z TAFs through 12z Thursday Morning)
Issued at 606 AM CDT Wed Apr 30 2025

MRMS imagery shows an area of generally light rain currently near I-70 lifting north toward central IL. This will move into the airfields 14-17z, with ceilings lowering with and behind it.
30.00z HRRR gives a 30-50% chance for MVFR ceilings this afternoon and evening as the rain turns to scattered showers.

Maintained a prob30 group for TSRA at SPI, DEC, and CMI as various convective allowing models (CAMs) depict storms firing along a warm front this evening. There could even be some localized hail in the strongest cells, but opted not to mention that as probabilities are too low.

Tonight, a compact surface low will lift through central IL, causing winds to change directions, especially at DEC and CMI where south-southwest winds will become gusty near the end of the forecast period. MVFR to IFR ceilings will arrive from the northwest behind the surface low near the end of the forecast period as well.

Bumgardner

ILX WATCHES/WARNINGS/ADVISORIES
None.