Marine Weather and Tide Forecast for Shipman, IL

SHORT TERM
(Through Wednesday Night)
Issued at 213 AM CDT Wed Mar 18 2026

A quick-moving clipper is passing through the region early this morning along a wing of WAA. This brings low chances (up to 30%) for flurries/sprinkles. Though radar trends show increasing activity to the northwest of St. Louis, it looks far more impressive than what ground truth is providing. Light precipitation is very brief or entirely absent, especially underneath lighter echoes. Therefore, I broadly cover the CWA with sub-15% PoPs and assigned sprinkles/flurries over the first few hours, progressing from northwest to southeast through 12z.

Dry conditions are expected after the clipper exits the region this morning. Temperatures become the main focus as the clipper results in a brief shift in flow along and north of I-70, where HRRR ensemble data shows a spread of 8-10 degrees. The southward progress of this boundary stalls as WAA eventually wins out. However, it is enough to influence high temperatures over the north/northeast sections of the CWA In these locations, I held highs to the upper 50s and used hi-res HRW products to better grasp the warming potential elsewhere. Temperatures were bumped by 1-2 degrees considering earlier clearing and longer duration of solar insolation.

The warming trends is amplified Thursday 0C H8 isotherm moves well east of the Mississippi River and mid-levels warm to 10-15C. Highs will jump another 10 degrees over today's warmth with max Ts in upper 60s to mid-70s. The warmest will once again be favored northeast of the Ozarks.

Maples

LONG TERM
(Thursday through Tuesday)
Issued at 213 AM CDT Wed Mar 18 2026

There is high confidence that the warming trend continues Thursday through Saturday with well above normal temperatures. A series of weak mid-level shortwave troughs eject southeast through the central U.S., which result in periodic changes in mid-level flow. While this isn't a huge influence on temperatures, it's just enough to impact the mid-level (H8) warmth by as much as 5C with the greatest difference along the north/northeast quadrant of the CWA Timing of these shortwaves will also be key, as mid-level warmth is greater in the morning periods before flow briefly turns west/northwesterly in the afternoon periods with momentary increases in mid/upper level RH, but unsaturated. Mostly sunny conditions are favored with a few/sct clouds east of the Mississippi River. With surface dewpoints in the 40s/50s, temperatures should easily make it into the 70s areawide with a couple of 80s Friday broadening northeast of the Ozarks as we go into Saturday.

Sunday remains a big question mark. NBM IQR has decreased by about 10 degrees (20 degrees spread) since showing spreads of approximately 30 degrees prior to, and leading up to, yesterday's guidances. Despite the decreasing spread, the deterministic solutions of the ECMWF/GFS couldn't be in greater disagreement. In fact, last night's runs had better agreement in the arrival of a cold front than tonight's vastly different scenario. GFS is now suggest a slower front with a weaker, 1030mb surface ridge stretching E to W across southern Canada.

ECMWF holds onto the stronger (1038mb), southern surface high that sets the stage for northeast/easterly flow and CAA. The latter solution would result in a non-diurnal curve with most locations seeing early-day highs that briefing stagnate and fall off through the afternoon. GFS draws a surface low across the Upper Midwest, south of the Canadian surface ridge with southwesterly flow pulling mid-level warmth eastward from the Plains. Mid-level air in the GFS is 2-3 standard deviation above normal with a ribbon of 20-25C H8 air compressed along and ahead of the front. This is rather typical for late-day fronts with ample warming on the southwest flow component. If the GFS solution comes to fruition, temperatures would warm well into the 80s, which challenge record high temperatures (STL-88 in 1907/COU- 90 in 1910/UIN- 84 in 1907). This level of warmth would lie well above the NBMs 90th percentile. Being such a drastic shift from 24 hours ago, I am reluctant to jump on this solution just yet. Additionally, the unimodal probability distribution function favors low-80s, making the current NBM forecast more reasonable. Confidence remains lower than average in this portion of the forecast with respect to temperatures. What looks more certain is a dry FROPA with limited access to moisture.

What transpires Sunday impacts early next week's temperature trends.
Overall, cooler conditions are most likely, ranging from seasonably cool (slightly below normal) to near normal Monday. The strength and position of the surface ridge and its eastward progression will determine how return flow plays into a warming trend Tuesday and beyond.

Maples

AVIATION
(For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1113 AM CDT Wed Mar 18 2026

VFR conditions are expected throughout the 18Z TAF period. Light southwest to west winds during the day today will become nearly calm overnight, and switch to the north near the end of the period as a weak cold front moves through the area. While mid and high level clouds are expected this evening, overnight, and tomorrow morning, ceilings will remain well above VFR levels.

BRC

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