Marine Weather and Tide Forecast for Palmyra, IL

SHORT TERM
(Through Late Tuesday Afternoon)
Issued at 248 AM CDT Mon Apr 21 2025

Low pressure continues to march off to the northeast, dragging the cold front east of the forecast area early this morning. Westerly surface winds gradually turn out of the northwest behind the departing low and associated cold front, gradually drawing cooler air into the region today.

Low clouds linger behind the system thanks in part to saturation below 800 mb. HRRR total cloud cover percentages show clouds breaking/clearing from west to east this morning into early afternoon. Deterministic guidance has this occurring as drier air continues to filter into the 925-850 mb layer, effectively scouring out any lingering low level saturation. Much of the region breaks out into sunshine by early to mid-afternoon with clearing occurring earlier in the day over central Missouri and locations along and east of the Mississippi River around/after 18z. HRRR ensembles show a pocket of greater spread (4-6 degrees F) extending down the back side of the cloud deck, signaling minor timing difference in the speed of clearing, but quickly erodes as temperatures respond rather quickly to sunshine. Highs will range from the mid-60s (north) to the low-70s (south). Surface high pressure maintains clear skies with light winds overnight, allowing temperatures to cool into the mid/upper 40s by Tuesday morning.

Low pressure tracks through the northern Plains as surface flow turns out of the south and southwest at the back side of the southeastern ridge. Milder air advects back into the region, resulting in mid-level temperatures warming around 10C Tuesday. In the process, upper level moisture increases enough to push high clouds in Tuesday afternoon. Cloud cover looks thin enough to have little impact on temperatures with highs in the mid-70s to near 80 degrees.

Maples

LONG TERM
(Tuesday Night through Sunday)
Issued at 248 AM CDT Mon Apr 21 2025

The synoptic pattern gets a little more challenging as the week progresses. The northern stream system includes a trailing cold front that eventually stalls as warm air advection pushes northward.
The end result is a stationary front that sets up somewhere in the vicinity of southern Iowa. Meanwhile, surface high pressure moves into the eastern Great Lakes while southeastern mid-level ridging remains fairly steady.

One thing that looks a little more clear across deterministic solutions is the presence of a dry layer that is crammed between moisture along and south of the MO/AR border and moisture pooling along the stalled boundary to the north. The dry layer may hold through the first half of Wednesday, possibly longer. By Wednesday afternoon, mid/upper shortwave energy moves into the central Plains and advects moisture in from the south. Low precipitation chances (20-40 percent) were originally dispersed across a large portion of the forecast area only a couple of days ago. Chances have gradually pulled to the north and will likely continue this trend as additional data in subsequent updates get a handle on the dry layer and timing of moisture advection in the later half of the week.

A series of generally west-to-east-moving shortwaves embedded in zonal flow aloft ride atop the stationary boundary that keep chance PoPs to the north at least initially. Chances increase in time as the stalled boundary is shunted southward as a corresponding surface low track northeast over northern Missouri and southern Iowa late Thursday into Friday. LREF ensemble members show the greatest spread in the forecast around this timeframe, indicating uncertainty in the where the boundary is positioned. 00z LREF data suggested the spread over the north near the boundary early Friday, expanding southward with the boundary through Friday afternoon. Shortwaves will take advantage of the increased moisture and surface boundary to give rise to scattered showers and thunderstorms in an increasingly unstable, weak flow environment. While exacting timing and rain potential is uncertain, the highest chances remain centered on Friday with the anticipation that the front drops southward through the forecast area and stalls to the south.

By next weekend, surface high pressure builds southeastward as an amplified upper level ridge moves east over the central U.S. Mild or even warm conditions are favored for now. Though part of next weekend looks dry, this will be highly dependent on both the trends in the stalled front to our south and how the pattern influences the track of additional disturbance later in the weekend.

Maples

AVIATION
(For the 06z TAFs through 06z Monday Night)
Issued at 1051 PM CDT Sun Apr 20 2025

Showers and thunderstorms will continue to exit the area through tonight. Low MVFR to IFR cloud cover is following behind. This deck will produce restricted flight conditions into late morning before scattering. Dry and VFR conditions will persist thereafter.
Otherwise, gusty winds will continue over a similar timeframe before diminishing in the afternoon and becoming light and variable areawide by evening.

Jaja

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