Marine Weather and Tide Forecast for Portage Des Sioux, MO

SHORT TERM
(Through Friday)
Issued at 218 AM CDT Wed Apr 23 2025

Modest ridging aloft continues today as surface high pressure shifts into the Mid Atlantic states keeping the southeast flow across our region. Moisture return from the Gulf remains focused across the Great Plains keeping thunderstorm activity to our west today. Moisture pooling near a remnant frontal boundary in southern Iowa also serves as a focus for convection this morning but this will continue lifting north further away from our region.
The end result for us is a dry and warm day with temperatures peaking around 80 degrees.

Moisture return broadens to encompass more of our area on Thursday with dewpoints rising through the 50s to near 60 degrees and introducing some instability into our area. Capping is likely to prevent convective initiation across our area on Thursday, but a shortwave trough organizing and tracking into the Plains is likely to serve as a better focus for the next round of showers and thunderstorms. Winds aloft remain fairly weak, so there's little support for storm organization. However, clusters of showers and thunderstorms are likely to develop to the west and eventually push into our area late Thursday and Thursday night as low level moist advection intensifies ahead of the approaching trough. This trough moves through our region on Friday leading to our greatest potential for showers and thunderstorms. Again, though, winds aloft remain weak making it difficult for storms to gain much organization. If any severe weather threat were to develop it would primarily be related to pulse thunderstorms or weakly organized convective clusters. As the trough moves through it will push a cold front southeast through the area, shutting off the moist flow and ending the showers and storms from northwest to southeast during the day Friday.

Kimble

LONG TERM
(Friday Night through Tuesday)
Issued at 218 AM CDT Wed Apr 23 2025

High pressure behind Friday's front brings a brief glancing blow from a cooler and drier air mass that is otherwise moving through the Great Lakes on Saturday. Dewpoints drop from the low 60s to the low 50s leading to a dry day with cooler temperatures near seasonal normals, around 70 degrees. This cool down is brief, though, as more amplified ridging develops in the Plains in the wake of Friday's trough out ahead of a stronger developing West Coast trough. This will allow the southerly flow to return quickly on Sunday ushering warmer and more humid air back into the region. The previously mentioned front is expected to stall south of our area on Saturday before southerly flow renews on Sunday.
Earlier guidance had suggested the front may maintain itself a bit better as it lifts north through our area on Sunday. However the trend in guidance has been to wash this front out Saturday into early Sunday with a more broad southerly flow developing. Without the focus provided by the front, there will be little to force the development of showers and thunderstorms on Sunday. Despite the return of low 60s dewpoints, ridging aloft effectively caps any developing instability on Sunday. As a result of these trends, forecast PoP has come down on Sunday, although NBM does continue some low chances. Among the 12Z ensemble guidance, less than 40 percent of members produce rainfall in our area Sunday afternoon compared to more than 50 percent in prior runs.

The western trough moves out into the Plains early next week while the ridge tilts eastward. With Gulf moisture still streaming northward we'll see increasing instability regionally as well as stronger flow aloft as the trough approaches. This will set the stage for the next potential rounds of more organized severe thunderstorms. How exactly that pans out, and when that threat may be realized in our area, is still a little murky. However guidance has come into a bit better agreement on the general progression of the upper trough. The current consensus is for an initial northern stream portion of this trough to move east across the Upper Midwest Monday into Tuesday. This places the greater focus for potential severe thunderstorms to our northwest on Monday into Monday night. Our area is more likely to remain capped and under the influence of the ridge, further removed from any low level forcing. This actually paints Monday as the warmest day of the forecast. NBM forecast highs are in the mid 80s, but the interquartile range shows that even some low 90s are feasible especially if the influence of the ridge holds strong. This would put us near record highs for late April.

While the northern stream trough pushes east through the Great Lakes, it drags a cold front southeast behind it. This brings the greater focus for convective activity into our area on Tuesday.
There's greater variance in the guidance on how strong of a southern stream trough lingers behind the northern stream one.
With a weak trough convective forcing will be somewhat reduced and the front will make faster progress through our area on Tuesday.
With a stronger southern trough, the front will be slowed by a renewed push of southerly flow and moisture into the boundary, keeping the threat for showers and storms through Wednesday. While these details remain somewhat unclear, it is likely that this Tuesday-Wednesday time period represents the greatest threat for severe thunderstorms or heavy rain in our area next week.

Kimble

AVIATION
(For the 06z TAFs through 06z Wednesday Night)
Issued at 923 PM CDT Tue Apr 22 2025

Dry and VFR conditions are expected to continue through the period. Winds will remain out of the southeast (130 to 160 degrees) at less than 10 knots.

Britt

CLIMATE
Issued at 218 AM CDT Wed Apr 23 2025

Unseasonably warm temperatures are expected on Monday, nearing daily records for late April. Here are the daily record highs for April 28.

LOCATION RECORD ST LOUIS 92 set in 1970 COLUMBIA 88 set in 1970 QUINCY 88 set in 1970

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