Marine Weather and Tide Forecast for Winchester, MO

SHORT TERM
(Through Late Thursday Afternoon)
Issued at 240 AM CDT Wed Apr 30 2025

At the big picture, a trough is currently situated near the Four Corners region of the desert Southwest while a broad, low amplitude ridge exists across the southeast US having been recently pushed back by a fast moving northern stream trough now in New England.
At the surface, a cold front has pushed southward across the central US including our entire forecast area in the wake of the northern stream trough. However, moisture continues to advect northward through the Southern Plains ahead of the Southwest trough. This has led to the development of more widespread thunderstorms across Oklahoma overnight near where this moist advection intersects the frontal boundary. These storms have already begun to organize into an MCS which will move off to the northeast through Missouri today. This MCS is expected to outrun its source of low level moisture and instability as it tracks north of the front, gradually weakening as it moves through our forecast area during the morning hours. Flow within and around the MCS itself will likely pull in greater instability just ahead of it, but this is expected to be elevated in nature as the surface front itself takes longer to react and buckle back northward today. So current thinking is that this MCS will weaken and pose a limited severe weather threat for our area. However, this could change if better surface based instability is able to develop ahead of it this morning.

As the southwestern trough moves out into the Plains today it will strengthen the low level moist southerly flow ahead of it, triggering another round of convection over Oklahoma. This again is likely to organize into a broader MCS and push northeastward into our forecast area this evening into the early overnight hours. By this time, the surface front will have pushed further northward opening more of the forecast area up to some surface based instability enabling this MCS to maintain its strength longer. Wind shear will be increasing as well as the upper trough approaches, so it is likely that this represents our greatest threat for severe weather. Damaging winds will be the primary threat, but there may be enough low level wind shear for a few QLCS tornadoes as well. The biggest limiting factor will be surface based instability which will be on a diurnal downward trend.

While this next MCS moves northeast and out of our forecast area early Thursday morning, surface low pressure will be tracking through northeast Missouri in response to the arrival of the upper trough. This will have the effect of halting the northward advance of the warm front and sending it back southeast as a cold front during the day on Thursday. Additional shower and thunderstorm activity is expected as the trough moves through, primarily ahead of the surface cold front. Wind shear will be weaker near the core of the upper trough, and it's unclear how much instability will be able to redevelop ahead of the front in the wake of the early morning MCS. These factors lead to a much more limited severe weather threat with this round. In fact, latest CAMs have any shower and thunderstorm activity on Thursday much more isolated in nature and the SPC outlook has shifted the core of the severe threat to the east of our forecast area.

One final note on total rainfall amounts. There are likely to be swaths of 1 to 2 or perhaps even 3 inches of rain with each of the broader convective complexes that move through the region this morning through tonight. Each of these swaths will be relatively narrow in width, with a broader area of more moderate rainfall of 0.5 to 1 inches. While 1 to 2 inches over the course of a few hours is not likely to cause flash flooding in general, this assessment could change if these swaths move across areas already significantly moistened by earlier rainfall. If any areas are affected by the more significant swaths of rainfall from both rounds, then a greater flash flood threat will result. As far as river flooding, the combined effect of several days of rainfall will lead to rises on nearly all creeks and rivers across the region. The degree of the rises on each river will be determined by where those swaths of heavy rain fall. There is a comparably greater chance that a few rivers will rise to flood stage in the coming days as all of this water has to go somewhere and will gradually collect into the larger rivers over the course of hours to days. At this time, confidence in flash flooding or river flooding in any particular area is too low for a Flood Watch.

Kimble

LONG TERM
(Thursday Night through Tuesday)
Issued at 240 AM CDT Wed Apr 30 2025

Thursday's cold front sends a cooler and drier air mass into the area. Dewpoints fall into the 40s on Friday while temperatures reach the 60s to low 70s, near or slightly below normal for this time of year. A secondary trough dropping south from the northern stream brings renewed cold advection and one more chance of showers. These showers on Friday will be driven by cold advection aloft rather than by moist advection in the low levels. As a result, instability will be meager and moisture quite limited. Rainfall amounts from this will be minor, with ensemble probability of 0.1 inch of rainfall peaking at only about 20 percent in our area on Friday. While we cannot rule out a few strikes of lightning, we do not anticipate severe weather.

Most guidance has Friday's trough exiting quickly to the east, replaced by ridging downstream of a developing western US trough.
However, cluster analysis shows that some guidance, led by the ECMWF and CMC, actually pull Friday's trough so far south that it gets cut off beneath the developing ridge and lingers over the Ohio Valley this weekend and right into next week. So while the general trend favors dry weather, ridging, and an eventual warm up, a lingering cut off low could spoil that somewhat. The practical difference would be lingering 60s and 70s vs a return to the 80s. There will also be some chances for light showers in the vicinity of the cut off low while ridging would favor more sunny conditions.

Despite the uncertainty in the upper air flow pattern mentioned above, all scenarios point to Gulf moisture remaining cut off and moisture return focused over the western High Plains. So we're not expecting any significant precipitation for several days, at least until that western trough begins to move east late in the week.

Kimble

AVIATION
(For the 12z TAFs through 12z Thursday Morning)
Issued at 624 AM CDT Wed Apr 30 2025

It's a rather complex forecast today and tonight. A dying thunderstorm complex is moving across the region this morning.
It's not certain whether thunder will occur at any TAF site, but this seems most likely in the southeast part of the St Louis metro in the next few hours. We do expect a break in the rain after this moves through, but some lower ceilings are lurking nearby and are likely to keep conditions MVFR or IFR for much of the morning into the afternoon at most sites. A warm front lifting north today may bring some clearing to VFR at central MO as well as the St Louis metro around midday or the early afternoon. But another round of thunderstorms is expected tonight, with a greater chance of impacting both central MO as well as St Louis. A return to lower ceilings is likely after this rain ends. Further north at Quincy, lower ceilings have yet to materialize and may not do so for some time. Quincy is also the least likely to see thunderstorms of any TAF site.

Kimble

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