Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

340
FXUS63 KLSX 271052
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
552 AM CDT Wed May 27 2026

.KEY MESSAGES...

- Showers and a couple of thunderstorms are expected today, mainly
  along I-70 in Illinois. Conditions trend drier through the
  weekend.

- Temperatures remain fairly steady through the forecast period,
  hovering near normal (upper 70s/mid-80s).


&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 332 AM CDT Wed May 27 2026

Hazards (Type/Potential):
1) Dense Fog/Low

Forecast Challenges (Topic/Confidence):
1) Precipitation Occurrence/Medium
2) Precipitation Location/Low
2) Thunderstorms/Low
3) Temperatures/Medium-High

The large scale upper level pattern shows an omega block that
includes an amplified ridge over the Midwest and longwave troughing
at either side of the ridge. One trough extends southward along the
Pacific coastline and includes a closed low over California. The
second is extends southward from Canada and encompasses the New
England Region. Surface analysis depicts dominant surface ridging
over Atlantic, extending into the southeast CONUS, while another is
centered over the western side of the Hudson Bay. Mixed into the
middle of it all is a pesky, meandering boundary and weak surface
low, all of which have been variably influential over the last few
days.

There is some concern for locally dense fog early this morning as
surface observations show dropping visibilities over the Ozarks. BL
conditions have become increasingly more moist in the last 24-36
hours with light/calm surface flow. A few observations have dropped
near 1/4 of a mile, mainly coinciding with small voids in the cloud
cover. GOES nighttime microphysics products show existing low
ceilings extending through he center of the CWA and slowly expanding
westward. Underneath the overcast cloud cover, only minor visibility
restrictions (as low as 4SM) have developed. At this time, there is
a concern, but confidence is low with respect to widespread dense
fog. Trends will be monitored in the event a Dense Fog Advisory is
needed.

Fog can also be attributed to additional moisture deposited to the
surface yesterday afternoon, which stems, in part, from the weak
boundary that is meandering through the region. This has created the
painful task of attempting to narrow down precipitation timing and
location, all in what is a weakly forced, low flow environment. The
pattern is one that supports episodic, low generally low
probabilities, and locally high precipitation rates. While many
locations remain dry, localized areas experience brief periods of
heavy rain, especially when thunderstorms are involved. Episodic
periods are most supported in relatively short timeline when higher
moisture occasionally overlaps with weak shortwaves/vorticity.
Thunderstorms have been limited in number and intensity with short-
lived updrafts in weak shear. Confidence is capped by the high
variability in QPF production over short distances, where the
forecast`s aerial QPF means are either overachieved on a localized
scale or inversely overstated at dry/drier locations.

The environment too much different today considering the persistence
in the pattern. PWATs have generally ranged 1.3-1.8" with a near-
daily north/south, push/pull behavior in higher moisture content. At
times, weak vorticity passes overhead, promoting development in the
periods of peak instability. What instability does exist is often
mitigated by remnant cloud cover, weak shear, and weak flow, leaving
little concern for strong storms and severe potential. While
temperatures have become persistent in recent days, rainfall impedes
warmth and creates afternoon/evening temperature disparity of
roughly 5-10 degrees (70s vs 80s). One thing that will be lacking
today is shortwave energy with signals of weakening vorticity. This
translates to coverage should be limited compared to yesterday. The
highest chances (40-50%) are over the eastern CWA in closer
proximity to what is a progressively muted shortwave.

As we progress through late this evening into Thursday, the strong
surface high drops south from the Hudson Bay along with a back door
cold front, resulting in dry, northeasterly flow underneath the
amplified ridge. This effectively limits rain chances as model
trends and soundings show the depth of dry air increasing from north
to south. Short and medium range guidance are in good agreement that
rain chances are shifting further southwest as the surface ridge
inhibits potential.

Therefore, rain chances (30-50%) exist today, but trend lower with
time (tonight into Thursday). Confidence in the exact timing and
direct impacts (by location) remains low. Confidence in temperatures
would be higher, if not for the disparity created by rainfall.
Another bout of fog potential exists late tonight and early Thursday
over southeast Missouri. That said, cloud cover should limit dense
fog.

Maples

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 332 AM CDT Wed May 27 2026

Hazards (Type/Potential): None

Forecast Issues (Topic/Confidence):
1) Precipitation Occurrence/Low
2) Precipitation Timing/Low

Thursday night into Friday has trended in favor of drier conditions
as the back door cold front shunts precipitation potential
southwest. That being said, a narrow corridor of showers and a few
thunderstorms line up through central/southwest Missouri, possibly
skimming the far western border of the CWA. ECM/GEFS QPF plumes show
a much tighter clustering of members with the upper quartile of the
IQRs at or below 0.5" at KCOU. The characteristics in the upper
quartile show where precipitation potential is slightly better as
KCOU data shows small, incremental increases through Friday and KSTL
remains nearly flat (dry). ECM would increase confidence in dry
conditions, while the GEFS broadens precipitation potential, likely
due to lower resolution output. This could be causing subtle
differences in precipitation placement provided that precipitation
potential is driven by subtle, weak features not fully resolved by
GEFS. Another indicator is that each of the ensemble suites have
lowered QPF values by 50-75% since yesterday. NAM does swing a bit
farther northeast, which begs to question the northeast extent of
the precipitation field. NBM seems to be a bit broad in the spatial
and temporal sense with the expectation that this area will narrow
in time. North and east of there, dry weather is becoming strongly
favored.

The pattern remains somewhat stuck heading into the weekend, which
keeps confidence low over the south and western sections of the CWA
(central and southeast Missouri). The upper level pattern then shows
some change heading into early next week with quite a bit of spread
in terms of precipitation potential. Once again, this is a product
of the weak flow environment with subtle surface features that
aren`t well resolved this far out. NBM has jumped ship on PoPs, but
I am not entirely sold. The omega block begins to shift westward as
troughing broadens over the eastern CONUS. This draws another back
door cold front into the region with weak vorticity/shortwaves
hinged up at its western periphery. While temperatures spreads
remain quite tight for this distance in the forecast, precipitation
potential remains in question.
Maples

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 538 AM CDT Wed May 27 2026

A shroud of cloud cover and scattered showers continue to impact
the region this morning. Most of the rainfall has been east of the
terminals, though additional development is possible (20-30%)
through late afternoon. Showers will slowly decrease in number and
coverage through the day as the system pulls east. Ceilings have
remained VFR overnight with scattered clouds hovering between
2-3k feet. Guidance has been more pessimistic than reality and the
window of opportunity for lower bases to fill in is closing.

Calm to weak surface flow continues through the day, largely light
and variable. The area will not be entirely void of MVFR
vsby/ceilings, but will be limited in temporal and spatial extent.
VFR conditions are favored across the area today. Some patchy fog
is possible tonight, a majority of which remains south of the
terminals.

Maples

&&

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

$$

WFO LSX