Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

790
FXUS63 KLSX 191904
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
204 PM CDT Tue May 19 2026

.KEY MESSAGES...

- Today`s cold front will bring in cooler and drier weather for
  the next few days.

- Rain chances increase again late this week into this weekend.

&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 203 PM CDT Tue May 19 2026

A cold front is slowly pushing southeast through the region this
afternoon. While a humid airmass still exists ahead of the front,
extensive cloud cover and light rain streaming across the area as
blow off from convection over Arkansas has really put a damper on
solar heating, reducing the chances for additional thunderstorm
development on the front as it moves through our area this
afternoon. Most of us will just see clouds and light rain with
perhaps a stray rumble of thunder through the evening. Better
chances of thunderstorm development will be focused closer to the
Ohio River Valley. As the front moves through, winds will shift to
the northwest and our temperature and dewpoint drop into the 50s.
This will be a noticeable change from our early season warm and
humid air mass we`ve felt for the last few days.

Extensive low level cloud cover behind the front lasts at least
through the night tonight, ensuring we only bottom out in the 50s
for most due to the cold advection and lack of additional
radiational cooling. If thick clouds linger through the day
tomorrow, then highs will struggle to make it out of the 50s, but if
we get more sun we could make a run at 70. Current NBM forecast is
on the higher end and represents expectations if clouds break up a
bit more, while the MAV and MET both suggest more widespread upper
50s to low 60s, below the 10th percentile of NBM guidance.

Kimble

&&

.LONG TERM...  (Thursday through Next Tuesday)
Issued at 203 PM CDT Tue May 19 2026

The mid level flow pattern across the continent will increasingly
feature some variation of troughing in the West and ridging over the
Southeast US coast. This puts our area in southwesterly mid level
flow steering subtle disturbances through the center of the country.
At the surface, strong surface high pressure over the Great Lakes
will maintain its influence locally, with easterly low level winds
and warm sector heat and humidity staying largely south of our
region. Thus while we see rain chances increasing late Thursday into
Friday and continuing on and off through the weekend, this will by
in large be showers and elevated thunderstorms with a minimal severe
weather risk considering the lack of access locally to the richer
low level moisture flowing off the Gulf. Greater confidence is with
the Thursday-Friday time frame as an initial trough moves northeast
through the flow. After that, guidance varies more considerably on
how to handle the remaining trough with some maintaining a more
robust cut off low over the Southern Plains which keeps us in the
line of fire for additional disturbances through the weekend while
others transition towards northwest flow. Latest NBM continues rain
chances through this weekend which is warranted, but our confidence
is lower on the timing and location of these rounds of rain.

Regarding temperatures, NBM continues to occupy the top spot among
all of guidance for maximum temperatures this weekend. Its spring
bias correction is dominating the physical forecast. For high
temperatures, modeled temperatures aloft are a first stop for any
forecast. This weekend among the long range ensemble guidance
there`s fairly good agreement that 925MB temperatures will be in
the 16-18C Friday through Sunday with an IQR of only 2 to 3C.
Assuming strong mixing to the surface, which can be expected on a
sunny May day, high temperatures would top out in the low to mid
70s. But strong mixing isn`t a given. As noted in the prior
paragraph, subtle disturbances in the southwesterly flow may bring
additional rounds of clouds and showers this weekend, and if that
occurs we would not expect full mixing. So while the official
forecast has temperatures drifting well into the 80s for the holiday
weekend, we have low confidence in this and strong reason to suspect
below normal temperatures continuing.

Kimble

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1229 PM CDT Tue May 19 2026

Thunderstorms to the south in Arkansas have spread a thick blanket
of clouds and light, high based rain showers across our region
this afternoon. Beneath all of this, a cold front is pushing
southeast across the region. Southerly winds ahead of the front
turn to the northwest behind it. Lower ceilings also accompany the
front`s arrival, with most locations upstream in the MVFR range,
but some areas immediately behind the front IFR for a few hours.
These lower ceilings likely last through the night and into
Wednesday morning before some improvement during the day
Wednesday. Although there`s an outside chance of a thunderstorm
developing in the vicinity of the front this afternoon, the
chances are too low to include in any TAF at this issuance.

Kimble

&&

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

$$

WFO LSX