Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

829
FXUS63 KLSX 190338
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1038 PM CDT Wed Mar 18 2026

.KEY MESSAGES...

- A significant warmup is nearly certain (90+%) between tomorrow
  and Saturday, possibly Sunday as well. Temperatures will quickly
  warm to between 20 and 25 degrees above average during this
  period.

- A dry cold front will halt this warming trend sometime between
  Sunday and Sunday night, but this cooldown is likely to be
  brief.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 252 PM CDT Wed Mar 18 2026

The main story over the next week continues to be our rapid recovery
and warmup after our brief bout of winter-like temperatures over the
past couple of days. While today`s temperatures are certainly not
the warmest we will see this week, we have already warmed up
considerably from the day before, and this will only continue
through Sunday.

There are two main factors that are driving this warmup. First, a
large upper level ridge is building across the western and central
U.S. While this is not centered directly overhead, it is enough to
cause geopotential heights to rise significantly in our area as
well, and thus allowing temperatures aloft to rapidly warm. Second,
a persistent regime of south to southwesterly low level flow has
begun today, and this will drive several consecutive days of modest
warm air advection. The end result will be steadily warming
temperatures through the end of the weekend.

For today`s part, this process has already led to rapid temperature
increase of anywhere between 25 and 40 degrees from the same time
yesterday, as noon temperatures have already reached the 50s and 60s
area-wide with another 5 degrees or so on the way. Meanwhile,
lingering mid-level cloud cover has almost completely cleared,
leaving the area under full sun. Overnight, surface winds are
expected to become nearly calm as a subtle meso-high moves through
the area, but another round of mid level clouds will likely inhibit
radiative cooling and keep temperatures relatively mild...from near
freezing at the coldest to the mid 40s.

During the day tomorrow, a very weak cold front will approach the
area from the north, but will be very far removed from it`s parent
shortwave and surface low. Without much of a cold push behind it,
this front is not expected to impact temperatures much, if at all,
and may not even move completely through the area before it
dissipates. While this may keep temperatures a couple degrees cooler
than they would be without it, temperatures are expected to climb
into the upper 60s to mid 70s regardless. Otherwise, no
precipitation is expected in the short term period.

For more context, our average afternoon high temperatures this time
of year range from roughly 52-57 degrees, which we have already
reached today, and are on track to exceed by 15 to 20 degrees
tomorrow.

BRC

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 252 PM CDT Wed Mar 18 2026

Our warmup will continue through Saturday and likely Sunday as well,
as the previously described synoptic pattern will remain largely
unchanged through this period. While there are a couple of minor day
to day changes to note, confidence remains high that temperatures
will reach roughly 20 to 25 degrees above average in most areas
during this period, and possibly even higher.

On Friday, another passing "clipper" shortwave will move through the
Great Lakes, and send another weak cold front into the middle
Mississippi River Valley. While slightly more potent than it`s
predecessor, it nonetheless will also be weak and may not
completely move through our area until late in the evening or
overnight Friday. As such, its impact on temperatures is expected
to be rather minimal overall, and with LREF ensemble mean 850 mb
temperatures reaching near the 98th percentile of climatology, the
going forecast of afternoon highs in the upper 70s to low 80s
appears to be reasonable.

After Friday night`s weak front, southerly flow will resume again
quickly Saturday, leading to yet another day of similarly warm
temperatures. In fact, we may even see another couple of degrees of
warming from Friday, although it may not be particularly noticeable
at that point.

However, more significant changes are likely on the way between
Sunday and Monday, as a large area of high pressure will push a
stronger cold front through the area during this timeframe. While
this front is almost certain to at least temporarily halt our
warming trend and bring our temperatures sharply downward, the exact
timing of this is still somewhat uncertain. Current ensemble means
project this front to move through the area sometime during the day
or overnight Sunday, and difference in the timing of this front will
make a huge difference in the afternoon temperatures that day. A
slower front would lead to yet another day of very warm temperatures
almost area-wide, while a faster front would start to cool off at
least parts of our area a bit sooner. This discrepancy is clearly
evident in ensemble temperature spreads Sunday both in the NBM and
LREF, particularly in our northern areas that would be the first to
be impacted by this front. We will also need to keep an eye on
Sunday as a potential fire weather day, due to the persistent low
humidity and lack of significant moisture return, and increasing
southwesterly surface winds ahead of the front.

Once the front passes though, whenever that occurs, temperatures are
likely to drop back to near seasonal averages. Once the actual FROPA
timing is factored out of the equation, spreads become much more
narrow and are roughly centered near seasonal averages. This drop
will likely be short-lived though, as long range ensemble means
quickly reassert the upper ridge and drive temperatures back to
above average toward the middle of the week. Meanwhile, chances for
precipitation remain rather low throughout the period, with only a
smattering of members producing light rain with the passage of
Sunday`s cold front. While the forcing is strong enough that this
can`t be discounted, a very dry airmass will significantly limit
this potential, and dry weather is expected to prevail for the vast
majority of the next week.

BRC

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1038 PM CDT Wed Mar 18 2026

VFR conditions are expected through the issuance. A weak cold
front will approach the area from the northwest, but the boundary
is expected to quickly wash out. There are some high clouds
currently overhead due to a passing upper level jet streak with a
general thinning in the cirrus forecast starting Thursday morning.
A weak mid-level enhancement is also allowing for some cloud cover
west of the TAF sites which is forecast to move east and cross the
TAF sites Thursday morning, but again VFR is expected. Winds will
also be mostly light with more of a southerly component Thursday
afternoon.

BAH

&&

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

$$

WFO LSX