Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

890
FXUS63 KLSX 200950
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
450 AM CDT Fri Mar 20 2026

.KEY MESSAGES...

- Elevated Fire Danger is expected this afternoon near the I-70
  corridor with lower confidence in criteria being met elsewhere.

- Well-above average, near daily record temperatures will persist
  into Sunday ahead of a cold front, before temperatures cool to
  average at the start of the next work week behind the front.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 219 AM CDT Fri Mar 20 2026

Upper-level northwesterly flow will persist across the Mid-
Mississippi River Valley on the northeastern periphery of an upper-
level ridge near the Four Corners Region. Compared to Thursday, high
temperatures are expected to be warmer and around 80 to the mid-80s
F (flirting with daily records), thanks to less cloud cover, warmer
850-hPa temperatures, and deep boundary-layer mixing (above 850
hPa). These conditions will also promote Elevated Fire Danger this
afternoon near the I-70 corridor, where there is greatest confidence
in the overlap of sufficient winds and low RH to promote erratic
fire behavior. A weak cold front will advance southward through the
CWA this afternoon/evening, but with weak/gradual low-level CAA in
its wake, it is not anticipated to have a significant impact on
daytime temperatures. With a mild post-frontal airmass, low
temperatures tonight will only fall to the mid-40s to low-50s F. As
the aforementioned front dissolves by Saturday, low-level flow WAA
with westerly flow will facilitate a quick recovery of high
temperatures ranging from the mid-70s F in south-
central/southwestern IL to the mid-80s F in central/southeastern MO
where WAA onset is earliest.

Pfahler

&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 219 AM CDT Fri Mar 20 2026

On Sunday, an upper-level trough will traverse the Midwest, forcing
a cold front southeastward through the CWA sometime Sunday. Model
guidance is coming into better agreement on the timing of the front,
arriving in northeastern MO/west-central IL during late morning and
along/south of I-70 during the afternoon and evening. The greatest
uncertainty and highest sensitivity to FROPA timing in high
temperatures is across northeastern MO/west-central with the NBM
interquartile range around 10 F, from the mid-70s to mid-80s F.
Along/south of I-70, anomalous 850-hPa temperatures exceeding the
seasonal climatology and favorable, prefrontal low-level
southwesterly flow downsloped off the Ozark Plateau support high
temperatures in the 80s to even around 90 F, which would once again
threaten daily records at least at KSTL. Anomalous temperatures
additionally at 700 hPa will contribute to a capping inversion
across the warm sector of the front. However, 20 to 40 percent of
global ensemble membership sufficiently cools/lifts the inversion
with large-scale ascent to allow showers to develop in southwestern
IL Sunday evening. Any precipitation should be mainly post-frontal,
but some deterministic models have enough lingering instability to
support a thunderstorm or two as well.

Upper-level flow across the Mid-Mississippi River Valley will
generally remain quasi-zonal to northwesterly through next week as
upper-level ridging over the Desert Southwest ebbs and flows.
Following a much stronger round of post-frontal, low-level CAA
Sunday night, temperatures will cool to near average on Monday
before warming back to above average through mid-week. However, to
what degree above average is uncertain with NBM interquartile ranges
expanding to around 15 F Wednesday/Thursday due to model guidance
spread on the northeastward advancement of a warm front through the
region. Much of this spread can be attributed to discrepancies in
amplitude of an upper-level shortwave passing around Tuesday into
Wednesday, modulating the position of the front and potentially
leading to WAA-driven showers. That being said, around half of
ensemble membership has solutions with the shortwave trough too
subtle to trigger showers. This factor, combined with the timing
differences, keeps PoPs too low to mention at this juncture. There
is a signal for another cold front to arrive late in the week,
cooling temperatures once again and providing a relatively more
confident opportunity for precipitation in the CWA.

Pfahler

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 450 AM CDT Fri Mar 20 2026

Dry and VFR flight conditions will prevail through the TAF period
with light westerly winds veering to northerly this afternoon and
evening as a weak cold front arrives. Winds will become variable
tonight.

Pfahler

&&

.CLIMATE...
Issued at 242 AM CDT Thu Mar 19 2026

Record Highs at STL/COU/UIN for 3/20-3/22
       STL        COU        UIN
3/20 86 (2017)  84 (2017)  81 (2012)
3/21 90 (1907)  92 (1907)  88 (1907)
3/22 88 (1907)  90 (1910)  84 (1907)


&&

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

$$

WFO LSX