Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

085
FXUS63 KLSX 191733
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1233 PM CDT Thu Mar 19 2026

.KEY MESSAGES...

- Well above normal warmth will encompass the region through at
  least Saturday with warmth lingering through Sunday for some
  locations.

- A dry cold front will bring a brief cool down early next week
  before temperatures rebound Tuesday into Wednesday.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 242 AM CDT Thu Mar 19 2026

Temperatures will continue to warm today through Friday with the
potential for near-record highs to close out the work week.

Considering the consistency in guidance and increasingly tight
clustering of the NBM output, there`s not much to question other
than minor details that seem to be less influential as they come
into view of the hi-res guidance. This primarily concerns multiple,
very weak, mid-level shortwave troughs that continue to round the
western ridge. Over the course of the week, medium range guidance
has shown brief wind shifts following each of these features with
the end result being a momentary pause to WAA, most notably over the
north/northeast quadrant of the CWA. However, the most recent
example was yesterday`s clipper system. Despite it being not too far
departed to our northeast (central IL), temperatures responded with
a quick turn to southerly winds and sunshine. Even after bumping
forecast highs by a couple of degrees, we still exceed forecasts by
3-4 degrees with sunshine and southwesterly flow.

Today will be a similar story. Surface/mid-level ridging over the N.
Gulf Region will be the catalyst in pulling warmer (15-18C at H8)
air eastward from the Plains into the mid-Mississippi Valley. Dry
air, sunshine, and deep mixing will send temperatures well into the
70s, nearing 80s degrees northeast of the Ozarks. This trend
continues into Friday with the aforementioned shortwave passing to
our north. It seems to exhibit less influence that in past guidance
updates with any reinforcement of cooler air stalling near the MO/IA
border. Therefore, another bump in temperatures is expected. Though
winds increase slightly, the northern stream system turns winds out
of the west through much of the day along with the introduction of
scattered high clouds. This might be the difference between record
highs (see climate section) and near-record highs. Nonetheless,
the well-above-normal forecast is on track.


Maples

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 242 AM CDT Thu Mar 19 2026

Saturday has potential to be the warmest day of the week, if not for
the weak steering flow in the surface to mid-level layer. While
anomalously warm air sits under the upper ridge over the
Intermountain West and Plains, southwesterly flow remains at or less
than 20 knots, increasing too late in the day for any substantial
impact. That being said, once again, recall the light southwesterly
component on Wednesday and it`s impact on temperatures northeast of
the Ozarks. H8 temperatures in the upper teens to around 20C will
send highs well into the 70s (IL) and low to mid-80s (MO). Dewpoints
do climb slightly, but only into the 50s. Unlike Friday, when
surface flow is westerly, Saturday`s southwesterly component under
mostly clear skies could result in slightly more efficient warming.
Model sounding show the top of the mixed layer reaching around 850MB
where winds increase to 40-45 knots. This should support increasing
potential for gusty conditions as diurnal processes increase
momentum transfer Sunday afternoon. Gusts of around 30-35 mph
aren`t out of the question. Current NBM forecasts are a reasonable
target and with records in the upper 80s/near 90 degrees, it
seems to be more of a notable reference at this point, as records
lie well above the 90th percentile of the NBM data. Additionally,
unimodal probability distribution functions still favor low-80s at
most locations.

Sunday is coming into slightly better agreement with NBM IQR ranges
narrowing substantially (~30 degree to ~10 degrees) over the last
couple of days. While the IQR spread has decreased, it`s still far
too large for comfort with 10 degrees being a sensible difference.
LREF ensemble data shows the areas in question beginning to shrink
in geographical extent with the lowest spread along and southeast of
I-44 (MO) and along and south of I-70 (IL). This provides better
confidence in the trends toward warmer temperatures for these
locations. On the other side of the coin, FROPA timing remains a
thorn in the Sunday forecast. Areas to the north, spread increases
to around 20 degrees from approximately Moberly, MO to Quincy, IL
and points north/west. Those ahead of the front could see some of
the warmest temperatures of the week (near-record) as the warmest
mid-level air elongates southwest/northeast just ahead of the front.
925mb temps are even flirting with 30C as the front approaches I-
44/I-70 Sunday afternoon, allowing temperatures to rise well into
the 80s. Current NBM temps may be too low on the warm side of the
front and too high to the north. One ares of high confidence is that
FROPA still looks to be dry with limited moisture return ahead of
the boundary. Expect the questions to be ironed out over the next
day or two as FROPA timing is fine tuned.

Confidence actually increases Monday through Wednesday as the cold
front clears the area and NBM IQR drop to around 5 degrees or less.
Considering the distance in time, this limited spread gives
credibility to a seasonably cool Monday as surface high pressure
funnels in cooler, drier air behind the front thanks to
northeasterly flow. As the surface ridge moves east, winds gradually
veer Tuesday into Wednesday with a return to warmer temperatures.


Maples

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1226 PM CDT Thu Mar 19 2026

VFR flight conditions will prevail through the period. Southerly
flow will prevail ahead of a weak trough of low pressure which
will drift into the are this afternoon and evening. Winds will
become light and variable as the trough drifts across the area,
and then turn back to the southwest Friday morning.

Carney

&&

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

Record Highs at STL/COU/UIN for 3/19-3/22
        STL         COU         UIN
3/19    84 (1907)   81 (2012)   80 (2012)
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