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FXUS63 KLSX 280351
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1051 PM CDT Fri Mar 27 2026

.KEY MESSAGES...

- A widespread freeze is expected tonight, but another warm up is
  around the corner. By early next week the 80s return. Periods of
  elevated fire danger are also expected.

- A cold front late Tuesday or early Wednesday brings our next
  chance of thunderstorms followed by a cool down.

&&

.SHORT TERM...  (Through Late Saturday Night)
Issued at 252 PM CDT Fri Mar 27 2026

While the short term period will feature largely benign weather
thanks to an expansive area of high pressure, a late-season freeze
is expected overnight tonight, and we will likely see localized
elevated fire weather conditions tomorrow afternoon.

Before we get to those items, rain has largely ended across the area
aside from a few very light straggling showers across the Ozarks,
and a much cooler airmass has become firmly established in its wake.
As of 1 PM, surface observations are about 40 degrees cooler than
the day before at the same time, which is quite a feat after setting
all-time March temperature records at our local climate sites. Even
still, temperatures are on track to reach the low to mid 50s, which
only about 5-10 degrees below seasonal average, and not particularly
unusual if not for the 90s we saw yesterday. Meanwhile, brisk north
winds are adding a bit of discomfort to these temperatures as well,
with sustained speeds of around 15 mph and gusts to 25-30.

Overnight, the aforementioned high pressure will sink into the area,
with the center of it being almost directly overhead by sunrise
tomorrow. As this occurs, very low dewpoint air (teens to low 20s)
will settle into the region and surface winds will weaken
considerably. Meanwhile, skies will continue to clear, and the
combination of these factors should lead to efficient radiative
cooling and cool air drainage. As a result, widespread near or below
freezing temperatures can be expected overnight, and it would not be
a complete shock to see a few protected valleys dip slightly below
20 degrees (as shown by recent MOS guidance). While the core of the
St. Louis metro area may get just enough of a boost from the urban
heat island to prevent a significant freeze, most other areas will
not get this boost. Not only this, but early season warmups have
given us just enough of a nudge into the growing season that there
may be some sensitive vegetation at risk from such a freeze, even
though we still have not yet reached the date of the average last
freeze in any of our counties. Given those factors, we opted to go
ahead and issue a Freeze Warning for the entire area with the lone
exception of St. Louis City and County, where a Frost Advisory has
been issued instead.

During the day tomorrow, winds will turn to the south as the surface
high slides eastward. While speeds are expected to be mostly light,
parts of NE/C MO, and possibly west-central IL, may see sustained
speeds approaching 10-15 mph by early afternoon. Meanwhile, humidity
is expected to be very low area-wide tomorrow afternoon thanks to
the persistence of low dewpoints, and temperatures climbing about 5
degrees higher than today`s values. Considering the very low
humidity, pockets of elevated fire weather are likely in those areas
where winds are slightly stronger. In spite of the recent rain, fine-
dead fuels will spend most of today drying out in the sun and wind,
and should be receptive to fire by tomorrow afternoon. Meanwhile,
greenup has begun across the area, but remains in the early stages
and most of the fuel bed remains dominated by cured winter-time
vegetation.

BRC

&&

.LONG TERM...  (Sunday through Next Friday)
Issued at 252 PM CDT Fri Mar 27 2026

While the remainder of the weekend will feature primarily high
pressure and (mostly) tranquil weather, a more unsettled pattern is
expected to gradually ramp up over the course of the week. This will
bring both the return of shower/thunderstorm chances and also yet
another substantial warmup by mid-late week.

By early Saturday, a large area of high pressure will settle almost
directly overhead, resulting in another mild and dry day. Very low
dewpoint air (likely in the low 20s or even upper teens) combined
with a slight increase in afternoon temperatures will very likely
yield humidity ranging from the low 20s to low 30s, maintaining
the potential for elevated fire weather. We will need to keep a
close eye on our western areas in particular (NE and C MO), as
southerly winds will begin to increase Saturday afternoon as the
surface high slides off to the east. Current wind speed
projections are marginal (sustained 5 to 10 mph), but we do
approach elevated conditions in the current forecast in these
areas. Much will depend on how much rain these areas receive
tonight, although by Saturday the fine-dead fuels will have had a
full day of breezy winds and low humidity to dry back out.

This threat may also continue into Sunday as well, as south-
southwest flow increases slightly more and expands into the
remainder of the area. Once again warm/moist advection will resume,
kicking off yet another substantial warming trend and also gradually
advecting higher dewpoint air into the area. Exactly how quickly
this increasing moisture arrives Sunday will likely determine the
degree of fire weather threat, as will the degree of warming. The
combination of cooler temperatures / higher dewpoints would lead to
a minimal threat, while temperatures on the higher end of the
ensemble envelop, and/or dewpoints on the lower end, could
reasonably result in widespread elevated conditions yet again.

Between Monday and Wednesday, much warmer temperatures will resume
as a broad upper ridge builds across the central CONUS, and south-
southwest flow continues largely unabated. By Monday, median NBM max
temperatures climb back into the mid to upper 80s area-wide, with
narrow ensemble spread, and considering that this flow regime is
very similar to what we`re experiencing now, it would not be a
surprise to reach the 75th+ percentile values of ensemble members
during this period. This is also supported by ensemble mean 850 mb
temperatures forecast to exceed the 97th percentile, and a
relatively robust ECMWF Extreme Forecast Index signal.

Given these very warm expected temperatures we will once again need
to keep an eye on the potential for marginal elevated fire
weather, but this should be offset by the increasing dewpoints.
Meanwhile, the potential for showers and thunderstorms will also
steadily increase by mid-week, particularly as shortwaves begin to
encroach upon the broad upper ridge. Day-to-day details remain
sparse at this time, but

BRC

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1050 PM CDT Fri Mar 27 2026

Dry, VFR conditions will prevail through the TAF period across the
region as weak northerly winds turn out of the south by Saturday
afternoon.

MRB

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Freeze Warning until 9 AM CDT Saturday for Audrain MO-Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln MO-Madison MO-
     Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike
     MO-Ralls MO-Reynolds MO-Saint Charles MO-Saint Francois MO-
     Sainte Genevieve MO-Shelby MO-Warren MO-Washington MO.

     Frost Advisory until 9 AM CDT Saturday for Saint Louis City MO-
     Saint Louis MO.

IL...Freeze Warning until 9 AM CDT Saturday for Adams IL-Bond IL-
     Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey
     IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Pike IL-Randolph IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX