Area Forecast Discussion

000
FXUS63 KLSX 270250
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
950 PM CDT Sun Sep 26 2021

.SHORT TERM...  (Through Late Monday Night)
Issued at 307 PM CDT Sun Sep 26 2021

Warm, dry, and sunny conditions continued today as the mid
Mississippi valley remains positioned along the northwestern
periphery of a broad area of high pressure. However, temperatures
managed to climb a few degrees warmer this afternoon than the day
before, generally in the low to mid 80s with a few locations
threatening to graze 90 degrees within the next hour or two. This
likely due to a combination of an approaching upper level ridge
from the west, and also the development of robust southwesterly
low level flow. These breezy southwest winds, which have
approached 25 mph at times across central and northwest Missouri,
will diminish overnight, and most can expect a cool, pleasant
evening and overnight period.

By tomorrow, the aforementioned upper ridge will continue to move
east, and by mid afternoon its axis should be centered across the
central plains. Meanwhile, a tightening pressure gradient will
bring slightly increased southwesterly winds to the region,
resulting in a hot but breezy afternoon. In fact, due to continue
narrow ensemble temperature spreads and a climatologically favored
setup for above normal temperatures in the region, forecast
afternoon maximums for Monday are well within striking distance of
all time records at all local climate stations (St. Louis,
Columbia, and Quincy). These conditions will also support an
increased risk of erratic fire behavior, which is discussed in
more detail in the fire weather section below. Winds will once
again diminish by early evening, and temperature should cool
quickly as well.

BRC

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 307 PM CDT Sun Sep 26 2021

By Tuesday, the upper ridge will continue to amplify and will likely
be centered directly above Missouri by mid afternoon. As such,
temperatures will remain well above average, with very little change
from Tuesday. Meanwhile, the pressure gradient is expected to relax,
which will act to substantially reduce wind speeds. The end result
will be yet another hot and dry late September afternoon, which may
feel less comfortable after the loss of those breezy afternoon
winds.

Mid week and beyond, models continue to indicate that the much
discussed upper ridge will continue to slowly move east, essentially
becoming squeezed between a slow-moving trough across the eastern
U.S., and another trough emerging from the Rockies. As such, this
will place the Mississippi valley within a region of southwesterly,
and even southerly upper flow at times. This will also open the door
for a weakening shortwave to move into the central plains, possibly
absorbing one or more impulses of with tropical origins as it does
so. However, given the nature of this weak system, models continue
to poorly handle many of the mesoscale features, and confidence
remains low regarding the impacts we will experience locally.

In general, moisture return is expected to increase ahead of this
system across the central plains and Mississippi valley Wednesday
and Thursday. Precipitation chances will also increase in kind, but
confidence remains very low regarding the timing and location of
precipitation, given the uncertainties already mentioned. In fact,
while there seems to be a slight trend toward a wetter overall
forecast, the majority of ensemble members remain quite dry locally
for the next week. The NBM remains especially dry, with 50th
percentile QPF values of 0" each day for the next week. It does seem
that there is a slight preference for areas of central and southeast
Missouri to see showers/thunderstorms, but again confidence remains
low.

Otherwise, well above average temperatures are likely to continue
Wednesday, with a gradual moderating trend expected over the latter
half of the week.

BRC

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 941 PM CDT Sun Sep 26 2021

Southerly surface winds will veer around to a southwest direction
Monday morning and become gusty with a surface ridge centered
over the southeastern US. A westerly low level jet over northern
MO and central IL will result in LLWS late tonight and early
Monday morning with west-southwest winds at 2000 feet in height
around 40-45 kts. A clear sky will continue through the period.

SPECIFICS FOR KSTL: Southerly surface winds will veer around to
a southwest direction Monday morning and become gusty with a
surface ridge centered over the southeastern US. A westerly low
level jet over northern MO and central IL will result in LLWS late
tonight and early Monday morning with west-southwest winds at
2000 feet in height around 40 kts. A clear sky will continue
through the period.

GKS

&&

.FIRE WEATHER...
Issued at 307 PM CDT Sun Sep 26 2021

Breezy southwest winds, low humidity, and well above average
temperatures will combine to produce elevated fire weather
conditions Monday afternoon.

Winds are expected to be light early tomorrow morning, but will
quickly increase during the mid to late morning. By early
afternoon, sustained wind speeds of 10 to 15 mph can be expected,
with gusts between 20 and 30 mph at times. Meanwhile, Relative
humidity values will likely fall to between 25 and 30 percent in
most areas by mid afternoon, with temperatures climbing into the
low 90s. The breeziest winds and lowest humidity values are both
expected to overlap across central and northeast Missouri, as well
as west-central Illinois. Meanwhile, a prolonged period of dry
conditions, coupled with the warm and breezy conditions today,
have allowed fine dead fuels to dry. While conditions are not
likely to reach "critical" levels, there is high confidence that
several hours of elevated fire weather conditions will be realized
from early to late afternoon Monday.


&&

.CLIMATE...
Issued at 335 AM CDT Sun Sep 26 2021

Record highs the next few days...

                   St. Louis     Columbia      Quincy
Sunday    (9/26)    94 (1897)    96 (1897)    91 (1956)
Monday    (9/27)    92 (2019)    93 (1897)    92 (1929)
Tuesday   (9/28)    97 (1953)    99 (1953)   100 (1953)
Wednesday (9/29)   102 (1953)    99 (1953)   100 (1953)


&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion