St. Joseph, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

110
FXUS63 KEAX 171153
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
653 AM CDT Thu Sep 17 2026

.KEY MESSAGES...

- Areas of dense fog (visibility < 1/4 mile) along the MO/IA/NE
  borders potentially extending to the US-36 corridor.

- Small chance for showers across the NW corner of MO this
  morning. Additional small chances in NE MO early Friday
  morning. More substantial rainfall is expected late Friday
  through Monday.

- Warm into the weekend before cooler, more seasonable
  temperatures return next week.

&&

.DISCUSSION...
Issued at 303 AM CDT Thu Sep 17 2026

Ridging and warm air pushed a little further north Wednesday
afternoon which was a bit further than anticipated, but not
surprising. This is part of a expansive high pressure across the SE
CONUS building a bit northwestward. The two primary effects of this
are warming temperatures and clearing skies through the overnight.
This has also pushed the flow of upper level shortwaves NW keeping
rain chance mostly across NE and IA, although there is a chance for
a stray shower across far NW MO during the early morning hours. What
is more likely though is some fog development as slowly departing
rains on Wednesday have left much of far northern MO saturated and
radiational cooling has fairly quickly shrunk dew point depressions
creating a favorable environment for fog. The nighttime microphysics
channel of GOES EAST shows low clouds and for extending from Holt
County MO northeast through Schuyler County. Areas of dense fog
(Visibility < 1/4) mile are possible yield a dense fog advisory for
the NW corner with possible expansion SE depending on how fog
advects from weather to the north. It is unlikely dense fog will
extend much past the US-36 corridor.

Fog dissipates after sunrise with southerly flow once again
dominating. The good news is that surface level southerly flow is
rather meager which results in weaker warm air advection. This keeps
the general pattern of more pleasant conditions across the north of
the area and much hotter to the south; however, the gradient become
much less stark. Highs north of I-70 range from the 80s to the low
90s with areas south of I-70 from the 90s to near 100F. Heat index
values crest 100F along and south of the MO River peaking at 105-107
across central and SW MO.

This warming trend continues into Friday as the high ever so slowly
build northward. However, on the opposite side of the country, a low
digs from the Pacific NW which has a little more success showing its
way south and eastward. This puts the exit region of this upper low
over the Rockies creating a channel for lee trough development. This
tries to piece together showers and storms Friday morning across NE
and IA, but becomes more successful during the afternoon and evening
as low level lee cyclogenesis develops across eastern CO and western
KS. Model guidance remains somewhat uncertain as to the location of
where this cyclogenesis will manifest itself, but consensus places it
in the eastern CO foothills to the NE Sand Hills. As such, this
looks to compress the pressure gradient across the central CONUS as
the system begins intruding upon the high to the SE. As it does so,
accelerated warm air and moisture advection lift temperatures.
Strangely, this will be on display overnight Friday into Saturday as
most areas will see lows in the low to mid 70s. The nocturnal LLJ
will also crank up combined with multiple avenues for ascent
resulting in showers and thunderstorms developing early Saturday
morning. Ensemble guidance places the most likely chances for
showers Saturday morning across far NW MO, but it is not implausible
for rain chances to extend southward toward the I-70 corridor.

As the Sat AM lee trough moves, it runs into resistance from the
high to the east. This deflects the system toward the northeast.
However, additional waves are expected to travel this path thanks in
part to a synoptic cold front that is expected to approach Saturday
afternoon. This large scale front also runs into resistance from the
high creating a channel across KS and NW MO for the waves and
accompanying rain to follow. This set up sticks around through
Sunday into early Monday looking fairly similar to what we saw
Tuesday and Wednesday. This brings the potential for training
showers and storms along a SW to NE oriented boundary. It remains
fairly uncertain the exact hazards and impacts as resolution of
convective variables remains rather course. The air mass behind this
front is notably cooler than what we currently have, and such a
transition is unlikely without at least a slim chance for isolated
robust convection. PWAT values around 2 inches are on the higher
side of normal creating an environment for heavy downpours.
Uncertainties will narrow as higher resolution guidance comes into
range.

The good news is that behind the cold front, temperatures dip back
into the 70s and 80s. The upper level high is slowly beat into
submission creating more zonal flow across the interior CONUS. This
brings more transitive flow of system through the continent which
looks to keep the extended pattern active with multiple chances
for rain through the next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 649 AM CDT Thu Sep 17 2026

Fog at STJ is expected to lift through the morning hours
rejoining the remaining terminal to VFR conditions. Winds start
out of the west becoming light through the afternoon and evening
as they shift to easterly during the overnight. High-res model
guidance is suggesting a low MVFR to IFR cloud deck overnight;
however, confidence is low for this current TAF issuance, so
just indicated the possibility with a low SCT deck.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...Dense Fog Advisory until 10 AM CDT this morning for MOZ001>005-
     011.
KS...None.

&&

$$

DISCUSSION...Pesel
AVIATION...Pesel