St. Joseph, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

045
FXUS63 KEAX 211723
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
1223 PM CDT Tue Jul 21 2026

.KEY MESSAGES...

- Drier air behind today`s slightly-ahead-of-schedule frontal
  passage will cap heat indices to around 100 degrees this
  afternoon in central Missouri, so the Heat Advisory has been
  cancelled early.

- Residual overnight showers and storms expected to dissipate by
  mid-morning today, giving way to mostly clear conditions this
  afternoon with the exception of some haze from wildfire smoke
  aloft.

- Cooler temperatures for the remainder of the work week with
  nightly rain chances in portions of the area Wednesday-Friday.
  Thursday and Friday both carry a Slight (Level 2 of 4) Risk of
  excessive rainfall leading to flooding.

&&

.DISCUSSION...
Issued at 214 AM CDT Tue Jul 21 2026

Current Conditions & Synoptic Overview:

The cold front is approaching the Missouri/Iowa and
Kansas/Nebraska state borders early this morning, with
scattered convection ongoing ahead of the synoptic front.
Multiple outflow boundaries are visible on early morning radar
imagery well south of the showers and storms, with some notable
lightning within the stronger cores. A secondary cold front has
been analyzed by WPC along a kink in the surface isobars
extending from the surface low near James Bay in Ontario
southwest across Lake Superior into central South Dakota, with
a plume of noticeably drier air visible on mid-level water
vapor satellite imagery north of this front. This dry air is
riding along the mid-level jet streak formed by the confluence of
flow along the northern edge of ridging over the western US and
the base of an upper-level trough pivoting across northern
Ontario.


Showers/Storms This Morning:

The outflow should act as a stabilizing force on the
environment, especially west of Highway 65, and should slowly
erode the convection moving in from southwest Iowa as well as
existing convection already across the area that is already
struggling to sustain within an increasingly capped environment.
Showers and storms will break apart and become increasingly
scattered as we approach sunrise and they drift further south,
with agreement from CAMs that the last showers should be
dissipated from the area by 10AM. We have seen fairly efficient
rainfall rates with some locations seeing 1-2" per hour with
the strongest storms, but the progressive motion and overall
weakening should prevent any flooding beyond temporary rate-
driven ponding. Isolated gusty winds will be possible through
5AM with rain cores that get pushed down to the surface, but the
window for severe weather has ended.


Temperatures/Wind/Heat Indices Today:

The outflow from storms will help to reduce the otherwise balmy
temperatures early this morning, and lingering cloud cover will
also help the cause, though the high cloud cover associated with
the precip is expected to clear after the rain ends, bringing us
to clear skies for this afternoon. The significantly cooler air
will lag behind the surface front a bit, meaning that southern
portions of the area won`t see significant cold air advection
until near/after peak heating, and high temperatures south of
I-70 could be similarly hot to yesterday.

Where the cold front will really provide relief is on the
moisture front (no pun intended). Not only will the front push
the 70+ degree dew points south and out of the area, winds will
gust up to 20-25 mph this afternoon behind the front, which will
increase the efficiency of deep mixing and act to reduce dew
points even further, into the low to mid-60s! Some may have
noticed that the Heat Advisory has been cancelled early, and
this is the reason why. The front has trended faster than
previous guidance suggested, which means the drier air can
progress further south before we reach peak heating. Even though
central Missouri will likely see one more day of mid- to upper
90s temperatures this afternoon, the sub-70 dew points only
produce heat index values up to 100 degrees.


Smoke:

The northwesterly flow aloft that moves into the area behind the
front will act as a conduit for smoke from wildfires far to our
northwest to move into the area this afternoon into this
evening, creating some hazy conditions despite mostly clear
skies. The RRFS indicates that air quality should remain yellow
(AQI 50-100) until the overnight nocturnal inversion sets in
tonight. Between 12AM and 10AM on Wednesday, the corridor that
is collocated with the most dense plume of smoke aloft may have
AQIs above 100, indicating air quality that may be unhealthy for
sensitive groups and potentially that you`d be able to smell
a faint smoky smell near the surface. The smoke plume should
move out to the southwest overnight and into Wednesday, with
haze clearing fully by Thursday.


Rainfall Later This Week:

Despite the shift to northwesterly flow, there are several
rounds of rain chances before week`s end. A series of shortwaves
will send vort maxes riding across the northern edge of the
anticyclonic circulation in the mid- and upper levels of the
atmosphere, which is located across Nebraska on Wednesday and
central Missouri on Thursday. These energy pulses will lead to
repeated rounds of rainfall/mesoscale convective complexes
Wednesday-Friday, with heavy rainfall looking increasingly
plausible in association with this activity. Rain chances sit
at 30-60% Wednesday night into Thursday morning in areas along
and west of I-49, and 45-80% Thursday night into the day Friday
areawide, lingering at 15-40% in southern portions of the area
into Friday night.

We begin to see more moisture return aloft into our area Thursday
and Friday, with a more favorable southwesterly wind for
moisture advection arriving as the embedded 700mb ridge pushes
across Missouri. PWATs increase above climatological average
Thursday morning and are pushing 2-2.15" by Friday afternoon,
which is above 80th percentile and as high as 97th percentile
for PWAT this time of year. The 06Z NAM indicates a small
embedded 700mb/500mb jet streak should develop across Kansas and
Missouri Thursday and strengthen into Friday, which would help
to initiate and sustain convection on Thursday night into
Friday. This jet streak will increase shear, which may reduce
the training potential a bit and keep systems progressive, but
extremely efficient tropical warm rain processes could still
prove problematic for flooding. Another concerning element
relating to heavy rainfall is that the small embedded jet
streak aloft sets up parallel to the expected 850mb temperature
gradient, which points towards the classic Maddox synoptic
flash flood conceptual model. For these reasons, WPC has
maintained a Slight Risk (Level 2 of 4) for excessive rainfall
leading to flash flooding for portions of the area on Thursday
and Friday.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1214 PM CDT Tue Jul 21 2026

VFR conditions will continue across the region over the next 24
hours. Northerly surface winds will prevail with occasional
gusts up to about 20 knots during the afternoon and early
evening hours today. Minimal cloud cover is expected; some high
clouds may begin to move into eastern Kansas and western/central
Missouri Wednesday morning. Some haze may be noted in the
upper levels as the jetstream pulls wildfire smoke into the
Plains/Midwest. Abstained from including FU or HZ in the TAF due
to the improbability of surface impacts at TAF sites.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...None.
KS...None.

&&

$$

DISCUSSION...Camden
AVIATION...Macko