St. Joseph, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

241
FXUS63 KEAX 201129
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
629 AM CDT Mon Jul 20 2026

.KEY MESSAGES...

- Dangerous heat and humidity combo is forecast today and
  Tuesday, with heat indices of 105-110 degrees. A Heat Advisory
  is in effect areawide from 1PM to 9PM today, and continues in
  portions of eastern Kansas and west-central and central
  Missouri through 7 PM Tuesday.

- A frontal boundary will bring a 30-50% chance of thunderstorms
  to far north-central and northeast Missouri early Tuesday
  morning, with the potential for some storms to be severe.

- Additional chances for widespread thunderstorms return to the
  forecast Thursday into Friday, along with cooler temperatures
  and lower humidity levels.

&&

.DISCUSSION...
Issued at 330 AM CDT Mon Jul 20 2026

Current Conditions & Synoptic Overview:

Ridging aloft spanned the western 2/3 of the CONUS and well
into central Canada in previous days, but this ridge is
beginning to be flattened by a shortwave trough pushing across
the Canadian Prairie. 00Z upper air analysis indicates that a
zonal upper-level jet is developing across the Northern Rockies
and into the Northern Plains, cutting into the northern extent
of the ridge, and the 00Z sounding from Glasgow, Montana has
already observed 100+kts within this strengthening jet streak.
A surface low has developed in Manitoba in conjunction with this
upper-level disturbance, with a cold front extending south from
the low into central South Dakota. Weak surface high pressure
sits over the Great Lakes on the other side of a stationary
front, which is spread from Sioux City, IA to the southeast
through Bethany, MO and towards St. Louis. Widespread visibility
reductions from wildfire smoke are apparent on regional
observations in areas east of the front as the nocturnal
boundary layer traps smoke near the surface.


Heat Today and Tuesday:

"Unpleasant" is not a strong enough word to describe today`s
forecast conditions. As the ridge is flattened and pushed
eastward, low-level flow becomes more westerly, increasing 850mb
temperatures by 2-4C. High temperatures in the upper 90s and dew
points in the mid- to upper 70s will combine to create
widespread heat indices of 105-110 degrees, likely with some
localized spots in excess of 110 degrees. Soundings continue to
suggest that afternoon mixing should help to combat rising dew
points, but Sunday afternoon obs recorded upper 70s dew points
in some locations during peak mixing, and winds will be
similarly light today to Sunday, so the mixing that occurs will
likely not be strong enough to be effective at limiting dew
points very much. As such, Heat Advisory remains in place
areawide from 1PM to 9PM this afternoon. Heat Risk guidance
depicts widespread Major (Level 3 of 4) Heat Risk, suggesting
impacts to anyone without effective cooling or adequate
hydration. Efforts should be made to stay indoors whenever
possible.

Little relief is expected during the overnight hours, with
tonight`s low temperatures only dropping into the upper 70s and
low 80s. As such, minimum heat indices will drop to upper 70s
in much of the area, but the urban heat island in Kansas City
will keep the minimum apparent temperature in the low 80s
overnight. The much-anticipated cold front looks to arrive so
late Monday night that it`s better described as Tuesday morning,
with areas south of Interstate 70 unlikely to see frontal
passage until after peak heating on Tuesday afternoon. For this
reason, kept the segment of the Heat Advisory that continues
until 7PM on Tuesday confined to these areas south of I-70,
where another day of 100-105+ degree heat indices are expected.


Storm Chances Late Tonight/Tuesday Morning:

Convection is expected to fire in Iowa late this afternoon into
this evening, initially as discrete cells and then forming into
multicell clusters. In the early hours of Tuesday morning, most
CAM guidance depicts storms becoming widespread and forming
into a line along the front in north-central and northeast
Missouri, with coverage becoming increasingly scattered/less
organized along the front as you get further west. Depending
where the prefrontal convection forms and develops to our north,
there is a scenario where we could see some storm leftovers
move into the area ahead of the actual cold frontal passage,
which would lead to multiple rounds of storms and an earlier
precip onset time. However, this is the least likely potential
scenario, with most CAM guidance depicting similar locations
and timing windows for showers and storms, and primarily keeping
the most widespread storms to the east of most of our area.

As the upper-level jet streak begins to move into the Midwest
Monday night into Tuesday, shear profiles begin to improve, with
30-40kts of shear by 00Z Tuesday and continuing to increase
through the overnight hours. Instability will be best (3000J/kg+
MUCAPE) during the evening hours and along the front to our
north, but wanes quickly after 1AM Tuesday, which is when the
window for the arrival of the front opens up. Due to the
unfavorable overlap of severe ingredients, the widespread
severe weather risk for most of the area should be limited, but
we will have to monitor for potential severe winds with any
clusters that develop to our north and move into the area
overnight. Areas along and north of a Unionville to Kirksville
MO line are currently in an SPC Slight (Level 2 of 5) Risk for
severe storms, with a very narrow Marginal (Level 1 of 5) Risk
bracketing its southern edge.


Smoke/Haze:

As the stationary front begins to lift back northeast this
morning as a warm front, the smoke in north-central and
northeast Missouri should get mixed out and clear by the
afternoon. However, northwesterly mid-level winds behind the
front on Tuesday will slowly begin to advect smoke from
wildfires in Canada back into the area by late Tuesday afternoon
into Wednesday, potentially causing a few days of air quality
concerns for sensitive groups as the smoke mixes down to the
surface. Additionally as a result, Tuesday and Wednesday should
have some colorful sunsets.


Midweek Into The Weekend:

Wednesday and Thursday`s temperatures will be much more
pleasant behind the cold front, with highs in the upper 70s and
mid-80s and much drier air. As the ridge continues to slowly be
smushed and pushed east through the week, most models indicate
several vort maxes traveling along its northern periphery. These
vort maxes appear likely to cause a couple of nocturnal MCSs
across the Northern Plains later in the week. Wednesday night
will likely be the first system we see, with 30-50% PoPs
confined to areas along and west of the Highway 65 corridor
(likely to be leftovers from a system that is more impactful for
areas to our west). Thursday night brings widespread 40-70% rain
chances, with Thursday night into Friday morning being our best
chance for a widespread wetting rain through the forecast
period.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 622 AM CDT Mon Jul 20 2026

VFR through the TAF period. Light and variable winds early this
morning will become south-southwesterly late this morning into
early this afternoon, with some low fair-weather cumulus
developing this afternoon, which are not expected to develop
into afternoon showers or storms today. Clouds should clear
after sunset, with a period of clear skies overnight before
clouds move back in with a cold front and associated scattered
showers/storms after 09Z on Tuesday.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory from 1 PM this afternoon to 9 PM CDT this
     evening for MOZ001>008-011>017-020>025-028>033-037>039.
     Heat Advisory from 1 PM this afternoon to 7 PM CDT Tuesday for
     MOZ040-043>046-053-054.
KS...Heat Advisory from 1 PM this afternoon to 9 PM CDT this
     evening for KSZ025-102>105.
     Heat Advisory from 1 PM this afternoon to 7 PM CDT Tuesday for
     KSZ057-060.

&&

$$

DISCUSSION...Camden
AVIATION...Camden