St. Joseph, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

434
FXUS63 KEAX 041120
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
620 AM CDT Tue Aug 4 2026

...Updated 12z Aviation...

.KEY MESSAGES...

- Warm Today

- Rain Showers Northern Missouri Late Tonight

- Showers and Thunderstorms Spread Across The Area Wednesday,
  Continue into Thursday

&&

.DISCUSSION...
Issued at 516 AM CDT Tue Aug 4 2026

What is left of the mid-level ridge axis has passed into the Great
Lakes Region, which has left a WAA regime and higher theta-e
transport into the lower Missouri River Valley. Short-wave trough
and notable vort maxima over the Northern Plains and Canadian
Prairie Provinces continues to move eastward, and has dug southward.
This has resulted in upper-level divergence across the eastern
Plains of the Dakotas toward the Upper Midwest. This pattern has
also created a few mid-level perturbations over the Rockies, and has
generated enough dCVA to provide lift to develop a surface cyclone.
As this has deepened, surface pressure falls have already been
extending eastward into portions of eastern Kansas this morning.
Over the Northern Rockies this a strong surface anticyclone is
developing behind the northern short-wave that has been breaking
down the ridge pattern. This is pushing a cold front across the
Plains, and overnight produced rain showers across parts of Nebraska
and Kansas. So far those have been on a downward trend, but may be
enough to result in sprinkle activity in far northwestern Missouri
this morning and afternoon. We will likely see increasing cloud
cover from the Plains activity later today, though we may get a
period of subsidence that helps to create breaks in the cloud cover.
With the deepening cyclone, low-level flow remains southerly, and
will provide WAA boosting temperatures into the 90s across most of
the forecast area. Far northwestern Missouri may stay in the upper
80s, as cloud cover may be more dense there. While there will
increasing surface convergence, mid-level kinematic support will be
lacking across forecast area for most of the afternoon, and
therefore will maintain a mostly dry forecast. However a healthy
instability axis is progged to setup across the area, that will set
the stage precipitation late Tuesday Night, and spreading across
most of the area Wednesday.

H5 height falls will pick up in pace late Tuesday evening, and the
surface cyclone will begin to track toward Central Kansas, with
inverted surface trough extending northeastward into north-central
Missouri. The cold front will continue to trail the cyclone. Recent
CAM runs have delayed the timing of rain shower activity late
tonight, not entering northern Missouri until after 04z. Most of
this activity is expected to be elevated, with a strong inversion in
place. Mid-level cooling though may help to steepen 700-500mb lapse
rates, and with increasing shear could try to help some activity
organize. But overall, the environment late tonight may struggle to
support stronger storms. Wednesday morning, we may start to see
activity spread as the cyclone continues to deepen and surface
convergence increases in strength. However, as the forcing moves
eastward, the instability may be very meager. Currently the HRRR is
only depicting a few hundred J/kg of CAPE throughout the warm
sector, which may keep updrafts fairly week. However, deep warm
cloud processes and PWATs in the warm sector of 1.65 inches could
allow even general shower activity to very efficient with rainfall
production, which may result in hydro issues even Wednesday morning.
Attention then turns to the afternoon, to see if any clearing can
occur after elevated morning activity. It is possible with the H5
pattern we may have be able to induce subsidence late in the morning
and early afternoon, that will allow the boundary layer to
destabilize, while surface cyclone continues to deepen and more
moisture transport occurs into the lower Missouri River Valley.
Surface pressure falls push east-southeast as the cold front
continues track across the area. This will be the main forcing
needed for activity. If the instability can be realized, bulk shear
values near the cold front should be around 30-40 kts, aiding in
helping convection become organized. However, with continued
moisture transport and no EML, mid-level lapse rates may only reach
between 5-6C/km, limiting the strength of updrafts despite having
stronger wind shear. Precipitation loading though could be enough to
produce wind gusts around 60 MPH with storms, especially if they
occur during a rapid decaying phase of the storm. Overall CAPE
profiles from model soundings late afternoon and into the evening on
Wednesday are fairly skinny. However PWAT values ahead of the cold
front are currently progged at over 1.80 inches with warm cloud
depths up to nearly 4km, and may result in hydro and flooding
issues, especially if multiple storms develop and train along the
front. Amongst HREF members, heaviest QPF values are favored for
northern and northeast Missouri. 00z HREF PMM values for QPF are
nearly 2.5 to 3.0 inches in our northeastern zones, then drop off
southward through central Missouri to the Interstate 70 corridor.
There is still uncertainty with where the heavier QPF axis may end
up though, as some of the 06z CAMs are not in agreement with each
other on the placement of the surface pressure falls and where the
best instability axis may be able to develop.

Another mid-level vort maxima helps to reinforce lift heading into
Thursday, which will continue shower activity and isolated
thunderstorms through the morning hours before pushing eastward.
Instability should be very limited at this point, and possibly the
surface cold front may be through the area, resulting in elevated
post frontal convection. Cloud cover Thursday along with the
passage of the cold front and cyclone should send temperatures back
into the mid 80s across most of the area.

Weather pattern remains unsettled heading into the weekend, as H5
ridge attempts to build over the western CONUS again. However several
short-waves may be able to move across the Central CONUS which could
provide additional rainfall activity, though forcing does not look
to be overly persistent with recent our recent model guidance runs.
However strong WAA is possible that could send temperatures back
into the 90s over the weekend, though cloud cover and rain showers
will add higher uncertainty to the temperature forecast over the
weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 618 AM CDT Tue Aug 4 2026

Clouds will move eastward out of Kansas today, but most of the
afternoon ceilings should be VFR. Light shower or sprinkle
activity is possible in northwest Missouri this morning. Cold
front will start to move closer late Tuesday through Wednesday
morning, and we may start to see shower development early
Wednesday morning at the TAF sites. Activity becomes more
widespread past 12z on Wednesday.

&&

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

&&

$$

DISCUSSION...Krull
AVIATION...Krull