St. Joseph, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

249
FXUS63 KEAX 080805
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
305 AM CDT Sat Aug 8 2026

.KEY MESSAGES...

- Heat will build into the region through early next week.
  Widespread highs in the 90s with heat indices in the 100s are
  expected Sunday through at least Tuesday. An extreme heat
  watch is in effect for areas south of U.S. Highway 50 for
  Sunday through Wednesday because of the extended nature of the
  heat.

- There are slight chances for storms (generally less than 30
  percent) this evening and tonight. An isolated severe storm is
  not out of the question, with damaging winds the main threat.

- The pattern will change late next week, with cooler weather
  moving back into the area and frequent chances for storms.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 221 AM CDT Sat Aug 8 2026

The forecast remains rather challenging during the short term,
with building heat the primary concern. However, there are
subtle chances for storms through Sunday morning, and questions
remain regarding any potential impacts on temperatures/heat on
Sunday.

The western U.S. ridge has amplified somewhat during the past
couple of days, with northwest flow downstream in the northern
Plains. This pattern will deamplify somewhat this weekend as the
ridge axis drifts eastward slightly. After a couple of
perturbations move through the northern/central U.S. today and
tonight, the slowly approaching ridge will lead to warming
temperatures Sunday and Monday. Forecast heat indices, in the
absence of convective interference (see below), will
approach/exceed heat advisory criteria Sunday and Monday (105+
degrees) in much of the forecast area. With the semi-persistent
ridging in the western U.S. through the next week, this heat
should continue for a lengthy period (through Tuesday in most of
the area and Wednesday for areas south of I-70/U.S. 50). With
confidence reasonably high that heat indices will meet/exceed
advisory criteria for several days in these areas, have hoisted
an extreme heat watch for the Sunday through Wednesday time
period. For the KC metro, northeast Kansas, and northern
Missouri, confidence is a little lower on the front end and the
back end of the heat event. Initially, storm chances through
Sunday morning may keep temperatures slightly at bay on Sunday,
especially in north-central and northeast Missouri. Meanwhile,
for Wednesday, a cold front will approach/move into the region
from the north, likely bringing cooler temperatures and
increased chances for storms. Thus, these areas will likely
require heat advisories some time during the Sunday through
Tuesday time window, but the duration of heat will not
sufficiently meet extreme heat warning criteria.

Subtle perturbations in the northwest flow in the northern U.S.
are expected to initiate storms/convective systems at times
through the weekend. Unfortunately, CAMs have continued to
exhibit poor run-to-run continuity and model-to-model agreement
on convective scenarios/evolutions. These discrepancies appear
right away, with the HRRR/RRFS/NAM Nest waxing and waning on a
forecast convective system moving southeastward from South
Dakota and Nebraska today. Some simulations keep such a system
fairly vigorous right through the evening hours as it would move
into the CWA. Others dissipate the convective system during the
day, well before reaching the CWA, or develop no such convective
system at all. Thus, the forecast is quite uncertain today.
Currently, PoPs are below mentionable levels through early
evening for the area. However, do have some slight-chance PoPs
tonight in northern Missouri, when CAMs have a more consistent
tendency to initiate storms as a perturbation moves through the
central Plains and the nocturnal low-level jet strengthens. Even
then, stronger ascent/forcing will be north of the forecast
area, so storms tonight are much more probable in Iowa than
northern Missouri.

The pattern may repeat itself Sunday afternoon through Monday,
with storms mostly confined to the faster northwest flow to the
north of the area. Ridging will also be stronger in the region
on Sunday and Monday, so storm chances seem even lower than on
Saturday. The highest chances are in far north and east parts of
the region during the nighttime hours, when forcing for ascent
attendant to shortwave troughs glances the region, aided by the
nocturnally enhanced boundary-layer wind maximum.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Issued at 221 AM CDT Sat Aug 8 2026

As the new week progresses, the repeated passage of northwest-
flow perturbations to the north of the forecast area will
eventually re-amplify the western-ridge/eastern-trough pattern.
Stronger vorticity maxima will dig southeastward Tuesday night
and Wednesday night through the central U.S. Eventually, these
shortwave troughs will enable a synoptic cold front to sag
southward into the forecast area. This will lead to a stout
cooling trend for the middle and latter portions of next week.
Additionally, the faster upper-level flow will sink southward
into the central Plains, leading to round after round of
vorticity maxima passing over the region. As a result, storm
chances will greatly increase Wednesday through at least Friday
across the CWA.

This pattern change is favorable for a swath of heavy rainfall.
Coarser physical/AI models show such swaths of heavier QPF (2-4+
inches) in a northwest-to-southeast swath near the storm track
that sets up. Of course, given the extended time range, these
swaths have considerable spatial variability given the lower
predictability. However, the general area of these swaths is
somewhere between central Iowa (ECMWF) to central Missouri
(AIGFS/CMC) or areas in between (GFS/EC-AIFS). The key here is
that this will be a period to watch for flooding potential, and
portions of our forecast area may be at heightened risk later
next week.

Of course, another question mark will be how quickly the heat of
the early week period dwindles with time. Uncertainty increases
considerably Wednesday and Thursday, with models tending to be a
little too conservative with the southward push of cooler air.
This will be largely dependent on the extent and evolution of
several convective systems in the early-to-mid week period. As a
result, substantial temperature and PoP forecast adjustments
may be required for the mid-week period.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1147 PM CDT Fri Aug 7 2026

There is some uncertainty within the TAF period, but more so
during the latter half vs the first half. For the overnight,
light and variable winds and clear skies likely to prevail over
the sites. It is possible prone areas see some shallow fog, but
this would primarily affect KSTJ among the TAF sites. Otherwise,
moisture profiles tend not to be terribly conducive. By around
18z, winds increase and prevail out of the SE, to around 10 kts.
At the same time, some guidance has suggested the potential for
an MCS or decaying MCS to be moving SE out of Nebraska around
the early to mid-afternoon time frame, however this is far from
consistent among CAM guidance and tends to lack run to run
consistency, so have left out any mentions at this point in
time. This potential hinges on any initial development
in/around the western Nebraska / South Dakota border area late
in the overnight tonight, so keep an eye there if desired.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...Extreme Heat Watch from Sunday afternoon through Wednesday
     evening for MOZ039-040-043>046-053-054.
KS...Extreme Heat Watch from Sunday afternoon through Wednesday
     evening for KSZ057-060.

&&

$$

SHORT TERM...CMS
LONG TERM...CMS
AVIATION...Curtis