St. Joseph, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

408
FXUS63 KEAX 171719
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
1219 PM CDT Mon Aug 17 2026

...Updated 18z Aviation...

.KEY MESSAGES...

- Severe storms are possible Tuesday afternoon into the
  evening/overnight hours. There is considerable uncertainty
  about the timing and location of this activity.

- Not as hot and less humid this week, with the exception of
  Tuesday.

&&

.DISCUSSION...
Issued at 214 AM CDT Mon Aug 17 2026

Water vapor imagery with 500mb heights plotted shows that the upper
ridge has been mostly suppressed to our south with quasi-zonal flow
or subtle northwesterly flow over the region. At the surface, high
pressure is building southward and the combination of the suppressed
upper-level ridging and building surface high pressure will lead to
more seasonal temperatures in the mid-80s and noticeably less humid
conditions. Dewpoints today should be 5-10 degrees cooler than
yesterday, topping out in the mid 60s vs the mid 70s we`ve seen
the last few days. The cooler air may also lead to some river
valley fog this morning, especially across northwestern MO/
northeastern KS where the high pressure center will be nearly
overhead by 12Z this morning.

That surface high shifts to the east of the area tonight, shifting
winds back to the south and leading some moisture streaming back
north into the area. There is decent agreement amongst the models in
developing a convective system Monday night to the northwest of the
area, most likely in northwestern Nebraska into western South
Dakota. This system tracks southeast early Tuesday morning and
may begin to affect northwestern Missouri late morning or into
the afternoon. This actually introduces a fair amount of
uncertainty with the forecast because of its implications on
convection later in the afternoon and into the evening/overnight
hours. Several scenarios appear possible with this setup. One
is that the MCS that develops Monday night is the main severe
weather threat for us Tuesday afternoon and evening. This would
require a later arrival into the forecast area, allowing for
greater destabilization. This is closer to what the NAM shows.
Another scenario is that the MCS weakens as it moves into NW/
northern MO but leaves a boundary that becomes the focus later
in the day, most likely further to the south and possibly draped
across the middle of forecast area. This scenario seems to be
favored by the GFS and the Canadian. Regardless, based on the
broader- scale pattern, with increasing flow aloft poleward,
shear will be favorable for organized storms with potentially
40-50+ kts of deep-layer shear Tuesday afternoon and evening.
This is coincident with steep mid- level lapse rates. At this
time, all severe hazards appear possible, including a small
potential for tornadoes. As is so often the case with these
setups, we will need to see how the earlier activity evolves and
where any resulting boundaries reside to better define a more
probable risk area.

For the remainder of the forecast, temperatures look near to
slightly below normal through late in the week, with a warming
trend for the weekend and into next week. Northwest flow will
become the predominate pattern again through the middle of the
country, with the upper ridge building over the western third of
the country. With this pattern, we`ll need to watch for
southeastward moving convective systems that often travel
further southeast than forecast. So for now, the forecast is
mainly dry but that could change if anything upstream of the
area persists longer or is stronger than forecasts. Eventually
that ridge shifts eastward with the axis moving from the Great
Basin to the spine of the Rockies. The increasing heights and
thicknesses should lead to warmer conditions late in the week
and beyond this forecast. That should tend to shift rain chances
north and northeast of the forecast area as well.

&&


.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1217 PM CDT Mon Aug 17 2026

High pressure will keep weather conditions mild this afternoon
and evening. A few cumulus clouds will be present during the
afternoon hours. Rain showers and thunderstorms are expected
Tuesday, but are expected to hold off until after 18z tomorrow,
outside of the current TAF period.

&&

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

&&

$$

DISCUSSION...CDB
AVIATION...Krull