St. Joseph, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

499
FXUS63 KEAX 062323
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
623 PM CDT Sun Sep 6 2026

...00Z Aviation Update...

.KEY MESSAGES...

- Shower and storm chances (30-50%) this afternoon and evening.
  There is a SPC Slight Risk (Level 2 of 5) for severe storms
  for most of the area. The main hazards are damaging wind
  gusts, hail, and locally heavy rainfall.

- Hazardous and prolonged heat continues. Extreme Heat Warning
  remains in effect until 8 PM tonight for areas generally south
  of US-36 and until Tuesday at 8 PM for the Kansas City Metro
  and some surrounding counties.

&&

.DISCUSSION...
Issued at 145 PM CDT Sun Sep 6 2026

Other than enhanced 250 mb winds on the leading edge of the Pacific
Northwest trough, 12Z upper-air observations show that the overall
synoptic pattern is mostly unchanged with the Omega-block still
clearly evident. However, beginning this afternoon and evening, the
thermal ridge will begin to erode as the region of enhanced winds
continues to intensify into a 120+ kt jet streak over the
Intermountain West on the upwind side of the ridge. This will
provide sufficient energy and momentum for the stagnant Pacific
Northwest trough to carried eastward, ultimately deamplifying the
ridge. Although it will be a days-long process, this transition is
high confidence with both the HREF and LREF 10th to 90th percentile
spreads showing a height difference of only about 1-3 dam through
Tuesday with the ridge being fully suppressed by Wednesday.

Overnight Saturday into Sunday, a backdoor cold front moved through
much of the CWA; latest observations and surface analysis suggest
that this boundary has stalled just west of the MO/KS border.
Temperatures are expected to top out in upper 80s/low 90s across
northern MO today behind that boundary. Further south where the
Extreme Heat Warning remains in effect, temperatures are anticipated
to be similar to yesterday in the mid/upper 90s and heat index
values around 105F or greater.

As we head into the afternoon and evening hours tonight, the
evolution of the environment will need to be monitored closely.
Compared to the previous forecast cycle, the likelihood of storm
development in the afternoon has increased (now 30-50% chance
generally along and west of the I-35 corridor). Cloud cover
associated with weak convection and showers to our north and west
have struggled to make it into Missouri. With abundant sunshine and
solar heating, considerable destabilization is underway. By late
afternoon, we could see up to 3500 J/kg MLCAPE and an eroding 850mb
warm nose. Additionally, an outflow boundary from decaying showers
in central Kansas has been noted throughout much of the late morning
hours from KTWX. Depending on how far east this outflow progresses,
it could be a focal point for storm development this evening. For
what it`s worth, the most recent runs of the CAMs do appear to be
initiating convection in a comparatively more organized manner
compared to the disorganized clusters noted in earlier runs which
does suggest some boundary interactions. SPC has maintained the
Marginal Risk (Level 1 of 5) for severe weather in our area this
afternoon and evening with the main threats being hail and damaging
winds. The severe threat appears greatest during daylight hours
today when buoyancy is better for lofting hailstones and sub-cloud
layer profiles are more suggestive of downburst wind potential.
Forecast PWATs are also near the top of climatology around 1.9" to
2.1" so isolated pockets of heavy rainfall will also be possible.
WPC has a Slight Risk (Level 2 of 4) of excessive rainfall in
northwestern Missouri today and tonight. After sunset, expect a
general downtrend in the severe threat with any ongoing storms
though the hydro threat may continue with additional showers/storms
moving into the area, mainly in northwest Missouri.

More uncertainty exists with the late evening and overnight
potential for showers and storms as it is more dependent on factors
across the Northern Plains where convection has been ongoing for
much of the morning and early afternoon. A shortwave helping sustain
this activity will continue eastward tonight which may encourage
continued development. Notably, the steering flow shrouding this
shortwave has a strong northerly component that could draw storms
into northern Missouri sometime after dark (roughly a 20-40%
chance). There would be a much lesser severe threat with these
storms, but heavy downpours and some gusty winds would still be
possible. Showers/storms should weaken and decay with time, but some
may linger through early Monday morning.

Areas across northern Missouri can also expect "cooler" high
temperatures in the upper 80s and low 90s once again on Monday, with
areas between the US-36 and I-70 corridors in the low/mid 90s. South
of I-70 and near the MO/KS border, temperatures are expected to
remain in the mid/upper 90s. The Extreme Heat Warning continues for
the Kansas City Metro and south until 8 PM on Tuesday where there is
higher confidence in 105F heat index values. Additional heat
headlines may need to be considered for portions of central Missouri
on Tuesday and Wednesday but will defer to future forecast cycles as
the timing of a midweek cold front remains unclear. Currently, the
most likely timeframe for the front to move through looks to be
overnight Tuesday into early Wednesday. If this holds true, a
headline on Wednesday would probably be unnecessary but a headline
may still be warranted in central MO on Tuesday. By Thursday,
widespread relief from that frontal passage will arrive with
temperatures in the low/mid 80s across northern Missouri and
northeastern Kansas and in the mid/upper 80s around and south of I-
70. Several more rain and storm chances are in the future,
specifically on Wednesday, Thursday, and over the weekend. Shear
certainly looks sufficient to support some organized convection, but
there are still too many details to be ironed out before any
definitive statements can be made.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 615 PM CDT Sun Sep 6 2026

Although VFR conditions are expected to prevail, isolated to
scattered pop-up thunderstorm development Sunday evening could
impact terminals across the area. PROB30s for -TSRA and MVFR VIS
reductions thru 04Z at KC Metro TAF sites and thru 07Z at KSTJ.
TSRA potential may continue beyond this timeframe, but
additional development is not expected after dark. Some storms
may move south out of Iowa and into northern MO late tonight but
confidence is low...will need to reevaluate at 06Z issuance.
Otherwise, improving conditions Monday morning.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...Extreme Heat Warning until 8 PM CDT Tuesday for MOZ028-029-037-
     043-053.
     Extreme Heat Warning until 8 PM CDT this evening for
     MOZ020>022-030-031-038>040-044>046-054.
KS...Extreme Heat Warning until 8 PM CDT Tuesday for KSZ025-057-060-
     103>105.
     Extreme Heat Warning until 8 PM CDT this evening for KSZ102.

&&

$$

DISCUSSION...Macko
AVIATION...Macko