St. Joseph, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

672
FXUS63 KEAX 171137
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
637 AM CDT Fri Apr 17 2026

.KEY MESSAGES...

- Strong to severe thunderstorms are expected across the region
  this afternoon. All severe hazards will be possible, but large
  hail should be the primary threat soon after storm initiation
  while damaging winds become more probable as storms organize
  into clusters or lines. Isolated tornadoes cannot be ruled
  out, especially if storms can remain discrete.

- Flash flooding and river flooding is possible this evening, as
  storms will be capable of producing torrential rainfall.
  Additionally, training storms may develop in southern portions
  of the forecast area, where local rainfall amounts of 2 to 4
  inches may occur. A flood watch is in effect late this
  afternoon through tonight roughly along and south of I-70.

- Much cooler temperatures are expected on Saturday.
  Temperatures may fall into the low to mid 30s on Saturday
  night, with areas of frost possible (up to a 50 percent chance
  north and east of the Missouri River).

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 237 AM CDT Fri Apr 17 2026

Primary concern in the short term remains the severe-weather
potential this afternoon and evening across the forecast area.
Objective upper-air analysis from this evening indicates a
split-flow trough in the western U.S., with notable vorticity
maxima near the Montana/Canada border, the Great Basin, and just
west of Baja California. All three should eject eastward today,
with the northern-most perturbation acquiring a neutral/negative
tilt by tonight. The Great Basin vort max will become sheared
and elongated north-to-south as it impinges on downstream
ridging in the Midwest. Meanwhile, smaller-scale perturbations
will eject northeastward from the Baja shortwave trough, which
will likely play a substantial role in areas of favored
convective initiation this afternoon.

Cyclogenesis downstream of the U.S./Canada border vort max will
induce rapid development of an upper jet streak in the Upper
Midwest this evening. An antecedent jet streak in the southern
Plains will provide support for a region of enhanced upper
divergence in the lower Missouri Valley. Substantial large-scale
ascent is implied in this pattern, provided by considerable
differential cyclonic vorticity advection from the approaching
deep trough and warm advection immediately downstream of a
southeastward-surging cold front across the northern/central
Plains. Strong frontal forcing combined with the aforementioned
large-scale ascent should rapidly destabilize the warm sector
and provide sufficient lift for convective initiation by early
afternoon. Models have been consistent in storm development near
and just in advance of the front in the 18-21z time frame, in
which the front should be approaching northwest portions of the
CWA. Given the strong/widespread lift in play today, numerous
storms should develop in a short amount of time. The
thermodynamic and kinematic environments today are certainly
favorable for severe storms (MLCAPEs >2500 J/kg; effective bulk
wind difference (BWD) 30+ kt). Noteworthy here is the
relatively modest 0-6 km BWD (25-35 kt during initial stages of
convection, potentially a relative minimum in our region given
our lack of proximity to the northern stream and southern stream
vorticity maxima). However, thermodynamic profiles suggest
particularly deep potentially buoyant layers today, implying
that a deeper layer than the standard 0-6 km depth may be more
indicative of convective wind shear profiles today. That said,
low-level helicity may be rather modest during the
initial/discrete phase of convection this afternoon, reducing
the threat of tornadoes somewhat. With upscale growth expected
to be quick, this suggests that large hail early on and damaging
winds later on are the primary severe-weather threats today. Of
course, isolated tornadoes remain possible, especially if at
least semi-discrete storms can be maintained into the early
evening, when low-level shear improves via the synoptically-
induced low-level jet.

On the north side of the CWA, storm motions will be fast, with
convective-system progression mostly downshear-propagating.
However, slower progression is anticipated in the southern CWA,
in closer proximity to the low-level jet and on the southern
periphery of the southwest-to-northeast oriented midlevel jet
streak. Convection allowing models (CAMs) are consistently
generating a swath of 2-4+" rainfall in a corridor from
southeast Kansas into west-central and central Missouri (roughly
near and south of U.S. Highway 50), in a setup favoring
training convection via upshear propagation effects. With this
area relatively vulnerable to flooding via recent heavy rainfall
events and in coordination with WFO SGF, hoisted a flood watch
for this potential. Additionally, given the unusually high PWs
in advance of the cold front (1.3-1.6+") for this time of year,
rainfall rates of 1-2 inches per hour are quite likely with the
strongest storms. This approaches 1-3 hour FFG in areas
near/south of I-70, especially in urban areas and flashy
creek/stream basins. Thus, I included the KC metro and areas
near/south of the I-70 corridor in the watch as well, especially
given (1) the coarser-scale model tendencies to keep the max-
QPF swath slightly farther north (though this is a common bias
relative to the CAMs), (2) elevated HREF probabilities of FFG
being exceeded in the watch area (20-50+ percent during the
evening hours), and (3) some indications from a subset of the
CAMs (e.g., NAM Nest; RRFS; GEM) of one or more swaths of
heavier rainfall immediately north of the strongest signal
near/within our far southern forecast area.

Overnight, convection should gradually slide off to the south
and east, with the severe threat predominantly done by midnight
and the heaviest rainfalls sagging southeastward with time.
Precipitation should largely be out of the area by sunrise on
Saturday. Strong cold advection on the upstream side of the cold
front should allow temperatures to fall to the 40s by Saturday
morning, which will be a sharp change from the upper 50s to 60s
we have seen of late.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 237 AM CDT Fri Apr 17 2026

Main forecast concern in the long term is the frost/freeze
potential on Saturday night.

Breezy northwest winds and dry conditions should be expected on
Saturday in the wake of today`s system. Highs will only reach
the 50s to low 60s (about 20-25 degrees colder than today). If
storms weren`t likely today, Saturday would be pretty favorable
for some fire-weather concerns, with relative humidity likely
falling below 30 percent during the afternoon. However, given
the recent rainfall (and more expected today) as well as the
recent green-up, not especially concerned about fire weather
this weekend.

The bigger concern is the drop in temperatures on Saturday night
as a surface ridge moves into the region. Winds should rapidly
diminish during the evening, and skies will be mostly clear.
Fairly ideal radiational cooling conditions will exist, so
temperatures should drop readily into the 30s. Expecting some
frost to develop, particularly in river valleys and in rural
areas of northern Missouri. Some areas could locally reach the
freezing mark on Sunday morning. We will monitor for the
potential for any frost/freeze headlines.

Following the relative chill of Saturday and Saturday night, a
broad upper ridge will move into the central U.S. late this
weekend into early next week. This will lead to a quick warm-up
across the area, with a nice multi-day stretch of dry
conditions. Models/ensembles are hinting at the next western
U.S. trough entering the central U.S. late next week, leading
perhaps to another active stretch to end the month of April.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 632 AM CDT Fri Apr 17 2026

Main concern for this TAF period remains the strong to severe
storms expected this afternoon and early evening at the
terminals. Primarily VFR expected through this afternoon (though
a few cloud decks near/below minimum VFR thresholds have
traversed the area early this morning), with south winds 15 to
20+ kt with gusts 25-30+ kt. A cold front will approach from the
northwest this afternoon, initiating storms between 18z and 21z.
Storms will move through the KC terminals between 21z and 00z with
noteworthy impacts expected, including torrential downpours and
sub-VFR CIGs/VSBYs, strong/erratic wind gusts, and possibly
some hail. Storms should move well southeast of the terminals
after 00z, with any lingering showers ending shortly thereafter.
Winds will become northwest 15 to 20+ kt with gusts to 30 kt.
Those winds should gradually diminish by sunrise Saturday.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch from 4 PM CDT this afternoon through late tonight
     for MOZ028>031-037>039-043>046-053-054.
KS...Flood Watch from 4 PM CDT this afternoon through late tonight
     for KSZ057-060-103>105.

&&

$$

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