Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

558
FXUS63 KLSX 300821
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
321 AM CDT Mon Mar 30 2026

.KEY MESSAGES...

- Near-record warmth is forecast today and tomorrow areawide,
  which will combine with dry and windy conditions to result in
  elevated fire danger for parts of the region both days.

- A cold front approaches Tuesday evening, bringing up to an
  80-90% chance for rain and embedded non-severe thunderstorms
  into Wednesday.

- This front is now more likely to stall across our region,
  serving as a catalyst for persistent rain and thunderstorm
  chances through the week.

&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 320 AM CDT Mon Mar 30 2026

Warmer (by 5-15 degrees) and mostly clear conditions are in place
across the Mid-Mississippi Valley compared to 24 hours ago. Further
west, weak but persistent cyclogenesis lee of the Rockies and a
fairly transient baroclinic zone across the northern CONUS is slowly
strengthening the surface pressure gradient across the central
Plains and Midwest. The resultant stronger boundary layer winds will
promote stronger warm air advection through the day today, which
will work with a mostly sunny sky to send temperatures into the
upper 70s to mid-80s (a 10-15 degree jump from yesterday). The
current forecast challenges high temperature records for March 30,
with high chances (90%) of tying/breaking records at Quincy and
Columbia according to the NBM. St. Louis has a roughly 60% chance of
tying or breaking their record, which is slightly warmer than the
other two sites and therefore harder to reach.

The stronger south-southwesterly wind we will experience today will
also introduce yet another day of elevated fire danger across east-
central and southeast Missouri. Most guidance continues to be far
too aggressive in building humidity back into the region, with
regional observations several dewpoint degrees drier than NWP data
at the same time. As such, this forecast leaned heavily on the
lowest end of the NBM probabilistic dewpoint data. Continued caution
with open flames and any activities that can cause sparks is advised.

A warm, fairly breezy night into Tuesday morning will bolster
overnight lows across the region to near-record warm minimum
temperatures. Through the day Tuesday, there is continued agreement
that a shortwave embedded in near-zonal upper-level flow will track
along the US/Canada border. That wave, and the attendant surface low
that tracks through the Great Lakes, will draw the aforementioned
cold front slowly through the Upper Mississippi Valley through the
day. While rain chances do increase to about 40% at most in northern
Missouri and west-central Illinois, we will be strongly capped
thanks to stout 850mb warm air advection. Any rain we manage to get
that morning would be LLJ-driven, and likely dissipate around
sunrise. Otherwise, the region will remain ahead of the front
through peak heating, keeping us largely dry with gusty winds up to
45mph. We also get another chance at breaking temperature records
across the region. Owing to uncertainty in cloud cover and slightly
warmer records overall, the chances of setting one last March record
are a bit lower (50-60%) according to the NBM. The prefrontal
southwesterly winds will also likely lead to localized
blocking/downsloping effects from the Ozarks, resulting in another
day of elevated fire danger for the same areas as today (east-
central and southeast Missouri mainly). With strong winds and RH
values approaching critical (Red Flag) values, we will need to watch
moisture trends closely given the recent poor performance of NWP in
this regard.

MRB

&&

.LONG TERM...  (Tuesday Night through Sunday)
Issued at 320 AM CDT Mon Mar 30 2026

There is better agreement that the front arrives in the northwest
corner of the forecast area by 00Z Wednesday. While the low-level
forcing of this feature should aid convection in overcoming the
gradually-eroding inversion, most of the more widespread
precipitation seems forced along the front at 925-850mb. This
potential is further supported by most model QPF occurring behind
the surface front itself. Deep convection also seems fairly
difficult to achieve without height falls aloft, as the
aforementioned shortwave will be well to the northeast by this
point. As such, a threat for any stronger thunderstorms is very low
(less than 10%). The potential for this front to not fully pass
through the forecast area continues to gain momentum with every
model run, and this solution is now depicted in a preponderance of
guidance. The axis of the heaviest rain (locally up to 1.50" by most
depictions) is looking more likely from central and northeast
Missouri up through west-central Illinois. While PWATs are quite
anomalous (99th climatological percentile) on Wednesday, other
metrics of efficient rainfall like warm cloud depths are more
marginal at best per model soundings. In the absence of convective
elements, I expect any threats from heavy rain to be few and far-
between. There will likely be a fairly stark difference in
temperatures across the region on Wednesday as well owing to the
stalled front, with mid-50s forecast on the cool side and low 80s on
the warm side.

The wave pattern aloft is still forecast to amplify with a longwave
trough digging in the western CONUS. The resultant southwest upper-
level flow will help the front drift back north Wednesday night into
Thursday, drawing warmer air back into a larger footprint of the
region. At the same time, a stronger shortwave amidst this amplified
global-scale pattern will approach the region from the Plains. With
near-record PWATs still in place and a low-level jet strengthening
overnight, this stronger mid-level ascent (along with some weak but
present jet-level dynamics) will lead to another round of showers
and thunderstorms across the region. The highest amounts will occur
closer to where guidance is hinting a pre-frontal convergence zone
will exist, whose location varies from eastern Kansas to central
Missouri. Regardless, this represents an additional threat for
locally-heavy rain. Areas that see higher totals from both rounds of
rain overnight Wednesday and overnight Thursday may see some
nuisance flooding and rises on creeks/streams, but there remains no
suggestion of any more significant impacts than that.

On the heels of that round, a much more potent wave aloft takes aim
on the Mississippi Valley late Friday into Saturday. As it currently
stands, this system looks more progressive than the sluggish, poorly-
forced waves earlier in the week. The track of the system varies
significantly across the ensemble suite, which has notable
implications for impacts with such a potent wave. We will need to
keep a loose eye on the threat for stronger storms, though right now
most machine learning guidance is quite pessimistic on that
potential. While rain chances are once again high (60-70%) by then,
this represents the last significant signal for widespread
precipitation before cooler, drier conditions take hold Sunday into
early next week. When all is said and done with this wet pattern, an
axis of 3.00-4.00" of rain may result somewhere in the region (more
likely in central Missouri than anywhere else). Even with this
amount of rain, HEFS probabilities of reaching minor flood stage on
our small streams and mainstems across the region are fairly low (10-
20%) thanks to recent dryness and a lack of significant snowmelt
from points north.

MRB

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1045 PM CDT Sun Mar 29 2026

Increasing wind flow aloft tonight will lead to low level wind
shear through the mid morning hours. Winds aloft are out of the
southwest at about 40 to 45KT while surface winds are generally
out of the south at less than 10KT. As the morning goes on and low
level mixing increases, this wind shear will go away. Surface
winds increase and winds aloft decrease. Otherwise VFR conditions
will continue at all terminals.

Kimble

&&

.CLIMATE...
Issued at 238 AM CDT Sun Mar 29 2026

Record Maximum Temperatures at Regional Long-Term Climate Sites

             March 30th   March 31st

St. Louis:   86F (1986)   87F (1981)
Columbia:    84F (1967)   86F (1940)
Quincy:      82F (1943)   81F (2010)

Record High Minimum Temperatures at Regional Long-Term Climate Sites

St. Louis:   67F (1998)   63F (1917)
Columbia:    65F (1967)   59F (1967)
Quincy:      61F (1998)   58F (2010)


&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX