Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

773
FXUS63 KLSX 061928
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
228 PM CDT Fri Jun 6 2025

.KEY MESSAGES...

- After this afternoon, the next round of storms moves in from the
  northwest Saturday afternoon. Large hail, damaging winds, and a
  few tornadoes are possible.

- After one more round of thunderstorms on Sunday, dry and mild
  weather is expected through at least the middle of next week.


&&

.SHORT TERM...  (Through Late Saturday Night)
Issued at 227 PM CDT Fri Jun 6 2025

An area of showers continues to push through the region this
afternoon. This is associated with a remnant Mesoscale Convective
Vortex (MCV) leftover from overnight convection that moved out of
Oklahoma. The bulk of the instability is off to the east of the main
convective cluster moving into the Ohio Valley at this hour. The MCV
itself is still hanging back in southwest Missouri having
essentially become occluded from the better low level moisture and
instability with only elevated showers wrapping into it at the
moment. Extensive cloud cover has led to cool, stable air in the low
levels. Some breaks in the clouds are starting to be observed just
ahead of the MCV and if this trend continues then some
destabilization could occur as the MCV continues off to the ENE this
afternoon and evening. If this occurs then a greater threat of
thunderstorms, some of which could be severe, would develop.
Damaging winds and a few brief tornadoes would be the primary
threats. This potential still looks fairly low at this point, but
MCVs are notoriously tricky which is why remain cautious to
completely sound the all clear on thunderstorms today.

Showers and any thunderstorms associated with the MCV move off to
the east this evening leaving drier conditions in its wake, at least
in terms of precipitation. Low level moisture remains high, though,
and if we do get clouds to clear out even for just a few hours then
radiational cooling will quickly cause fog to develop. This
potential is greatest across central Missouri while clouds are more
likely to hang in around St Louis and eastward preventing the
cooling needed to produce that fog. It is pretty close, though, as
cool, damp evening conditions are ripe for fast and dense fog
development if clear skies can allow just a couple of degrees of
cooling. Cloud cover trends this evening will give some greater
confidence to this part of the forecast.

While another convective complex is expected to develop over
Oklahoma tonight, the mid level flow supports this moving more ESE
and staying south of our area tonight into Saturday morning. The
main focus for Saturday is with a more pronounced shortwave trough
moving into the region from the northwest during the afternoon. This
is expected to trigger the next round of showers and thunderstorms
as it tracks through our region Saturday afternoon and evening.
There will be greater wind shear to work with as this trough moves
through, with a 50-60KT westerly jet at 500MB over the top of
southerly surface winds. That`s plenty of shear for supercell
thunderstorms which would be capable of hail, damaging winds, and
perhaps a tornado. However, the biggest question is the instability.
Cloud cover once again plays the crucial role in the northward
development of instability ahead of the trough on Saturday. If we
get more sun, then we can develop some pretty robust CAPE to go
along with that shear and create the potential for severe storms.
HREF 90th percentile of surface based CAPE is at or above 2000
across the southern portion of our area during peak heating, so this
represents the higher end potential. This is also why the SPC
outlook favors the southern half of the forecast area with the
Slight Risk tomorrow. Further north it becomes increasingly less
likely that robust instability will develop before the shortwave
arrives, limiting the severe potential.

Saturday`s trough does push a subtle cold front through the region
behind it. So we`ll see winds shift to the northwest and see some
drying out overnight. Dewpoints falling back into the 50s suggest
that with good cooling conditions, temperatures will fall similarly
into the low 60s to upper 50s.

Kimble

&&

.LONG TERM...  (Sunday through Next Friday)
Issued at 227 PM CDT Fri Jun 6 2025

While we will be in a drier, post-frontal air mass on Saturday,
we`ll actually see a second cold front coming in on Sunday. This
front is associated with a much deeper trough developing over the
Upper Midwest. Model guidance continues to show another round of
showers and thunderstorms developing along this front as it arrives
Sunday afternoon and continuing southward through the overnight.
This is not the typical severe weather setup as low level wind flow
will be out of the northwest. In fact I`m a little suspicious of the
forecast arrival of higher dewpoints with a flow from that
direction, and models may be a little too aggressive in developing
instability and convection ahead of the front if dewpoints don`t
rise as forecast. That said, the trough moving in aloft is pretty
deep, so the cold air associated with it will aid in
destabilization. Mid level flow will also be increasing ahead of the
trough, so we may once again see just enough combination of
instability and shear to produce a final round of severe
thunderstorms. I think that if this round does occur, though, the
primary threats will be damaging winds and large hail as the low
level wind shear is not as favorable for tornadoes.

Sunday evening`s potential thunderstorms should be our last round
for a while, though, as the air mass behind this cold front will be
cool and dry, shutting off our access to the moisture that has
brought our frequent rains in recent weeks. In fact, some guidance
suggests that after another reinforcing front late Monday we could
see dewpoints dip into the 40s. While this all does point to a drier
stretch of weather, and our current forecast PoPs are near zero from
Monday through Wednesday, the only potential spoiler to that is the
trough itself wobbling through the Upper Midwest into the Great
Lakes. Mid level moisture associated with spokes of energy within
that trough will lead to areas of light shower activity. This
potential is much greater to our north closer to the core of the
upper trough. Only up to 20 percent of 00Z ensemble members produce
measurable rainfall across our area Monday into Tuesday.

This is a pretty deep, cold trough for this time of year. Even with
a full June sun we`re only forecasting highs in the upper 70s to low
80s. NBM interquartile range gets quite small early next week, only
about 3 degrees of spread. This indicates fairly high confidence in
these temperature forecasts as the low levels should be well-mixed
during afternoon heating. As the trough moves east and is replaced
by a ridge moving in from the west, we`ll see a trend toward warmer
temperatures later in the week. The next substantial rain chances
come around the Friday time frame as a weak trough trapped under the
ridge in Texas eventually escapes as the ridge axis moves east.

Kimble

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1221 PM CDT Fri Jun 6 2025

Showers are moving through central Missouri and the St Louis metro
this afternoon. Couldn`t rule out a few rumbles of thunder, but
confidence is too low to include that in any TAF at this time.
Quincy should remain dry, but some minor visibility reductions
have continued up there all morning. This may improve briefly
before coming back down this evening.

Biggest uncertainty is with ceilings and visibility overnight
tonight. Areas of rain this afternoon are causing some IFR
ceilings and are likely to leave some fairly extensive clouds in
their wake even after the rain stops. But if clouds clear out,
then it won`t take much cooling at all to cause fog or very low
ceilings to develop again as the near-surface is able to cool in a
very moist low level environment. With this TAF issuance, we have
more confidence in some clearing in central Missouri so fog was
included there. However, clouds are more likely to linger in the
St Louis area and prevent the overnight fog development. However,
a lot of model guidance does show this fog development, and trends
in cloud cover this evening will go a long way in helping gain
some confidence on whether this will occur or not.

Kimble

&&

.CLIMATE...
Issued at 227 PM CDT Fri Jun 6 2025

St Louis has still not seen 90 degrees yet in 2025. The average
first 90 degree reading is May 15. The most recent late 90-degree
start was June 10, 2021. If St Louis doesn`t hit 90 by June 10, it
will be the latest first 90 degree day since at least 1995 (June
19). The latest date of first 90 degrees on record was July 4 in
both 1961 and 1912.

Columbia has also not yet seen a 90 degree reading in 2025, however
the average first date is much later (June 10). The latest date of
first 90 degrees on record was July 14, 1904.

Quincy reached 90 degrees on May 15 of this year, about 3 weeks
earlier than their average first 90 degrees (June 7).

Kimble

&&

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

$$

WFO LSX