St. Peters, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

590
FXUS63 KLSX 102035
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
235 PM CST Sun Nov 10 2024

.KEY MESSAGES...

- Dry conditions are favored through much of the week with
  temperatures running near to slightly above normal.

- The next chance (30-50%) of rain arrives Wednesday into
  Wednesday night. Rainfall amounts remain light with widespread
  precipitation totals of one-tenth to one-quarter of inch.


&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 234 PM CST Sun Nov 10 2024

Water vapor, in conjunction with pressure analysis, shows a broad,
stacked low continuing to rotate northeast through the Upper Midwest
into the Great Lake Region this afternoon. The associated front that
resulted in rainfall Saturday into Saturday night has moved to the
east, evacuating moisture eastward with dewpoint falling from the
50s into the 40s. Cloud cover has been limited to far northern
fringes of Missouri, where model soundings show a shallow saturated
layer between 800-850 MB. The thin veil of moisture erodes to the
south, where ample sunshine has supported deeper mixing, gusty
southerly winds and consequently led to warmer temperatures.
Adjustments were made accordingly with upper 60s to low-70s across
the southeast half of the CWA.

Surface ridging builds eastward from the front range of the central
Rockies tonight, effectively relaxing surface winds under mostly
clear skies. Radiational cooling will drop temperatures 5-10 degrees
cooler than last night with Monday morning lows in the upper 30s to
mid-40s. Given dewpoint depressions in the low single digits to near
zero, remnant surface moisture from recent rainfall and warm river
water, steam fog and valley fog is likely tonight. Though winds will
be light and variable in most cases, predominant, light westerly
surface flow may end up supporting instances of denser fog along the
Missouri River and other larger stream running parallel with the
light westerlies.

Expect fog to have a typical diurnal behavior, much in the same
manner as Sunday morning. Fog erodes through mid-morning with
pleasant condition for Veteran`s Day with high temperatures near to
slightly above normal. Though ridging initially builds in from the
west, a second, strong surface high builds in from the northern
Plains into the Great Lakes Monday into Monday night. A west-east
oriented cold front presses south through the afternoon, keeping far
northern sections of Missouri and west-central Illinois slightly
cooler (upper 50s). Short/medium range guidance shows cooler
temperatures being funneled south through eastern Wisconsin into
Illinois Monday night around the eastern side of the surface high.
This cooler airmass is then pushed west-southwest into the CWA.
It`ll be a cool, crisp fall night/Tuesday morning with low largely
in the 30s. I wouldn`t rule out an isolated reading in the upper
20s, mainly the notoriously cooler rural locations over central and
northeast Missouri, as well as northeast fringes of the CWA.

Maples

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 234 PM CST Sun Nov 10 2024

Provided the predominant warmth felt in recent weeks, Tuesday will
feel a bit cool despite being close to normal. There was some
initial concern of just how cool it would be given the late spread
that appeared in NBM data 24 hours ago. However, the disagreement
wasn`t anything to impressive and simply provided a signal of
uncertainty in temperatures behind the cold front. This seems to
have been resolved with the latest data more tightly clustered.
While I initially considered lowering temperatures 1-2 degrees from
previous forecasts, the NBM did come in ever-so-slightly cooler. I
feel comfortable with current forecast highs (ranging through the
50s) as they line up near the 50th percentile. There is also little
disparity between the 50th/25th percentiles, showing 1-2 degrees
difference in most cases, which provides confidence that there will
be no discernible difference even if we end up on the cooler side.

The next system originates from the western CONUS in the form of an
amplified trough. The trough remains amplified as it crosses the
Rockies with a surface low developing at the lee side of the mountain
range. The surface low is quickly ejected north-northeast into the
Upper Midwest with a cold front trailing almost due south. As much
of the lift goes well north, it leaves any hope for precipitation on
the front and available moisture. A narrow corridor of PWATs of 1-
1.25 inches extend south/north along the front as it progresses west
to east through Missouri Wednesday. However, there is little sign of
convective potential with the highest MUCAPE found in the
deterministic GFS. Even it shows fragmented area of 100-200 J/kg
with few GFS/ECM ensemble members showing the same. A majority of
the same ensembles depict one-tenth to potentially one-quarter of an
inch of total precipitation by Thursday morning given the
progressive nature of the system and short duration of rainfall.

Surface high pressure builds in behind the front with a modest mid
to upper level ridging pattern taking shape late in the week. The
pattern should support dry conditions and moderating temperatures
with highs returning to the 60s. While there is the potential for an
active pattern to set up late in the weekend into early next week,
there is greater spread in the long range NBM data. Generally
speaking, deterministic solutions how much of the upper level
support driving north of the area with a strong ridging pattern over
the southeast CONUS. The southwesterly flow is a good setup for
ejecting lows northeast into the Plains. The southeastern ridge and
any variability in its strength and placement will be at least one
of the primary factors in just how much of this come to fruition
locally.

Maples

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1150 AM CST Sun Nov 10 2024

VFR conditions are expected to persist at most site with exception
to terminals located near rivers and adjacent valleys (KSUS, KJEF
and KCPS). Initially, gusty southwest flow will impact all
terminals through the afternoon hours with winds expected to
subside this evening. As surface flow become light and variable,
fog is likely to develop over milder rivers and larger streams.
Additionally, recent rainfall has added moisture to the surface
soil, which will support fog in low lying valleys, especially
those adjacent to rivers. MVFR visibilities are forecast at the
aforementioned TAF site above. A brief period of IFR cannot be
entirely ruled out if denser fog is carried into one of these
terminals through the early morning hours.

Maples

&&

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

$$

WFO LSX