754
FXUS63 KLSX 091120
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
620 AM CDT Sun Jun 9 2024

.KEY MESSAGES...

- The threat of showers and thunderstorms will move southward out
  of the area later this morning into the early afternoon. Confidence
  in strong to severe thunderstorms is very low at this time.

- Thunderstorms this morning will still be capable of up to an
  additional 3 inches of rainfall across portions of southeastern
  Missouri. The Flood Watch remains in effect until early this
  afternoon.

- Below normal temperatures are expected through Tuesday, with
  more summer-like temperatures returning to end the week.


&&

.SHORT TERM... (Through Monday Night)
Issued at 305 AM CDT Sun Jun 9 2024

A slow, southward-moving cold front is currently stretch west to
east across the CWA in southeastern Missouri and southwestern
Illinois. Convection continues to blossom along this front and an
outflow boundary across far southern Missouri at the nose of a low-
level jet. The nose of the jet is expected to remain well
south/southwest of the CWA early this morning, so other than a stray
shower or thunderstorm across southeastern Missouri, confidence is
low that the CWA will see much convection prior to sunrise.

Our attention quickly turns to an MCS currently traversing the front
across southeastern Kansas. This MCS is expected to continue being
fed by the low-level jet and push eastward along the front early
this morning, reaching far south-central Missouri around 6-8am.
Given the expected southward progression of the cold front and
decreasing instability over southeastern Missouri through the
morning, the better chances for strong to severe thunderstorms
within this MCS is expected to be just south of the area. However,
with the trajectory of the MCS, portions of southeastern Missouri
could still experience heavy rainfall later this morning, with
localized amounts up to 3" possible. Given this threat, we`ve
decided to maintain the current Flood Watch for now.

As the MCS departs the region late this morning and the cold front
continues to sink southward, dry conditions will take hold across
the entire CWA this afternoon. Thanks to a trough digging across the
eastern CONUS and a surface high sliding into the Great Plains and
Midwest, deep northwesterly flow will advect cooler air into the
CWA, with temperatures this afternoon running right at to almost 10
degrees below climatological normals. The coolest temperatures (mid
70s) will reside over far southeastern Missouri where the morning
rain and lingering cloud cover will prevent much surface heating.

The eastern trough continues to dig equatorward tonight and Monday,
strengthening northwest flow aloft and pushing the surface high
further into the Midwest. The result will be that Monday is the
coolest day of the week, with temperatures running about 10 degrees
below normal (mid to upper 70s).

Elmore

&&

.LONG TERM... (Tuesday through Saturday)
Issued at 305 AM CDT Sun Jun 9 2024

Guidance consensus is that the axis of an upper-level ridge will be
passing through the Midwest at the start of the extended period on
Tuesday. In turn, the surface high responsible for our calm, cool
weather early in the week will shift eastward, with southerly flow
returning to the area on the western periphery of the high.
Temperatures as a result will begin to warm closer to seasonal
normals on Tuesday, with ensembles clustering around 80 degrees for
much of the area.

While this ridge will phase quickly eastward, another stronger upper-
level ridge will expand across much of the southern CONUS during the
middle of the week and into the end of the week. This will allow for
low to mid-level flow to remain south-southwesterly, continuing to
pump warm, moist air into the CWA. While this will cause
temperatures to rise just above normal, guidance consensus is that
the positioning of a surface high east of the area will keep higher
dewpoints and thus greater humidity west of the CWA. So while it
will be warm to end the week, the more humid conditions look to stay
away for now.

To the degree that moisture over the area will increase near the end
of the week, we will still have to watch for rain and storm chances,
as the CWA remains close enough to the northern periphery of the
ridge to be impacted by ridge-running disturbances. Other than a
trough impeding on the ridge sometime next weekend, deterministic
guidance does not have a clear signal on any ridge-runners near the
end of the week, and ensemble guidance remains mostly dry.
Therefore, a dry forecast for much of the week has been maintained for
now.

Elmore

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 612 AM CDT Sun Jun 9 2024

A complex of thunderstorms is moving eastward across far southern
Missouri, with light rain north of the complex extending along the
I-70 corridor in Missouri. This light rain and occasional
lightning strikes are currently impacting KCOU and KJEF and will
do so through the next few hours. This light rain is moving
southeastward, with KSUS, KSTL, and KCPS expected to be on the
northern fringes of it later this morning. Confidence is high that
rain will remain light and have little to no impact to
visibility. Once rain clears the terminals later this morning or
at the latest early this afternoon, dry and VFR flight conditions
are expected through the remainder of the forecast period.

Elmore

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch until 1 PM CDT this afternoon for Crawford MO-Iron
     MO-Madison MO-Reynolds MO-Saint Francois MO-Washington MO.

IL...None.
&&

$$

WFO LSX