603
FXUS63 KLSX 092301
AFDLSX

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

.KEY MESSAGES...

-Monday will be the coolest day of the week.

-Temperatures will start to warm Tuesday and jump above normal by
 Thursday, lingering into the weekend.


&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 115 PM CDT Sun Jun 9 2024

Precipitation will continue to weaken and push southeastward this
afternoon in tandem with the mid-level disturbance across southern
Missouri. A surface high is pushing into the mid-Mississippi Valley
from the northwest, which is also helping to shunt precipitation
and associated cloud cover out of the forecast area. Aloft a mid-
level trough is digging into the eastern CONUS while a mid-level
ridge strengthens across the inner Mountain West. The resulting
deep northwesterly flow will bring cool air into the region
starting today, and a clearing sky and light winds will promote
additional cooling tonight. Temperatures overnight will cool into
the 50s.

Patchy fog formation is possible tonight within the river valleys
and hollows where winds will be able to go calm, specifically across
southeast Missouri where rain lingered longer today and where the
overnight lows will come close to the crossover temperature from
this afternoon.

Deep northwesterly flow will continue Monday while the axis of the
surface high scoots into the mid-Mississippi Valley. Despite the
clear sky, cool 850 mb temperatures in the upper single digits and
northwesterly surface flow will keep temperatures roughly 5-10
degrees below normal for early June. The axis of the surface high
will slide across the forecast area overnight, allowing surface
winds to go calm. Efficient cooling combined with calm surface winds
will make Monday night the coolest of the week.


MRM

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 115 PM CDT Sun Jun 9 2024

Surface and low-level flow will become more southerly Tuesday as the
axis of the surface high moves east of the region, and warm air
advection will increase across the area. Thus begins the warming
trend that will last through the week as low-level winds remain
southwesterly, bringing warm, moist air into the mid-Mississippi
Valley. While there are areas of uncertainty with regard to the high
temperature through the remainder of the work week and into the
weekend (cloud cover, surface wind direction, precipitation
chances), the interquartile spread for high temperatures is around 5
degrees. Even the 25th percentile is above normal from Thursday
onward, both of these increase confidence that summer-like
temperatures will take hold of the region through the end of the
extended period.

By mid-week the mid-level trough over the eastern CONUS will exit
into the Atlantic and a broad but progressive ridge will build into
the Desert southwest. The mid-level ridge will slide eastward across
the southern US through the second half of the work week, while the
forecast area remains on the northern edge of the ridge. This leaves
the region open to ridge-running disturbances that could bring
precipitation chances to the region, though there is little signal
for these disturbances at this point. Rather, long term guidance has
been hinting at at least one frontal passage moving through the mid-
Mississippi Valley associated with a low over the Great Lakes region
during the mid to late week period. Confidence in this occurrence is
low at this point, given the run to run changes in the strength and
timing of these features, but it is something to watch as it could
bring our next chance of showers and thunderstorms to the region.
MRM

&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 601 PM CDT Sun Jun 9 2024

Dry and VFR flight conditions will persist through the TAF period.
Surface high pressure currently over the northern planes will move
into the Mid-Mississippi River Valley through Monday with light
north-northwesterly winds overnight becoming northerly by Monday
morning. Expect diurnal cumulus to develop during the day on
Monday.

MMG/Kimble

&&

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

$$

WFO LSX