986
FXUS63 KLSX 081932
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
232 PM CDT Sat Jun 8 2024

.KEY MESSAGES...

-Thunderstorms will move into the forecast area this evening,
capable mainly of damaging winds, large hail, and heavy rainfall.
The best location for severe thunderstorms is across southeast
Missouri.

-Additional thunderstorms will form overnight across southeast
 Missouri and locally heavy rainfall of up to 3-5" is possible.
 The Flood Watch remains in effect for this area.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 228 PM CDT Sat Jun 8 2024

This morning`s MCS pushed convection and the associated outflow into
central Arkansas this afternoon, and is no longer the focus for
thunderstorm development across our CWA today. The focus for
convection will be a warm front that is currently developing across
central Kansas into western Missouri near Kansas City, while a cold
front is draped from roughly northeastern Iowa into southeast
Nebraska. Across the warm sector dewpoints are surging into the
70s and MLCAPE has built to 1000-2500 J/kg, with 0-6 km shear
around 40kts. The warm front will continue to extend eastward
through the day as warm, moist air is advection northeastward into
central and eastern Missouri. Isolated warm air advection showers
have formed near the warm front in western Missouri and tracked
eastward into the western CWA. So far convection has struggled to
grow upscale due to the weak forcing and weak, mid-level height
rises. Warm air advection may be strong enough across central
Missouri to form more isolated showers and thunderstorms this
afternoon.

The better chances for severe thunderstorms continues to be this
evening as a subtle mid-level shortwave passes over the area and
interacts with the better surface convergence in southwestern
Missouri. The thunderstorms will track southeastward along the deep
layer shear vectors into south central and southeast Missouri this
evening. Recent runs of hi res guidance have continued to shift this
area of thunderstorms further south, and the best location for these
storms continues to be across southern and southeast Missouri.
Overnight, a WSW to ENE oriented LLJ will ramp up across southwest
Missouri, enhancing thunderstorm development across the southern
portion of the state and into southern Illinois.

Thunderstorms that form during the afternoon and early evening will
be a mixture of discrete and multi-cell clusters. These storms will
become more linear with time as the LLJ kicks up overnight and
generates more convection. With initially discrete/multi-cell
clusters, damaging winds, large hail, and heavy rainfall are the
main concerns. There is a low threat for a tornado with a discrete
storm that forms along the front in the afternoon to early evening
where the weak 0-1 km shear and helicity could be locally enhanced.
As storms become more linear the threat will transition to mainly
damaging winds and heavy rainfall.

Additional shower and thunderstorm development is possible across
west-central Illinois along the weak cold front as it slides
southeastward through the forecast area overnight, but confidence in
development is low given the uncertainty in strength of low-level
convergence. As the WSW to ENE LLJ kicks up overnight convection
will become more widespread in southern Missouri, increasing the
risk for flash flooding particularly in areas that already saw
rainfall from thunderstorms during the early evening. There has been
a southward shift in convection within the last several runs of the
CAMs, which would result in a southward shift of the heaviest axis
of precipitation. So while confidence is high a narrow band of heavy
rainfall will occur in southern Missouri, where exactly it occurs
remains uncertain. HREF LPMM continues to indicate areas of 3-5
inches of rain are possible across portions of southern and
southeast Missouri, with locally higher amounts up to 7 inches
possible across portions of southern Missouri. These highest amounts
would occur with training convection and will be highly isolated.

Showers and thunderstorms will diminish as the LLJ weakens Sunday
during the day. Most of the forecast area will be largely dry
Sunday, except for portions of far southeast Missouri where rain
could linger into the afternoon. A surface high will slide into the
area during the evening to help shunt any lingering precipitation
south of the forecast area.

MRM

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 228 PM CDT Sat Jun 8 2024

The surface high will remain the dominate feature across the mid-
Mississippi Valley for the first half of the work week while a mid-
level shortwave ridge pushes through the region. Northwesterly low-
level flow will keep temperatures below normal while the surface
high and mid-level height rises will keep the area dry. A weak mid-
level trough axis will pass through the region mid-week as the mid-
level trough slides through the Great Lakes region. The associated
surface low will likewise track through the Great Lakes region, and
the attendant cold front will be weak as it moves through the
mid- Mississippi River Valley. Differences remain in timing and
strength of the front which results in uncertainty in mid-week
precipitation chances.

Southwesterly low-level flow will become established behind the
surface high and cold front, warming temperatures for the end of the
work week and start of the weekend. 850 mb temperatures will climb
into the upper teens to low 20s, which will push high temperatures
above normal during this period. How far above normal will depend on
cloud cover and precipitation chances which will come into focus in
coming days.

MRM

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1211 PM CDT Sat Jun 8 2024

Broken MVFR ceilings have moved into the area behind this
morning`s precipitation, but are expected to improve to VFR this
afternoon with deeper mixing. VFR conditions are expected to
prevail through the remainder of the TAF period. Previously
another round of showers and thunderstorms was expected overnight
into Sunday morning, but the threat for this precipitation has
shifted southward. The mid-Missouri terminals have the best chance
of seeing a shower or thunderstorm in the early morning hours
(10-13Z), but confidence in the northern extent of the
precipitation is low, so have changed the mention to VCSH. While I
can`t rule out a brief period of showers and/or thunderstorms at
the other terminals (KUIN, KSTL, KSUS, KCPS), I have removed the
mention of precipitation all together, as confidence is even lower
in the occurrence of precipitation at this time.

Through the course of the TAF period winds will become westerly
and then northerly as a largely dry cold front pushes through the
region.


MRM

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch from 7 PM CDT this evening through Sunday afternoon
     for Cole MO-Crawford MO-Franklin MO-Gasconade MO-Iron MO-
     Madison MO-Moniteau MO-Osage MO-Reynolds MO-Saint Francois
     MO-Washington MO.

IL...None.
&&

$$

WFO LSX