100
FXUS63 KLSX 111108
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
608 AM CDT Tue Jun 11 2024

.KEY MESSAGES...

- Well above normal temperatures will move in by Thursday and persist
  through the weekend. This combined with increasing moisture
  will create heat indices in the 100 to 105 range by Sunday.

- Severe weather is possible Thursday afternoon through evening
  with the main threats being large hail and damaging winds.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 313 AM CDT Tue Jun 11 2024

Dry weather will persist through the short term. Otherwise, the
surface ridge will continue to weaken and slowly slide off to the
east over the next 36 to 48 hours. So surface flow will gradually
shift to the south to southwest today. However, it will be a fairly
weak flow thus temperatures will only be around 5 degrees warmer
than yesterday with some high thin cirrus streaming in.

In the meantime, a system will continue to slide east along the
U.S./Canadian border today, dragging a cold front across the upper
Midwest. The latest guidance has the southern end of the cold front
approaching northern Missouri by this afternoon, but moisture
remains limited and the front weakens and washes it out, thus no
rain is expected.

By Wednesday, 850mb temperatures will be rising into the upper
teens, thus highs will be in the upper 80s to low 90s. Latest LREF
ensemble concurs, as 40-70% of the members have highs greater than
85 degrees. Even though low level moisture will be on the increase
with dewpoints rising back into the 60s from west to east, heat
indices will be near actual surface temperatures on Wednesday.

Byrd
&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 313 AM CDT Tue Jun 11 2024

As upper level ridging continues to build across the central
part of the country mid week, zonal flow along the U.S./Canadian
border will remain active through the period. The next system will
be moving through the upper Midwest Wednesday night into Thursday
and activity associated with it should remain well north of the
forecast area with complex weakening as it pushes east southeast
into the lower Great Lakes Thursday morning.

In the meantime, the latest deterministic as well as ensembles
indicate that 850mb temperatures will be rising to between 20 and
22C on Thursday. Thus expect widespread highs in the low to mid 90s.
This combined with dewpoints in the 60s will create heat indices
near 100 for the first time this summer.

As for rain chances Thursday afternoon through evening, with
increasing instability, ML CAPEs 3000+ J/kg, 0 to 6 km bulk shear 20-
30kts and ML LR around 7.5C/km, may support the potential for
supercell development initially just to our west, then transition to
line segments as the activity moves east across the region, mainly
along and north of I-70. The main threats will be large hail and
damaging winds. As the cold front sinks south, the activity will
taper off late Thursday night.

By Friday morning, the cold front will be south of the forecast area
and stall out, before moving back north as a warm front on Saturday.
So temperatures on Friday will be a bit cooler, but still above
normal in the upper 80s to low 90s.

Beyond that, there is a lot of uncertainty on additional chances of
showers and storms due to the differing solutions among the
deterministic and ensembles as disturbances slide along the
periphery of the upper level ridge. For now the main forecast issue
will be the well above normal temperatures through the weekend and
into early next week.

Byrd
&&

.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 607 AM CDT Tue Jun 11 2024

Dry, VFR flight conditions through the forecast period. Some
patchy fog in the river valleys this morning, especially across
the St. Louis metro, as well as southeast Missouri and southwest
Illinois. Added tempo group from 12z to 13z for MVFR visibility
in fog at KSUS and KCPS. Otherwise, light and variable winds
becoming south to southwest at KUIN, KCOU and KJEF.

Byrd
&&

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

$$

WFO LSX