813
FXUS63 KLSX 211122
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
622 AM CDT Fri Jun 21 2024

.KEY MESSAGES...

- Hot weather continues into the beginning of next week with
  temperatures in the mid to upper 90s most days. Humidity
  increases early next week creating the potential for greater
  heat risk Sunday thru Tuesday.

- The best chance of rain comes Saturday night as a cold front coming
  from the north triggers some thunderstorms. Not everyone will
  get rain, but northern areas have the best chance (70+ percent).
  Although there is some potential for damaging winds with
  thunderstorms Saturday night, the risk remains fairly low at
  this time.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 221 AM CDT Fri Jun 21 2024

The large ridge of high pressure which has brought the early summer
heat to much of the country is centered over the Tennessee Valley
this morning on a gradual trek back to the southwest. To the north,
influences from the jet have kept a parade of thunderstorms across
the Dakotas into Minnesota, well out of range of our forecast area.
Under full control of the ridge today we will see temperatures rise
to near or slightly warmer than we saw yesterday across the region,
mostly in the low to mid 90s. We`ll likely see our warmest
temperatures on Saturday as low level southwest flow continues to
pump in that warm air while the influence of the ridge holds on
enough to keep us dry during the day.

As a shortwave trough tracks through the Great Lakes on Saturday it
will push a cold front south behind it. Thunderstorms are expected
to form on this front Saturday afternoon and evening over Iowa
before pushing south and east overnight Saturday night. We`re not
sure how well these will hold together as they push into our area
Saturday evening and into the overnight, but no doubt the northern
areas have the best chance of being affected. Enough instability and
shear exist to pose a risk for strong to severe storms with damaging
winds the primary threat, but it`s unclear how far into our area
this threat may extend. Thunderstorms are likely to weaken as they
move southeast and may dissipate altogether before the cold front
makes it into the center of our forecast area Sunday morning.

Kimble

&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 221 AM CDT Fri Jun 21 2024

The front slows down and stalls in or near the southern part of our
forecast area on Sunday adding some uncertainty to the temperature
forecast. North of the front there will be at least some cooler air
and some places may only peak in the 80s. To the south of the front
the heat continues with some added humidity as well, creating the
instability needed for thunderstorms to redevelop along the front
Sunday afternoon and evening. Where those storms form early, some
heat relief will come with the rain, but until then heat and
humidity south of the front pushes heat index values near 100.

Sunday`s front washes out as ridging builds over the Plains on
Monday helping to push the hot weather fully back into our area,
accompanied by greater humidity this time. More widespread dewpoints
in the 70s are expected Monday and Tuesday helping to push the heat
index several degrees higher than the forecast highs. While there is
some uncertainty on the temperature forecast with NBM being near the
top of the available guidance, I wouldn`t get too hung up on the
forecast high temperature numbers. The story will be in the heat
index which is going to be climbing above 100 Monday and Tuesday due
to that added humidity even if we don`t hit the more extreme air
temperature values. Synoptically it makes some sense for Tuesday to
be the hotter of the two days as the air mass peaks just before the
arrival of the next cold front, but there is some uncertainty on
that. If the trough and cold front are a little quicker, or
thunderstorms develop earlier in the day, then the near-record 100+
air temperatures will be less likely.

Speaking of that trough, there is strong agreement that there will
be a shortwave trough moving through the center of the country
Tuesday into Wednesday with an air mass changing cold front
accompanying it. The uncertainty lies in the timing and strength of
this wave. Thunderstorms likely accompany the front, but how strong,
where, and when is still uncertain. While we do expect a significant
cool down (10 degrees or so) it`s less clear how long that cool down
will last. That will depend on how deep this trough develops over
the southeast US and how quickly the ridge builds back in from the
west behind it. If we remain more under the influence of the trough
then we`ll see more days in the 80s for the latter part of next
week. But the hot weather isn`t that far away and it will build back
in again by the weekend. If the ridge builds back quicker then we
could see those mid to upper 90s return as early as Thursday.

Kimble

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 616 AM CDT Fri Jun 21 2024

VFR flight conditions and light south-southwest winds are expected
to prevail through Saturday morning. Expect scattered cumulus to
develop late this morning/early afternoon between 5000-7000ft.
There may be enough moisture across central and northeast Missouri
into west central Illinois for the cumulus to go broken at times.
Low clouds should disspate during the evening.

Carney

&&

.CLIMATE...
Issued at 221 AM CDT Fri Jun 21 2024

With hot temperatures forecast next week, here are some of the
daily high temperature records:

            MON JUN 24     TUE JUN 25
ST LOUIS    102 in 1988    102 in 1954
COLUMBIA    103 in 1988    102 in 1988
QUINCY       99 in 1988    102 in 1931


&&

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

$$

WFO LSX