656
FXUS63 KLSX 220741
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
241 AM CDT Sat Jun 22 2024

.KEY MESSAGES...

- Hot weather continues today, but humidity increases early next
  week making it feel even hotter. The greatest heat risk will be
  Monday and Tuesday when Heat Index values near 105 degrees are
  expected.

- Our best chance of rain is tonight when thunderstorms forming in
  Iowa move south ahead of a cold front. These storms are expected
  to be weakening as they arrive this evening, with the chances
  for rain decreasing as the front moves south through the night.
  Although some of the strongest storms could contain damaging
  winds, the severe weather threat remains low. The next chance
  for rain comes Tuesday into Wednesday when the next cold front
  approaches.


&&

.SHORT TERM... (Through Sunday)
Issued at 240 AM CDT Sat Jun 22 2024

Upper level ridging over the Lower Mississippi Valley this morning
will continue to build back to the west today. We`ll be on the
northern periphery of the influence of this ridge with hot
temperatures expected. Low level southwesterly winds will aid in low
level mixing downstream of the Ozarks helping to add a degree or two
to the temperature across the Missouri Valley and into the St Louis
metro. So while temperatures the last few days may have been a touch
cooler than expected, confidence is greater that temperatures today
will be warmer especially in that downslope affected area.
Thankfully, though, humidity will not be extreme, only adding a
couple of degrees to the Heat Index, peaking near 100.

The best low level moisture has been pooling across Nebraska and
Iowa ahead of a surface front. This has been where most of the
thunderstorms have been tracking the last few days and that will be
the case again this evening. A shortwave trough tracking east
through the Upper Midwest will give that front a push southward
tonight. Thunderstorms are expected to initiate in central and
eastern Iowa this afternoon and evening in the axis of greater
instability ahead of the front. As the shortwave trough moves by
aloft it will add just enough wind shear into the mix to create the
potential for more organized thunderstorms to develop. While
individual storms and clusters will be moving east with the mid
level flow, the overall line will be sinking southward as the front
moves south this evening. It is likely that we`ll see at least some
of this activity move into our area, but CAMs are generally in
agreement that storms will be weakening and eventually dissipating
as they head south and away from the better moisture and instability
while the best lift with the shortwave trough pushes off to the
east. There continues to be at least some risk for strong to severe
storms with damaging winds the primary threat this evening, but the
risk remains low as the overall convective trend will be decreasing
as storms arrive. The best time window for our area to see severe
storms is from about 9PM to 1AM. Unfortunately there`s a chance that
most of us won`t see rain from this, but it is our best opportunity
for rain in a while and our last opportunity before the heat builds
again.

Models continue to trend rather quick with Saturday night`s cold
front, with strong agreement that it will push south of our area by
Sunday morning. As a result, the forecast continues to trend a bit
cooler on Sunday with thunderstorm chances along the front shifted
further south and mostly out of our area by Sunday afternoon.

Kimble

&&

.LONG TERM...  (Sunday Night through Friday)
Issued at 240 AM CDT Sat Jun 22 2024

Upper level ridging reorganizes over the Rockies and shifts into the
Plains early next week. This will push the hot weather quickly back
into our area, this time accompanied by greater humidity. We still
have high confidence that the greatest heat risk for our area will
be Monday and Tuesday. While NBM continues to be at the top of the
guidance spread in terms of air temperatures, it`s not so much the
air temperature but the Heat Index that is the greater focus.
Dewpoints near 70 will make this round of heat feel noticeably more
intense, with heat index values peaking near 105 degrees. It is
likely that we will need a Heat Advisory for much of the area on one
or both days.

The next trough rounding the top of the ridge and tracking east
across the northern part of the country will send a cold front
southward Tuesday into Wednesday. This will provide at least a brief
break from the heat and our next chance for thunderstorms. While we
certainly couldn`t rule out a chance for strong to severe storms at
some point as the front moves through, it`s not a strong chance at
this point. While instability will likely be strong in the hot and
humid air mass, the bulk of the forcing and better wind shear seems
more likely to remain to the north closer to the Great Lakes. So at
this point I think the main story here is that this represents our
next chance of rain, while the severe weather story is still murky.

The cold front does provide a brief break from the heat, but it
doesn`t last long. Models are coming into better agreement that the
ridge builds back in rather quickly, with temperatures pushing back
into the mid 90s again before the end of the week. It looks like it
will also be accompanied by at least moderate humidity as well, so
we may be looking at another period of greater heat risk next
weekend.

Kimble

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1152 PM CDT Fri Jun 21 2024

VFR conditions continue tonight and into Saturday. Winds pick up
a bit more tomorrow out of the southwest, decreasing in the
evening. Thunderstorms forming over Iowa in the evening are
expected to decrease in intensity and coverage as they drop
southeast late Saturday evening into the overnight. The best
chance of seeing impacts will be at UIN, with considerable more
uncertainty on whether they will survive to reach the St Louis
metro later in the night.

Kimble

&&

.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