Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 022035

Area Forecast Discussion
National Weather Service Saint Louis MO
335 PM CDT Sat Jul 2 2022

.SHORT TERM...  (Through Late Sunday Night)
Issued at 332 PM CDT Sat Jul 2 2022

The primary driver of today`s weather has been a slowly progressing
cold front, which as of 2:30 PM has finally moved south of the area
and into far southern MO and IL. The cold front served as the focal
point of multiple rounds of convection throughout the morning and
early afternoon, producing efficient rain rates within an
environment featuring deep warm cloud layers and anomalously high
moisture content (~2 inches), along with occasional gusty winds
within the strongest cores. However, almost all of this activity has
ceased locally with the southward progression of the front, leaving
behind only spotty stratiform precipitation behind it.

While there remains a bit of elevated instability lingering just
behind the cold front across SE MO and SW IL, this lull in
precipitation is expected to continue through the evening and early
overnight hours. However, by early tomorrow morning this front will
begin to lift back to the north as a diffuse warm front in response
to pressure falls across the plains. As this occurs, additional
rounds of convection will be possible early in the morning along the
advancing boundary (and other lingering surface boundaries),
although confidence is very low regarding exactly when this will
occur. Meanwhile, instability is expected to gradually build into
the afternoon, which may support further convective development
as well.

In any case, any additional convection that occurs between now and
Sunday afternoon is expected to be widely scattered and rooted to
any boundaries where localized convergence exists. Instability will
be meager in the morning hours, with only modest wind shear (~35kt)
and this will limit the potential for any of these storms to be
strong to severe. Meanwhile, MLCAPE will likely increase to around
1500 J/kg by early afternoon, but shear will actually weaken over
the course of the day, which will also significantly limit severe
potential as the day progresses. As a result, expect widely
scattered short lived convection at times throughout the day, with a
preference for central and southeast Missouri, with a lull expected
during the evening. The primary hazards with any additional
convection will be lightning and brief heavy rain rates.

Convection should mostly wane by early evening Sunday, but a passing
weak shortwave to our north may provide just enough forcing to
produce a few additional showers and storms across northeast MO and
west-central IL very late in the night, or possibly early in the
morning Monday.


.LONG TERM...  (Monday through Next Saturday)
Issued at 332 PM CDT Sat Jul 2 2022

The primary concern Monday and beyond will be the increasing
potential for multiple days of excessive heat throughout the region,
including over the 4th of July holiday.

By Monday, an upper level ridge will once again build across the
region, bringing with in an anomalously warm and very humid airmass
that will persist for several days. 850mb temperatures will reach
above the 90th percentile, particularly Tuesday and Wednesday, which
will bring temperatures well into the upper 90s and even near 100
degrees at times during the hottest days. Meanwhile, rich moisture
content will return northward, and while there will be some
afternoon mixing, heat indexes are likely to easily reach 100
degrees throughout the area, and likely 105 on Tuesday and
Wednesday. The end result will likely be four consecutive days of
excessive heat, with the worst of it occurring on Tuesday and
Wednesday. At a minimum it seems very likely that Advisory-level
heat will be reached, with the potential for Warning level heat as
well. As for specifically the July 4th holiday, please consider this
heat when making outdoor plans. This is not likely to be the hottest
day of the week, but it will be plenty hot enough to present a
hazard for those sensitive to heat or those with prolonged exposure.
At least some heat relief is likely Friday onward as the upper level
ridge begins to break down.

As for precipitation, the building ridge is expected to reduce
precipitation chances Monday through Wednesday, although a few stray
afternoon showers can`t be completely ruled out during this period.
Precipitation chances begin to increase again late in the weak as
the upper level ridge weakens and a cold front sags into the area.
However, confidence remains very low beyond Thursday, particularly
regarding precipitation chances.



.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1215 PM CDT Sat Jul 2 2022

Widespread showers and a few thunderstorms will continue to impact
terminals along the I-70 corridor through the afternoon today.
While the deepest and most significant convection is expected to
largely remain south of these areas across the Ozarks, periodic
visibility reductions and MVFR ceilings can be expected through at
least the remainder of the afternoon and possibly into the early

A lull in convective activity is expected during the late evening
and overnight, but there is some potential for redeveloping
convection early in the morning, with additional rounds possible
continuing through the day Sunday. However, there is a high degree
of uncertainty regarding when and where this convection will
occur, if it does at all, and as such we`ve opted to avoid using
a prevailing SH or TS for this activity at this time.





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