National Weather Service Raw Text Product

156 
FXUS63 KLSX 202341
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
641 PM CDT Fri Jun 20 2025

.KEY MESSAGES...

- There will be a prolonged period of dangerous heat and humidity
  for Saturday through next Tuesday, and possibly later into next
  week. Heat index values of 100+ degrees are expected each day.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 253 PM CDT Fri Jun 20 2025

An upper level ridge is building across the eastern Plains and 
Midwest this afternoon, while a closed low is digging into the 
Pacific Northwest.  The pattern will progress eastward tonight and 
Saturday, with the upper ridge strengthening to 594 dam over the 
Mid/Lower Mississippi Valley and the trough moving over the Rockies 
by 00Z Sunday.  The approaching trough is forcing lee-side 
cyclogenesis over the Great Plains this afternoon, resulting in deep 
low level southerly flow.  This is bringing more humid air from the 
southeast Plains into the Missouri and Mississippi Valley.  Dew point 
temperatures have already risen into the low to mid 70s along and 
west of the Mississippi River this afternoon, and heat index values 
in central Missouri are 100 degrees and above in some locations. The 
high heat index values would probably stretch all the way up to 
northeast Missouri and maybe west central Illinois this afternoon, 
but the persistent remnants of an overnight MCS have kept those 
areas mostly cloudy today with a few sprinkles and rain-cooled air. 
No MCS activity is expected in our region tonight with the ridge 
building overhead, and tomorrow looks sunny, hot, and humid.  Latest 
guidance shows temperatures rising to at least the mid 90s across 
the entire area, with highs approaching the century mark in the St. 
Louis Metro area due to the urban heat island effect.  Have therefore 
upgraded the Extreme Heat Watch for the Metro area to an Extreme 
heat warning as heat index values are expected to be 105+ in the 
Metro Area from Saturday through next Tuesday.  Heat Advisories 
continue across the remainder of the area for temperatures of 100-
105 through Tuesday.


Carney

&&

.LONG TERM...  (Saturday Night through Next Friday)
Issued at 253 PM CDT Fri Jun 20 2025

Dangerous heat will continue into at least early next week. The 
overall pattern starts out at a fairly high amplitude with 
the ridge over the eastern U.S. and a trough over the west. 
Deterministic and ensemble guidance shows the upper ridge building 
to nearly 600 dam over the Ohio Valley and Mid Atlantic states by 
Sunday morning, where it will stay through most of the week. Both 
the trough and ridge are forecast to weaken a bit by the end of the 
week, which may be enough to lower temperatures a few degrees. 
Interquartile temperature ranges on the LREF for the latter half of 
the week do start to drift lower  Additionally, the weakening ridge 
may allow some afternoon convection to develop Wednesday through 
Friday which could also bring much needed relief from the heat. The 
slight chance/low chance PoPs in the going forecast for Wednesday 
through Friday continue to look justified with no more than 40 
percent of the LREF members showing precip at any given time.  In 
fact the number is far less than 40 percent for most of that period. 
That said, the heat advisory/warning products may need to be 
extended beyond Tuesday if the ridge hangs on stronger than is 
currently forecast.

Carney

&&

.AVIATION...  (For the 00z TAFs through 00z Saturday Evening)
Issued at 638 PM CDT Fri Jun 20 2025

VFR conditions will prevail through the period. A few wind gusts
remain possible through 01z before subsiding. However, some
terminals show gusts above 20 knots may already be subsiding with
less than 10 knots difference between gusts and sustained speeds. 
Therefore, gusts were pulled from prevailing groups for 
simplification.

Maples

&&

.CLIMATE...  
Issued at 1225 PM CDT Thu Jun 19 2025

Record maximum temperatures at St. Louis, MO (STL), Columbia, MO (COU), 
and Quincy, IL (UIN) along with the year of the record:

     |   6/21    |    6/22    |    6/23    |    6/24    |    6/25   
--------------------------------------------------------------------
STL |  99 (1988) | 102 (1930) | 101 (1930) | 102 (1988) | 103 (2024) 
    |            |            |            |            |
COU |  98 (1988) | 100 (1988) | 100 (1988) | 103 (1988) | 102 (1988)
    |            |            |            |            |
UIN | 100 (1988) | 100 (1930) | 100 (1934) |  99 (1988) | 102 (1931)


&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory from noon Saturday to 9 PM CDT Tuesday for 
     Crawford MO-Franklin MO-Gasconade MO-Iron MO-Lewis MO-
     Lincoln MO-Madison MO-Marion MO-Montgomery MO-Pike MO-Ralls 
     MO-Reynolds MO-Saint Francois MO-Sainte Genevieve MO-Warren 
     MO-Washington MO.

     Extreme Heat Warning from noon Saturday to 9 PM CDT Tuesday for 
     Jefferson MO-Saint Charles MO-Saint Louis City MO-Saint 
     Louis MO.

     Heat Advisory until 9 PM CDT Tuesday for Audrain MO-Boone MO-
     Callaway MO-Cole MO-Knox MO-Moniteau MO-Monroe MO-Osage MO-
     Shelby MO.

IL...Heat Advisory from noon Saturday to 9 PM CDT Tuesday for Adams 
     IL-Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene 
     IL-Macoupin IL-Marion IL-Montgomery IL-Pike IL-Randolph IL-
     Washington IL.

     Extreme Heat Warning from noon Saturday to 9 PM CDT Tuesday for 
     Jersey IL-Madison IL-Monroe IL-Saint Clair IL.

&&

$$

WFO LSX