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afdlsx

Area forecast discussion...updated aviation
National Weather Service Saint Louis MO
1131 PM CDT sun Jul 23 2017

Update...
issued at 947 PM CDT sun Jul 23 2017

Isolated thunderstorms continue to slowly move south this evening
north of I-70 along a Post-frontal trough. These storms will
dissipate the next few hours as instability decreases and low
level moisture convergence weakens along the trough. The rest of
the night will be dry with partly cloudy skies, with some cirrus
over southern Missouri occurring from storms over Arkansas.

The heat warning has expired and temperatures are not a warm as
the past few nights. Have made minor adjustments to going lows
based on current temperature trends.

Britt

&&

Short term... (through late Monday afternoon)
issued at 350 PM CDT sun Jul 23 2017

Isolated to scattered thunderstorms have developed near a cold front
which is slowly sinking southward through Missouri and Illinois.
Convection will likely continue through the evening hours before
dissipating with the loss of diurnal heating. There is much less
instability and there are far less favorable lapse rates this
afternoon compared to yesterday afternoon, and both the air
temperature and the dew point will be decreasing overnight behind
the front. Although an isolated strong to severe storm is possible,
a repeat of last night's severe weather is not anticipated.

Heat index values were hovering near the century mark this
afternoon, therefore the excessive heat warning will be retained
through the early evening with the expectation that it will be
cancelled or allowed to expire this evening. Overnight lows will
likely fall into the 60s areawide (closer to 70 in the urban core of
St. Louis). Highs tomorrow will be 5-10 degrees cooler across the
area except over the Eastern Ozarks where temperatures will likely
be similar to what they were today.

42

Long term... (monday night through next sunday)
issued at 350 PM CDT sun Jul 23 2017

Main focus will be temps on Wed with a relatively uneventful week
ahead.

Mdls are in fairly good agreement thru the period. Period begins
with weak northwest flow aloft and a sfc ridge building into the region
from the Great Lakes. Light Ely flow and a mostly clear sky shud
allow for ample radiational cooling and have trended aob the cooler
guidance.

With sfc winds becoming more sly on tues and the upper ridge
building into the area, temps shud warm up quickly. The main warm up
is still expected to be Wed. The GFS suggests convection possible as
early as mid morning thru central portions of the County Warning Area on the ern
fringes of the cap with good low level support. While this can not
be ruled out, does not seem the most likely soln attm. Have
therefore continued temps in the mid to upper 90s due to 850mb temps
around 22c.

A cdfnt shud push thru the County Warning Area thurs and Fri bringing thunderstorms and rain with it.
Given amount of cape that shud be available ahead of the fnt, a
severe threat shud exist on thurs and possibly Fri. However, weak
deep layer shear will help keep threat limited. With k-index values
around 40c, will need to monitor this event for heavy rain
potential.

A large sfc ridge builds into the region behind the cdfnt with northwest
flow aloft. Much cooler conditions currently expected with 850mb
temps in the 12c to 14c range.



Tilly

&&

Aviation... (for the 06z tafs through 06z Monday night)
issued at 1123 PM CDT sun Jul 23 2017

Showers and thunderstorms have dissipated. Winds will remain
light.

Specifics for kstl:

Dry and VFR conditions are expected through the period. Winds will
remain light.

Britt

&&

Lsx watches/warnings/advisories...
MO...none.
Illinois...none.
&&

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