Scientific Forecaster Discussion
fxus63 klsx 190908 cca
Area forecast discussion
National Weather Service Saint Louis MO
321 am CDT Fri Jul 19 2019
Short term... (through late Saturday afternoon)
issued at 311 am CDT Fri Jul 19 2019
With the jet stream stuck across the US/Canadian border through
Saturday, this dangerously hot airmass will remain across the area.
As mentioned in previous discussions, we may see a bit more
mixing today and tomorrow. However the resultant slightly lower
dew points and higher temps will result in very similar heat index
readings; between 105 and 110 across much of the region.
Overnight temps should be quite similar to what we're seeing this
morning. With these dangerous conditions continuing through
Saturday, the excessive heat warning will remain in effect through
Long term... (saturday night through thursday)
issued at 311 am CDT Fri Jul 19 2019
A cold front will sweep through the region on Sunday which will
bring an end to the heat wave. Unfortunately models have been slow
to zero in on frontal timing and sunday's highs remain a big
question mark. Despite showing a bit more of a progressive upper
wave, the Euro continues to show the front passing after 18z.
Meanwhile the GFS and NAM show the fropa prior to 18z. Should the
front come in on the slow side, it's possible that we push back
toward excessive heat warning criteria. That said, confidence in
this occurring remains low, so will not be expanding the heat
warning into Sunday.
The frontal passage is also likely to bring showers and storms to
the region, but questions remain here as well. Guidance show the
majority of the precip after 00z Monday, well behind the front.
However, given the setup with a warm, moist, and unstable airmass
ahead of the front, I would expect to see storms along the front in
the afternoon. Considering the differences in the guidance and the
fact that the guidance is somewhat out of line with my mental model,
confidence on precip timing is fairly low. Therefore despite high
confidence in precip occurrence, I stuck with around 50 percent
chance pops on Sunday afternoon and evening. The atmosphere should
be rather unstable ahead of the front thanks to the lingering high
dew points, and this will likely cause some of the storms to become
strong. However, with fairly weak deep layer shear, there is only a
marginal chance for severe storms.
Behind the front, northwest upper level flow will dominate through the
remainder of the period. This will usher in much cooler
temperatures as a strong surface high builds into the region.
Models in good agreement showing 850 temps hovering around or just
below +15c through much of the work week. This should translate
to highs in the low 80s on Monday and Tuesday before gradually
pushing toward normal by the end of the week. The flow behind the
the front does not look particularly dry, but with no clear
forcing mechanism, the forecast will remain dry.
Aviation... (for the 06z tafs through 06z Friday night)
issued at 1112 PM CDT Thu Jul 18 2019
Just patchy mid level clouds late tonight, then scattered diurnal
cumulus clouds late Friday morning and afternoon. South-
southwesterly surface winds will continue through the period.
There will be low level wind shear in uin late tonight/early Friday morning due
to a southwesterly low level jet.
Specifics for kstl: just patchy mid level clouds late tonight,
then scattered diurnal cumulus clouds late Friday morning and
afternoon. South-southwesterly surface winds will continue
through the period.
MO...excessive heat warning until 8 PM CDT Saturday for Audrain MO-
Boone MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-
Gasconade MO-Jefferson MO-Knox MO-Lewis MO-Lincoln MO-
Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike
MO-Ralls MO-Saint Charles MO-Saint Francois MO-Saint Louis
City MO-Saint Louis MO-Sainte Genevieve MO-Shelby MO-Warren
Heat advisory until 8 PM CDT Saturday for Iron MO-Madison MO-
Illinois...excessive heat warning until 8 PM CDT Saturday for Adams Illinois-Bond
Illinois-Brown Illinois-Calhoun Illinois-Clinton Illinois-Fayette Illinois-Greene Illinois-
Jersey Illinois-Macoupin Illinois-Madison Illinois-Marion Illinois-Monroe Illinois-
Montgomery Illinois-Pike Illinois-Randolph Illinois-Saint Clair Illinois-Washington