Webster Groves, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

851
FXUS63 KLSX 090346
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1046 PM CDT Tue Oct 8 2024

.KEY MESSAGES...

- Dry conditions with low humidity continue this week with
  gradually warming temperatures. By Friday and Saturday
  widespread 80s are expected.

- A strong cold front on Sunday will send temperatures downward
  for next week. Confidence in the colder temperatures has
  increased with a few frosty mornings likely (up to 70 percent)
  next week.


&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 207 PM CDT Tue Oct 8 2024

The upper air pattern across North America is dominated by a trough
centered near James Bay in Canada and a broad ridge over the western
US nosing up into Manitoba. The northwest flow between these
features is promoting high pressure over the Midwestern US, with the
center of the surface high over Missouri as of early this afternoon
although its influence continues to expand eastward.

Despite some warmer temperatures today under full sunshine, we
expect another chilly night tonight as the high remains over the
region. Calm winds, a clear sky, and continued dry air set up
another good radiational cooling scenario. Dewpoints today have been
a little lower than expected in most places as the recovery models
had forecast was primarily due to local evapotranspiration rather
than any sort of moisture advection. With the lack of recent
rainfall and the trend toward dormant vegetation, that dewpoint
recovery has been lacking. As a result, dewpoints in the 30s set up
another low floor for temperatures tonight with the colder spots
(valleys, open pastures) dropping into the 30s and the warmer
locations (urban areas) staying in the mid to upper 40s.
Temperatures should be a couple of degrees warmer near the center of
the high than they were yesterday, so the chance of frost is lower
tonight than last night. Similarly, with our location near the
center or southwest part of the broader surface high we will be in a
more favorable position for morning fog. This is most likely in the
river valleys of southern Missouri up to and including the Missouri
River valley.

Not much change is expected for Wednesday as as the general pattern
remains similar with Hurricane Milton charging eastward toward
Florida well to our south. The surface high does nudge a bit further
east opening us up to a bit more synoptic southerly flow enabling an
even further warm up on temperatures. Mid 70s to low 80s are
expected with the warmest temperatures in the west further from the
slowly departing surface high. This is some 5 to 10 degrees above
normal for this time of year. Lows fall off strongly again Wednesday
night but a bit warmer than prior nights due to slightly stronger
winds and slightly higher dewpoints. Lows in the 40s to near 50 are
right around normal for this time of year.

Kimble

&&

.LONG TERM...  (Thursday through Next Tuesday)
Issued at 207 PM CDT Tue Oct 8 2024

Surface high pressure continues to gradually shift east while the
upper ridge axis itself also tilts eastward toward our region. This
will allow the warm up to continue Thursday, Friday, and into
Saturday with more and more 80s expected. The warmest day is likely
Saturday when this air mass peaks in the mid to upper 80s, a few
degrees shy of record highs near 90. Overnight lows creep upward as
well, but not as much as the dry air and light winds continue to
allow strong cooling at night. So while temperatures are almost like
summer on Saturday, the low humidity and crisp nights will remind us
that it is in fact just a stretch of fall warmth.

A pattern change is in the works for early next week. A shortwave
trough rounding the top of the western ridge dives southeast through
the central US driving a strong cold front southward as well. Models
have come into much greater agreement on this trough, with the
consensus now pointing toward the sharper trough and thus colder
solutions. Among the 00Z ensemble guidance, the interquartile range
(25th to 75th percentile) for 850MB temperatures Monday afternoon
has fallen sharply to only on the order of 3C (-1C to +2C). Just
comparing to 00Z the day before when this range was well over 10C
(0C to +14C), the shift in guidance toward the colder scenarios
becomes clear. Diving into the cluster analysis, only one of the 4
clusters continues to hold on to the warmer scenario, representing
only 18 percent of ensemble guidance. The overwhelming majority of
guidance now points to the sharp cool down behind the front. All of
this is to say that while yesterday we discussed this front as a
potential for a strong cool down or just a glancing blow, our
confidence in us seeing a stronger cool down has increased sharply.

When it comes to the temperature forecast, there continues to be
high uncertainty on Sunday relating to the timing of the frontal
passage. Ahead of the front it`ll still be in the 80s, while behind
the front the cool down begins sharply. The front is likely to be
near the center of our forecast area Sunday morning, so highs in the
north are more confidently in the 60s while southern areas have a
greater chance of nearing 80 degrees again before cooling off in the
afternoon. In between represents a much more low confidence blend of
the two extremes.

By Monday the entire area will be solidly into the colder air mass.
850MB temperatures around 0C represent fully mixed surface
temperatures only in the 50s. With the greater confidence in the
cool down, we see NBM forecast temperatures have also fallen sharply
into the 50s to low 60s both Monday and Tuesday. Overnight lows are
now also more confidently in the 30s, although just how cold these
get will depend on when the surface high moves through and the
degree of cloud cover. Under ideal cooling conditions of light winds
and a clear sky, subfreezing temperatures become a real possibility
with even the probabilistic NBM indicating up to a 50 percent chance
of hitting 32 in some of the typically colder parts of our area. The
chances of frosty temperatures just above freezing are even higher
and more widespread.

The greatest uncertainty at this point is no longer on whether it
will get cold, but more on how long it will last. The glancing blow
scenario is increasingly less likely, and the guidance trend has
been to hold on to the cold air for longer. Some of the
deterministic guidance doesn`t move the surface high through until
Wednesday or Thursday which means we could have multiple days in the
cold air mass and multiple nights threatening a freeze. NBM
probabilities of freezing temperatures continue to be noted right
through Thursday morning as a result of that timing uncertainty. The
most likely scenario is that we`ll have one very cold night when the
high moves through, it`s just not clear whether that will be as
early as Tuesday morning or as late as Thursday morning.

Kimble

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1038 PM CDT Tue Oct 8 2024

Surface high pressure currently centered near St. Louis remains in
control resulting in light winds and decent radiational cooling.
This should allow for some river valley fog overnight, especially
on the Missouri River, and some spots of radiational fog as well.
Still expect the greatest impacts at KJEF where visibilities in
the 1/2 to 1 1/2SM range are forecast from 09-13z. At KSUS and
KCPS there is fog potential as well but confidence is not as great
and have a short period where IFR conditions are possible between
10-12z. Otherwise VFR flight conditions are expected. Surface
winds will remain light but obtain some southerly component on
Wednesday as the surface high oozes eastward.

Glass

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX