917
FXUS63 KLSX 101101
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
601 AM CDT Thu Oct 10 2024

.KEY MESSAGES...

- Widespread 80s are forecast today through Saturday, with highs
  on Saturday approaching record territory.

- A potent cold front on Sunday will drop temperatures
  substantially next week. Frost development is likely,
  especially on Tuesday and Wednesday mornings.

- We may also see our first freeze on these mornings. The greatest
  potential for sub-freezing lows will be in low-lying and
  sheltered areas.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 243 AM CDT Thu Oct 10 2024

Surface high pressure continues to dominate our sensible weather.
Highs today will be a few degrees warmer than yesterday due to
another day of abundant insolation. Widespread 80s are forecast,
which will be 10 to 15 degrees above normal for mid-October. These
temperatures will only climb through the rest of the week as the
high slides east and opens us up to low-level southwesterly flow. By
Saturday, highs in the mid to upper 80s will be encroaching on
record territory (SEE CLIMATE SECTION). Overnight lows will continue
to gradually climb through Saturday morning as well. The influence
of surface high pressure through Saturday will keep promoting the
development of patchy river valley fog each morning.

Jaja

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 243 AM CDT Thu Oct 10 2024

A mid-level trough digging into the Upper Midwest and Great Lakes
regions is forecast to drag a potent cold front through the Mid-
Mississippi Valley on Sunday. Although guidance is converging on
Sunday being another warm day, there is still uncertain regarding
the exact temperature forecast. Confidence is high in a strong, cold
airmass following the front, and deterministic guidance shows the
front clearing the forecast area by midday. How far the airmass
follows behind the front will dictate how warm a given location will
get on Sunday. Our current forecast has portions of northeast
Missouri struggling to reach 70 degrees while southeast Missouri
achieves 80 degrees with an even gradient in between. The low and
high end values seem realistic, but the gradient values are likely
too washed out due to low model resolution and differences in timing
among different models.

The cold, dry airmass will encapsulate us fully by Monday.
Confidence remains high in a below average temperature forecast for
at least Monday and Tuesday, with highs only managing to reach the
50s and 60s areawide. As surface high pressure centers itself over
the Mid-Mississippi Valley, cool north winds will wane and
radiational cooling conditions will become more prevalent in the
week. When exactly this will happen is uncertain. If we are able to
achieve efficient radiational cooling conditions within the peak of
the cool air, we`ll be able to cool more at night. This solution
would increase the potential of seeing a frost or perhaps even a
freeze sometime next week. Recent NBM ensemble runs have been
trending pretty steadily regarding the potential for frost (T<=36)
and freeze (T<=32). Probabilities are for frost are still high
(>70%) on Tuesday and Wednesday morning in northeast Missouri,
decreasing with southeastward extent. Probabilities for a freeze,
however, remain much lower (<30%). Again, model resolution and
differences likely contribute to this since low-lying and sheltered
aren`t considered on the map. If high pressure centers over the
region overnight on Tuesday, more of the area will have the
potential to see a freeze on Wednesday morning. Until then, the
greatest potential for a freeze lies in the aforementioned low-lying
and sheltered areas.

How long the cold air sticks around is in question. 24 hours ago,
the NBM interquartile range was sub-10 degrees through the middle of
next week, but it`s since risen beginning on Wednesday. This is due
to differences in the low-level ridge from mid-week onward. If the
ridge axis passes, we`ll be open to low-level southerly flow and may
be able to warm faster. If the ridge is less progressive, we`ll be
under the influence of the cold airmass for longer. Guidance is
consistent in showing a warming trend for next week regardless, but
the swiftness of the trend will depend on the behavior of the
high.

Jaja

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 553 AM CDT Thu Oct 10 2024

MVFR to IFR visibilities caused by patchy river valley fog will
improve shortly after sunrise. From there, dry and VFR conditions
with light and variable winds will prevail through the TAF period.

Jaja

&&

.CLIMATE...
Issued at 220 PM CDT Wed Oct 9 2024

October 12th Record Daily High Temperatures:

KSTL: 89 in 1890
KCOU: 94 in 1899
KUIN: 88 in 1975


&&

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

$$

WFO LSX