278
FXUS63 KLSX 172050
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
250 PM CST Mon Nov 17 2025

.KEY MESSAGES...

- A warm front tonight brings briefly warmer air for Tuesday
  before a shift back to cooler weather behind Tuesday`s cold
  front.

- A prolonged period of wet weather is expected Wednesday night
  through late Friday.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 248 PM CST Mon Nov 17 2025

The upper level pattern across North America features a large
northern stream ridge extending well into central Canada and a
downstream trough over the Northeast US and Canadian Maritimes.
Beneath the large ridge, a shortwave trough is pushing across the
central Rockies this afternoon, with surface low pressure developing
over northeast Kansas. Our area is currently within the cool and
very dry remnants of the air mass that moved in behind Saturday`s
cold front. But just to our west a stream of moisture is being
pulled northward by the low pressure system developing in the
Central Plains. The initial thrust of moisture northeastward is
occurring almost entirely aloft, and has already led to the
development of some thunderstorms over southwest Missouri. This will
gradually push northeastward through our forecast area late this
afternoon and evening with what is likely to amount to a relatively
narrow area of showers and embedded thunderstorms along the leading
edge of the warm front aloft. As we go into this evening, coverage
of showers is likely to increase as the low level jet strengthens
and pushes more moisture northeastward. However, the threat for
thunderstorms decreases with lessening instability further east.
With thunderstorms being elevated in nature, the only potential
threat beyond lightning is hail. With increasing clouds and rising
dewpoints we won`t cool off that much tonight. Lows will be 10 to 20
degrees warmer than this morning.

The surface low actually tracks ESE through our forecast area
tomorrow, roughly from St Joseph to Cape Girardeau, though the
system overall will be weakening as it does so. South of the low
track we see winds shift from southerly to westerly before finally
turning northerly. The temperature warms into the 70s ahead of the
low, with dewpoints rising to near 60. That`s a massive increase
from our current dewpoints near 20. There`s some potential for
another round of thunderstorms to develop in that moist air just
ahead of the surface low and cold front on Tuesday afternoon. If
they do, they`ll have a better environment to work with as
instability will become more surface based. However, confidence
remains low that we will see storm development in our area. Only a
handful of CAMs have begun to show this potential, with this
activity occurring primarily to the east later in the day when the
front has largely moved through our forecast area. Still, it remains
a scenario to watch for as there will be a broader severe weather
threat if storms were to occur Tuesday afternoon.

Kimble

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 248 PM CST Mon Nov 17 2025

Tomorrow`s front sinks south of our area on Wednesday, so we`ll be
solidly in the cooler air once again. The surface high associated
with this air mass pushes eastward through the Great Lakes and into
New England, so we only get a peripheral shot of cooler air. The
front itself loses its southward push and stalls near the MO/AR
border, setting the stage for the next round of wet weather.

A larger southern stream trough currently arriving in California
will dig into the Southwest US over the coming days. As it does so,
it will reinvigorate a moist southerly flow over the Southern Plains
out ahead of it. This moist flow pushes northward into the stalled
frontal boundary producing rounds of rain stretching from Texas to
the Ohio Valley and encompassing much of the southern half of our
forecast area. This rain begins as early as Wednesday night but
continues through Thursday and Friday before the main trough finally
pushes eastward and halts the moist flow into the boundary. It`s
becoming increasingly clear that the southern half of the forecast
area is the focus for this prolonged period of wet weather. Northern
areas north of the Missouri River may miss out on most of these
rounds of rain, with the last round on Friday being the most likely
to affect the entire region.

The quality of moisture being pulled northward during this period is
pretty high. Precipitable water values rise well over 1 inch to as
high as 1.4 inches at times. However, rainfall rates are not
expected to be heavy enough for a significant flash flood threat as
deeper instability remains south of the frontal boundary. The total
duration of rainfall is what stands out the most, here, with 48 to
60 hours of on and off rainfall in the vicinity of the Ozarks. The
primary impact from this will be rising water levels on streams and
rivers. However, these water levels are already quite low due to the
lack of rain in recent weeks. So even with the widespread soaking
rain we do not expect a river flood threat from this. Model forecast
rainfall amounts for the duration of this event have continued to
tick lower over the last several model runs. Now broadly less than
40 percent of long range ensemble members produce 1 inch or more of
rain over this 48 hour period.

Though we remain largely on the north side of this frontal system,
it is a southern stream system without a significant source of cold
air with it. So we will remain mild and well above freezing through
the duration of this wet period, mainly in the 50s and 60s. We will
see a cool down behind the final wave Friday into Saturday (which
day it comes through is still uncertain). But the air mass behind
this wave remains mild for late November standards. The northern jet
stream is expected to remain well north of the region right through
the beginning of next week. In fact, we will see another large
southern stream trough tracking across the southern tier of the
country next week, though when and where is still quite variable in
the available guidance. On the early side of things, this could
begin to impact our area with some rain as early as next Monday, but
other scenarios delay this until Wednesday or largely miss our area
altogether.

Kimble

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1139 AM CST Mon Nov 17 2025

Southeast wind continues this afternoon under VFR skies. However,
thunderstorms have developed over southwest Missouri and will
track northeast across the region this evening. Expect thunder
chances to decrease as it heads east, however overall coverage of
showers increases to the east and north. This round doesn`t last
very long as it is narrow and moves east quickly. Stronger SW winds
aloft tonight will create the potential for low level wind shear.
It`s possible that moisture advecting on these SW winds may bring
in some MVFR ceilings Tuesday morning before winds shift to the
west and then northwest during the day Tuesday drying things back
out.

Kimble

&&

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

$$

WFO LSX