Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 020924

Area Forecast Discussion
National Weather Service Saint Louis MO
424 AM CDT Sun Apr 2 2023

.SHORT TERM...  (Through Late Tonight)
Issued at 424 AM CDT Sun Apr 2 2023

A ridge of high pressure extending from the eastern Great Lakes
region southwest through the Lower Mississippi Valley will drift
east today as a low moves across the Northern Plains.  The wind is
already turning to the south as the ridge retreats, and the
southerly flow should increase through the day as the pressure
gradient tightens in response to low to our northwest.  Strong
insolation under a mostly clear sky along with the southerly flow
will push temperatures back up well above normal into the upper 60s
to low 70s along and west of the Mississippi.  Warming will be
somewhat weaker across south central Illinois where warm advection
will be weaker due to proximity to the ridge.

The northern Plains low will drag a cold front through Iowa into
northern Missouri by 03-06Z this evening.  All of the upper level
support for the low will remain up along the US/Canada border, and
the flow aloft over the Mid Mississippi Valley will remain quasi-
zonal.  This will allow the front to stall over northern
Missouri/central Illinois, trailing off to the southwest over the
central Plains.  A weak low will develop on the baroclinic zone
tonight which will cause the low level jet to increase to around 25-
30kts south of the front.  RAP/GFS/NAM all print out precip over the
area as the LLJ forces weak moisture convergence along and south of
the front. Convection allowing models show widely scattered showers
developing around 03Z and continuing through most of the night. This
looks reasonable given the set up and presence of weak moisture
convergence.  The RAP shows some pretty decent elevated instability
with MUCAPE in excess of 1000 J/Kg at times overnight.  GFS isn`t
nearly as beefy, nor is the HREF mean MUCAPE with values only in the
200-500 J/Kg range, so the RAP may be overdone.  Regardless, there
will almost certainly be some thunder in the mix tonight.


.LONG TERM...  (Monday through Saturday)
Issued at 424 AM CDT Sun Apr 2 2023

Weak upper level ridging builds across the Mid Mississippi Valley on
Monday as the upper pattern amplifies ahead of the next long wave
trough.  The ridging will likely suppress convection across most of
the area...except possibly in the vicinity of the stationary front
over northern Missouri and west central Illinois.  Continuing
southerly flow on Monday pushing temperatures well into the 70s for
most locations.  The exception will be far northern parts of the
CWFA where clouds and potential showers will keep highs in the mid
to upper 60s.  Warm advection continues Monday night which will keep
mild temperatures in the upper 50s to low 60s across most of the
area, of course temperatures will likely be lower in the upper 40s
to low 50s in the vicinity of the front, with a continuing chance
for rain.

There`s little change to the overall forecast for Tuesday through
Wednesday. A strong long wave trough will dig into the west central
Rockies by 12Z Tuesday forcing lee-side cyclogenesis over eastern
Colorado.  The trough then ejects northeast Tuesday and Wednesday
with the surface low tracking through the east central Plains into
the upper Midwest by 06-12Z Wednesday.  Uncertainty remains on the
timing of the front, and this will likely be critical for severe
weather potential for our area.  Current guidance shows the front
moving through the CWFA after 06Z Wednesday morning.  While there is
quite a bit of instability during the daylight hours of Tuesday with
CAPE values in excess of 2000 J/Kg that instability falls off
rapidly overnight Tuesday night.  Long range GFS soundings show a
very capped airmass over the area Tuesday afternoon, and that cap
doesn`t really erode with time, it`s only the front coming through
overnight that finally breaks it.  Of course by then, the
instability is pretty meager, with the GFS down to 500-700 J/Kg
ahead of the front at 06-09Z.  There does seem to be quite a bit of
uncertainty in how much instability there will be as the NBM shows
500+ J/Kg between the 25th and 75th percentile between 06-12Z ahead
of the front.  Of course, dynamics will be significant with 0-3km
and 0-6km shear around 50kts, so it won`t take a very strong updraft
to potentially be severe.  Details should come into greater clarity
as we get closer in time.

The remainder of the forecast continues to look more tranquil,
although it will likely be windy again on Wednesday behind the
front.  Dry weather with below normal temperatures can be expected
Thursday and Friday as high pressure moves across the region and
then warmer temps near normal on Saturday as the high moves east and
southerly flow returns.



.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1021 PM CDT Sat Apr 1 2023

Dry and VFR conditions are expected through the period. Light
and variable winds will turn out of the south around 10 knots
between 10-13Z with gusts to around 25 knots by 18Z. Winds will
decrease after 00Z.



Saint Louis     69  53  74  62 /   0  30  20  30
Quincy          68  48  67  54 /   0  30  30  40
Columbia        72  52  75  60 /   0  30  20  20
Jefferson City  73  52  76  62 /   0  30  20  10
Salem           63  51  71  62 /   0  40  20  30
Farmington      67  52  74  62 /   0  30   5  10




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