Area Forecast Discussion Issued by NWS St. Louis, MO
000
FXUS63 KLSX 180855
AFDLSX
Area Forecast Discussion...Corrected
National Weather Service Saint Louis MO
336 AM CDT Mon Mar 18 2024
.KEY MESSAGES...
- Temperatures will struggle to reach the low to mid 40s today,
and a hard freeze (lows <= 28F) is expected again tonight
across much of the area.
- It will be much warmer on Tuesday with highs reaching the mid to
upper 60.
- Temperature trends remain very uncertain for Wednesday through
next Sunday.
&&
.SHORT TERM... (Through Late Tuesday Afternoon)
Issued at 334 AM CDT Mon Mar 18 2024
.KEY MESSAGES...
A cold Canadian high pressure system will drop from the Dakotas into
the southeast Plains today. Chilly morning lows in the low to mid
20s across most of the area combined with northwest flow will make
for a cool Mid-March day with highs struggling into the low to mid
40s. As the high continues moving south and east tonight, winds
across the area will briefly become light and variable, and then
turn to the southwest. This period of light wind combined with a
clear sky will produce excellent radiational cooling conditions and
allow temperatures to drop very quickly into the mid and upper 20s
again. Increasing southwest flow overnight should stop the cooling
and even bump temperatures up a few degrees by sunrise. Tuesday
still looks like the warmest day of the week with west-southwest
flow ahead of another cold front. Guidance is in good agreement
that temperatures will rise back into the mid to upper 60s in most
locations on Tuesday afternoon.
Carney
&&
.LONG TERM... (Tuesday Night through Sunday)
Issued at 334 AM CDT Mon Mar 18 2024
Temperatures and precip chances remain uncertain for Wednesday
through next Sunday as the long wave pattern shifts and becomes less
meridional and more zonal. With that said, the latest guidance is
cooler than previous runs as the pattern shift is pushed further
into the future and is less pronounced at...least initially. The
deterministic GFS and NAM show the cold front down across southern
Missouri by 12Z Wednesday. North-northeast flow behind the front
should suppress temperatures, and the models are also showing some
mid-upper level moisture which should be good for some cloud cover.
The current forecast shows highs around 50 in northeast Missouri and
west central Illinois, near 60 along the I-70/64 corridor, and up to
around 70 in southeast Missouri. This looks too warm given the
pattern, and perhaps the NBM forecast high temperatures have been
been influenced by bias-corrected models. The latest run of the NBM
still looks too warm, particularly south of Farmington where it`s
still showing highs around 70. Blending the NBM with an consensus
model guidance brought temps down a few more degrees, particularly
in the warm south. Overall this knocks 5-7 degrees off the previous
forecast. With all that said, the LREF mean and spread temperatures
have also fallen over the past few runs, but the difference between
the top and bottom quartile is still almost 10 degrees indicating a
great deal of uncertainty.
The theme of uncertainty continues through the remainder of the
forecast as the LREF 25th-75th percentile spread remains around 10
degrees or more. This peaks on Saturday and Sunday where the
differences are 15 and 16 degrees respectively. With that in mind,
the cooler trend in guidance continues Thursday with easterly flow
and clouds ahead of the next upstream wave which will be moving into
the Plains. The deterministic GFS and ECMWF are even kicking out a
spattering of QPF as the 850mb flow turns to the south-southwest
ahead of the wave and warmer air overruns the colder air at the
surface. The cold front associated with the surface reflection of
the wave passes through Friday with another few spits of QPF. There
should be a brief window for warming up Friday ahead of the front,
however the timing of the front that far out is very uncertain. The
deterministic GFS and ECMWF show very different temperature
forecasts for Saturday north of the front with the GFS being much
colder due to a more amplified solution with the short wave which
allows a much greater penetration of cold air south into the
Mississippi Valley on Saturday. The LREF clusters (unsurprisingly)
also show these differences with cluster-1 giving St. Louis a 2
meter temperature of 48 at 18Z Saturday, and cluster-3 showing 63!
Guidance is in general agreement that we`ll transition from zonal to
southwest flow by Sunday as a deep long wave trough digs into the
western U.S. However, LREF cluster analysis shows some pretty huge
differences in both the amplitude and position of that trough, so
the details of the surface low it starts generating east of the
Rockies on Sunday are also questionable, and therefore so is the
temperature and precipitation forecast east of it in the Mid-
Mississippi Valley.
Carney
&&
.AVIATION... (For the 06z TAFs through 06z Monday Night)
Issued at 1047 PM CDT Sun Mar 17 2024
It is a persistence forecast with VFR conditions continuing
through the period. Northwest winds will increase mid-morning
Monday with occasional gusts near 20 knots. Winds lighten Monday
evening as they shift out of the southwest late in the period.
Maples
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX