499 
FXUS63 KLSX 251749
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1149 AM CST Sat Jan 25 2020

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 315 AM CST Sat Jan 25 2020

Cyclonic flow will continue today in the wake of the upper low 
departing the OH Valley. Stratus blankets the region within this 
flow extending back into eastern KS. I think clearing will be slow
and am leaning towards the more pessimistic guidance suggested by
the RAP 925 mb RH. This would bring potential clearing first into
the southern CWA later this afternoon which seems reasonable 
given the notch in the stratus over far SW MO at this time. The 
combination of the stubborn low clouds and weak low level CAA will
make for a small diurnal temperature range for all but the 
aforementioned southern CWA where afternoon clearing is expected. 
All in all the highs today will be on the order of 3 to 10 degrees
below average.

The stratus should continue clearing eastward across the CWA
tonight. However the low clouds will be chased by increasing mid-
high clouds spreading in from the west-northwest in advance of 
several northwest flow short wave trofs with the progressive split
flow pattern. The main waves pass to the north and south on 
Sunday. The 00z ECMWF is quite a change from 24 hours ago when it 
showed light precipitation across the entire CWA. All the models 
are now in rather good agreement keeping any precipitation south 
of the CWA, more in line with the better forcing across the lower
MS and western TN Valleys. That said we will still need to keep 
an eye on the far southern CWA counties for any fluctuations in 
location of the forcing and moisture, and possibility of light 
precipitation.

Glass

.LONG TERM...  (Sunday Night through Friday)
Issued at 315 AM CST Sat Jan 25 2020

Much of the week ahead looks dry with the progressive split flow
regime continuing into late week. There is a rather potent short 
wave trof forecast to move across the region on Monday that bears
watching. Timing varies a bit with this system but it does have
some decent large scale forcing, and the CMC GEM is the sole model
showing the possibility of a quick hit of light snow with a band
across central and east central MO. 

Another series of migratory short waves are forecast to traverse
the area Tuesday night into early Wednesday. The global models and
GEFS have been trending drier in this time range with a growing
consensus that the waves won't phase and precipitation will
largely be associated with the southern wave across the lower MS
Valley.

A pattern change begins to evolve late week into the weekend
featuring large scale amplification. In the process we could see
some precipitation and at least a short period of above normal
temperatures.

Glass

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1120 AM CST Sat Jan 25 2020

SPECIFICS FOR KCOU and KUIN:
Stratus producing MVFR conditions currently sits over KCOU and
KUIN while patches of VFR conditions from higher cloud bases and
holes exist further upstream. Over the period the stratus will
move out to the northeast as the parent low pressure system
continues to move northeast as well. 

There is the possibility that holes in the stratus deck and 
associated VFR conditions could expand and bring KCOU up to VFR 
conditions sooner than forecast. MVFR conditions are forecast to 
persist at KUIN as the stratus deck continues to encompass the 
region. As with KCOU, there is a chance that upstream VFR stratus 
advects into KUIN bringing slightly improving conditions this 
evening, though confidence in this occurring is low. Some guidance
shows IFR stratus currently over eastern Nebraska moving into 
KUIN early tomorrow morning, but without greater confidence have 
hinted at this possibility using a SCT009.

Northwest winds in the mid to low teens will diminish over the 
day to become light and variable as a surface ridge moves into the
region.

SPECIFICS FOR KSTL, KSUS, and KCPS: 
MVFR stratus will persist at the metro terminals, including KSTL,
for the remainder of the day, only improving slightly overnight as
the stratus continues to lift out of the area with the
northeastward moving low pressure system. As with KUIN there is a
possibility that IFR stratus will move through the metro area
early tomorrow morning and have included SCT009 tomorrow morning 
to hint at this. 

Northwest winds in the mid to low teens will diminish over the 
day to become light and variable as a surface ridge moves into the
region.

MRM

&&

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

$$

WFO LSX