432 
FXUS63 KLSX 050227
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
927 PM CDT Sat May 4 2019

.UPDATE...
Issued at 922 PM CDT Sat May 4 2019

A nice tranquil night is still expected with surface high 
pressure in control. High clouds across southern/eastern IL will 
continue to depart as the upper trof centered in the lower MS 
Valley moves east, while a little high cloudiness from the Plains 
associated with dying convection may filter into the area 
overnight. May see some radiational fog, especially in favored low
lying spots and also south central IL. Lows overnight will be a
bit below average as temps bottom out in the 40s.

Glass

&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 404 PM CDT Sat May 4 2019

The upper trough axis has shifted eastward and a high pressure
center was building into the region. This will ensure dry weather
for tonight and tomorrow. 

There may be some fog across the area tonight due to the 
combination of good radiational cooling conditions and ample low-
level moisture from the recent heavy rainfall over the last few 
days. Factors which might interfere with fog formation are the 
drier air filtering into the region and the earlier clearing today
which has promoted good diurnal mixing.

Tonight's lows in the 40s will be near normal for this time of
year, but it will also be the coolest night out of the next
several nights. Highs on Sunday will generally be in the 70s
across the area.

Kanofsky

.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 404 PM CDT Sat May 4 2019

Despite differences regarding the details, models remain in 
general agreement on an active weather pattern for most of next 
week. A closed low over the Pacific is forecast to reach the CA 
coast by Sunday afternoon and then continue progressing inland. 
By the time it reaches the Four Corners region on Wed morning, a 
separate PV anomaly will have been diving southward out of western
Canada. A third PV anomaly is also forecast to be over south 
central Canada. Models show different degrees of interaction 
between these three features, yielding different upper air 
patterns by the end of the week. Several smaller PV anomalies are 
also forecast to lift through the central CONUS during this time. 
Taken together, there will likely be several rounds of SHRA/TSRA 
from Monday through Thursday as these upper features interact with
and sharpen existing baroclinic zones. 0-6 km shear values of
30-50 kts on Wed into Thu suggest that strong to severe 
thunderstorms will be possible. 

By Thursday evening, the last in the series of surface lows is 
forecast to have lifted northeastward into the Great Lakes,
dragging a cold front through the region. Models then show a 
surface high pressure center which slides southeastward into 
MO/IL. This would bring dry and quiet weather to the region for 
Thursday night through Saturday. 

With a quasistationary front located across the region for most 
of the week, temperatures will depend on where the front is 
located on any given day. The position of the effective synoptic 
scale boundary could also be affected by thunderstorm outflows. 
Highs will generally be in the 70s to near 80 degrees on the warm 
side of the front and in the 60s on the cool side of the front. 
Overnight lows will generally be in the 50s to around 60 degrees. 
The exception is on Thursday night when lows should drop into the 
40s behind the cold front.

Kanofsky

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 620 PM CDT Sat May 4 2019

The main item for overnight is the potential for radiational fog.
Surface high pressure will dominate overnight into early Sunday
morning bringing light winds and radiational fog potential. At
this point I just have a period of MVFR vsbys/fog with a TEMPO
group at KSUS and KCPS. Will have to further evaluate on adding 
fog to the KCOU TAF for the 06z issuance as some of the guidance 
is also suggesting potential. Otherwise VFR flight conditions are 
expected through the forecast period with southerly surface winds 
developing on Sunday.

SPECIFICS FOR KSTL: 

VFR flight conditions are expected through the forecast period.
Surface winds become light this evening and then southerly on
Sunday afternoon.

Glass

&&

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

$$

WFO LSX