Area Forecast Discussion
Issued by NWS St. Louis, MO

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KLSX 211204
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
604 AM CST Fri Nov 21 2014

.SHORT TERM:  (Through Late This Afternoon)
Issued at 355 AM CST Fri Nov 21 2014

Surface ridge to continue moving off to the east ahead of next
weather system. Winds to become southeasterly by midday as weak warm
front lifts north through area. This will bring in slightly warmer
temps to the region with temps rising above freezing most locations
by 18z. In the meantime, low level moisture will be on the increase,
but will take awhile to moisten the column as there is a lot of dry
air to overcome. Will see showers develop over southwestern and
southern Missouri and spread to the north and east, moving into
central MO and southern portions of forecast area by 17z.
Fortunately temps will be above freezing when the rain does move in
so no mixed precipitation expected. Precipitation will be scattered
in nature. Highs will be in the upper 30s to mid 40s.

Byrd

.LONG TERM:  (Tonight through Thursday)
Issued at 355 AM CST Fri Nov 21 2014

(Tonight through Sunday)

Rain chances should be on the increase as we head into the weekend
as moisture and dynamics slowly intensify over the region.   Having
a hard time pinning down too many specifics in PoP trends for
tonight and Saturday as models indicate weak, broad forcing and lift
along with a gradual but limited increase of moisture, so getting
the impression that a scattered/chance type PoP is the best way to
go for tonight, with model consensus indicating a slightly better
chance of rain over southern sections of the CWA by Saturday.  It`s
not totally out of the question that there could be a threat of some
freezing rain for a very brief period of time early this evening in
our far northern/northeast counties if precip becomes intense
enough to generate some evaporative cooling, but based on
conservative hourly temp trends believe any period of temps aob
32 would be quite brief.  Obviously, we will keep an eye on precip
and temp trends during the afternoon.

Certainly, greatest rain chances will be late Saturday night and
especially on Sunday, when main upper level system and associated
dynamics swing into the area from the southern Plains.  While
moisture increase may be a struggle tonight and into Saturday, by
early Sunday ams should be quite moist, with forecast soundings
indicating lower troposphere nearly saturated aob 500mb.  Because of
this moisture and strog lift have gone with categorical PoPs over
the entire area for Sunday.   Have also maintained mention of
thunder similar to what`s in going forecast, and although models are
suggesting some CAPE on Saturday and Saturday night in the elevated
warm advection regime, believe primary thunder threat will be
associated with the main system on Sunday.

Based on aforementioned lift and moisture this system should be a
decent rain producer across the region; widespread rains of 1 to 1.5
inches can be expected in the late Saturday night-Sunday time frame,
with isolated higher amounts certainly possible.

Another round of precip, albeit lighter, is expected on Sunday
night. Although main shortwave is forecast to push east of the
Mississippi River by early Sunday evening, there is good agreement
in the 00z models that strong shortwave digging into the central
CONUS in the wake of the first system will generate a band of
mid-level frontogenetical forcing that will produce a secondary area
of precip from sw MO into s IL.  Although this secondary band of
precip will be falling into a colder ams, at this time it appears
that temps will remain warm enough that it will remain liquid.
However, if precip where to become intense enough a drop in the
freezing level could make ptypes a bit more problematic in some
areas.

(Monday-Thursday)

Secondary area of precip should wind down from west to east on
Monday, but 00z medium range models are in fairly good agreement
that another fast moving shortwave will drop into the deepening long
wave trof over the central CONUS by Wendesday, resulting in a slight
chance of light snow over northern sections of the CWA.

Solutions diverge considerably by Thanksgiving, with ECMWF
indicating a deeper longwave trof over the Ohio Valley and a deeper
intrusion of cold air into our area, while GFS hints at a less
amplified upper air pattern which keeps the baroclinicity...and
potential overrunning precip threat...over our area.  For now have
maintained extended initialization guidance, which indicates some
low PoPs during this time.

Truett
&&

.AVIATION:  (For the 12z TAFs through 12z Saturday Morning)
Issued at 603 AM CST Fri Nov 21 2014

Ahead of next weather system, winds have become easterly and will
veer to the southeast as a weak warm front lifts northward through
region today. SC deck continues to develop and slide north towards
taf sites. Low end VFR/high end MVFR cigs to move into KCOU by 18z,
then into metro area by 20z and KUIN by 22z. As for precipitation
chances, a lot of dry air to overcome so coverage will be
scattered through this evening. Probably a bit of a break in
activity late this evening through the overnight hours.

Specifics for KSTL:
Ahead of next weather system, winds have become easterly and will
veer to the southeast as a weak warm front lifts northward through
region today. SC deck continues to develop and slide north towards
taf sites. Low end VFR/high end MVFR cigs to move into metro area
by 20z. As for precipitation chances, a lot of dry air to
overcome so coverage will be scattered between 00z and 05z Saturday.
Probably a bit of a break in activity late this evening through
the overnight hours with more rain moving in by 14z Saturday.

Byrd
&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$
WFO LSX





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.