Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 150947
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
347 AM CST Fri Dec 15 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 334 AM CST Fri Dec 15 2017

A weak shortwave trough is moving southeast across Missouri and
Illinois early this morning.  Regional radars are showing some weak
returns over southern Iowa early this morning which may be enough
for scattered flurries across parts of northeast Missouri and west
central Illinois through mid morning.  Thereafter, drier air will
move into the area bringing a mostly dry day.  Skies will be mainly
cloudy in the morning, but should turn partly cloudy during the
afternoon.

With the return of some sun today, temperatures will climb to near
normal for highs.  This supported by MOS and SREF mean temps.  Lows
tonight only fall off into the 30s as winds back out of the
southwest and increase overnight.

Britt

.LONG TERM...  (Saturday through Thursday)
Issued at 334 AM CST Fri Dec 15 2017

The large scale pattern is forecast to become more active and
undergo several major pattern shifts over the next 7 days. The first
of these will be well underway on Saturday with heights rising aloft
and ridging developing as a mean trof deepens in the western
U.S.. This trof will feature several prominent short waves: one
weakening as it ejects northeast from northern Mexico into west TX
and the upstream kicker digging into the Great Basin. The combination
of the ridging aloft, a pronounced low level WAA regime featuring
veering southwest to west flow, and abundant sunshine will lead
to another unseasonably mild day on Saturday with highs around 20
degrees above normal.

We should see our next decent chance of rainfall Saturday night
into Sunday. The aforementioned west TX short wave will continue
to weaken as it ejects northeast across the southern/central
Plains on Saturday night and through the Mid MS Valley on Sunday.
Height falls and weak large scale ascent spread into southern and
southwest sections of the CWA during the overnight hours,
overspreading the remainder of the area on Sunday morning.
Moisture won`t be overwhelming and initially will be largely
focused in the mid-upper levels. This looks like a high
probability/low QPF event.

The ECMWF and GFS then begin to diverge Monday/Monday Night on the
southern stream of a split flow regime present at that time. The GFS
has a lead, weakening short wave ejecting across the area Monday
afternoon/evening and accompanying chance of rain, followed by a
well-defined cold frontal passage. Alternatively the ECMWF is dry
with a weak WAA regime, with an ejecting short wave and cold
fropa about 24 hours later. Despite the difference in fropa
timing, neither have exceptionally cold air and temperatures
generally remain above normal Wednesday as the post-frontal high
pressure system begins to retreat. The next progressive and
deepening upper trof will then move from the western U.S. into the
Plains region on Thursday driving a rather strong cold front into
the MS Valley during the day. While this is quite far off in the
forecast, the front looks to remain to the west during the
daylight hours with another day of mild temperatures, followed by
strong CAA on Thursday night and markedly colder weather on
Friday.

Glass

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1130 PM CST Thu Dec 14 2017

VFR conditions throughout the TAF period for all sites. All sites
will remain dry for the period with the exception of UIN. Slight
chance for light snow showers/flurries just before sunrise at
UIN. I think that the snow will occur but not a measurable amount
and will not affect visibilities. Winds will shift from the
northwest to the west overnight before turning southwest in the
early afternoon Friday. Gust of 15-20 kts are expected in the
afternoon tomorrow.

SPECIFICS FOR KSTL:

Dry VFR for the entire forecast period. There are some patches of
MVFR around the STL metro but should be moving out of the area by
TAF valid period, so they were kept out of this forecast. Winds
will back from the northwest overnight to a gusty west wind in the
late morning Friday. Gusts of 15-20 kts are possible. Winds will
decrease and turn to the southwest Friday evening.

Walsh

&&

.FIRE WEATHER...
Issued at 334 AM CST Fri Dec 15 2017

Unseasonably mild temperatures on Saturday combined with a dry air
mass will result in low afternoon relatively humidity with
minimum values of 20 to 30 percent. These low RH values, along
with southwest winds of 10 to 15 mph, and dry fuels will promote
heightened fire danger across central and eastern Missouri and
portions of western Illinois on Saturday afternoon.

Glass

&&

.CLIMATE...
Issued at 334 AM CST Fri Dec 15 2017

Record high temperatures for Saturday December 16, 2017

St. Louis  70 in 1889
Columbia   70 in 1889
Quincy     65 in 2006

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     43  34  62  39 /   0   0   0   5
Quincy          41  31  57  35 /  10   0   0   0
Columbia        42  33  61  38 /   0   0   0  20
Jefferson City  44  32  63  38 /   0   0   0  30
Salem           41  29  56  37 /   0   0   0   5
Farmington      44  29  59  38 /   0   0   0  30

&&

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

$$

WFO LSX



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