Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 190907
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
307 AM CST Wed Nov 19 2014

.SHORT TERM:  (Through Late This Afternoon)
Issued at 306 AM CST Wed Nov 19 2014

A deep upper level TROF continues to dominate eastern North America,
with resultant NW flow aloft for our region.  A pair of disturbances
of note exist within this flow.  The first was over southeast MN and
is helping to generate an area of snow for parts of the upper MS
valley.  Another disturbance was rather well sheared and stretched
from the mid-MO valley and back into the northern High Plains and
was not associated with any pcpn but did correlate well with clouds.
At the surface, a warm front was nosing into central MO and
resulting in rising temps into the lo 40s, with readings remaining
in the 20s for most areas to the east of it.  Much further to the
northwest, another cold front was entering northwest IA and was
surging southeastward.  The latest satellite loop shows a lot of mid
level cloud over our region from the approaching warm front, with a
more significant area of low clouds further to the NW near the cold
front.  Our region was pcpn-free.

The warm front is expected to push into STL metro by 12z and then
thru the rest of the forecast area by 15z providing a brief temp
surge upward before the cold front arrives a few hours later.  The
cold front is also expected to be accompanied by a push of low
clouds as well.  This will mean morning max temps for most locations
with steady to slowly falling temps during the afternoon with
decently strong CAA behind the front.  Prefer colder MET MOS for the
northern forecast area, such as UIN, due to doubts on warm air surge
reaching there in the first place, and COU where warm air be snuffed
out early.  Prefer the warmer MAV MOS for around STL metro and
further S and E where warm air surge will at least make it into to
have an impact on max temps in the first place.

Low amounts of moisture, only weak cyclonic flow, and lack of upper
level support with only real disturbance rolling thru will be
heavily sheared should result in a dry day with even flurries
struggling to appear.

Despite the very cold start this morning, daytime max temps should
be warmer than persistence for the MO side of the river thanks to
decent levels of sunshine and surface flow becoming more W-SW,
promoting deeper mixing layers and strongly favoring the higher MAV
MOS.  Where the clouds are more numerous in IL, persistence a good
forecast guess where MOS blend preferred.

TES

.LONG TERM:  (Tonight through Tuesday)
Issued at 306 AM CST Wed Nov 19 2014

(Tonight through Friday)

Not many changes from the prev forecast thru this period. Main
change has been mdl solns slowing the retreating sfc ridge on Thurs
night into Fri and also slowing the onset of precip.

Trended twd cooler guidance tonight due to fropa today. Since most,
if not all, of the snow cover shud melt today, have trended twd the
warmer guidance beyond except as mentioned below.

Mdls are in very good agreement wrt mass fields thru this period.
Timing of the leading s/w that may bring the first round of precip
to the region late Thurs night. However, as mentioned yesterday,
this system is still off the wrn U.S. coast and still will not be
well sampled by 12z this morning.

One area where mdl solns begin to greatly differ is the thermal
profile, esp within the boundary layer. For now, have trended temps
twd the GFS soln with the ECMWF as a warmer soln and the NAM/local
WRF as a colder soln. Based on fcst soundings, it appears that at
least some of the QPF the mdls suggest is due to low level moisture
return and not actual precip. Precip for Fri night and beyond
appears to be associated with the leading s/w and is supported well
by low level forcing. Still, this portion of the event is expected
to be low precip.

With the colder solns, precip may begin as IP, then gradually
transition to FZRA as the wrmfnt arrives. However, with trending
twd the GFS soln, have kept p-type as all FZRA for now.

(Saturday through Tuesday)

Not much change from yesterday. 19/00z guidance has come into better
agreement and therefore increased PoPs for Sat thru Sun. Continued
warm trend thru the weekend then gradually cooling beginning next
week. With an upper trof returning by Mon, continued cooler trend
thru the rest of the forecast.


Tilly

&&

.AVIATION:  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1126 PM CST Tue Nov 18 2014

Mid-level cloudiness is increasing across the area ahead of
approaching cold front. Low-level wind shear still a good bet for
KCOU and metro TAF sites per 0000 UTC RAOBS and latest NWP
guidance and fine-tuned timing a bit. Regarding fropa timing...still
appears mid/late morning. Winds will shift to the northwest
immediately behind the front and become gusty in the 20-25 kt
range. Ceilings will also lower to MVFR at KUIN...and low end VFR
for metro TAF sites. Winds will lighten substantially by late
tomorrow afternoon as pressure gradient relaxes. Skies are also
forecast to at least scatter out by Wednesday evening.


Specifics for KSTL:

Mid-level cloudiness is increasing across the area ahead of
approaching cold front. Low-level wind shear still a good bet per
0000 UTC RAOBS and latest NWP guidance for 3-5 hours late tonight.
Regarding fropa timing...still appears around 1700 UTC. Winds will
shift to the northwest immediately behind the front and become
gusty in the 20-25 kt range. Ceilings will also lower to low end
VFR and cannot rule out a brief period of MVFR. Winds will
lighten substantially by late tomorrow afternoon as pressure
gradient relaxes accompanied by decreasing sky cover.

Gosselin

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     38  21  36  22 /   5   0   0   5
Quincy          30  16  30  15 /   5   0   0   0
Columbia        36  17  37  22 /   5   0   0   5
Jefferson City  37  17  39  22 /   5   0   0   5
Salem           38  20  35  19 /   5   0   0   5
Farmington      43  19  40  23 /   5   0   0  10

&&

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

$$

WFO LSX






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