AFOS product AFDLSX
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Displaying AFOS PIL: AFDLSX
Product Timestamp: 2019-11-26 05:31 UTC

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193 
FXUS63 KLSX 260531
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
1131 PM CST Mon Nov 25 2019

.UPDATE...
Issued at 1051 PM CST Mon Nov 25 2019

Raised overnight lows by a few degrees due to increasing cloud
cover and winds becoming southeast to south as stalled frontal
boundary lifts northward. Still expect scattered showers will 
develop and track to the north as this front lifts northward 
through the day on Tuesday. Best chances of rain will be north of
the I-70 corridor. 00z model runs as well as latest
HRRR/experimental HRRR develop a north/south line of storms 
during the evening hours over central MO and track east between
00z and 06z Wednesday, so raised pops to categorical a bit 
further west during this period.

Byrd
&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 217 PM CST Mon Nov 25 2019

Increasing cloudiness can be expected later tonight with spotty 
light rain possible late tonight/early Tuesday morning, mainly 
across southeast MO and southwest IL as low-mid level warm air 
advection increases over our area well ahead of a developing low 
pressure system in the Lee of the Rockies. The coverage of showers
will increase on Tuesday as the upper level trough moving into 
the northern Plains takes on a more negative tilt with increasing 
upper level divergence over our area. With the surface low 
tracking northeastward through northwestern MO and eastern IA 
Tuesday evening our forecast area will be in the warm sector of the
storm system with any wintry precipitation remaining north and 
northwest of our forecast area. Deep layer wind shear will 
increase Tuesday night as a 100 kt plus mid level speed max moves 
through the region south-southeast of the upper level low. It 
appears that there will be enough low level moisture and 
instability for the development of not only thunderstorms, but 
possibly also severe storms as well mainly Tuesday evening. Some 
of the CAMS develop low-topped supercells across southwest MO, 
ahead of the approaching cold front extending south of the surface
low, which congeal into a line of storms which race eastward 
through our area Tuesday evening. The primary threat will be 
damaging winds, but isolated tornadoes can not be ruled out. The 
showers and storms should shift east of our forecast area by early
Wednesday morning. Very strong and gusty winds can be expected 
particularly late Tuesday night and Wednesday morning after the 
passage of the cold front due to a tight surface pressure gradient
south of the deepening surface low. A wind advisory may be needed
for much of the area Tuesday night and Wednesday. 

GKS

.LONG TERM...  (Wednesday through Next Monday)
Issued at 217 PM CST Mon Nov 25 2019

Colder, but dry conditions can be expected Wednesday and 
Wednesday night as a surface ridge shifts eastward through the 
region, while an upper level ridge builds over the central US. 
Precipitation will spread eastward into much of our area on 
Thanksgiving due to increasing low-mid level warm air advection, 
and as a southwesterly low level jet brings increasing low level 
moisture into our area. Very dry air initially in the 
surface/boundary layer will slow the onset of the precipitation, 
while evaporative cooling may result in a brief period of snow or 
sleet Thursday morning, but the precipitation type should change 
over to liquid rain Thursday afternoon. Prefer the operational GFS
and ECMWF model solutions which have consistently had the higher 
QPF over southern portions of MO and IL over the NAM which has the
better QPF further north which would lead to a greater potential 
of wintry precipitation. The precipitation will become lighter and
may shift south of our forecast area Thursday night, but will 
ramp up again on Friday as another storm system develops and moves
eastward into the Plains. The track of the surface and upper 
level low is even further northwest than the Tuesday/Tuesday night
low pressure system so precipitation type should be liquid rain 
for our area. The dry slot south of the upper level low will shift
northeastward into our area on Saturday with most of the rain 
shifting east of our forecast area by Saturday night. Colder 
conditions can be expected Saturday night and Sunday after passage
of the cold front, and with a deep upper level low just north-
northeast of our area. Some of the model guidance hints at the 
possibility of light snow, mainly for northeast MO and west 
central IL late Saturday night and Sunday on the backside of the 
low pressure system.

GKS
&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1051 PM CST Mon Nov 25 2019

A stalled frontal boundary remains over the St. Louis metro area 
as of 05z Tuesday. Increasing low level moisture and weak WAA 
will be a bit slower moving in than thought, so the ceilings 
will not lower to MVFR/IFR til mid morning on Tuesday. Otherwise,
deepening surface low in the leeside of the Rockies will begin to
lift northeastward by midday Tuesday, lifting stalled frontal 
boundary back to the north as a warm front. Best chances of 
showers and storms will be north of warm front especially over 
KUIN Tuesday afternoon. Then as main system approaches region,
will see a line of convection develop and slide east across region
between 00z and 06z Wednesday. As for winds, they will veer back 
to the south and increase once front slides northward. Winds will
be sustained between 15 and 20 kts with gusts as high as 30 kts.

SPECIFICS FOR KSTL: 
A stalled frontal boundary remains over the St. Louis metro area
as of 05z Tuesday. Increasing low level moisture and weak WAA will
be a bit slower moving in than thought, so the ceilings will not
lower to MVFR/IFR til 14z Tuesday. Otherwise, deepening surface
low in the leeside of the Rockies will begin to lift northeastward
by 18z Tuesday, lifting stalled frontal boundary back to the north
as a warm front. Best chances of showers and storms will be north
of St. Louis metro area Tuesday afternoon, so just kept vicinity
thunderstorm mention for this period. Then as main system
approaches region, will see a line of convection develop and slide
into metro area after 02z Wednesday. As for winds, they will veer
back to the southeast to south and increase once front slides
northward. Tuesday afternoon/evening, winds will be sustained 
between 15 and 20 kts with gusts as high as 30 kts.

Byrd
&&

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

$$
WFO LSX