Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 132242
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
542 PM CDT Sun Apr 13 2014
.SHORT TERM: (Through Late Tonight)
Issued at 359 PM CDT Sun Apr 13 2014
Main question tonight will be severe weather chances. Large area of
stratiform rain currently over the CWA may suppress these chances as
latest SPC objective MUCAPE analysis is mostly below 500 j/kg except
across northern Missouri and west central Illinois. The latest runs
of the HRRR has been trending toward weaker storms these evening
because weaker instability. However, if the rain can mover out of
the area, there are very steep lapse rates over the Central Plains
that could help quickly destabilize the atmosphere ahead of the line
of the storms currently over eastern Kansas. Deep layer shear
between 00-03Z will be between 35-50kts which will be sufficient for
organized severe storms.
Otherwise, forecast did not require too much changes as I still
expect front to march southeast across the CWA tonight.
Thunderstorm threat will end with the front and change to a plain
cold rain. Have kept likely chances to for rain on Monday as the
ECMWF/GFS/NAM all mid-level frontogenesis moving across the region
during the day. Also added likely chances over the eastern counties
on Monday evening as ascent from the mid level trough will not clear
the CWA until overnight Monday night. Forecast soundings and
critical thicknesses still point to snow mixing with the rain from
northwest to southeast during the day on Monday. Do not have any
accumulating snow at the moment as the low atmosphere will be rather
warm during the day, as will the surface temperatures after this
unseasonably warm weekend.
With the much colder air moving into the area, temperatures will
fall below freezing over the entire CWA on Monday night. Many areas
will see temperatures in the mid to upper 20s.
.LONG TERM: (Monday through Next Sunday)
Issued at 359 PM CDT Sun Apr 13 2014
Upper trough will move east of the area by Tuesday bringing dry
weather for mid week. While Monday night looks like the coldest,
Tuesday night will likely still have temperatures around freezing
before lows become more seasonable later in the week.
While the ECMWF has trended deeper and consequently slower with the
trough that will move through the central CONUS late this week, it
is still not as deep as the GFS or the Canadian GEM. Will stick
with the more consistent ECMWF as the GFS is quicker to move the
front through the area on Thursday night than it was before. Will
keep Thursday dry with the front staying to the northwest most of
the day with a chance of showers Thursday night and Friday as the
front moves across the area. By next weekend, winds turn out of the
southwest quickly behind a retreating high allowing gulf moisture to
move north from the Gulf quickly into the area.
.AVIATION: (For the 00z TAFs through 00z Monday Evening)
Issued at 512 PM CDT Sun Apr 13 2014
Cold front extending from a weak surface low over southeast IA
southwest through northwest MO and southeast KS will move sewd
through UIN and COU this evening, and through the St Louis metro
area just after 06z Monday. Scattered showers will continue ahead
of the front early this evening with a line of thunderstorms
along the cold front moving through the taf sites later this evening.
Relatively strong and gusty sly surface winds will veer around to
a nwly direction after fropa and remain strong and gusty late
tonight and Monday due to a tight surface pressure gradient.
Ceilings will likely fall into the IFR catagory behind this front.
There will be some post frontal light rain on Monday, possibly
mixing with or changing to light snow in UIN and COU as colder air
continues to filter sewd into the area.
Specifics for KSTL: Showers and thunderstorms over south central
MO will move northeastward into STL later this evening, while a
line of thunderstorms along the cold front over northwest and west
central MO moves into the STL area by late evening. Strong and
gusty sly winds will veer around to a wly direction late tonight
after fropa and a nwly direction Monday morning. The wind will
remain strong and gusty through Monday, then diminish Monday night
as a surface ridge approaches and the surface pressure gradient
relaxes. The cloud ceiling will lower into the IFR catagory late
tonight after fropa, then rise into the MVFR catagory Monday
afternoon or evening. Periods of light rain can be expected on
Monday, possibly changing to a little light rain/snow mix before
ending Monday evening.
Issued at 330 AM CDT Sun Apr 13 2014
RECORD LOWS FOR 4/15:
STL - 27 IN 1928
COU - 25 IN 1928
UIN - 24 IN 1928
FAM - 24 IN 1928