Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 140415

1115 PM CDT Sun Apr 13 2014

Issued at 903 PM CDT Sun Apr 13 2014

Two areas of SHRA/TSRA of interest at the moment. The first area
moved thru southeast MO and into STL Metro earlier this evening
and has dropped up to 1.25" of rain in spots with many areas
receiving between 0.3 and 0.75" in the main area of effect. No
severe weather is anticipated here with the atmosphere worked over
well and not that unstable. Some elevated instability, though, has
produced imbedded thunder.

The other area is a squall line that had developed over western MO
and eastern KS this afternoon and has progressed steadily
eastward, but has thus far produced wind gusts up to 50mph. Severe
thunderstorm watch #75 continues for a reduced area in east-
central MO until midnight CDT, but anticipate this watch being
cancelled probably around 10-1030pm given current trends and
timing of progression of thunderstorm line.

All of this will exit STL metro during the early overnight and
late tonight in southwest IL. The next round of more stratiform
frontogenetical pcpn is not anticipated until mid-late Monday
morning in central MO, expanding elsewhere later on Monday. It is
with this area of pcpn, and behind an increasingly chilly airmass,
that some snow will be possible, but it remains doubtful on
ability to accumulate considering warm ground and surface temps
above freezing throughout. Nevertheless, the mere presence of
falling snow in mid-April rather unusual in these parts.



.SHORT TERM:  (Through Late Tonight)
Issued at 359 PM CDT Sun Apr 13 2014

(Tonight-Monday Night)

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 06z TAFs through 06z Monday Night)
Issued at 1028 PM CDT Sun Apr 13 2014

Cold front extending from a surface low over northwestern IL
southwest through UIN and COU will move sewd through the St Louis
metro area just after 06z Monday. The more significant showers and
storms will shift east of the taf sites by 06z Monday, but there
may be lingering patchy light rain or isolated light showers til
around 08z Monday. Surface winds will veer around to a nwly
direction after fropa, and will be relatively strong and gusty late
tonight and Monday due to a tight surface pressure gradient. The
wind will gradually diminish Monday night as a surface ridge
approaches and the surface pressure gradient relaxes. Ceilings
will likely fall into the IFR catagory behind this front, down to
around 1000 ft or slightly lower late tonight and early Monday
morning. The cloud ceiling will gradually rise Monday afternoon,
becoming VFR Monday evening. There will be some light rain mainly
Monday afternoon as an upper level disturbance moves through the
area, 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: The cold front will move southeastward through
STL just after 06z Monday. The more significant showers and
storms will shift east of STL by 06z Monday, but there may be
lingering post frontal patchy light rain or isolated light showers
until around 08z Monday. The surface wind will veer around to a
nwly direction late tonight after fropa. The wind will remain
strong and gusty through Monday, then diminish Monday night. The
cloud ceiling will lower into the IFR catagory late tonight and
early Monday morning after fropa. The cloud ceiling will gradually
rise into the MVFR catagory Monday afternoon, VFR Monday evening,
then finally clearing out completely late Monday night. Periods
of light rain can be expected Monday afternoon, possibly changing
to a little light rain/snow mix before ending early Monday evening.





STL - 27 IN 1928
COU - 25 IN 1928
UIN - 24 IN 1928
FAM - 24 IN 1928




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