Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 220925
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
325 AM CST Sat Nov 22 2014
.SHORT TERM: (Through Late This Afternoon)
Issued at 322 AM CST Sat Nov 22 2014
Main area of precipitation has moved out of region, though there is
some widely scattered activity as well as drizzle over northern
portions of forecast area early this morning. Next shortwave to
slide northeast through forecast area today, but precipitation will
continue to be scattered in nature. Some elevated instability over
southern portions of region this afternoon, so still could see
isolated thunder in this area. Otherwise, just scattered showers
under cloudy skies. Temperatures to be near normal or just above
normal in the mid 50s to low 60s.
.LONG TERM: (Tonight through Friday)
Issued at 322 AM CST Sat Nov 22 2014
Overall foreast trends still looking pretty good, and main changes
will be an attempt to fine-tune these trends.
This afternoon`s expected scattered coverage will likely linger into
this evening, but precipitation threat should ramp up considerably
late tonight and into Sunday as dynamics from strong upper system
working northeast from the southern plains and increasing moisture
begin to come into phase over the region. Like the trends suggested
by 00z model QPFs that by Sunday morning main focus of rain will
stretch from southwest into northeast Missouri, with this band of
rain then expanding and working east during the day. With the above
trends in mind, I`ve also attempted to minimize PoPs in our far e
counties until Sunday afternoon, as moisture and lift will be
somewhat limited in this part of the FA until then. Although
instability is progged by all models to remain quite limited due to
saturated AMS I`ve continued a mention of thunder over the Ozarks
tonight and into the southeast half of the CWA on Sunday.
All of the 00z output is continuing to suggest that as dynamics with
the first system pushes into the Ohio Valley on Sunday evening, a
secondary area of precip should develop in its wake as another
shortwave drops into the base of the longwave trof. Ptypes could
become an issue by late Sunday night on the back edge of this round
of precip as southward surge of cold air will be causing the
freezing levels to drop; however at this time not expecting any
major issues as forecast soundings suggest ams will get cold enough
to support snow just as the precip begins to wind down. Threat of
measurable precip with this secondary shortwave should come to an
end on Monday morning, although we do anticipate that some flurries
will linger into the afternoon over northern sections of the CWA
where cold advection and cyclonic low level flow will be the
Today`s moderation in temps will persist into Sunday, but return
of cold air will mean more below average temperatures for the
start of the new week.
Surface ridge is expected to work across the region on Tuesday,
giving the FA chilly but dry late November weather. It still
appears that another fast moving shortwave digging into
progressive longwave trof will produce a quick shot of lift across
the region by Wednesday, but strongest dynamics will be north of
our area and moisture will be quite limited, so going slight
chance/low chance PoPs still look good at midweek.
Medium range solutions still leaving questions regarding sensible
weather trends heading into the Thanksgiving holiday. GFS is now
supported by the GEM in suggesting much less deepening of the
longwave trof over the eastern CONUS. This keeps baroclinicity
further north and allows the next fast moving shortwave to interact
with this thermal gradient, which would suggest a threat of some
light precip on Thanksgiving over northern sections of the CWA.
ECMWF is still deeper with the trof to our east, but its interesting
that its not as deep as was suggested in yesterday`s guidance, and
in fact has trended a bit more towards a flatter mid level flow.
For now will maintain dry forecast, but this trend will be
interesting to watch over the next few forecast cycles.
With the reintensification of the trof over the eastern CONUS temps
will remain well below normal during the latter half of the
upcoming work week, although exact extent of the cold will
obviously depend on the intensity of the trof. Highs primarily in
the 30s heading into Thursday and Friday look like a good starting
point for now.
.AVIATION: (For the 06z TAFs through 06z Saturday Night)
Issued at 1134 PM CST Fri Nov 21 2014
MVFR conditions are expected to prevail overnight and for most of
tomorrow. Some improvement is possible at KCOU between 22/21z and
23/06z before conditions deteriorate again. Light drizzle is
possible overnight. Widespread rain is likely just beyond the end
of the 24-hr TAF period.
Specifics for KSTL: Although conditions may occasionally lift to
VFR for brief periods overnight, MVFR cigs are expected to prevail
until mid to late morning. Light drizzle is also possible.
Widespread rain is likely towards the end of the 30-hr TAF period