Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 110442
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1142 PM CDT Thu Apr 10 2014
Issued at 743 PM CDT Thu Apr 10 2014
Updated POPs to pull higher POPs further nwd thru this evening
mainly across the ern half of the CWA based on latest mdl guidance
and RADAR trends. Latest RAP/local WRF, and to a lesser extent the
HRRR, suggest main focus of precip will be the 850mb fnt
stretching from just n of KSET to K3LF region. Believe the sfc fnt
will remain capped enuf thru at least the next few hours to
prevent more than CU from forming. However, these mdls do suggest
the fnt may become more active after Midnight tonight. By that
time, the fnt shud be s of the CWA.
Have kept POPs in the chance cat, albeit the high end, as precip
is falling out of a 10 to 12 kft ceiling. Have also reduced TS
coverage to isod as generally less than 500 J/kg of MUCAPE exist
across the region. Will continue to monitor trends thru the
evening and update as the situation changes.
.SHORT TERM: (Through Late Tonight)
Issued at 334 PM CDT Thu Apr 10 2014
Cold front that is currently near a Springfield, IL to St. Louis to
Jefferson City line will continue to move southeast this evening.
The models show this front slowing down over the southern CWA
tonight. The RAP does show an increase in low level moisture
moisture convergence along and ahead of the front the next few hours
at the same time that the HRRR depicts scattered showers and
thunderstorms developing over the southern half of the CWA. Have
maintained chance pops for tonight. MOS lows tonight are in good
agreement and generally followed.
.LONG TERM: (Friday through Next Thursday)
Issued at 334 PM CDT Thu Apr 10 2014
(Friday - Saturday night)
Cold front is expected to be just south of CWA early Friday morning and
will become quasi-stationary by afternoon. Chance PoPs will be confined to
along/just north of aformentioned boundary for Friday. Temperatures will be
cooler on Friday by about 10 degrees for most locations behind the cold front.
Quasi-stationary front is expected to lift back north as a warm front Friday
night as lee-side cyclogenesis commences and mid/upper-level heights rise.
Expect Saturday to be mainly dry and kept dry forecast going as very strong
cap is forecast to exist according to NWP model soundings. In addition...
large-scale forcing for ascent looks fairly weak across the area indicating
cap will likely hold.
Unseasonably warm conditions are expected on Saturday night ahead of
approaching cold front. Went a couple of degrees above guidance as
CWA will remain in warm sector with increasing clouds and south winds
around 10 knots.
(Sunday - Sunday night)
An unsettled and wet period is forecast for Sunday/Sunday night as cold front
moves across the area. Negatively tilted shortwave trough will eject toward
the mid-Mississippi Valley late Sunday/Sunday evening with widespread showers
and thunderstorms expected with cold frontal passage. Could also be some
strong thunderstorms through Sunday evening with ~30kts 0-6km shear and
modest instability though higher severe weather threat should exist over
the lower Mississippi Valley where much greater instability will reside.
Temperatures on Sunday look to be quite difficult as degree of cloudiness
and frontal passage timing are a bit uncertain. Leaned warmer than guidance
a couple of degrees for now based on current projections of fropa as most
of CWA would be ahead of front through early afternoon at least.
(Monday - Thursday)
Light rain may linger across portions of the area on Monday as secondary
shortwave trough moves southeastward. Temperatures with clouds and rain
chances along with strong CAA at low levels will yield a cold and raw
early/mid April day. Forecast highs in the upper 40s north to mid 50s far south
still look on track.
Two cold nights with near freezing low temperatures appear possible Monday
night as well as Tuesday night...especially for northern areas. If lows
do dip into the upper 20s...frost/freeze headlines may become necessary
as vegetation begins to grow/bloom...especially over the southern CWA.
Remainder of extended looks dry with slowly moderating temperatures to
near normal by Thursday.
.AVIATION: (For the 06z TAFs through 06z Friday Night)
Issued at 1141 PM CDT Thu Apr 10 2014
VFR conditions will prevail at the TAF sites thru the valid
period. Last gasp SHRA to the east of the STL Metro area are
expected to again get close but will overall struggle to build
much into that area. May still throw in VCSH for STL and CPS for a
brief period at the beginning of the period. Front should then be
too far to the south to have any impact on Friday. Otherwise,
look for gradually veering light winds from the E by late tonight
becoming variable as a ridge of hi pressure builds in and finally
from the SE to S Friday night as the ridge pulls away.
Specifics for KSTL: VFR conditions will prevail thru the period.
May place a brief VCSH for last-gasp SHRA that are to the east of
STL Metro. Cold front should then be too far south on Friday to
have any impact. Otherwise, look for winds to slowly veer from
the E by Friday morning becoming variable with a ridge of high
pressure building in and finally from the SE Friday night with
departure of the ridge. May see the northern edge of some lower
cloud reach the terminal late Friday night. Current indications
are that the bases will be straddling MVFR-VFR categories and may
not have much of a chance to establish itself before sunrise.