Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 130545
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1145 PM CST Sun Feb 12 2017

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 315 PM CST Sun Feb 12 2017

A strong and gusty north-northwest surface wind continued this
afternoon due to the tight surface pressure gradient between a
strong surface high centered over Nebraska and Kansas and a surface
low moving into the Mid-Atlantic region, and also daytime heating
and mixing.  These strong winds coupled with low relative humidity
values were leading to an elevated fire danger across much of MO
this afternoon.  These winds will diminish this evening as the
surface high center moves southeastward into western MO. Colder
conditions are expected tonight due to good radiational cooling with
only some high level clouds, a surface wind becoming light by late
tonight, and surface dew points only in the upper teens to lower 20s
across most of the area.  Lows tonight will be just a couple of
degrees above normal which will feel cold compared to the recent
unseasonably warm temperatures.  Dry conditions will continue on
Monday with surface ridging across the area.  Highs on Monday will
be about 10 degrees above normal with increasing mid-high level
cloudiness ahead of an approaching shortwave.

GKS

.LONG TERM...  (Monday Night through Next Sunday)
Issued at 315 PM CST Sun Feb 12 2017

The synoptic pattern at the start of the long term period will
feature a split flow regime with one trough within the active
northern stream across the Northeast, and another trough embedded
within the southern stream digging into portions of the Southwest
and northern Mexico.  Given this upper-level flow regime, systems
will tend to pass by to the north and to the south of the region,
leading to a mainly dry period.

The trough across the Desert Southwest will meander into portions of
TX/OK by Tuesday morning.  As it does, some mid-level moisture will
be advected northward into portions of central and eastern MO.  This
moisture will become co-located with confluent flow in the mid-
levels, which will help induce a weak area of mid-level
frontogenesis from Kansas into portions of central Missouri.
However, the low-levels will continue to remain very dry beneath
this frontogenetical circulation, so it will be a case where much
(if not all) of the precipitation will not reach the ground.  Given
some signals in guidance for measurable QPF and in an effort to
maintain a consistent forecast, will continue with a very slim
chance of rain Monday night across central MO. Anything that is able
to fall would be very light and will do nothing to help our
abnormally dry conditions.

A strong PV anomaly diving into the Great Lakes will help shunt the
bulk of the southern stream system south of the area Tuesday into
Wednesday.  However, surface winds will turn northerly on Wednesday
as a cold front moves through and a trough is carved out across the
Great Lakes/Northeast region.  After highs in the mid 50s on
Tuesday, they will dip into the low to mid 40s on Wednesday.

By the end of the week into the upcoming weekend, an upper-level
ridge will slide into the central CONUS.  This will allow for yet
another period of very mild weather.  Given the tendency for
temperatures to overachieve the past few days, coupled with another
5-6 days of drying soils, think guidance is likely too low for
temperatures Thursday-Saturday given the expected southwesterly
flow.  Therefore, have nudged temperatures up above guidance during
this period, with readings expected to top out in the mid/upper 60s
Friday into the upcoming weekend.

KD

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1139 PM CST Sun Feb 12 2017

VFR flight conditions will prevail through the forecast period
with increasing high clouds overnight into Monday morning,
followed by thickening mid clouds from late afternoon into Monday
evening. There could be some light rain on Monday night along and
south of a line from KCOU-KSTL, however probabilities are too low
to mention at this time. Surface winds will be light overnight as
high pressure settles into central MO, and then will become south
to southwesterly on Monday as the surface high retreats.

SPECIFICS FOR KSTL:

VFR flight conditions are expected though the forecast period with
increasing high clouds Monday and increasing mid clouds Monday
night. There could be some light rain on Monday night, however
probabilities are too low to mention at this time.

Glass

&&

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

$$

WFO LSX



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