Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 122115
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
315 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 18z TAFs through 18z Monday Afternoon)
Issued at 1050 AM CST Sun Feb 12 2017

A surface high centered over western Nebraska will continue to
build into MO this afternoon. Relatively strong and gusty north-
northwesterly surface winds can be expected this afternoon due to
the tight surface pressure gradient between the strong Plains
ridge and a surface low in the OH Valley region. The surface wind
will diminish tonight as the surface high center moves into MO.
Only high level clouds are expected this afternoon and tonight.
Some mid level cloudiness will likely move into our area Monday
morning ahead of an approaching upper level disturbance.

SPECIFICS FOR KSTL: A surface high centered over western Nebraska
will continue to build into MO this afternoon. Relatively strong
and gusty north-northwesterly surface winds can be expected this
afternoon due to the tight surface pressure gradient between the
strong Plains ridge and a surface low in the OH Valley region. The
surface wind will diminish tonight as the surface high center
moves into MO. Only high level clouds are expected this afternoon
and tonight. Some mid level cloudiness will likely move into our
area Monday ahead of an approaching upper level disturbance. The
surface wind will back around to a southwest direction Monday
afternoon, albeit still weak.

GKS

&&

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

$$

WFO LSX



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