Area Forecast Discussion
Issued by NWS St. Louis, MO

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007
FXUS63 KLSX 071058
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
458 AM CST SUN FEB 7 2016

.SHORT TERM: (Through late this afternoon)
Issued at 320 AM CST Sun Feb 7 2016

Enjoy today if you like mild temperatures. It will be the last one
like it for at least a week. Big changes on the way over the next
24-36 hours and a return of winter cold in response to tremendous
large scale amplification of the upper air pattern. Two short wave
trofs of interest early this morning, one moving through the upper
MS Valley and another moving out of Saskatchewan into the northern
Plains. The lead wave will weaken and shift eastward into the
Great Lakes this morning while the trailing wave will deepen and
dig rapidly southeastward thanks to an attendant 125+ kt ULJ. This
wave will reach the Mid MS Valley by 00Z, and will drive a front
through the CWA beginning after 15z. Veering southwest-west winds
ahead of the front, continued low level WAA, and relatively mild
early morning temps should allow most locations to climb into the
50s before the fall begins during the later afternoon. There is
still some question as to whether we will see any precipitation
today along/ahead of the front. Large height falls/increasing
large scale ascent and moisture during the afternoon associated
with the upper system may be sufficient to generate spotty showers
across east central/southeast MO into southwest IL in the 21-03z
time frame.

Glass

.LONG TERM: (Tonight through Saturday)
Issued at 320 AM CST Sun Feb 7 2016

A secondary cold surge/front, denoted by increasing and gusty
northwest winds and trofing the cyclonic surface flow, will enter
the area later in the evening bringing strong CAA and much colder
temperatures, and some snow. Monday will be a Winnie The Pooh type
day with cold, blustry conditions. The coverage of snow is the
biggest question mark. Model QPFs are rather light through 00z
Tuesday, and numerous CAMs showed narrow cyclonically curved bands
overnight Sunday into Monday. Model soundings indeed show favorable
shear and stability profiles for horizontal convective rolls in
the lowest 10 kft. This would suggest some spots could get no more
than a light dusting while others might see snow accumulations of
up to an inch.

Below average temperatures and cold will dominate Tuesday and
Wednesday as a deep expansive upper trof dominates the eastern
2/3rds of the Nation. During the later part of the week and into
the weekend, heights aloft rise as the amplitude of the trof
diminishes and becomes more broad, with flow aloft backing from
NNW to WNW. This would suggest at least some moderation of
temperatures, however maybe not as much as the GFS and MEX MOS
might suggest. The ECMWF is much colder with sharper cyclonic
curvature to the flow aloft, allowing another cold surge on Friday
that lasts into the weekend.

Glass

&&

.AVIATION:  (For the 12z TAFs through 12z Monday Morning)
Issued at 434 AM CST Sun Feb 7 2016

Strong low pressure system will move into the Great Lakes region
and control the weather throuh the period. Cold front moving into
northwest MO will race across the state today with the southwest
wind shifting to west northwest with gusts in the 20 - 25 kt
range. Continued cyclonic flow in the upper atmosphere will
produce some bands of light snow late in the period. Nothing
widespread expected and impossible to pin down so no visibility
restrictions will be entered at this time. Cloud cover looks to
stay VFR today, with some marginal bands moving into northeast MO
by 03z.

Specifics for KSTL: Cold front should arrive around Noon with
winds going west and gusting aroud 20 knots. Not much expected
until the colder air really begins surging into the area tonight.
A period of marginal ceilings would be most likely after 06z. Some
light snow will likley be in the air but nothing consistent.

JPK

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX



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