Area Forecast Discussion
Issued by NWS St. Louis, MO

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984
FXUS63 KLSX 042036
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
236 PM CST THU FEB 4 2016

.SHORT TERM:  (Through Late Tonight)
Issued at 219 PM CST Thu Feb 4 2016

The GFS and ECMWF are in good agreement that upper trough
currently seen on water vapor over the upper Midwest will rotate
eastward across the Great Lakes tonight. As it does it will cause
its attendant cold front currently over the Dakotas and Minnesota
to dive southeastward across Missouri and Illinois late tonight.
Still do not expect any precipitation with the passage of this
front as the low-mid level moisture is very limited. Temperatures
tonight will easily fall back down to MOS temp guidance with
clear skies and cold air advection behind the cold front.

Britt

.LONG TERM:  (Friday through Next Thursday)
Issued at 219 PM CST Thu Feb 4 2016

Shortwave ridging aloft combined with a surface high pressure
center passing through the ARKLATEX region will ensure quiet wx
conditions across the CWA on Fri. A couple of upstream shortwaves
will move across the central and southern CONUS on Fri night into
Sat, possibly phasing over the south-central CONUS by 12z Sat
depending on which model solution ultimately has the better
handle on the position of the northern vort max. An overall
increase in cloudiness is expected ahead of these features, and a
few locations might see sprinkles or flurries on Fri night or Sat
morning.

A warming trend will continue across the area through Sunday with
highs on Sunday reaching the upper 40s to mid-50s. Thereafter, a
significant change in the upper air pattn will usher in a period
of much colder temperatures for at least the early and middle
part of next week due to periodic intrusions of Arctic air
masses. Overnight lows in the teens and 20s are expected on
Monday night and Tuesday night.

A vigorous shortwave is forecast to move onshore near WA/OR
around 06z Sat. RAOB sampling may not occur until 12z Sat. After
this feature crosses the Rockies, it then dives southeastward
into the plains and western Great Lakes. Meanwhile, an amplifying
ridge over the west coast induces a downstream trough over the
eastern half of the CONUS, which is then reinforced by the
aforementioned shortwave as well as several additional shortwaves
diving southward out of Canada during the early part of next week.
Ultimately, a large closed low should settle somewhere over the
Great Lakes region and upper Ohio valley for the first half of
next week.

The next opportunity for widespread precipitation will occur
from Sunday night through Monday night with the initial approach
of the aforementioned vigorous shortwave. Attm it looks like a
straightforward RA/SN mix (depending on the thermal profile at any
given location) transitioning to light snow due to the increasing
depth of cold air. Decent H7-H5 lapse rates, cyclonic flow, and
synoptic scale lift support the idea of isolated to scattered
instability snow showers on Monday on the back side of the newly
stacked upper low. A similar scenario is anticipated on Tuesday,
although by that time the upper low will have shifted just far
enough eastward to confine precip chances to the easternmost
portion of the CWA.

Kanofsky

&&

.AVIATION:  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1224 PM CST Thu Feb 4 2016

Dry and VFR conditions are expected through the period. A series
of fronts moving through the area will cause some minor wind
shifts at the terminals.

Specifics for KSTL: Dry and VFR conditions are expected through
the TAF period.

Britt

&&

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

$$

WFO LSX



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