Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 080541
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1141 PM CST SUN FEB 7 2016

.UPDATE:
Issued at 936 PM CST Sun Feb 7 2016

Isolated-scattered very light rain showers and sprinkles have
affected portions of the area this evening. Looking
upstream...radar imagery shows streaks of snow across the mid-
Missouri Valley. This activity is expected to move south and east
into our region overnight tonight. Some uptick in the intensity
still seems probable with some of the snow showers briefly
reducing visibilities very late tonight/early Monday morning.
Pinpointing where and when is still futile even at this range...so
maintained high chance PoPs beginning late tonight and lasting
into Monday.

Gosselin

&&

.SHORT TERM: (Through Monday Afternoon)
Issued at 320 PM CST Sun Feb 7 2016

Between a passage of the initial cold front thru the region by early
this afternoon and/or thickening cloud cover, temps have largely
already hit their daily maxes and will either stagnate or slowly
begin to fall, after having resulted in another mild day, with max
temps in the upper 40s to mid 50s.

A strengthening upper LOW over the arrowhead region of MN will
help govern the tracks of various disturbances around it over the
next couple of days as it digs the flow to be more from the N-NW.

The first few disturbances are starting to come into focus now
and we can, with some degree of confidence, focus on the tracks and
timing.  The first is over northwest MO and is helping to kick off
some pcpn echo over the MO-IA border just downstream from it.  This
is liquid pcpn.  This disturbance will essentially drop straight
southward, with some east movement, and should help to perhaps kick
off light rain or sprinkles this evening for parts of central and
southeast MO, and perhaps into far southern IL.  The pcpn-type is
expected to remain liquid with temps still in the 40s for most areas
during this time.

The second disturbance is located near Sioux Falls, SD (KFSD), and
will have more of a true SE movement to it, likely tracking thru the
heart of our CWA from late this evening thru the overnight.  This
will have better coverage pcpn with it, and due to its forward
speed, now looks like it will outrun the surface cold air a bit and
probably begin as rain showers for an hour or so, then changing to
snow showers.  Overall preferred warmer MOS temps but diffs were
very small, and temps by daybreak at most locations will be at or
below freezing.

The third disturbance is more directly associated with the storm
center over the MN arrowhead, and as that digs, will track more S
initially then SE late, and will likely affect areas near the MS
river and east during Monday morning and early afternoon.
Pcpn-types here will be all snow, with temps probably not rising from
previous nighttime mins at all, and probably losing a few degrees by
mid-afternoon.

Low level CAA will strengthen significantly after midnight tonight
and will remain decently strong thru the day on Monday, and will
also be accompanied by an increase in NW wind and gusts to 35mph
most locations with some 40mph possible in northeast and central MO.

The wind combined with the scattered snow showers that will be
ongoing will result in rapidly fluctuating visibilities, but lower
liquid to snow ratios than one might expect for cold air like this,
due to the well sifted nature of any snow that does accumulate, and
leaned strongly towards 12-15:1 versus te model suggested 20:1.
Snow accums for most locations should be just a dusting of snow, but
where discrete snow bands can set up and persist for a period of
time, we could see localized accums of an inch or more.  Any
identification of the location of these discrete snow bands will
likely have to be now-casted, with the forecast amounts strongly
weighted towards the median, and not the exception.

Due to the anticipated localized nature of any accums beyond a
dusting, no winter headlines will be issued at this time.

TES

.LONG TERM:  (Monday Night through Next Sunday)
Issued at 320 PM CST Sun Feb 7 2016

Deep cyclonic flow and additional, yet sheared, disturbances will
only allow the threat for snow showers to slowly retreat eastward
and may allow flurries well into Tuesday.  One trend that all of the
models have settled on is for this Arctic airmass to build over our
region first before heading east, and will thus prolong its presence
here--likely into Thursday--as well as prolonging the moderately
strong wind with gusts at times at least into Wednesday.  This will
create the threat for wind chill advisory criteria (-15F) to be met
late Tuesday night into Wednesday morning for some areas in northern
MO and central IL.

Otherwise, NW flow aloft continues into next weekend.  Very low
confidence on any additional wx-making disturbances track/timing and
have kept the forecast dry because of it.  Something that could
change in a couple of days, so stay tuned.  Temps remain below
average, though, with perhaps some recovery back to near average by
Thursday-Friday.

Of better confidence is another intrusion of Arctic air for late
week, around Friday, and may continue into early next week.  And
that gets me to my next item:  models have, for some time, been
advertising a system that will affect us in mid-February, but true
to form for our region, can`t make up their mind on how much cold
air will be here and what form most of the pcpn will take.
Something to watch and stay tuned for as we move thru the upcoming
week.

TES

&&

.AVIATION:  (For the 06z TAFs through 06z Monday Night)
Issued at 1136 PM CST Sun Feb 7 2016

Upper-level trough continues to dig southward and this will help
bring both much colder air to the region but also some
predominantly scattered snow showers through much of the period.
These snow showers may briefly reduce visibilities and ceilings
down into IFR. Otherwise...expect gusty NW winds along with a
high-end MVFR ceilings along with the snow showers/flurries.


Specifics for KSTL:

Timing of MVFR ceilings and snow showers still appears to be in
the predawn hours of Monday morning. Once again...some of these
snow showers may be heavy enough at times through Monday morning
to reduce visibilities and ceilings down to IFR. Best chances of
these heavier snow showers/squalls for the terminal attm appear to
be in the 1000 and 1600 UTC range give or take a couple of hours.
Otherwise...NW winds will pick up with gusts near 30 knots along
with ceilings between 2500 and 3000 ft AGL.

Gosselin

&&

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

$$

WFO LSX



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