Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 051221
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
621 AM CST Thu Dec 5 2013
.SHORT TERM: (Today through Friday)
Issued at 334 AM CST Thu Dec 5 2013
Focus remains on wintry precip today through Friday as to shortwaves
moves over the Arctic airmass building across the region. The first
shortwave is right over the gulf of California at this time and will
be moving rapidly northeast toward our area through the morning.
Unfortunately it looks like it won`t quite make it into U.S.
airspace so we can sample it with radiosondes for the 12Z models.
Here`s hoping the Mexican National Meteorological Service can get
some sondes into it this morning...please...por favor.
This morning`s update is basically a refinement of earlier
forecasts. The northern edge of the precipitation looks to be very
sharp for this event. This is due at least partially to the very
dry air that is pushing into the region with the Arctic high. The
precipitation will come primarily in two waves. The first arriving
late this morning or early afternoon as the shortwave arrives.
Latest guidance is now showing some low to mid level frontogenesis
along the thermal gradient draped across the area from around 850mb
up to 700mb. This should enhance precipitation allowing for greater
liquid equivalents today and this evening. While the precip will
likely taper off tonight, it probably won`t end entirely across the
eastern Ozarks. The second wave will move in Friday morning as
another slug of vorticity is ejected northeast out of the base of
the deep longwave trof over the western U.S. This should be all
snow, and there is now an 850mb reflection of the wave which ripples
up from Arkansas over the Boot Heel of Missouri causing significant
moisture convergence along the baroclinic zone over the southern
portion of the CWFA. Have boosted snowfall totals down there
accordingly, but again the north-south gradient of accumulation will
be very tight.
Expect the gradient to stretch from near Osage Beach east-northeast
across the St. Louis Metro area up to near Litchfield Illinois.
Across the gradient snowfall amounts will go from 0 to 1-3 inches of
snow with a little sleet mixed in. Further southeast from near Cuba
to around Vandalia expect 3-5 inches of sleet and snow, with around
6 inches of snow stretching from Salem Illinois down through Sparta
and Farmington. Across our far southern counties it looks
particularly messy with freezing rain and sleet at the outset,
mixing and changing to snow tonight. Look for about 2/10 of an inch
of ice with 5-7 inches of sleet and snow. Have laid out advisories
and warnings accordingly.
.LONG TERM: (Saturday through Wednesday)
Issued at 405 AM CST Thu Dec 5 2013
Cold air will settle across the area Saturday as a 1040+ mb high
pushes southeast from the Great Plains. Temperatures will bottom
out in the single digits and low teens across the area. Afternoon
highs will be 20-25 degrees below normal in the low to mid 20s.
This will set the stage for another shot of winter weather late
Saturday night into Sunday. The upper pattern begins to shift
Saturday night with the longwave currently over the western U.S.
moving across the Rockies. Low level warm advection ramps up as
the flow at 850mb turns to the south-southwest. Forecast soundings
indicate primarily snow along and north of the I-70 corridor with
snow perhaps mixing with sleet or maybe even freezing rain in
southern zones. Partial thickness is also agreeable with these
precip types. Model QPF is light, generally 1-2 tenths of an inch,
but is very widespread and not focused in any real discernible
band. Have kept pops nearly identical to previous forecasts with
generally high chance across the entire area.
Another slug of Arctic air will push down from the Northern Plains
into the Mid-Mississippi Valley Sunday night and Monday. The mean
upper level trof is forecast to dig over the eastern 1/2 of North
America Tuesday into Wednesday which will lock this cold airmass
into place. Temperatures will therefore remain as much as 25
degrees below normal into midweek.
.AVIATION: (For the 12z TAFs through 12z Friday Morning)
Issued at 619 AM CST Thu Dec 5 2013
Showers have developed from southwest Missouri northeastward into
southwest Illinois. There have reports of freezing rain, sleet,
and snow grains and light accumulations in this area of
precipitation. Expect this precipitation to affect the St. Louis
metro TAF sites through at least 14Z before it ends this morning.
This may produce some light icing on untreated surfaces. Additional
snow and sleet will move into the St. Louis metro TAF sites from
the southwest late this afternoon and this evening before moving
out by midnight. 1 to 2 inches of snowfall is possible with this
round. Another round of snow is expected to move into the area by
12Z on Friday.
Specifics for KSTL: Expect a mix of freezing rain, sleet, and snow
through at least 14z before the band moves to the east. Then
expect a lull in the precipitation before snow and sleet moves
into the terminal between 22-02Z from the southwest. Will see
another lull in the precipitation overnight before more snow moves
into terminal around 12Z Friday. Expect to see around 1 inch of
snow and sleet accumulation from both tonight`s and tomorrow
morning`s waves of precipitation.
.PRELIMINARY POINT TEMPS/POPS:
Saint Louis 29 19 27 11 / 70 70 60 10
Quincy 24 11 21 5 / 10 10 20 5
Columbia 23 13 23 7 / 30 30 40 5
Jefferson City 25 15 24 7 / 50 50 50 5
Salem 33 22 27 13 / 90 100 90 10
Farmington 30 18 27 9 / 100 100 90 10
MO...WINTER WEATHER ADVISORY from Noon today to 6 PM CST Friday FOR
Crawford MO-Jefferson MO-Washington MO.
WINTER STORM WARNING from Noon today to 6 PM CST Friday FOR Iron
MO-Madison MO-Reynolds MO-St. Francois MO-Ste. Genevieve MO.
IL...WINTER WEATHER ADVISORY from Noon today to 6 PM CST Friday FOR
Bond IL-Clinton IL-Fayette IL-Monroe IL-St. Clair IL.
WINTER STORM WARNING from Noon today to 6 PM CST Friday FOR
Marion IL-Randolph IL-Washington IL.