000
FXUS63 KLSX 112051
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
351 PM CDT Tue Mar 11 2014

.SHORT TERM: (Tonight through Wednesday)
Issued at 327 PM CDT Tue Mar 11 2014

A very dynamic storm system will impact the region over the next
18 hours bringing a variety of weather. The postitively tilted
upper trof moving into the central Rockies at this time is forecast
to dig east-southeastward tonight with the primary vort max
tracking across southern KS to near St. Louis by 12z Wednesday. In
response the surface low currently just NW of Emporia KS will
track across southern MO and eastward near the OH River while the
attendant cold front sweeps eastward with the low, and the east-
west boundary across northern MO and IL sags southward. Large
scale ascent will spread across the region this evening in
association with the digging upper trof leading to widespread
precipitation development, especially in the cool air. There are 3
main elements that will accompany this dynamic system. The first
is there will be a threat of scattered thunderstorms in the warm
sector ahead of the low and immediately in the cool air north of
the sagging e/w boundary. Steep mid level lapse rates have overspread
the area with accas present. This combined with low level advections
of warm air and moisture should yeild MUCAPES between 250-500 J/KG
this evening. The second element will be snow. Its hard to believe
we are evening discussing this given the current temperatures in
the 70s to lower 80s. All the guidance is very emphatic that cold
air advection/deepening of the cold air in the wake of the surface
low will support a changeover from rain to snow. This should begin
late this evening in far NE MO and gradually spread sewd overnight
in response to strong CAA. The greatest potential for accumulations
will be across northeast MO into west central IL where forcing and
ascent will be strongest - which is also where the GYB heavier
precipitation track is aligned. The negative factors are the warm
ground but in this spot the snowfall intensity should be great
enough for accumulations of 2-3 inches. Further south the air
temperatures will be more marginal, and you combine this with
lesser intensity snowfall rates and the warm ground and
accumulations may be hard to come by. I have generally gone with
trace to half inch amounts along the I-70 coridoor. Areawide the
greatest accumulations will be on elevated or grassy surfaces.
Some lingering light snow with the deformation zone will likely
impact the area from St. Louis eastward through around 15z
Wednesday, but will shift east quickly. The third and last element
will be the wind. A very tight pressure gradient develops tonight
as the low moves across and to our east and this should result in
strong northwest gradient winds gusting to 40+ knots. The strong
and gusty winds should persist into Wednesday morning, gradually
decreasing in intensity through the day and also from west to east
as the low pulls away. I have 2 headlines with this forecast
package. The first is a winter weather advisory for a small
portion of northeast MO and west central IL to account for the
snow and blowing snow due to the strong winds, and also a wind
advisory for the entire CWA. Wednesday will be a world of
difference from today with the wind, and temperatures 35-40
degrees colder than today.

Glass

.LONG TERM: (Wednesday Night through Next Tuesday)
Issued at 327 PM CDT Tue Mar 11 2014

We should have a cold night on Wednesday night as the weak surface
ridge moves across and then a moderation in temperatures should
begin on Thursday as low level warm advection gets underway via south
southwest winds. A series of weak cold fronts then move thru in
the Friday night through Saturday time frame with increasing
cooling. By early next week however we get right back into a warm
advection regime.

Glass

&&

.AVIATION:  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1254 PM CDT Tue Mar 11 2014

VFR flight conditions and southwesterly flow will continue this
afternoon. Developing storm system over Kansas/Oklahoma border will
move east into this evening. Expect stationary front over northern
Missouri/central Illinois to begin drifting south over the next
couple of hours and should be near a KCOU-KPPQ line by 00Z. Short-
range guidance is showing showers and a few thunderstorms
developing ahead of the front. Expect more widespread rain to
develop after FROPA. Rain will change to snow through the night as
cold air is drawn into the storm system. Think ceilings will
quickly fall to IFR this evening after the steadier rain begins.
Wind will increase from the north-northwest to 30 gust 40 KTS in
the wake of the low tonight. Should see flight conditions improve,
and winds diminish somewhat as precipitation ends between 12z and
18z Wednesday.

Specifics for KSTL:

Expecting VFR flight conditions and southwest flow to continue
into early evening. Expecting showers and a few thunderstorms to
develop in the vicinity of the terminal between 01Z and 03Z this
evening. Not certain how much thunderstorm coverage there will be,
but do feel pretty confident that Lambert will receive some rain
after 01Z. Cold front is expected to shift the wind to the
northwest after 02Z...there is still some differences in timing in
the short range models, but expect it should be through the
terminal by 03Z. IFR flight conditions should accompany the front
with a steadier rain and increasing winds. Expect windiest
conditions to be after 06Z with sustained northerly flow at 30 kts
with gusts to 40 kts. Rain will change to snow before ending Wednesday
morning. Expect flight conditions to improve and wind to diminish
after the precip ends between 12Z and 15Z.


Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...WIND ADVISORY from Midnight tonight to 10 AM CDT Wednesday FOR
     Crawford MO-Franklin MO-Iron MO-Jefferson MO-Madison MO-
     Reynolds MO-St. Charles MO-St. Francois MO-St. Louis City
     MO-St. Louis MO-Ste. Genevieve MO-Washington MO.

     WIND ADVISORY from 10 PM this evening to 7 AM CDT Wednesday FOR
     Audrain MO-Boone MO-Callaway MO-Cole MO-Gasconade MO-Knox
     MO-Lewis MO-Lincoln MO-Marion MO-Moniteau MO-Monroe MO-
     Montgomery MO-Osage MO-Pike MO-Ralls MO-Shelby MO-Warren MO.

     WINTER WEATHER ADVISORY from 1 AM to 7 AM CDT Wednesday FOR
     Lewis MO-Marion MO.

IL...WIND ADVISORY from Midnight tonight to 10 AM CDT Wednesday FOR
     Greene IL-Jersey IL-Macoupin IL-Madison IL-Monroe IL-St.
     Clair IL.

     WIND ADVISORY from 10 PM this evening to 7 AM CDT Wednesday FOR
     Adams IL-Brown IL-Calhoun IL-Pike IL.

     WIND ADVISORY from 1 AM to 1 PM CDT Wednesday FOR Bond IL-
     Clinton IL-Fayette IL-Marion IL-Montgomery IL-Randolph IL-
     Washington IL.

     WINTER WEATHER ADVISORY from 1 AM to 7 AM CDT Wednesday FOR
     Adams IL-Brown IL-Pike IL.

&&

$$

WFO LSX