Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 250958
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
358 AM CST Wed Feb 25 2015

.SHORT TERM:  (Through Late This Afternoon)
Issued at 353 AM CST Wed Feb 25 2015

Split flow upper level pattern feature two systems. A nthrn wave
that will begin affecting the FA later this aftn into Thu mrng and a
stronger sthrn stream storm. The sthrn energy is expected to track
from the Red River Valley today into the sthrn Appalachians
tonight. This path will keep the effects from this feature well to
the south of the CWA...though will be a significant impact for
locations from NE TX east into the Carolinas. The nthrn system is
dropping SE out of the Dakotas this mrng with a SFC low in along the
NE/SD border as of 9Z with a bndry extending SE across sthrn
IA...nthrn IL/IN and arcing NE in Canada. The bndry is expected to
slowly sag south thru the day with the low tracking just to the SW
of the bndry...which takes it from ern NE this mrng to somewhere
across far ern KS or wrn MO by 00Z this evng. The SREF and ECMWF
appear to be wrn outliers. This system will be in a weakening mode
as it drops SE thru the region overnight. Overall speed of the system
seems to have slowed some over the past 24 hrs and as such have backed
off on increasing PoPs across the nthrn zones until late this
aftn. The slower system also means thicker cloud cover will be
delayed allowing temps to rise a bit more than previously thought.
Temps may be marginal for snow at the onset of the event as
well...allowing for a possible rain snow mix. Therefore...have
significantly lowered QPF and snow accums prior to 00z and have
them confined primarily along and north of US HWY 36 with snow
accums of less than an inch. Have also delayed the start time of
the ADVY til 21Z due to the above reasoning. Added Brown and Pike
Counties in IL to the ADVY and now have it ending at 15Z
Thu...instead of 12Z.

2%

.LONG TERM:  (Tonight through Tuesday)
Issued at 353 AM CST Wed Feb 25 2015

Clipper system centered over west central Missouri will continue
to slide to the southeast tonight...with colder air filtering in
from the north. Because of slightly warmer temps over central MO
could still see some mixed rain and snow over this region for a
few hours after 00z Thursday. Otherwise, heaviest snowfall will be
across northeast MO and west central IL. Even though system
weakens as it exits region, will see lingering light snow through
at least 18z Thursday before tapering off. Storm total numbers
will range from 3 to 4 inches far north to less than an inch
southeast of the St. Louis metro area.

Colder air to filter into the region on Thursday, so will have
non-diurnal temps, with mid morning highs most locations, then
either steady or falling temps through the afternoon hours. Thursday
night will be our coldest night as fresh new snowfall, light north
wind and clearing skies allow temps to fall below zero for areas
north of the I-70 corridor. Rest of forecast area will see lows in
the single digits above zero. As for wind chill indicies,
approaching advisory criteria for northeast MO and west central IL,
but it`s too early to issue an advisory at this time.

Beyond that, the extended models continue to have timing, placement
and strength differences with the prolonged period of precipitation
this weekend and into early next week. Best chances of precipitation
continues to be the Saturday night/Sunday timeframe and Monday
night/Tuesday timeframe. Continue to check back frequently for
updates to this event.

Byrd
&&

.AVIATION:  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1120 PM CST Tue Feb 24 2015

VFR stratus that was over terminals earlier this evening has
advected southeastward and dissipated with time. Clear skies for
most of the rest of tonight is expected before midlevel clouds
advect into region from the northwest ahead of clipper-like
disturbance. Ceilings should lower through the day on Wednesday as
top-down saturation occurs. Timing of light snow looks to be a bit
slower than previous TAF package...starting at KUIN around 2200
UTC 25 February...KCOU 0300 UTC 26 February and KSTL 0700 UTC 26
February. Light snow should begin at KSUS and KCPS just after this
valid TAF package. Snow is expected to intensify a bit at KUIN
with IFR visbys/ceilings becoming more likely by late Wednesday
evening.


Specifics for KSTL:

Clear skies for most of the rest of tonight is expected before
midlevel clouds advect into region from the northwest. Ceilings
should lower through the day/evening on Wednesday. Timing of
light snow looks to be about 3 or 4 hours slower than previous TAF
package after analyzing latest model guidance. Now have light snow
beginning at KSTL at 0700 UTC 26 February. Snow may
intensify a bit between 0900 and 1200 UTC Thursday with IFR
visbys/ceilings possible...though since it was at the very tail
end of this valid TAF package elected not to put in those lower
visbys/ceilings quite yet and will let mid shift evaluate things further.


Gosselin
&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...WINTER WEATHER ADVISORY from 3 PM this afternoon to 9 AM CST
     Thursday FOR Knox MO-Lewis MO-Marion MO-Monroe MO-Ralls MO-
     Shelby MO.

IL...WINTER WEATHER ADVISORY from 3 PM this afternoon to 9 AM CST
     Thursday FOR Adams IL-Brown IL-Pike IL.

&&

$$
WFO LSX




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