Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 270545
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1145 PM CST Wed Nov 26 2014
Issued at 836 PM CST Wed Nov 26 2014
Light snow continues to fall across much of the forecast area
this evening associated with a northwest flow shortwave and an
associated weak surface low now near STL. Most of the
precipitation was in the form of light snow, although there was
also light rain across portions of central and southeast MO ahead
of a cold front which extended from just east of COU southwest to
just east of SGF where there was a wedge of warmer air southwest
of the surface low and an occluded front. There was also patchy
drizzle or freezing drizzle where the lift was weak and the low
level cloud cover quite shallow. Only minor additional snow
accumulations of under one inch are expected tonight with much of
the area receiving a total of around one inch of snow depth with
isolated spots up to 2 inches. There should just be some lingering
flurries late tonight. As temperatures cool well below freezing
late tonight there may be some slick icy spots on untreated
roads, sidewalks, driveways and parking lots where melted snow
.SHORT TERM: (Through Late Tonight)
Issued at 351 PM CST Wed Nov 26 2014
Clipper system continues to impact our forecast area at this time.
At 21z...a low pressure center was located in northeast MO and
was moving slowly to the southeast. A warm front extended to the
south-southeast of this low pressure area into east-central MO--just
west of the STL metro area--where temps have risen into the upper
30s and low 40s. The cold front associated with this system is
gaining on the warm front and was now located from this low pressure
area and to the south into central MO. Temps ahead/east of the warm
front have remained in the low-mid 30s. An area of precipitation
extended in a band on the IL side of the river mostly. Nearly all of
this precipitation was snow. Drizzle has developed on the backside
of this main band and into the vicinity of what is beginning to be
an occluded front, as the cold front catches the warm.
The low pressure in northeast MO is occluding with all anticipation
that a new triple point will develop over TN this evening. In the
meantime, the front over our region will become occluded as well and
simply a wind shift line and focus for drizzle.
Temps near the MS river and IL will stall this evening and then
slowly fall, while a more normal diurnal trend will be seen for
central MO and southeast MO. Min temps tonight will strongly favor
the higher MET MOS values with low clouds expected to stick around
The precipitation band is expected to soon stall over in IL and
gradually weaken this evening as the new focus shifts well to the
southeast for the overnight. Leftover diurnally generated scattered
showers...mostly snow by this point...will wander into the areas
where the main pcpn band has vacated along with patchy drizzle
associated with the occluded front moving thru. Temps may be cold
enough for some FZDZ to result as well.
Additional snow accums will be minimal...with up to an inch extra in
southwest IL. Icing potential will need to be watched carefully
with models and radar not picking up on this too well yet but
scenario does favor drizzle thru the evening.
.LONG TERM: (Thursday through Next Wednesday)
Issued at 351 PM CST Wed Nov 26 2014
Ridge of high pressure to move into the region on Thanksgiving with
colder temperatures. Clouds will be slow to clear out so temps to
only rise into the mid 20s to around 40.
Another cold night Thursday night with lows in the 20s. Then surface
ridge moves to the east allowing southerly winds to return and
become gusty on Friday. So highs will be near normal in the mid 40s
to mid 50s.
Warmer weather to persist through the weekend with highs in the mid
50s to mid 60s on Saturday and lows Saturday night in the low 40s to
low 50s. Models still bring a cold front into region during the day
on Sunday. High temp forecast to be tricky depending on timing of
this frontal boundary. For now have highs in the upper 40s far north
to the mid 60s far south. Otherwise, low level moisture will be on
the increase ahead of this front so could see some rain across
southern half of forecast area Sunday through Monday with it mixing
with or changing over to snow at times. Lows Sunday night will be in
the upper teens to mid 30s. Highs on Monday will be in the low 30s
to low 40s.
Weak surface ridge to build in Monday night and Tuesday. So will see
dry conditions with lows Monday night in the low 20s to low 30s and
highs on Tuesday in the 40s.
Beyond that extended models have differing solutions with ECMWF a
bit faster with next frontal passage and drier vs. GFS which is
slower and much wetter solution. For now went with a blend, have
slight chance pops Tuesday night and chance pops on Wednesday.
Temperatures to be near freezing Tuesday night in northern portions
of forecast area so could see a mix of rain and snow. Otherwise,
rain possible for mid week next week.
.AVIATION: (For the 06z TAFs through 06z Thursday Night)
Issued at 1134 PM CST Wed Nov 26 2014
IFR flight conditions were widespread earlier this evening across
eastern MO and western IL into southeast IA. However over the last
few hours there has been a dramatic improvement as the surface low
redevelops in the TN valley, winds shift to north and northwesterly,
and snowfall diminishes. Radar and present trends suggest snow
should end across the St. Metro area within the next hour or two
with conditions improving at that time to MVFR. Elsewhere MVFR
conditions will persist overnight. During the day on Thursday the
cig heights are expected to gradually improve with VFR flight
conditions evolving from midday into the afternoon.
Specifics for KSTL:
Snow is expected to end by 07z with flight conditions improving at
that time to MVFR. MVFR flight conditions will then persist
through early afternoon with cig heights gradually rising, with
VFR conditions around 21z.