Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 270956
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
356 AM CST Thu Nov 27 2014
.SHORT TERM: (Today through Saturday)
Issued at 356 AM CST Thu Nov 27 2014
Clipper system is now well southeast of the CWFA, and only a few
lingering flurries remain. Expect any lingering precip to end by
12Z this morning and for the rest of the day to be cold and dry.
Some uncertainty on sky condition today as stratus over Iowa is
clearing fairly slowly from northwest to southeast. Short range NAM
and RAP 925mb RH field has a decent handle on the clouds at this
time, so have used a combination of these guidance products and
satellite observations to try and time gradual clearing today.
Canadian airmass over eastern Dakotas at this time will drift
southeast today and will provide the area with unseasonably cold
air. Cannot argue with MOS high temps in the mid-upper 20s to mid
30s across the area due to this cold high pressure system`s
Models continue to advertise a general pattern shift Friday into the
weekend with mid-upper level flow becoming more zonal. This will
allow warmer air to flow back into the area as the storm track
shifts north. Temperatures will moderate on Friday as the flow
shifts to the south-southwest on the western side of the Canadian
high which will have settled in over the Eastern CONUS. Expect
temperatures on Friday to be at least 10 to 15 degrees warmer than
today. Boundary layer moisture will also be on the increase, and
low level RH progs for Friday night/Saturday morning are showing
very moist conditions across the area by 12Z Saturday from about
900mb down to the surface. Have therefore increased cloud cover on
Saturday morning with some gradual clearing during the afternoon.
Models continue to spit out light QPF Saturday, but am still
skeptical due to the models` tendency to develop precipitation in
strong moisture return situations even with lifting mechanisms
aren`t present. Indeed, in this case model soundings are showing a
strong subsidence inversion in the low levels and positive values of
omega in the moist layer which would tend to lend credence to a dry
(tho cloudy/mostly cloudy) forecast for Saturday. Am still sticking
with above normal temperatures Saturday, though due to expected
cloud cover have backed off a little bit from warmest MOS guidance.
.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.
.PRELIMINARY POINT TEMPS/POPS:
Saint Louis 32 26 50 39 / 0 0 0 0
Quincy 24 20 45 36 / 0 0 0 0
Columbia 32 25 54 40 / 0 0 0 0
Jefferson City 33 26 56 41 / 0 0 0 0
Salem 30 23 45 37 / 5 0 0 5
Farmington 35 24 49 39 / 0 0 0 0