Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 262153
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
353 PM CST Wed Nov 26 2014
.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 18z TAFs through 18z Thursday Afternoon)
Issued at 1155 AM CST Wed Nov 26 2014
Low CIGs will prevail with the onset of the pcpn for MS river
sites and continue for COU for much of the valid TAF period given
expected flow at cloud level and where the low clouds are now and
how it will develop with this system. This will translate to IFR
and low-end MVFR CIGs. May need to expand IFR CIGs over a larger
area based on trends heading into early this evening. These clouds
should then break up during Thursday (Thanksgiving) morning. Wind
trends were updated with expected positions of the front with
FROPA around 00z but wind speeds not expected to pick up much near
the MS river until later tonight due to frontal proximity.
Specifics for KSTL: Currently have MVFR CIGs and these should at
least continue into Thursday morning. IFR a possibility later
tonight and will bear watching but prefer to see things develop to
our NW first before committing. Warm front FROPA around 00z, which
at that time will be close to when the cold front catches up
anyway, where winds shift from S to W. Otherwise, heaviest snow
during the early-mid afternoon with more scattered SHSN late
afternoon and evening.