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Area forecast discussion...updated aviation
National Weather Service Saint Louis MO
557 PM CST Thu Feb 23 2017

Short term... (through late Friday afternoon)
issued at 343 PM CST Thu Feb 23 2017

Surface frontal boundary was located from near jef thru the northern
stl Metro area and just north of Litchfield, Illinois. This front has
made somewhat better northward progress in Illinois than in MO but all of
that should be changing with the entire front moving north as a
strong surface wave located in far western OK/southwestern Kansas
approaches. A decent temperature gradient exists thanks to this
front with readings ranging from around 50 in northeast MO to the
mid 70s in a few areas south of the front. Showers have mostly been
limited in coverage to the northern forecast area across parts of
northeast and central MO and west-central Illinois and its southward
extent has been gradually retreating to the north during the

The strong surface wave will track northeastward into west-central
Illinois by 12z/Fri, which will push the old frontal boundary--now warm
front-- thru the entire forecast area tonight, and also drag a cold
front into the western forecast area by 12z/Fri. Precipitation
chances should be limited for much of tonight for areas north of the
warm front, meaning northeast MO and west-central IL, but should
begin to see some expansion of chances into much of the rest of the
area late tonight in response to broadscale lift and warm air advection as the
upper level support begins to approach from the west as well as the
approaching cold front. This trend should then continue into Friday

By the time surface based convection can take hold late Friday
morning or midday, the surface cold front should be in the far
eastern sections of the forecast area in southwestern and southern
Illinois. It is this area that continues to hang on to a marginal severe
threat with a relatively small time window to do it in--from late
morning thru early afternoon.

The surface cold front will also deliver more seasonable
temperatures, which relatively speaking, will result in falling
afternoon temps as we go from much above normal to normal, as well
as windy conditions with winds from the west. Tonight will feature
unusually warm temperatures with lows in the 50s to around 60.


Long term... (friday night through next thursday)
issued at 343 PM CST Thu Feb 23 2017

The cold front should be through the area by 00z Saturday with
perhaps a few lingering showers in the cold sector over our eastern
Illinois counties. Guidance continues to show a fairly broad swath
of light quantitative precipitation forecast across our northern counties as the primary shortwave
moves across the area. This will be a solid shot of cold air which
will swiftly bring temperatures back to near normal levels. Lows
Saturday morning should dip into the mid 20s to around 30 with highs
Saturday struggling to get into the upper 30s and low 40s.
Relatively cool weather will continue on Sunday, but warm advection
will develop on the western side of the cool high. This will likely
bring the area some light rain...possibly starting out as a little
light snow over parts of central Missouri before low level
temperatures warm up from morning lows. This will start a period of
relatively wet weather for US. An upper level trof will settle over
the western 1/3 of the Continental U.S. Early next week and move east through
the week. The longwave trof will eject shortwaves out across the
plains ahead of it which will produce periods of rain and probably
some thunderstorms. While medium range models are in pretty good
agreement on the over all mid and upper level pattern next week,
there is little agreement in the low levels. Stuck with ensemble
guidance rather than leaning one way or another due to the
uncertainties. This yields above normal temperatures through the
period with at least a chance of precipitation hanging on through
Tuesday night.



Aviation... (for the 00z tafs through 00z Friday evening)
issued at 537 PM CST Thu Feb 23 2017

Developing sfc low over Kansas will move newd tonight. As it does, the
wrmfnt shud lift nwd with winds becoming sly at all terminals and
cigs lifting at uin. There is a threat, albeit low, of showers
mainly late tonight into Fri morning just ahead of the approaching
cdfnt. There is some disagreement regarding if cigs will be lower
with the fnt for an extended period of time or if terminals will
see the dry slot move in before the lower cigs later Fri evening.
For now, have trended twd lower cigs from prev taf, but will keep
only a fairly brief period of MVFR cigs. However, at uin, cigs are
expected to be lower with the sfc low passing closer to the



record highs

2/23 2/24

Stl: 77/1996 81/1930
cou: 73/1933 81/1930
uin: 70/1922 73/1930

Record high minimums

2/23 2/24

Stl: 55/1930 58/2000
cou: 53/2000 61/1930
uin: 49/2000 55/1930


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