Scientific Forecaster Discussion
fxus63 klsx 182335
Area forecast discussion...updated aviation
National Weather Service Saint Louis MO
535 PM CST Mon Nov 18 2019
Short term... (through late Tuesday night)
issued at 315 PM CST Mon Nov 18 2019
Much of the period will be quiet in relative terms with little
concern for impactful weather. The initial issue will be
addressing the weak system sliding northwest to southeast through
the area this evening.
So far, the result has been an increase in mid to high clouds
with overcast skies through the region. Much of the day has only
resulted in isolated to scattered shower activity along a narrow
corridor of mid-level lift that stretched through central Missouri.
Showers may become a bit more numerous (not widespread) late this
evening and overnight as an area of better lift drift southeast
out of Iowa. Expect this to be a quick pass with light rain moving
along and east of the Mississippi River into Tuesday. All
precipitation should progress into Illinois and east of the County Warning Area
Dry conditions are anticipated through the remainder of Tuesday as
ridging builds in from the west. Southerly winds will also give a
slight boost to temperatures, which will trend warmer from east to
west. Expect highs Tuesday to range from near 50 in interior
section of Illinois to the upper 50s over central and southeast
Long term... (wednesday through next monday)
issued at 315 PM CST Mon Nov 18 2019
The primary message in the long term relates to much milder
weather through the midweek stretch, along with a more active
pattern that sets up over the region.
An upper ridge begins to build east over strengthening surface
high pressure that will center over the Ohio Valley through
Wednesday. Southerly flow will couple with dry conditions to push
temperatures well into the 50s over much of the area with lower
60s being favored through central Missouri.
The next system will come into focus late Wednesday into Thursday.
Guidance remains is good agreement in placement of a surface low
tracking northeast through the plains and into the upper
Mississippi Valley. Deep southerly flow will pump moisture
northward out of the Gulf and send pwats above one inch. A cold
front extending south of the system will be the primary source for
rain chances Wednesday night into Thursday morning, as the bulk of
lift remain north in relation to the closed upper low. So, while
categorical chances are in the forecast, any widespread, long
duration precipitation is likely to affect locations north of the
County Warning Area.
There is the potential that temperatures on Thursday will be even
milder than Wednesday. However, it will likely be reliant on the
timing of the late Wednesday/Thursday morning rainfall and
trailing cold front. Temperatures ahead of the front may climb
well into the 60s with ensemble member approach 70 degrees in many
instance. Current forecasts for low to mid-60s just east of
Columbia, running east along and south of I-70. Colder air will
begin to work in behind the front through the day, ultimately
sending temperatures down through the afternoon.
Guidance diverges greatly beyond Thursday. The general theme is
for colder air to return as the boundary stalls to the south. This
will become the focus for an additional system to track out of the
southwest later in the week. This could be key in introducing
moisture over a colder surface to bring wintry weather back into
the picture later Friday into Saturday. Confidence is very low,
though, given the spread in guidance and timing issue.
The remainder of the period looks drier beyond the weekend with
temperatures near to slightly above normal into early next week.
Aviation... (for the 00z tafs through 00z Tuesday evening)
issued at 526 PM CST Mon Nov 18 2019
Low pressure over Iowa and Minnesota will slide south-southeast
tonight into the mid Mississippi Valley. Light rain and sprinkles
will accompany the low, along with lowering clouds. Although most
of the area is expected to remain VFR with this light
precipitation and the lowering cloud deck, it looks likely that
parts of northeast Missouri and west central Illinois will see
MVFR ceilings between 1500-2800 feet between 07z-15z. Some models
are even showing IFR ceilings in this area, though confidence is
not yet high enough to mention in the KUIN taf. Expect wind to
increase from the northwest as the low continues moving east-
southeast on Tuesday with gusts up to around 20kts.
Specifics for kstl:
VFR flight conditions with occasional sprinkles are expected at
Lambert this evening. There may be more light rain or sprinkles
overnight, but little or no impact to flight conditions is
expected at this time. Wind is expected to increase to between
10-15kts Tuesday morning with gusts to around 20-25ks, diminishing
in the afternoon with continuing VFR flight conditions.