Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 231558
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
1058 AM CDT Mon Apr 23 2018

.UPDATE...
Issued at 1048 AM CDT Mon Apr 23 2018

A narrow band of showers continue to rotate back across Missouri
and Illinois into the afternoon hours on the north side of the
upper low. These showers will decrease in areal coverage through
the afternoon as the RAP depicts weakening low level moisture
convergence and mid-level ascent over the area. While there will
be some thinning of the clouds over northeast Missouri, most of
the area will see cloudy skies through the afternoon which will
keep temperatures below normal for the later half of April.

Britt

&&

.SHORT TERM...  (Through Late Tonight)
Issued at 327 AM CDT Mon Apr 23 2018

Low pressure continues to wobble its way through the lower
Mississippi Valley this morning.  As expected, the low is wrapping a
lot of moisture back to the north into the mid Mississippi
Valley...and all guidance agrees that this will continue today. Best
chance for rain will continue to be across east central and
southeast Missouri as well as southern Illinois...although an
isolated shower or sprinkles will continue to be possible as far
west as Columbia today.  Expect rainfall amounts to continue to be
light especially in east central Missouri and southwest/south central
Illinois north of I-64 due to a persistent northeast wind which
continues to funnel in dry air from the Great Lakes and Ohio Valley.
 Expect temperatures today to be similar to Sunday`s with highs
ranging from the mid 50s in the showery precip to the upper 60s
further north where it will be dry and cloud cover will be much
thinner.

The low continues meandering eastward into the Tennessee Valley
tonight...but doesn`t make a whole lot of progress.  Our forecast
area should be west of the low level trof by 03-06Z tonight which
will cut the chances for continuing precip significantly. Still...an
isolated shower will be possible across parts of southeast Missouri
and southern Illinois for much of the night and even into Tuesday
morning.  Still not seeing a significant airmass change behind this
system, so overnight lows should be very similar to what we`ve seen
the past couple of days in the mid 40s to low 50s.

Carney

.LONG TERM...  (Tuesday through Sunday)
Issued at 327 AM CDT Mon Apr 23 2018

The long range will bring a welcome shift in the overall pattern.
In general, drier conditions, more sunshine and milder temperatures
are not far down the road. Ahead of the shift, we will contend with
the departing system Tuesday and couple of brief bouts of precip
Wednesday and Friday.

The bi-state region will be on the back side of the departing system
Tuesday morning through early Tuesday afternoon. I limited chances
for lingering showers to the east of the Mississippi River as
moisture and lift associated with the system begin to wane.
Enough dry air makes it into the mid and upper levels to bring
some sunshine to Central Missouri for the second half of Tuesday,
where temperatures will respond accordingly. Highs will range
from the low/mid 60s in IL to lower 70s in Central MO.

Wednesday mornings precipitation is likely to remain west of the
Mississippi, where the upper low and better lift is dedicated to the
KS/MO/AR borders. This will be shunted south fairly quickly as
high pressure and much drier air builds in from the north. This
should set up for a very nice Thursday with little to no cloud
cover and temps well into the 60s.

The next chance at precip will progress fairly quickly from
northwest to southeast Friday morning through early Friday
afternoon. This will coincide with a narrow ribbon of convergence
and moisture along the front, which should be through most areas
before noon. Just enough precip could fall to wet the ground
before exiting...more so just another nuisance rain.

The big change comes late in the period. While long range models
differ to some degree on exact solution, the general consensus is
for upper ridging to build over the Central U.S. Positive H5
anomalies are situated overhead through next weekend. Temps in
the upper 60s/lower 70s could be on the conservative side with
some solutions pointing to the mid/upper 70s by Sunday.

Maples

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 637 AM CDT Mon Apr 23 2018

Low pressure centered near the Kentucky/Missouri border will drift
east today. Showers will continue to rotate northwest around the
center of the low across eastern Missouri and southern Illinois.
Rain should remain light for the most part, and the latest
guidance is showing the areal coverage of the showers decreasing
significantly between 15-18Z. Most models have MVFR ceilings over
southeast Missouri spreading back to the north/northwest this
morning...and 1500-2000ft ceilings have made some progress in that
direction over the past few hours. However, models have been too
bullish in lowering ceilings over the past 24-48 hours with this
system, and they continue to be a little too fast when compared to
observations. I delayed onset of MVFR ceilings at the terminals
from what guidance gave me, but still think that we`ll see
lowering ceilings this afternoon and evening. MVFR will likely
prevail across much of eastern Missouri and southern Illinois by
this afternoon and continue to spread west into central Missouri
during the evening.

SPECIFICS FOR KSTL:

Think it`s only a matter of time before the ceiling lowers to MVFR
at Lambert. Think the latest guidance is too fast...so have pushed
back the lowering til around 17Z though my confidence is not
especially high on that timing. Expect MVFR ceilings to prevail
after the low clouds finally push in. IFR is possible
tonight...though I don`t think it`s as likely since the models
have been too low with ceilings over the past couple of days.

Carney

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     57  52  67  49 /  80  30  10   5
Quincy          67  50  68  47 /  10   5   5  10
Columbia        66  49  71  48 /  10   5   5  10
Jefferson City  64  50  71  48 /  10  10   5  10
Salem           59  52  64  48 /  70  40  20  10
Farmington      56  50  65  47 /  50  30  20   5

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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