Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 151801
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
101 PM CDT Sun Oct 15 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 325 AM CDT Sun Oct 15 2017

The cold front is passing through west central Illinois and central
Missouri at this time.  Showers containing moderate to occasionally
heavy rain are moving east ahead of the front and there are a few
lightning flashes embedded in the line of showers.  Expect the line
to continue moving east through the predawn hours with the heaviest
rain likely clearing eastern sections of the CWFA before 12Z.  An
area of stratiform rain behind the line will likely persist along
and just behind the front through 12-15Z this morning...which should
generally be pretty light.  Model consensus has the cold front
exiting our southeastern counties by 12Z and the last of the
precipitation behind the front exiting by 15Z.

There`s a wide area of stratocu extending north into Iowa and
Minnesota behind the cold front.  Given the strong pressure gradient
and resulting cold advection, this area of stratocumulus should
continue to build south-southeast today and will likely blanket the
CWFA through late morning into early afternoon.  Expect clearing
from northwest to southeast with most areas becoming mostly sunny by
19-20Z.  Gusty northwest flow will bring much cooler air to the
region and highs are only expected to hit the low 60s in most
locations...likely not even cracking 60 in northeast Missouri and
west central Illinois.  With a clear sky tonight and a diminishing
wind, we should have excellent radiational cooling conditions.
Guidance is showing lows in the upper 30s to low 40s in most
locations outside the urban heat island of St. Louis.  This looks
reasonable and would make tonight coolest night of the Fall season
so far.  This will likely be just outside the best temperature range
for widespread frost, but wouldn`t be surprised to see some isolated
frost Monday morning in well protected low lying areas.

Carney

.LONG TERM...  (Monday through Saturday)
Issued at 325 AM CDT Sun Oct 15 2017

Northwest flow aloft will begin the work week on Monday and should
persist until Wednesday, gradually de-amplifying with time.  A
RIDGE aloft is then expected to build over our region on Thursday
and then shift eastward, resulting in a SW flow aloft heading into
next weekend.  At the surface, the cool Canadian RIDGE of high
pressure will begin overhead and shift into the southeastern CONUS
and linger thru much of the remainder of the week, giving us a
southerly surface flow.  The atmospheric column will begin the
period quite dry and NW flow aloft and a RIDGE axis extending along
the Gulf Coast should only serve to maintain that.  Any upper level
disturbances detected or not will struggle mightily to generate any
clouds or pcpn and dry weather is favored thru at least Friday.

The southerly low-level flow will give us a warming trend with
temperatures already back to above average by Tuesday with 80s
possible in places for the second half of the week.

The models favor an approaching upper TROF and surface cold front
late next weekend and it looks like this will have the first real
potential for our next rain chance just beyond the end of the
forecast period.

TES

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1240 PM CDT Sun Oct 15 2017

Post frontal cumulus field over our area well behind the deep
surface low moving northeastward into the northeastern US. Will
be scattered to broken this afternoon, but mainly just above
3000 feet. This cloud cover will dissipate or shift east-
southeast of the taf sites early this evening. Relatively strong
and gusty northwest surface wind will diminish early this evening,
becoming light by late tonight as the surface pressure gradient
relaxes as a strong surface ridge builds eastward into our area.

SPECIFICS FOR KSTL: Post frontal cumulus field over the STL area
well behind the deep surface low moving northeastward into the
northeastern US. Will be scattered to broken this afternoon, but
just above 3000 feet. This cloud cover will dissipate or shift
east-southeast of the STL area early this evening. Relatively
strong and gusty northwest surface wind will diminish early this
evening, becoming light by late tonight as the surface pressure
gradient relaxes as a strong surface ridge builds eastward into
the STL area.

GKS

&&

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

$$

WFO LSX


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