Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 241732
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
1232 PM CDT Tue Apr 24 2018

.UPDATE...
Issued at 1232 PM CDT Tue Apr 24 2018

Erosion of cloud field continues but has been slowed down by the
sun transitioning the northwest edge to a more cumuliform. This
gradual clearing is then expected from northwest to southeast this
afternoon and early evening. Weak yet deep cyclonic flow over the
area may be able to still kick out a short-lived shower during
peak heating for areas S and E of STL this afternoon as this
region of more cumuliform clouds near the cloudy-clear boundary
slides southeastward.

Temps will be a challenge depending on how fast things clear out,
with values pushing mid 70s where there is plenty of sun in the
west with barely getting into the 60s where clouds are dominant
in the east.

TES

&&

.SHORT TERM...  (Through Late Tonight)
Issued at 332 AM CDT Tue Apr 24 2018

Regional IR satellite continues to show clouds wrapping around the
pesky upper level system we have been dealing with the last couple
of days. Surface analysis depicts a stark divide in the moist
surface layer that extends as far west as Eastern Missouri. Much
drier air lies just a bit further west across Central Missouri,
where clouds cleared yesterday and allowed temperatures to rebound
into the 60s and 70s.

Low level moisture will hang on just bit longer along the
Mississippi and eastward. There will be the potential for a few
showers and patchy fog through the early morning, but chances for
rain diminish with the ever-so-slow eastward trend in the dry air
and decreasing cloud cover early this afternoon. Forecast soundings
suggest we could see another day with a fairly sharp divide with low
clouds and higher RH hanging on to eastern counties of the forecast
area. Those further west will see improvement with sunshine possible
across southwest IL by mid to late afternoon. Where sun does appear,
we could get better mixing, resulting in some gusty winds.

High pressure builds from the north and west through Tuesday night.
Mid level clouds will linger and begin to thicken again late in the
period ahead of the next system. Chances for precip should hold off
until the very tail end of the period. Even then, only the western
fringes of the forecast area run a slight chance of POPs.

Maples

.LONG TERM...  (Wednesday through Monday)
Issued at 332 AM CDT Tue Apr 24 2018

The synoptic pattern at the start of the long term period will
feature a fairly active northwest flow regime which will allow for a
couple PV anomalies to slide through the region and reinforce an
eastern CONUS trough. However, by the end of the week into this
upcoming weekend mid-level heights will finally begin to rise as a
ridge builds into the central CONUS. This ridging aloft will bring a
highly anticipated warmup to the area this weekend and into early
next week.

A fairly strong but compact PV anomaly will be across portions of
the central Plains Wednesday morning. It will quickly dive southeast
into the southeastern CONUS by Thursday morning. It appears this
track will keep the bulk of the large-scale ascent to the southwest
of the area. Additionally, this track will enable a fairly dry low-
level airmass to remain locked in place over the region. The end
result of these two factors is that much of the region will remain
dry, although a few showers may clip portions of central and
southeast MO on Wednesday as the system passes through.

Quick on its heels will be another trough which will plow through
the area Thursday night into Friday. Guidance differs a bit with the
strength of this system, with the Euro suggesting more of a split
trough whereas the GFS is stronger and more phased. The GEM and the
other ensemble data tend to suggest the GFS is likely an outlier,
thus have favored a weaker solution and have gone with mainly slight
chance pops with this passing trough and associated surface cold
front Thursday night into Friday.

A fairly significant pattern shift then looks to take place by next
weekend as a trough builds into the southwestern CONUS and ridging
takes hold over the Plains and Midwest. As surface ridging slides
off to the east, winds will turn to the southwest and the warmup
will commence especially Sunday into Monday. After highs in the 60s
for the rest of this week, they will push into the 70s this weekend
and perhaps even into the lower 80s by early next week. It appears
the operational GFS and the operational Euro high temperatures are
both on the higher side of their ensembles, so will not get too
carried away on raising temperatures for Sunday into early next week
at this point in time.

Deitsch

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1225 PM CDT Tue Apr 24 2018

Improvement to VFR, particularly at STL metro sites, is expected
by later this afternoon with VFR conditions to then prevail
thereafter for the remainder of the valid period. Northerly
surface winds will also continue, diminishing below 10kts by
tonight. Pcpn chances will remain too lo for TAF mention although
best probs will be later in the morning at COU where a VCSH was
added.

SPECIFICS FOR KSTL: Improvement to VFR expected by late this
afternoon. Otherwise, northerly winds and dry thru the period.

TES

&&

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

$$

WFO LSX


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