Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 151806
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
106 PM CDT Tue May 15 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 405 AM CDT Tue May 15 2018

A cold front stretched from KS through northern MO and into
southeastern IA at 08z, and it is forecast to slowly sink S/SE today
and tonight due to a ridge of high pressure extending into the Great
Lakes. This boundary has consistently provided a focus for SHRA/TSRA
over the last few days, and today should be no exception. Isolated
to scattered convection is expected to develop once again today
invof the front while the boundary remains over the region. The
highest chances for SHRA/TSRA appear to be during afternoon peak
heating and into the early evening hours. Unlike the last few
nights, no LLJ is forecast to impinge upon the boundary (H85 winds
will be northeasterly to northerly due to the ridge axis), therefore
the chance of rain should be much lower overnight tonight compared
to locations near the boundary on previous nights.

Highs today will range from the upper 70s in northeastern MO to the
upper 80s in southeastern MO, which will be several degrees cooler
than the last few days but still unseasonably warm. Lows tonight
should be similar to or a few degrees cooler than last night.

Kanofsky

.LONG TERM...  (Wednesday through Monday)
Issued at 405 AM CDT Tue May 15 2018

Models have been trending the western CONUS Rex-block to possibly
persist thru this weekend and beyond, which if realized, will tend
to keep a flatter upper flow over our region as well as make it open
to intrusions by upper level disturbances shooting eastward from the
LO component of the block.  This will keep a generally active
weather pattern going for our region thru these disturbances and the
only other item to evaluate will be if available moisture,
especially at the low levels, will be sufficient to justify PoPs.

By Wednesday morning, the main surface cold front should have pushed
to the south of the forecast area, with a drier northeast to east
low level flow in place behind it for our region.  This will make
rain chances overall harder to come by and confine the best rain
chances to our far southern or southeastern forecast area.  This
regime should continue from Wednesday thru Friday with influence of
the large high pressure system to our northeast to be maintained.
Temperatures look to be above average thru Friday, but not as
unseasonably hot as what we saw this past weekend with either
clouds/rain or the frontal boundary being to the south contributing
to greater moderation towards climatological normals.

Models are still trying to develop an attempt at an upper RIDGE into
the Mid-Mississippi Valley heading into the upcoming weekend, but
looks to be short-lived with additional disturbances approaching
from the west from the established, yet cycling, Rex-block in place.
The old surface front to our south will also begin to buckle back to
the north on Saturday and the additional moisture expected to yield
from that and the approach of the next upper level disturbance
should result in the return of more widespread PoPs into our region
late Saturday and into Sunday with the cold front then slowly
pushing thru.  PoPs may linger into Monday depending how
successfully the front can push southward.  Temperatures are
expected to trend higher for the weekend with a more favorable warm
pattern in place but this looks to be short-lived thanks to the cold
front and its associated clouds/rain chances then pushing thru on
Sunday.

TES

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1246 PM CDT Tue May 15 2018

Variable flight conditions are expected across the area through
Wednesday morning. An upper level disturbance is moving across
Missouri into Illinois. A few showers are are moving across the
forecast area...and the areal coverage is expected to increase
this afternoon into the evening due to daytime heating. Some of
the showers will probably grow into thunderstorms as well. Expect
generally VFR conditions this afternoon and evening, but there are
some lower clouds moving south through central Illinois and
northeast Missouri. Additionally, any showers or storms that
affect the area will be capable of producing MVFR/IFR flight
conditions.

A weak cold front is drifting through the area. A band of
MVFR/IFR ceilings is likely to form north of the front tonight
and affect parts of central, southeast, and east central Missouri
as well as southwest Illinois early Wednesday morning. Lower
ceilings will probably last until at least 16-18Z.

SPECIFICS FOR KSTL:

Expect VFR flight conditions to prevail at Lambert through this
afternoon into tonight. Showers will continue to move near the
airport through the afternoon into the evening...and there might
be a thunderstorm as well...though this is less likely. MVFR
ceilings are likely to form north of a weak cold front which is
passing through the region at this time. There is also a
possibility that the ceilings could drop to IFR before daybreak.
Low flight conditions will likely prevail until late morning or
early afternoon.

Carney

&&

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

$$

WFO LSX



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