Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 151200
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
700 AM 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 12z TAFs through 12z Wednesday Morning)
Issued at 631 AM CDT Tue May 15 2018

SPECIFICS FOR KUIN, KCOU: Isolated SHRA/TSRA are possible before
15/18z, then scattered SHRA/TSRA are expected between
15/18z-16/02z near a slow-moving cold front. VFR conditions are
expected for most of the TAF period, although conditions could
fall to MVFR or IFR if SHRA/TSRA move directly over the terminals.
Some models suggest MVFR ceilings at KUIN during the last 6 hours
of the TAF period, but confidence was too low to include in this
set of TAFs. Initially southwesterly to westerly winds will become
northerly to northeasterly behind the front.

SPECIFICS FOR KSTL, KSUS, KCPS: Isolated SHRA/TSRA are possible
before 15/18z, then scattered SHRA/TSRA are expected between
15/18z-16/02z near a slow-moving cold front. VFR conditions are
expected for most of the TAF period at the St. Louis terminals,
but conditions could fall to MVFR or IFR if SHRA/TSRA move
directly over one of the TAF sites. Initially southwesterly to
westerly winds will become northerly to northeasterly behind the
front.

Kanofsky

&&

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

$$

WFO LSX



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