Area Forecast Discussion
Issued by NWS St. Louis, MO

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884
FXUS63 KLSX 231749
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
1249 PM CDT Sat Sep 23 2017

.UPDATE...
Issued at 1249 PM CDT Sat Sep 23 2017

Added in slight chance PoPs for areas in northeast, central,
southeast MO and western portions of STL metro where this looks to
be the more probable area where SHRA/TSRA will form. Otherwise,
temps on target for another day of much above average temps in the
90s. Due to the more easterly direction of surface winds, temps
should be a deg or two less than persistence.

TES

&&

.SHORT TERM...  (Through Late Tonight)
Issued at 349 AM CDT Sat Sep 23 2017

Summer-like weather pattern will continue today and tonight.  Upper
level ridge extending from eastern OK northeast through MO to
southern MI will gradually shift northeastward into the OH Valley
region tonight.  Our forecast area will continue to be on the
western periphery of a surface ridge centered over the northeastern
US.  Unseasonably warm temperatures will continue today and tonight.
Highs today will be at least 15 degrees above normal for late
September, and close to record highs for this date.  The highs today
will be similar to yesterday, maybe a degree or two cooler due
mainly to more diurnal cumulus clouds expected this afternoon. It
will be humid, although some of the guidance does indicate some
lowering of the surface dew points this afternoon due to daytime
heating, mixing and drying.  Could not rule out an isolated
afternoon shower, but it appears the CAMS are overdone with their
spotty small showers their developing today.  Prefer the dry
operational model guidance of the NAM and ECMWF models.

GKS

.LONG TERM...  (Sunday through Friday)
Issued at 349 AM CDT Sat Sep 23 2017

The synoptic pattern at the start of the long term period will
feature a fairly amplified upper-level regime, with a deep trough
across the western CONUS and a downstream ridge over the
central/eastern portions of the country.  This pattern will
deamplify by the end of next week as the western trough moves into
the north-central CONUS.

The generally benign and seasonably warm pattern will likely persist
through early Tuesday.  While a stray storm cannot be ruled out in
southeast/central MO Sunday or Monday, think most areas remain dry
and hot through Monday.  Temperatures will continue to top out in
the upper 80s to low 90s, making for a fairly impressive stretch of
warm weather in September.

The upper-level trough will attempt to push east/northeast by
midweek, helping to push a surface cold front into the area Tuesday
into Wednesday.  However, this front will become increasingly
displaced from the better upper-level ascent associated with passing
PV anomalies within the trough to the northwest. This lack of
forcing coupled with fairly meager low-level moisture will keep any
thunderstorm activity isolated to widely scattered Tuesday into
Wednesday.

While the front won`t bring much in the way of rainfall (which is
becoming needed across the area), it will bring a return to more
seasonal temperatures.  After the streak of upper 80s/low 90s
through Tuesday, Wednesday into the end of next week will feature
highs returning back to the 70s.

KD

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1242 PM CDT Sat Sep 23 2017

VFR conditions and light southeasterly surface winds will prevail
at the TAF sites thru the valid period. Patchy fog may once again
briefly impact SUS and CPS, but will wait a few more hours before
including, to see realized crossover temps. Isolated TSRA/SHRA
anticipated to form in central and southeast MO but probs too low
for TAF mention at this time but will bear watching. A similar
setup expected for Sunday afternoon.

TES

&&

.CLIMATE...
Record Max Temperatures Through Saturday

              KSTL  KCOU  KUIN
Sept 23     94 (1891)   94 (2007)   95 (1937)
Sept 24     94 (1891)   95 (1891)   94 (1935)


Record High Min Temperatures Through Saturday

              KSTL        KCOU        KUIN
Sept 22     73 (2005)   71 (2005)   71 (1930)
Sept 23     73 (1884)   73 (1937)   73 (1937)


&&

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

$$

WFO LSX



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