Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 171030

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
530 AM CDT MON OCT 17 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 245 AM CDT Mon Oct 17 2016

Our region remains sandwiched between a strong RIDGE over the south-
central and southeastern CONUS, and streams of Pacific upper level
disturbances tracking to our north in a west-southwest flow.  At the
surface, a tight pressure gradient is resulting in a moderate
strength sustained wind from the south with periodic gusts.  This
southerly flow, despite the mostly clear skies, has kept
temperatures quite warm for this time of year, with current readings
in the upper 60s and lower 70s.  An axis of a 45-50kt low level jet
extends from southeast KS to northeast MO.

Various high-res discrete models are hinting that the low level jet
may be enough to break thru the convective cap early this morning
that is currently in place over parts of northern MO and central IL,
but lower cloud field has been fading, if anything, so this window of
opportunity may be closing for now.  Something to monitor over the
next several hours.

Otherwise, main story today will be the unseasonably warm temps
expected and the strong and gusty south-southwest winds.

Very warm start to the day, with anticipated 12-13z temps near
or above current high low records (see CLIMATE section below), and
with conditional climo supporting diurnal swings of at least 20-25
degrees due to strong south winds and clear skies, max temps in the
upper 80s and lower 90s should be very attainable, matching or
exceeding records at all sites (STL, COU, UIN).

Speaking of the strong south winds. between the tight pressure
gradient and the support of the H925 low level jet, should see gusts
of at least 30-35mph areawide by late morning and thru much of the
afternoon, with the strongest anticipated gusts near the low level
jet axis, covering parts of central and northeast MO and west-
central IL, where max gusts should be around 40mph.  This is just
below Advisory criteria of 45mph so wind headlines not currently


.LONG TERM...  (Tonight through Sunday)
Issued at 402 AM CDT Mon Oct 17 2016

A cold front will drop southeastward into our forecast area on
Tuesday.  With only shallow moisture and little upper level forcing
there should only be isolated showers along this front. Although
high temperatures will be a little cooler on Tuesday they will still
be about 10 to 15 degrees above normal.  Should see more coverage of
showers and a few storms along the front Tuesday night as it becomes
nearly stationary across southern portions of MO and IL.  The
coverage of showers and storms should continue to increase on
Wednesday and Wednesday night as a deepening upper level trough
approaches and induces a weak surface wave along the front  The
front may lift back north slightly on Wednesday as the trough
approaches.  The NAM model appears a little too far south with this
front and a little deficient with its QPF and prefer the GFS and
ECMWF solutions.  Will continue to see a gradual cooling trend.
Should only be some lingering post frontal showers or rain across
southeast MO and southwest IL Thursday morning.  Much colder
temperatures can be expected Thursday and Thursday night as the deep
upper level trough moves eastward through our area and a strong
surface ridge builds southeastward into the region behind the cold
front. Temperatures should be slightly below normal by Thursday
night and feel quite cold after the current stretch of unseasonably
warm weather.  Dry weather can be expected for the rest of the work
week and the weekend with a warming trend on the weekend as an upper
level ridge approaches from the southern Plains leading to rising
upper level heights over the forecast area.  Also the surface wind
will become southerly as the surface ridge shifts east of the area.



.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 530 AM CDT Mon Oct 17 2016

VFR conditions, southerly surface winds, and dry wx will prevail
at the TAF sites thru the valid period. Strong wind gusts of 25 to
35kts can be expected from late morning thru much of the
afternoon as a persistent low level jet mixes down to the surface.
These gusts should disappear by nightfall and be replaced with
LLWS for much of tonight. A surface cold front will be just
upstream of UIN and COU by the end of the valid period and just
west of STL by the end of its 30-hour valid period.



Issued at 245 AM CDT Mon Oct 17 2016

Unseasonably warm conditions are expected to persist through
Tuesday and may approach record territory. The following lists
record high temperatures and record high minimum temperatures for
St. Louis, Columbia and Quincy during these times.

St. LouisColumbiaQuincy

10/17High Low:66/199864/196566/1935

Tuesday High:87/195386/195387/1924
10/18High Low:68/198564/197166/1938




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