Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 242028

Area Forecast Discussion
National Weather Service Saint Louis MO
328 PM CDT FRI JUN 24 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 324 PM CDT Fri Jun 24 2016

At 19z, the old frontal boundary that moved thru our region
yesterday remains across southeast MO and far southern IL, but has
since buckled northward towards central MO further to the west.  A
persistent old convective vorticity center aloft has maintained an
area of showers across parts of southeast MO today but is showing
signs of diminishment with time.  Another disturbance aloft is
maintaining showers and a few TSRA over eastern KS.  Despite most of
our region being north of a frontal boundary, temps have still
managed to climb into the 85-90 range for most locations, except
remaining in the 70s in parts of southeast MO where the persistent
showers were located.

Model guidance both weakens and exits the old convective vort to our
south late today with any rain chances then coming from the slowly
approaching warm front, although lift here is expected to be weak
and there should be somewhat slightly better rain chances after
midnight with the disturbance aloft from KS approaching from the
west. Model guidance does weaken this feature as it propagates
east and with not exactly the best coverage currently in eastern
KS, is a big question mark on how much coverage of pcpn it will be
able to result for Saturday when it moves thru. Kept chance
category PoPs for this period given the uncertainty and lack of
confidence, with better chances during the afternoon with diurnal
influences more prevalent.

Otherwise, MOS min temps in the low-mid 70s look tough to beat with
a MOS blend preferred for Saturday, which will yield max temps in
the 90-95 range for most sites.  Humidity will make a return
Saturday with passage of the warm front, but indications of a lot
of convective debris clouds and the persistent threat for rain
should prevent temps, and thus heat index values, from getting
high enough to warrant a Heat Advisory. A change to a drier,
sunnier forecast will almost mandate it, though.


.LONG TERM...  (Saturday through Next Friday)
Issued at 324 PM CDT Fri Jun 24 2016

(Saturday Night - Monday)

Slight chance of showers and thunderstorms on Saturday evening for
areas along/east of the Mississippi River in the vicinity of old
frontal boundary/convergence zone moving off to the east. Synoptic
cold front attendant from a sfc low moving through south-central
Canada will move into northern portions of the CWA late Saturday
night bringing a chance for showers and thunderstorms. Leaned a bit
toward a slower fropa into the CWA and would not be surprised if
front ends up slowing down a bit more over the next 24-36 hours.
Lows ahead of this boundary will be quite mild once again with lows
across the area in the 70s.

Chance of showers/storms will move slowly south and east with the
cold front during the day on Sunday. Deep layer shear will be very
modest (on the order of 10-20 knots) but high instability could be
enough to compensate and produce a couple of strong to severe
thunderstorms with strong winds the primary threat.

Temperatures on Sunday will be tricky as exact timing of frontal
passage will be key in addition to the amount of sky cover and
coverage of storms. Current thinking is that there should be enough
clouds to limit the temperatures from rising high enough to create
heat index readings from reaching advisory (105+) levels...but if
temperatures are a bit warmer than currently forecast...heat index
values would likely approach if not exceed 105 degrees as dewpoints
are expected to be in the low to mid 70s pooling along the front.

Dry weather is expected on Sunday night and Monday. Airmass behind
this front has no teeth to it so highs on Monday will actually be as
warm if not warmer than on Sunday. should feel a bit
nicer as dewpoints drop 5+ degrees compared to those expected on

(Tuesday - Next Friday)

Large scale pattern will undergo amplification heading into the
middle of the next work week. Another cold front will swing through
the area on Monday night and will bring much cooler and less humid
air into the mid-Mississippi Valley for Tuesday. Below normal
temperatures will should then remain across the area for the rest of
the week. Next chance of widespread rainfall looks to be Wednesday
night/Thursday timeframe but uncertainty with track/timing of
shortwave embedded within NW flow aloft precludes PoPs any higher
than chances at this time.



.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1235 PM CDT Fri Jun 24 2016

VFR conditions will prevail at the TAF sites thru the valid
period. An old frontal boundary over southern and western MO will
gradually buckle back to the northeast as a warm front late this
afternoon thru Saturday, and will result in the potential for
showers and thunderstorms tonight and Saturday. Currently, the
probs are too low for mention in the TAFs at all sites save COU,
where a VCTS has been introduced. A VCxx group may need to be
added to the other sites as needed once convection coverage can be
better verified. Otherwise, light winds will become easterly
tonight and veer south-southeast on Saturday.





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