Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 300456
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1156 PM CDT Wed Apr 29 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 330 PM CDT Wed Apr 29 2015

Shortwave over southeast Missouri will continue moving south tonight
while the second wave up over the northern Great Lakes region
likewise dives south into the Ohio Valley.  GFS and NAM are pretty
insistent there will be precipitation on the western side of the
wave as the vortmax chain dives south through Illinois.  This looks
reasonable and there this some light rain already showing up on
radar over southern Michigan.  Kept low chance/slight chance PoPs
going east of the Mississippi river for this evening...tapering off
after 06Z.  Temperatures may be a little tricky between the variable
cloudiness which would tend to keep things a little warmer, and
light northerly flow which should provide a little cool advection
tonight.  Bumped temperatures up a bit over guidance to account for
the increased cloud cover, but generally stuck with lows in the mid
to upper 40s.

Carney

.LONG TERM:  (Thursday through Next Wednesday)
Issued at 355 PM CDT Wed Apr 29 2015

(Thursday and Friday)

Another weak ridge of high pressure will build down across the
Mississippi River while upper level ridging develops aloft.  This
should keep the area cooler than today with little or no chance of
precipitation.  Temperatures near normal highs in the upper 60s to
low 70s with lows mainly in the mid 40s look good.

(Saturday through Wednesday)

Upper level pattern will start to transition to a more zonal flow
over the Midwest over the weekend.  The low level ridge will shift
east over the Atlantic Seaboard which should swing our winds around
to the south-southwest.  Guidance has trended a little drier and a
little further north with the best low level baroclinicity, so I`ve
shifted the chances for precip a bit northward from the previous
forecast, but the flavor is still the same.  Increasing chances for
showers and thunderstorms primarily across northern Missouri into
central Illinois into early next week with temperatures rising above
normal into the upper 70s and low 80s.  Models are advertising
another amplified wave over the western CONUS by midweek.  GFS and
ECMWF do print out some precip over the area on Wednesday, but the
timing of the precip will likely change several times over the next
7 days.  Stuck with mid-high chance PoPs with continuing warm
temperatures rather than some of the higher PoPs recommended by
guidance for Wednesday.

Carney

&&

.AVIATION:  (For the 06z TAFs through 06z Thursday Night)
Issued at 1148 PM CDT Wed Apr 29 2015

Main batch of mid clouds is now centered over IL, and with shortwave
energy rotating into base of Great Lakes pushing into IL overnight
most of this cloudiness should remain east of the Mississippi River.

Still appears we will see deep mixing tomorrow afternoon, which
should produce some high-based CU (aoa 5kft) along with north
winds that could gust to around 20kts from time to time. These
clouds and winds should diminish rapidly heading into Thursday evening.

Specifics for KSTL: Patchy mid clouds with bases aoa 10kft expected
overnight, with some diurnally driven, high-based CU (aoa 5kft)
developing by midday Thursday. Light northerly winds overnight
tonight should increase on Thursday morning with the onset of
daytime heating, with gusts up to 20kts possible during peak heating.

Truett

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX





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