Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 272252
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
552 PM CDT Wed Aug 27 2014
.SHORT TERM: (Through Late Tonight)
Issued at 344 PM CDT Wed Aug 27 2014
Area of showers and thunderstorms over northern Missouri has almost
totally dissipated as of 20z, and convection has refocused to to the
south and east along the outflow boundary produced this morning by
convection over northern Missouri, as well as the very ill-defined
remains of the surface frontal boundary. Storm coverage should
remain scattered due to upper level ridging over the area, but
continue to monitor the stronger storms for an isolated/pulse-type
severe weather threat over the next hour or two.
With no upper support, expect this largely diurnally-driven
convection to dissipate this evening with loss of heating, with
thunderstorm threat once again shifting back to our northwest
overnight. Shortwave topping ridge and the associated low level
forcing/warm advection should lead to a a fairly large convective
complex forming over the mid Missouri River valley (northwest of our
FA) during the predawn hours. While the bulk of this activity
should remain northwest of our forecast area, there should be some
threat of convection in northern sections of our CWA, either from
the leading edge of this activity, or perhaps from additional
convection that will attempt to form in the very weak zone of low
level warm advection in advance of the complex.
.LONG TERM: (Thursday through Next Wednesday)
Issued at 344 PM CDT Wed Aug 27 2014
Nocturnal convection should be winding down during the morning, but
not before producing some thunderstorms over parts of central and
northeast Missouri. It looks like the main area of precip will be
further west over northwest Missouri again nearest to the low level
baroclinic zone. With lingering cloud cover and the upper level
ridge slowly breaking down, expect that temperatures will be cooler
Thursday than in recent days. With highs ranging from the mid 80s
to around 90 instead of mid 90s, it looks like heat index values
will miss the magic 100 degree mark by 2-3 degrees in most
locations. While still hot and humid, it should feel...less bad.
Expect widely scattered afternoon thunderstorms to help keep a lid
on temperatures as well. Will therefore let the heat products
expire on schedule this evening.
Thursday night and Friday will be a repeat of tonight and Thursday
as a weak low level jet provides just enough lift to potentially
force some isolated to widely scattered convection. With overnight
lows in the upper 60s to mid 70s and highs Friday in the mid 80s to
around 90, we should be able to stay heat-headline free.
Additionally, the trof of low pressure currently spinning over
southwest Wyoming will be moving into the eastern Plains
Friday/Friday night which will further weaken the upper level ridge
and allow more widespread convection late Friday afternoon and
Friday night primarily over central and northeast Missouri. The
trof will be directly over the CWFA Saturday which should continue
to produce thunderstorms and keep temperatures suppressed in the 80s.
Another stronger trof will dig into the Great Plains on Sunday.
This will keep the upper ridge at bay and continue to keep
temperatures in the 80s. Can`t rule out a few afternoon
thunderstorms Sunday as well since the upper ridge will be well to
our east. The trof continues eastward Sunday night and Monday which
will bring us increasing chances for rain. medium range models are
in decent agreement regarding the cold front associated with the
trof. It should push into the CWFA late Monday afternoon/Monday
evening and bringing the threat of more thunderstorms to the area.
Models stall the front out over southern Missouri Tuesday and then
allow it to creep back to the north Wednesday. This won`t be a big
blast of cold air behind the front...rather just enough cool air to
bring temperatures down to near or slightly below seasonal normals.
.AVIATION: (For the 00z TAFs through 00z Thursday Evening)
Issued at 525 PM CDT Wed Aug 27 2014
Most of the convection impacting the St Louis metro area should
dissipate early this evening with the loss of daytime heating.
Mainly just mid-high level clouds for the remainder of the night
with most of the nocturnal convection remaining north of the taf
sites, although there may be a few storms impacting the UIN area
towards morning. There will likely be some fog late tonight/early
Thursday morning in COU and the St Louis metro area with light
surface winds and high surface dew points, particularly in areas
which had recent rainfall. Surface winds will pick up from a sely
direction on Thursday as the surface ridge centered over the Great
Lakes region shifts slowly eastward. Scattered diurnal cumulus
clouds will develop again late Thursday morning and afternoon
along with at least isolated afternoon and early evening
Specifics for KSTL: Thunderstorms should dissipate early this
evening, by 01z or 02z. Mainly just mid-high level clouds for the
remainder of the night with fog possible late tonight/early
Thursday morning. The surface wind will diminish and become light
later this evening, then pick up to around 8 kts Thursday
afternoon from a sely direction. There will likely be isolated to
scattered thunderstorms Thursday afternoon into the early evening.
.PRELIMINARY POINT TEMPS/POPS:
Saint Louis 76 91 76 90 / 30 40 20 20
Quincy 69 87 71 88 / 20 50 30 30
Columbia 72 92 71 88 / 20 30 20 40
Jefferson City 72 92 72 89 / 20 20 20 40
Salem 71 89 71 89 / 30 40 30 20
Farmington 71 90 70 88 / 30 20 10 20
MO...HEAT ADVISORY until 8 PM CDT this evening FOR Audrain MO-Boone
MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
Iron MO-Madison MO-Moniteau MO-Montgomery MO-Osage MO-
Reynolds MO-St. Francois MO-Ste. Genevieve MO-Warren MO-
EXCESSIVE HEAT WARNING until 8 PM CDT this evening FOR Jefferson
MO-Lincoln MO-St. Charles MO-St. Louis City MO-St. Louis MO.
IL...EXCESSIVE HEAT WARNING until 8 PM CDT this evening FOR Bond IL-
Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-
Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
Randolph IL-St. Clair IL-Washington IL.