Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 251749
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1249 PM CDT THU AUG 25 2016
.SHORT TERM... (Through Late Tonight)
Issued at 330 AM CDT Thu Aug 25 2016
Main concern in the short term is thunderstorm chances through
tonight. Thunderstorms that produced radar estimates of 3+ inches
of rainfall over northeast Missouri has already moved out of the
area. With just scattered thunderstorms moving into central Missouri
early this morning, plan on canceling the watch early.
Cold front that currently extends from southeast Iowa into west
central Missouri will move slowly southeast today under the west
southwesterly flow aloft. Thunderstorm coverage this morning will
be isolated as the low level jet veers and low level moisture
convergence weakens over the area. Chances will increase this
afternoon and tonight as a weak vort shortwave moves through the
area and low level convergence increases once again on the nose of
the low level jet. A few strong or severe thunderstorms will be
possible given MLCAPES around 1500 J/kg and deep layer shear near
High temperatures today will warm back up close to normal ahead of
the cold front where mixing will be up to 850mb.
.LONG TERM... (Friday through Wednesday)
Issued at 330 AM CDT Thu Aug 25 2016
The cold front now looks like it won`t get much further south than I-
70 by 12Z Friday. It then begins drifting back to the north and is
forecast to be near the Missouri/Iowa border by 00Z Saturday. Pretty
much all short-range models show this now rather than the more
southerly solution favored yesterday. This probably warrants
bumping PoPs back up to chance category across most of the area.
MLCAPE gets upto 1500-2000 J/Kg according to the GFS Friday
afternoon with 15-25kts of 0-6km shear as well, so storms could
organize into strong multi-cell clusters or lines.
Models more or less continuously print out light QPF for Saturday
through Wednesday next week. With no really strong features in the
mass fields to latch on to and help focus precip chances, I can`t
say that any one period or another will be wetter or drier.
Convection will most likely be highly diurnal with afternoon and
evening being the most active, and then possibily another round of
widely scattered storms during the pre-dawn hours each morning as 10-
15kt 850mb flow forces weak to moderate moisture convergence over
the area. Unfortunately this means we`ll be using a pretty broad
brush to paint chance PoPs across the area through midweek.
Temperatures through the period look to remain seasonably warm with
highs in the 80s and lows in the 60s.
.AVIATION... (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1249 PM CDT Thu Aug 25 2016
An MCV continues to push across northern MO along a cold front
located from UIN southwest to near MCI. This system will be the
focus for renewed thunderstorm development this afternoon/evening.
Have highest confidence in TSRA at UIN, with less confidence due
to lower expected coverage further to the south at the other
sites. Therefore, will continue with just VCTS at these sites and
amend as necessary once convection begins to develop. Outside of
any storm, expect MVFR cigs to continue for the next hour or two
at UIN before lifting to VFR cigs as the thunderstorms approach.
VFR cigs expected elsewhere with WSW winds around 10 knots.
SPECIFICS FOR KSTL:
Convection should develop to the northwest this afternoon and
slowly spread east/southeast through the early evening. A bit
uncertain with thunderstorm coverage along the I-70 corridor, so
will introduce just VCTS for now. Winds will continue out of the
SSW at around 10 knots, slackening tonight. Additional convection
will be possible overnight into Friday morning, but uncertainty
too high to include at this time.
.PRELIMINARY POINT TEMPS/POPS...
Saint Louis 92 75 86 72 / 30 30 30 40
Quincy 83 67 81 69 / 60 20 30 50
Columbia 88 69 83 68 / 40 40 40 50
Jefferson City 89 70 84 69 / 20 40 40 50
Salem 91 71 86 71 / 10 20 30 20
Farmington 90 71 86 70 / 10 30 40 30