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Area forecast discussion 
National Weather Service St Louis MO
344 am CDT Friday Aug 28 2015

Short term: (through late this afternoon)
issued at 340 am CDT Friday Aug 28 2015

Middle and high clouds associated with showers and thunderstorms
continue to stream in across forecast area early this morning ahead
of cold front. Despite low level moisture that will be on the
increase today on southerly flow ahead of the cold front, there is a
lot of dry air to overcome. Feel that best chances of some showers
and a few thunderstorms will be over central and northeast Missouri
as well as west central Illinois, but coverage will be scattered.
Otherwise, temperatures to remain a bit below normal in the low to
middle 80s.


Long term: (tonight through thursday)
issued at 340 am CDT Friday Aug 28 2015

There is good agreement in the 00z guidance that frontal
boundary and associated shortwave should allow thunderstorms
threat to slowly expand over the northwest half of the County Warning Area
tonight...with the stl metropolitan likely on the eastern edge of the
threat during the predawn hours. Due to prognosticated low level
forcing ahead of the front, have upped probability of precipitation into likely category
over our extreme northwest counties.

However...from Saturday morning on features and model specifics
begin to diverge and become increasing nebulous. While models do
agree that northern portion of the shortwave will continue to press
into the lower Great Lakes during the day...they disagree with their
handling of the southern portion of the shortwave energy as it
stretches southeast and possibly merging with another weak
circulation along the Gulf Coast (which appears to originate with
a bit of energy that breaks off from the base of the current East
Coast trof). GFS and NAM suggest some type of remnant circulation
taking up residence in the vicinity of SW MO by Sunday with
residual surface front becoming stationary over the area...while
European model (ecmwf) wants to push the increasingly weak shortwave energy and
surface boundary south with time.

If NAM and GFS solutions do come to fruition on Sunday...and if NAM
low level moisture forecast (which is often too high) also
verifies...then the dry forecast on Sunday will be in jeopardy.
However...would like to see additional support for these weak
features and trends before reintroducing convection on Sunday. So
for now have continued to trend the forecast to the European model (ecmwf)
solution...namely thundestorm chances expanding southeast across the
County Warning Area during the day on Saturday then gradually diminishing from northwest to
southeast late Saturday afternoon and Saturday night.

Despite the discrepancy in the upper air forecasts on Sunday...medium range
solutions remain in good run to run and model to model agreement
that western ridge willl be expanding east into the middle Mississippi
and Ohio valleys during the upcoming week. This should mean dry
weather for the forecast area...along with temperatures rebounding to late
Summer levels with highs in the upper 80s-lower 90s.



Aviation: (for the 06z tafs through 06z Friday night)
issued at 1200 am CDT Friday Aug 28 2015

Except for some River Valley fog between 28/06z and sunrise
(especially at ksus where T-dew point spreads have already fallen to 1
degree), VFR conditions are expected to prevail for the majority
of the taf period. There is a chance of sh/ts late in the taf
period (after 29/03z) ahead of an approaching cold front, but
confidence in the timing/coverage is too low to include in the
tafs at this time. Winds will remain out of the southeast to south.



Preliminary point temperatures/pops:
Saint Louis 83 69 86 69 / 10 20 30 30
Quincy 80 66 81 64 / 20 50 30 10
Columbia 82 67 83 65 / 20 40 20 20
Jefferson City 83 67 84 65 / 20 40 20 20
Salem 82 65 85 67 / 5 10 20 30
Farmington 81 63 84 65 / 5 10 20 20


Lsx watches/warnings/advisories:


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