Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...updated 
National Weather Service St Louis MO
857 PM CST Monday Nov 30 2015

issued at 855 PM CST Mon Nov 30 2015

In the process of making generally minor tweaks to forecast to
reflect latest surface ob, radar and satellite trends. Primary
pops (in the chance category) for the remainder of the night
should be along and ahead of front/wind shift line, although with eax's
88d imagery is still indicating spotty -ra exiting kc Metro will
maintain slight chance pops in the wake of the wind shift until
low clouds begin to break up.

Regarding clouds...clearing line has just worked across the MO/Kansas
border in west central MO over the last hour. Extrapolation of
the clearing based on low cloud satellite imagery suggest clearing
working into mid MO between 05-06z, and reaching stl Metro in the
08-09z time frame. Lower clouds rotating around the upper low over
the mid Missouri Valley may spin their way back into our far
northern counties, so sustained clearing in this part of our County Warning Area
not as certain as the clearing expected along and south of the i70



Short term: (through late tonight)
issued at 245 PM CST Mon Nov 30 2015

Upper level low over Nebraska will move northeastward into northwest
Iowa later tonight with its associated surface low over northeast
Nebraska moving into southwest Minnesota. The surface low will drag
an occluded front eastward through our forecast area this evening.
The best chance of measurable rain should occur across west central
Illinois with mainly just a little light rain or intermittent drizzle
elsewhere, mainly this evening. The rain and drizzle will finally
come to an end late tonight as the dry slot moves northeastward into
the area south of the upper level low, along with low level drying
behind the occluded front. Should be some clearing late tonight
into central MO. Low temperatures tonight will be a little colder
than the previous night across northeast and central MO and west
central Illinois as lower surface dew points advect southeastward into
this area.


Long term: (tuesday through next monday)
issued at 245 PM CST Mon Nov 30 2015

Clouds are expected to clear from most areas during early Tuesday
morning, and from all areas by late morning. With plenty of
sunshine in its wake, a breezy west-southwest surface flow which should
promote relatively deep mixing for this time of year, and only
a weak push of cooler air behind passage of the occluded front
the previous night, should see a robust temp recovery for areas near
and south of I-70. Started with the highest MOS values for daytime
Max temps, and adjusted another deg or two higher for areas near
I-70 and south.

An actual cold front will move thru Tuesday night and should at
least bring with it increasing clouds, including a field of low
clouds. Of perhaps more interest is in addition there will be a
strong upper level disturbance rotating around the southern
periphery of the still wound-up storm system to our north that will
track thru much of our northern County Warning Area later Tuesday night and
Wednesday morning. While the column will be rather dry overall,
the forcing/upper level support provided by this feature along with
cyclonic flow at the low levels and the likely presence of a field
of low clouds should at least provide for the potential of a seeder-
feeder setup and the threat for falling pcpn from this. While
keeping pops for measurable pcpn low at this time, have introduced
the mention of pcpn into the forecast beginning late Tuesday evening
thru late Wednesday morning. The atmosphere will be cold enough for
any pcpn to fall as snow--the only mention of snow in this forecast
package. For now have drawn the southern boundary of the flurries
mention to just north of a Mexico, MO to Salem, Illinois line.

Otherwise, after one day of below average temps on Wednesday
following passage of the cold front Tuesday night, we should then
see an extended period of above average temps Thursday thru early
next week with a synoptic pattern that keeps the cold air locked
up well to the north. Friday and Saturday look especially favorable
for well above average temps, where some locales may see low 60s.

On a side note during this period, the models seem to have come into
better agreement on handling of the development of a storm system
for the southeastern Continental U.S. On Thursday, and largely making it a
non-issue for our area.

Another strong Pacific storm system still looks set to become cutoff
and affect our area for early next week, with slower timing
preferred amongst the models considering a jet stream ridge will be
also developing over the central Continental U.S.. should hold off until after
the weekend, and we have it impacting our area instead on Monday.



Aviation: (for the 00z tafs through 00z Tuesday evening)
issued at 559 PM CST Mon Nov 30 2015

IFR ceilings and occasionally visibility in fog and patchy drizzle will
continue to prevail tonight ahead of a cold front. Expect visibility
to improve quickly after a cold front sweeps through the region
later this evening and overnight. IFR ceilings will likely persist
for a few hours behind the front, but should be lifting to MVFR
and then scattering out from west to east through the pre-dawn and
early morning hours of Tuesday. West-southwest flow and VFR flight
conditions will prevail on Tuesday after the ceilings scatter out.
Wind will gust to 20-25kts at times late Tuesday morning into the

Specifics for kstl:

IFR flight conditions will prevail at Lambert ahead of a cold
front which will sweep through the terminal between 05-06z. Should
see visibility improve quickly behind the front as wind shifts to
the west-southwest bringing in drier air. Some uncertainty tho on
how long IFR ceilings will prevail... with drier air moving in,
ceilings should start to rise and observations over western
Missouri bear this out. Timing is uncertain though...and the
current taf will likely need tweaking as trends become more clear.
West-southwest flow and VFR flight conditions will prevail on
Tuesday after the ceilings scatter out. Wind will gust to 20-25kts
at times late Tuesday morning into the afternoon.



Lsx watches/warnings/advisories:


Weather forecast office lsx

National Weather Service Glossary of Abbreviations