Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 301734
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
1134 AM CST Wed Nov 30 2016

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 259 AM CST Wed Nov 30 2016

Mid/upper level low pressure continues to spin over the upper
Midwest as it slowly progresses eastward. A weak shortwave is
currently rotating around the backside of low pressure. This wave
will track over portions of NE and IA as it will ultimately
reinforce another shot of cooler air. The cooler temperatures and
wrap around moisture has supported an expansive area of low to mid
cloud cover, which is spreading southeastward this morning. The
forecast area appears to remain on the southern edge of this cloud
shield for most of the day and into the evening. Therefore highs
today will struggle to reach the low to mid 40s. The low pressure
system has kept the pressure gradient from relaxing over the plains
so expect another windy day today as surface mixing begins.
Northwest winds will be around 15 to 25 mph with gusts up to 35 mph.
Later this evening and overnight the clouds should clear out allow
for some radiational cooling and decoupling of the winds off the
surface. This along with the cooler air mass will support lows in
the 20s with the coldest temperatures in central KS.

.LONG TERM...(Thursday through Tuesday)
Issued at 259 AM CST Wed Nov 30 2016

Wednesday night through Friday night, An upper level trough will move
onshore across the western coast of the US, then dig and amplify
southeast into northern Mexico. The zonal mid-level flow across
central and southern plains will become southwesterly ahead of the
upper trough digging southeast into northern Mexico. Expect dry
conditions with highs in the mid to upper 40s and overnight lows in
the 20s.

Saturday through Sunday, The extended range model solutions diverge.
The ECMWF and GEM lift the the northern Mexico H5 trough northeast
into southwest TX where if phases with a norther stream H5 trough
moving east across the central high plains. If both of these
solutions were to verify we would see more widespread light rain on
Saturday which would mix and possibly change over to light snow
Saturday night into Sunday morning as the forcing ahead of the more
amplified trough cools the temperature profiles aloft below
freezing. This would provide the CWA with the potential for a light
snow accumulation of 1 to 2 inches. The GFS solution keeps the
southern stream upper level trough as a closed low across northern
Mexico and moves a weak open H5 trough across the central plains on
Saturday. The GFS solution would provide a chance for rainshowers
Saturday into Saturday evening and if the colder air moves southeast
across the CWA during the late evening and early morning hours then
the light rain may be mixed with snow before ending, or if the mid-
levels are dry there could be some spotty freezing drizzle early
Sunday morning before the weak open upper trough shifts east of the
CWA.

Sunday night through Monday night, another upper level trough will
move onshore across the western US and dig southeast across the
desert southwest. Monday may be the warmest day of the forecast
period with highs in the upper 40s to lower 50s. As a lee surface
trough develops across the high plains and causes the low-
level winds across eastern KS to be southerly.

Tuesday through Wednesday, the 00Z GFS solution has a much more
amplified solution with a deep upper trough lifting northeast across
the plains Tuesday night through Wednesday night. The GFS shows the
potential for a winter storm across eastern KS with significant
snowfall possible. However, the 00Z ECMWF came in with a less
amplified solution and is much more progressive moving the upper
trough east across the central and southern plains. The ECMWF shows
all the moisture remaining well southeast of the CWA with dry
conditions for the same period. The 00Z run of the ECMWF is much
different from the previous 12Z run that showed an amplified upper
trough lifting northeast across the plains and a potential heavy
snow band extending from western KS, northeast across north central
KS, and then northeast into the IA and WI. We`ll watch the next
several model runs and see if both extended range models can
converge on a solution.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1134 AM CST Wed Nov 30 2016

Main concern is the potential for MVFR-level cloud to move back in
from the northwest. Observations suggest the models are not
handling this too well. Went ahead with a TEMPO high MVFR deck in
the next several hours.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Sanders
LONG TERM...Gargan
AVIATION...65


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