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000
FXUS63 KTOP 020544
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1144 PM CST Sun Dec 1 2013

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Monday)
Issued at 306 PM CST SUN DEC 1 2013

By late this afternoon, the region was wedged between surface low
pressure stretching from the Southern Plains to the Great Lakes
region and surface high pressure stationed over the Northern Plain.
A weak cold front continued to shift southward into central Kansas
this afternoon with light and variable winds noted across much of
the forecast area.

As of 20z, water vapor imagery showed the main system we`ll be
focusing on by mid-week approaching the Pacific Northwest. Ahead of
this system, much of the central and eastern U.S. remained under
fairly zonal flow. However, water vapor imagery showed an embedded
shortwave ahead of this system moving eastward across the Northern
Plains. Models keep this shortwave north of the forecast area,
tracking into the Great Lakes region tonight into Monday. The only
impact we can expect here is an increase in mid-level clouds, which
is already apparent on visible satellite with a nose of mid-level
clouds stretching southward into northwest Kansas this afternoon and
should continue to spread eastward into the forecast area tonight
through Monday morning.

For tonight, surface high pressure will overspread the region from
the north, with winds becoming light out of the southwest. Despite
some periods of scattered mid-level clouds from the passing
shortwave, several short-range models are continuing to show an
increasing potential for some fog development late tonight into
Monday morning, particularly across extreme eastern Kansas and
western Missouri. Similar to this morning, some localized dense fog
will be possible, especially over extreme east central Kansas. We
will continue to monitor this threat through the evening and
overnight hours.

By Monday morning, the strong mid-level low should be moving into
the Pacific Northwest, with the associated surface low pressure
system being pushed eastward into the Northern Plains and nosing
southeastward toward the Central Plains. With this advancing surface
low to the northwest and surface high pressure over much of the
eastern U.S., light southwesterly winds will be in place over the
area. This southwesterly flow will aid in some waa into the region
with afternoon high temperatures expected to rise into the upper 50s
to low 60s, which is 10F to 15F degrees above the seasonal normals.

.LONG TERM...(Monday Night through Sunday)
Issued at 306 PM CST SUN DEC 1 2013

An upper level trough across the northwest US will dig southeast
across the western US and phase with a second upper level trough
digging southward across west-central Canada. This will create a
longer wave length positive tilt upper level trough that will
extend from south central Canada, southwest into the extreme
southwestern US by Thursday.

Strong CAA will develop across the northern plains Monday night into
Tuesday and will cause an arctic front to move southward across the
central plains Tuesday morning and across the southern plains by
Tuesday evening. The 12Z NAM model shows the front moving across the
CWA Tuesday afternoon. This is about 4 to 6 hours faster than the
GFS and ECMWF. The NAM model usually handles the barrier jet
formation of accelerating arctic cold front down the high plains
better than other numerical models. So, I`m going with the faster
NAM FROPA solution, highs on Tuesday will occur in the mid and
late morning hours across the northwest counties of the CWA, most
likely the upper 40s to around 50 with falling temperatures
through the afternoon hours. Highs across northeast and east
central KS will reach the upper 50s to lower 60s ahead of the cold
front during the early afternoon hours, then temperatures may fall
back into the 40s by late afternoon. The low-levels of the
atmosphere look too dry for any type of precip ahead or behind the
surface cold front as the strong ascent ahead of the broad H5
trough will remain well west and northwest of the CWA.

Tuesday Night through Saturday, looks quite frigid as the arctic
surface ridge builds southward across the central and southern
plains. The positive tilt H5 trough across the west central conus
will shear apart with the main upper trough lifting northeast across
the upper Midwest and the southwest section of the H5 trough moving
east across TX and OK. There may be enough ascent for some periods
of light snow or snow flurries Wednesday night into Friday morning
across the CWA. Snow amounts will be less than as inch as the better
frontogenetical forcing, moisture and instability remains well south
across OK into AR and southern MO, where accumulating snowfall may
be possible Thursday night into Friday morning.

Highs on Wednesday will only reach the lower to mid 30s. As the
center of the arctic ridge builds southward, highs Thursday through
Saturday will only reach the lower 20s with upper teens along the NE
border. Overnight Lows will be in the teens with single digits
possible Saturday morning.

Sunday...the Arctic surface ridge will slide east into the MS river
valley. An H5 trough will dig from the Pacific Northwest across the
west-central conus. There may be a slight chance of light snow as a
weak H5 trough lifts northeast across the plains along with WAA
providing some additional ascent. The best chances for measurable
snowfall will occur across NE and spread northeast across IA into MN.
Highs may warm slightly into the mid to upper 20s.

&&

.AVIATION...(For the 06Z TAFs through 06Z Monday Night)
Issued at 1144 PM CST SUN DEC 1 2013

Low cloud and fog continues to advect north to northwest, though
perhaps slowing a bit on its western flank. Even given the
possible slowdown, still appears LIFR to VLIFR conditions in FG
will impact KTOP and KFOE around 10Z with improvements likely
holding off until at least 14Z, but veering winds by this time
could bring a quicker improvement. These veering winds should keep
conditions at KMHK much higher, with high clouds helping keep
radiation fog in check.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY until 9 AM CST Monday FOR KSZ056-058-059.

DENSE FOG ADVISORY until 9 AM CST Monday FOR KSZ040-054-055.

&&

$$

SHORT TERM...Hennecke
LONG TERM...Gargan
AVIATION...65