Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 281720
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1120 AM CST Wed Jan 28 2015

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 341 AM CST WED JAN 28 2015

09Z water vapor imagery shows mid level ridging along the Great
Plains. There are a couple shortwaves upstream of the ridge, one
over northern UT and southern ID with the second over central
Saskatchewan. At the surface, observations show a broad area of low
pressure elongated north to south through the plains. Dewpoints show
a modest increase over the southern plains, but the higher values
appear to be staying over the gulf.

For today and tonight, models show mid levels of the atmosphere
remaining to dry for any precip. This seems to make some sense with
925MB and 850MB profiler data showing winds from the southwest,
which are progged to remain this way through the day. Nevertheless
models pick up an a decent PV anomaly moving over northeast KS this
evening as the shortwave over the Rockies moves out across the
plains. Given that there should not be much in the way of deep
moisture advection ahead of this system, have left the forecast dry.
Although the strength of the PV anomaly suggests the chances for
sprinkles is not zero. As for highs today, the models show the low
level thermal ridge moving into eastern KS this afternoon. The GFS
forecast soundings have done a better job in this semi-arid airmass
we`ve been in for the last several days. So mixing the boundary
layer to almost 850MB continues to support highs in the lower 70s
across east central and northeast KS. The tricky part will be how
much mixing will occur across north central KS as the trough axis
move in this afternoon. With reasonable sunshine filtered by some
high clouds, think highs across north central KS are still likely to
be in the upper 60s. Cold air advection and surface wind speeds
increase behind the front overnight. Models have trended stronger
with the surface pressure gradient showing pressure rises on the
order of 4 to 7 MB in 3 hr into north central KS. This would likely
cause northwesterly winds to gust to near 30 MPH towards daybreak.
With a well mixed boundary layer, lows are expected to only fall
into the mid and upper 30s. The NAM (and to a lesser extent the GFS)
shows the possibility for some stratocu to move into northeast KS
within the cold air advection. With this in mind have increased
cloud cover for the early morning hours.

.LONG TERM...(Thursday through Tuesday)
Issued at 341 AM CST WED JAN 28 2015

As tonight`s shortwave trough exits to the east on
Thursday...gusty north to northwest winds in the morning will
usher in colder air through the midday hours before decreasing in
the afternoon. Highs should top out in the mid 40s under mostly
sunny skies all areas by midday. With the combination of drier air
in place...clear skies and light winds...have lowered low temps
Thursday night into the upper teens and lower 20s. Although warm
advection aloft will begin to develop/increase through the day on
Friday...the cold start to the day and increasing afternoon clouds
may be on offsetting factor...so have kept highs in the low to
middle 40s.

By Friday night...the combination of the exiting high pressure
center to the east and strengthening leeside trough in the high
plains should increase low and mid level warm air and moisture
advection across the region overnight and into the day Saturday.
While the atmosphere will initially be quite dry west to east across
the CWA Friday evening...moisture and warm air advection will start
to saturate through a deep layer overnight. Expect a slight chance
for precip over the north central in the evening...with a chance all
areas overnight. Forecast soundings overnight Friday have trended
warmer from yesterday and while dewpoints on Friday will be in the
teens and lower 20s to start the day...readings may rise to near 30
degrees in the north central by sunrise Saturday. Although not
strong...the warm air advection will persist through the day
Saturday. Therefore...expect rain at this point to be the main
weather element...although with low freeze levels continuing through
the day...certainly cannot rule out some snow mixing in at times.
Models are not in total agreement on the timing of the approaching
upper trough from the high plains...but all do increase lift
substantially across the CWA Saturday afternoon and night as the
cold front plunges into the area. Have increases pops to likely all
areas and transitioned precip type to mainly snow northwest to
southeast Saturday night. All in all...Saturday looks like a
cool...cloudy and wet day across the area with highs in the upper
30s/near 40...then a colder and blustery day Sunday with decreasing
chances for early day light snow west to east. Still expect at least
some light snow accumulations across the area Saturday night...but
amounts will depend highly on how quickly the colder air arrives
before precipitation tapers through the night and early Sunday.
Again...models differ significantly on this with the GFS the slowest
and the EC the faster exit of the system. For now...have trended
more with the GEM which is in between and fairly consistent with
past runs.

Models are in good agreement on the stronger push of cold air into
the area Sunday and Monday with highs mainly in the 20s and lows
Sunday night in the single digits. Weak warm air advection ahead of
another shortwave trough moving across the plains by Tuesday should
help to moderate highs back into the 30s. Confidence on additional
snow chances with this system is low at this time...so have left
forecast dry for now through Tuesday.

&&

.AVIATION...(For the 18Z TAFs through 18Z Thursday Afternoon)
Issued at 1115 AM CST WED JAN 28 2015

VFR conditions expected through the evening hours. Later tonight a
cold front will move through the area causing an increase and
shift of the winds to the northwest. MVFR ceilings will also move
in behind the front. Timing may need adjusting, but there are
indications these clouds persist until around the end of the taf
period.

&&

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

$$

SHORT TERM...Wolters
LONG TERM...63
AVIATION...Sanders






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