Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 210547
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1147 PM CST Thu Nov 20 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Friday)
Issued at 240 PM CST THU NOV 20 2014

A few hours of light freezing drizzle could make for a slick commute
on Friday morning.

Abundant sunshine across the forecast area today, as high pressure
moves along and just east into Missouri.  High temperatures have
reached into the 40s, save the far northeastern counties which are
likely still cooler due to close proximity to the high center, and
with light northeast flow off what remains of melting snow to our
northeast.

For tonight, quiet weather expected this evening and for much of the
overnight before the next clipper wave lifts out of the Texas
panhandle and into our area early Friday. This will bring a chance
for freezing drizzle / drizzle as it does so.  290 K isotropic
chart compared to sounding temperatures suggest that it will be a
race between how fast the mid level air moving northward can
saturate and how fast the lower levels can warm up. The 18z run of
the NAM appears to saturate slightly slower than the 12z run, which
would bode for a shorter window in the freezing drizzle variety.

At this time, thinking is that southern counties will see a chance
for freezing drizzle generally starting around 7-8am, with surface
temperature changing over around 10am to back above freezing.  Lift
is also slightly stronger over this area as is QPF, although still
less than a 10th of an inch, some of which will fall as just plain
drizzle.  Along I70, counties warm to around freezing in the
10 to 11am window, and if later run verifies and freezing drizzle
starts more toward 8 or 9am, this window of opportunity for freezing
drizzle will be short before temperatures rise.  However with cold
overnight lows in the lower 20s, and frost depth here at the office
still an inch, even as temperature of the droplets rises above
freezing, have some concerns that roadways and elevated surfaces may
need a little more time to respond to this rise, especially in the
absence of strong sunshine to aid in surface insolation.  By the
time drizzle makes it to the northern border, also think surface
temperatures will have risen to above freezing as well.  Drizzle
continues through the afternoon hours, with temperatures overall
rising into the upper 30s to low 40s.  The wave that brings the lift
is on the eastern border of the CWA by 0z, and have ended
precipitation in the western counties as a result.

.LONG TERM...(Friday Night through Thursday)
Issued at 240 PM CST THU NOV 20 2014

Strong shortwave trough moving onshore along the US West Coast
this afternoon is forecast to move into the Southern Plains by 12z
Saturday while another upper trough pushes into the Pacific
Northwest. The 12Z models are in good agreement with respect to the
mass fields lifting the southern wave into the mid Mississippi
Valley this weekend while the northern stream system moves into
the Northern Plains. The northern and southern stream systems do
not phase as quickly or as well as they were forecast to
yesterday. The lack of phasing results in the surface low to be
well to the east of where it was supposed to by 12Z Monday. For
eastern Kansas, we should remain in a prolonged period of low-
level warm and moist advection along with weak isentropic lift. We
should be on the west side of the more significant precipitation
shield with the above mentioned storm systems. With that said, I
made very little changes to the ongoing precipitation forecasts
which had a nice west to east POP gradient. Temperatures should be
mild with low diurnal temperatures trends and they should be above
freezing.

A Pacific cold front moves through on Sunday associated with the
northern stream shortwave. Model soundings support decent winds
Sunday afternoon and again on Monday with mixed layer winds of
25-35 knots. Modest cold advection since the source region of the
airmass does not appear to be arctic or polar. The models are not
in good agreement in the extended, but 12Z ECMWF solution of
another northern stream shortwave dropping into the plains seems
reasonable since the mean long-wave pattern is not changing much
in time. This should result in a period of warm advection midweek
with recovering temperatures and a frontal passage towards the end
of the forecast period which does look like it is polar in nature.

&&

.AVIATION...(For the 06Z TAFs through 06Z Friday Night)
Issued at 1147 PM CST THU NOV 20 2014

VFR conditions expected through 16Z then lowering to MVFR by 18Z.
Some MVFR vsbys expected with drizzle expected after 17Z or SHRA
with drizzle again possible after 00Z along with IFR cigs. Slower
saturation of the lower levels and onset of precipitation and
warmer temperatures will keep all precipitation all liquid at the
terminals.

&&

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

$$

SHORT TERM...67
LONG TERM...Johnson
AVIATION...53






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