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Area Forecast Discussion
Issued by NWS Topeka, KS
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FXUS63 KTOP 010520
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1120 PM CST Tue Jan 31 2017

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Wednesday)
Issued at 306 PM CST Tue Jan 31 2017

On Tuesday afternoon, west northwest upper flow stretched from
Montana all the way to the east coast. One weak disturbance of
interest, evident in WV imagery, was crossing the Rockies and
beginning to move into western Nebraska. The upper flow pattern
and associated airmass differences has allowed an elongated band
of mid level frontogenesis to develop with reflectivity echoes
extending more-or-less along a line from western Montana through
eastern Nebraska to West Virginia this afternoon. Much of this was
not reaching the ground, particularly in the eastern Nebraska to
northern Missouri region, but intensification was evident in
advance of the incoming short wave trough from western SD into
north central NE where the frontogenesis and additional vertical
motion was being enhanced. This trend should continue toward the
east and southeast tonight with a surface frontal boundary also
diving south into KS. Low-level moisture is lacking in this
region, and current indications are that the best intersection of
frontogenesis and moisture will occur north of the KS/NE border.
Have thus gone with a dry forecast tonight, but will want to
monitor the location and southward extent of that light
precipitation band in case it should build closer to far northeast
KS. Otherwise, expect the mild conditions and light winds to
persist through this evening before the cold front moves across
the forecast area overnight. Will then see an increase in north or
northeasterly winds with gusts in the 10- 20 mph range, and cold
advection will bring an airmass supportive of highs only in the
upper 30s north to middle 40s south on Wednesday...although there
is potential for a bit of low stratus to develop in which case
highs could be a bit lower

.LONG TERM...(Wednesday night through Tuesday)
Issued at 306 PM CST Tue Jan 31 2017

Northwest flow dominates the end of the week periods with Canadian
high pressure of southwest province origin continuing to build into
the Plains. This keeps lows around 20 and highs in the 30s Thursday
and Friday with periods of mainly mid and high cloud. The NAM is
stronger with a weak wave passing across the Northern Plains and
does bring some warm air advection in the low levels but is the
outlier. The persistence of the above pattern allows mid-level
frontogenesis to combine with enough moisture for a slight chance
for light snow in northern areas Thursday night. Much of the
forcing looks to be used to saturate the mid levels, with forcing
for ascent weakening as the moistening occurs, so anything more
than very light accums seem unlikely.

Upper flow backs ahead of a weak progressive wave Friday night and
Saturday, with the wave passing Saturday night. Low level moisture
increases on 850mb southwest winds around 50kts, though both
the ECMWF and GFS bring mid-level dry air in. This continues to
bring a setup for mainly drizzle and perhaps some freezing drizzle
as temps rise in the morning. Models are showing a decent spread
in surface temperature specifics along with questions on how much
drizzle can be precipitated out of purely warm air advection. This
leads to little confidence on how much if any freezing precip
will occur.

Moderate upper ridging then builds in Sunday into Monday for warming
temps. There is some agreement in a weak wave moving through late
Sunday night and early Monday with moisture quality again
questionable and will leave these periods dry. A stronger wave
quickly crosses through Monday night into Tuesday, though warm
air aloft may keep much precip in check here. Enough agreement
and strong forcing for a chance PoP here. If this system slows,
chances for thunderstorms would increase.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1120 PM CST Tue Jan 31 2017

VFR conditions are expected through the period. Winds north northeast
near 10 kts through the period.

&&

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

$$

SHORT TERM...Barjenbruch
LONG TERM...65
AVIATION...53
National Weather Service Regional Headquarters
