Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 271711
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1111 AM CST Tue Jan 27 2015

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 343 AM CST TUE JAN 27 2015

A mid level ridge axis was set up from the TX big bend northwest
through the northern Rockies per the 08Z water vapor imagery. A
couple shortwaves were noted along the west coast. One along the
southern CA coast and a second moving towards the British Columbia
coast. At the surface, a weak ridge of high pressure was noted in
the surface observations over the southern and central plains with
an area of low pressure over MT and southern Saskatchewan.

For today and tonight, models continue to show a dry airmass in
place with 925MB and 850MB winds generally from the west and
southwest. Because of this any moisture advection is expected to be
very shallow this afternoon and overnight. No organized forcing
mechanism is progged to affect the area as the mid level ridge
slowly moves east. There are indications of mid level isentropic
upglide developing as theta-e advection increases, however there is
no moisture in mid levels. Therefore dry weather with clear skies
are anticipated through this evening. The MAV guidance has done a
better job with afternoon highs than the cool MET. Mixing from 900MB
to the surface as the GFS would suggest continues to show temps in
the 60s are plausible. Given that there should be full sunshine with
dry ground and limited moisture in the boundary layer, think most
areas will see highs in the 60s this afternoon. far northeast KS is
the exception where mixing probably will not be as deep.
Nevertheless have gone a degree or two warmer than MAV guidance due
to the anticipated insolation. Lows tonight are expected to fall
back into the mid and upper 30s. The MSL pressure gradient is
progged to gradually strengthen overnight helping to keep some
mixing of the boundary layer and hopefully preventing observation
sites from plummeting temps.

.LONG TERM...(Wednesday through Monday)
Issued at 343 AM CST TUE JAN 27 2015

As upper low over the Great Basin lifts northward then tops the
flattening ridge in the Rockies Wednesday...warm advection will
continue through the morning and midday. The combination warm air
advection...sunny skies and a nearly unidirectional low level
wind field should produce deeper mixing and have trended warmer
highs in the middle 60s far northeast to lower 70s southwest county
warning area. Although the next cold front will move into the
western CWA in the afternoon...feel it will not move through quick
enough to keep highs cooler than the mid to upper 60s. If the
expected arrival time of the front slows...then highs may need to be
edged upwards most areas.

The front and remnant shortwave trough will pass through dry with
cold air advection in its wake. Highs for Thursday will be 20 to 25
degrees cooler across the area...although still above normal with
readings generally in the middle 40s.

Next northwest flow shortwave phases with cutoff low over the far
desert southwest and spreads warm air advection and moisture
northeastward across the CWA Friday night into Saturday. Model
forecast soundings differ on the degree of cold air in the low
levels that remains in place Friday night through Saturday as
moisture and warm air advection dominate...so have kept a mixture
potential with highs in the upper 30s to lower 40s into Saturday.
The chances/confidence for all snow increase by Saturday night as colder
air aloft moves into the CWA behind the next cold front...so have
trended more towards snow at that time. Still too early to forecast
any snow amounts...but there is the potential for at least some
light accumulations across the area...mainly near the end of the
event Saturday night.

Will continue trend of decreasing pops Sunday...then dry on into
Monday. Highs both days should be in the 30s.

&&

.AVIATION...(For the 18Z TAFs through 18Z Wednesday Afternoon)
Issued at 1110 AM CST TUE JAN 27 2015

For the 18z TAFs, VFR conditions are expected through period. Expect
winds to veer from southeast to southwest by Wednesday morning as a
weak cold front approaches the region mid-day on Wednesday.

&&

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

$$

SHORT TERM...Wolters
LONG TERM...63
AVIATION...Hennecke





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