Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 062321
AREA FORECAST DISCUSSION
National Weather Service Topeka KS
521 PM CST SAT FEB 6 2016
...Update to aviation forecast discussion...
.SHORT TERM...(This Evening through Sunday)
Issued at 257 PM CST SAT FEB 6 2016
Northwest flow continued over the central and western U.S. per the
20Z water vapor imagery. An upper low over LA was moving away from
the forecast area while a shortwave over the northern Rockies dug
southwest towards the Dakotas. At the surface, an area of low
pressure was deepening over southern Canada with a strengthening
trough of low pressure extending south through the northern plains.
For tonight and Sunday, models show the airmass remaining too dry
for any precip in spite of the shortwave over the northern plains
expected to move across northeast KS in the morning. About the
only thing models prog with the wave is a deck of mid clouds in
the morning. Lows tonight are forecast to be a little warmer than
this morning as a west wind continues to bring some modest warm
air east. Think temps will bottom out in the upper 20s to around
30. Models show good mixing for Sunday, mixing the boundary layer
above 850 MB. However there is also some modest cold air advection
progged by the models in addition to northwest surface winds
coming off the snow pack across NEB. Because of this think the
prev forecast highs still look good with readings expected to be
in the lower 40s adjacent to the snow and around 50 across east
central KS. The pressure gradient should increase through the
afternoon Sunday as high pressure moves into the central Rockies.
This along with the steep low level lapse rates and deep mixing is
expected to bring some gusty winds of 35 to 40 mph to the area.
Although progs of MSLP and the pressure gradient do not appear to
be strong enough for wind advisory criteria in the afternoon.
Nevertheless it looks to become windy during the afternoon and
later shifts will need to keep an eye on whether stronger winds
being mixed down could cause gusts to be a little stronger.
.LONG TERM...(Sunday Night through Saturday)
Issued at 257 PM CST SAT FEB 6 2016
Concerns for high winds and some light snow continue for Sunday
night and Monday. Increasing height/pressure gradients and continued
cold air advection behind the upper trough brings wind speeds up
with decent depths of moisture into the ice crystal formation zone
in deep mixing for at least some snow shower potential, mainly after
midnight Sunday night into midday Monday. Strength of gradients
again not quite to what is expected for sustained Advisory level
winds, but speeds in the middle to upper portion of the mixed
layer around 45kt could easily get brought to the surface for
gusts near Advisory range. Confidence is not yet high enough for
headline issuance, especially given its atypical onset time. Any
snow amounts still look light at best, but restricted visibilities
when combining the falling snow with this type of wind could lead
to intermittent travel problems. The exiting system should allow
for improving conditions in both snow and wind concerns by mid-
late Monday afternoon.
Much of the remainder of the forecast looks benign. Upper heights
gradually rise but western CONUS ridge and Hudson Bay/Great Lakes
trough remain rather persistent. Tuesday looks to bring a sharp
gradient in temperatures across the area as the cold air moves off
with well over 10F spreads possible, but temps should generally be
near to slightly above normal in this regime with little
opportunity for precipitation.
.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
Issued at 521 PM CST SAT FEB 6 2016
VFR conditions are expected throughout the period. Winds will be
the biggest forecast challenge, with gusty NW winds expected to move
in early morning and ramp up in the afternoon. Although it will be
on the marginal end, have decided to include LLWS overnight at
TOP/FOE where it looks like the boundary layer will decouple for the
longest period of time. Winds will rapidly pick up after 18Z with
gusts up to 35kts possible throughout the afternoon.