Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 222347
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
547 PM CST Sun Jan 22 2017

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Monday)
Issued at 302 PM CST Sun Jan 22 2017

20Z water vapor imagery shows the upper low now over the lower MS
river valley and continuing to move east. The corresponding surface
low was along the gulf coast with weak high pressure building in
across the plains. Another upper low was seen just off the Pacific
northwest coast with upper ridging moving over the Rockies.

For tonight and Monday, low level moisture remains the main headache
as models have not handled the low level stratus very well. Overall
moisture will be on the decrease as northerly and northwesterly
winds advect in some dryer air. With the system well east of the
forecast area now, forcing for precip should be on the decline.
However with the stratus today, we have not been able to mix the
boundary layer out very much so there are concerns that some
patchy fog may form overnight as models show the stratus
eventually moving out. Confidence in dense fog is low since there
should be some low level dry air advection. But with winds
becoming light within the surface ridge axis and skies clearing,
the setup for radiational fog should be there. All indications are
for the fog to be fairly shallow and that it would burn off by mid
morning once the surface winds begin to pick up.

Lows tonight should be in the mid and upper 20s with some dryer air
moving in helping radiational cooling. Highs Monday are expected to
be influenced by some weak warm air advection late in the day and
modest mixing. With forecast soundings mixing to around 900MB, highs
should range from the upper 40s to lower 50s.

.LONG TERM...(Monday night through Sunday)
Issued at 302 PM CST Sun Jan 22 2017

Main periods of interest in the longer term remain to be early.
Models continue to show considerable differences with the track of
the upper wave and attendant surface low moving through the Central
Plains Tuesday into Wednesday. Even the stronger and more southern
solutions keep the bulk of the mid level moisture and any measurable
precip north of the Nebraska state line however. The ECMWF maintains
some light amounts Tuesday as the strong warm air advection from
overnight brings good low level saturation, while the Canadian is
the outlier in some development in the weaker trough rotating behind
the parent trough Wednesday. Will maintain small precip chances
at this point in mainly northern areas given track differences.
Kept Monday night on the warm end of guidance with the strong
advection, but colder air pushes back in by late Tuesday
afternoon. Mixing depths also vary considerably and could bring
rather warm and breezy conditions Tuesday, but again too little
confidence in going on one end of guidance, but generally warming
the forecast still seems in order.

Northwest flow still to dominate the late week and weekend periods
with little opportunity for precipitation. Have kept temps close to
normal but there will likely be at least one modified Pacific front
passing through in the later periods for more day-to-day variability
than what is included.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 540 PM CST Sun Jan 22 2017

MVFR stratus continues to push eastward and out of the area. MHK
has already scattered to VFR with the Topeka terminals expected
within the hour. The biggest question mark within the period is LL
moisture resulting in fog or stratus. Short-term guidance has
mixed solutions. I went with more of a fog solution given the
existing BL moisture and surface ridge moving in. As stratus
exits the area, sufficent radiational cooling and light winds will
allow for areas of fog to develop from 10Z-15Z. All sites return
to VFR after 15Z Monday morning.

&&

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

$$

SHORT TERM...Wolters
LONG TERM...65
AVIATION...Baerg



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