Area Forecast Discussion
Issued by NWS Topeka, KS

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633
FXUS63 KTOP 211740
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1140 AM CST Sat Jan 21 2017

...AVIATION UPDATE...

.SHORT TERM...(Today and tonight)
Issued at 313 AM CST Sat Jan 21 2017

Early this morning, water vapor imagery showed the mid-level low
spinning northeastward out of KS and toward Iowa. Low-level moisture
along the southern edge of the low was resulting in stratus clouds
extending across much of the outlook area. With enough low-level
moisture trapped beneath this stratus deck, some areas of dense fog
had developed across portions of north central to northeast KS early
this morning, which prompted the issuance of a Dense Fog Advisory.
As the surface low continues to lift to the northeast, expect the
stratus deck to gradually lift northeastward out of the area as well
through the morning hours. This diminishing stratus deck should
result in some diminished fog and improving visibilities.  However,
with relatively light winds still expected behind this stratus deck,
there would still be the potential for some radiational fog
development, so we will need to continue to monitor that potential.
With all of these factors in mind, there still is some uncertainty
with when exactly the areas of dense fog will diminish. However
model soundings seem to suggest that conditions should improve by
mid morning, if not earlier, for most locations.

With diminishing cloud cover this morning from the exiting surface
low and with light southwesterly winds in place, expect unseasonably
mild temperatures once again today with highs reaching into the low
to upper 50s.  However, cloud cover will likely increase across east
central Kansas this afternoon as the latest model runs have now been
tracking the next surface low further north than in previous runs.
Surface low pressure over Arizona/New Mexico this morning will
progress eastward into Oklahoma later today with wrap-around
precipitation now looking to extend northward into east central KS
late this afternoon through tonight before exiting to the east on
Sunday.  The cloud cover from this scattered light precipitation
will aid in keeping temperatures warmer overnight with lows only
dropping into the mid/upper 30s over that region.  As a result, any
scattered light precipitation will be in the form of rain showers.

.LONG TERM...(Sunday through Friday)
Issued at 313 AM CST Sat Jan 21 2017

Sunday through Tuesday are likely to remain warmer than normal
with highs in the 40s and 50s, and lows in the upper 20s and 30s.
Sunday could end up a bit cooler given potential for lingering
cloud cover through the daytime hours. Otherwise upper ridging
builds overhead on Monday and strong warm advection is expected on
Tuesday ahead of an incoming storm system.

Model guidance is in strong agreement regarding an intensifying
storm system moving across the KS/NE region Tuesday into
Wednesday. There area differences in the timing of this rather
fast-moving storm system, but otherwise agreement in various
characteristics is strong. For starters, it will be quite warm
ahead of the system as the surface low deepens rapidly and
warm/moist advection ensues in advance of the low. Winds are also
likely to increase in the presence of the deepening surface low
and have utilized the high end of forecast guidance for the wind
forecast although storm timing differences lend some uncertainty
in wind direction at any given time. North of the surface low is
where the majority of precipitation is expected given expected
system dynamics and moisture profiles, and this will probably
occur in a transition zone from rain to snow from south to north.
Precipitation then changes to all snow from northwest to southeast
as the surface low passes and strong cold advection ensues. The
main question for the local forecast area lies in the exact storm
track as multiple models (the ECMWF most aggressively) track far
enough south to pull snow into northern KS with some accumulation
possible. Meanwhile, other model tracks (particularly the GFS)
track only slightly farther north...but far enough to keep most of
the area dry with only very small chances for light snow. At this
time will play the middle ground but knowing very well that the
range of possibilities runs from totally dry to accumulating snow
in northern KS.

After this storm system passes, the upper flow pattern becomes
very meridional with strong cold advection bringing a return of
more winter-like temperatures through the remainder of the
forecast period. Have a dry forecast at this point, but a couple
of weak waves diving south across the Plains could possibly
squeeze out some light precipitation by next weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1139 AM CST Sat Jan 21 2017

Models show moisture advection through the evening as an upper
level shortwave passes south of the area. With some weak forcing
and upper level divergence, there should be some scattered showers
across east central KS this evening. Think the terminals may see
some MVFR VSBY with the moisture advection but forecast soundings
keep CIGS above 3KFT. The bigger uncertainty is whether dense fog
redevelops on the northern fringes of the cloud cover and
eventually moves back into the terminals once the rain and cloud
cover passes east. Some of the high resolution solutions show this
potential. Went with the consensus which keeps any dense fog north
along the MO river, but will need to monitor trends in the models.

&&

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

$$

SHORT TERM...Hennecke
LONG TERM...Barjenbruch
AVIATION...Wolters



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