Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 141138
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
538 AM CST Sun Dec 14 2014

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 339 AM CST SUN DEC 14 2014

The short term forecast through tonight will be dominated by the
warm sector of a rather powerful storm system. Today will start as
many recent days have...overcast with areas of light drizzle and
fog. It will also be quite warm in the middle 50s. These conditions
will continue through the morning hours without much change.

The afternoon into overnight hours get a bit more interesting as the
upper low currently on the CO/NM border moves into northeast Kansas.
Dewpoints will be in the mid 50s with temperatures in the upper 50s
as the lead lobe of energy swings out into the Plains this
afternoon. Expect showers and thunderstorms to develop in a broken
line and move steadily northeast. This activity is expected to enter
areas from Minneapolis to Abilene between 2 and 4 PM, and push east
to near the Missouri border by between 6 and 8 PM. Should have some
instability present with this line of storms, potentially near-
surface-based but rather weak. Could experience some gusty winds
with the strongest storms as wind fields just above the surface will
be strong, but severe storms with this initial band seem quite
unlikely.

Subsidence will overtake the area briefly in the wake of the initial
wave of precip but the center of the closed upper low will then
approach the area with another round of concentrated ascent. Lapse
rates will steepen markedly as the upper low approaches, lending to
the presence of instability well after dark and even after midnight
as the low moves overhead. Additional thunderstorms are expected to
develop near the low during the afternoon in southwest KS with the
system gradually moving northeast. The environment with these
storms would stand at least a slightly better chance for a few
strong storms given strong shear profiles and modest instability.
However, any of these storms that develop are likely to lose some of
their energy by the time they get to the local forecast area. The
instability and shear will be focused in the low levels, and will
have to keep a close eye on storms for low-topped supercell
structures and associated mesocyclones, but it appears that the
overall severe potential is very low. Thunderstorm activity will
persist near and ahead of the upper low track through the overnight
hours. The SHERB3 (Severe Hazards in Environments with Reduced
Buoyancy) briefly approaches or exceeds a value of 1 near the upper
low which can at times be a signal for weak instability severe
weather, but at this time will use it as a signal for continued
forecaster evaluation as the event evolves. Again, there is plenty
of vorticity available for these storms to work with but especially
given time of day and limited instability...the severe potential
currently appears low.

Temperatures will rise slightly today with highs in the upper 50s,
and will not drop much until late Sunday night as colder air finally
starts to work into the area.

.LONG TERM...(Monday through Saturday)
Issued at 339 AM CST SUN DEC 14 2014

By Monday morning, models are in fairly good agreement in showing
the surface and mid-level lows vertically stacked over the forecast
area with the associated cold front tracking eastward across the
area. As this system continues to progress northeast of the forecast
area, expect the best precipitation chances to be focused across far
northeast Kansas as precipitation diminishes from southwest to
northeast through the day and into the early evening hours. Models
show the winds beginning to veer to the northwest across north
central Kansas by Monday morning with the entire forecast area under
northwesterly flow by early afternoon. These northwesterly winds
will usher cooler air into the region, resulting in steady and then
falling temperatures through the day. Temperatures shouldn`t drop to
near the freezing mark until late afternoon and evening, in which
only some light precipitation may be left lingering across far
northern and northeast Kansas. As a result, expect most of the
precipitation to remain in the form of rain with only a slight
chance for a brief rain/snow mix as the system finally exits the
area. As cold air continues to surge into the region behind this
exiting system, expect low temperatures Monday night to drop into
the mid 20s to around 30 degrees.

Conditions will be dry Tuesday through Wednesday as surface high
pressure builds into the central U.S. Temperatures will be near or
below normal with highs in the 30s and lows in the 20s. During this
time models show another mid-level trough moving onshore to the
west, with the mid-level low gradually progressing across the
southwestern U.S. With an area of low pressure centered over the
southern Rockies on Wednesday, models are showing the southerly
winds on the lee side of the system advecting moisture from the Gulf
of Mexico northward toward the area. There are still discrepancies
between the GFS/ECMWF with regards to how far north this moisture
will extend, but some light precipitation may be possible Wednesday
night into Thursday before the main system over the southwestern
U.S. lifts into the area during the Thursday night through Friday
night timeframe. While the GFS has trended a bit closer to the ECMWF with the
timing/tracking of precipitation by late week, there are still
notable differences, so confidence is low with this late week
system. At this time, have chance PoPs in the forecast from
Wednesday night through Friday with diminishing PoPs Friday night as
the system exits to the east. Models have been trending a bit cooler
with temperatures during this time, so snow or a rain/snow mix will
be possible.

&&

.AVIATION...(For the 12Z TAFs through 12Z Monday Morning)
Issued at 528 AM CST SUN DEC 14 2014

Ceilings for much of the night have been above 1000 feet, but have
been decreasing since 10Z, and have moderate confidence in IFR
cigs at TOP/FOE through around 17Z, with less IFR potential at
MHK. After 17Z, there is a good chance of cig improvement to
around 1500 ft. A broken line of TSRA is expected to approach MHK
around 23Z and TOP/FOE around 00Z. May have a break after this
initial line of storms before additional TS move in near the end
of the TAF period. There is some potential for IFR after 04Z, but
confidence is low and kept MVFR cigs at this time.

&&

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

$$

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





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