Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 250451 AAA
AFDTOP

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TOPEKA KS
1151 PM CDT Tue Mar 24 2015

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Wednesday)
Issued at 314 PM CDT TUE MAR 24 2015

At 3 PM Tuesday, Surface low pressure was located in southeast KS
with a warm front nosing just into the southeast corner of the
forecast area and a westerly wind shift intersecting this warm front
in Anderson county. Visible satellite indicated a broad area of
agitated cumulus and a few towering cumulus focused just south of
Anderson county. Meanwhile, the strong upper level short wave trough
was quite evident in water vapor satellite imagery over north
central KS and moving quickly east.  For the most part, parcels in
northern KS remained capped and unable to realize the very steep
lapse rates aloft. However, vertical motion has been sufficient to
support showers and briefly lived convective features in north
central KS under the trough...moving generally east northeast. This
is likely to persist into far northeast KS and out of the area.
Farther south, it appears that the bulk of convection will be held
southeast of the forecast area, although there is some small
potential for elevated parcels to become briefly uncapped in east
central KS before 6 PM, and this could result in one or two
thunderstorms capable of producing some hail. Overall though, deep
convection looks unlikely.

This strong storm system moves out of the forecast area along with
any remnant showers by 8 PM or so with clearing skies filling in.
While odd with a departing strong surface low, winds are likely to
become nearly calm by midnight as a new jet max and upper low
quickly cross the Central Rockies...effectively neutralizing the
surface pressure pattern. Areas that received rain overnight are not
expected to see much dry advection after today`s system departs, but
clear skies and light winds could allow fog to develop especially in
low areas. Have not included it in the forecast at this time, but
will have to monitor trends this evening for fog potential. Any fog
is expected to decrease close to or just after sunrise as low level
flow increases with the strengthening surface low to the southwest.

On Wednesday, a warm front will lift back north in the morning but
should not make it much farther north than the KS/OK border. Will
likely see some overrunning of moisture into southeast KS and this
could result in showers or even a few storms into east central KS
particularly in the afternoon. Farther north, a strong northern
stream vort max will be moving south through the day. The vertical
motion with this trough will be associated with frontogenesis and
some elevated instability...and should be sufficient to overcome an
initially dry low/mid level airmass. Thus expect a band of rain
showers to move southeast across the area from very late morning
through the afternoon hours.

.LONG TERM...(Wednesday Night through Tuesday)
Issued at 314 PM CDT TUE MAR 24 2015

Progressive shortwave trough passing through the region on Wednesday
will surge a stronger cold front southeast during the early evening
period. Residual moisture behind the front is meager at best however
descent ascent along the h85 boundary should develop light rain
showers across much of the area through midnight. Weak instability
noted along and south of Interstate 35 by early evening may produce an
isolated thunderstorm or two, with the higher thunderstorm coverage
along the surface front across southern Kansas into Oklahoma.

Upper trough lifts eastward Thursday with northwesterly winds at 10
to 15 mph during the afternoon. A much cooler air mass fills into
the area with highs in the upper 40s to lower 50s Thursday and
Friday. A secondary, weak upper trough quickly translates through
the predominant northwest flow, entering north central areas by late
afternoon Thursday and spreading across the CWA Thursday evening.
Forecast soundings between guidance are showing slight discrepancies on
lift maximizing at similar time periods. 12Z GFS and GEM are faster
in carrying precip mainly in the form of rain while the NAM, SREF,
and ECMWF solutions are a bit slower, allowing surface temps to
reach closer to the freezing mark. For now will maintain mention of
rain and snow Thursday evening, however believe most of it will be
in the form of rain with no accumulations anticipated. A third
similar shortwave trough impacts northern and eastern portions of
the CWA Friday evening. Much of the light precip is expected to fall
as rain during the early evening hours, with perhaps a rain and snow
mix after midnight as lows fall to the lower 30s.

Air mass modifies once again for the weekend as upper ridging builds
over the region while a lee trough develops over western Kansas.
Better mixing through the boundary layer on Saturday lead to raising
highs a few degrees towards the mid 60s for central portions of
Kansas, while weaker advection results in upper 50s for far eastern
Kansas. Southwest flow increases Sunday in response to the next
front entering in the morning to mid afternoon time frame. Models
are still handling the speed of the system differently, yet are
pretty similar in increased sfc heating to the low 70s Sunday. Left
out mention of precip for now as the better forcing still lies north
and east closer to the trough axis. Southerly flow resumes for
Monday and Tuesday as a shortwave trough develops over the southwest
CONUS, impacting the southern and central plains on Tuesday. For now
have a mention of slight chances for thunderstorms as models are
much different on timing and depth of the system.

&&

.AVIATION...(For the 06Z TAFs through 06Z Wednesday Night)
Issued at 1142 PM CDT TUE MAR 24 2015

Mvfr/ifr stratus and fog will slowly dissipate aft 12z. Otherwise
mid and high clouds will then linger with vfr conditions through
17z before stratocu deck around 3500 ft affects the terminals
beyond 18z in the wake of the next cold front as it moves through
with gusty north winds over 20 kts. Light rain is expected behind the
front but vsbys should generally remain VFR.

&&

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

$$

SHORT TERM...Barjenbruch
LONG TERM...Bowen
AVIATION...63





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