Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 222309
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
609 PM CDT Sun Mar 22 2015

...AVIATION UPDATE...

.SHORT TERM...(This Evening through Monday)
Issued at 232 PM CDT SUN MAR 22 2015

A weak shortwave in the northwest flow aloft will track over the
upper Midwest this evening and overnight. This will drag a cold
front through the area, which is currently located in NW KS and
central NE. Ahead of the front low level moisture advection has
worked into central KS this morning as evident by the cumulus field
that has developed. This will inhibit how low the dew points mix out
in that region, while further east the dew points mix out much lower
into the 30s. There is decent agreement on the timing of the front,
which should enter north central KS around sunset. As the front
moves southeastward into the slightly better moisture an isolated
shower may develop along the front. There will be a decent amount of
dry air closer to the surface which may make it difficult for
precipitation to accumulate much over a few hundredths. With this
increased moisture the elevated cape overnight should range from
300-500 j/kg, therefore can not rule out the possibility of some
thunder. If the showers can develop it will be brief as the front
continues to progress eastward, and dry air moves behind the front
in the 900-850 MB layer. The highest chance are across far northeast
and east central KS.

This front is forecast to stall out in far southern KS tomorrow
morning. Overnight low temperatures will range from the upper 40s in
southeast KS to the upper 30s in north central KS. Cooler air moving
in behind the front places highs tomorrow in the 60s. During the day
tomorrow a shortwave will track over the central Rockies and
eventually the central plains overnight. Increased southerly flow
ahead of the wave lifts the front back to the north. Also, an
increasing low level jet advects higher moisture from the south into
southern KS. This higher moisture should help to erode the cap along
and north of the warm front. Showers and thunderstorms will increase
in coverage in the late afternoon and early evening.

.LONG TERM...(Monday Night through Sunday)
Issued at 232 PM CDT SUN MAR 22 2015

Monday Night - Thunderstorm coverage will increase through the
evening and overspread the area through the night. This will be in
response to a strong low level jet bringing quick moisture
advection, warm air advection, and enhanced isentropic ascent
underneath a plume of fairly steep mid level lapse rates. A broad
area of mid/upper level forcing will also overspread the area
during the evening and overnight hours. The moisture influx into
the region will be nearly continuous, as will storm development,
but the focus area for development will gradually shift to the
north and east and should exit the forecast area near or shortly
after sunrise on Tuesday. MUCAPE is likely to exceed 1000 J/kg at
times with strong mid/upper flow supportive of some elevated
supercell structures and large hail associated with a few of these
storms. Pockets of heavy rainfall will also be possible with the
continued storm development through the night.

Tuesday - The weather scenario on Tuesday remains complex but at
least most model guidance is beginning to resolve low level
features that fit the conceptual model of this type of strong
negatively tilted short wave trough. The upper short wave is still
forecast to deepen sharply during the day on Tuesday as the heart
of the trough tracks from SW Colorado into far southeast NE. A
strong mid level jet max will track along the southern periphery
of the trough, and expect surface low pressure to translate from
SW Kansas into NW Missouri. The NAM is a notable outlier in the
track of the surface low and tracks it south of the forecast area
(although still pulling south winds and higher dewpoints well
north into the forecast area with another weak sfc low a bit
farther northwest. Moisture return will be efficient on Monday
night into Tuesday ahead of this system, but the moisture source
will be modified continental air so looking at max dewpoints only
in the mid to perhaps upper 50s in the warm sector. Expect to see
at least some partial clearing and warming in the warm sector in
SBCAPE may exceed 1000 J/kg. Deep layer wind shear will be very
strong, and if storms develop they should quickly obtain supercell
structure as they move quickly to the east. Given the strong
dynamics with this storm system, it would now make sense for
storms to develop a bit earlier in the afternoon along the dry
line and under the rapid mid level cooling associated with the
upper trough. Feel that the ECMWF (which is quite similar to the
GFS and GEM) rendition of thunderstorm initiation occurring in the
local forecast area with some strengthening and organization
possible as they cross eastern KS near/south of the surface low
track. So, will re-introduce the potential for some strong to
severe thunderstorms for a few hours during the early/mid
afternoon on Tuesday with hail and damaging winds the main
hazards in the local forecast area. Aside from the warm sector,
elevated instability remains in place north of the surface low
track as well, and will likely support scattered showers and a few
thunderstorms as the system moves through. With the very strong
trough aloft, there may be some chance for a bit of hail even
north of the low. It now appears that the driest air behind the
system may remain just south and west of the area, so while it
will be windy late Tuesday the RH may remain above critical levels
locally and likely rainfall on Monday night could limit the fire
danger.

Tuesday night - Saturday - This system moves quickly northeast and
out of the area and expect dry conditions after sunset on Tuesday.
Wednesday will still be fairly warm but another strong upper
trough will dive across the Plains from the northwest with a much
cooler airmass moving in with it. Depending on airmass moisture in
place in advance of this system, there could be scattered showers
with the front passage late Wednesday. Temperatures then become
much cooler and there appears to be some strong potential for a
freeze...and perhaps a hard freeze...Friday morning and Saturday
morning. Currently have lows in the upper 20s but if skies are
clear on Saturday morning and the surface high is perfectly timed,
could end up in the low to middle 20s. The recent warm
temperatures may increase the impacts of a hard freeze but will
have to look deeper into this and how far along the growing season
is at this time. Warmer temperatures are then in store again for
next weekend.

&&

.AVIATION...(For the 00Z TAFs through 00Z Monday Evening)
Issued at 609 PM CDT SUN MAR 22 2015

Not sure SH activity along the front will hold together once the
sun sets. But with HIRES models still hinting at some isolated
convection with the boundary, will maintain a VCTS for a couple
hours. Otherwise VFR conditions should prevail with winds shifting
to the northwest and north behind the front.

&&

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

&&

$$

SHORT TERM...Sanders
LONG TERM...Barjenbruch
AVIATION...Wolters





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