000
FXUS63 KTOP 191723
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1223 PM CDT Sat Apr 19 2014

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 333 AM CDT SAT APR 19 2014

Early this morning, water vapor imagery shows the northern stream
upper trough translating eastward over southern Saskatchewan while
the southern stream trough was rotating into Arizona. Upper level
moisture is increasing eastward into the western plains ahead of
ridging across northeast Kansas. At the surface, temperatures were
generally mild this morning in the upper 40s to low 50s. Southerly
winds are beginning to increase across central and northeast Kansas
as the pressure gradient tightens ahead of the shortwave trough
centered over eastern Colorado.

Another windy and warmer afternoon is expected across northeast
Kansas as the approaching trough returns strong southerly flow. By mid
morning, speeds between 15 to 25 MPH with gusts from 30 to 35 mph
are likely through the afternoon. Decent warm air advecting h85
temps between 9 and 12C into the area will raise highs this
afternoon into the upper 70s and low 80s. The exiting northern
stream trough will usher a cold front south, progged to setup from
western Kansas through south central Nebraska by late afternoon.
Despite moisture advecting northward ahead of the boundary, mixing
of the boundary layer will minimize RH values into the low and mid
30s in late afternoon. Therefore rangeland fire danger remains in
the high category.

Focus turns to convection developing just to the north and west of
the CWA late this afternoon or early evening. The NAM, SREF, and GFS
are fairly consistent in maintaining the capping inversion over
north central Kansas through 00Z, prohibiting surface based
development. However, the GFS appears a bit weaker than the NAM
suggesting an updraft may overcome the inversion just to the west of
Cloud and Republic counties. Decided to insert slight chances for
development from 4 PM to 7 PM. Best chances for thunderstorm
development will focus along and ahead of the cold front in south
central Nebraska/central KS where strong surface convergence
suggests multiple updrafts to form and move into north central
Kansas after 00Z. Elevated cape values average from 300 to 800 J/KG
while 0-6 KM bulk shear is marginal (25-30 kts). A few organized
updrafts are possible, but hazards would mainly consist of small to
marginally severe hail. Forecast soundings at CNK note very steep
sfc lapse rates up to 800 MB with a well mixed boundary layer. The
inverted V signature is suggestive of a downburst or localized
strong wind potential with any developing storm from the afternoon
through early evening for locations near and in Cloud to Republic
and Washington.

Should expect any thunderstorm activity to progress eastward
overnight tonight as the h85 jet, and approaching upper trough
maintain updraft development. Placed chances for precip mainly north
of Interstate 70, highest along and north of highway 36. Elevated
instability gradually wanes, reducing severe weather potential after
midnight. Most areas along and south of Interstate 70 should remain
dry through at least Sunday morning. Increasing insulation keeps
lows mild in the mid and upper 50s.

.LONG TERM...(Sunday through Friday)
Issued at 333 AM CDT SAT APR 19 2014

Models continue to show relatively little inhibition to convection
Sunday through Monday as the southern stream wave moves over the
region. The cooler mid level temps associated with the wave are
expected to keep lapse rates steep enough for showers and
thunderstorms to develop with the heating of the day by Sunday
afternoon. Then weak forcing persisting through the night and into
Monday along with a frontal boundary moving through the area is
likely to keep precipitation going. Deep layer shear remains
unimpressive with 0-6 KM shear up to 20KT, so concerns for severe
thunderstorms remains low. However PWs are forecast to increase to
near 1.5 inches which is about two standard deviations above
normal for late April. So there could be some locally heavy rainfall
with some of the stronger storms. It still looks like there could
be some modest insolation early Sunday as southerly winds continue
to advect warmer air north. With this in mind have kept highs in
the mid and upper 70s. Monday morning lows should also be mild due
to southerly winds and overcast skies limiting radiational
cooling. But through the day Monday winds are expected to shift to
the north with some cold air advection. Combined with mostly
cloudy skies and the potential for precip think highs should be
cooler with readings in the lower 70s.

Models continue to show a signal for elevated storms late Tuesday
night and into Wednesday with the low level jet advecting mid
level moisture back north. The better theta-e advection and
saturation on the isentropic surfaces appears to be pretty high
based around the 700MB level, but forecast soundings hint at some
weak elevated instability. Therefore it is hard to rule out the
chances and with the models persistent in this idea, and have kept
some small pops in the forecast.

Better chances for thunderstorms should be Wednesday night and
Thursday as a longer wave length trough approaches from the west.
There remains some differences in timing as well as evolution of
the wave between the models, causing lower confidence in the
forecast. However the models seem to be pointing towards
thunderstorm development along a dryline or Pacific cold front by
Wednesday evening and bringing a linear convective system across
the forecast area. Moisture should not be a problem due to a lack
of strong ridging along the gulf coast keeping the gulf opened.
Because of this will continue with chance POPs Wednesday night
into Thursday. Perhaps the least confident part of the forecast is
timing the end to precip with ECMWF showing the upper wave to the
northeast of the forecast area by Thursday evening. Have trended
Thursday night POPs down and will continue to refine the forecast
with later runs.

Wednesday continues to look like the warmest day of the week as
surface winds from the south strengthen and 850 temps warm to
near 16C over central KS. Then the forecast trends temps cooler
for Thursday and Friday expecting the Pacific cold front to move
through. With the northern and southern streams phasing together
by the end of the week with cyclogenesis progged to occur over the
upper Midwest, there is a greater chance for some modified
Canadian air to move south through the plains by Friday. Expecting
some modest cold air advection, have kept highs for Friday
generally in the upper 60s.

&&

.AVIATION...(For the 18Z TAFs through 18Z Sunday Afternoon)
Issued at 1219 PM CDT SAT APR 19 2014

Expect VFR conditions through the next 24 hours. Southerly winds
of 18 KTS to 23 KTS with gusts of 26 KTS to 34 KTS will continue
through the afternoon hours. By sunset winds should diminish below
14 KTS. High and mid level clouds will increase through the night
into Sunday morning.

&&

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

$$

SHORT TERM...Bowen
LONG TERM...Wolters
AVIATION...Gargan