000
FXUS63 KTOP 211707
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1207 PM CDT Mon Apr 21 2014

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 306 AM CDT MON APR 21 2014

Tricky precipitation forecast for this morning into the afternoon
due to the poor handling by short and mid term guidance of the
upper shortwave trough centered over northwest Oklahoma. Multiple
vorticity maxes can be seen this morning on water vapor imagery;
the main area of lift over Oklahoma with weaker areas noted in
northern Missouri, western Arkansas, and north central Kansas.
Radar trends over north central Kansas show the MCV continuing to
weaken as it touches the edge of Cloud and Republic counties.
Further east, broad and weak ascent ahead of the wave was
developing scattered showers, spreading northeast across the area.
This scattered activity is expected to continue into the morning
period. Main hazard would be an isolated lightning strike or two
as elevated instability is on the weakening trend.

Attention turns to the cold front currently situated over central
Nebraska. Ongoing thunderstorms will continue to weaken as they push
southeast towards the Kansas border. Uncertainty exists as the upper
trough tracks eastward into MO by mid morning if there will be
enough convergence along the front to maintain and/or re-develop
showers and thunderstorms. The latest NAM focuses the main
convection over east central and far northeast KS, closer to the
trough axis while very little QPF is generated along the frontal
boundary as it crosses the CWA through the day. However, the
HRRR/RUC along with mid term guidance develop light and scattered
showers and thunderstorms along the boundary as it crosses the CWA
through the day. Profilers also show an increase in moisture
advection from Texas, completely saturating the column. For these
reasons have maintained widespread chances for the area, increasing
to likely along/east of highway 75. The scattered nature of the
showers translates to light QPF amounts. Elevated instability near
500 J/KG and weak shear profiles suggest severe storms are not
expected.

North winds increase behind the boundary between 15 and 20 mph with
gusts near 25 mph during the afternoon for north central areas. Lack
of cold advection behind the boundary will warm highs into the low
70s. Dry air moving into north central KS may help to increase
highs to the middle 70s.

High pressure settles into the area this evening, quickly bringing
precip chances to an end by 7 PM. Decent radiational cooling and
weakening north winds through the period will cool lows to near 40
degrees in northern areas, while SCT cloud cover should keep
readings in the middle and upper 40s.

.LONG TERM...(Tuesday through Sunday)
Issued at 306 AM CDT MON APR 21 2014

An active pattern appears to be in store for the long term portion
of the forecast. Models seem to be in reasonable agreement for
Tuesday night through Thursday as the next upper trough moves
across the central and northern plains. There remains a signal for
some high based storms across central and northern KS late Tuesday
night and Wednesday morning. However think the greatest chance for
precip will be Wednesday night. The general consensus is for
storms to form along a dry line or pacific cold front late
Wednesday afternoon over western KS and then sweep across
northeast and east central KS overnight and through Thursday
morning. Initially there looks to be enough instability along with
good deep layer shear for storms to organize out west. However as
storms approach the forecast area, they may evolve into more of a
squall line with the potential for strong winds and hail. With all
of the guidance pointing towards this, have continued with likely
POPs for Wednesday night. The system appears to be fairly
progressive with the front pushing through the area by the late
morning Thursday. Think temps will remain mild for Tuesday through
Thursday as there does not appear to be much in the way of cold air
behind the Pacific cold front Wednesday night.

After a brief period of shortwave ridging Thursday night and
Friday, the models show another trough moving across the west and
try to cut off an upper low just west of the forecast area for
Sunday. The GFS appears to be the most aggressive and amplified
solution, especially with its cutoff low over the New England
states. Because of this is tends to bring a stronger surface ridge
south into the central plains. The GEM and ECMWF show something
similar in terms of a surface ridge sliding south, but to a lesser
degree than the GFS. Because of this there is a fair amount of
uncertainty in the cool down currently in the forecast. The ECMWF
is less amplified over the northeast and doesn`t push the front as
far south. Instead it develops cyclogenesis in the lee of the CO
Rockies lifting a warm front into the area. So there is quite a
difference in thermal profiles between the GFS and ECMWF by
Sunday. In general think there is a chance for precip for Saturday
and Sunday as the upper trough approaches from the west. Although
confidence in specific details of any given model is low at this
point. Therefore have not strayed away from the model blend
approach for the weekend. This keeps a cool down for the weekend
with highs generally in the 60s. Think this is reasonable at this
time since the GFS has shown slightly better run to run
continuity then the ECMWF over the past several runs. But again
confidence in the forecast for next weekend is low.

&&

.AVIATION...(For the 18Z TAFs through 18Z Tuesday Afternoon)
Issued at 1207 PM CDT MON APR 21 2014

For the 18z TAFs, scattered showers and possibly a few isolated
thunderstorms will continue to develop near the TAF sites through
early to mid afternoon as a cold front tracks eastward across the
area. A brief period of MVFR cigs/vis will be possible when any of
this scattered precipitation. By later this afternoon, conditions
will clear out, with winds shifting more to the north behind the
front and become light overnight. By Tuesday morning, these winds
will start veering further to the east.

&&

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

$$

SHORT TERM...Bowen
LONG TERM...Wolters
AVIATION...Hennecke