Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 231934
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
234 PM CDT Mon Mar 23 2015
...Update to aviation forecast discussion...
.SHORT TERM...(Today and Tonight)
Issued at 347 AM CDT MON MAR 23 2015
Weak cold front was progressing southeast through the CWA overnight.
Appears moisture amounts and convergence along it is too weak to
overcome a weak cap aloft for showers to develop in eastern Kansas,
but lowering cloud heights in south central Kansas suggests somewhat
deeper moisture, so a shower or two in far southern locations would
seem possible yet in the next few hours. A strong upper trough was
making quick eastward progress out of the western states overnight
with ridging over the Rockies.
The upper ridge passes through Kansas today with a lead wave working
into central portions of the state as the front stalls over southern
Kansas. Mid level isentropic upglide ensues in the afternoon though
north lower level winds keep the lower troposphere dry and expect
any precipitation to likely hold off until the evening hours, but
will keep small chances in the late afternoon. With higher cloud
already into western Kansas this morning and north to east surface
winds, have lowered highs a bit.
Lower theta-e advection increases quickly this evening as 850mb
winds ramp up from the south at 30-40kt. There is fairly good
agreement with two main periods of moisture surges north and east
through the area, with somewhat less impressive forcing and moisture
in southeastern areas. There remains some differences however in the
track of the deepening surface low from southeastern Colorado into
southern portions of Kansas tonight, and this will play a significant
role in where the best persistence and coverage of convection will
be. Have kept southeastern areas slightly lower on potential but
still appears most locations will see at least one period of precip.
Decent elevated lapse rates and 850mb dewpoints into the 6-10C range
may bring CAPE values to around 1000 J/kg with 1-6km shear around
50kt supporting some potential for large hail, with multiple round
potential with precipitable water values around 2 times normal for
locally heavy rain possibilities.
.LONG TERM...(Tuesday through Sunday)
Issued at 347 AM CDT MON MAR 23 2015
Expect convection to be ongoing across the CWA at the start of the
period with low level jet/isentropic lift over the warm front which
is forecast to extend eastward from a surface low in central Kansas
to around Garnett. Models still show elevated instability and good
moisture advection and expect showers along with isolated
thunderstorms to move northeast through the morning hours. Used the
GEM as a compromise between the models with the location and
movement of the surface low through the day on Tuesday with the NAM
and the ECMWF south and the GFS north with the low as it progresses
northeast through the day. Vigorous upper trough will move out
across the Central Plains with a bit of a negative tilt as it moves
across Kansas. Forecast soundings show capping in the warm sector on
Tuesday with the cap eroding as the upper trough moves through.
Shear and instability are sufficient for thunderstorms, some
possibly severe in the far eastern counties late in the afternoon.
The convection should quickly move off to the east into MO by early
evening. Showers and thunderstorms will develop north in the cool
sector as ascent increases with the passage of the upper trough.
Temperatures will range from the 70s in the warm sector to the upper
50s along the Nebraska border. Drier air behind the surface low
looks to remain just to the west of the forecast area and although
it will be windy do not expect extreme fire danger, but still very
high fire danger in the afternoon hours to develop.
Tuesday night the upper trough quickly moves out with dry conditions
until Wednesday when another upper trough will move across the
plains with another cold front moving through the area. Soundings
show steepening lapse rates which may lead to isolated thunderstorms
in the afternoon hours with the passage of the upper trough. Another PV
anomaly moves southeast across the Central Plains Thursday night.
Q-vector convergence increases as will as low to mid level
frontogenesis in the far southwestern counties into south central
Kansas Thursday night. Forecast soundings from the GFS and ECMWF
show thermal profiles favorable for snow. The system moves off on
Friday and expect dry conditions heading into the weekend with a
warming trend with the return of southerly flow Saturday.
.AVIATION...(For the 18Z TAFs through 18Z Tuesday Afternoon)
Issued at 232 PM CDT MON MAR 23 2015
Update at FOE in the short term as they are burning grass near the
airfield. Smoke from this fire is affecting visibility over the
airfield and will continue to do so through approximately 22Z.
VFR conditions are expected through the afternoon into early
evening with high confidence before the low pressure system off to the
southwest starts to become more organized and impacts the TAF
sites late evening and into the morning tomorrow. Activity will
begin out near the KMHK site after 0z as showers with the
potential for some thunderstorm activity after 3z followed by low
cigs into the IFR category. This will gradually shift East into
the KTOP/KFOE sites by 3-6z time frame. Confidence is on the low
end with actual thunderstorm coverage, but widespread showers and
low cigs are a very good likelihood as the atmosphere saturates
deeper throughout the evening and overnight.