Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 210425
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1125 PM CDT Mon Apr 20 2015
...Update to aviation forecast discussion...
.SHORT TERM...(This Evening through Tuesday)
Issued at 331 PM CDT MON APR 20 2015
High pressure extended from Montana southeast into Oklahoma at 20Z.
Surface low pressure over Lake Superior this afternoon will move
northeast overnight with high pressure gradually moving off to the
southeast. Northwest flow aloft will continue across the Central
Plains tonight and Tuesday. A few embedded waves will move across
central and eastern Kansas tonight and Tuesday. Models show mid
level moisture increasing with the approach of one of the waves
later tonight. Isentropic lift and moisture return increases late
tonight across southeast into east central Kansas. Forecast
soundings are rather dry below 750 mb so initial lift will go into
saturating the column. The low level jet veers later tonight into
Tuesday morning across southern Kansas into southern Missouri with
moisture axis extending east-west. Tuesday afternoon MLCAPE
increases into the 300-500 J/kg in the moisture axis and low level
confluence area across southeast and east central Kansas into
Missouri. May see some scattered showers and isolated thunderstorms
in the afternoon south of a Lawrence to Council Grove line as
another weak wave moves through in the afternoon. Hail will be the
main hazard from the stronger storms. Lows tonight will range from
the mid 30s to lower 40s, have not included frost with clouds
developing with the aforementioned wave later tonight and soundings
showing not much in the way of low level saturation. Highs Tuesday
mainly in the 60s.
.LONG TERM...(Tuesday Night through Monday)
Issued at 331 PM CDT MON APR 20 2015
In the medium range (Tuesday night through Thursday), at the start
of this period, broad cyclonic flow remains over the eastern CONUS
with the southern stream from the desert southwest through the
southern plains. The models are in better agreement today
concerning the timing of a cold front which is scheduled now to
cross the forecast area Tuesday night. Moisture will be very
limited with the front. Based on model soundings, the low-levels
will be particular dry. There may be enough moisture to support the
mention of showers and maybe elevated thunderstorms across the
southeast corner of the forecast area.
For Wednesday and Wednesday night, cyclonic flow aloft continues
with a cold core surface ridge centered over the Missouri valley.
The cool air should be pretty deep over northeast Kansas with the
frontal inversion between 800-850 MB at 00 UTC per the 12 UTC GFS
BUFR soundings. The lack of any significant forcing and moisture
should result in dry weather through Thursday. Precipitation chances
should increase as we move into Thursday night, but will leave
Thursday dry for now.
Given the source of our airmass, temperatures will remain on the
cool side, or below normal.
For Thursday Night thru Monday, the models are still in slight
disagreement with the strength and timing of a shortwave that will
track over central KS Friday and Saturday. Overall, this shortwave
will move northeast from the southern California/Arizona region to
overhead of Kansas by Saturday morning. Thunderstorm chances will
be on the increase Friday with widespread activity anticipated as
abundant moisture moves into the area. The ECMWF and GEM show the
best shear/instability Friday afternoon and Friday evening ahead
of the shortwave. From here, models diverge a bit more, but slight
chances for PoPs remain until Monday associated with a secondary
shortwave. Temps remain steady in the mid 60s throughout the
period, with a slight decrease Saturday with increasing CAA this
day from the passing shortwave.
.AVIATION...(For the 06Z TAFs through 06Z Tuesday Night)
Issued at 1123 PM CDT MON APR 20 2015
VFR prevails through period while weak passing systems bring sct
to bkn mid level clouds. Westerly winds gust near 20 kts in the
afternoon while sct thunderstorms that develop should remain
south of the terminals.