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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

FXUS63 KTOP 222350

Area Forecast Discussion
National Weather Service Topeka KS
650 PM CDT Fri Mar 22 2019

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Saturday night)
Issued at 333 PM CDT Fri Mar 22 2019

20z water vapor imagery shows a closed upper low moving over the 
four corners region. Further west an upper trough was moving towards 
the Pacific Northwest coast. An area of low pressure was slowly 
deepening along the lee of the southern Rockies. Surface obs showed 
low level moisture beginning to surge north into west TX. 

For tonight through Saturday night, models show the better low 
level moisture advection holding off until later in the day 
Saturday as a surface low moves into central KS. But large scale 
forcing is progged to move over the region overnight tonight. As 
theta-e advection increases after midnight along with the 
strengthening dynamics, showers are forecast to move north and 
east into the forecast area. Instability in the morning looks 
lacking so I don't anticipate many thunderstorms. This initial 
wave may fall apart or move east by late morning. There should 
still be some upper level difluence along with the moisture 
increasing that scattered showers and possibly a thunderstorm 
could pop up through the afternoon. But the better chances for 
showers and thunderstorms appear to be across northern KS as the 
upper low moves east northeast along the NEB state line. There 
looks to be some reasonable elevated instability of a couple 
hundred J/kg of CAPE due to the steepening lapse rates. The shower
and thunderstorm activity is expected to move east with the upper
low Saturday night with POPs gradually decreasing through the 
night as the large scale forcing diminishes. Forecast soundings
show the effective inflow layer shear to be rather marginal and
deep layer shear of 35 to 40KT along with the modest CAPE points
to a low risk for severe convection. 

Lows tonight and Sunday morning are expected to remain pretty mild
with readings in the 40s thanks to a southerly component to the
winds tonight and a lack of cold air with the low pressure system
Sunday. Highs Saturday should be a little cooler from today given
overcast skies and periodic rain showers. Think afternoon highs
should top out in the mid and upper 50s. 

.LONG TERM...(Sunday night through Friday) 
Issued at 333 PM CDT Fri Mar 22 2019

For Sunday through Monday, the models have become less defined
with any sort of wave and instead show some vort maximum within
the developing northwest flow. As a result synoptic scale forcing
parameters have little in the way of vertical motion. 
Additionally a northerly winds is expected to bring cooler temps 
and less moisture making it difficult for any instability to 
develop. Precip chances are non-zero through the period but think 
they are to small to include a mention of precip in the forecast. 
Highs Sunday should be in the mid 50s to around 60. Monday looks 
slightly cooler with surface ridging building in so have highs in 
the mid 50s. 

Tuesday should be dry with mid level ridging over the central
plains. By Wednesday and through the end of the week, models show
a southerly return flow with a modified gulf airmass moving north.
The GFS continues to hint at some potential for elevated
thunderstorms Tuesday night and possibly Wednesday night. 
Forecast soundings seem to support the potential Tuesday night, 
but they show a decent elevated mixed layer moving in by Wednesday
night. Since the GFS is the only solution to depict the elevated 
storms Tuesday night, only have some slight chance POPs going. 
Better chances for thunderstorms may come Thursday night and 
Friday as a frontal system moves into the central plains. However 
there is some uncertainty as the ECMWF and Canadian show different
timing and tracks with the system and the GFS is much weaker with
the overall pattern. So for not just show some chances POPs for 
the end of the forecast period. Highs should trend warmer with 70s
in the forecast by Thursday. 


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 645 PM CDT Fri Mar 22 2019

For the 00z TAFs, VFR conditions are expected tonight with areas
of rain showers moving over the TAF sites predominantly overnight
through much of the day Saturday. However, there should be some 
breaks in the precipitation through the day Saturday, but there is
still some uncertainty in the timing of these breaks. By late 
morning/early afternoon Saturday, expect MVFR cigs with the 
ongoing scattered rain showers with IFR cigs possible at KMHK by 
mid/late afternoon. 




SHORT TERM...Wolters
LONG TERM...Wolters