Area forecast discussion 
National Weather Service Kansas City/Pleasant Hill MO 
326 PM CDT Sat may 18 2013 


Short term...(this evening through sunday) 
issued at 326 PM CDT Sat may 18 2013 


Deepening upper trough over the High Plains is expected to produce 
multiple rounds of severe weather across the plains and Midwest over 
the next few days, starting with a severe weather outbreak over 
western and central Kansas this evening. Upper shortwave responsible 
for this activity, currently near Dodge City, will track into eastern 
Kansas and western MO late tonight. Quite a few questions remain 
regarding this feature and if it will be able to spark convection 
overnight this far east, especially with a significant capping 
inversion in place. Latest aircraft soundings out of mci depict a 
very strong inversion of 16 degrees c around 770 hpa which is quite a 
bit stronger than what models had been forecasting. This inversion 
is likely to keep our area dry at least through the early evening. 
However, a 40-50 kt low-level jet is progged to nose into northwest 
MO between 06z and 09z. Convergence at the leading edge of this 
feature could produce enough lift to weaken and possibly overcome 
the cap and spark a complex of thunderstorms over northeast Kansas and 
northwest MO overnight. Models are in very poor agreement with this 
potential overnight activity so confidence is not high. However, 
should storms develop, elevated instability is forecast to be strong 
to extreme, so these storms could produce severe hail and very heavy 
rainfall. 


Sunday still appears active as the upper trough to the west pushes 
into the eastern plains. Model spread remains rather high with the 
middle- and lower-level jet structure and timing of smaller-scale 
features, which makes it somewhat difficult to pinpoint exact storm 
location, timing and severity. Further complicating matters will be 
any overnight convection that lingers into Sunday morning. This could 
cut back on instability Sunday afternoon, and is also producing 
feedback issues in the model forecasts. It still appears that if 
things were to come together correctly, parts of eastern Kansas and 
western Missouri could see a line of supercells capable of producing 
very large hail (baseball-size or larger), damaging winds and 
tornadoes. Exact tornado threat, and any potential for long-lived 
strong tornadoes, will depend on the evolution of low-level wind 
fields and low-level instability which are difficult to get a feel 
for given the model spread. Taking a blend of the faster NAM and 
slower GFS would put result in wind fields and thermal profiles 
supportive of an enhanced tornado risk along the Kansas/MO border late 
Sunday afternoon and early evening, with an even greater risk further 
south toward Tulsa. 


Boundary-parallel storm-relative flow is likely to cause any 
supercells to gradually congeal into a line over western Missouri 
Sunday evening, maintaining the potential for large hail and damaging 
winds. This activity could maintain its severity as far east as 
central Missouri Sunday night. 


Long term...(sunday night through saturday) 
issued at 326 PM CDT Sat may 18 2013 


Large question Marks remain for the convective forecast on Monday, 
given substantial uncertainties on the evolution of thunderstorm 
activity Sunday afternoon and night. As mentioned in previous 
discussion, there will likely be some lingering thunderstorm 
activity early Monday morning as an embedded shortwave rotates 
northeast of the area and the low level jet slowly veers, however it's 
possible that much of the morning and early afternoon hours will be 
dry as the area is between shortwaves. Moderate to strong 
instability will begin to grow ahead of an elongated surface 
boundary over east central Kansas and northwestern Missouri during 
the afternoon hours. By the mid-late afternoon hours a secondary 
shortwave and mid-level jet streak will rotate into the area, 
reigniting convection over NE OK, southeast Kansas and into areas of west 
central MO. Initially discrete in nature, fairly rapid transition 
towards a linear convective Mode is anticipated further NE given 
unidirectional shear. Substantial mid-level cape values will 
support very large hail, with dry air intrusion indicating the 
potential for a quick transition to a strong wind producing mesoscale convective system as 
this system moves across the area. 


Tuesday-saturday: 


Upper level troughing will swing through the Midwest by Tuesday 
bringing cooler temperatures and dry conditions into Thursday. A 
building mid-level ridge will gradually slide eastward by the end of 
the week and next weekend. Moisture will gradually return to the 
Western Plains bringing renewed chances for showers and 
thunderstorms to portion of Kansas by next weekend. 




&& 


Aviation...(for the 18z tafs through 18z Sunday afternoon) 
issued at 1220 PM CDT Sat may 18 2013 


Cumulus field is rapidly expanding, and an area of IFR/MVFR ceilings 
is lingering west of the area across central Kansas. Southeast flow 
is expected to keep those ceilings well to the west of the 
mci/mkc/ixd corridor, and VFR will be the rule through the evening. 
While confidence in the latter half of the period is not high, most 
models do suggest thunderstorms developing late tonight and early 
Sunday across much of the region. Timing this activity is difficult 
at this point, but it appears it should hold off until well after 
midnight, so pushed back the timing of vcsh until 09z for areas near 
the Kansas/MO border. 




&& 


Eax watches/warnings/advisories... 
Kansas...none. 
MO...none. 
&& 


$$ 


Short term...hawblitzel 
long term...dux 
aviation...hawblitzel