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fxus63 ktop 182049 
afdtop 


Area forecast discussion 
National Weather Service Topeka Kansas 
349 PM CDT Friday Jul 18 2008 


Discussion... 


Water vapor satellite imagery this afternoon along with the 12z 
upper air maps showed a broad upper ridge extending across the 
southern Continental U.S.. zonal flow continued across the northern Continental U.S. With 
a shorter wave length upper trough moving across the Great 
Basin...and across the norther Great Lakes states. An mesoscale convective vortex was 
located across the north central and northeast counties of the County Warning Area 
this afternoon. Lift ahead of the mesoscale convective vortex was causing an area of light 
rain across Brown and northern Jefferson counties. Scattered showers and 
isolated thunderstorms were developing along the west side of the mesoscale convective vortex 
over southern NE...and were moving southeast into the north central 
counties of the County Warning Area. 


Tonight...an outflow boundary extended from southwest and south 
central Kansas east and northeast across the southeast counties of the 
County Warning Area. A band of numerous showers and isolated thunderstorms extended 
along and just north of the ofb. I kept a chance of showers across 
most the County Warning Area for night as deep moisture continued across the region. 
Weak isentropic lift north of the ofb combined with lift associated 
with mesoscale convective vortex may keep at least a chance of showers and isolated 
thunderstorms through the evening hours. I placed likely probability of precipitation for 
areas south of an Emporia to Lawrence line as numerous showers and 
isolated thunderstorms will move northeast across the southeast 
counties of the County Warning Area through at least the evening hours. The cloud 
cover this afternoon kept temperatures cooler and highs will 
probably remain in the upper 70s and lower 80s across the County Warning Area during 
the late afternoon hours. Due to the lack of surface heating the 
atmosphere never really destabilized...thus any thunderstorms that 
develop will only produce brief heavy rainfall. Later tonight the 
NAM and GFS show the surface ofb dissipating and the mesoscale convective vortex over northeast 
Kansas tracking eastward across northern MO. This should bring an end to 
our rain chances later tonight. If skies clear late tonight and 
through the early morning hours we may see some patchy fog develop 
due to the deep moisture in place and moist ground from this morning 
rainfall. 


Saturday...I kept a slight chance for showers and thunderstorms 
during the morning hours across the County Warning Area in case there is enough 
isentropic lift to cause isolated showers or thunderstorms to 
develop around sunrise. As the boundary layer mixes deeper during 
the middle and late morning hours we should see any chance for isolated 
showers or thunderstorms during the morning hours come to an end. A 
500 mb ridge axis across Colorado will build east across Kansas. Skies should 
clear from west to east during the late morning hours. Insolation 
should help afternoon temperatures reach the lower to middle 90s. The 
deep moisture will continue across the southern and Central Plains. 
At this time the models do not show any minor 500 mb troughs or mcv's moving 
east across the state. There may be a chance that the ofb this 
afternoon may not dissipate and drift northward across the County Warning Area on 
Saturday. This could provide enough lift for isolated showers and 
thunderstorms to develop across the County Warning Area late Saturday afternoon and 
early evening...especially if there is enough insolation to get surface 
temperatures close to convective temperatures. The chances do not 
look all that good...so I kept probability of precipitation at 14 percent across the entire 
County Warning Area. 


Wg 


Saturday night have left a very small chance of precipitation in 
extreme northeast Kansas as frontal boundary across Nebraska 
interacts with a wave moving across the northern plains into the 
into the western lakes by Sunday morning. This interaction may fire 
thunderstorms in Nebraska that could move southeast and clip the 
northeast corner of the County Warning Area. 


Sunday into Monday a ridge builds over eastern Kansas with the 
westerlies retreating northward across the northern plains into the 
Great Lakes. Temperatures on Sunday in north central Kansas may 
reach near the century mark. Lows will be near 70 Sunday morning. 


For the rest of the extended period uncertainty continues with the 
strength of the upper ridge over the southern and Central Plains. 
Models differ with the presence of a frontal boundary across 
Nebraska...Iowa into Missouri. New European model (ecmwf) from 12z showing front 
remaining to the northeast of the County Warning Area through middle week with it 
possibly moving into the area by weeks end. Given model differences 
and Reliance on ensemble members of the European model (ecmwf) confidence remains too 
low at this time to insert precipitation into the forecast. Will not 
be surprised if a boundary or outflow moves into northeast Kansas 
middle week and increases chances of precipitation. Atmosphere for most 
of the County Warning Area will remain capped with presence of eml. Temperatures 
will remain in the 90s through the period with lows mainly in the 
upper 60s to lower 70s. 


53 


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Aviation... 


An outflow boundary extended south of the taf sites this afternoon. 
Kmhk had lower stratus overcast with 1,500 feet ceilings after 
1745z...though as the afternoon progresses these ceilings should 
rise to near VFR levels. Ktop and kfoe may have MVFR ceilings early 
this afternoon but these should rise to above VFR criteria after 
21z. A weak upper level trough may provide for some isolated 
scattered showers and perhaps a thunderstorms this afternoon and 
through the night. Though the cloud cover will limit surface heating 
and instability...limiting the threat for thunderstorms to develop 
at the taf sites. Some of the forecast soundings Show Low stratus 
and perhaps light fog developing at the taf sites around sunrise on 
Saturday. I placed in a sct010 for all taf sites after 10z Saturday. 


Wg 


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Top watches/warnings/advisories...none. 


&& 


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