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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

FXUS63 KTOP 182006

Area Forecast Discussion
National Weather Service Topeka KS
306 PM CDT Wed Sep 18 2019

.SHORT TERM...(This evening through Thursday)
Issued at 306 PM CDT Wed Sep 18 2019

As of 19Z Wednesday afternoon, the longwave midlevel pattern remains 
stagnant across the CONUS with a very-amplified ridge across the 
eastern US and troughing across the west. At the surface an inverted 
trough extended from the TX Panhandle northeastward through north-
central KS and into southwest MN. A drastic theta-e gradient exists 
along the front with temperatures/dew points in the 70s/40s 
northwest of the front and 90s/60s southeast of the front. As a 
result, another hot and muggy day is ongoing across the area with 
heat indices in the mid to upper 90s area-wide. Very isolated 
showers/storms continue across southeast NE in response to modest 
WAA, although this activity should diminish through the afternoon. 

A quiet night is the most likely scenario across the forecast area. 
A weak shortwave trough is noted on WV across northern CO/southern 
WY and is progged to lift across northern NE/SD tonight. This 
feature combined with the most favorable isentropic ascent remaining 
north of the area, should favor any shower/storm activity remaining 
north of the area. That being said, any organized MCS would likely 
propagate southeastward across northeastern MO -- along the theta-e 
gradient -- and could push an OFB into the area, possibly resulting 
in showers/storms after sunrise tomorrow morning. Furthermore, if 
any OFB does push into the area, temperatures could be cooler than 
currently expected, although another warm/humid day is most likely 
with highs near 90. 

.LONG TERM...(Thursday night through Wednesday)
Issued at 306 PM CDT Wed Sep 18 2019

Transitioning into the extended period, the primary focus remains on 
the potential for multiple rounds of heavy rain throughout the 

By Thursday night, another LLJ of 25-35 kt could foster a few 
showers/storms, although this potential remains low. Rain chances 
will increase through the daytime hours Friday as the western trough 
begins to traverse the Rockies, providing some ascent across the 
Plains. By the weekend, model solutions continue to diverge with the 
evolution of the western trough and the attendant surface front. The 
GFS continues to lift the main trough northeastward, limiting the 
southern push of the front across the Plains, whereas the ECMWF has 
a southern track, allowing the front to traverse the CWA through the 
weekend. That being said, both suggest the potential for heavy 
rainfall within the forecast area, especially Saturday night into 
Sunday. In addition, the frontal position could provide a focus for 
a few severe thunderstorms. Confidence in the temperature forecast 
Sunday into early next week is low given the uncertainty with the 
frontal position -- i.e the ECMWF has highs in the 70s/low 80s and 
the GFS has highs remaining in the mid to upper 80s. 


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1154 AM CDT Wed Sep 18 2019

Relatively dry low levels are expected to keep VFR conditions at 
the terminals through Thursday morning. The magnitude of the low 
level jet is progged to be weaker tonight, so LLWS looks to be 
less of a concern.