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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

                            
000
FXUS63 KTOP 190903
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
403 AM CDT Thu Sep 19 2019

.SHORT TERM...(Today and tonight)
Issued at 401 AM CDT Thu Sep 19 2019

A unseasonably sticky and humid day has turned into an unseasonably 
sultry night.  Much the same will likely continue for the short term 
forecast period.

Currently, the upper level pattern is mostly meridional across the 
CONUS with a strong pronounced ridge generally working into the 
eastern CONUS.  Meanwhile, a deep and slightly positively tilted 
trough has worked onshore over the western CONUS.  Southwest flow 
regime is in the transition zone across the center of the country. A 
moderately strong LLJ is focused into NE where flooding is ongoing 
from training and backbuilding storms.  Much of this activity is 
progged to begin propagating southeast with time and will likely 
miss the area as the better instability remains through portions of 
Iowa into northern Missouri.  Some short-term hi-res models suggest 
that an outflow boundary may be able to make its way into portions 
of far east and northeastern KS by mid to late morning today. 
Therefore, have maintained some slight chance PoPs in the forecast. 
However, confidence in storms is low and may not materialize at all. 
High temps today will again rise to around 90 with dewpoints in the 
upper 60s.  

Thursday night into Friday morning will likely see another LLJ over 
western KS which will be a focus for storms to develop in the 
overnight period.  As the western trough begins to translate east a 
few ill timed lead waves begin to impact portions of the central 
Plains and into the northern Plains.  The WAA pattern may support 
some increasing chances for showers and storms into the late morning 
and afternoon on Friday as isentropic ascent increases with deeper 
moisture per sounding profiles.  As a result instability will also 
increase across the region.  Therefore, can't rule out at least 
slight chance to chance PoPs generally increasing through the day 
into the evening hours.  It does look like shear profiles will be 
minimal, so organized updrafts don't appear likely. 

.LONG TERM...(Friday through Wednesday)
Issued at 401 AM CDT Thu Sep 19 2019

For the mid to long range forecast the main concern will become the 
potential for severe weather into Saturday afternoon and evening as 
well as heavy rainfall Saturday night into Sunday.  

It does appear that overall better agreement amongst longer range 
solutions and ensembles is coming into focus which supports the 
thinking of several inches of heavy rainfall into Saturday night and 
early Sunday across the area with some of the highest amounts likely 
being focused across portions of east central into northeast KS as a 
slow moving frontal boundary tracks across the area.  Saturday 
afternoon will likely see the risk for severe storms develop across 
the area on the warm side of the southwest to northeast oriented 
baroclinic zone.  As upper southwest flow associated with the main 
trough moves closer to the region, shear profiles could increase to 
levels that would be supportive for more organized updrafts which 
could give rise to a few supercells.  One caveat right now appears 
to be that hodograph structures appear to have several inflections 
which would make for a challenging environment for more organized 
storms to maintain themselves or develop to the most severe limits.  

Probably the larger concern comes by late evening and into the 
overnight period.  As a LLJ develops and focuses strong moisture 
flux into already statistically very high PW air into the baroclinic 
zone, the expectation is that several inches of rain would be likely 
across the area.  Right now, overall soil moisture is still high 
which may increase some flooding concerns over the area. 
Additionally, much of the overall steering flow will be along the 
boundary within a deeply saturated environment.  Can't rule out that 
a flash flood watch may be needed in subsequent forecast periods. 
But right now would be premature.  

Past Sunday, too much spread in guidance gives rise to lesser 
confidence in the overall forecast or environmental setup. 
Therefore, keeping off and on rain chances Tuesday through Thursday. 
 Eventually, with modified Canadian air intrusions, lower overall 
dewpoints are expected by the end of next week and lower PW air will 
result in much more comfortable conditions. 

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1129 PM CDT Wed Sep 18 2019

For the 06z TAFs, VFR conditions are expected through the period 
with southerly winds remaining less than 10kts. 


&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Drake
LONG TERM...Drake
AVIATION...Hennecke