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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

                            
000
FXUS63 KTOP 212253
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
553 PM CDT Sun Jul 21 2019

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 248 PM CDT Sun Jul 21 2019

19Z water vapor and profiler data show a MCV along the KS/NEB state 
line over Republic CO while synoptically a shortwave was moving into 
the Upper Midwest. Upper ridging was gradually strengthening over 
the desert southwest and four corners region. At the surface, a 
couple outflow boundaries had moved into the area. At 19Z, this 
boundary appeared to be located from near Ottawa to near Abilene. 
Although it is not that well defined. Because of the outflow 
boundary, observations and model progs show the best instability 
setting up across the southern portions of the forecast area, 
generally south of Interstate 70. 

&&

.SHORT TERM...(This evening through Monday)
Issued at 248 PM CDT Sun Jul 21 2019

For this afternoon and this evening, models have been consistent in 
redeveloping convection over the area as the boundary layer becomes 
more unstable. While the CAMs have not had the best handle on the 
showers and storms from this morning, they have been consistent in 
developing storms between 4 and 6 PM. The current thinking is storms 
will form over north central KS in the vicinity of the MCV with 
development favored into east central KS along the instability axis. 
Deep layer shear is only forecast to be around 25KT or 30KT, but 
hodographs show a nice shape with easterly surface winds. So there 
does appear to be an organized severe weather risk, but think the 
SWODY1 outlook is a little to far north with the slight risk up to 
the NEB state line. Based on the RAP and NAM instability progs, the 
corridor for severe weather may be more from Minneapolis to Ottawa. 
If a supercell storm can maintain a reasonable mesocyclone, there 
could be a large hail risk. But with freezing levels nearly 15 KFT, 
the more likely concerns are for damaging winds and torrential 
rainfall. Forecast soundings show deep warm layers within the cloud 
while precipital water values approach 2.5 inches. This looks to 
be a favorable setup for efficient rain production and storm 
motions may only be 10KT to 20KT. So there is the potential for an
isolated location to get a lot of rain in a short period of time.
Unfortunately confidence in where this may happen in very low. 
Considered putting out a flash flood watch through this evening, 
but given this uncertainty and that the likely area to see rain 
hasn't had any precip in several days with flash flood guidance up
to 3 inches in an hour, felt the risk was not widespread enough 
to warrant a watch. 

Models show the upper wave exiting the forecast area by 12Z Monday, 
so think much if not all the precip will be over by Monday morning. 
Lows are expected to fall into the 60s for most areas while the 
surface gradient keeps enough mixing to prevent temps from bottoming 
out. Much cooler and pleasant temperatures are expected on Monday 
with highs around 80. The best part will be dryer air as dewpoints 
stay in the lower and middle 60s. 

.LONG TERM...(Monday night through Sunday)
Issued at 248 PM CDT Sun Jul 21 2019

For Monday night through next weekend, Models amplify the upper 
ridge to the west through Tuesday. This is expected to keep 
northerly upper flow over the central plains and the surface ridge 
in place until it starts to break down on Wednesday. By mod week, 
the pattern becomes less amplified wile the mean westerlies remain 
across the northern tier of the country. So precip chances become a 
little more dependent on mesoscale features. For now with no obvious 
forcing for precip, the forecast is dry through the weekend. With 
the surface ridge weakening and southerly low level flow returning 
on Thursday, temps should trend warmer. Models show the warm temps 
advecting back into the plains by Sunday when highs could be back 
into the middle 90s. 

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday) 
Issued at 553 PM CDT Sun Jul 21 2019

Main challenge is figuring out where TS will go. Latest ons show
the best instability has developed south of the terminals and many
of the CAMs now show TS to be more likely south of I-70. Because
of this will remove the TEMPO and only go with a VCTS thinking the
stronger storms will remain south of the airports. There looks to
be a brief period of MVFR CIGS into the night before dry air works
in from the south. Think VFR conditions will prevail by sunrise
and through the day Monday. 

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 7 PM CDT this evening for KSZ058-
059.

&&

$$

SYNOPSIS...Wolters
SHORT TERM...Wolters
LONG TERM...Wolters
AVIATION...Wolters