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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

                            
000
FXUS63 KTOP 202343
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
643 PM CDT Fri Sep 20 2019

.SYNOPSIS...
Issued at 334 PM CDT Fri Sep 20 2019

A closed upper low was noted over eastern ID on the 20Z water 
vapor imagery while remnants of Imelda caused showers and 
thunderstorms along the Red River Valley and AR. Between an upper 
ridge to the southeast and the closed low over the Rockies, 
southwest flow persisted over the central plains. At the surface, 
lee troughing along the central high plains and ridging over the 
southeast continued to favor a southerly surface wind and 
dewpoints ranged from the upper 60s to mid 70s from the central 
plains to the southern plains. 

&&

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Saturday)
Issued at 334 PM CDT Fri Sep 20 2019

Some isentropic lift has aided in the light shower activity 
across the forecast area this afternoon. The saturation along this
area of lift is progged to diminish this evening so I do not 
expected the rain to continue all night. However height falls are 
progged to spread east through the day Saturday. Weak 
perturbations within the southwest flow along with increasing Q 
vector convergence suggests scattered showers and thunderstorms 
are probable through the day on Saturday. And this activity may 
start as early as sunrise. There continues to be a risk for severe
storms as model show an improving wind profile through the day as
a 500MB jet max noses into the region. And models prog CAPE 
values of 2000 to 3000 J/kg developing by the afternoon. However 
the low clouds may through a wrench into the instability, 
especially across northeast and east central KS where models hang 
onto the stratus for much of the day. Forecast hodographs show 
good low level veering of the winds and develop 0- 1KM SRH of 
around 200 m2/s2. Because of this there is some potential for a 
tornado or two. However forecast soundings also show a weakness in
the wind profile around 3km that causes an inflection in the 
forecast hodograph. This suggests there could be storm 
interactions that disrupt updrafts and limit the time a supercell 
storm could remain discrete. And by the evening, linear forcing 
from the frontal boundary suggests storms may develop into a line.
So the main hazards continue to be large hail and damaging winds 
during the afternoon and into Saturday evening.

Temps tonight are expected to only cool off a few degrees as 
southerly winds and cloud cover prevent much radiational cooling. 
Lows are forecast to be around 70 by Saturday morning. With clouds 
expected to linger across the easter portions of the forecast area, 
have lowered Saturday's highs into the upper 70s and keep highs in 
the lower 80s across north central KS where there should be more 
insolation.

.LONG TERM...(Saturday night through Friday)
Issued at 334 PM CDT Fri Sep 20 2019

There continues to be better confidence in torrential rainfall 
developing Saturday night and Sunday morning. Continued moisture 
advection into the frontal boundary with anomalously highs 
moisture is expected to favor very high rainfall rates with the 
thunderstorms. So have continued the flash flood watch and 
expanded it to include Coffey and Anderson counties. Although 
models seem to have backed off slightly on QPF amounts. Ensemble 
plumes from the SREF and GFS ensemble show a good clustering of 
solutions between 1 and 3 inches for storm totals. Although there 
are a few solutions with amounts greater than three inches. 
Overall the forecast has widespread 2 to 3 inch amounts and have 
kept the 2 to 4 inch wording in the watch. The timing of the front
is a little slower than yesterday in the operational solutions. 
So Sunday morning is looking a little wetter. But the front is 
progged to eventually push south of Anderson Co by the early 
evening. So have the forecast with decreasing POPs through the 
afternoon. Highs Sunday are likely to be cooler with clouds 
initially and some modest cold air advection behind the front. The
forecast has in the lower and mid 70s. 

A break from the weather is forecast for Monday with shortwave 
ridging aloft and surface ridging weakening. There is a little 
better consensus among the models with the synoptic pattern for next 
week. Unfortunately there remains several opportunities for precip. 
So POPs remain spread out through the forecast from late Monday 
night through Friday. There are indications of a weak wave moving 
across the central plains on Tuesday though along with some 
southerly return flow could bring some storms to the region. Then a 
weak frontal boundary is progged to move into central or southern KS 
on Wednesday. An increasing low level jet into this boundary 
Wednesday night could help storms to develop. There is some 
variability in the location of this boundary and where the storms 
develop so POPs are not that high. Then models show energy lifting 
out of the southwestern U.S. Thursday night and Friday with a low 
pressure system lifting mainly to the northwest of the forecast 
area. There are some small POPs in for this but the dry slot may 
also limit those chances. Temps look to remain fairly close to 
seasonal normals through next week with models showing no signs of 
strong temp advection. So the model blend has highs generally around 
80 and lows in the upper 50s to the mid 60s. 

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 640 PM CDT Fri Sep 20 2019

For the 00z TAFs, MVFR cigs will prevail through the period, and
cannot rule out the potential for borderline IFR cigs at times. 
Isolated showers will remain near the TAF sites this evening with 
increasing chances for thunderstorms by Sat. afternoon. Southerly 
winds will remain gusty at times this evening, with prevailing 
gusts expected through the day Saturday. 

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from Saturday evening through Sunday afternoon 
for KSZ010>012-022>024-026-035>040-054>056-058-059.

&&

$$

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