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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

                            
000
FXUS63 KTOP 221130
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
630 AM CDT Wed May 22 2019

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 321 AM CDT Wed May 22 2019

A brief reprieve across the area tonight as the upper low that 
brought heavy rain and a few tornadic storms across the area on 
Tuesday lifts into the northern plains states. South southwesterly
surface flow around the system continues overnight, slowly 
advecting increased moisture out of the southern plains. Much of 
the day today will bring mostly sunny skies and temperatures 
rising into 70s. By mid afternoon, focus will turn to the area 
generally along and southeast of I-35 as atmosphere becomes 
considerably unstable in in daytime heating and with increasing 
boundary layer moisture. Soundings suggest cap weakens by around 
21z, with enough convergence in the wind field to get storms to 
develop into an atmosphere with 2000j/kg or more of CAPE and 
40-60kts of bulk shear. Large hail and damaging winds are the 
primary concerns along with locally heavy rainfall, and with low 
level helicity values potentially 200- 400m2/s2 will need to 
monitor tornado threat as well. The threat for strong storms could
continue a few counties to the northwest. Models indicating the 
boundary that generates these storms pivots into an east west 
direction overnight, as a front from the north works in concert 
with the warm front lifting northward by the LLJ overnight, and 
will continue the potential for storms to train overnight. Will 
therefore run a flash flood watch across Coffey and Anderson 
counties, especially considering they had 4-6 inches of rainfall 
from the system on Tuesday. Overnight lows fall into the 50s to 
low 60s.

.LONG TERM...(Thursday through Tuesday)
Issued at 321 AM CDT Wed May 22 2019

The big change in the models has been to bring a frontal boundary
further south across east central KS to begin Thursday. Also it 
looks like 850MB winds may be veered slightly more than previous 
forecast showed. Although there still looks to be some theta-e 
advection and speed convergence along and north of the frontal 
boundary. So think there could be some elevated storms to begin 
the day Thursday. Although models do not seem to be generating 
much QPF. 0-6km sheer vectors of 50KT to 60KT with MUCAPE values 
progged to be around 2000 J/kg would certainly support to 
potential for supercell storms with large hail Thursday morning. 
Later in the day an upper low is expected to lift northeast 
through the central Rockies. As it does, the frontal boundary is 
progged to lift north through the forecast area. Plenty of 
instability is forecast within the warm sector with deep layer 
sheer remaining around 50KT, supportive of organized storms. 
Models continue to show the idea of storms initiating along the 
dryline / triple point in southwest KS and the panhandles with 
these storms moving into north central KS by the late afternoon or
early evening. So there could be a couple opportunities for 
severe storms on Thursday. Highs for Thursday could end up being 
tricky because of the surface front. Models are showing a lot of 
moisture in low levels implying broken ceilings along and north of
the front. With a northeasterly wind along the NEB sate line, 
highs could struggle to make it into the 70s. Further south, think
highs could reach 80 with the warm sector advecting north through
the afternoon. 

For Friday through Sunday, the model consensus shows southwesterly
flow aloft persisting with no synoptic scale wave to speak of. At
the same time models maintain a moist and unstable airmass across
much of the region with little inhibition to convection and some 
hints of a weak boundary in the area. So it is difficult to see a 
period where there is not a chance for precip. And given the 
instability, chances for severe weather are likely to continue. 
This period is likely to be driven more by mesoscale forces with 
convection on one day impacting where storms develop the next day.
So have not strayed to far from the model consensus for POPs. In 
general expect thunderstorm chances to be maximized in the 
afternoon and evening time frame. Temps look to remain seasonal 
through the period with highs around 80 and lows in the 60s. 

By Monday and Tuesday, some differences between the GFS and ECMWF
start to become a little more apparent. The biggest difference is
the GFS bringing another closed low out into the plains while the
ECMWF hold the upper low back across the intermountain west.
Unfortunately neither solution would bring an end to the precip
chances. Although confidence in the details is low given the
uncertainty in how the pattern will evolve. Temps look to remain
seasonal with highs around 80 and lows in the 60s. 

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 628 AM CDT Wed May 22 2019

VFR conditions forecast for this period, although a small shift
northward in storm track could put terminals back in thunderstorms
later this afternoon into the overnight hours. At this time
appears they will stay south. Southwesterly winds through the day
today, becoming light and north this evening and overnight.  

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from this evening through Thursday morning for 
KSZ058-059.

&&

$$

SHORT TERM...67
LONG TERM...Wolters
AVIATION...67