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Area Forecast Discussion (AFD)

Issued by Topeka, KS (TOP)

FXUS63 KTOP 161149

Area Forecast Discussion
National Weather Service Topeka KS
649 AM CDT Tue Apr 16 2019

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 325 AM CDT Tue Apr 16 2019

Today will be another warm day ahead of a system set to bring some 
storms to the area tonight and tomorrow.

As of 08Z, water vapor imagery showed an amplified trough moving 
onshore over the west coast with moisture streaming out ahead of it, 
and more of a zonal flow over the eastern half of the CONUS. At the 
surface, low pressure was evident over western KS with a stationary 
front extending northeastward toward the KS/NE border. WAA will 
occur in the low levels of the atmosphere today with southerly 
winds. 925mb temps look to warm to near +20C by 00Z Wednesday with 
850mb temps near +15C. As surface heating gets going with decent 
solar insolation today, mixing of the PBL looks to occur up to 
around the 850-825mb range. All things considered, high temperatures 
are expected to be a touch warmer than yesterday, reaching the low 
to possibly mid 80's in most locations.

The stationary front will start moving northward as a warm front 
tonight as a nocturnal low level jet kicks in. The main question 
for the overnight timeframe is whether we will see some 
showers/storms develop. The jet will provide some lifting over the
area and soundings are indicating a shallow layer of nearly 
saturated air in the low levels, with the NAM more aggressive in 
this solution than GFS. Currently have at least low POPS going 
overnight with a slight chance for thunder since soundings are 
also showing at least some elevated CAPE remaining in place during
the overnight hours.

.LONG TERM...(Wednesday through Monday)
Issued at 325 AM CDT Tue Apr 16 2019

Focus for Wednesday is on the chance for severe storms. 
Persistent southerly low level flow is expected to continue 
bringing better gulf moisture north through the day Wednesday. As 
a result, models are showing instability developing ahead of a 
surface front on the order of 2000 to 3000 J/kg by Wednesday 
afternoon. But the dynamics could be better. Models are in
agreement that the upper flow will remain split into the evening
with closed low moving south across the southern plains and an
upper trough over the northern plains. This makes for a less than
ideal wind profile late in the afternoon and through the evening
for discrete supercells. Additionally forecast soundings suggests
a big component of the storm motion could be nearly parallel to 
the surface front with surface winds ahead of the boundary veered 
to the southwest. This would favor more of a broken line of storms
with storm mergers making it hard for an updraft to remain 
discrete. So the most likely hazards with the thunderstorms looks
to be hail and damaging winds, while the wind profile seems 
unfavorable for a significant tornado risk. Timing of the storms 
seems to favor late afternoon and evening. Forecast soundings show
a decent elevated mixed layer ahead of the front capping the 
boundary layer. It appears storm development may hold off until 
the upper dynamics and height falls overspread the front and 
weaken the cap. Models show a steady progress to the front just 
that it may be exiting Anderson CO shortly after midnight. 

Models show the upper trough remaining over the area through the
day Thursday with fairly steep lapse rates through the day.
Moisture is expected to be more limited with northwesterly low 
level flow so there is not a great deal of instability progged by 
the models. But it is not out of the question for an isolated 
shower to develop so have held onto some small POPs during the 
day. The northwest flow is expected to bring cooler weather to the
area. Although the airmass moving in appears to be a modified 
Pacific airmass with not a great deal of cold air with it. So 
think highs will still be able to manage the lower lower 60s for 
most areas. 

Upper level ridging is expected to move overhead for Friday and
Saturday with dry weather persisting. Temps should modify nicely 
with return flow developing by Saturday. Have highs in the mid 70s
to around 80 by Saturday. 

Confidence in the forecast decreases quite a bit for Sunday and
into the first half of next week. The GFS wants to develop more of
a longwave trough over the western U.S. with southwesterly flow
persisting into next week while a frontal boundary hangs up over
the region. On the other hand the ECMWF and Canadian show a less
amplified patter with a progressive boundary eventually moving
south of the forecast area sometime Monday. With the boundary
expected to move into the area by Sunday evening, there are some
chance POPs in the forecast. There are some slight chance POPs
into Monday to account for the uncertainty in the forecast. Also 
temps on Sunday and Monday are forecast to be a little closer to 
climatological normals because of the uncertainty. 


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 625 AM CDT Tue Apr 16 2019

A surface boundary was located near the KMHK terminal at TAF
issuance time and winds were out of a northerly direction. The
boundary is expected to shift north this morning, so winds 
through most of the TAF period will be southerly. Gusts near 20 
kts will be possible this afternoon at all terminals. CIGS look 
to drop into the high end MFVR category after midnight as a system
approaches the area.




LONG TERM...Wolters