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Area Forecast Discussion (AFD)

Issued by Kansas City/Pleasant Hill, MO (EAX)

                            
000
FXUS63 KEAX 180448
AFDEAX

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
1148 PM CDT Fri May 17 2019

.Discussion...
Issued at 308 PM CDT FRI MAY 17 2019

Upper level ridging and southerly flow allowed Friday to be a nice 
summer like day with highs getting into the mid to upper 80s with a 
nice breeze out there to help it not feel too hot. All this changes 
tomorrow as an upper level shortwave trough exits into the central 
plains this afternoon helping to develop lee-side cyclogenesis over 
western KS/NE. Tomorrow still remains a complex forecast as a 
secondary low pressure system will develop over SW KS Saturday 
morning as a negatively tilted secondary shortwave trough moves over 
that area and sets the stage for a very wet Saturday.

Confidence is high for really only one thing tomorrow and that is 
that it is going to rain, the uncertainty comes into play with 
timing and intensity of that said rainfall. A minor mid-upper level 
shortwave trough will move along the SW flow aloft overnight helping 
to bring in cloud coverage and a few rain chances tomorrow morning, 
mainly over N central Missouri. The main cause of uncertainty starts 
with that feature as guidance does not have consensus on how quickly 
cloud coverage can clear out or if it will clear out at all. This 
will need to occur for us to destabilize early in the afternoon 
before the main forcing from southern secondary low pressure can 
move into the area. GFS indicates much more mid and high cloud 
coverage limiting the surface heating which results in much lower 
CAPE than the NAM or CAMs currently show. I tend to lean more 
towards the GFS on this aspect as it handles that type of cloud type 
much more accurately than the others. So while the higher clouds 
will limit heating there still appears to be enough MLCAPE (1500-
2000 J/kg) and 0-6km bulk shear (30-35kts) to cause potential severe 
weather. If the area does happen to clear out and get heating before 
noon then the NAM and CAM solutions may be more in line which would 
up the potential CAPE up to 2500-3000 J/kg with similar shear. Model 
soundings and hodographs indicate the main threat looks to be large 
to significant hail and isolated damaging winds. The hail size will 
depend on available MLCAPE in the early afternoon. The tornado 
threat looks low, but is not zero as there is some possible low 
level storm relative helicity as the warm front pushes through. 
Storm initiation time seems to be consistent in the guidance of late 
morning early afternoon as the upper level trough and low level 
forcing move into the area from the SW. Outside the threat of severe 
weather the threat of heavy downpours and frequent lightning will be 
constant for any outdoor activities tomorrow afternoon into the 
overnight hours with the severe weather only adding to the danger if 
we can destabilize. Storm mode looks to evolve throughout the day as 
this system pushes through. The warm front will pushes to the NE 
potentially clearing out central Missouri in the late afternoon 
shifting the threat from large hail and winds threat to a potential 
wind threat only as a line of storms form over northeast KS and 
northwest MO form up along a low level convergent area ahead of a 
cold front extending from the northern low. This line will likely 
develop in the late afternoon and then move through the area as a 
possible QLCS from W to E around and after sunset. The NAM 0-3km 
bulk shear vectors look got stay out of the SW at 30kts so this will 
limit any enhancement of the QLCS as it moves through the area and 
keep the tornado threat low for that feature. There is some flood 
threat with this system, but overall the flash flood guidance is 2.5-
3" for a 3 hours period and the overall QPF with this system is in 
the 1-2" range. This event will most likely just be a primer for the 
event Monday into Tuesday that looks more of a flooding threat to 
the area. Rain chances will last through the early morning hours as 
this system pushes through, but will quickly exit Saturday morning 
leaving quite a nice day in store for Sunday with highs in the lower 
70s. 

Monday looks to remain rather nice as surface high pressure and 
upper level ridging keep us dry and below average for temperatures 
on the backside of Saturdays system. This changes rather quickly 
Monday night though as another negatively tilted upper level 
shortwave exits into the central plains. A deep low pressure system 
will quickly form along the lee-side of the Rockies and occlude 
quickly with the triple point and vorticity maximum expected to go 
right through our area Monday night into Tuesday morning. A strong 
LLJ of 50kts will create strong convergence along the warm front and 
induce strong dynamic lift along that boundary. PWAT values of 1.7-
1.8" will be in place with a strong connection to the Gulf of Mexico 
in the low levels and a nice mid and upper level connection to 
Pacific moisture. This is the synoptic set up that tends to result in 
very high QPF events for this area. Currently we are going for 3-4" 
of QPF with this event, but there may be come convective 
contamination in the model QPF so it is difficult to get a true 
consensus between them. This is especially true on the placement of 
the axis of highest QPF. If this amount of rainfall does occur there 
may be minor to moderate river flooding along the main stem of the 
Missouri River and associated tributaries. Flash Flood guidance will 
likely be lower from Saturday's event so this hazard also comes into 
play Tuesday morning into the early afternoon. This system clears 
out Tuesday evening making for nice Wednesday before another 
shortwave moves through Thursday bringing rain chances back to the 
area. 

&&

.Aviation...(For the 06Z TAFS through 06Z Saturday Night)
Issued at 1148 PM CDT FRI MAY 17 2019

Low confidence forecast this go around as models do not have a
good grasp on ongoing convection early this morning. The first
round of showers across central Kansas is timing to approach the
terminals around 10Z but should remain north of the TAF sites. The
main round of showers and thunderstorms is expected to approach
from the south btn 16Z-18Z and affect the terminals much of the
afternoon and evening hours. There should be a break in the storm
during the evening however a second round of storms is expected
with the passage of a surface low during the evening. Best timing
for the second round of storms appears to be 02Z-06Z right now.
Otrw...cigs should remain VFR expect during storms when MVFR
cigs/vis will be poss. Winds will be out of the south around 15kts
with gusts to around 25kts thru tomorrow evening when winds will
diminish to around 10kts.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
MO...NONE.
&&

$$

Discussion...Barham
Aviation...73