098 
FXUS63 KEAX 181537
AFDEAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
1037 AM CDT FRI SEP 18 2015

.UPDATE...
Issued at 1037 AM CDT FRI SEP 18 2015

After much deliberation...have elected to hoist a flash flood watch
for the entire forecast area...with headline running from 10 AM
today through 7 AM Saturday. A few things has led us to this
decision...which we/ll try to elaborate on in this update AFD. First
thing of notice is the very high precipitable water content air that
remains in place this morning. Quick look at the SPC Meso page
reveals values of approximately 1.9" inches...directly over the EAX
CWA. These values are further confirmed on the 12z TOP RAOB which too
showed a PWAT value of 1.8". Secondly...layered precipitable water
satellite imagery continued to highlight converging subtropical and
northern stream moisture plumes over the Lwr Missouri Vly this
morning. Subtropical moisture feed is very well-established...and
see no interruption until main front goes through later tonight. And
thirdly...mid-morning mosaic radar imagery shows additional rounds of
thunderstorms inbound from the south Central Plains this
morning...as strong warm air advection remains in place ahead of the
main cold front. All told...cannot rule out repeated rounds of heavy
rain over any one particular area and considering the amount of 
atmospheric moisture in place...felt best to hoist the watch.

In addition...we/re still concerned for developing severe convection
later this morning/afternoon. Shear values will increase throughout
the day as mid-level speed max approaches the area. Main caveat right
now appears to be the degree of destabilization that can be achieved
later today thinks in part to this morning/s convection.
Regardless...early morning ROABs from TOP/OAX show plenty of
instability aloft which will certainly help maintain ongoing
convection across the area. Will continue to monitor and update as
necessary. 

&&

.DISCUSSION...
Issued at 421 AM CDT FRI SEP 18 2015

Today/tonight: A complex forecast exists over the next 18 hours as 
several surface and upper air features will provide the potential 
for multiple rounds of convection in varying locations. The forecast 
reflects a blend of operational models, convective-resolving models, 
and current conditions and trends. As of early this morning, pockets 
of deep convection were redeveloping over west central Missouri into 
south central Kansas. Satellite imagery showed a region of ACCAS in 
the area of ongoing convection southwestward into northern Oklahoma. 
Water vapor showed a strong wave over Wyoming with strong diffluence 
ahead of the disturbance. At the surface, a cold front was nearly 
stationary over the northwest quarter of the forecast area in 
northwest Missouri. This front has and will initially make little 
progress southward in response to pressure falls upstream from a 
developing surface low currently located over southwest Kansas. 

Much uncertainty lies with the potential for morning convection and 
the effects from said activity to later convective 
potential/severity. Most high-res models suggest additional 
convection to develop over south and east central Kansas during the 
next 3-6 hours, partially in response to the surface low progressing 
northeastward up the frontal boundary and increasing large scale 
ascent. Based on the current convection in KS, which is several 
hours earlier than models depicted, and ACCAS observations, 
confidence is moderate some degree of convection will continue 
developing/evolve over eastern Kansas within the warm sector and 
move into the forecast area during the mid/late-morning hours. Some 
of these storms may be strong, but widespread severe weather is 
currently not expected as a diurnal minimum of instability will be 
present downstream of convective activity, with ~1000 J/KG of 
MUCAPE. A second area of convection is expected to develop around 
sunrise north of the cold front over northwest Missouri, generally 
NW STJ. These post-frontal storms will be partially tied to the 
increasing large-scale ascent with the approach of the upper wave. 
These storms will expand in coverage, spread to portions of far 
northern Missouri, before mainly lifting into Iowa by early 
afternoon.

To what degree the warm sector convective coverage becomes this 
morning is challenging to ascertain at this time, but the potential 
exists for these storms to partially reduce strong insolation over 
much of the CWA, likewise limiting the overall severe weather threat 
this afternoon. Areas of the far southeastern CWA may have the best 
potential to destabilize by this afternoon, with moderate CAPE-shear 
combo to support robust severe convection. With the uncertainty in 
other areas, the simplistic approach is areas that are south of the 
front and see the sun for an extended period of time this 
morning/early afternoon will see a risk for severe weather during the 
afternoon and early evening. A mixed storm mode is expected with an 
eventual evolution into a line along whatever serves as the 
effective cold front. Large hail and damaging winds will be the 
primary severe weather concerns. A tornado cannot be ruled out with 
supercellular-like storms along an existing boundary and immediately 
ahead of the surface low where low-level winds can back, but the 
threat is not particularly high based on the overall pattern at 
hand. That said, if the surface low is slower and deeper as one 
model suggests, a slightly increased risk could develop, once again 
assuming moderate instability can materialize. Localized flash 
flooding will also be possible in areas with repeated strong 
convection as PW values near 2 inches, which is relatively high for 
this time of year. With the progressive nature, do not expect to see 
widespread flash flooding, and should be confined to repeat areas. 
Convection is expected to exit the CWA between 02-06Z Sat.

Temperatures today will be strongly tied to morning convection and 
remnant cloud debris, as well as the position of the cold front. 
Highs in the 70s are expected in far NW MO, with 80s elsewhere. 

Weekend and beyond: A dry and fall-like weekend is expected, with 
highs in the upper 60s to middle 70s. No notable weather is expected 
next week with gradually moderating temperatures with highs back in 
the upper 70s to lower 80s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday Morning)
Issued at 612 AM CDT FRI SEP 18 2015

VFR conditions will generally prevail at TAF sites, although cannot
rule out brief periods of MVFR if robust portion of storms moves
overhead. Most precipitation will be VFR in nature with relatively
high ceilings and visibility. Two rounds of thunderstorms are
anticipated, the first between 12-16Z and the next between 20-03Z.
Precipitation will end thereafter, but MVFR stratus is expected to
move into sites overnight. 


&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...FLASH FLOOD WATCH through Saturday morning for KSZ025-057-060-
     102>105.

MO...FLASH FLOOD WATCH through Saturday morning for MOZ001>008-
     011>017-020>025-028>033-037>040-043>046-053-054.

&&

$$

UPDATE...32
DISCUSSION...Blair
AVIATION...Blair