Colorado Mesoscale Discussion

Areas affected…Northwest through Central Kansas

Concerning…Heavy rainfall…Flash flooding possible

Valid 080717Z – 081130Z

Summary…Thunderstorms developing along a moisture convergence
axis will become nearly stationary through the next few hours. An
MCV moving eastward will gradually bring an end to the heavy
rainfall from west to east, but 1-3″ of rainfall, with locally
higher amounts, is possible before winding down. This may lead to
flash flooding.

Discussion…Local radar from KGLD WSR-88D early this morning
shows a cluster of thunderstorms exiting eastern CO and moving
across the town of Goodland, KS. Broad rotation within this
cluster suggests the presence of an MCV, with a small region of
cloud tops as cold as -79C on GOES-16 IR imagery further evidence
of this feature. Ahead of the MCV, a line of convection has
blossomed, oriented from NW to SE, along the nose of a 20-30kt LLJ
and collocated with a strong moisture gradient at 850mb. This
elevated front will continue to serve as a focus for convective
regeneration, acting with the eastward moving MCV to cause
torrential rainfall overnight.

As the LLJ persists, convection should nearly continuously
regenerate along the convergence boundary as isentropic lift
becomes maximized due to the LLJ moving atop. Additionally, this
LLJ will transport warm moist air into the region, providing a
resupply of a favorable thermodynamic environment for
thunderstorms with heavy rainfall. The 06Z RAP analysis depicted a
ribbon of 1.7-2.0 inch PWATS collocated with a robust MUCape
gradient with instability as high as 2000 J/kg just south of the
boundary. The continued ascent along this boundary, combined with
enhancement due to the PVA ahead of the MCV and its convectively
reinforced mid-level shortwave, will drive rain rates to above
1″/hr, and recently observed rainfall topped 2″ in 1 hour at
Parsons, KS, and reached 1.53″ in 1 hour at Goodland, KS. HREF
probabilities suggest rain rates of 1-2″ per hour will persist
along the boundary, and the potential for rates above this exists
just ahead of the MCV as it interacts with this additional
low-level convergence.

Although FFG across this area is generally high, 2-3″/1hr, and
3-4″/3hrs, training of echoes from NW to SE along the thickness
gradient is likely as noted by well aligned 0-6km mean wind. This
implies little N-S fluctuation of the boundary until the MCV
pushes through, so repeated rounds of heavy rainfall are possible
across the discussion area. Although HREF v2 exceedance
probabilities for 1-hr and 3-hr are modest, there should be
pockets of rainfall above the needed FFG values which may produce
flash flooding.


…Please see for graphic product…



LAT…LON 40090108 40090052 40069965 39999871 39769768
39589742 39499742 39099753 38809773 38559826
38589912 38669992 38720074 38850138 39060191
39250211 39650217 39860205 40000176 40070118

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