Areas affected…northeast CO…northwest KS…southern NE
Concerning…Heavy rainfall…Flash flooding likely
Valid 102358Z – 110558Z
Summary…Showers and thunderstorms continue to develop off the
Front Range and into the central Plains late this afternoon with
plenty of moisture, instability and atmospheric lift available. An
expansion and upscale growth of these cells are expected into the
evening hours, with areas of flash flooding likely.
Discussion…Ridging across the Plains continues to spill
monsoonal moisture and mid-level impulses into the central Plains.
These features moving atop surface fronts and outflow boundaries
have already helped to grow convection this afternoon, with the
recent uptick over southern NE seemingly tied to increasing 850mb
easterly flow along the front.
Impressive Precipitable water (2 inches) and instability (MUCAPE
>4000 J/kg) is noted across the Plains. In fact, we have a rare
combination of overlapping PWs and MLCAPE both approaching near
climatological record values. High surface dewpoints and a
mid/upper level moisture connection to the Pacific, as noted on
CIRA layered PW products, are likely resulting in these impressive
PW values. Cells thus far have been slow moving, seemingly tied to
the front and tight instability gradient…with the increasing low
level easterly flow balancing out the deeper layer westerly flow.
Given the high CAPE/PW environment, these cells will likely be
efficient rainfall producers, and thus at least some flash
flooding appears likely given slow cell motions over southern NE
and far northeast CO.
Expect we will continue to see an expansion of convection over
this region through the evening hours. Would expect to gradually
see cells take on more of an easterly motion with the approach of
a wave and gradual veering/increase of the low level inflow over
KS. This increasing low level flow over KS should support a
continued threat of west to east training of cells as they build
south and east towards the KS/NE border and into northwest KS.
There remains some uncertainty with regards to the exact evolution
of cells over the next several hours. However, the general idea of
slow moving cells initially, followed by an expansion south and
east with some training component, seems likely. Given the CAPE/PW
environment in place…cells that are either slow moving or
exhibit any training component will be capable of producing very
heavy rainfall rates and flash flooding. Thus at least pockets of
flash flooding are considered likely over southern NE and
northwest KS as we head through the evening hours.
…Please see www.wpc.ncep.noaa.gov for graphic product…
LAT…LON 40979962 40439920 39799910 39199918 38919945
38880019 38830138 39050201 39140208 39600260
40090284 40370260 40690162 40880055