Areas affected…Central to Northeast CO…Far Southeast
WY…West-Central to Southwest NE…Northwest KS
Concerning…Heavy rainfall…Flash flooding likely
Valid 112010Z – 120210Z
SUMMARY…Heavy showers and thunderstorms developing over the CO
high-country will begin to expand east across the High Plains in a
few hours and become locally concentrated across areas of
northeast CO, and eventually far northwest KS and far southwest
NE. Some flash flooding will be likely given the expectation of a
few inches of rain in a very short period of time.
DISCUSSION…The latest radar imagery is showing plenty of shower
and thunderstorm activity expanding in coverage across central CO
including areas near and along the Front Range. The convection is
developing within an increasingly moist and unstable airmass and
facilitated by strong diurnal heating and orographics.
This activity is expected to begin expanding much farther off to
the east very soon, with rapid convective iniation and expansion
likely within the next 1 to 2 hours across northeast CO. In fact,
the latest surface analysis is showing an area of low pressure
just west of Monument, CO and quasi-stationary frontal zone
extending east from it across northeast CO and into northwest KS.
The latest GOES-16 Split-Window imagery is showing an axis of
focused surface moisture convergence from near the Denver
metropolitan area east across Adams, Arapahoe, Washington and Yuma
counties with and focused essentially along and just north of the
front. An agitated CU field has developed across these areas over
the last hour. There is a fetch of very moist low-level east to
northeast flow to the north of the front, and this is helping to
contribute a moderate to strongly unstable boundary layer with
MLCAPE values of 2000 to 2500 j/kg.
The latest hires model guidance takes a weak mid-level vort, which
is seen in visible satellite imagery currently over central CO,
gradually off to the east this afternoon and east of the Front
Range by 00Z. This energy will interact with the highly favorable
downstream thermodynamic environment over northeast CO for
convection to rapidly grow upscale and become organized. While the
most organized convection will tend to be over northeast CO
initially, adjacent areas of far southeast WY, as well as
southwest NE and eventually northwest KS are expected to be
impacted as well. In all likelihood a strong MCS will evolve from
northeast CO into northwest KS and at least peripherly impacting
southwest NE.
PWATs across northeast CO and southwest NE in particular are
within the 90th percentile of climatology with values of 1.25 to
1.50 inches, and certainly a notable contribution from the high
surface dewpoints north of the front.
Given the environment, very heavy rainfall rates of locally over 2
inches/hr are expected, and these intense short-term rainfall
rates will certainly foster some rapid runoff problems. The hires
model consensus led by the 12Z HREF suite of guidance favors as
much as 3 to 4 inches of rain, with isolated heavier totals going
through 00Z. Some areas of flash flooding are expected given these
totals and especially with the enhanced short-term rainfall rates.
Orrison
…Please see www.wpc.ncep.noaa.gov for graphic product…
ATTN…WFO…BOU…CYS…GLD…LBF…PUB…
ATTN…RFC…ABRFC…MBRFC…
LAT…LON 41670405 41420300 41300256 40870179 40500131
39820109 39190158 39210278 38990363 38870381
38490435 38390490 38810509 39250548 39740493
40610471 41400479