Areas affected…eastern WY into far western NE and north-central CO
Concerning…Severe potential…Watch likely
Valid 111728Z – 111930Z
Probability of Watch Issuance…80 percent
SUMMARY…Thunderstorms will increase in coverage and intensity over
the next couple of hours. All severe hazards will be possible (large
hail, damaging gusts and a couple of tornadoes) and a watch is
expected in the next 1-2 hours.
DISCUSSION…Modest destabilization is occurring across eastern
WY/CO into the central Plains at midday. Low level stratus over far
eastern WY into the NE Panhandle and northeast CO is slowly eroding
and this trend is expected to continue through the afternoon.
However, this cloud cover may limit convective initiation/eastward
progression of thunderstorms until later this afternoon into the
evening.
In the near-term, a more confined severe threat is expected mainly
across eastern WY and perhaps into far north-central CO. Stronger
forcing for ascent associated with a shortwave impulse lifting
northeast across the Great Basin is now ejecting into western
WY/northwest CO as indicated by WV imagery and an increase in
thunderstorms developing across the higher terrain of south-central
WY into far north-central CO. As stronger heating occurs across this
region in broken mid/upper level cloudiness, MLCAPE should increase
to 500-1500 J/kg by 19-20z. 12z regional RAOBs show steep midlevel
lapse rates across the region ranging from 7.5-8.5 C/km in the
presence of strong shear supportive of rotating updrafts. This will
result in a threat for large (some greater than 2 inches) hail. Dew
points across eastern WY are generally in the low to mid 50s with
higher quality moisture existing well to the east. Nevertheless,
backed low level winds and low LCLs for this region could be
sufficient for a couple of tornadoes, mainly across southeast WY.
Fast storm motion also will aid in damaging wind potential. Given a
more meridional and unidirectional component to vertical winds above
around 2 km, some bowing segments/clusters also will be possible in
addition to more discrete convection. A watch will likely be needed
for portions of the MCD area in the next 1-2 hours.
..Leitman/Hart.. 09/11/2019
…Please see www.spc.noaa.gov for graphic product…
ATTN…WFO…UNR…BOU…CYS…BYZ…RIW…
LAT…LON 41360335 42380329 43020351 43740394 44730481 44920559
44680618 42420709 41640726 41100690 40580619 40440520
40570425 41360335