Areas affected…Portions of southeastern WY…the NE
Panhandle…and northeastern CO
Concerning…Severe potential…Watch likely
Valid 111854Z – 112100Z
Probability of Watch Issuance…80 percent
SUMMARY…Severe threat is expected to increase this afternoon, with
both large hail and damaging winds possible. A tornado or two may
also occur. Watch issuance is likely by 21Z (3 PM MDT).
DISCUSSION…With weak surface lows analyzed over east-central CO
and southeastern WY, persistent easterly low-level upslope flow will
continue to encourage gradual convective development along the
Laramie Mountains and Front Range in southeastern WY/northeastern
CO, respectively. In addition, at least modest large-scale ascent
associated with an upper low over the northern Rockies will continue
to overspread the central Rockies this afternoon and evening.
Mid-level southwesterly winds are forecast to only modestly
strengthen to 25-35 kt through the remainder of the day, but a
strongly veering wind profile from the surface through mid levels
noted in RAP forecast soundings will contribute to around 30-40 kt
of effective bulk shear.
Continued boundary-layer heating will erode remaining convective
inhibition over the next couple of hours to the north of a remnant
outflow boundary extending across northern KS into northeastern CO.
The presence of low to mid 60s dewpoints across much of this region
in combination with steepening mid-level lapse rates emanating from
the central Rockies will promote MLCAPE of generally 2500-3500 J/kg
by peak afternoon heating. The expected combination of strong
instability with sufficient shear will likely support a mix of
supercells/multicells initially. Large hail would probably be the
main threat with this semi-discrete development, although a tornado
or two could also occur near the surface boundary in northeastern CO
where backed low-level flow will locally augment effective SRH.
Eventual storm mergers/clustering should occur with eastward extent
into the NE Panhandle and northeastern CO as a low-level jet
strengthens by early evening. Damaging wind potential would likewise
increase if this occurred. With severe potential expected to
continue increasing this afternoon, watch issuance is likely by 21Z
(3 PM MDT).
…Please see www.spc.noaa.gov for graphic product…
LAT…LON 39320473 41240520 42950513 42960211 40800206 39640209
39120305 39120391 39320473