Alert archive / Colorado / Mesoscale Discussions in 2021

Mesoscale Discussion 434

April 27, 202111 counties in Colorado

The Storm Prediction Center issued this mesoscale discussion at Apr 27, 2021, 11:15 AM MDT for 11 counties in Colorado. It was in force for 3 hr.

The area

The outline as issued.

The facts

Issued: Apr 27, 2021, 11:15 AM MDT (17:15 UTC)
Expired: Apr 27, 2021, 1:45 PM MDT
In force: 3 hr
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch likely
Chance of a watch: 80%

Counties Adams County, CO, Arapahoe County, CO, Elbert County, CO, Kit Carson County, CO, Lincoln County, CO, Logan County, CO, Morgan County, CO, Phillips County, CO, Washington County, CO, Weld County, CO, Yuma County, CO

The radar

The Denver radar (KFTG), 85 km from the middle of the area, began a volume at 17:17 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Severe Thunderstorm Watch 112Apr 27, 11:45 AM MDT

The nearest sounding before it

Denver, CO (KDNR), launched 12:00Z, 5.3 hours before the alert went out and 35 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 3214 m above ground
0-6 km bulk shear: 67 kt
0-1 km storm-relative helicity: 51 m²/s²
0-3 km storm-relative helicity: 72 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

945 
ACUS11 KWNS 271716
SWOMCD
SPC MCD 271715 
KSZ000-COZ000-271945-

Mesoscale Discussion 0434
NWS Storm Prediction Center Norman OK
1215 PM CDT Tue Apr 27 2021

Areas affected...portions of northeastern Colorado

Concerning...Severe potential...Watch likely 

Valid 271715Z - 271945Z

Probability of Watch Issuance...80 percent

SUMMARY...Convective initiation is underway across portions of
northeast Colorado. The threat for severe hail is expected to
gradually increase through the afternoon and a Severe Thunderstorm
Watch issuance is likely.

DISCUSSION...Overcast skies are overspreading a post-cold frontal
airmass across northeast Colorado, with surface temperatures varying
in the lower 50s to near 60F, and with 40-50F dewpoints noted.
Nonetheless, RAP forecast soundings suggest 100 mb deep rich
low-level moisture is in place, and is being overspread by 8+ C/km
mid-level lapse rates (evident via the 12Z DNR observed sounding).
With continued diurnal heating and the approach of an embedded
mid-level vort-max in New Mexico, an uptick in convective coverage
and intensity is expected. Increasing mid-level wind speeds are
fostering 50+ kts of effective bulk shear, suggesting that any
storms that can mature may remain organized long enough to support
the production of large hail. With modest low-level lapse rates in
place, a couple damaging gusts also cannot be completely ruled out.
As such, a Severe Thunderstorm Watch issuance is anticipated.

..Squitieri/Hart.. 04/27/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...GLD...PUB...BOU...

LAT...LON   38650418 38830453 39270469 39850482 40470499 40820490
            40910457 40980399 40940297 40680240 40200207 39710203
            39330215 39080231 38790269 38590304 38500363 38650418

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 27, 11:45 AM MDT	Severe Thunderstorm Watch	SPC	Adams, Arapahoe, Cheyenne, Douglas, Elbert, Kit Carson and 8 more	7 hr
Apr 27, 2:32 PM MDT	Mesoscale Discussion	SPC	Adams, Arapahoe, Elbert, Kit Carson, Lincoln, Logan and 6 more	118 min
Apr 27, 4:24 PM MDT	Mesoscale Discussion	SPC	Cheyenne, Kit Carson, Lincoln, Phillips, Washington, Yuma	2 hr

Nearby

Mesoscale Discussions in Colorado, 2021 Every mesoscale discussion in 2021

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.