Mesoscale Discussion 1418

Issued

Aug 3, 2021, 2:26 PM MDT (20:26 UTC)

Expired

Aug 3, 2021, 5:00 PM MDT

In force

3 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

5%

Counties Ada County, ID, Adams County, ID, Canyon County, ID, Gem County, ID, Payette County, ID, Washington County, ID, Baker County, OR, Grant County, OR, Harney County, OR, Malheur County, OR, Union County, OR, Wallowa County, OR

The Boise radar (KCBX), 129 km from the middle of the area, began a volume at 20:30 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.

323 
ACUS11 KWNS 032026
SWOMCD
SPC MCD 032026 
IDZ000-ORZ000-WAZ000-032300-

Mesoscale Discussion 1418
NWS Storm Prediction Center Norman OK
0326 PM CDT Tue Aug 03 2021

Areas affected...portions of eastern Oregon into far west-southwest
Idaho

Concerning...Severe potential...Watch unlikely 

Valid 032026Z - 032300Z

Probability of Watch Issuance...5 percent

SUMMARY...A damaging gust or brief instance of marginally severe
hail is possible over the next few hours as storms increase in
coverage and intensity. The severe threat is expected to be sparse,
and a WW issuance is not expected.

DISCUSSION...High-based, pulse-cellular storms have recently
initiated across far southeast OR (per latest MRMS mosaic radar
data), with visible satellite imagery showing a developing CU field
across northeast OR. With continued heating/boundary-layer mixing,
storms are expected to increase somewhat in coverage and intensity
across eastern OR into western ID through the afternoon. Latest
METAR observations show temperatures exceeding 90F across eastern
OR, with dewpoints in the upper 40s, yielding a 40+ F
temperature/dewpoint spread in a few spots, indicative of a
well-mixed boundary layer already in place. 18Z RAP forecast
soundings for the 20-22Z period suggest that the boundary layer
extends above 600 mb, with 0-3km lapse rates reaching 10 C/km. 

The very steep low-level lapse rates and deep, dry boundary layer
will foster the potential for a couple damaging gusts with the
heavier storm cores. In addition, with 8+ C/km mid-level lapse rates
in place, a severe hailstone or two cannot be ruled out with the
strongest updrafts, especially if a transient supercell structure
develops. However, marginal instability (500-1000 J/kg MLCAPE) amid
poor deep-layer shear suggests that any severe wind/hail threat that
develops will be quite sparse and short-lived, and the issuance of a
Severe Thunderstorm Watch appears unlikely.

..Squitieri/Grams.. 08/03/2021

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

ATTN...WFO...MSO...BOI...OTX...PDT...MFR...

LAT...LON   42041926 42531961 43381983 44241956 45171907 46051829
            45971720 45581664 44711627 44031615 43691613 42921616
            42481638 42021690 42041926

Mesoscale Discussions in Idaho, 2021Mesoscale Discussions in Oregon, 2021Every mesoscale discussion in 2021

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.