Alert archive / Idaho / Mesoscale Discussions in 2020

Mesoscale Discussion 621

May 17, 202014 counties in Idaho; Baker County, Union County, Wallowa County, Oregon; 5 counties in Washington

The Storm Prediction Center issued this mesoscale discussion at May 17, 2020, 3:01 PM MDT for 14 counties in Idaho; Baker County, Union County, Wallowa County, Oregon; 5 counties in Washington. It was in force for 119 min.

The area

The outline as issued.

The facts

Issued: May 17, 2020, 3:01 PM MDT (21:01 UTC)
Expired: May 17, 2020, 5:00 PM MDT
In force: 119 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 20%

All 22 counties

Adams County, ID, Benewah County, ID, Bonner County, ID, Clearwater County, ID, Gem County, ID, Idaho County, ID, Kootenai County, ID, Latah County, ID, Lewis County, ID, Nez Perce County, ID, Payette County, ID, Shoshone County, ID, Valley County, ID, Washington County, ID, Baker County, OR, Union County, OR, Wallowa County, OR, Asotin County, WA, Columbia County, WA, Garfield County, WA, Spokane County, WA, Whitman County, WA

The radar

The Pendleton radar (KPDT), 183 km from the middle of the area, began a volume at 21:03 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 nearest sounding before it

Spokane, WA (KOTX), launched 12:00Z, 9.0 hours before the alert went out and 185 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: 1279 m above ground
0-6 km bulk shear: 48 kt
0-1 km storm-relative helicity: 190 m²/s²
0-3 km storm-relative helicity: 177 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

131 
ACUS11 KWNS 172102
SWOMCD
SPC MCD 172101 
MTZ000-IDZ000-ORZ000-WAZ000-172300-

Mesoscale Discussion 0621
NWS Storm Prediction Center Norman OK
0401 PM CDT Sun May 17 2020

Areas affected...Far northeast Oregon...far southeast
Washington...northern Idaho

Concerning...Severe potential...Watch unlikely 

Valid 172101Z - 172300Z

Probability of Watch Issuance...20 percent

SUMMARY...Strong storm coverage is expected to increase through the
rest of the afternoon into early evening. A few of the strongest
storms may produce large hail and damaging gusts. Given the expected
isolated nature of the severe threat, a WW issuance is not currently
expected.

DISCUSSION...Strong southwesterly mid-level flow will overspread
much of the Pacific Northwest east of the Cascades as a mid-level
trough gradually advances eastward. Surface lee troughing and modest
diurnal heating from the Columbia Basin southward to the Harney
Basin have promoted adequate low-level lift to support recent
convective development, with a stronger cell noted in the
Garfield/Whitman County WA vicinity. Further diurnal heating and
eastward advancement of the upper trough is expected to foster
additional storm development for the next several hours. 

Modest low-level moisture (up to upper 40s surface dewpoints) and
7.5-8.5 C km low-level lapse rates suggest adequate buoyancy is in
place, with 150-400 J/kg MLCAPE supporting occasional robust updraft
development (per latest Mesonanalysis). Meanwhile, strong mid-level
flow will contribute to 45-55 knot effective bulk shear, also
supporting storm organization and longevity. The most intense,
organized storms may obtain transient supercell or small-scale
bowing structures capable of producing large hail given modest (7
C/km) mid-level lapse rates, and damaging gusts given steep
low-level lapse rates and a well-mixed boundary layer.

Nonetheless, the severe threat is expected to be relatively sparse,
precluding a WW issuance at this time.

..Squitieri.. 05/17/2020

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

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

LAT...LON   43881772 44881818 46321809 47951767 48401695 48381631
            48111610 47011537 46531506 46011493 44991527 44351567
            43881652 43881772

Nearby

Mesoscale Discussions in Idaho, 2020 Mesoscale Discussions in Washington, 2020 Mesoscale Discussions in Oregon, 2020 Every mesoscale discussion in 2020

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.