Alert archive / Oregon / Mesoscale Discussions in 2017

Mesoscale Discussion 922

May 30, 20175 counties in Oregon; 4 counties in Washington

The Storm Prediction Center issued this mesoscale discussion at May 30, 2017, 2:48 PM PDT for 5 counties in Oregon; 4 counties in Washington. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: May 30, 2017, 2:48 PM PDT (21:48 UTC)
Expired: May 30, 2017, 5:15 PM PDT
In force: 2 hr
Issued by: the Storm Prediction Center
Chance of a watch: 20%

Counties Gilliam County, OR, Morrow County, OR, Sherman County, OR, Wasco County, OR, Wheeler County, OR, Benton County, WA, Kittitas County, WA, Klickitat County, WA, Yakima County, WA

The radar

The Pendleton radar (KPDT), 115 km from the middle of the area, began a volume at 21:49 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

Salem/Mcnary, OR (KSLE), launched 12:00Z, 9.8 hours before the alert went out and 228 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: 530 m above ground
0-6 km bulk shear: 27 kt
0-1 km storm-relative helicity: -7 m²/s²
0-3 km storm-relative helicity: 62 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

900 
ACUS11 KWNS 302149
SWOMCD
SPC MCD 302148 
WAZ000-ORZ000-310015-

Mesoscale Discussion 0922
NWS Storm Prediction Center Norman OK
0448 PM CDT Tue May 30 2017

Areas affected...portions of the OR/WA Columbia Basin

Concerning...Severe potential...Watch unlikely 

Valid 302148Z - 310015Z

Probability of Watch Issuance...20 percent

SUMMARY...Isolated small to marginally severe hail and severe gusts
are possible late this afternoon (south) through the late evening
(north).

DISCUSSION...Visible satellite imagery shows a cumulus field across
central OR to the east of a northeast migrating mid-level shortwave
trough forecast to move into central WA tonight.  Lightning data and
radar mosaic show isolated storms have developed across
north-central OR within a warm/well-mixed boundary layer (40 degrees
F temperature-dewpoint spreads).  Very steep low- to mid-level lapse
rates will favor strong evaporative cooling potential for a couple
of the stronger thunderstorm cores.  Strengthening mid-level winds
will act to organize cold pools and a skeletal band of storms may
develop by early evening.  If a linear cold pool develops, it is
possible scattered strong to severe gusts may occur on the leading
edge of outflow.  Short-term trends will be monitored.

..Smith/Guyer.. 05/30/2017

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

ATTN...WFO...OTX...PDT...

LAT...LON   44942131 46512135 47182082 47261970 46901907 45031899
            44421972 44472070 44942131

Nearby

Mesoscale Discussions in Oregon, 2017 Mesoscale Discussions in Washington, 2017 Every mesoscale discussion in 2017

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.