Alert archive / Washington / Mesoscale Discussions in 2012

Mesoscale Discussion 1513

July 20, 2012Nez Perce County, Idaho; 4 counties in Oregon; 10 counties in Washington

The Storm Prediction Center issued this mesoscale discussion at Jul 20, 2012, 9:32 AM PDT for Nez Perce County, Idaho; 4 counties in Oregon; 10 counties in Washington. It was in force for 88 min.

The area

The outline as issued.

The facts

Issued: Jul 20, 2012, 9:32 AM PDT (16:32 UTC)
Expired: Jul 20, 2012, 11:00 AM PDT
In force: 88 min
Issued by: the Storm Prediction Center
Chance of a watch: 60%

Counties Nez Perce County, ID, Baker County, OR, Umatilla County, OR, Union County, OR, Wallowa County, OR, Adams County, WA, Asotin County, WA, Benton County, WA, Columbia County, WA, Franklin County, WA, Garfield County, WA, Grant County, WA, Lincoln County, WA, Walla Walla County, WA, Whitman County, WA

The radar

The Pendleton radar (KPDT), 67 km from the middle of the area, began a volume at 16:34 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 499Jul 20, 11:40 AM PDT

The nearest sounding before it

Spokane, WA (KOTX), launched 12:00Z, 4.5 hours before the alert went out and 227 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: 2619 m above ground
0-6 km bulk shear: 35 kt
0-1 km storm-relative helicity: -1 m²/s²
0-3 km storm-relative helicity: 66 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

385 
ACUS11 KWNS 201632
SWOMCD
SPC MCD 201632 
IDZ000-ORZ000-WAZ000-201800-

MESOSCALE DISCUSSION 1513
NWS STORM PREDICTION CENTER NORMAN OK
1132 AM CDT FRI JUL 20 2012

AREAS AFFECTED...PARTS OF NE OREGON/ERN WASHINGTON AND ADJACENT
IDAHO

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 201632Z - 201800Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...TRENDS ARE BEING MONITORED FOR AN INCREASING SEVERE THREAT
THAT COULD REQUIRE A WATCH BY EARLY AFTERNOON.

DISCUSSION...MID-LEVEL FLOW STILL APPEARS GENERALLY SUBSIDENT ALONG
THE EASTERN FRINGE OF A 50-60 KT SOUTHERLY 500 MB JET STREAK LIFTING
THROUGH EASTERN OREGON AND WASHINGTON.  BUT CLEAR TO PARTLY CLOUDY
CONDITIONS ARE ALLOWING FOR CONSIDERABLE INSOLATION...AND
DESTABILIZATION OF A MOIST BOUNDARY LAYER ACROSS THE WALLOWA/BLUE
MOUNTAINS VICINITY NORTHWARD THROUGH MUCH OF THE COLUMBIA BASIN. 
LATEST OBJECTIVE ANALYSES AND MODEL FORECASTS SUGGEST THAT CAPE IS
IN THE PROCESS OF BECOMING MODERATELY LARGE...ON THE ORDER OF 1000
TO 2000 J/KG...AND THIS IS EXPECTED TO BECOME SUPPORTIVE OF VIGOROUS
CONVECTIVE DEVELOPMENT AS MID-LEVEL FORCING FOR ASCENT INCREASES
AHEAD OF AN UPPER TROUGH BEGINNING TO LIFT NORTHEAST OF THE
CASCADES.  GUIDANCE INDICATES STORM DEVELOPMENT MAY INITIATE AS
EARLY AS 18-19Z...BEFORE INCREASING IN COVERAGE/INTENSITY DURING THE
AFTERNOON.  VERTICAL SHEAR WILL BE MORE THAN SUFFICIENT FOR
SUPERCELLS WITH AT LEAST A RISK FOR LARGE HAIL AND LOCALLY DAMAGING
WIND GUSTS.  LOW-LEVEL HODOGRAPHS ARE MORE UNCERTAIN...BUT AN
ISOLATED TORNADO MAY NOT BE OUT OF THE QUESTION...PARTICULARLY EAST
OF THE SURFACE LOW...NEAR/NORTH OF THE YAKIMA VALLEY.

..KERR/HART.. 07/20/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

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

LAT...LON   46281975 47572017 47821808 46491682 45411636 44581779
            45411903 46281975

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 20, 11:38 AM PDT	Severe Thunderstorm Watch	SPC	Benewah, Bonner, Boundary, Clearwater, Idaho, Kootenai and 4 more	7 hr
Jul 20, 1:29 PM PDT	Mesoscale Discussion	SPC	Benewah, Bonner, Clearwater, Kootenai, Latah, Lewis and 2 more	91 min

Nearby

Mesoscale Discussions in Washington, 2012 Mesoscale Discussions in Oregon, 2012 Mesoscale Discussions in Idaho, 2012 Every mesoscale discussion in 2012

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.