Alert archive / Oregon / Mesoscale Discussions in 2017

Mesoscale Discussion 29

January 7, 20174 counties in Oregon; Clark County, Cowlitz County, Wahkiakum County, Washington

The Storm Prediction Center issued this mesoscale discussion at Jan 7, 2017, 9:20 AM PST for 4 counties in Oregon; Clark County, Cowlitz County, Wahkiakum County, Washington. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued
Jan 7, 2017, 9:20 AM PST (17:20 UTC)
Expired
Jan 7, 2017, 3:15 PM PST
In force
6 hr
Issued by
the Storm Prediction Center

Counties Clatsop County, OR, Columbia County, OR, Multnomah County, OR, Washington County, OR, Clark County, WA, Cowlitz County, WA, Wahkiakum County, WA

The radar

The Portland,OR radar (KRTX), 63 km from the middle of the area, began a volume at 17:25 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, 5.3 hours before the alert went out and 28 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-pSkew-T log-p diagram, Salem/Mcnary, OR at 12:00Z on 2017-01-07Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Salem/Mcnary, OR at 12:00Z on 2017-01-07The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 193 square meters per square second.1939587897117Sfc1 km3 km6 km9 kmRMLM
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
1596 m above ground
0-6 km bulk shear
50 kt
0-1 km storm-relative helicity
193 m²/s²
0-3 km storm-relative helicity
300 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

308 
ACUS11 KWNS 071721
SWOMCD
SPC MCD 071720 
WAZ000-ORZ000-072315-

Mesoscale Discussion 0029
NWS Storm Prediction Center Norman OK
1120 AM CST Sat Jan 07 2017

Areas affected...Western OR and southwest WA

Concerning...Winter mixed precipitation 

Valid 071720Z - 072315Z

SUMMARY...Light to moderate freezing rain will persist across the
southern Willamette Valley this afternoon with sleet and freezing
rain expected to spread/develop north into portions of southwest WA
later this afternoon.

DISCUSSION...Precipitation is gradually spreading north across OR
ahead of a notable short-wave trough that is quickly approaching the
coast.  Latest water vapor imagery suggests a vort max is located
roughly 100mi west of 4mk and ascent ahead of this feature should
encourage precip to eventually moisten the boundary layer farther
north.  Forecast soundings suggest freezing rain will linger across
the southern valley, and near the coast, well into the evening hours
while sleet will initially be the primary type across the northern
Willamette Valley near the WA/OR border.  Changeover to freezing
rain should occur in the Portland vicinity between 01-03z.

..Darrow.. 01/07/2017

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

ATTN...WFO...PQR...

LAT...LON   43982338 45712329 45722391 46372387 46262266 45462210
            44932260 44012284 43982338

Nearby

Mesoscale Discussions in Oregon, 2017Mesoscale Discussions in Washington, 2017Every 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.