Alert archive / Washington / Mesoscale Discussions in 2018

Mesoscale Discussion 9

January 4, 20188 counties in Washington

The Storm Prediction Center issued this mesoscale discussion at Jan 4, 2018, 10:52 PM PST for 8 counties in Washington. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Jan 4, 2018, 10:52 PM PST (06:52 UTC)
Expired: Jan 5, 2018, 4:45 AM PST
In force: 6 hr
Issued by: the Storm Prediction Center

Counties Benton County, WA, Chelan County, WA, Douglas County, WA, Grant County, WA, Kittitas County, WA, Klickitat County, WA, Okanogan County, WA, Yakima County, WA

The radar

The Spokane radar (KOTX), 195 km from the middle of the area, began a volume at 06:57 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 00:00Z, 6.9 hours before the alert went out and 285 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: 1153 m above ground
0-6 km bulk shear: 15 kt
0-1 km storm-relative helicity: 113 m²/s²
0-3 km storm-relative helicity: 129 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

266 
ACUS11 KWNS 050653
SWOMCD
SPC MCD 050652 
WAZ000-ORZ000-051245-

Mesoscale Discussion 0009
NWS Storm Prediction Center Norman OK
1252 AM CST Fri Jan 05 2018

Areas affected...Portions of the eastern slopes of the Cascades and
Columbia Basin

Concerning...Freezing rain 

Valid 050652Z - 051245Z

SUMMARY...Multiple waves of light to occasionally moderate freezing
rain will likely impact points east of the Cascade crest through the
overnight hours. Freezing rain rates of a few hundredths of an inch
per hour will be possible.

DISCUSSION...Ahead of a shortwave trough over the eastern Pacific,
southwesterly mid-level flow is transporting increased moisture
across the Pacific Northwest late this evening. Within this moist
conveyor, weak warm advection and related isentropic ascent will
yield two or more rounds of precipitation overnight, with one
currently advancing northward across western Washington. While most
of the heavier precipitation will likely fall west of the Cascades,
occasional light to moderate precipitation will likely occur across
eastern Cascade slopes and into the Columbia Basin. Antecedent high
pressure over the interior is maintaining a shallow layer of
near-surface temperatures in the upper 20s/lower 30s across this
region, and forecast soundings indicate a sufficiently deep warm
nose aloft for complete melting of most hydrometeors. In turn,
occasional freezing rain (characterized by rates of a few hundredths
per hour) will remain possible into the morning hours.

..Picca.. 01/05/2018

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

ATTN...WFO...OTX...PDT...SEW...PQR...

LAT...LON   45682042 45692132 45742157 45852168 47172143 47652113
            48952057 49011930 49011912 48781892 48171856 47641843
            46391904 45682042

Nearby

Mesoscale Discussions in Washington, 2018 Every mesoscale discussion in 2018

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.