Alert archive / Washington / Mesoscale Discussions in 2011

Mesoscale Discussion 155

February 27, 20119 counties in Washington

The Storm Prediction Center issued this mesoscale discussion at Feb 27, 2011, 5:02 PM PST for 9 counties in Washington. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Feb 27, 2011, 5:02 PM PST (01:02 UTC)
Expired: Feb 27, 2011, 11:00 PM PST
In force: 6 hr
Issued by: the Storm Prediction Center

Counties Chelan County, WA, Clark County, WA, Cowlitz County, WA, King County, WA, Lewis County, WA, Skagit County, WA, Skamania County, WA, Snohomish County, WA, Whatcom County, WA

The radar

The Seattle radar (KATX), 120 km from the middle of the area, began a volume at 01:05 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

Quillayute State, WA (KUIL), launched 00:00Z, 1.0 hours before the alert went out and 220 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: 17 J/kg
Mixed-layer CIN: -10 J/kg
Mixed-layer LCL: 607 m above ground
0-6 km bulk shear: 75 kt
0-1 km storm-relative helicity: 150 m²/s²
0-3 km storm-relative helicity: 179 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.2

Open this sounding in Storm Lab

The text

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

877 
ACUS11 KWNS 280103
SWOMCD
SPC MCD 280102
WAZ000-280700-

MESOSCALE DISCUSSION 0155
NWS STORM PREDICTION CENTER NORMAN OK
0702 PM CST SUN FEB 27 2011

AREAS AFFECTED...CASCADES OF WA

CONCERNING...HEAVY SNOW

VALID 280102Z - 280700Z

SNOWFALL RATES OF 2 INCHES PER HOUR...WITH LOCALLY HIGHER
RATES...ARE ANTICIPATED ACROSS THE CASCADES OF WA THIS EVENING INTO
TONIGHT.

STRONG LOW/MID-LEVEL W-SWLY TO WLY FLOW /CURRENTLY 80-85 KT AT 500
MB PER RUC ANALYSIS/ WILL CONTINUE TO IMPACT THE PACIFIC NW INTO
TONIGHT AHEAD OF LOW PRESSURE DROPPING S-SEWD NEAR THE PACIFIC
COAST. AS DEEP-LAYER MOISTURE /PWAT VALUES AROUND 0.50 INCH
ACCORDING TO AMSU-SSMI BLENDED TPW IMAGERY/ IMPINGES ON THE
CASCADES...THE UPSLOPE COMPONENT OF THE FLOW WILL SUPPORT SNOWFALL
WITH RATES OF 2 INCHES PER HOUR THIS EVENING INTO TONIGHT. THIS WILL
BE FURTHER ENHANCED BY INCREASING DEEP-LAYER ASCENT OVERNIGHT
TONIGHT. THIS WILL ESPECIALLY BE THE CASE OVER THE CASCADES OF SRN
WA...WHERE THE 21Z RUN OF THE EXPERIMENTAL HRRR DEPICTS THE HIGHEST
SNOWFALL RATES /POTENTIALLY UP TO 3 INCHES PER HOUR/ AFTER 06Z.

..COHEN.. 02/28/2011

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

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

LAT...LON   45712201 45772253 46182279 46562269 46862225 47012209
            47372191 47902189 48122195 48512208 48822198 48942167
            48962105 48672069 48102048 47342091 46342109 45992141
            45812171 45712201

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Feb 28, 1:56 PM PST	Mesoscale Discussion	SPC	Skamania	3 hr

Nearby

Mesoscale Discussions in Washington, 2011 Every mesoscale discussion in 2011

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.