Alert archive / Washington / Mesoscale Discussions in 2011

Mesoscale Discussion 20

January 11, 201110 counties in Washington

The Storm Prediction Center issued this mesoscale discussion at Jan 11, 2011, 5:01 PM PST for 10 counties in Washington. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued
Jan 11, 2011, 5:01 PM PST (01:01 UTC)
Expired
Jan 11, 2011, 9:00 PM PST
In force
4 hr
Issued by
the Storm Prediction Center

Counties Island County, WA, Jefferson County, WA, King County, WA, Kitsap County, WA, Mason County, WA, Pierce County, WA, Skagit County, WA, Snohomish County, WA, Thurston County, WA, Whatcom County, WA

The radar

The Seattle radar (KATX), 24 km from the middle of the area, began a volume at 01:07 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 148 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, Quillayute State, WA at 00:00Z on 2011-01-12Temperature 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, Quillayute State, WA at 00:00Z on 2011-01-12The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 202 square meters per square second.19395878Sfc1 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
542 m above ground
0-6 km bulk shear
57 kt
0-1 km storm-relative helicity
202 m²/s²
0-3 km storm-relative helicity
487 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.

295 
ACUS11 KWNS 120102
SWOMCD
SPC MCD 120101
WAZ000-120500-

MESOSCALE DISCUSSION 0020
NWS STORM PREDICTION CENTER NORMAN OK
0701 PM CST TUE JAN 11 2011

AREAS AFFECTED...WRN WA

CONCERNING...WINTER MIXED PRECIPITATION

VALID 120101Z - 120500Z

PRECIPITATION IS EXPECTED TO INCREASE DURING THE NEXT SEVERAL HRS
OVER WRN WA. INITIAL PRECIPITATION TYPE WILL FAVOR SNOWFALL OVER THE
OLYMPIC PENINSULA AND PUGET SOUND REGION...WITH RATES AOA 1 IN/HR
ACROSS THE OLYMPIC MTNS AND ACROSS THE NRN CASCADE MTNS. A
TRANSITION TO A MIX OF SNOW...FREEZING RAIN...OR RAIN IS FORECAST TO
OCCUR OVERNIGHT ACROSS THE LOWER ELEVATIONS...EVENTUALLY BECOMING
ALL RAINFALL BY MID-MORNING.

SEVERAL LOW-AMPLITUDE IMPULSES OBSERVED IN RECENT WATER VAPOR
IMAGERY WILL AFFECT PORTIONS OF THE PAC NW LATE THIS EVENING INTO
THE WED MORNING. ONE IMPULSE POSITIONED NEAR THE CA/OR BORDER WAS
WEAKENING AND QUICKLY MOVING INLAND...WHILE ANOTHER WAS LOCATED WELL
OFFSHORE THE COAST OF BC. PRECIPITATION HAS REMAINED LIMITED ACROSS
MUCH OF WRN WA...WITH LARGE T-TD SPREADS /NEAR 20 DEG F IN SOME
LOCATIONS/ AND ELY DOWNSLOPE FLOW OBSERVED ACROSS PUGET SOUND. AN
ATTENDANT SFC LOW /NEAR 994 MB PER RECENT SFC OBJECTIVE ANALYSIS
FIELDS/ PRECEDING THE AFOREMENTIONED OFFSHORE UPPER IMPULSE WILL
BEGIN TO DEEPEN WITH APPROACH OF A STRENGTHENING UPPER LEVEL JET AND
PROGRESS TOWARDS THE ENE.

LOW-LEVEL MOISTURE ADVECTION ASSOCIATED WITH STRENGTHENING
DEEP-LAYER FLOW WILL LEAD TO INCREASING PRECIPITATION RATES OVER THE
OLYMPIC PENINSULA INITIALLY...AND SPREADING INLAND TOWARDS PUGET
SOUND BY 06Z. WET-BULB COOLING WILL BE SUPPORTIVE OF SNOWFALL /RATES
LESS THAN 1 IN PER HR/ OVER THE LOWER ELEVATIONS /INCLUDING MUCH OF
THE SEATTLE METRO AREA/...AND HIGHER SNOWFALL RATES 1-2 INCHES PER
HR OVER THE OLYMPIC MTNS AND NRN CASCADE MTNS. STRONGER FORCED
ASCENT WILL BE POSITIONED TO THE N OF THE REGION...WHICH SHOULD
LIMIT HIGHER PRECIPITATION RATES FROM DEVELOPING. WITH
TIME...WARMING TEMPERATURE PROFILES MAY LEAD TO MIXED PRECIPITATION
TYPES ACROSS LOWER ELEVATIONS...EVENTUALLY TRANSITIONING TO ALL
RAINFALL LATER IN THE MORNING.

..ROGERS.. 01/12/2011

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

ATTN...WFO...PDT...SEW...

LAT...LON   48962146 48182122 47472120 46972165 46812217 46952303
            47142374 47532405 47972409 48162345 48122301 48182272
            48652261 48812232 48812212 48962146

Nearby

Mesoscale Discussions in Washington, 2011Every 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.