Episodic Dust Events of Utah’s Wasatch Front and Adjoining RegionJeffrey D. Massey1, W. James Steenburgh1, and Thomas H. Painter2

1Department of Atmospheric Sciences, University of Utah, Salt Lake City, UT2Jet Propulsion Laboratory, Pasadena, CA

Contact: jeff.massey@utah.edu

Introduction

• Episodic dust events produce hazardous air quality in the Salt Lake City metropolitan area. From 2002–2010, wind-blown dust events produced 13 exceedances of the National Ambient Air Quality Standard for PM2.5 or PM10.

Derived from:1. North American Regional Reanalysis (NARR)2. GOES satellite imagery3. Salt Lake City (KMTX) radar imagery4. Hourly observations and remarks from DS-3505

Long term climatology (1930-2010)

• Dust loading in the nearby Wasatch Mountains affects a snowpack that serves as the primary water resource for ~400,000 people and enables a $1.2 billion winter sports industry, known internationally for the “Greatest Snow on Earth.”

• Observations from Colorado’s San Juan Mountains indicate that dust loading increases the snowpack’s absorption of solar radiation, thus decreasing the duration of snow cover by several weeks

12 MST 13 MST 14 MST 15 MST

Snowpack impacted by episodic dust eventsAlta, UT, 30 Apr 2009 NARR analyses of 850-hPa geopotential height (black) and

temperature (color shaded) at 17 MST 10 May 2004.

Type 3: Stationary Baroclinic Trough or Cold Front (18%)Example: 10 May 2004

Conclusions• Dust events at KSLC occur throughout the historical record, with

considerable interannual variability • Dust events have a bimodal distribution, with a peak in Apr and a

secondary peak in Sep, and are most common during the afternoon• KSLC dust events are mainly caused by Intermountain baroclinic

troughs, cold fronts, and airmass convection• Emission sources are concentrated in low elevation Late Pleistocene to

Holocene alluvial environments in southern and western Utah and southern and western Nevada

• Dust generated in prefrontal environment of upstream baroclinic trough or quasi-stationary front

• Baroclinic trough or cold front does not pass reporting station within 24 hrs of initial dust observation

Dust free snowpackBen Lomond Peak, 26 Apr 2005

Dust Event: A day (MST) at Salt Lake City International Airport (KSLC) with at least one blowing dust, dust in suspension, or dust storm report with visibility < 10 km in the Global Integrated Surface Hourly Database (DS-3505)

Type 1: Baroclinic trough or cold front (48% of events)Example: 10 May 2004

Type 2: Airmass Convection (33% of events)Example: 19 May 2006

Elevation (m)

1350

1700

2050

2400

Reflectivity (DbZ)

10 20

30

40

50

60

.5 degree NEXRAD KMTX reflectivity for 16:06 MST 19 May 2006

Time(MST) Direction Speed

(m s-1)Gust

(m s-1)Visibility

(km)

16:00 190 5.6 n/a 16

16:07 200 27.8 31.9 6.4

17:00 130 22.6 26.2 16

18:00 110 4.6 n/a 16

11:30 MST 12:30 MST 13:30 MST 14:30 MST

NARR analyses of 850-hPa geopotential height (black) and temperature (color shaded) at 11 MST 19 April 2008.

Dust Source regions

Wasatch M

tns

KSLC .CarsonSink

SevierDesert

Escalente Desert

Milford Valley

Frontal Passage

> 3 hrs before

< 3 hrs before

< 3 hrs after

> 3hrs after

25% 50% 87.5% 12.5%

Dust reports relative to surface frontal passage for all

baroclinic trough or cold front events

•Dust plumes are typically generated in the prefrontal environment and extend to the Wasatch Front.

•Dust may be entrained into the post-frontal airmass through cold-frontal convergence

•Airmass convection events are produced by thunderstorm outflow and are typically short-lived, but intense, events

Dust plume starting locations and orientations for all recent Intermountain West dust days from GOES imagery

Major Sources:1. Carson Sink2. Sevier Desert3. Sevier Lakebed4. Milford Valley5. Escalente Desert6. West Desert

Wind rose of conditions at the onset of each dust event

• Considerable interannual variability (4.3 per WY)• A bimodal monthly

distribution with a primary maximum in Apr and secondary maximum in Sep• An afternoon peak• Predominately southerly

winds at the onset

U13B-07

Dust events exhibit:KSLC observations

surrounding 16:07 MST dust observation

KSLC

Recent Event Characteristics (2001-2010)

GOES visible imagery with applied dust detection algorithm (red)

• Emission sources are concentrated in low elevation Late Pleistocene to Holocene alluvial environments in southern and western Utah and southern and western Nevada.

SevierLakebed