Overview of the February 2, 1999 Eastern WA and North ID Wind Storm

INTRODUCTION

Strong winds developed over eastern Washington and Northern Idaho on 02 Feb 1999. Wind speeds of 50 mph were common across many locations in Eastern Washington and Northern Idaho, with over 70 mph wind gusts recorded in Spokane. As a result, numerous trees and powerlines were toppled. In addition, structural damage to many homes and businesses was reported. KXLY news also reported 8000 to 10000 of AVISTA's customers were without power during the height of the wind storm. To gain an understanding of the cause and extent of the wind damage, an overview of model data, satellite data, and surface observations will be presented. In addition, reports of damage receieved by NWS Spokane will also be presented.

 

SYNOPTIC ENVIRONMENT

 

An upper level low was heading east into the coast of southern BC and shearing apart at 12 UTC 02 Feb 1999 (Fig. 1). Meanwhile 500 mb short wave trough was moving east toward western Washington. Strong 850 to 700 mb warm air advection over eastern Washington ahead of the short wave trough was producing snow from Spokane and Collville east into the Idaho Panhandle. The snow ended over the area by late morning as strong subsidence associated with the 500 mb short wave spread into the area. (Fig. 2).

 

A strong jet, with 250 mb winds in excess of 120 kts at 12 UTC, was situated to the south of the low over Washington. Once the shortwave trough moved through northeast Washington, the 250 mb jet increased to 160 knots (Fig. 3).

 

Wind speeds in the mid to low levels over Washington were also exceptionally strong with 850 mb wind speeds near 50 kts at 12 UTC (Fig. 4). The surface pressure gradient was also exceptionally tight as an area of low pressure moved southeast through British Columbia (Fig. 5).

 

Surface Conditions

 

Surface wind speeds over the east slopes of the Cascades began to increase considerably by late morning. Sedge Ridge RAWS reported a wind gust of 95 mph while Washington Pass Raws reported a wind gust to 55 mph. Wind gusts began to slacken off by early afternoon over the Cascades. Meanwhile, over eastern Washington wind speeds increased dramatically through early afternoon. By 2200 UTC, most locations over Eastern Washington reported wind gusts over 45 mph including Spokane Felts Feild (SFF) where a wind gust of 63 mph was recorded ( Table 1).

The stiff sustained winds were a result of a very tight pressure gradient. However, it is likely the higher wind gusts that caused most of the damage were a result of mid level winds accelerating down to the surface. One indication of this is a number of surface observations reporting rapidly a falling pressure, followed by a rapidly rising surface pressure, and then another rapidly falling surface pressure. Water Vapor imagery also indicates that this type of phenomena may be occuring (Fig. 6). Visible imagery also clearly shows the impact of subsidence associated with the short wave trough (Fig. 7).

Damage Reported

 

Wind damage over Douglas and Northern Grant County began to occur before noon and by early afternoon in Spokane and Coeur D'Alene. The most common type of damage was due to fallen trees and downed power lines. Power outages were reported in most towns across the Basin along with the Palouse and Spokane and Coeur D'Alene areas. Outages ranged from just a few hours in Lewiston to over 12 hours around Spokane and Coeur D'Alene. More serious types of damage such as blown off roofs and trees falling on structures were generally confined to Spokane and Coeur D'Alene areas ( Table 2). The fact that the ground was wet and soft from recent rain and snow along the Spokane River Valley likely aided in producing the large number of downed trees and power lines.

 

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Table 1 - Maximum Surface Wind Speeds across KOTX CWA  Values in red meet high wind criteria
Observations	Maximum Wind Speed (kts)	Time (UTC)
WA Zone 32/ ID Zone 26
Lewiston (LWS)	40 Gust to 45	2153
Lewiston (LWS)	32 Gust to 56	2235
WA Zone 33/ ID Zone 03
Pullman (PUW)	31 Gust to 54	2356
WA Zone 34
Ephrata (EPH)	46 Gust to 63	1856
WA Zone 36/ ID Zone 02
Spokane (GEG)	39 Gust to 47	1956
Spokane (GEG)	31 Gust to 53	2135
Spokane (SFF)	26 Gust to 63	2045
Otis Orchards (spotter)	Gust to 73	2012
Coeur D'Alene (COE)	38 Gust to 61	2115
Foss Maritime (north side of Lake Coeur D'Alene)	Gust to 67 mph	2235
WA Zone 37
Deer Park (DEW)	31 Gust to 48	2053
WA Zone 38
Nespelem (RAWS)	25 Gust to 45 mph	2054
WA Zone 42
Washington Pass (RAWS)	26 Gust to 55	1957
Douglas Ingram (RAWS)	17 Gust to 35	2030
Leecher (RAWS)	20 Gust to 48	1954
NCSB (RAWS)	33	2058
First Butte (RAWS)	16 Gust to 34	1856
WA Zone 43
Kramer (RAWS)	21 Gust to 37 mph	2056
WA Zone 43
Douglas (RAWS)	26 Gust to 44 mph	2040
ID Zone 04
Mullan Pass (MLP)	Gust to 46 mph	0108
Other Observations
Rattlesnake Ridge	82 Gust to 97 mph	2335
Grey Back (RAWS)	Gust to 79 mph	1911
Sedge Ridge (RAWS)	Gust to 95 mph	1721
Hanford (HMS)	41 Gust to 64 mph	2356

 
 

Table 2 - Reports of Wind Damage across KOTX CWA Damage reports were not received in counties not included
Location of Damage	Damage type	Approximate Time
WA Zone 32/ ID Zone 27
Lewiston/Clarkston Vicinity	A few downed trees and breif power outages.	Late Afternoon
WA Zone 33/ ID Zone 03
Whitman County	Many trees and Power lines downed. A few blocked roads due to debris.  Power outages of at least 10 hours.	Late Afternoon
WA Zone 34
Grant County	Entire roof blown off a mobile home near Ephrata. Trees and Power Lines downed.	Late morning into early afternoon.
WA Zone 35
Adams County	Parts of roofs blown off buildings, mainly northeast sections of Adams County.	Late afternoon into early evening.
Lincoln County	Shingles blown off roofs. Metal roofs partially blown off barns and other structures.	Late morning into early afternoon.
WA Zone 36/ID Zone 02
Spokane & Coeur D'Alene	Parts of roofs blown off buildings. Business signs blown apart. Many traffic light poles were turned and caused to be facing the wrong direction.  Numerous trees down, 2 known large trees blown onto homes. Numerous power lines down. Power outages impacted over 8000 people, some for over 12 hours. Roads blocked by debris, as many as 12 intersections at one time.	Noon into mid afternoon.
WA Zone 37
Deer Park and vicinity	A few trees downed into power lines.	Noon into mid afternoon.
By Don Moore