Site Name

IMPROVE: SULA1 (Sula, Montana)

Region

Central Rockies

Terrain

Terrain is shown in the 2 km terrain map and the 20 km terrain map.

The Selway-Bitterroot Wilderness Area consists of ~ 1,340,460 acres staddling the Bitterroot Range that is the border between Idaho and Montana. Eighty percent of the Wilderness is on the Idaho side. Terrain is rugged steep mountains and deep canyons. Elevations range from near 550 m (1,800 ft) on the Selway and Lochsa Rivers to 3,097 m (10,157 ft) at the summit of Trapper Peak.

The IMPROVE site representing the Selway Bitterroot and Anaconda-Pintler Wilderness Areas is SULA1 located near the town of Sula Montana in the valley of the East Fork of the Bitterroot River. The site is 20 km east of the eastern Selway Bitterroot Wilderness boundary and 17 km west of the western Anaconda-Pintler Wilderness boundary. The East Fork of the Bitterroot River has it headwaters in the west portion of the Anaconda-Pintler Wilderness Area. The SULA1 IMPROVE site is near the top of Sula Peak at an elevation of 1,903 m (6,242 ft).

Representativeness

SULA1 is at a hilltop location above the Bitterroot River East Fork valley that extends down from the western reaches of the Anaconda-Pintler Wilderness and is midway between Anaconda-Pintler and Selway Bitterroot Wilderness Areas. With respect to the Selway Bitterroot Wilderness, it is across the upper Bitterroot valley to the east of the Wilderness with an unimpeded vista into the eastern Wilderness area. It should be representative of aerosol concentration and composition at similar elevations, and of regional haze generally. It is separated from western Selway Bitterroot Wilderness locations by the Bitterroot Divide with elevations exceeding 3,000 m and may at times be less representative of lower elevations on the west side that are impacted by local sources.

Nearby Population/Industrial Centers and Local Sources

This northern Idaho/western Montana Wilderness area is remote from any major source regions. The nearest population center is Missoula Montana ~ 100 km north of SULA1 via the Bitterroot River valley. The major industry is timber.

Nearby Meteorological Network Monitoring Stations

Nearby meteorological monitoring network stations are shown in the data network map and at the US Climate Archive and RAWS station US Climate Archive sites. Long-term meteorological data from Missoula may be representative of concurrent meteorological conditions at SULA1. Historical data for Missoula and other first order NWS stations are available via the EPA Technology Transfer Network website. 

The closest and most representative upper air site is at Great Falls Montana (TFX). This and other upper air sites are accessible via the University of Wyoming Dept of Atmospheric Science web page.

Wind and Transport Patterns

Regionally, wind patterns and transport flows are dominated by westerly synoptic flows, with frequent easterly flows from the Canadian interior in the winter. Monthly Missoula Montana wind roses indicate this pattern, with northwesterly flow predominant at this surface station and a significant east-southeasterly component in the winter. Note that these surface wind patterns may differ somewhat from upper level winds because of terrain effects. Locally near the SULA1 monitoring site, mountain valley circulation will prevail in the absence of strong synoptic forcing. Nighttime drainage along the East Fork of the Bitterroot, near SULA1, will be from the Anaconda-Pintler Wilderness to the east, thence north towards Missoula. Afternoon upvalley flow will be southward from Missoula.

Inversions/Trapping

The upper Bitterroot East Fork valley where SULA1 is located may be subject to wintertime nocturnal surface based inversions, although the SULA1 elevation near the top of Sula Peak may keep it above such inversions much of the time. In the summer regional subsidence inversions during periods of high pressure and stagnation can result in regional aerosol buildup over periods of days. High regional aerosol concentrations may occur during summertime stagnation and subsidence inversion periods in conjunction with western wildland fires.

Climatological Statistics

Missoula Montana Normals Means and Extremes are representative of similar elevation locations in western Montana. Other Idaho Climate Summaries and Montana Climate Summaries are available from the Western Regional Climate Center.

Meteorological Indicators for Local Sources

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