Regional and Mesoscale Meteorology Branch

Wind Regime Composites for NWS Sites

Introduction

Following the example of the Tallahassee summer sea-breeze composites, a set of generalized wind regime climatologies have been generated from satellite data over each of the continental United States NWS sites.

Like the Tallahassee climatology, the 1000 – 700mb Mean Layer Vector Winds(MLVW) are used. This parameter is derived from the 12 UTC ETA model analysis fields in the vicinity of each AWIPS site and represents a ‘sounding’. While the Tallahassee wind regimes were designed specifically for that area, the data for this project were separated into nine more generalized regimes. These cover the eight points of the compass and a calm (< 5 m/s) regime, as listed in the table to the right.

Wind Regimes for the AWIPS sites

Collection of two-byte GOES East and West imagery over the continental US began September 1, 1997 and is on-going. (see CONUS page for example.) Starting December 1997, monthly products are produced from this collection for a 320 by 120 pixel area centered on each AWIPS site for each regime containing data. These include a cloud cover percentage product from the visible channel using a threshold method described in Reinke et. al. 1992. For more information, click here. In 2003, an IR cloud detection method was added.

As each year of data is added, the products for each hour of a given month are combined into one climatology. Below are a couple of examples from these cloud composites from the visible channel.

San Francisco Bay Area, CA

This first example is over the San Francisco Bay area for 1900 UTC. Each image represents the total percentage of cloud cover during the given wind regime over a five year period.

January 1998-2002

Calm winds (<5 m/s) – 31 cases

Southwest winds – 24 cases

Northwest winds – 25 cases

Note:

• The differences between each regime
• In the Calm regime, the higher % of cloud in California’s Central Valley — Probably fog
• Note the very high cloud % in the Southwest regime. This regime occured more often during an El Nino year.

July 1999-2002

Calm winds (<5 m/s) – 70 cases

Southwest winds – 8 cases

Northwest winds – 28 cases

Note:

• The differences between July and January composites
• All three regimes show higher cloud % (80-100%) over ocean – marine stratus.
• All three show very low (0-10%) over land

1=Calm;2=North;3=Northeast;4=East;5=Southeast;6=South;7=Southwest;8=West;9=Northwest

Another valuable tool is to see how many days fall within each region. The graph to the left is for San Francisco during the time of the above composites.

Hastings, NE

The second example is Hastings, NE at 1645 UTC

January 1998-2002

Calm winds (<5 m/s) – 13 cases

North winds – 15 cases

Southwest winds – 13 cases

July 1999-2002

Calm winds (<5 m/s) – 41 cases

North winds – 10 cases

Southwest winds – 48 cases

1=Calm;2=North;3=Northeast;4=East;5=Southeast;6=South;7=Southwest;8=West;9=Northwest

Note: The number of cases for each regime appears to switch between January and July.

For two NWS sites, we have worked with the offices to develop climatologies geared specifically to the needs of that site. For more information, see Wakefield and Cheyenne pages). We would appreciate any suggestions or feedback as to what types of climatologies would be valuable (i.e. fog/low cloud, minimum nighttime temps, etc)