Mesoscale Modeling


The towers in the INL Mesonet [link] provide comprehensive information about the current state of the weather in the Snake River Plain, but they do have some limitations. First, most of the towers are 15 m tall, so they mainly provide a picture of near-surface conditions. Given the nearby mountainous terrain, the conditions at even a small height aloft can be quite different from those observed by the towers. A second limitation of the towers is that they show the current state of the weather, but do not forecast what conditions will be in the future. Many of ARLFRD's partnership activities with INL (e.g., dispersion modeling and wildfire support) involve forecasting winds and weather several hours into the future rather than just providing current conditions.

One approach to overcome some of these data limitations is to run a mesoscale weather prediction model over the region of interest. Such models provide a three-dimensional representation of the atmosphere and are similar to the numerical models run by NOAA to provide national weather forecasts. ARLFRD currently runs the WRF ARW mesoscale model [link] as part of its collaboration with INL.


ARLFRD runs the WRF mesoscale model to make high-resolution 6-12 hour forecasts in the vicinity of INL.

WRF Configuration

ARLFRD runs WRF with two grids as shown in the figure. The outer grid spans most of southern Idaho and parts of the surrounding states; it uses a 20 km horizontal grid spacing. The nested grid uses a horizontal spacing of 4 km. Additional configuration details are given below:

  • ARW model version 2.2 (soon to be upgraded to 3.2).

  • 33 vertical levels.

  • Two-way nesting.

  • Initialized from 20 km RUC model output.

  • RUC land-surface model.

  • Mellor-Yamada-Janjic PBL scheme.

  • Ferrier microphysics scheme.

  • Kain-Fritsch cumulus scheme on coarse grid.

  • Model runs every three hours

Output from the daily model runs are available here


Map showing the two WRF grids. The innermost grid covers the INL and surrounding towns and cities.

Linkage to HYSPLIT

Another advantage of the mesoscale modeling is that the WRF output is easily ingested into the ARL HYSPLIT dispersion model [link]. This provides ARLFRD with the capability of making INL dispersion forecasts that account for the full three-dimensional structure of the winds. In contrast, the current modeling based on MDIFF [link] is limited to a two-dimensional wind field based on the Mesonet data. The figure shows one example of HYSPLIT output based on mesoscale modeling for INL. HYSPLIT was run in full particle mode, and the release point was set near TAN at the northern end of INL. The particle colors are based on their height above ground level, with blue particles being closest to the ground and red particles being the highest aloft.

As can be seen, pollutant dispersion at INL can potentially be highly complex due to interactions with the nearby terrain. Many particles have been drawn up the Little Lost River Valley, and others have collected at the mouth of the Big Lost River Valley near Arco. Vertical motions associated with the mountains have lifted many of the particles near Arco to higher altitudes. A fraction of the original plume has remained in the Snake River Plain and continued moving off to the southwest.

Modified: March 29, 2011
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