Pu, Zhaoxia, and Hailing Zhang, University of Utah,
Salt Lake City, UT
Accurate forecasting of
near surface atmospheric conditions, especially those over complex terrain,
presents a challenge in numerical weather prediction. This study evaluates the
performance of the modern Weather Research and Forecasting (WRF) model in
predicting near surface atmospheric temperature and wind conditions under
various terrain and weather regimes.
Three individual cases
under strong synoptic-forcings (i.e., a frontal system, a low-level jet and a
persistent cold air pool) are first evaluated. The WRF model is able to
reproduce reasonable simulations of these weather phenomena. The verification for near surface
conditions (i.e., temperature at 2-m of height and wind at 10-m of height)
against the surface mesonet observations is then conducted. Results indicate
that forecasts of near surface variables over flat terrain generally agree well
with the observations while errors could also occur, depending on the modelŐs
predictability in terms of the atmospheric boundary layer. Over complex
terrain, the forecasts not only suffer from the modelŐs ability in reproducing
accurate atmospheric conditions in lower atmosphere but also struggle with the
representative issues due to mismatches between model and realistic terrain. In
addition, over complex terrain, simulations at finer resolutions do not
over-perform those at coarser resolutions.
A statistic analysis is
also performed for 120 forecasts during one-month period to further investigate
the forecasting error characteristics over complex terrain. Results illustrate
that forecast errors in near surface variables remarkably depend on the diurnal
cycle of surface conditions, especially when the synoptic-forcing is weak.
Under the strong synoptic-forcings, the diurnal patterns in the errors are
broken while the flow-dependent errors are clearly shown.