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Research using data assimilation models investigates summer rainfall timing

NLDAS data used to examine diurnal precipitation peak times during summer in the U.S.

Research using data assimilation models investigates summer rainfall timing

Diurnal precipitation maxima timing for summer in the U.S. The 4 regions are investigated in Matsui et al. This figure indicates only the timing, and not the strength, of the diurnal signal. "LST" stands for "Local Solar Time" (24 hour clock).

Research using data assimilation models investigates summer rainfall timing

When is it going to rain?   That's a question that gets asked frequently, and it's pretty important in the summer, when an ill-timed thunderstorm can interrupt a round of golf, baseball and softball games, outdoor barbecues, maybe even an outdoor wedding -- and the timing of storms can also have important bearing on human health and safety.    New research by a group led by Goddard Space Flight Center (GSFC) Laboratory of Atmospheres scientist Toshihisa Matsui investigates when (on average) it is most likely to rain during any given summer day – even though it can't tell us what specific day it will rain in the summer, unfortunately.

A new Science Focus article in the GES DISC hydrology portal, "Diurnal cycle of summertime precipitation from NLDAS data products", describes Matsui et al.'s research;   a paper describing these results has been published in Geophysical Research Letters.    Matsui and his colleagues used a 10-year climatology spanning 1998-2007 of assimilated hourly rain gauge data from the North American Land Data Assimilation System (NLDAS-2) for this research.   The results clearly indicated a peak in rainfall over the Rocky Mountains in the early afternoon, and this peak gets later and later in the day going eastward into the Great Plains, until it becomes an early morning peak, based on local solar time (LST).  This timing indicates that many summer storms in the Midwest are strongest in the early morning hours, when most people are sleeping, and thus severe storm and tornado watches and warnings may go unheard and unheeded.

The most robust signals appear in the interior of the Florida peninsula, with a maximal peak timing between 4 and 6 PM.  In the summer, millions of people visit famous amusement parks in central Florida, such as Disney World or Sea World near Orlando. Thus, this analysis recommends an early-arrival and early-departure plan for visitors to avoid late-afternoon thunderstorms (as well as the traffic jam of other tourists leaving the parks later in the day).

In the southern and eastern regions of the United States, peak rainfall time in the summer occurs in the early afternoon.   An interesting pattern is observed for residents of Virginia and Maryland (such as those of us who work at Goddard Space Flight Center):  the precipitation peak timing extends into the evening hours on the Chesapeake Bay and the Delmarva Peninsula, indicating the common pattern of afternoon thunderstorms moving eastward from the Blue Ridge mountains over the Piedmont, and then to the Atlantic coast.     Matsui investigated and identified regions of precipitation propagation using Hovm√∂ller diagrams for four regions extending from the Rockies to the Atlantic coast.

NLDAS data is currently available at the GES DISC from the Hydrology DISC and Mirador.

For more information:

Hydrology Data Holdings



Matsui, T., D. Mocko, M.-I. Lee, W.-K. Tao, M. J. Suarez, and R. A. Pielke Sr. (2010) Ten-year climatology of summertime
diurnal rainfall rate over the conterminous U.S. Geophysical Research Letters, 37, L13807, doi:10.1029/2010GL044139



Toshihisa Matsui -  Goddard Laboratory for Atmospheres and the Goddard Earth Science and Technology Center, University of Maryland - Baltimore County.

David Mocko -  GSFC Global Modeling and Assimilation Office and Science Applications International Corporation (SAIC)

Myong-In Lee - School of Urban and Environmental Engineering, UNIST, Ulsan, Republic of Korea.

Wei-Kuo Tao -  Goddard Laboratory for Atmospheres.

Max J. Suarez  - GSFC Global Modeling and Assimilation Office 

Roger A. Pielke, Sr. - Department of Atmospheric and Oceanic Sciences, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder

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Last updated: Jul 15, 2010 01:48 PM ET