White House Joins CoCoRaHS; A Belated March Arrival of Severe Weather

The fine art of weather watching at the nation’s capital, which goes all the way back to Thomas Jefferson, Philadelphia, and the Declaration of Independence, got a shot of adrenaline with the announcement that a CoCoRaHS rain gauge was being installed at 1600 Pennsylvania Avenue in Washington, D.C. The news broke on Monday as part of the fourth annual White House Science Fair.

CoCoRaHS, the Community Collaborative Rain, Hail and Snow network (CoCoRaHS), involves more than 20,000 volunteers across the U.S. and Canada who collect precipitation data and report it online each morning. The network is North America’s largest single source of daily precipitation data.

Figure 1. CoCoRaHS founder and Colorado state climatologist Nolan Doesken shows off a CoCoRaHS gauge at the White House Science Fair on Monday, March 23. Image credit: Darlene Cavalier.


CoCoRaHS originated in the wake of a deadly flash flood in Fort Collins, CO, on July 28, 1997. The disaster caused more than $200 million in damage, much of it at Colorado State University. State climatologist Nolan Doesken, whose office is at CSU, was frustrated by the lack of reliable data on the massive rainfall that fed the local floods. The experience led Doesken to develop a county-wide network of volunteer observers, starting in 1998. CoCoRaHS gradually spread to other parts of Colorado over the next several years; the second state (Wyoming) joined in 2003, and the 50th state (Nebraska) signed on in 2013. The network also extends to Puerto Rico and the U.S. Virgin Islands as well as Canada.

Automated observing systems have many strengths, including the ability to give quick notice on when precipitation starts or stops at a given location. However, CoCoRaHS uses only manual rain gauges, hail pads, and snowboards: these generally provide the highest accuracy for daily precipitation totals, provided the equipment is placed in an appropriate spot and used properly. CoCoRaHS offers extensive training through a network of county coordinators, as well as a collection of training videos and webinars available on YouTube.


Figure 2. A still image from one of the colorful CoCoRaHS training videos. Image credit: CoCoRaHS.


Because of the simplicity of CoCoRaHS volunteering--all that’s required aside from training is an inexpensive set of standard equipment and a good observing site--it plays well with other types of weather engagement, such as maintaining a personal weather station in the WU network. Data are entered through a CoCoRaHS interface and viewable through maps and station records on the CoCoRaHS website. (CoCoRaHS reports are received by WU, although the once-a-day readings are not currently displayed on the continually updated WunderMap.)




Figure 3. The White House station made its first official appearance on the CoCoRaHS map at 7:00 AM (the standard time for local data collection) on Monday, March 23. The gauge is located in the vicinity of the Kitchen Garden on the South Lawn of the White House. Image credit: CoCoRaHS.

Participants in the WU network and CoCoRaHS can also join NOAA’s venerable Cooperative Observer Program (COOP), which is celebrating its 125th anniversary this year. There are more than 8,000 COOP observers nationwide who collect and file daily reports of maximum and minimum temperature as well as precipitation totals. Several COOP participants have put in more than 70 years of service, and last summer 101-year-old Richard Hendrickson was the first to be honored for more than 80 years of volunteering.

First storm risk of spring Tues-Wed in southern Great Plains
A moderately strong upper-level trough moving through the central U.S., coupled with a strengthening surface low in Kansas, is triggering a two-day period of potential severe weather on Tuesday and Wednesday. A severe thunderstorm watch stretching from eastern Oklahoma to southern Missouri was issued Tuesday afternoon by NOAA’s Storm Prediction Center (SPC). The watch was more noteworthy than usual, since it’s the first watch of any type (tornado or severe thunderstorm) since February 25, and only the fifth watch of any type this year. In records going back to 1970, this is the latest we’ve gone in March before our first watch of any type. Stu Ostro (The Weather Channel) notes that by March 24 of last year, we were up to watch #32; in 2013, #63; and in 2012, #108.

SPC has issued “enhanced” risk areas for both Tuesday and Wednesday, a new rating between “slight” and “moderate” (see our explainer post from Monday for details on the new system). Moisture was still limited near the surface low on Tuesday afternoon, with dew-point temperatures only in the mid-50s. However, low-level wind shear was somewhat favorable near an east-west warm front, and a tornado or two is possible in any supercell thunderstorm that forms near the surface low this evening. As the surface low and upper trough shift east, a robust cold front will barrel across Oklahoma on Wednesday. There should be a short-lived risk of supercells close to the Oklahoma City-Tulsa corridor, likely followed by a southward-charging squall line.

Bob Henson



Figure 4. The Day 2 outlook issued at 1730 GMT Tuesday, valid on Wednesday, March 25, shows much of Oklahoma with an enhanced risk of severe weather. Image credit: NOAA/SPC.