Here is the Virginia Water Central News Grouper’s monthly water-status report on precipitation, stream flow, flooding, and drought, as of the end of December 2020. The Virginia Water Resources Research Center thanks the agencies mentioned below for providing the data and maps used in this post. Icons for precipitation, stream flow, groundwater, and drought are by George Wills of Blacksburg, Va. (https://www.etsy.com/people/BlacksburgArt). For previous monthly water status reports, please see this link: https://vawatercentralnewsgrouper.wordpress.com/?s=Water+Status.
Here are National Weather Service (NWS) preliminary (still needing verification) precipitation totals for December 2020 at 12 Virginia or near-Virginia locations, along with the “normal” (three-decade average) for this month of the year at each location. Also shown are the precipitation totals at each location for the previous 12 months and the annual precipitation normals for each location. The values are in inches.
|Location||December 2020 Observed||Monthly Normal||Jan. 2020- Dec. 2020 Observed||Annual Normal|
|Reagan National Airport4||4.96||3.05||57.34||39.74|
1 – The Bluefield location is the Mercer County, W. Va., airport, near the Va.-W.Va. state line.
2- The Bristol location is the Tri-Cities Airport in Tenn., about 20 miles from Bristol, Va./Tenn.
3 – The Charlottesville location is the Charlottesville-Albemarle Airport.
4 – Reagan National Airport is in Arlington County.
5 – Wallops Island is in Accomack County.
6 – Washington-Dulles Airport is in Loudoun County.
Precipitation sources: Climate pages of the following National Weather Service Forecast Offices:
Blacksburg, Va. (https://w2.weather.gov/climate/index.php?wfo=rnk);
Morristown, Tenn. (https://w2.weather.gov/climate/index.php?wfo=mrx);
Baltimore-Washington (https://w2.weather.gov/climate/index.php?wfo=lwx); and
Wakefield, Va. (https://w2.weather.gov/climate/index.php?wfo=akq).
The normal values used by the National Weather Service (NWS) in these provisional reports are based on the period from 1981 to 2010. The National Climatic Data Center released these normal values in July 2011. For information on the normal values, see the National Climatic Data Center Web page at http://www.ncdc.noaa.gov/data-access/land-based-station-data/land-based-datasets/climate-normals.
For graphs of precipitation, visit the High Plains Regional Climate Center at https://hprcc.unl.edu/maps.php?map=ACISClimateMaps), where you can find maps of total precipitation and percent of normal precipitation for the past 7, 30, 60, or 90 days for all U.S. regions; or the NWS’ Advanced Hydrologic Prediction Service at http://water.weather.gov/precip/ for a map of precipitation nationwide or by state, with capability to show county boundaries, and archives available for specific days, months, or years. Shown below are the preliminary maps from the High Plains Center of the percent-of-normal precipitation for the southeastern United States for the previous 30 days, 60 days, and 90 days, and for Virginia for the previous 30 days, all through December 30, 2020.
Shown below is a color-coded percentile map of monthly average stream flow values for December 2020 at stream gages in Virginia and just beyond the state border, compared to the historical range for each gage. The map is from the U.S. Geological Survey (USGS) WaterWatch for Virginia, accessed online at https://waterwatch.usgs.gov/index.php?m=mv01d&r=va&w=map. The chart below the map shows the color codes/percentile classes used by USGS to compare flows to historical records for the month.
An overall look at Virginia streamflow conditions is provided in the USGS WaterWatch summary plot of daily average streamflow conditions, compared to historical records for any given date. Below is the summary plot for 89 Virginia sites during the 45-day period ending December 31, 2020, accessed on January 1, 2021, at https://waterwatch.usgs.gov/index.php?id=pa01d&sid=w__plot&r=va.
NATIONWIDE FLOODING OVERVIEW
Following is the National Weather Service’s Advanced Hydrologic Prediction Service’s (AHPS) map of stream and river levels relative to flood stage (color-coded) for the continental United States, as of 11:37 a.m. EST on December 31, 2020. The current map is available online at http://water.weather.gov/ahps/forecasts.php; at that site, one can select Virginia or any other state of interest.
Information on current groundwater levels in Virginia monitoring wells is available from the U.S. Geological Survey’s National Water Information System, online at http://waterdata.usgs.gov/va/nwis/current/?type=gw.
DROUGHT IN VIRGINIA
The weekly U.S. Drought Monitor report from the University of Nebraska-Lincoln (http://droughtmonitor.unl.edu/) for December 29, 2020, categorized Virginia as drought-free. That drought-free categorization began the week of August 18, 2020; prior to that, Virginia had been categorized as having some level of drought since the week of June 16, 2020.
Drought Monitor categories are as follows:
D0 = abnormally dry;
D1 = moderate drought;
D2 = severe drought;
D3 = extreme drought;
D4 = exceptional drought.
The Drought Monitor notes that it “focuses on broad-scale conditions [and] local conditions may vary.”
For comparison, here are Virginia ratings from previous Drought Monitors from about one month, two months, three months, and one year ago:
11/24/20 – drought-free;
10/27/20 – drought-free;
9/29/20 – drought-free;
12/31/19 – 1.5% abnormally dry.
On November 1, 2019, the Virginia Drought Monitoring Task Force (DMTF), a collaboration of state and federal agencies, issued its most recent report (as of 9-30-20). A link to that report, along with other current drought-status information, is available online at https://www.deq.virginia.gov/water/water-quantity/drought. The DMTF’s reports typically include information from some or all of the following agencies: University of Virginia Climatology Office, U.S. Geological Survey (USGS), and the Virginia departments of Agriculture and Consumer Services, Health, and Environmental Quality.
The December 29, 2020, U.S. Drought Monitor categorized about 57.0% of the United States (including parts of 42states plus Puerto Rico) as being abnormally dry or worse. (The highest percentage in the abnormally or worse categories—that is, in all categories—reported by the Drought Monitor since it began in 2000 was 72.38 % of the country for the week of July 17, 2012.) The Drought Monitor categorized about 28.6% of the country (including parts of 21 states) as being in severe drought or worse (categories D2, D3, and D4); this percentage was the highest nationwide percentage of severe-or-worse drought since the Drought Monitor report for the week of September 10, 2013. (The highest percentage in the severe-or-worse categories reported by the Drought Monitor since it began in 2000 was 38.48% of the country for the week of August 7, 2012.)
The nationwide percentages for abnormally dry or worse (categories D0-D4) and severe or worse (categories D2-D4) in the previous three months and one year ago were as follows:
11/24/20 – 58.2% abnormally dry or worse; 26.8% severe drought or worse;
10/27/20 – 56.0% abnormally dry or worse; 25.0% severe drought or worse;
9/29/20 – 55.5% abnormally dry or worse; 22.9% severe drought or worse;
12/31/19 – 21.5% abnormally dry or worse, 2.6% severe drought or worse.
The following states had 50% or more of their land area categorized by the December 29, 2020, Drought Monitor as being in severe-or-worse drought:
Arizona = 98%;
California = 74%;
Colorado = 94%;
Nebraska = 51%;
Nevada = 92%;
New Mexico = ~100% (99.6%);
North Dakota = 69%;
Oregon = 70%;
Texas = 50%;
Utah = 97%;
Wyoming = 54%.
Following is part of the nationwide summary by the Drought Monitor earlier in December 2020 (December 8, 2020, report) on dry conditions in the western United States, particularly Arizona and California:
“This U.S. Drought Monitor week saw intensification of drought across parts of the western U.S. including California, Nevada, and Colorado, where precipitation has been below normal since the beginning of the Water Year (Oct 1). In California, statewide snow water content (SWE) is currently at 36% of the historical average for the date (Dec 7) and Water-Year-to-Date (WYTD) precipitation (statewide) is ranging from the bottom 10% to the bottom 33% with some areas in the Mojave Desert experiencing the driest on record for the period. According to NOAA’s National Centers for Environmental Information (NCEI), the 6-month period from June to November 2020 was the hottest and driest on record for both Arizona and California.”
Following is part of the Southeast Region comments earlier in December 2020 (December 8, 2020, report) on wet conditions in fall 2020 across the region, including in Virginia:
“According to NOAA NCEI climatological rankings, the September-November 2020 period was marked by above-normal precipitation across the Southeast with statewide precipitation ranks (where 1=driest on record and 126=wettest on record) for the period as follows: Virginia–123, North Carolina–118, South Carolina–107, Georgia–110, Alabama–104, and Florida–117.”
90-DAY DROUGHT OUTLOOK
For a look ahead, the National Weather Service/Climate Prediction Center’s “U.S. Seasonal Drought Outlook” is available at http://www.cpc.ncep.noaa.gov/products/expert_assessment/sdo_summary.php. Shown below is the outlook map available on December 31, 2020.