The U.S. Drought Monitor week ending March 17 saw another round of winter storms, bringing above normal precipitation to parts of the northern High Plains, Southwest, southern plains, and Tennessee Valley.
Many areas recorded totals that exceeded 200% of normal over the seven-day period, leading to improvements to areas of abnormal dryness and drought in areas where the excess moisture erased deficits and improved soil moisture and streamflow.
Once again, precipitation over the Northwest and Gulf Coast states was below normal with most areas having received less than 50% of their normal amount over the last 30 days. The lack of precipitation, combined with warmer than normal temperatures, led to expansions in pockets of abnormal dryness and drought.
The general pattern of rain in the northern tier of the region and dry weather in the south continued again last week. Much of the Tennessee Valley and Southern Appalachia received amounts in the range of 0.5 to 3 inches, while regions near the Gulf coast had little to no rainfall.
Changes to this week’s map include small expansions of D0 (abnormal dryness) in southern Alabama, the extreme western Florida Panhandle, and the central and southern Florida Peninsula as rainfall shortages in these have reached about 3 to 4 inches over the last 30 days, drying soils and lowering streamflow.
Should they miss out on next week’s forecast rainfall, areas to watch for deteriorating conditions include Virginia and northern North Carolina where moisture deficits are beginning to build.
Last week, a band of heavy rainfall fell across the northern half of the region, extending from West Texas to western Tennessee with amounts ranging from 1 to more than 4 inches (equivalent to more than 300% of normal in some locations).
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In southwest Oklahoma and northeast Texas, the excess moisture erased short-term precipitation deficits and recharged streamflow leading to reductions in D0 (abnormal dryness) and D1 (moderate drought). Additionally, the “S” was removed from the “SL” drought designation to indicate that drought and dry conditions are now only present at timescales longer than six months.
With over an inch of rain falling after the close of the Drought Monitor week (Tuesday, 8:00 AM EDT) and more expected on the way, additional reductions may take place on next week’s map.
Other areas seeing improvements include West Texas with reductions to D0 and D1. Unfortunately, the rain missed the parts of south Texas that need it most and conditions continued to deteriorate, resulting in expansions to ongoing areas of abnormal dryness and drought and the introduction of D4 (exceptional drought).
Supporting data include rainfall deficits of 2 to 8 inches (25 to 50% of normal) over the last six months combined with mean temperatures consistently ranking in the top 10 warmest over the same time interval. The combination of dry weather and high temperatures has dried out soils and stressed vegetation with USDA reporting only 28% of topsoil as adequate for crops in the southeast and 3% in the southwest.
Other areas seeing deterioration this week include southwest Louisiana and southeast Mississippi with expansions in D0.
The Midwest remains free of any drought or abnormal dryness. While Missouri and Kentucky saw precipitation totals in excess of 150% of normal, the rest of the region received amounts near or slightly below normal continuing a drying trend that began in February.
In general, the relatively dry weather has been welcome, enabling producers to begin field work. Soil moisture and streamflow levels remain high from 2019’s record-breaking precipitation and a wet January.
The map’s drought depiction is unchanged this week in the High Plains. A winter storm during March 13-14 brought snow to the west and central parts of the region and rain to locations in the south and east. The Black Hills saw the highest totals, reporting from 6 to 12 inches of snow while portions of western and central South Dakota and Nebraska reported several inches of accumulation.
Dry conditions continue to persist in the drought and abnormally dry areas in eastern Colorado, western Kansas, and southwest Nebraska where less than 0.50 inches of precipitation (about 50% of normal or less) has fallen so far this month.
As we transition to normally wetter conditions in the spring, hopefully this area will begin to see relief from the deficits that have built over the last six to 12 months.
February’s dry spell over California finally broke as a late winter storm brought heavy showers to southern California and over 2 feet of snow to the Sierra Nevada. In southern California, the excess rainfall improved soil moisture and streamflow levels leading to reductions in areas designated as D0 (abnormally dry) or D1 (moderate drought).
Despite the rain and snow, the maps depiction remained unchanged for the majority of the northern two-thirds of the state. Water year-to-date precipitation is more than 12 inches below normal (50% of normal or less) in the Sierras and the north coastal and north central regions. Soil moisture and streamflow values remain low and satellite based indicators of vegetation health continue to show stress across the Central Valley.
Extreme northern California and southern Oregon missed out on the heavy precipitation further deteriorating drought conditions and leading to the expansion of D1 and introduction of D2 (severe drought).
The Oregon state drought coordination team noted increasing water supply concerns in this region as many locations show record low streamflow values, declines in groundwater, and low reservoirs. Other changes in Oregon include minor improvements D1 areas in the west-central and eastern parts of the state where heavy precipitation fell.
Having missed out on last week’s precipitation, Nevada and Utah both saw and expansion of D0 in the north. Further south, rainfall of 1 to 3 inches helped erase precipitation deficits, replenish soil moisture, and improve streamflow in southern Nevada, southwest Utah, and northwest Arizona resulting in reductions in D0, D1, and D2.
Drought depictions in Washington, Idaho, Montana, Colorado, and New Mexico were left status quo.
While much of the northeast received precipitation last week, totals in southern and coastal New England continued to be below normal, further contributing to deficits of 6-plus inches over the last 90 days.
The lack of rain and snow combined with unseasonable warmth – with many stations reporting mean temperatures in the top five on record over the last month, low streamflow values, and low groundwater levels — led to the introduction of a swath of D0 (abnormal dryness) from eastern Massachusetts southward to northern New Jersey.
According to local media reports, the dry conditions combined with high winds contributed to brush fires in eastern Massachusetts, Rhode Island, and southeast New York.
Alaska, Hawaii, and Puerto Rico
After last week’s improvements, Alaska remains free of abnormal dryness and drought. Above normal precipitation and snowpack has left the state in good shape heading into the drier summer months.
In Hawaii, heavy rain events in progress at the close of the Drought Monitor week brought widespread flash flooding across the entire state and set a daily rainfall record in Honolulu, prompting the removal of the D0 (abnormal dryness) introduced on Oahu last week. With rain continuing the remainder of the week, additional improvements may be warranted on next week’s map.
Near to above normal precipitation continued this week across the majority of Puerto Rico. After last week’s removal of D0, the island remains free of any dryness on the map.
The National Weather Service Weather Prediction Center forecast for the remainder of the week shows a winter storm developing east of the Rockies and tracking northeast across portions of the north and central Plains into the Upper Midwest.
This storm is expected to bring heavy snow to the southern and central Rockies with a swath of light to moderate snow extending from Nebraska northeast into Minnesota and Wisconsin. A cold front associated with the storm system is forecast to trigger showers and thunderstorms from the southern plains into the Mississippi, Ohio, and Tennessee valleys.
Temperature are expected to be below normal by 10 to 20 degrees across California into the Central Great Basin and Southwest. Meanwhile, the Gulf Coast states and Ohio and Tennessee valleys can expect temperatures 3 to 6 degrees above normal. The Central Plains should see large temperature swings as the system passes through.
Moving into next week, the Climate Prediction Center six to 10 day outlook (valid March 22-26) favors below normal temperatures for much of the western half of the CONUS, especially near the West Coast, near normal temperatures east of the Mississippi, near normal temperatures in the Midwest and Northeast, and above normal temperatures for states along the Gulf and Southeast Coasts.
The precipitation outlook favors an active storm track and above normal amounts for nearly the entire CONUS. Probabilities are highest for California, parts of the Great Basin, and the Tennessee and Ohio valleys.