This Week's Drought Summary (4/16)
An active pattern brought snow, rain, thunderstorms and severe weather over much of the United States. Most of the precipitation was east of the Missouri River valley and the greatest amounts were centered over Tennessee, Arkansas, Kentucky, western Virginia and the northern portions of Mississippi, Alabama, and Georgia, where more than 3 inches of rain was widespread. Southern California also had record-breaking rains continue, while snow was recorded in portions of the northern Plains and Midwest. Temperatures were generally warmer than normal over the country with just the Southwest and northern Plains being below normal. The greatest departures were in Florida where temperatures were 6-8 degrees above normal for the week and in Montana and southern California where temperatures were more than 10 degrees below normal.
Temperatures were warm over most of the region, with departures of 4-6 degrees above normal over the Mid-Atlantic to up to 2-3 degrees below normal in Maine and New Hampshire as well as portions of southern New York. Most of the region recorded precipitation for the week with areas of the Mid-Atlantic at more than 300 percent of normal, while in New England, areas of New York were below normal. Overall, pockets of dryness have been developing through the region, but timely precipitation has prevented the introduction of abnormally dry conditions up to this point. The area remains drought free for this week.
Temperatures were above normal throughout the region this week with departures of 4-8 degrees above normal. South Florida had the warmest temperatures, with departures of 8-10 degrees above normal. Most all of the region was above normal to well above normal for precipitation as a significant storm system moved through the region Saturday through Monday. Much of region recorded 130-175 percent of normal precipitation. With the weekend rains, some areas of abnormally dry conditions were improved in Georgia and Alabama. The outlier was most of Florida and the Gulf Coast of Alabama and the outer banks of North Carolina. These areas were drier than normal, with some areas only seeing 50 percent of normal rain for the week and some parts of central Florida receiving less than 5 percent of normal for the week. Short-term dryness has plagued the Gulf coast areas and Florida; over the last 90 days, this area is running precipitation deficits of 4-8 inches below normal. With many of the drought indices and indicators paving the way for degradation this week, a large area of severe drought was introduced over portions of central and northern Florida. Without rain, further degradation is anticipated in the coming weeks.
Most of the region had above-normal temperatures for the week with departures of 2-4 degrees above normal. Areas of Wisconsin, Iowa, and Minnesota were cooler than normal for the week with temperatures of 3-5 degrees below normal. The eastern extent of the region recorded above-normal precipitation for the week with 200-400 percent of normal over Ohio and Kentucky. Dryness was widespread over Indiana, Illinois, Missouri, western Iowa and into Minnesota with less than 75 percent of normal precipitation for the week. Overall, the region has been drier than normal the last few weeks, but for agricultural purposes, this has been welcomed, especially after the last few years where the region had an abundance of spring moisture. Even with some areas drying out, there was no need to introduce abnormally dry conditions for this week and the region remains drought free.
It was mostly dry over much of the region this week with just areas of northern Wyoming, southwest South Dakota, and north-central Nebraska recording above-normal precipitation. Temperatures were below normal in the Dakotas, northern Nebraska, and Wyoming with departures of up to 8 degrees below normal. Areas of Colorado, Kansas and southwest Nebraska were above normal with departures of 2-4 degrees above normal. There are some pockets of dryness developing in portions of Nebraska and Kansas, but no changes were made there this week, although the area of south-central Nebraska and central Kansas is trending toward the introduction of abnormally dry conditions. Eastern Colorado and southwest Kansas remain the driest portion of the High Plains. Severe drought was expanded over southeast Colorado this week and moderate drought and abnormally dry conditions were pushed eastward. This area will need to be watched for further degradation in the weeks ahead.
Warmer than normal temperatures were widespread throughout the region with departures of 6-8 degrees above normal along the Gulf Coast. Precipitation was mixed over the area with portions of southeast Oklahoma, central to southern Texas, Arkansas and northern Louisiana and Mississippi all recording well above normal precipitation with readings of 150-400 percent of normal. Conditions remained dry over the Gulf Coast as well as west Texas. In west Texas, moderate drought was introduced and abnormally dry conditions were expanded this week. In central and south Texas, there was a mix of degradations and improvements as some areas were still realizing the impact of previous rains that allowed for some areas of extreme and severe drought to improve. A new area of severe drought was introduced in far southeast Louisiana and some improvements were made to the abnormally dry conditions in Mississippi. There is a very tight gradient setting up going inland from the Gulf Coast as these coastal areas continue to miss out on any precipitation and have had above-normal temperatures too.
Most of the region was dry this week outside of a few areas in Montana and western Wyoming while in the Southwest, record-setting rains continued in southern California and into Arizona. Over the last 6 weeks, areas in and around Kern County, California have gone from significant precipitation deficits to well above normal readings accompanied by flooding in the region. Most of southern California recorded 800 percent of normal precipitation just in the last week and 200-400 percent of normal over the last 30 days. Temperatures were cooler than normal over the southwest areas of the west and Montana while most of the rest of the region was 2-4 degrees above normal and northern California was 6-8 degrees above normal. The current water year has been dry over much of the region and this has allowed further degradations to be shown in portions of northern California up to Washington. In western Oregon, the current conditions are similar to 2000-2001 and 2004-2005 with the exception of the near-normal snowpack. Some counties in southwest Oregon are reporting the earliest start to the irrigation season since 2000-2001 with several counties preparing to file drought declarations with the state of Oregon. Severe drought was expanded over much of northwest California northward into Oregon. Severe drought was also expanded in the interior of Washington. Abnormally dry conditions and moderate drought were also expanded over eastern and western portions of Oregon and Washington this week as well as western Montana and northern Idaho. In southern California, moderate drought and abnormally dry conditions were removed from Kern County and vicinities in response to the record-breaking precipitation. Improvements were also made to areas of severe and moderate drought in northeast Arizona and to abnormally dry areas of northeast and north central Arizona.
Alaska, Hawaii, and Puerto Rico
There were no changes in Alaska and Puerto Rico this week. In Hawaii, more abnormally dry conditions were added to the Big Island while on Lanai, most of the abnormally dry conditions were improved outside of the northernmost extent of the island.
The weather conditions across the U.S.-Affiliated Pacific Islands (USAPI) during this USDM week (4/8/20-4/14/20) consisted of a fragmented Inter-Tropical Convergence Zone (ITCZ) continuing across southern portions of Micronesia, especially in the east, and a dry trade-wind regime dominating northern and western Micronesia. A near-equatorial trough extended from the ITCZ across western Micronesia for much of the week. Smaller surface troughs, trade-wind disturbances, and weak circulations migrated westward across Micronesia within and near the ITCZ and near-equatorial trough, with trade-wind convergence frequently occurring in the east and upper-level divergence occasionally enhancing showers in the eastern Federated States of Micronesia (FSM). The surface convergence, upper-level divergence, and circulations brought abundant rainfall over portions of eastern FSM, while the dry trade-wind pattern inhibited circulations and disturbances as they moved over the Marianas and western FSM. South of the equator, weather over the Samoan Islands was influenced by an elongated surface trough associated with Tropical Cyclone Harold. The tropical cyclone stayed south of the islands, but its associated trough lingered and was enhanced by an extremely moist and unstable air mass, bringing heavy rainfall and flash flooding to American Samoa.
Satellite-based estimates of 7-day precipitation (QPE) showed patchy bands of rainfall extending northwest to southeast from Micronesia to the Samoan Islands and beyond. A distorted band of 1+ inches of rain extended across the Marshall Islands (RMI) and eastern half of the FSM, with areas of 2+ inches over Kosrae State and parts of the southern RMI. Isolated patches of 1+ inches were over the northern RMI and near Yap and Koror. The satellite QPE generally showed little to no rainfall over most of the western half of the FSM and over the Marianas. A broad band of 2+ inches of rain stretched northwest to southeast across the Samoan region. Within this band, an area of 4+ inches was over and south of American Samoa.
In the Republic of the Marshall Islands (RMI), the southern islands of Jaluit and Mili remained free of dryness. Mili was especially wet, with well over 4 inches of rain reported during the drought-monitoring period. Jaluit received 2 to 6 inches of rain each of the previous 4 weeks, but reported less than an inch during the week ending April 14. Majuro retained an abnormally dry (D0-S) status due to lower-than-optimal reservoir storage, despite April 1-14 rainfall totaling 5.79 inches (138% of normal). Majuro's April 14 storage of 26.577 million gallons (73.8% of capacity) was down from 28.631 million gallons (79.5%) on April 8. On Ailinglapalap, where moderate drought (D1-S) was introduced a week ago, less than an inch of rain fell for the fourth consecutive week; further drought intensification may occur unless appreciable rain soon arrives. Kwajalein experienced a slightly wetter week, with 2.21 inches reported from April 8-14. The week's wettest day on Kwajalein was the 14th, when 1.36 inches fell; however, severe drought (D2-S) was retained, as March was very dry (total of 1.54 inches) and drought impacts have worsened in recent weeks. Similarly, extreme drought (D3-S) was retained for Utirik, despite a weekly rainfall of 2.38 inches (with one day missing). Previously, Utirik had experienced 10 consecutive weeks with less than an inch of rain. Data from Wotje was missing; thus, no drought assessment was made.
In the Federated States of Micronesia (FSM), the eastern islands of Kosrae and Pohnpei remained free of dryness. Weekly rainfall was particularly heavy, in excess of 12 inches, on Kosrae. Pingelap received more than 4 inches of rain for the second consecutive week, resulting in elimination of abnormal dryness (D0-S). In the south, Kapingamarangi remained free of dryness. Abnormal dryness (D0-S) was retained for Lukunor and Nukuoro, despite periods of beneficial rainfall in recent weeks; both islands received above-normal March rainfall but also report lingering agricultural impacts related to earlier dryness. Conditions worsen to the north and west, with moderate drought (D1-S) continuing a Chuuk Lagoon. At the end of the drought-monitoring period, 2.16 inches of rain fell at Chuuk Lagoon on April 14; however, month-to-date rainfall remains slightly below normal and year-to-date rainfall is nearly 5 inches below normal. Chuuk Lagoon will be monitored for possible improvement if beneficial rainfall continues. Serious drought persisted in western sections of the FSM, including Ulithi (D2-S), Woleai (D2-S), and Yap (D3-S). Ulithi reported a tenth consecutive week with less than an inch of rain. Woleai received 2.89 inches of rain (with one day missing), but continued to experience significant drought impacts. Likewise, Yap reported increased rainfall, but continued to note agricultural impacts and water-supply concerns. Despite rainfall totaling 0.99 inch on April 14, Yap's month-to-date total stood at 2.14 inches (86% of normal). Further, Yap's January 1 - April 14 rainfall totaled just 8.02 inches (38% of normal).
In the Republic of Palau, drought impacts are similar to those reported across western sections and the FSM and include water-supply shortages, agricultural damage, and an enhanced threat of wildfires. At the international airport, April 1-14 rainfall totaled 0.92 inch (25% of normal), while year-to-date rainfall stood at 18.08 inches (56%). Like last week, Palau is considered to be in moderate drought (D1-S). According to a National Weather Service meteorologist, the Palau Public Utilities Corporation (PPUC) reported during the first week of April a Water Shortage Alert for Aimeliik, Airai and Ngerchelong. By April 7, mandatory conservation was implemented, limiting water use to essential purposes (e.g. car washing prohibited). By April 13, water levels were reported to have declined substantially for the Ngerikiil water source and slightly for Ngerimel Dam, leading to water rationing from 11 pm to 5 am local time until further notice.
In the Commonwealth of the Northern Mariana Islands (CNMI), drought continued to gradually intensify. For Rota and Guam, drought intensity was changed from moderate to severe drought (from D1-S to D2-S). Many reporting sites in the CNMI have received less than an inch of rain for 10 consecutive weeks. According to the National Weather Service, the Keetch-Byram Drought Index, indicative of fire danger and reported on a scale from 0 to 800, was noted on Guam to be 721 (in the extreme category) on April 14. To the north, Saipan's drought intensity (extreme drought, or D3-S) remained unchanged.
American Samoa is experiencing neither dryness nor drought, and in fact remains very wet, courtesy of recent tropical moisture. During the first 12 days of April, rainfall at the Pago Pago International Airport totaled 11.32 inches.
For the third consecutive week, mostly dry conditions dominated the U.S. Virgin Islands. From March 24 - April 13, a volunteer observer at Windswept Beach on St. John reported rainfall totaling just 0.07 inch. During the same 21-day period, rainfall totaled 0.31 inch at King Airport on St. Thomas and 0.55 inch at Rohlsen Airport on St. Croix. However, the recent dry spell was immediately preceded by unusually wet weather in early to mid-March. Short-term (1-month) SPI values do net yet indicate significant dryness, and USGS well data suggests that depth to water has only recently begun to increase in response to the short-term dryness. As a result, St. John and St. Thomas remain free of dryness and drought, while abnormal dryness (D0-L) is retained for St. Croix due to much longer-term precipitation deficits and chronically low groundwater levels.
Over the next 5-7 days, it is anticipated that the eastern half of the United States will stay quite wet, with the Southeast projected to record the most precipitation. Some relief may come to the Gulf Coast region as well. The Northern Plains and upper Midwest look to be dry while the central and southern Plains will see up to an inch of precipitation. Precipitation looks to be scattered through the West with some upper elevations seeing the most precipitation. Temperatures during this time are expected to be cooler than normal over most of the United States with departures of 9-12 degrees below normal over the Midwest to New England.
The 6-10 day outlooks show much of the central U.S., West, Southeast, and Alaska having a greater than normal probability of above-normal temperatures while the Midwest and Northeast show a higher than normal probability of below-normal temperatures. The greatest probabilities of recording above-normal precipitation are over the Four Corners into the south to the Southeast and interior Alaska.