This U.S. Drought Monitor week saw intensification of drought across parts of the western U.S. as hot and dry conditions persisted with a historic heat wave currently gripping much of the region. Since last Friday, dozens of high temperature records were broken across the West including a scorching 130° F recorded at the Furnace Creek Visitor’s Center in Death Valley National Park. If verified, this high would represent the hottest temperature on Earth since 1913. Accompanying the extreme heat, numerous lightning-ignited wildfires broke out across California during the past week causing air-quality issues across parts of the region. In the Southwest, the continued weak monsoon has led to expansion and intensification of drought-related conditions with areas of Arizona and New Mexico observing less than 50% of normal precipitation since the beginning of the monsoon season. Similarly, drought conditions in the western half of Texas have deteriorated from persistent dry conditions and extreme heat. In the Midwest, short-term precipitation deficits (past 60 days) have led to the expansion of areas of drought, particularly in Iowa, where impacts are being reported in the agricultural sector. In the Northeast, anomalously warm temperatures and below-normal precipitation during the past 90-day period have led to deterioration in drought-related conditions in parts of New England—including Massachusetts where state officials declared a Level 2 drought on August 14 for all regions of the state.
On this week’s map, areas of the region—including central and western Pennsylvania, south-central New York, Connecticut, Massachusetts, southeastern New Hampshire, and northern Maine—saw expansion and intensification of areas of drought in response to a combination of factors including short-term precipitation deficits, dry soils, and low streamflows. In the Finger Lakes region of New York, short-term rainfall has been spotty with some areas in the region reporting agricultural impacts (reduced hay yields). In Connecticut, Massachusetts, New Hampshire, and Maine, areas of Severe Drought (D2) expanded on the map in response to mounting precipitation deficits (4 to 8 inches) during the past 90 days and reduced streamflows. In southeastern New Hampshire, the Department of Environmental Services is reporting that numerous municipalities and community water systems have implemented mandatory outdoor water-use restrictions in response to the dry conditions. For the week, the region was generally dry with some light precipitation accumulations (generally <1 inch) observed in eastern and southern Pennsylvania, Upstate New York, and in eastern Maine. Average temperatures for the week were 2-to-10 degrees above normal. According to the National Centers for Environmental Information (NCEI), the Northeast Climate Region experienced its warmest (+4.6° F anomaly) July on record.
During the past week, scattered precipitation was observed across the region with rainfall accumulations ranging from 1-to-10+ inches with areas of Virginia experiencing the heaviest accumulations. On the map, nearly all of the region remained drought-free with the exception of a few isolated pockets of Moderate Drought (D1) in Alabama and Georgia as well as a newly introduced area of Moderate Drought (D1) along the west-central and southwest coastal areas of Florida where precipitation deficits are ranging from 5-to-10+ inches for the past 60-day period.
On this week’s map, drought intensified across the western half of Texas in response to continued anomalously hot temperatures, high winds, and mounting precipitation deficits. Changes on the map for Texas include expansion of areas of Moderate Drought (D1), Severe Drought (D2), Extreme Drought (D3) as well as the introduction of an area of Exceptional Drought (D4) in the Trans-Pecos region. According to the Texas A&M Agrilife Extension (August 11), the Far West region had reports of very poor rangeland conditions with many grass fires in addition to reports of a number of crops struggling—including cotton, corn, and sorghum. In Oklahoma, areas of drought intensified in the extreme southwestern part of the state with agricultural producers reporting very poor rangeland conditions and dry stock tanks. According to the Oklahoma Mesonet, for the period from January 1 to August 18, southwestern Oklahoma had experienced more than 30 days with temperatures exceeding 100° F. Elsewhere in the region, improvements were made in areas of Abnormally Dry (D0) in Arkansas, Louisiana, Mississippi, and Tennessee in response to showers and thunderstorm activity during the past week. For the week, most of the significant rainfall activity occurred in areas not experiencing drought with the heaviest accumulations observed in west-central and southwestern Arkansas where 5-to-8 inch accumulations were observed. Average temperatures were well above normal across much of Texas with areas in the Trans-Pecos and West Central Texas experiencing temperatures ranging from 6-to-10 degrees above normal for the week.
On this week’s map, some improvements were made to areas of Moderate Drought (D1) in Ohio in response to rainfall events during the past several weeks. Further to the west, areas of Moderate Drought (D1) and Severe Drought (D2) expanded in western and northeastern Iowa in response to short-term precipitation deficits during the past 60-day period, dry soils, and agricultural impacts including reports of supplemental feeding from deteriorating pasture conditions, water hauling, and reductions in corn yields. In southeastern Minnesota and southwestern Wisconsin, short-term dryness (past 60 days) and dry soils led to the introduction of areas of Moderate Drought (D1). In northern Minnesota, dry conditions this summer have reportedly impacted the availability of wild berries in forested areas leading to an increase in the frequency of bears coming into rural areas in search of food, according to the Minnesota Department of Natural Resources. For the week, the heaviest precipitation was observed in central Minnesota (3-to-5 inch accumulations) while the rest of the region was generally dry with the exception of isolated areas in southern Indiana, southern Illinois, and Ohio that received modest accumulations (<1 inch).
On this week’s map, areas of the region—including central North Dakota and western Nebraska—saw modest expansion in areas of Moderate Drought (D1) and Severe Drought (D2) in response to below-normal precipitation during the past 30-to-90-day period. Elsewhere, drought-related conditions deteriorated in southwestern South Dakota leading to the expansion of areas of Moderate Drought (D1). In northeastern Wyoming, some minor improvements were made in an area of Moderate Drought (D1) where precipitation has been above normal during the past 30-60-day period. For the week, average temperatures were mainly above normal with the greatest anomalies occurring in eastern Colorado, southeastern Wyoming, western Nebraska, and southwestern South Dakota where temperatures were 2-to-8 degrees above normal. Overall, the region was generally dry with some lesser accumulations (generally < 1 inch) observed in the Dakotas, eastern Montana, Nebraska, and Kansas.
During the past week, an intense heat wave impacted the region as a strong mid/upper level ridge of high pressure parked over the region. Since Friday, numerous high temperature records were broken in cities across the West including Phoenix, Flagstaff, Oakland, Sacramento, and Reno—to name a few. In addition to the extreme heat, thunderstorm activity caused dozens of lightning-ignited wildfires to break out across central and northern California leading the Governor to declare a state of emergency on Tuesday, August 18. The wildfires have intensified and spread quickly leading to large-scale evacuations across numerous communities in northern California. On the map, areas of Severe Drought (D2) and Extreme Drought (D3) expanded in Arizona, Colorado, and Utah. To date, the monsoon has been a “bust” across much of the Southwest with cities like Phoenix, Tucson, Albuquerque, Las Vegas, and El Paso all reporting well below-normal precipitation totals for the monsoon season.
On this week’s map, no changes were made in Alaska or Puerto Rico. In the Hawaiian Islands, dry conditions during the past few weeks led to expansion of areas of Abnormally Dry (D0) on the windward slopes of the Big Island and Molokai. Additionally, a small area of Moderate Drought (D1) was added near South Point on the Big Island where vegetation-based satellite indicators were showing areas of dry vegetation. In Alaska, average temperatures for the week were well above normal (6-to-10 degrees F) on the North Slope while temperatures were 2-to-6 degrees above normal across parts of the Interior. In Southeast Alaska, average temperatures ranged from 2-to-8 degrees below normal. Precipitation was below normal across the western half of the state while the eastern portions (eastern Interior, Southeast) were well above average for the week.
The weather across the U.S.-Affiliated Pacific Islands (USAPI) during this USDM week (8/12/20-8/18/20) consisted largely of a monsoon trough in western Micronesia, a near-equatorial trough with trade-wind convergence over eastern Micronesia, and several weak circulations moving within these troughs. A Tropical Upper Tropospheric Trough (TUTT) at the upper levels stretched east-west across the breadth of Micronesia but around 20 degrees North latitude, and the northern TUTT cells and an upper-level low near western Micronesia provided divergence aloft which enhanced showers generated by surface convergence. Daytime island heating aided the development of showers over Guam and other Marianas islands. A surface ridge of high pressure kept showers at a minimum over southern portions of eastern and central Micronesia. South of the equator, a convergence zone/stationary front brought abundant rain to American Samoa.
Satellite-based estimates of 7-day precipitation (QPE) showed bands of precipitation stretching east from Indonesia comprising the climatological Inter-Tropical Convergence Zone (ITCZ) and southeastward from Indonesia comprising the South Pacific Convergence Zone (SPCZ). Two large regions of 1+ inches of rain, with embedded areas of 4+ inches, covered Micronesia, one over Palau and Yap State and the other over Kosrae State and the Marshall Islands (RMI). Areas of 1+ inches of rain dotted the Marianas and Chuuk and Pohnpei States. But southern portions of much of central and eastern Federated States of Micronesia (FSM) had little to no rain indicated on the QPE. The satellite analysis depicted several areas of 1+ inches of rain over and around the Samoan Islands.
In the Republic of Palau, over 10 inches of rain fell at the Palau IAP (10.74 inches) and Koror COOP station (11.02); these are well above the weekly minimum (2 inches) needed to meet most water needs. With the monthly totals so far well above the 8-inch monthly minimum at Palau IAP (19.07 inches) and Koror COOP (17.03), and April-July wet, D-Nothing continued at Palau.
This week was wet (above the 1-inch weekly minimum needed to meet most water needs) in the Marianas. Guam recorded 1.67 inches of rain and Rota 2.41 inches. On Saipan, 1.45 inches was reported at the IAP and 2.37 inches at the NPS station, but 0.74 inch was recorded at the ASOS station. It has been wet so far in August, and July was wet, but previous months were quite dry. At Saipan IAP, in spite of the July wetness, March-July 2020 still ranked as the driest March-July in the 40-year record. D2-SL continued at Rota and Saipan to reflect the longer-term dryness. Guam was D-Nothing last week. Based on local reports, Guam has been receiving just enough rain for the vegetation to turn green, but the streams are still dry. Based on this impacts data, Guam’s status was changed to D0-L.
Parts of the Federated States of Micronesia were wet (above weekly minimums), while others were dry (below weekly minimums). Weekly rainfall gauge reports ranged from 2.18 inches at North Fanif to 4.47 inches at Pohnpei on the wet end of the scale, and from 0.05 inch at Lukonor to 1.94 inches at Mwoakilloa on the dry end of the scale. Reservoirs on Yap are full with no drought impacts reported. Kapingamarangi recorded 0.31 inch of rain this week. Recent weeks were below the 2-inch weekly minimum, but not by much, and enough rain has been falling spaced close enough across the days that vegetation is green, crops are in good shape, and water supply in the catchments has improved. Based on these reduced impacts, the USDM status at Kapingamarangi was improved from D2-S to D1-S. With weekly and/or monthly precipitation above corresponding minimums, D-Nothing continued at the rest of the locations. However, Ulithi has had weekly rainfall totals below 2 inches for each of the last 3 weeks, so D0-S may be considered in future weeks if the dryness continues or impacts (such as low catchments) are reported.
In the Marshall Islands, no data was received from Utirik this week or the last 3 months so an analysis could not be made there. Weekly rainfall totals ranged from 0.33 inch at Ailinglapalap to 1.09 inches at Majuro and 1.29 inches at Kwajalein, on the dry side of the scale, and from 2.33 inches at Jaluit to 5.43 inches at Mili and 7.04 inches at Wotje, at the wet end of the scale. Based on an August 14 report, the reservoir level at Majuro was 84% of maximum, which is above the threshold for concern. With 1.29 inches of rain so far this week continuing a string of dry weeks, and a monthly total so far of 3.49 inches, D0-SL continued at Kwajalein. The 7.04 inches received this week at Wotje increased the monthly total for August to 9.36 inches, which is above the monthly minimum; water catchments have replenished some, but it will take a while for vegetation to recover; the status was improved to D2-SL at Wotje. With weekly and/or monthly precipitation above corresponding minimums, D-Nothing continued at the rest of the locations.
It was a wet week (and month so far) in American Samoa. Over 5 inches of rain was recorded for the week at Pago Pago (5.61 inches) and the NPS station at Siufaga Ridge (5.77), and nearly 3 inches was recorded at the NPS automated station at Toa Ridge (2.98). D-Nothing continued at Tutuila.
The weather conditions across the U.S. Virgin Islands (USVI) during this USDM week (8/12/20-8/18/20) were dominated by high pressure ridging, dry air masses, and occasional subsidence. A couple tropical waves moved through the area during the week, and Tropical Storm Josephine passed well north of the USVI later in the week, but Josephine fell apart as it passed by and the rain associated with this tropical system was less than expected.
Radar-based estimates of rainfall for the 7 days ending at 12z on Tuesday showed the heaviest rain over northern Puerto Rico and much less over the USVI. Half an inch was indicated for parts of St. Thomas, a fourth of an inch over parts of St. John, and less than a fourth of an inch for St. Croix.
Weekly rainfall totals on St. Croix ranged from 0.11 inch at the Henry Rohlsen Airport to 0.22 inch at East Hill and 0.32 inch at the Christiansted 1.8 ESE CoCoRaHS station. The monthly total for August 1-18 was 0.19 inch at Rohlsen AP, which was about 11% of normal, and 0.71 inch at East Hill, which was about 43% of normal. East Hill had the fourth driest 8/1-8/18 and 10th driest 4/1-8/18 (out of 48 years of data). Rohlsen AP had the driest 8/1-8/18 and fourth driest 4/1-8/18 (62 years of data). The Standardized Precipitation Index (SPI) values for the Rohlsen AP were at D1 levels for the 1- and 9-month time scales and at D3 level for the 12-month time scale. The SPI values for East Hill were at D1 levels for the 3- and 12-month time scales. Maximum temperatures were above normal each day this week at Rohlsen AP, with record highs on the 12th (93), 13th (94), 16th (93), 17th (95), and 18th (95); the average max temperature for 8/1-8/18 ranks 2020 warmest in the 62-year record, and 4/1-8/18 ranks second warmest. The average temperature for 4/1-8/18 ranks third warmest and for 4/1-8/18 ranks second warmest. The Adventure 28 well had no data since April 25 due to equipment malfunction. D1-SL continued on St. Croix.
On St. Thomas, a fifth of an inch of precipitation or less was recorded for the week at the King Airport (0.15 inch) and CoCoRaHS stations at Charlotte Amalie 1.4 NE (0.20) and Anna's Retreat 2.5 ESE (0.13). The total for the month so far is 0.49 inch at King AP, which is 25% of normal, 0.55 inch at Charlotte Amalie 1.4 NE, and 0.19 inch at Anna's Retreat 2.5 ESE. King AP had the third driest 8/1-8/18 and tenth driest 4/1-8/18 (with 6 days missing) (out of 58 years of data). The SPI at King AP was at the D0 level for the last 6 and 12 months. The USGS Grade School 3 well has had no data since July 29 due to equipment malfunction. D0-S continued on St. Thomas.
On St. John, about a third of an inch of rain was measured in rain gauges this week at the Windswept Beach station (0.34 inch) and CoCoRaHS stations at Cruz Bay 0.8 NE (0.39) and Cruz Bay 1.6 E (0.28). The total for the month so far ranged from 0.50 inch at Cruz Bay 0.8 NE to 0.53 inch at Windswept Beach, which is about 20% of the long-term average, to 0.67 inch at Cruz Bay 1.6 E. The SPI at Windswept Beach is at the D0 level for the last 3 months, but at the D1 level for the last 6 and 12 months. The USGS Susannaberg well has had no data since June 23 due to equipment malfunction. D1-S continued on St. John.
Looking Ahead
The NWS WPC 7-Day Quantitative Precipitation Forecast (QPF) calls for light-to-moderate accumulations ranging from 1-to-5 inches across portions of the South, Southeast, and the Mid-Atlantic with Florida and eastern portions of the Gulf Coast expected to receive the heaviest accumulations. In the Upper Midwest and northern portions of New England, accumulations of less than 1 inch are expected. Elsewhere, generally dry conditions are expected across the remainder of the conterminous U.S. with some isolated thunderstorm activity expected across the Southwest, central and northern Rockies, and the Great Basin—although rainfall accumulations are expected to be light (<1 inch). The CPC 6-10-day Outlook calls for a moderate-to-high probability of above-normal temperatures across most the conterminous U.S. with the exception of the far northern portions where temperatures are expected to be normal except for the Upper Midwest where below-normal temperatures are expected. In terms of precipitation, there is a moderate-to-high probability of above-normal precipitation across parts of the West including the Great Basin and areas of the Intermountain West including Utah, Wyoming, Idaho, and Montana. Other areas with a moderate probability of above-normal precipitation include much of the Midwest and the eastern tier. Conversely, drier-than-normal conditions are forecasted for western portions of Oregon and Washington as well as the Desert Southwest, northern Texas, and the Southern Plains.