This Week’s Drought Summary
Two upper-level weather systems danced across the contiguous U.S. (CONUS) during this U.S. Drought Monitor (USDM) week (September 21-27). One partner of the pair was an upper-level low pressure trough which twirled from the West Coast to the northern Plains then migrated to the Northeast. The other partner was a high pressure ridge. As they did a kind of do-si-do, the ridge swung from the southern Plains to the western CONUS. Other players danced at the periphery – Hurricane Fiona moved across the Canadian Maritime Provinces, spreading rain over New England at the beginning of the week, while Hurricane Ian brought rain and wind to southern Florida as it bore down on the state just as the week ended. The high pressure ridge brought hot temperatures to the southern states at first, then to the West later in the period. The trough generated a storm track across the northern states, then sent a large cold front into the Southeast as the period ended. Monsoon showers joined in over the Southwest in these waning days of summer. The end result was a weekly precipitation pattern that was wetter than normal over parts of the West, southern Plains, Great Lakes, Northeast, and southern Florida. The rain missed large parts of the West, which received little to no precipitation, and much of the Plains, Mississippi to Ohio Valleys, and Southeast to Mid-Atlantic states were drier than normal as well. Temperatures for the week averaged warmer than normal over the southern Plains to Lower Mississippi Valley and across parts of the Southwest and Northwest. The week ended up cooler than normal from the northern Plains to Northeast and into parts of the Southeast. The hot temperatures and continued dry conditions, especially in the South, further dried soils. According to the U.S. Department of Agriculture (USDA), national topsoil moisture rated very short to short (dry or very dry) reached 54%, a high for the year to date and very close to the recent maximum of 56% achieved on October 18, 2020. This is the third year in a row that a peak greater than 50% has occurred. Drought and abnormal dryness contracted where it rained in the Southwest, Northeast, and southern Florida. Drought and abnormal dryness expanded where it didn’t rain, including the Northwest, Great Plains to Mississippi Valley, and Mid-Atlantic states.
About half an inch of rain fell across a few parts of Texas, Mississippi, and Tennessee, but otherwise the South region was dry this week. Hot and mostly dry conditions were observed this past week especially across the Arkansas-Louisiana-Texas area, with near record high temperatures recorded each day as readings neared the century mark. This marks nearly the third straight week with near cloud-free conditions, with below normal relative humidity for this time of year yielding high evaporation rates. Grounds have quickly dried out over much of the area, which has yielded an increased frequency of small wildfires especially across eastern Texas and portions of southeastern Oklahoma. In southeast Oklahoma, hydrological impacts were increasing as Broken Bow Lake was over 11 feet below conservation pool stage, with Pine Creek Lake down about 5 feet. USDA reports indicated 91% of the topsoil short or very short of moisture in Oklahoma. Rapid drying of soils has occurred in Arkansas, with the USDA statistic exploding from 40% on September 11 to 58% on September 18 and reaching 88% on September 25. According to news reports, fierce heat and drought in Arkansas have limited hay and grass growth; August rains allowed farmers to grow some hay, but farmers still do not have enough to get through the winter. Dried ponds, cracked earth, and no forage (pasture) for farm animals were common, especially in western Arkansas. D0 spread across much of Louisiana, Mississippi, and western Tennessee, with D0-D3 growing in Arkansas and D2-D4 expanding in Oklahoma. D0-D4 expanded in parts of northern, eastern, and central Texas, while contraction of D0-D1 occurred along parts of the Rio Grande River.