Summary
Two rapidly-moving strong storm systems, one “bombing out” in the central Plains during mid-week while a second storm intensified over the middle Mississippi Valley during the weekend, brought severe weather and widespread precipitation to many areas of the lower 48 States, including heavy snows to parts of the north-central Rockies, north-central Plains, and western Great Lakes region. In the Northwest, moderate precipitation falling on an unseasonably late (and above-normal) mountain snow pack (due to a minimal melt from a cold spring) produced near- to record high stream flows in much of Oregon and southern Washington. Widespread precipitation, including mountain snows, fell across Idaho, Montana, northeastern Nevada, Utah, and Wyoming. In the Plains, moderate to heavy rains (1-3 inches) were measured in the south-central sections (Oklahoma and Texas), which then moved into the lower Mississippi and Tennessee Valleys (up to 6 inches in northern Louisiana). To the north in colder air, South Dakota was buried under heavy snow (locally over 2 feet). Moderate to heavy snows also blanketed Minnesota, Wisconsin, northern Michigan, and northern Illinois. Meanwhile, light to moderate precipitation was measured in the eastern third of the Nation, with a stripe of heavier rainfall (1.5-3 inches) falling from northern Georgia northeastward into southern New England. In contrast, most of the Southwest, extreme southern, central, and extreme northern Plains saw little or no precipitation. Temperatures generally averaged below-normal in the western two-thirds of the U.S., especially in the northern Plains and upper Midwest (6 to 12 degF), and above-normal in the eastern third of the Nation (6 to 9 degF in the Carolinas)…
High Plains
The mid-week storm system tracked out of the Northwest and into Wyoming, finally dropping decent precipitation (including heavy snow) across much of the state before it moved eastward into South Dakota (up to 26 inches), southern Minnesota (nearly a foot), and central Wisconsin (to 10 inches) by Friday. Liquid equivalents of 1-3.5 inches fell across central Wyoming and much of South Dakota, which was welcome for Wyoming as drier conditions had prevailed there before this week. The storm increased the WYTD basin average precipitation and SWE in Wyoming, with some basins now with WYTD surpluses. Accordingly, a 1-cat improvement was made in central Wyoming where the heaviest totals occurred and WYTD surpluses existed. In northwest Montana, 1-3 inches of precipitation in northwestern Teton, western Ponderosa, and southwestern Glacier Counties was enough to remove D0 as WYTD precipitation and SWE edged above 100% on April 16. Decent precipitation also fell on northwestern Montana (Lincoln County), but longer-term deficits lingered, and D0(L) remained. In Colorado, some scattered precipitation (0.25-1 inches) fell on southern D0 and drought areas, but it was not enough for additional improvements. Drier weather prevailed in Kansas and eastern Nebraska, but that was welcome after wet and cold weather earlier this spring…
West
Two storm system brought moisture to most of the Pacific Northwest, northern Rockies, and southward into northeastern Nevada and most of Utah. In the Pacific Northwest (mainly Oregon and Washington), this week’s precipitation + late-season snow melt = record high stream flows (flooding), even though WYTD was below-normal in northern areas, and long-term drought (more than 1 year) lingered in some Pacific Northwest areas. Fortunately, reservoirs were filling with the high stream flows, and were expected to rise to normal levels. Accordingly, improvements were made where 12-month SPEIs were normal to wet, precipitation fell this week, and WYTD surpluses existed. Thus, D0 was removed along the southern & eastern edges in Oregon, in central Washington’s Grant & Kittitas Counties, and D1 was shrunk (western edge) in the northern Cascades where 2-5 inches of precipitation fell. In Utah, the same storm system dropped 1-3 inches of precipitation in northern and central Utah, bumping WYTD basin average precipitation to 130-150% and SWE to 150-180% of normal as of April 16. 12-month SPEIs are normal or even wet, thus the western edge of D1 was shrunk and D0 erased thru central Utah. Little or no precipitation fell across the Southwest, but with late winter and spring surplus precipitation, generally below-normal temperatures this year, and mostly WYTD precipitation surpluses, no changes were made in California, Arizona, New Mexico, and Colorado…
South
With the mid-week (first) storm system mainly impacting areas farther north, the second system that occurred during the weekend developed and rapidly intensified over the southern Plains and lower Mississippi Valley. Widespread moderate to heavy rains (2-4 inches, locally to 6 inches), including numerous reports of severe weather that took several lives, soaked parts of the South, resulting in 1-cat improvements in southwestern and southeastern Oklahoma, northern and central Texas, central Louisiana, and southwestern Mississippi. Arkansas, Tennessee, and northern Mississippi also received abundant rains and remained drought free. In contrast, the rains missed southern sections of Texas and Louisiana, leading to status-quo or some slight D0-D1 expansion. The small D0-D1 area in southwestern Louisiana was shifted southward to better line-up with the driest short-term conditions…
Looking Ahead
During the next 5 days (April 18-22, 2019), another strong storm system will impact the eastern half of the Nation, bringing heavy rains (2-3 inches) and possible severe weather to the Tennessee, Ohio, and lower and middle Mississippi Valleys and the East Coast. Unsettled weather will also impact the Northwest, Rockies, and most of the Plains, although precipitation totals will be much lower. Temperatures will average above-normal across much of the contiguous U.S., with closer to normal readings likely in the Southeast.
The CPC 6-10 day extended range outlook (April 23-27, 2019) favors above-normal precipitation from the Rockies eastward to the Appalachians and in southern and eastern Alaska, with the strongest probabilities over the southern Plains and the lower Mississippi Valley. Below-normal precipitation odds are likely in California. Above normal temperatures are favored for much of the lower 48 States, while Alaska is expected to see below-normal readings.
Here’s the one week CONUS change map.
