Click here to go to the US Drought Monitor website. Here’s an excerpt:
Summary
(Note: The weather summary covers the full 7-day period – to 12Z Dec. 23; some product tools only cover the first 6-day period – to 12Z Dec. 22 due to the holiday-shortened, 1-day early release time constraints). Early in the week, another in a series of Pacific storm systems (since after Thanksgiving) impacted the West Coast, with the bulk of the heaviest precipitation (4 to 8 inches, locally to 12 inches) shifted a bit farther north into western Oregon instead of north-central California as observed during the previous two weeks. Still, decent precipitation (more than 2 inches) fell as far south as central coastal California and on the northern Sierra Nevada Mountains, with lower amounts (an inch or less) to the south. To the east, as a storm system and associated cold front departed the Atlantic Coast, the southern section of the front became stationary in the Gulf Coast. Waves of low pressure developed along the stationary front and tracked northeastward, triggering showers and thunderstorms along parts of the Gulf Coast region. Moderate to heavy rains (more than 2 inches) fell on southeastern Texas, southern sections of Louisiana, Mississippi, and Alabama, and north-central Florida. Toward the end of the period, a change in the upper-air pattern over the West (ridging) brought drier and colder conditions to the region, while a storm in the Nation’s mid-section generated light to occasionally moderate precipitation to most of the eastern half of the U.S. In Hawaii, light showers were generally limited to windward locations except toward the end of the period (Sunday into Monday) when more widespread, heavier rains fell across the western islands of Kauai and Oahu. In Puerto Rico, moderate to heavy (1-4 inches) rains fell across northeastern and central sections, enough to deter the spread of the small D0 area northward. Weekly temperatures averaged well above-normal in most of the West, Plains, upper Midwest, New England, and Alaska, and near- to slightly above-normal in the southeastern quarter of the Nation…
Central and Southern Plains
Most of the central and southern High Plains saw little or no precipitation (less than 0.3 inches) after last week’s “bonus” amounts in the central Plains, so status-quo here, while locations to the east measured higher totals (0.5-1 inch), although most of that fell on non-drought areas in eastern sections of Nebraska, Kansas, Oklahoma, and Texas. An exception was in southeastern Texas where 2-5 inches of rain fell along the western Gulf Coast (especially near Houston), providing some relief to D0-D2 areas near Victoria and Corpus Christi. As mentioned in the Tennessee and lower Mississippi Valley narrative, D0 was added between northeastern Texas and central Arkansas as lower weekly totals (less than 0.5 inches) and 60- and 90-day deficits were similar enough to merge the two D0 areas. Farther to the west, D2-D4 was degraded by a category in north-central Texas as continuing short-term deficiencies and long-term drought impacts mounted, especially in Palo Pinto and Parker counties. Lake Palo Pinto was down to 9% full as of Dec. 23, down from 100% full in early 2012, and at its current rate of drawdown, it would be empty within 6 months. In addition, the impact line was also adjusted to put this area in short and long-term drought (SL). Similarly in south-central Texas (small D3 area), Medina Lake was only 3.3% full, another good example that some areas of Texas have yet to recover from the long-term drought, even with occasional periods of wetness since it started in 2011…
Northern Plains and upper Midwest
Light precipitation fell on most of the region, with southern North Dakota, northern and western South Dakota, northeastern Minnesota, and northwestern Iowa measuring between 0.2-0.6 inches of liquid equivalent. The light precipitation was enough to maintain conditions there. Across northern North Dakota and western Minnesota, however, little or no precipitation occurred, and 60- and 90-day precipitation was under half of normal. With northwestern North Dakota also drying out the past 2-3 months, D0 was expanded to incorporate this area. An expansion of D1 to northeastern North Dakota and western Minnesota was considered with precipitation less than 25% and 50% of normal at 60- and 90-days, respectively, but deficits were relatively small (less than 3 inches), so no increases were made this week…
Southwest
With mostly light precipitation (less than 0.5 inches, locally to an inch) recorded across the Four Corners region, generally surplus precipitation in the short-term (30-days) and medium-term (6-months from an active southwestern monsoon), and below normal in-between (at 2 and 3 months), conditions were left unmodified. However, as of Dec. 22, Water Year-to-Date (WYTD, since Oct. 1) precipitation is below normal, as is the Snow Water Equivalent (SWE) in the basins of Arizona, New Mexico, Utah, and Colorado. With WYTD average basin precipitation ranging between 60-80% of normal and SWE at 30-80% of normal (lowest in Arizona and western New Mexico), this region will be watched closely for WYTD precipitation and snow pack numbers to increase as the winter progresses to ensure adequate spring snow melt runoff and recharge for rivers and reservoirs…
The West
Another in a series of Pacific systems affected the West, with the latest one dropping the greatest precipitation totals on western Oregon and Washington (4-12 inches), although the northern half of California received 2-6 inches, with lesser amounts to the south (generally an inch or less). Although the recent precipitation was not as great as the past 2 weeks, the total capacity of water at the major reservoirs in northern and central California (e.g. Trinity, Shasta, Oroville, Folsom, and San Luis Lakes) did slightly increase on Dec. 16 from 29, 32, 33, 38, and 33% to 32, 38, 36, 41, and 36% as of Dec. 22, respectively. Unfortunately, these values are still well below the historic average capacity for Dec. 22 (47, 62, 59, 85, and 54%, respectively), with the Sierra Nevada basin average SWEs also well below normal (45-72%). The Northern Sierra 8-station precipitation index on Dec. 22 was at 22.4 inches, or 146% of normal, while the San Joaquin 5-station index was at 8.8 inches, or 78% of normal. And similar to last week, major reservoirs to the south showed little or no increase this week with the lower totals. Therefore, even with the additional precipitation, no modifications were made to California this week.
In the Pacific Northwest, with most basins reporting near to above normal WYTD precipitation, generally normal to surplus precipitation at short, medium, and long-term periods (except in southern Oregon, closest to California), the heavy precipitation was enough to slightly trim (improve) the edges of the D0-D2 in northwestern and northeastern Oregon, western Washington, and western Idaho, especially where the long-term SPIs (12- and 24-months) were wet. Since improvements were made in north-central Washington last week, no modifications were made this week. A major concern this Water Year has been the warm component of the storms. Even though WYTD average basin precipitation for the Cascades ranged between 103-134% of normal as of Dec. 22, SWEs remained quite low, ranging between 10-65% of normal. Fortunately, SWEs were close to normal in the northern and central Rockies. Across the West, not only will continued ample moisture be crucial, but also occur in combination with enough cold air to produce adequate winter mountain snow pack for spring snow melt, runoff, and reservoir recharge…
Looking Ahead
For the upcoming 5-day period (December 24-28), light to moderate precipitation (0.5-2 inches, locally to 3 inches along the Pacific Northwest Coast) is forecast for the Northwest, and with temperatures expected to be below normal, the precipitation should mainly fall as snow on the Cascades, northern Sierra Nevada, and the northern and central Rockies. Farther east, moderate (more than 0.75 inches) to heavy precipitation (over 2 inches) is forecast for the eastern third of the U.S., with most of the Southeast expecting over 2 inches of rain, and locally 4-6 inches along the east-central Gulf Coast. Readings should average above normal across the eastern half of the Nation.
For the ensuing 5-day period (December 29-January 2), the CPC 6-10 day precipitation outlook paints a dry outlook for the West (good odds of below median precipitation), but favorable probabilities of above median precipitation for Alaska, the southern Plains, Southeast, and mid-Atlantic, with the best chances along the Gulf Coast. Temperatures are expected to average below normal in the western two-thirds of the Nation, with above median temperature probabilities limited to southern Florida and Alaska.