Drought Monitor: Temperatures cool, rain across the East

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Weekly Weather Summary: With cooler temperatures and greatly reduced evapotranspiration, this is normally the time of the year when precipitation greatly aids with the recharging of soil moisture and hydrologic conditions (as long as the ground or streams are not frozen). As the week commenced, a storm system in the middle Mississippi Valley quickly tracked northeastward off the New England Coast, but not before bringing light to moderate precipitation to the eastern third of the nation. Farther west, a strong storm system brought moderate to heavy precipitation to the Pacific Northwest. By the weekend, the western system had rapidly traversed to the Mississippi Valley but then stalled as a large dome of high pressure was entrenched over the East. As the period ended, the stalled system, now with an intense area of low pressure, slowly tracked northward from the South toward the eastern Great Lakes region, dumping widespread moderate to heavy precipitation on much of the eastern third of the U.S. Between the two storm systems, many stations from southeastern Texas to the Florida Panhandle and northward to the eastern Great Lakes region reported 2 or more inches of precipitation for the week. In contrast, it was mostly dry from southern California and the Great Basin northeastward into the northern Plains and upper Midwest. Temperatures averaged above to well above normal for most of the lower 48 States. In Hawaii, light to moderate showers were limited to the windward sides.

Southeast:  Widespread moderate to heavy showers and thunderstorms (more than 2 inches, locally to 10 inches) provided at least a 1-category improvement of drought in much of the region. This included most of Louisiana (except the extreme northwestern and southeastern sections where an inch or less fell); Mississippi (except along the Gulf Coast); Alabama (but not in the southeast where about an inch fell and in the northwest where 30- and 60-day percentages remained between 50-75%); northern Georgia and small areas in the southeast; western and eastern South Carolina; and parts of southwestern and south-central North Carolina. Heaviest rains (4 to 10 inches) fell from northeastern Alabama and northwestern Georgia into east-central Tennessee and on the southern Appalachians in western North Carolina. In Arkansas, another wet week (0.5 to 1.5 inches, locally 1.5 to 3 inches in the extreme eastern sections) was enough to remove the lingering short-term D0, while 2 to 3 inches in western Tennessee alleviated D0 there. USGS 7-day average stream flows (ending Nov. 29) were generally at or above-normal levels where 2 or more inches of rain occurred. With a relatively wet Fall season across the region, short-term departures were relegated to western Louisiana and the east-central Gulf and southern Atlantic Coasts, although long-term deficits remained throughout the Southeast. In contrast, only the southern two-thirds of Florida and southeastern Louisiana escaped this week’s rains. Although November has been relatively dry in Florida, a very wet September and October has kept most of the state drought free.

Southern and Central Plains:  Another round of light to moderate precipitation fell on most of the southern and central Plains, continuing a pattern of near to above normal precipitation that started in mid-September. This was good news after Texas recorded the driest October-September period (12-months) on record (since 1895) in 2010-2011, with Oklahoma and New Mexico experiencing their second driest such period, Louisiana their third driest, and Kansas their tenth driest. In Texas, 1 to 3 inches of rain was recorded in southeastern sections, while 0.5 to 1 inch fell on east-central and northeastern sections. Farther north, 0.5 to 1.5 inches of precipitation occurred along the Kansas and Oklahoma border, while 0.3 to an inch was measured in the rest of Oklahoma and central and eastern Kansas. Combined with lower temperatures and declining evapotranspiration rates, a thorough reappraisal of Texas was made (courtesy of Texas A&M, Professor Neilsen-Gammon, and the short and long-term SPI blends), along with surrounding states. Accordingly, some 1-category improvements were made in eastern, south-central, southeastern, north-central, and northern Panhandle of Texas, in eastern Oklahoma, and along the Kansas-Oklahoma border. The Impact Lines were modified to reflect more of the impacts from long-term drought as short-term impacts have lessened recently. In Oklahoma, the run off from recent rains have filled Lakes Hugo (Choctaw County), Broken Bow (McCurtain County), and Wister (Leflore County). USGS stream flows bordering Arkansas are averaging 80 percent of normal or better. In contrast, lake levels remained essentially unchanged from last week elsewhere. Major soil moisture issues below the topsoil remained in west-central and northwestern areas. Lakes at Great Salt Plains (Alfalfa County), Fort Supply (Woodward County), Canton (Blaine County), Altus (Greer County), Tom Steed (Kiowa County), and Skiatook (Osage/Washington Counties) are down 40-80 percent with almost no recharge in the past month. Therefore, D3 and D4 remained in western and central Oklahoma.

Midwest and Northern Plains: A swath of moderate precipitation (1 to 2 inches) fell across north-central Missouri and into northwestern Illinois (and even larger totals to the east), effectively easing short-term drought (D1 and D0) by a category in this region. Most of northern Missouri is experiencing a top 10 historical wet November (150 to 200 percent of normal precipitation), resulting in adequate top soil moisture and no major impacts. The 30- and 60-day AHPS precipitation are now close to or above normal, with only some minor 90-day deficits left in the D0 of northern Missouri. In southeastern Missouri, 2 to 3 inches of rain erased the small area of D0. In southwestern sections of the state, the D1 edges were trimmed away, but kept where weekly precipitation was less than 0.5 inches. In western Illinois, although D0 was removed after 1 to 2 inches of rain, Lake Decatur in Macon County remained a concern as it was still below normal levels. In Iowa, 0.5 to 1 inch of precipitation in southeastern portions was enough to improve drought (D0 and D1) by a category, but drier weather over the rest of the state kept conditions status-quo. November has been a month of contrasts in Iowa, with Keokuk (in the southeast) recording 6.23 inches (third highest November total among 140 years of record), while Sioux Center (in the northwest) measuring only 0.03 inches (fourth lowest November in 105 years of records). In Minnesota and the Dakotas, an unseasonably dry autumn continued, with many areas of southern Minnesota (and bordering areas of South Dakota) ranking below the first percentile for precipitation. As a result, any area in this percentile was made at least D1. Farther north, D1 was added by the North Dakota and Minnesota border for the same reason, while D2 was expanded in northeastern Minnesota where 18 week departures exceeded 7 inches. The separate D0 area of southwestern North Dakota and northwestern South Dakota was expanded eastward and merged with the large D0 area as short-term conditions (at 30-, 60-, and 90-days) were essentially the same across southern North Dakota. Fortunately, the spring and summer months were relatively wet or conditions would be much worse now.

The Southwest: While most of the region saw little or no precipitation, a small band of moderate precipitation (0.5 to 1.5 inches) fell on extreme southeastern Arizona northeastward into south-central New Mexico. Consequently, most of the D4 area in southwestern New Mexico was improved to D3, with only a small portion left as D4 where the rains missed. In south-central New Mexico, the D4 line was pulled eastward in Lincoln County (0.2 to 0.7 inches) to focus the extreme drought on the NM southeast plains instead of the south-central mountains where conditions are a bit better. In extreme southeastern Colorado (Baca County), D4 was slightly trimmed away in response to recent rains (about 0.5 inches). Although no degradation was made this week, concerns remained in the Southwest due to long-term precipitation deficiencies accumulated during past critical seasons (winter/spring and most of the summer monsoon). 

The Northwest: Although heavy precipitation (2 to 6 inches, locally to 12 inches) drenched the Pacific Northwest coastal areas (from northern California northward) and the northern Rockies in northern Idaho and northwestern Montana (2 to 4 inches), interior Northwest areas saw much less, including sections of east-central Washington and eastern Oregon where little or no precipitation occurred. Accordingly, D0 was expanded southward into Adams County of interior Washington. Although the winter wheat crop is mostly good, soil moisture is in short supply and precipitation will be needed soon. Farther south in Oregon, the D0 was extended into northwestern Nevada as short-term (30-, 60-, and 90-days) and long-term (180-days) conditions were similar.  In contrast, however, some parts of the two D0 areas (northeastern Washington and southwestern Oregon) measured 1 to 2 inches, and D0 was trimmed there.

Hawaii: Scattered showers were generally limited to windward sides of the islands (1 to 2 inches, locally up to 6.89 inches at Puu Kukui, Maui) during the week. Meanwhile tranquil weather occurred on the leeward sides as little or no rain occurred. No changes were made this week as D0-D3 persisted, especially on the leeward sides.

Looking Ahead:  For the ensuing 5 days (December 1-5), a storm system is expected to develop and strengthen in the Southwest. This system will slowly track eastward, bringing welcome precipitation to the Southwest and eventually to the southern and central Plains. Largest 5-day precipitation totals (2 to 3 inches) are expected in Texas, northern Louisiana, and Arkansas. Meanwhile, little or no precipitation is forecast for both coasts. 5-day average temperatures should be subnormal in the Intermountain West, Rockies, and Plains, and above-normal in the eastern third of the nation.

The CPC 6-10 day outlook (December 6-10) indicates enhanced odds for above normal precipitation east of the Mississippi River (except Florida), along the western Gulf Coast, in the extreme northern Plains, and throughout Alaska. Below normal precipitation is expected in the Pacific Northwest and Great Basin, central Plains, and southern Florida. Subnormal temperatures are predicted in the western half of the nation, especially in the Southwest, with above normal readings limited to New England, southern Florida, and western Alaska.

Author: David Miskus, NOAA/NWS/NCEP/Climate Prediction Center

Dryness Categories
D0 ... Abnormally Dry ... used for areas showing dryness but not yet in drought, or for areas recovering from drought.

Drought Intensity Categories
D1 ... Moderate Drought
D2 ... Severe Drought
D3 ... Extreme Drought
D4 ... Exceptional Drought

Drought or Dryness Types
S ... Short-Term, typically <6 months (e.g. agricultural, grasslands)
L ... Long-Term, typically >6 months (e.g. hydrology, ecology)

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