National Drought Summary for October 6, 2015
Summary
Record rains and flooding inundated much of eastern and central South Carolina and extreme southeastern North Carolina as a very slow moving upper-air low over the Southeast funneled tropical moisture from Hurricane Joaquin (stalled over the central Bahamas) into the southern Atlantic Coast region for several days. More than 10 inches of rain fell on the eastern half of South Carolina, and well over 20 inches drenched east-central sections of the state. During the first 6 days of October, maximum Carolina storm amounts totaled 26.88 inches at Mt. Pleasant, SC, and 22.25 inches at Calabash, NC. Heavy rains (more than 2 inches) also fell across much of the eastern third of the Nation, easing or eliminating lingering short-term drought and dryness. An unsettled weather pattern in the West and High Plains also brought unseasonably heavy rains to parts of California, the Great Basin, Southwest, and northern third of the Rockies and Plains. Tropical moisture from former Pacific Hurricane Marty fueled heavy rains in New Mexico and west Texas. Wet weather continued across most of Alaska and Hawaii easing drought and dryness while light to moderate showers across southern Puerto Rico maintained conditions. In sharp contrast, mostly dry weather occurred throughout the Pacific Northwest, Great Plains, and Mississippi Valley. Ever since record wet May and June rains eliminated long-term drought in Texas and Oklahoma, very little precipitation has fallen in parts of the southern Great Plains and lower Mississippi Valley since early July, creating large short-term (at 2- and 3-months) deficits and extreme drought, especially from eastern Texas into central Mississippi.
Alaska, Hawaii and Puerto Rico
In Alaska, another week of wet weather across most of the state punctuated a wet September, with the wettest September on record at Anchorage (7.71 inches) and the wettest September at Fairbanks (3.74 inches) since 1925. Both Denali National Park HQ and Juneau had the wettest July-September of record. An exception was found at Kodiak where fish processors were asked by the city to limit water usage due to low water supply behind the dam due in part to the driest June-September at Kodiak since 1956 and the warmest since 1979. As a result, the two small D1 areas in south-central Alaska were improved to D0, and a large portion of the D0 in southwestern Alaska was erased.
In Hawaii, scattered light to moderate showers fell across the islands during the week, continuing a wet pattern since August that nearly eliminated all drought and dryness in the 50th State. With pastures and general vegetation finally recovering and greening up, the last remaining small D0 areas in southern Kauai, southern Maui, and extreme southern Big Island were removed.
In Puerto Rico, light to moderate showers (0.5 to 2 inches, locally to 3.6 inches) were observed across the southern half of the island and in the far eastern tip, with totals great enough for some weekly surpluses, but not large enough to dent the long-term drought. The island will need many more weeks of sustained rains like this to put a significant dent in the long-term deficits (6-month shortages exceeded 20 inches in eastern sections, equating to 25-50% of normal).
California and Great Basin
With September and October normally one of the driest months in California, any significant rain (more than 0.5 inches) that falls during this time will usually produce large percentages. This was the case this week when a strong upper-air trough (low pressure) affected the West Coast, drawing in Pacific moisture to most of California and the Great Basin. Unseasonably heavy precipitation (0.5 to 1 inch, locally to 2 inches) was observed in extreme southwestern California (near San Diego vicinity), the Sierra Nevada, and most of northern and western Nevada including the Las Vegas area. Although the rains were welcome and aided in the suppression of wild fire conditions and increased topsoil moisture, it did little for the long-term drought and reservoir storages, thus no changes were made to the drought map. At the end of September, the water conservation efforts in California were noticeable when compared to last year. The amount of water saved came to about 705 KAF – so that this year’s major reservoir storage was only slightly below the storage from a year ago when there were no mandatory water restrictions.
Lower Mississippi Valley and Southern Plains
While the East Coast was getting soaked, a dry week throughout these two regions worsened short-term dryness and drought. The only exception was tropical moisture from remnants of Pacific Hurricane Marty that brought 0.5 to 2 inches of rain to extreme southwestern and western Texas and the Oklahoma Panhandle (which were mostly drought-free), although a small area of D0 and D1 in west-central Texas Panhandle (near Lubbock) was improved a category. Elsewhere, however, after much of Texas and Oklahoma endured record May and June rains and flooding that quickly erased the long-term (hydrological) drought, dry and warm weather since early July has rapidly brought back short-term (topsoil) drought. As a comparison, the Madill, OK Mesonet station measured 43.61 inches of rain from April 1-July 8, and only 1.16 inches in the 89 days since then. In Texas, Muenster (Cooke County) recorded 41.67 inches during April 1-June 30, 4.40 inches July 1-September 30, and only 1.91 inches since July 9. At the USHCN station Blanco (Blanco County), 8.55 inches fell on May 24, but only 0.48 inches since July 1 – so it seems likely that Blanco received as much rain in 14 minutes on May 24 as in the most recent 140,000 minutes (97 days). In Arkansas, several stations established new record lows (Minden 0.02”; Pine Bluff 0.03”; Shreveport 0.07”; and Little Rock 0.12”) for the driest September ever.
During the past 90-days, portions of central and northeastern Texas, southeastern Oklahoma, northern Louisiana, southern Arkansas, and west-central Mississippi have measured less than 2 inches, with several sites reporting under an inch. Normally, central Texas receives 6-8 inches, northeastern Texas and southeastern Oklahoma 8-10 inches, and northern Louisiana, southern Arkansas, and west-central Mississippi 10-15 inches during this 90-day period. This translates into a large area with less than 25% of normal precipitation, and deficiencies ranging from 4-6 inches (central Texas) to 8-12 inches in northern Louisiana and west-central Mississippi. Accordingly, widespread 1-category downgrades were made based upon the severity of the SPIs at 2- and 3-months, plus other products and indices. Fortunately, the record wet May and June in Texas has left statewide monitored reservoirs at 78.6% full as of October 7, although USGS average 28-day stream flows are generally below to much-below normal, as are river gauges in most of Louisiana, southern Arkansas, and Mississippi. According to USDA/NASS statewide statistics on Oct. 4, the percentage of topsoil/subsoil moisture short to very short was: Arkansas (81/74), Mississippi (80/76), Louisiana (69/60), Texas (67/64), and Oklahoma (50/54).
Midwest
Most of the region saw little or no precipitation except for the Ohio Valley (Ohio, southern Indiana and Illinois, and most of Kentucky) where 1-3 inches of rain fell on the eastern halves of Kentucky and Ohio, and parts of southern Indiana and Illinois. These rains were enough to reduce or eliminate short-term deficits and improve D1 and D0 by a category in these same areas. In contrast, where little or no rain fell, short-term dryness (D0) expanded based upon 60- and 90-day shortages. This included central and western Missouri into northeastern Kansas, the UP of Michigan into northern Wisconsin, and western Minnesota (into southeastern North Dakota and northeastern South Dakota). In these areas, 90-day percentages were between 25-75%, and accumulated deficits were 2-6 inches, with a new D1(S) in central Missouri where 90-day shortages reached 6-8 inches.
New England and mid-Atlantic
Early in the period, a slow-moving cold front laden with moisture dropped widespread, moderate to heavy (1 to 3 inches, locally to 6 inches) rains from the eastern Tennessee Valley and mid-Atlantic northward. A few days later, rains from the Southeast upper-air low (infused with Joaquin moisture) and stalled cold front located off the East Coast brought another 1-2 inches of rain to the mid-Atlantic, but high pressure kept most of New England dry and cool. For the week, however, the widespread moderate to heavy rains were enough to greatly reduce the short-term dryness in both regions, and trim away some of the D1 along coastal New England. In the latter area, short-term (less than 3-months) deficits were diminished, but lingering medium-term (3- to 6-months) shortages of 4 to 8 inches and longer (year-to-date) deficiencies of 8 to12 inches remained from northeastern New Jersey into southeastern Maine, thereby justifying D1(L). Similarly, short-term (2- to 3-months) deficits of 2-4 inches still persisted after the rains where totals were lower, thus D0(S) was depicted in these areas. The USGS average stream flows in New England for 7-days ending 12Z Oct. 6 were above to much above normal, but had dropped back to below to much below normal at 12Z Oct. 7 in the D1 areas. Meanwhile, river flows were still above to much above normal in the mid-Atlantic for both time periods.
Northern and Central Plains
A slow-moving frontal system, embedded with waves of low pressure and ample moisture to work with, produced unseasonably heavy precipitation from the Southwest northeastward into the northern Plains. The greatest amounts in the Plains included 1-2 inches in central Montana, western South Dakota, and north-central Nebraska. Most of this area, however, was drought free, except for D0 in eastern and central Montana and southwestern South Dakota where the abnormal dryness was reduced. In contrast, drier weather affected eastern sections, and D0 was expanded as short-term shortages increased (as mentioned in the Midwest summary for the eastern Dakotas and northeastern Kansas).
Pacific Northwest and Northern Rockies
Little or no precipitation fell across the Northwest as temperatures averaged close to normal. With much of the region in D2 or D3 and the rainy season normally commencing later this month and into November, no changes were made this week. In the north-central Rockies, however, the continued wet weather in southeastern Idaho and northern Utah was enough to warrant a 1-category improvement there, matching the water reservoir storage conditions of the Snake River. Slight improvements were made in the Boise basin due to a wet July and September that significantly helped preserve the reservoir storage within the basin, and which now has the best reservoir conditions in Idaho outside of the Bear River basin in the southeast.
Southeast
The Southeast was a tale of (historical) haves and have nots as a stalled upper-air pattern locked the weather conditions in place, leading to copious rains and flooding (in the Carolinas) versus persistent dryness and growing drought (in Mississippi and western Alabama). As mentioned in the Summary, the eastern half of South Carolina measured at least 10 inches of rain this week, with more than 20 inches recorded in east-central sections. The persistent fetch of tropical moisture from Hurricane Joaquin (stalled over the central Bahamas) courtesy of the upper-air low over the eastern Gulf Coast caused record rains and flooding in most of South Carolina and southeastern North Carolina, with 7-day averaged USGS stream flows at record high levels as of 12Z October 5 from South Carolina northward into southwestern Virginia. Needless to say, all short-term drought was removed from the Carolinas (including D2 to nothing, a 3-cat improvement), except an area of D0 and D1 bordering southern South Carolina and southeastern Georgia where totals were lower (0.5 to 2 inches, locally to 5) but still enough to warrant a 1-cat improvement. In contrast, rainfall gradually tapered off as one headed west, with little or no rain measured in Mississippi and western Alabama. In-between the two extremes, light to moderate showers, with heavier amounts (2 inches plus) in northern, eastern, and southwestern Georgia and north-central Florida, was enough to trim some of the D0 and D1 in Georgia. In southeastern Alabama, additional rain (0.5-2 inches) on top of last week’s deluge effectively created short-term surpluses, thus D0(S) was removed. Light rain fell on eastern Alabama and southern Florida, keeping them at status-quo, but another dry week and growing short-term deficits (3-6 inches at 90-days) in southwestern Alabama expanded D1 there. The deterioration in Mississippi will be detailed in the Lower Mississippi Valley and Southern Plains summary (next).
Southwest
The same slow-moving storm system in the Great Basin and Rockies also dropped light to moderate (0.5-2 inches) rain across parts of northern and central Arizona and southern Utah while tropical moisture from the remnants of Pacific Hurricane Marty generated 0.5 to 3 inches of rain in central and eastern New Mexico and west Texas. Most of the significant rains fell on non-drought areas, although the 1-2 inches in southeastern New Mexico was enough to reduce or eliminate short-term deficits (one D0 area shrunk, one erased). Since it had been dry in central and northern Arizona for a while, the rains came in time to prevent degradation.
Looking Ahead
For the upcoming 5-day period (October 8-12), mostly light (0.25-0.75 inches) precipitation will occur in the eastern third of the Nation, with totals of up to 1-1.5 inches possible in the northern Rockies, Great Lakes region, central Appalachians, and eastern Florida. Farther west, heavy precipitation (1-3 inches) is expected in the southern High Plains and Rio Grande Valley, and 2-7 inches in western Washington. Elsewhere, little or no precipitation is expected. Temperatures across the lower 48 States will average above normal, especially in the West and Plains.
For the ensuing 5 days (October 13-17), the odds favor above-median precipitation from the Southwest northeastward into the central Corn Belt, and throughout the southern two-thirds of Alaska. In contrast, sub-median precipitation is favored in the Northwest and Southeast. A strong tilt toward above-normal temperatures is expected in the western half of the U.S., with lower but still above-normal odds in the eastern half of the nation. Alaska also favors above-normal temperature chances, especially in the south.
Author(s):
David Miskus, NOAA/NWS/NCEP/CPC
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)