Widespread Heavy Rains Miss Southwest, Southern Plains04/14/2017
Moderate to heavy precipitation (generally 0.5-3.0 inches, locally greater) was widespread across the contiguous U.S. (CONUS) during the past 7-days, with the notable exception of the Southwest and the southern High Plains region. There were also numerous reports of severe weather over the central and eastern CONUS, and strong winds over portions of the Pacific Northwest and northern Rockies on April 7th.
The Lower Ohio Valley
Increasingly dry conditions have been observed across far southern parts of Indiana. This area has significant ACIS Percent-of-Normal Precipitation (PNP) values between 50-90 percent out at 90-days, low stream flows (ranging between the 10th and 24th percentiles of the historical distribution for the day), and there is also some indication for reduced soil moisture amounts, as noted by the North American Land Data Assimilation System (NLDAS) which monitors soil moisture across the country.
An observer in French Lick, IN (Orange County) noted unusually low water levels for the Patoka River. Based on these considerations, abnormal dryness (D0) was introduced to far southern portions of the state of Indiana.
In North Carolina, several small adjustments were made to the drought depiction this week. Some of the D1 near and northwest of Asheville (counties of Buncombe and Madison) was trimmed away. The North Carolina Drought Group (NCDG) supported a slight retraction of the D2 line in Haywood County (extreme western NC).
This was based on short- and long-term factors, and the 6-month Standardized Precipitation and Evapotranspiration Index (SPEI), which shows the north-south gradient of the pattern in this area.
In South Carolina, the D0 line was removed from the Columbia area in the central part of the state, while widespread one-category improvements were rendered across the Upstate region which generally received 1-4 inches of rain this past week. Now that we are moving into a climatologically drier and warmer period, along with increased evapo-transpiration, these short-term gains may be short-lived.
In north-central Georgia, recent rain merited a broad one-category improvement in the drought depiction, while conditions deteriorated one-category (from D0 to D1) in extreme southeastern parts of the Peach state.
Widespread one-category deterioration was rendered across the central and southern Florida Peninsula this week. A broad expansion of severe drought (D2) was made in this area, based on Percent of Normal Precipitation (PNP) values less than 50-percent since the beginning of the Water Year (Oct 1, 2016), and on wildfire potential. There were corresponding adjustments made to the D0 and D1 lines as well.
One small area of Florida that actually saw some improvement in conditions was in the northern part of the Peninsula, which received 3-4 inches of rain just beyond the data cutoff time last Tuesday. Accordingly, the strip of D1 stretching across Levy and Alachua Counties was removed.
In Alabama, several small improvements were made in the north-central portion of the state based on recent precipitation. In general, climatology of median stream flows is now on the decline, suggesting even if actual stream flow discharges are reduced somewhat, they may still be fairly close to normal.
An expert observer in the state noted little to no water seepage from exposed limestone bluffs and other outcrops, and road-cuts, from the winter and early spring rains that have deeply soaked the ground above.
The Lower Mississippi Delta
Light precipitation (less than 0.5-inch) fell across this region during the last 7-days, with many areas reporting little to no precipitation. However, significant improvements were still needed in Louisiana after the heavy rainfall of the past few weeks.
A lot of the abnormal dryness (D0) was eliminated from south-central Louisiana this week. The D0 line was retracted southward by about half-a-parish across far eastern portions of the state to take into account some of the recent wetness over the past month. In north-central Louisiana, moderate drought (D1) was removed from the parishes of La Salle and Grant, due to 5-8 inches (locally 10 inches) of rain that fell a week ago, along with widespread flash flooding.
In adjacent portions of southwestern Arkansas, D0 was eliminated from northern Miller and southwestern Hempstead Counties, with the Texarkana Regional Airport being free of any dryness. Several very small-scale alterations were also made to the depiction in this area.
Recent rainfall, adequate soil moisture, and near- to above-normal stream flows, all lead to widespread one-category improvements across this region. This means a large reduction in D0 coverage, and the removal of the two D1 areas in Missouri and Illinois. In fact, perhaps the main issue in portions of Missouri and Illinois is the inability to plant crops at this time, due to muddy conditions.
The latest National Agricultural Statistics Service (NASS) report shows that only 4-percent of the topsoil moisture in Illinois is rated as “short”, and only 8-percent of the subsoil moisture is considered “short”. There is lingering concern, however, for far southeastern portions of Illinois along the Wabash River, where precipitation deficits out to 90-days are still substantial (ACIS PNPs 50-70 percent of normal).
The northern and central Plains
The dryness/drought area over the northern Plains was re-configured this week, after a regional reassessment of conditions. The moderate drought (D1) area was shifted a bit to the west into northeastern Wyoming. This re-configuration reflects the recent precipitation that has been beneficial at the start of the growing season, and is focused primarily on the past 30-60 days.
In addition, D0 was expanded in southwestern North Dakota to include the counties of Hettinger, Grant, Adams, and western Sioux.
In southwestern Kansas, where generous rains (4-7 inches) fell during the past 30-days, a one-category improvement was made to the depiction. In contrast, where 1.5-3.5 inches fell during the same period, a one-category degradation was rendered to the depiction in northwestern and north-central Kansas.
Several small-scale improvements were also made in eastern Colorado this week, including the removal of severe drought (D2) in north-central portions of the state, and much of the nearby D1 area.
The southern Plains
A one-category improvement was made in the Oklahoma Panhandle this week, which resulted in the elimination of lingering severe drought (D2). ACIS PNPs out through at least the past 90-days are easily in excess of 100-percent of normal, and often 200-percent or higher.
This past week, 4-inches or more of rain merited a one-category improvement for the extreme southeastern Oklahoma counties of McCurtain and eastern Choctaw. In the eastern portion of the state, D2 (S) was expanded, and connected with the D2 area in neighboring Arkansas.
In Texas, minor revisions were rendered to the depiction, until the final precipitation numbers came in for rainfall received between 12z Monday and 12z Tuesday (the final 24 hours of the data inclusion period for the week). This rainfall (in some cases up to 8-inches) resulted in substantial one-category improvements across the northeastern part of the Lone Star state.
No changes were made to the drought depiction this week across the West. Recent stats for California (taken from the California-Nevada Drought Monitor Discussion Call) show an incredible year for precipitation and runoff. In the Sacramento area, the precipitation percentages since October 1, 2016 range from 120-percent to 300-percent or more of normal.
The Northern Sierra 8-station index is at 205-percent of normal, only 0.8-inch away from the 1982-83 El Nino record, and the Central Sierra 6-station index is at 195-percent of normal. Snowpack is equally impressive at 157-percent and 180-percent of normal for this date in the Northern and Central Sierra, respectively.
The Sierra reservoirs have made an amazing recovery this winter, with all the reservoirs at or just above their Top of Conservation levels.
The Northeast and Mid-Atlantic
According to the Applied Climate Information Service (ACIS), moderate precipitation (0.5-2.0 inches) fell over much of the region. Some areas south of the Mason-Dixon Line received less than a half-inch of rain for the week. Small-scale, one-category improvements were noted across portions of New England, New York, New Jersey, and Pennsylvania.
Some areas (though not all) of New England have been deeply affected by the approximately one-year drought in terms of reduced groundwater supplies and reduced reservoir filling.
According to the website “unionleader.com”, surface water supplies in New Hampshire appear to be okay, but there are concerns whether or not the groundwater recharge that typically occurs in March and April will be enough to help avoid a repeat of last summer’s extreme drought that affected countless private wells and forced towns and cities to restrict water usage.
In Massachusetts and Connecticut, three areas where groundwater recharge are being monitored includes southeast MA, the Cape and islands, and the southern part of the Connecticut River Valley. In contrast to these reduced groundwater concerns, other areas of the region experienced minor flooding, which illustrates the complexity of weighing short-term drought vs. long-term drought considerations.
USGS stream flows across most of this region register near- to above-normal conditions, except for some locales south of the Mason-Dixon Line, most notably in the Washington, D.C. to Wilmington, DE corridor.
No revisions to the U.S. Drought Monitor map were made in Virginia, Delaware, or Maryland this week, based largely on the lack of agricultural impacts. However, there are hydrological impacts as noted by a local expert in northern Maryland who found adequate soil moisture and stream flows in his region, but very low groundwater levels. This is significant, especially for residents that operate on well water.
Alaska, Hawaii, and Puerto Rico
In Hawaii, a dry pattern has now persisted for more than a few weeks. The trade winds usually increase in frequency across the area, but this has not been the case. The result is increasing rainfall deficits over even the normally wet windward slopes. A local expert noted the Upcountry Maui water system, which depends heavily on windward rainfall, is seeing decreased reservoir levels due to a significant drop in stream diversion supply levels.
The Maui County Department of Water Supply requested voluntary reduction in water use for Upcountry residents. The abnormal dryness (D0) on Maui was changed to moderate drought (D1), and all remaining dryness-free areas over the Hawaiian Islands were given a D0 designation.
In Alaska, an updated Snowpack map (as of April 1, 2017) shows near- to above-normal snowpack in northwestern portions of the state, and near- to below-normal snowpack in southwestern portions of the state. No revisions were made to the Alaska depiction this week, and none were made in Puerto Rico.
During the next five days (April 13-17), the Weather Prediction Center (WPC) predicts 1.0-2.5 inches of precipitation from the southern High Plains northeastward across the mid-upper Mississippi Valley and into the western Great Lakes region.
Heavy precipitation (3-4 inches, liquid equivalent) is expected across the Coastal Ranges of the Pacific Northwest and northwestern California, the Cascades of the Pacific Northwest, and the California Sierras. However, these areas are no longer in drought or dryness.
For the ensuing five-day period (April 18-22), there are elevated odds for above-median precipitation across most of the northern and central thirds of the CONUS, while near- to below-median precipitation is favored across the southern tier of states. Below-median precipitation is also favored for all of Alaska.
Source: UNL Dought Monitor