NOAA Seasonal Drought Outlook – June, July, Aug.

Drought coverage continues to decrease across the Lower 48 states, after a relatively wet winter and early spring for many areas. CPC’s monthly and seasonal precipitation outlooks, valid for June and Jun-Jul-Aug (JJA) respectively, favor large areas of above normal precipitation across the CONUS, except parts of the Pacific Northwest, the Southwest and the Alaska Panhandle where below normal precipitation is favored.

These outlooks, a generally favorable JJA climatology, and a wide array of dynamical and statistical models and tools, support drought improvement/removal over most residual drought areas over the Four Corners region.

The exception is Washington state and northwestern Oregon, which recorded large precipitation deficits (12 to 16 inches) this past winter and early spring, unlike most other portions of the West. Although some precipitation is expected during the next few weeks, the Pacific Northwest is entering its dry season. Climatological considerations, in addition to CPC’s June and JJA 2019 precipitation outlooks convincingly tilt the odds towards drought persistence in north-central Washington, with parts of region of drought development expected.

Drought coverage over the Southeast decreased recently. However, precipitation deficits in southeastern Georgia are on the order of 2-6 inches for the past 3-months. The CPC June and JJA precipitation and temperature outlooks favor above normal temperatures with no strong precipitation signal during both June and JJA. Drought persistence is favored.

United States Seasonal Drought Outlook Graphic - click on image to enlarge

Click Image to Enlarge

The dry signal predicted over the Pacific Northwest during JJA is expected to also influence the Alaska Panhandle region. The southern Panhandle has been in hydrologic drought for many months, and the low reservoir levels have resulted in reduced hydropower production. Drought may extend northward during this JJA season to include parts of the northern portion of the Panhandle.

In Hawaii, the climatological rainy season will soon give way to its dry phase, and this dry signal is expected to be reinforced by a weak El Niño. With increasingly persistent trade winds a common feature during the Hawaiian dry season, leeward slopes are expected to miss out on the heavy rainfall amounts that are usually received on the windward slopes. Drought persistent is forecast with possible drought development over parts of leeward areas of Lanai and Big Island.

In Puerto Rico, the remaining area of moderate drought over the central part of Puerto Rico is expected to persist as the climatologically wet JJA season advances, but with warm and dry signals in the monthly and seasonal forecast tools.

Forecast confidence is moderate to high for drought persistence and development across the Pacific Northwest, and moderate for the remaining drought areas in the West.

  • Precipitation has averaged at or above normal throughout much of California, the Great Basin, and the Southwest since the start of the current Water Year (October 1, 2018). Basin average snow water content (SWC) is also above average across these areas, ranging from 103% to 437% of average.
  • The ample precipitation and snowfall this Water-Year-To-Date (WYTD) resulted in major drought reduction throughout much of the Western region. According to the U.S. Drought Monitor, drought coverage (D1-D4) in this region decreased from 59% at the start of October 2018 to 4.2% by early May 2019.
  • For areas that are still in drought, such as New Mexico and northeast Arizona, drought improvement and/or removal is forecast. This is supported by CPC’s extended range forecasts, monthly and seasonal precipitation outlooks, valid for June and JJA, respectively. The onset of spring-summer snowmelt and summer monsoon will also assist in the mitigation of residual drought across these areas.
  • In the Pacific Northwest, however, prospects for significant improvement are poor after the next several weeks. SWC ranges from 27% to 95% for the area that includes western and central Washington and far northwestern Oregon. WYTD values mostly range from 50%-90% of normal, with a few spots as low as 25% to 50%.
  • Precipitation deficits of 12-16 inches are common across this region for the past 90-days. USGS 28-day stream flows are low, with values in the lowest quartile of the historical distribution.
  • Based on SWC, WYTD deficits, and stream flow considerations, and both the June and JJA official precipitation outlooks favoring below normal precipitation and above normal temperatures; and the fact that the rainy season out West is over, drought persistence is favored for north-central Washington, with drought development indicated elsewhere.

Forecast confidence is moderate to high for the High Plains region.

  • The northern and central Great Plains remain drought-free, and above normal precipitation this winter resulted in major flooding along the Lower to Middle Missouri River Valley. Drought development is not anticipated during the outlook period at this time, but these areas are climatologically vulnerable to fast-developing drought with multiple weeks of insufficient rainfall and above average temperatures during the late spring and summer.
  • Small areas of moderate drought (D1 on the U.S. Drought Monitor) remain over north-central Wyoming (low snowpack associated with the Big Horn Mountain Range). However, June and JJA climatologies, and the CPC precipitation outlooks for both June and JJA favor the removal of this drought.

Forecast confidence is moderate to high across the South.

  • The South region has remained drought-free. During the past 30 days, precipitation surpluses exceeded 4 to 15 inches across large portions of the Middle and Lower Mississippi Valleys, with soil moisture ranking at or above the 95th percentile.
  • The monthly and seasonal precipitation outlooks from CPC, and climatology in general, favor near to above normal soil moisture conditions across most areas. Drought-free conditions across the South is anticipated.

Forecast confidence is moderate to high for the Midwest Region.

  • Moderate to major flooding continues across parts of the Midwest region. During the past 90 days, precipitation surpluses exceeded 8 inches across portions of the Midwest and Ohio Valley, with soil moisture ranking at or above the 95th percentile for this time of year.
  • Given such wet initial conditions and coming wet season, drought development is unlikely during the outlook period. However, subsequent monthly Outlook will closely monitor for any fast-developing abormal dryness or drought.

Forecast confidence is low for the Southeast Region.

  • Moderate drought currently exists over southeastern Georgia and adjacent parts of coastal South Carolina. Precipitation deficits in southeastern Georgia are on the order of 2-6 inches for the past 3-months.
  • The CPC June and JJA precipitation and temperature outlooks favor above normal temperatures with no strong precipitation signal during both June and JJA. Therefore, drought persistence is favored.

Forecast confidence is moderate to high for the Northeast Region.

  • The Northeast region has remained drought-free since early November. Based on wet initial conditions, near to above average soil moisture values, and the absence of a dry signal among CPC’s monthly and seasonal precipitation outlooks, drought development is unlikely through the end of August.

Forecast confidence is high for Alaska.

  • Moderate to severe drought coverage remained nearly steady along the southern Alaska Panhandle this past winter and early spring. Since JJA is a relatively drier time of year, CPC’s June and JJA outlooks favor below normal precipitation and above normal temperatures over these areas, persistence of this long-term drought is forecast, along with drought development possible for parts of the northern Panhandle region.

Forecast confidence is moderate to high for Hawaii.

  • The increasingly persistent trade winds imply favorable precipitation for windward slopes of Hawaii. However, the outlook for leeward slopes, which are located in rain shadow areas downwind of the mountainous topography, favors drought persistence and/or development.
  • The Seasonal Drought Outlook attempts to highlight broad-scale drought features, and not localized microclimates. It is interesting to note however, that the Kona Coffee belt area near the western coast of the Big Island, at an approximate elevation range of 1000-3000 feet, is the only leeward area of Hawaii that typically experiences its rainy season during the summer.

Forecast confidence is low for Puerto Rico.

  • Drought coverage across Puerto Rico peaked at 42.66 percent at the beginning of March, but decreased to 16 percent as of May 7. Although the climatology becomes increasingly wet during June and JJA, dry signals in the monthly and seasonal forecast tools favor drought persistence.

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