After a phenomenal wet season for California and other parts of the western contiguous U.S. this winter, the climatological dry season is approaching. Any lingering pockets of moderate drought or abnormal dryness are expected to persist during the April-May-June (AMJ) 2017 season.
Across the central portion of the Lower 48 states, 35-50 percent of the annual precipitation received typically comes during this season, favoring large areas of drought improvement/removal. Exceptions may include from central Colorado southeastward to central Oklahoma, where drought persistence is considered more likely. Drought development is favored for far eastern New Mexico and the Texas Panhandle area.
Drought improvement/removal is also forecast for the Florida peninsula, with the climatological onset of their rainy season expected near the end of May. CPC’s precipitation outlooks for both April and AMJ favor increased odds of above-median precipitation across much of the Lower Mississippi Valley, supporting drought improvement/removal in that region. Drought improvement/removal is also anticipated across Missouri and surrounding areas, though with lower confidence.
In the Southeast, northernmost areas of the long-term drought area may see some improvement/removal, as this area is expected to be close enough to passing storm systems. Southern portions of this drought region are considered more likely to persist.
In the Northeast and mid-Atlantic, recent heavy precipitation and the forecast passage of occasional low pressure systems favors the improvement/removal of drought.
In Hawaii, the only remaining drought area (on the Big Island) is favored to persist, as the climatological dry season sets in.
Confidence is considered low to moderate for the Southeast.
- For the Southeast United States, Applied Climate Information System (ACIS) 30-day DNPs ranged mostly from 1-5 inches below normal, with the larger deficits (3-5 inches below normal) observed in parts of South Carolina, Georgia, and northern Florida. CPC’s 30-day and 90-day temperature outlooks call for enhanced chances of above-normal temperatures, and mostly Equal Chances (EC) for precipitation.
- With the onset of the primary growing season and warmer temperatures comes increased evapo-transpiration (ET) and water demand.
- The last few runs of the deterministic GFS model suggest that the northernmost areas of the Southeast may experience some improvement or removal of long-term drought, though prospects are not as promising for southern portions of the region.
- In southern Florida, removal of drought is considered likely, as the climatological rainy season typically begins near the end of May and continues throughout the remainder of the AMJ season.
Confidence for the Lower Mississippi Valley is moderate, and confidence for the Middle Mississippi Valley is low.
- Across the Lower and Middle Mississippi Valley, precipitation deficits over the last 30-days (as depicted by ACIS data) generally range up to about 2 inches below normal, with up to 2-4 inch deficits in Louisiana and Mississippi. A surplus in precipitation (up to 2 inches) was noted in much of Arkansas.
- The CPC monthly and seasonal precipitation outlooks indicate elevated odds of above-median precipitation for much of the Lower Mississippi Valley, especially Louisiana and southern Mississippi.
- Predicted precipitation at time-scales out to a month in advance favor near- to above-median precipitation for the region. Drought improvement/removal is indicated for the area.
Confidence for the Central and Southern Lower Plains is considered moderate; confidence for the Central and Southern High Plains is considered low.
- For the Central Great Plains, precipitation deficits over the past month ranged from near 0-2 inches below normal. The Southern Great Plains were generally wetter, with much of the region depicting precipitation surpluses up to 2 inches, and between 3-5 inches over southern Texas.
- The Climate Prediction Center’s Median Percent of Annual Precipitation for the Apr-May-Jun season shows the Great Plains typically receive 40-50 percent of its annual precipitation during these three months.
- The ACIS Percent of Normal Precipitation (PNP) maps depict a more serious drought picture for the northern Texas Panhandle, the Oklahoma Panhandle, and southwestern Kansas, where PNPs are easily within the lowest quartile of the historical distribution, and in some cases, within the lowest 5 percent.
- The April and AMJ precipitation outlooks from CPC extend the relative wet signal from the Lower Mississippi Valley westward to include the southeast third to one-half of Texas. All remaining areas are forecast as EC.
- Considering that the AMJ season encompasses the bulk of the severe weather season in the Central and Southern Plains, and that 40-50 percent of the annual precipitation is typically received during these three months, improvement/removal of drought is favored for the Lower Plains, and portions of the Central High Plains.
- Prospects for drought persistence are enhanced from central Colorado southeastward to western Oklahoma, while drought development is possible for far eastern New Mexico and the Texas Panhandle.
Confidence for the Northern Great Plains is considered moderate to high.
- Across the Northern Great Plains, there are several factors that support the removal of lingering drought, despite the long-term nature of the drought in this region.
- CPC’s April and AMJ precipitation outlooks tilt the odds towards above-median precipitation for both time periods, and almost half of the annual precipitation that falls in this region tends to fall during the AMJ season.
- Though precipitation amounts for Week-1 are predicted to be light, CPC’s 6-10 day, 8-14 day, and Weeks 3&4 precipitation forecasts predict increased odds of above-median precipitation.
Confidence for the Southwest and California is considered moderate to high.
- The ACIS PNP map for the Southwest and California during the past 30-days shows a very spotty and highly localized precipitation anomaly pattern. With the wet season winding down across the West, climatology begins to favor increasing dryness.
- Massive improvements have occurred with the multi-year drought in California, thanks to precipitation amounts 2-3 times the seasonal norm, resulting in large part to a significant number of atmospheric river events (which tap into large quantities of subtropical moisture from the general direction of Hawaii).
- Most reservoirs have been recharged, though in southwestern portions of California there continues to be lingering groundwater and reservoir issues that may not be fully resolved before the end of this wet season.
- For California and the Southwest, drought persistence is indicated.
Confidence is moderate for the Northeast and mid-Atlantic.
- In the Northeast and mid-Atlantic regions, the Applied Climate Information System (ACIS) 30-day Departure from Normal Precipitation (DNP) map depicts precipitation deficits of 1-3 inches near and along the coast, including much of southern New England and Long Island, NY, eastern New Jersey, and parts of the Delmarva Peninsula and Virginia.
- Well inland, from western Pennsylvania across much of Upstate New York and northern New England, precipitation surpluses of up to 2 inches are depicted.
- The April and Apr-May-Jun (AMJ) temperature outlooks from CPC call for increased chances of above-normal temperatures across the region, and the precipitation outlooks favor Equal Chances (EC) of below-, near-, and above-median precipitation.
- A look at the Weather Prediction Center’s (WPC) Week-1 precipitation outlook, and CPC’s 6-10 day, 8-14 day, and Weeks 3&4 precipitation outlooks all indicate precipitation anomalies may be near- to above-median during the next several weeks, associated with the occasional passage of low pressure systems.
- Improvement and/or removal of drought is therefore anticipated. It is also thought that the next few weeks of occasional storminess will provide enough precipitation to reverse the recent drying trend across the mid-Atlantic area.
Confidence is considered moderate for Hawaii.
- Residual drought remains in parts of the Big Island of Hawaii. Coming out of the winter wet season, odds favor persistence of drought throughout the spring season.
- There is no drought at this time across Alaska or Puerto Rico.