Tools used in the U.S. Monthly Drought Outlook (MDO) included the official Climate Prediction Center (CPC) updated (0.0 month lead) temperature and precipitation outlooks for April 2016, various short- and medium-range forecasts and models such as the 7-day precipitation totals from the Weather Prediction Center (WPC), the 6-10 day and 8-14 day CPC Extended-Range Forecasts (ERFs), Weeks 3 and 4 experimental outlooks, the NAEFS precipitation outlooks, dynamical models including the CFSv2 and GFS, climatology, El Nino composites, and initial conditions.

Thanks to surplus precipitation and seasonable temperatures during March which kept or increased Water Year To Date (WYTD) basin average precipitation and Snow Water Contents (SWC) to near or above normal levels, plus expected unsettled weather during early April, continued drought improvement is forecast for the northern portion of the drought area in the Far West. With the peak snow pack normally occurring on April 1, the March 30 SWC in the northern, central, and southern Sierras stood at 97, 88, and 72% of normal, respectively, or 87% overall for California, which was much better than the past four years. With historical averages for most major reservoirs in the north (Shasta, Oroville, Folsom) above normal levels, the Department of Water Resources increased its water delivery estimate (allocation) for most recipients to 45% of requests for 2016 on March 17, up from an initial 10% in December, 15% on January 26, and 30% on February 24. April is a transitional month between the wet winter and dry summer months; however, April climatology has trended wetter in recent years (last 15 years), especially in the Cascades, Sierras, and Great Basin. Although the short-term (5-day) WPC forecast is for mostly dry and warm weather, the extended range forecasts (days 6-10 and 8-14) have favorable odds of above-median precipitation in the Sierras and Great Basin, as well as the updated April precipitation forecast, albeit with rather low odds. Thus, with the best April 1 precipitation, snow water content, and reservoir conditions during the past 4 years, and expected unsettled weather during most of April, additional drought improvement should occur in most of northern California, eastern Oregon, and northwestern Nevada by the end of April. In sharp contrast, much drier conditions have occurred in southern sections of the West (southern California and the Southwest) this winter and March where the expected El Nino induced enhanced sub-tropical jet (that brings surplus winter precipitation) failed to materialize, thus providing no relief from the long-term drought in southern California. Although the extended range forecasts (days 6-10 and 8-14) odds favor near to above-median precipitation in southern California and the Southwest, April is a normally dry month (3.5-7% of annual total) here (unlike locations to the north), so above-median amounts are still rather low. Thus, when taking into account the prolonged multi-year drought that received little to no help during December-March (one-third to two-thirds of normal precipitation), no improvement (persistence) is expected by  the end of April, and some slight deterioration is possible in the desert Southwest.  
Forecast confidence for the Far West (Oregon, California, and Nevada) is moderate (northern) to high (southern).

The areas of drought in the northern and central Intermountain West and Rockies shrank as a bountiful Water Year 2015-16 continued during March. One to two categories of drought improvement were made on the U.S. Drought Monitor (USDM) between late February and late March in Idaho, western Montana, and northern Nevada as WYTD basin average precipitation and SWC remained near or above normal throughout much of this region as of March 30. Stream flows remained at near to above normal levels, and most reservoirs continued to fill. Most of the remaining small areas of drought (D1 and D2) that lingered in northern Idaho, northwestern Montana, central Wyoming, and northwestern Utah are expected to improve. Recent precipitation (not incorporated into the latest USDM), increasingly wet climatology, typical soil moisture increases during April (via CPC soil moisture calculations), and favorably wet April forecasts for all time periods in central sections should decrease drought in Utah, Wyoming, and northern Idaho (where initial conditions are favorable). In northwestern Montana, however, initial conditions were much worse than surrounding areas, including WYTD average basin precipitation and SWC at 76% and 68%, respectively, thereby persistence was forecast here.    
Forecast confidence in the northern and central Intermountain West and Rockies is moderate.

Similar to southern sections of California and Nevada, the Southwest experienced an extremely dry winter with many locations measuring only one-third to two-thirds of normal precipitation. The first 29 days of March have been even drier, with nearly all of Arizona and New Mexico receiving less than 25% of normal precipitation, and many locations less than 5% (less than 0.1 inches). If it was not for a very wet October and above-normal January, the WYTD precipitation would not be as high as it is (between 65-98% of normal). The March 30 SWC, however, does depict the relative lack of winter snow across central Arizona and parts of New Mexico as basin average SWCs ranged between 1-50% in Arizona and 0-76% in New Mexico. As of March 1, state reservoir storage for Arizona and New Mexico were well below average, and should be even lower on April 1 with the extremely dry March. Although the extended-range forecasts (days 6-10 and 8-14) favor above-median precipitation chances along with the updated April precipitation outlook, the climatology for Arizona and New Mexico is rather dry, with southern sections of the states normally receiving 1-2% of the annual total during April, and northern sections only a bit more (2-5%). Therefore, with much of the Southwest and south-central Plains already in D0 (and some D1), development of drought is expected (and probably imminent) within the next week or two, and should persist even if above-median precipitation occurs around mid-month.
Forecast confidence for the Southwest is moderate to high.

In the Plains, small areas of moderate drought existed in southeastern North Dakota, and in southwestern Kansas, southeastern Colorado, western Oklahoma, and the northern Texas Panhandle. The south-central Plains drought was recently added during the past month as extremely warm, dry, and windy weather accelerated plant growth (e.g. winter wheat), raising concerns for topsoil moisture availability, as well as reports of numerous wild fires and low stock ponds and streams. The return of short-term dryness and drought in the south-central High Plains, even after a very wet October and November across much of Nation's mid-section, highlighted that this area never fully recovered hydrologically from the long-term drought during 2011-14. The precipitation climatology of the south-central Plains is relatively dry during April, but rapidly increases as the summer progresses. The forecasts for this region are complicated, with the more confident short-term outlooks favoring continued dryness and probable drought development during early April (like the Southwest), but a lower confidence tilt toward wetness by mid-month and late April. The wetness would tend to negate any drought development from early April or even possibly eliminate the D1 areas, so a compromise was made to leave the south-central Plains as persistence. It should be noted, however, that if the late April rains failed to materialize, development of drought would greatly expand, hence the lowered confidence in the south-central Plains forecast.  In North Dakota, with no appreciable tilt toward dryness or wetness during the first half of the month, a slightly dry April climatology (5-7% of annual total), and favorable odds for sub-median precipitation in the updated April outlook, persistence was kept in North Dakota.
Forecast confidence in the northern Plains is moderate, and low in south-central Plains.

Although unseasonably heavy February showers brought some unexpected relief to Puerto Rico that month, March, normally one of the driest months of the year, was true to form. Light to moderate rains fell across the island, but amounts were not high enough for any improvement nor low enough for deterioration, so no changes were made to the USDM. With April precipitation climatology also somewhat dry, and no large tilt toward wetness indicated in any outlooks, drought should persist in southeastern sections of the island. A better chance of drought improvement is more likely during the summer and fall months when the Caribbean and Atlantic tropical season is ongoing, especially since the demise of El Nino should remove the tilt toward subnormal summer tropical activity from the basin.
Forecast confidence for Puerto Rico is moderate.

Drier than normal conditions associated with the strong El Nino event continued into March across most of Hawaii, especially on the Big Island. However, with the expected rapid demise of the El Nino toward ENSO neutral conditions by late spring or early summer, the El Nino induced dryness in Hawaii should fade. With this in mind, windward areas currently in D0 are not expected to develop into drought as the normal trade showers should return during April. The windward locations currently in drought, however, are forecast to persist as the trade rains will most-likely not be enough for any improvement by April 30. Drought should also persist on the normally drier leeward sides. 
Forecast confidence for Hawaii is moderate.

Forecaster: David Miskus

Next Monthly Drought Outlook issued: April 30, 2016 at 3:00 PM EDT