As the dry season starts in late May and June for the western contiguous U.S. and based on precipitation and temperature forecasts and outlooks at most time ranges, the most likely outcome is for current drought to persist and for potential new drought development in currently anomalous dry areas in the Pacific Northwest, the Northern Intermountain Region, parts of central California and the Central Great Basin.
This is associated with well below normal precipitation since the beginning of the Water Year (Oct 1, 2019) and the expectation of warm, dry conditions in Jun-Jul-Aug (JJA). Drought removal or improvement is favored for parts of the Central and Southern High Plains, with the expectation of a favorably wet JJA climatology and all range forecasts and outlooks.
For the areas of drought near the Gulf Coast, nearly all official precipitation outlooks from one week to one season in advance favor at least a one-category improvement in drought conditions, resulting in drought removal for most areas.
Elsewhere across the Lower 48 states, no broad-scale areas of drought are expected to develop.
In Hawaii, with the rainy season ending and outlooks at all time ranges favoring warm and dry conditions, either new drought development or persistence of existing drought is favored in most of the leeward areas. The only exception is the west side (Kona slopes region) of the Big Island, which has its wet season during the summer.
There is no drought at the current time in Alaska, and there are no convincing indications to the contrary for the June-August season.
Drought in the southern Puerto Rico is likely to persist for June-August.
Forecast confidence for the West is moderate to high.
- Across the Western states during the past 14-days, precipitation amounts ranged between 1.0-5.0 inches for the Cascades, the Coastal Ranges of the Pacific Northwest, the Sierras, and portions of the Rockies.
- Northern Nevada generally received 1-inch of precipitation or less. Some of the drier locations included parts of the Central Rockies, which saw precipitation amounts that ranged from zero up to a quarter-inch.
- As of May 17th, SNOTEL basin-averaged Snow Water Equivalent (SWE) was generally near to below average across the West (0-90 percent of average, the Sierras, Nevada, Arizona and New Mexico being on the low end), while the Northern and Central Rockies were in good conditions (90-164 percent of average).
- Precipitation across the West during the upcoming week is predicted to be light (less than 0.5-inch) for the valleys and lower elevations, with orographic enhancement leading to somewhat higher amounts (0.5-2.0 inch) for the mountainous regions.
- Little to no precipitation is expected in California, Arizona, New Mexico, or to the lee of the Cascades in Washington and Oregon.
- During week-2, below normal precipitation is favored for most of the northwestern US, and near to above normal precipitation is forecast across parts of the Southwest.
- CPC’s June and JJA precipitation outlooks favor below normal precipitation for most of the northwestern areas and Equal Chances (EC) for the remaining West. This is consistent with the onset of the dry season across most of the West starting in May, and with the climatological onset of the monsoon in late June/early July.
- Therefore, drought persistence is indicated for the current drought areas depicted across the West.
- In addition, warm, dry conditions anticipated in JJA support new drought development for adjacent areas of this region, such as northeastern Nevada eastward into northern Utah, western Oregon, central and southwestern Idaho, and parts of Washington state.
Forecast confidence for the High Plains region is moderate.
- During the past 14-days over the High Plains region, moderate precipitation (0.1-2.0 inches) fell across most of the Northern Plains. Departure from Normal Precipitation (DNP) over the past two weeks ranged from 1-3 inch deficits in most areas.
- Up to two inches of precipitation is predicted across the region during the next week, with slightly more possible in eastern Kansas.
- CPC extended range forecasts (6-10 days and Week-2) predicted below normal precipitation over the region.
- The June, and JJA precipitation outlooks from CPC all favor above normal precipitation in the eastern parts of this region, but near to below normal precipitation in most remainding areas.
- Generally all range forecasts predict near to above normal surface temperatures for the next three months.
- Given a wet JJA climatology but overall above normal temperatures and below normal precipitation outlooks, drought persistence is predicted at this time.
- However, this region is prone to flash droughts, which by definition develop quickly, and will need to be monitored in the weeks and months ahead.
Forecast confidence for the Midwest is moderate.
- Moderate to high precipitation (0.1-4.0 inches) fell across the Midwestern states over the past two weeks, with 4-7 inch totals (locally greater) observed in northern Illinois, Michigan and Ohio. This resulted in rainfall surpluses of 3-6 inches in these three states.
- In contrast, rainfall deficits of 1-3 inches were noted over much of the Upper and Middle Mississippi Valley.
- Soil moisture anomaly change over the past two weeks reveals soil moisture values have diminished by 0.5-3 inches over parts of the Midwest.
- During Week-1, northern portions of the Midwest are forecast to receive little precipitation.
- Southwestern and southeastern portions of the Midwest, however, are predicted to receive up to 1.0-2.0 inches of precipitation.
- Above normal temperatures and above normal precipitation (albeit with modest probabilities) are favored over the Midwest during the Week-2 period. CPC’s 30- and 90-day outlooks favor near to above normal rainfall.
- As was the case with the High Plains region, given favorable precipitation outlooks and JJA climatology, there is little reason to go with developing drought at this time.
- However, this region is also prone to rapidly-developing flash drought, and will need to be under careful surveillance in the weeks and months ahead.
Forecast confidence is considered moderate across the South.
- Across the South, precipitation totals (0.1-10 inches) were observed over the last 14-days from western Texas generally northeastward across the Arklatex region, most of Arkansas and Tennessee, and the northern half of Mississippi.
- This wet period is attributed to plentiful low-level Gulf moisture, active baroclinic zones, mid-level disturbances, and severe weather.
- In contrast, less than a half inch of rain fell across western and northern Oklahoma, and West Texas.
- Remaining areas of the South saw rainfall totals in the moderate range with the highest rainfall in southeastern Louisiana.
- During the past two weeks, 1-3 inch rainfall deficits were noted in north-western Oklahoma and Texas, and parts of eastern Texas.
- A review of precipitation outlooks for time periods of one-week to one-season in advance shows that all agree on the more significant precipitation amounts falling over eastern and central portions of the Southern region, with little to none across western Texas.
- Based on the various rainfall outlooks and favorable climatology, the current drought areas in the Southern Region are expected to either improve or be removed, while drought persistence is predicted in western Texas.
Forecast confidence is moderate to high across the Southeast.
- Precipitation amounts generally ranged from 0-10 inches over the region during the past 14-days. Most areas reported 0.0-3.0 inch rainfall deficits.
- The only place that observed more than 3.0-6.0 inch rainfall surpluses was parts of southern Florida and the Carolinas.
- Nearly all outlooks, from one week to one season in advance, favor at least a slight tilt in the odds towards above normal precipitation across the Southeast.
- Given these official outlooks, and the climatological onset of Florida’s rainy season, drought removal is favored for the Florida Peninsula, and one-category improvement is forecast for the remaining region, meaning either improvement or removal of drought areas for the Southeast.
Forecast confidence for the Northeast is moderate.
- In the Northeast region, 0-4 inches of precipitation fell from the Central Appalachians northeastward across eastern Pennsylvania, New Jersey, Long Island, and New England.
- Two-week precipitation surpluses ranged from 0.5 to (locally) 3.0 inches and were reported over western New York and northwestern Pennsylvania, while the remaining areas reported 0-3 inches rainfall deficits.
- Up to an inch of precipitation is forecast for the southern Northeast during Week-1. Near to below normal precipitation is predicted for Week-2. EC is forecast for the month of June.
- For the JJA season, odds favor above normal precipitation for the southern Northeast Region, and EC is most likely for the northern Northeast.
- At this time, there is little evidence to support significant areas of drought development across the region.
Forecast confidence for Hawaii is moderate to high
- With the dry season starting for the Hawaiian archipelago, it becomes increasingly difficult to reduce or eliminate remaining drought.
- CPC outlooks valid for June and JJA favor above normal temperatures and below normal precipitation. Therefore, new drought development or persistence of existing drought is favored in most of the leeward areas in the state (except the Kona region, which has its wet season during the summertime).
Forecast confidence is moderate for Alaska.
- There is no drought at this time in Alaska.
- In Alaska, there are mixed climate signals out through the seasonal period (JJA).
- For the shorter-term (Week-2), near to above normal precipitation is forecast across the state. The June and JJA outlooks tilt the odds towards near to above normal precipitation for the state.
- Given the climatology and outlooks over relevant time periods, there is no clear reason to favor drought development in JJA.
Forecast confidence is moderate for Puerto Rico.
- For Puerto Rico, although the climatology becomes increasingly wet during June and JJA, the NMME forecasts favor the existing drought to persist over the region.