Tools used in the Drought Outlook included the official CPC long-lead
precipitation outlook for June-August, the Palmer Drought Index Probability Projections for August,
various medium and short-range forecasts and models such as the 6-10
day and 8-14 day forecasts, and the soil moisture tools based on the GFS model and the Constucted Analogues for the season.
The drought forecast for the interior West continues to call for persisting drought as the snow
season comes to an end and streamflow diminishes in response to below-normal spring snow
pack in most states. A fairly stormy pattern developed in May, bringing rain and snow to
northern parts of the Rockies, and some central areas as well, and above-normal precipitation
should continue at least into late May. Although this may not have a large impact on water
supplies, the moisture will benefit agriculture and ease wildfire danger. The forecast map depicts
some improvement in Montana and the High Plains in response to the short-term outlook for
wetness. The improvement shown is relatively modest as there are some indications—such as
shown in the Constructed Analogue Soil moisture forecasts--that a drier and hotter pattern will
take hold later in the forecast period across the northern Rockies.
In the Pacific Northwest, there are conflicting signals between the short-term and the long-term
forecasts, with normal to above-normal rainfall on tap for the first 2 weeks of the forecast period
and abnormally dry and warm weather forecast for the June-August period. The area shown as
developing drought shows the area at highest risk based on current conditions and the forecasts
for the various time periods. Drought is not forecast along the coasts of Washington and Oregon
because of minimal impacts expected this time of the year. Where development is shown, most
of the impacts would be on fire danger and non-irrigated agriculture, as reservoirs are generally
in good condition.
In the Southwest, the area of some improvement expected across southern Arizona and central
and southern New Mexico is based on typical patterns resulting from the summer monsoon rains,
which mostly fall in July and August. Such rains have little impact on water supplies but do
benefit fire danger and non-irrigated agriculture. There are no strong forecast signals for either
an above normal or below normal monsoon at this time, so the drought outlook is based on
historical mean data in the Southwest.
The near-term rainfall forecasts as well as climatic probabilities result in the depiction of
continued improvement in the upper Midwest, consistent with the theme of the past several
outlooks. Recent rains already eased drought in this region, especially in the Minnesota area,
and more rain is expected during the second half of May.
The forecast depiction is more pessimistic for the southern Plains this month, as forecast models
show a ridge building up during the last half of May, leading to a dry and hot weather pattern.
Since short-term dryness has already been on the increase during May in the Oklahoma area, hot,
dry weather during the last half of May would result in a good chance for drought development
over parts of Oklahoma and northern Texas by the time June begins. The duration of any such
drought is very uncertain, as the seasonal June-August models generally do not support below-
normal rainfall in this area.
In the Southeast, the area of increased drought risk shown in the April outlook did see
development in April, although heavy rains at month's end and early May brought some relief.
Most forecast models are ambiguous about the June-August rainfall prospects for the Southeast,
but climatological drought probabilities suggest improvement for much of the affected region by
the end of August, and the northern parts of the drought area should see at least normal rainfall
during the latter half of May. Increased heat expected with typical summer weather may make
further drought relief slow and difficult, and above-normal temperatures are in the June-August
forecast. The outlook calls for improvement for this area, but confidence is relatively low.