Latest Seasonal Assessment -
Recent late-season rainfall eroded moisture deficits in some core drought areas of the interior Northwest, but
further improvement during the climatologically drier summer season is less likely. Enhanced chances of
above-median precipitation during the second half of June for the northern Rockies may further ease drought
conditions in northern Idaho, while drought persistence is expected across the remainder of the region. Drought
persistence is also expected across the west-central Great Basin where the summer months are climatologically
drier, though some short-term improvement is possible in south-central Oregon. Further south, monsoon-generated
thunderstorm activity might bring some improvement to drought areas in Arizona and New Mexico. Across the upper
Mississippi Valley and Great Lakes regions, thunderstorm and MCS activity may locally increase topsoil moisture,
but significant improvement of the multi-year hydrological drought remains uncertain. To the south, although
short term forecasts indicate dry, hot conditions across the southern Plains states and lower Mississippi Valley,
daily air-mass thunderstorm development and the potential for tropical-cyclone related moisture influxes
maintain prospects for some drought improvement. Drought conditions are expected to persist and expand across
interior Alaska, and climatologically drier conditions across the leeward side of the Hawaiian islands will
promote drought persistence.
Tools used in the U.S. Drought Outlook (USDO)
included the official CPC precipitation outlook for July 2010 and the long lead forecast for
July - September 2010, various medium- and short-range forecasts and models such as the 6-10 day and 8-14 day forecasts, the
soil moisture tools based on the GFS model and the Constructed Analogue on Soil (CAS) moisture, the Climate Forecast System
(CFS) seasonal precipitation forecasts, climatology, and initial conditions.
In recent weeks, the Upper Midwest
has received beneficial rainfall, and stream flows have accordingly been given a much-needed boost.
Additional heavier rain events will be needed however, to overcome what has been a long-standing, nearly two
year drought in some areas such as northern Wisconsin. Prospects for substantial mitigation of drought are
anticipated to improve during the next two weeks and into July, especially for the western and central
portions of the drought area, based on extended-range predictions of an upstream upper-air trough and
multiple opportunities for precipitation. However, eastern Upper Michigan and northern Lower Michigan have
reduced odds of receiving above-median rainfall during the same period, and therefore persistence of drought
conditions is deemed the most likely outcome. In the longer ranges, the odds favor neither abnormally wet nor
dry conditions. During the summer season however, frontal boundaries and thunderstorm complexes tend to
affect this general area, but it is nearly impossible to tell this far ahead how much of an impact these
factors may have on the regional drought.
Forecast confidence for the Upper Midwest and northern Michigan is low to moderate.
Moderate to severe drought continues
across northern and central sections of Louisiana, and small areas of bordering states. This drought is
particularly noticeable at longer-ranges, according to departure from normal precipitation maps for the past
90-days and past 180-days. The official CPC monthly precipitation outlook for July indicates no discernible
tilt in the odds for either abnormally wet or dry conditions. CPC's July-September 2010 precipitation outlook
however, favors above-median rainfall in this area. Scattered airmass thunderstorms are a common occurrence
across the lower Mississippi Valley in the summertime, and across the Southeast in general, which will likely
result in very localized, spotty relief. Another consideration for this Drought Outlook in the lower
Mississippi Valley is the NOAA forecast of an active tropical cyclone season in the Atlantic basin. Some
improvement in the drought is therefore anticipated across this region, but confidence is low. The small area
of moderate drought in southwestern Oklahoma is expected to see some improvement as well.
Forecast confidence for the lower Mississippi Valley and southwestern Oklahoma is low.
Abnormally wet conditions have
prevailed across the northern and central Rockies during the past few weeks. USGS stream flow gauges
throughout this region are primarily reporting flow values that are close to normal for this time of year.
Experimental soil moisture forecasts based on CFS model ensembles support a slow drying trend over the next
few months, which is generally consistent with CPC's official monthly and seasonal precipitation outlooks.
The July 2010 precipitation outlook calls for no significant tilt in the odds for abnormal wetness or dryness
in this drought area. In August and September, it will be very difficult to overcome dry summertime
climatology. Therefore, most of this drought area is predicted to persist throughout this period, with the
exception of limited improvement expected in the second half of June across northern Idaho.
Forecast confidence for the northern and central Rockies is moderate.
In the Southwest, very little rain
has fallen over the moderate to severe drought area encompassing northern and central portions of Arizona and
New Mexico. Even though dryness is favored in the ensuing few weeks, much will depend thereafter on both the
strength and duration of this summer's monsoon, which at this time is unknown. The experimental soil moisture
forecasts based on CFS model ensembles support initial wetness in July, with a gradual drying trend throughout
August and September. The most likely scenario would favor some improvement across the desert Southwest.
Forecast confidence for the Southwest is moderate.
In the far West (west-central Great
Basin), light amounts of rain have fallen in recent weeks. Given we are now in the hot, dry summer season, it
will be extremely difficult to overcome regional climatology. Therefore, persistence of drought conditions is
anticipated for nearly all of this area, with the exception of south-central Oregon, where some improvement
is expected in the shorter-term.
Forecast confidence for the far West is high.
Moderate to extreme drought
continues across the leeward sides of the Hawaiian Islands. Forecasts for these areas call for below-median
rainfall during the July - September 2010 season, leading to drought persistence. In addition, with this
typically being a drier time of the year, it is difficult to see how drought amelioration may come about,
excluding of course, any tropical storms or hurricanes.
Forecast confidence for Hawaii is high.
Moderate drought persists in the
central Interior of Alaska, and has been accompanied by a significant number of early season wildfires.
Localized summer thunderstorm activity in the Interior is often accompanied by little rain, lightning,
gusty winds and small hail, the first two of which are particularly dangerous in heavily wooded conifer
forests. In addition, drought is expected to expand across most of the central Interior during this period.
The CPC Precipitation Outlooks valid for the month of July, and the July - September season, do not show a
tilt in the odds for either abnormally wet or dry conditions for this area.
Forecast confidence for Alaska is moderate.