Discussion for the Seasonal Drought Outlook
Tools used in the Drought Outlook included the
official CPC precipitation outlook for August 2008 and the long lead forecast for August-October 2008, the four-month
drought termination and amelioration probabilities, 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 CFS seasonal precipitation forecasts, and climatology.
Improvement for drought across the interior Southeast is expected
during the very early portion of the assessment period due to weak low pressure which is forecast to move across the area.
The most likely area of improvement is over the southeast portion of the drought area which is closest to the forecast
track of the area of low pressure. The 6-10 day, 8-14 day, and 90-day forecasts also indicate the
likelihood of above median precipitation over this area. This area may also see some relief from tropical
systems during late summer and the fall. The improvement is also based on historical outcomes as shown
by the NCDC Palmer probability maps for October. It should be noted that hydrological drought indicators
such as reservoirs and groundwater are unlikely to see significant improvement during the summer in
the absence of a tropical system. The hatched area of some improvement over eastern Tennessee was
extended southwestward to over northeast Alabama (at the expense of the green area of improvement)
to reflect the idea that drought relief is more likely closer to areas near the southeast coastal regions.
Confidence of the interior Southeast: Moderate
In Texas, significant rains (over several inches) fell
in the first half of July over the southernmost part of the state. This rainfall resulted in enough improvement
that extreme southern Texas is no longer considered to be in drought. Most of the drought areas over the remainder of the state
have not received much in the way of beneficial rains. Short and medium range forecasts indicate
the possibility of above median precipitation over southern and southeastern Texas which
implies improvement over the area. 30 day and 90 day forecasts indicate equal chances of above
or below median precipitation. East Texas will be more vulnerable to tropical cyclone activity,
and west Texas should continue to be affected by monsoonal showers and thunderstorms as the summer progresses.
For the Drought Outlook, key long-range indicators included the
Palmer drought alleviation probabilities going through October and consideration of monthly normal rainfall totals
(which includes the increased likelihood of tropical activity). The area of green improvement
has been expanded eastward across southeastern New Mexico at the expense of the hatched area
of some improvement to reflect the robust monsoonal activity currently occurring and expected to
continue. The green area of improvement over the Red River along the Texas/Oklahoma border
indicated in the previous drought outlook has been replaced by a hatched area of some improvement to
reflect increased uncertainty for relief over this area as short and medium range
forecasts suggest a drier than normal pattern while longer range forecast indicate equal chances
for above or below median precipitation.
Confidence for Texas and eastern Colorado: Moderate
Confidence for the Southwest: High
Confidence for Nebraska: Moderate
In west-central North Dakota, the area of drought has expanded a
bit to the east. The area is left as brown persist toward the west since expected precipitation in the short and medium
ranges is likely to be offset by a period of warmer than normal temperatures. For the longer ranges, climatology suggests
little to no improvement for this area.
Confidence for North Dakota: Low
For the West, the ongoing dry season results in expected persisting
drought for the California area, while the CPC 30 day outlook for August and the 90 day Outlook for August-October indicate
drier than median conditions for northern California, southeastern Oregon and southwestern
Idaho. The 90 day Outlook also indicates drier than median precipitation for eastern Washington
state. For these reasons an area of drought development has been indicated
for parts of northeastern California, eastern Oregon, southwestern Montana and southeastern
Washington state. For the northwestern portion of the western drought area, soil moisture
forecasts based on climatology suggest some relief is possible in October.
In Hawaii,the drought forecast is little changed from the preceding
forecast, although the area of drought over the Big Island has expanded eastward and is expected to persist or intensify.
This is consistent with the seasonal forecast for below-normal rainfall. In Puerto Rico, medium range forecasts and
climatology point to improvement for the small area in the southeast.