August - October 2008

Latest Seasonal Assessment - Improvement is on tap for southern and eastern Texas with more limited relief for central and southwestern Texas.  Southern Texas experienced beneficial rains in the first half of July which effectively ended the area of developing drought over that part of the state.  Extended-range forecasts suggest improvement during the second half of July due to a favorable upper air pattern.  Later in the season there is an overall climatological increase in the odds for rain from tropical activity.  For central Texas, some improvement is forecast due to the odds favoring improved soil moisture by late in the eason.  However, the water supply situation, including groundwater levels, should see little improvement unless a tropical weather system strikes the area.  To the west, with the robust onset of the summer monsoon during the first week in July,  New Mexico and extreme western Texas has seen an increase in rainfall amounts. Farther west, the official forecasts for all time ranges show little rainfall across California,  and it is unlikely that the state will experience significant improvement during the ongoing dry season.  In fact it is likely that the area of drought over the west will expand northward in California and southern Oregon/southwestern Montana, and southward into southwestern Idaho. After a dry start for the month of July,  North Dakota is expected to receive precipitation in the short and medium range periods but this will likely be offset by a period of above normal temperatures so little improvement is expected for the region. In the Southeast, an area of improvement is indicated across coastal areas and into the Piedmont region of the Carolinas, associated with the rainfall expected during the short range, the forecast of above median precipitation in the medium range,  and the increased possibility of tropical systems later in the summer. The Hawaiian Islands are likely to experience expanding drought, especially along the leeward slopes.

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.