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Climate Prediction Center

 
 
 

September - November 2009

 

Outlook Graphic: GIF   PDF Adobe PDF Reader

 

Latest Seasonal Assessment - As southern Texas continues to struggle with an historic drought, there are indications that the drought may begin to loosen its grip on some areas going into autumn. The beneficial impacts from the ongoing El Niño are usually more pronounced in this region from November on, but long-range forecasts suggest decreasing odds for below-normal rainfall by October. As a result, some improvement is forecast for the Texas drought areas over the next 3 months, especially for eastern sections of the drought region. Above normal rainfall is anticipated for eastern Louisiana and southern Mississippi during the medium- and long range periods, which should contribute to drought improvement for the region. Indications from several of the medium and longer range tools used to prepare the forecast suggest improvement over eastern North Dakota. Recent rains have eliminated the small area of drought that was present over northwestern Oklahoma. Some of the medium and longer range guidance and various soil moisture forecasts lead to a forecast of some improvement for the long-term drought affecting Wisconsin and parts of Minnesota. In the Pacific Northwest, the impacts from El Niño suggest drought persistence and perhaps some eastward drought expansion over central Washington State. Across coastal Washington and Oregon, an increasingly wet climatology during the fall supports some improvement. It should be noted that even below-normal precipitation could provide improvement due to relatively high normal values. A weaker than normal monsoon has led to below-normal rainfall over Arizona for August and the development of drought areas over the eastern part of the state. Short-range guidance suggests a resurgence of late season monsoonal activity. Some longer range guidance also suggests near to above normal precipitation for the region, so some improvement is anticipated, especially over southern portions of the drought regions. Continued drought is called for in California and parts of Nevada. In the Pacific, tropical activity is expected to continue over the eastern part of the basin. Some of this activity may affect Hawaii, which leads to a low confidence forecast of some improvement for the region. The small areas of drought that recently developed over North and South Carolina are expected to be short-lived as medium range forecasts indicate above normal precipitation for the region.

 
Discussion for the Seasonal Drought Outlook
 

Tools used in the Drought Outlook included the official CPC precipitation outlook for September 2009 and the long lead forecast for September – November 2009, the four-month Palmer 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 Climate Forecast System (CFS) seasonal precipitation forecasts, El Niño precipitation and temperature composites for September-November, climatology, and initial conditions.

The Wisconsin-Minnesota drought area has seen near to above normal precipitation over the most recent 30-day period. The area is forecast to see little precipitation during the short range period. The CPC 6-10 day and week 2 forecasts indicate near to above normal precipitation for the region, especially for the western portion of the area. The 30-day forecast for September indicates equal chances of a given precipitation anomaly category for the northeastern portion of the drought region, and above normal precipitation for the southern portion of the area. The 90-day forecast for September-November shows equal chances for each of the precipitation categories for Sep-Nov. The official Sep-Nov temperature forecast for the region from CPC indicates above normal temperatures. The CFS forecast for Sep-Nov indicates mostly near-normal precipitation for the region while the El Niño composites for the same period show near to below normal precipitation for the area. Various soil moisture tools suggest the region will see some improvement over the next three months. For these reasons a forecast of some improvement will be continued for the eastern portion of the drought region while improvement is indicated for the southern and western sections.
Forecast confidence for Wisconsin and Minnesota is moderate.

For eastern North Dakota rainfall has mostly been near normal over the last 30 days. The HPC forecast for days 1-5 depict little to no precipitation over the area. 0z and 6z runs of the GFS show light 2-week precipitation totals over the area. The 6-10 day and 8-14 day forecasts indicate a tilt of the odds for above normal precipitation for the region. The CPC monthly and seasonal precipitation outlooks indicate equal chances for each of the possible precipitation categories. El Niño composites for Sep-Nov suggest above normal precipitation, while the CFS forecast for Sep-Nov is for near to above normal precipitation for the region. For these reasons a forecast of improvement will be retained for the area.
Forecast confidence for North Dakota is moderate.

For Southeast Nebraska the drought area has received near to above normal precipitation over the last 30 days. The latest drought monitor no longer indicates drought for this region although a small area retains the abnormally dry designation. Short and medium ranges forecasts suggest the area will have above normal precipitation. The 30-day forecast for September indicates the likelihood of above normal precipitation while the 90-day forecast for September-November shows equal chances for each of the precipitation categories during the period. The CFS forecast for September-November shows near normal precipitation while the El Niño composites for September-November indicate a likelihood of near to above normal precipitation for the region. For these reasons it is not likely that drought will re-develop over the region during the forecast period.

In northwestern Oklahoma near to above normal precipitation over the past 30 days has eliminated drought conditions although parts of the area remain abnormally dry. The HPC precipitation forecast for days 1-5 for the region indicate little to no precipitation for the region. The CPC 6-10 and week 2 forecasts indicate above normal precipitation is likely for the region. According to the CPC forecasts for September and September-November there is little tilt in the odds for a given precipitation category. The CFS forecast for September-November shows above normal precipitation for the region, while El Niño composites indicate mostly near normal precipitation for the area. For these reasons the region is not expected to see drought re-development.

In Texas, the lingering small drought area in north-central Texas is forecast to experience only light precipitation during the short range period. The CPC 6-10 and week 2 forecasts indicate near to above normal precipitation for the region. The CPC 30-day forecast for September and 90-day forecast for September-November indicate equal chances for each of the possible precipitation anomaly categories. CFS forecasts for September and September-November suggest above normal precipitation for the region while El Niño composites indicate near to above normal precipitation. For these reasons a forecast of improvement is indicated. Southern and south-central Texas continues to endure one of their most intense droughts on record. The odds for significant improvement increase considerably starting in November based on composites from historic El Niño episodes and seasonal forecasts from the global models, such as the CFS, but the outlook into October is not as clear cut. Monthly El Niño composites indicate the dry signal for southern Texas ends after September, while the CFS is depicting above-normal rains for September over the far northern portion of this drought region. The weight of the evidence from the various seasonal models, El Niño soil moisture composites, and forecasts from the short term out to the 3-month time periods suggests that the odds for some improvement increase toward the north and the coast. For these reasons southern Texas is forecast to have some improvement over the current drought areas, except over the coastal sections and the northeastern part of the drought region, where improvement will be indicated.
Forecast confidence for Texas is moderate.

Recently rainfall has been near to below normal over the drought area in Louisiana/Mississippi. The HPC forecast for days 1-5 indicates light precipitation for the region. The CPC 6-10 day forecast shows near normal precipitation is likely while the week 2 forecast indicates above normal precipitation for the region. The CPC monthly forecast for September indicates no tilt of the odds for above or below normal precipitations while the seasonal forecast for September-November shows a relatively high probability for above normal precipitation. The CFS forecast indicates near to below normal precipitation is favored during September-November, while the El Niño composites for September-November suggest above normal precipitation. For these regions a forecast of improvement is specified.
Forecast confidence for Louisiana and Mississippi is high.

The latter part of the Southwest monsoon season has been weak, especially in Arizona, where several areas have quickly dried out over the last few weeks and small regions of drought have recently developed over the eastern part of the state. It now appears that the majority of the moisture associated with tropical system Jimena will remain south of the U.S.-Mexican border. On the other hand some of the residual moisture from the tropical system may get drawn northward in association with a burst of monsoonal activity expected over the region. CFS forecasts indicate near to above normal precipitation for September-November while El Niño composites for the same period indicate near to below normal precipitation for much of the region. An area of improvement is depicted over the southern section of eastern AZ, an area of some improvement is depicted for central Arizona, and an area of persist is forecast for the northwestern most portion of the current drought area. Further to the east over New Mexico longer range forecasts, especially the CFS precipitation forecast for September-November, paint an optimistic picture for near to above normal precipitation so a forecast of some improvement is specified, except over the southern part of the drought region where the expectation of late season monsoonal activity leads to a forecast of improvement.
Forecast confidence in Arizona and New Mexico is moderate.

The Outlook continues to indicate persisting drought in California and Nevada. Although the West Coast typically sees a pickup in rainfall during October, little change in drought conditions is anticipated before December, when much larger increases in precipitation typically occur. El Niño has the potential to bring above-normal precipitation this winter, especially over southern California. The most recent 30 days have seen near normal (essentially no) precipitation across the state. For the next two weeks little precipitation is expected.
Forecast confidence for California and Nevada is high.

Rainfall over the small drought area in northwestern Montana has been near to above normal over the past 30 days. For the next 5 days HPC forecasts little precipitation over the region. The CPC 6-10 day and week 2 forecasts indicate near to above normal precipitation for the region. The CPC monthly forecast for September depicts equal chances for a given precipitation category while the CPC forecast for September-November suggests a slight tendency for below normal precipitation. For these reasons the drought area over Montana is expected to show some improvement. Over Washington State little precipitation is expected over the interior sections of the region for days 1-5, while moderate to heavy precipitation is anticipated over the western coastal regions of Washington and Oregon. Above-normal precipitation is forecast during the 6-10 day period while near normal precipitation is forecast during the week 2 period. The CPC monthly forecast for September indicates equal chances for each of the precipitation categories while the CPC seasonal forecast for September-November depicts below normal precipitation for most of the region. For interior Washington the drought outlook specifies persist, and even some eastward expansion of the drought area. The drought areas for coastal Washington and Oregon are specified as some improvement due to short and medium range precipitation forecasts and to the fact that in an area that normally has abundant precipitation drought improvement can occur even when below normal precipitation is observed.
Forecast confidence for Montana, Washington, and Oregon is moderate.

The small areas of drought over North Carolina and South Carolina depicted in the latest Drought Monitor are forecast to show improvement as short, medium, and longer range forecasts suggest near or near to above normal precipitation over the region. In addition El Niño composites for September-November indicate above normal precipitation for these areas. It should be noted that September-November is a climatologically dry time of year for the region.
Forecast confidence for North and South Carolina is moderate.

Normal to above-normal rains for southeastern Alaska during the first 2 weeks, and the seasonal trend toward lower temperatures and more precipitation thereafter make the re-development of drought over Alaska unlikely.

For Hawaii, recent rainfall associated with tropical systems has offered relief to some of the drought areas. Model forecasts suggest additional tropical activity in the eastern Pacific. As these systems move westward additional rainfall is possible over the region. Since confidence is low in any given system affecting Hawaii the drought outlook indicates some improvement over the remaining areas of drought.
Forecast confidence for Hawaii is low.


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Page Author: Climate Prediction Center Internet Team
Page last modified: September 3, 2009
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