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Climate Prediction Center


October - December 2003


Latest Seasonal Assessment - Heavy rains toward the end of August and during the first half of September relieved drought over the central and northern Plains, and the outlook calls for more improvement in coming months, especially from Oklahoma into South Dakota and Minnesota. Improvement is expected to be more limited in Michigan and Wisconsin, although forecast rains during the last half of September will be beneficial. Drought is forecast to persist in southern Iowa and northwestern Missouri, as precipitation is expected to be below normal during October-December. Turning toward the West, September rains have already begun to relieve drought in Washington and Oregon, and additional improvement is anticipated into December for the Pacific Northwest. Some improvement is on tap for the Great Basin and central and northern Rockies, although pronounced relief from the water shortages will depend on the upcoming winter snow season. A tendency toward above-normal temperatures and below normal precipitation means that drought should largely persist across the Southwest. Limited drought improvement should continue in the Hawaiian islands.

Discussion for the Seasonal Drought Outlook

Tools used in the drought outlook included: the official CPC long-lead precipitation outlook for the next 90 days, the Palmer Drought Index probability projections for the next 3 months, and various medium and short-range forecasts and models such as the 6-10 day and 8-14 day forecasts and the 2-week soil moisture forecast. Additional tools included the constructed analogue from soil moisture forecasts.

As in the previous forecast, with weak signals from the various forecast tools regarding the 3-month outlook for precipitation over most of the country, this forecast focuses on climatology, the Constructed Analogue Soil moisture tool for December, and the near-term circulation trends as seen in the latest model runs.

The soil moisture Constructed Analogue tool, CAS, implies a tendency for drought improvement across the northwest quadrant of the country with below-normal precipitation leading to persisting or even worsening drought across the Southwest. This would be consistent with a trough near the Northwest coast. A constructed analogue forecast of 500-hpa height anomalies based on August SST data does suggest troughing over western Canada with ridging to the west near the Aleutians. This pattern, including above-normal heights over eastern North America, also correlates with the negative QBO. This is in contrast to the pattern expected over the next 2 weeks or so, which shows troughing over the central or eastern United States and ridging over the West. Since the near-term pattern differs considerably from the pattern implied for the long term by the Constructed Analogue tools, confidence for this forecast is quite low.

CAS shows dryness for October-December extending from the Great Lakes southward through the Ohio Valley and westward to the southern Plains. With the near-term outlook showing normal to above-normal rainfall for much of the Midwest, the drought forecast indicates the ambiguity of the situation by showing limited improvement for the Michigan-Wisconsin area. Recent trends, short term forecasts, Palmer Drought Index probabilities, and QBO correlations argue for improvement in much of the Great Plains. The lingering drought shown in southern Iowa and northwestern Missouri is consistent with the CPC forecast of dryness for Oct-Dec, but improvement was shown in western Iowa and northeastern Kansas because of ample rain expected in the near-term. Both short-term and long-range forecasts imply improving conditions in central Kansas and central Oklahoma.

NOAA/ National Weather Service
NOAA Center for Weather and Climate Prediction
Climate Prediction Center
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Page Author: Climate Prediction Center Internet Team
Page last modified: September 18, 2003
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