Weekly Threats Assessment
These deviations from the climatological flow pattern cause upper level winds to be more westerly, on average, over the Nation. They also lead to a region of abnormal cyclonic vorticity over much of the southern U.S.. These conditions are associated with increased storminess across the southern U.S. and dry, relatively warm conditions in the north.
Days 3-5 Forecasts
Days 6-10 Forecasts
Days 8-14 Forecasts
For background the CPC soil model was integrated starting in 1931, and is updated each month. The 1961-90 climatology is subtracted to form the anomalies shown. The current latest map is for the end of November 1997.
The forecasts for soil moisture anomlies at the end-of-April and June 1998 are the composite mean for the 10 past cases when DJF was a warm El Nino event. The units are standard deviation (X100). Clearly, the soil moisture anomaly integrates the precipitation and temperature anomalies associated with a warm event into a fairly smooth and large-scale field. The relationship between ENSO and soil moisture is not simultaneous, because soil moisture reflects past conditions. Contrary to the more noisy temperature and precip, soil moisture has reasonably high skill under cross validation through at least July of next summer. I.e., as of now we have a forecast with 7 month lead and a good guarantee for skill. Significant moisture shortage is thus to be expected at the beginnning of the growing season in the Ohio Valley. The dryness lingers and expands areally to cover much of the east by July. The SW emerges with a very wet soil from the El Nino winter, and this feature too persists into the summer. By August all memory is lost, and the soil climate resets itself. (HVD 12/23/97)