Future Drought Conditions (Experimental)

How to read these maps

Initial Condition Map

• The initial condition is obtained from the drought nowcast system. It is the daily average soil moisture expressed as precentiles with respect to the historical distribution.
• The percentile value can be interpreted as the probability of historical observations being smaller than the current value.
• Visually, the green regions are wetter than normal and yellow/red regions are drier than normal.
• The contours indicate the change in soil moisture in the last 7 days, also expressed as changes in percentiles.

• These forecasts are produced monthly at the beginning of each month using the initial condition that is closest to the first day of the month.
• The CFS-base forecast uses all CFS seasonal forecast initialized during the previous month. For example, to make seasonal drought forecast starting from 21080801, we use CFS forecast initialized during 21080701 to 21080731 (62 members) to form the forecast distribution before applying the Bayesian merging method.
• The CPC outlook-based forecast uses the CPC output releases during the previous month as the forecast distribution for each climate division. For example, to make seasonal drought forecast starting from 21080801, we use CPC outlook released on 21080717.
• Each column is the 6-month soil moisture forecast from one forecast approach, and each row is the forecasts from all approaches for each individual month, showing monthly average.
• The drought estimate is a composite map. Values showing on the map are the conservative estimate of drought conditions based on the ensemble forecast when the forecast probability of an event is larger than the climatological probability. For example, the probability of soil moisture below 5th percentile is 5%, and the forecast probability of soil moisture below 5th percentile is larger than 5%, the estimated soil moisture condition is 5 (percentile), unless a lower threshold is exceeded.
• The first column (CFS-based forecast, full) use all the 20 ensemble members to calculate the median and spread. Ten of the twenty members are selected based on a historical-analog criterion, hence they can be sorted.

Target Month	CFS-based Forecast (full) released on 200801	CPC Outlook-based Forecast released on 200801	Nowcast (monthly mean)
Initial condition
200801
200802
200803
200804
200805
200806