There has been a problem with the EDDI product over the northeastern and north-central regions of CONUS during this past winter (and perhaps still), with EDDI indicating extensive and severe dry conditions (ED1-ED4) over much opf the region during this period.
The source of the problem is with the NLDAS-2 drivers of EDDI themselves. Over this past winter, the NLDAS-2 forcing data (at NASA GES DISC) appeared to diverge from other independent observations. For example, starting from about November 2022, the NLDAS-2 2-meter air temperature differed considerably from (i.e., was warmer than) NOAA-Climate Prediction Center's T2m observations, whereas they normally are in good agreement and were so before October of last year. This led to EDDI often showing extensive ED4 (98%ile drought) over much of northern and northeastern CONUS, which is not reflected in the USDM or in other non-NLDAS-driven products.
NASA has located the likely source of the error. They found an issue in the production of the operational version of NARR, where the precision of the snow depths that are ingested by the NLDAS-2 system changed significantly, which potentially led to strong underestimation of snow cover, and subsequently impacted other variables, such as overestimation of T2m over snow-covered regions. NASA is performing test runs to confirm this. Hopefully, there will be a new reprocessing of NLDAS-2. At that point, we will re-run and re-post EDDI.
We sincerely regret these errors. We are dependent on the quality of the input data that we use, and any issues therein will be reflected in our product. We hope to be able to correct these errors soon.