High Confidence Forecast for Lengthy Drying Out Period; Slow WarmingSeptember 23rd, 2013 at 9:52 pm by Don Paul under 4 Warn Weather
A slow moving ridge will keep the big features in our sensible weather rather predictable into the weekend. After a cool start, very gradual warming by mid and late week will bring temperatures back above average into and through the weekend. Readings will be Seasonably mild, not “summery”. The next chance of showers at this writing appears to be no earlier than late Sunday night and more likely Monday.
In the longer range, confidence is much lower. The indices are still pointing in roughly the same direction as they did last week. However, -NAO and -AO still have a fair amount of spread in their ensemble members, as does the +PNA. Possibly working against the climatology of those indices is the still-active MJO, which is expected also to continue unseasonably lower activity in the Atlantic hurricane basin over the next 2 weeks. The Canadian ensemble mean shows clear signs near the end of its run of a west central US ridge and troughing in the midwest and Great Lakes. However, the GFS and European means do not show such a clear trend. Both point to an ill-defined, broad trough across the upper midwest and Grt Lks which would bring less cooling than the outlierish Canadian. CPC prog discussions are also low confidence with, again, no reference to the indices above. Still, I’m not in agreement with CPC’s positive temperature anomaly for the the northern tier of the US for the whole 6-14 day period. Short waves in that range can’t be reliably predicted, especially in the 8-14 Day. But given the high uncertainties, I would have favored a neutral/normal temp outlook for the latter part of the extended range.