Blocking Dominates Northern Hemisphere

First - the last three days have had high temperatures of 100, 101, and 100 F at the airport (TUS). The slow moving, 500 mb, short wave that will close off over the Southwest during the coming week will drop temperatures. This may be the last cooling period before 100 F temperatures become much more routine.

The current 500 mb pattern around the Northern Hemisphere is dominated by pronounced blocking - above is GFS ensemble-mean pattern at 12 UTC this morning (19 May 14), below is same figure but for 12 UTC on May 22nd, and bottom graphic is same but for 00 UTC on 26 May 14. This morning a Rex block sits over the middle Pacific, while Omega blocks dominate the central Atlantic and eastern Europe.

By mid-week, above, the Omega blocks remain strong, while the Rex block has evolved into a large, bent-back ridge. Note that the GFS forecasts an anticyclone over Louisiana and Mississippi with 500 mb heights greater than 5880 m - I think that this is the first time heights have been forecast this high over the CONUS during 2014 (not absolutely certain of this). Lower than normal heights are parked over the Southwest.

Below, out at seven days, the blocks persist, but have weakened, which is to be expected since climatology is coming into play this far out. The European block dominates at this time in the forecasts and it has gradually shifted westward. So a fairly stagnant pattern, but one that will provide us in southern Arizona a brief respite from the May heat.