We're starting a very warm week in California, and conditions will be about as summer-like as they get in San Francisco. As a strong ridge of high pressure strengthens over the West Coast, temperatures will warm and offshore winds will keep the marine layer out of the Bay Area. For much of the week daily high temperatures in San Francisco will reach the low- to mid-80s, well above normal, and many locations in the region will likely set new daily record highs over this period. The image on the right shows forecast highs for Friday, but similar temperatures can be expected Wednesday and Thursday as well. The dry, offshore winds will also result in fire concerns, and the NWS has issued a Red Flag Warning for the North and East Bay hills. Any unattended fires could quickly get out of control given the hot, dry, windy conditions and abnormally dry vegetation for this time of year.
In the central and eastern U.S., temperatures have finally warmed up to near normal after a cool March and most of April. However, the warm up is short lived as anomalously deep upper level trough moves into the region. The images on the right are forecast 500 mb heights, winds, and vorticity for Tuesday night and then Friday morning. On Tuesday, a strong trough is noted over the western Plains region. However, instead of progressing quickly eastward as would typically be expected, this trough closes off and detaches from the steering flow (or jet stream). Without the upper level steering, this closed low will be left to drift across the central Plains and will only slowly move east. The system will bring unseasonably cold temperatures, with highs only in the 40s for many locations where average highs are well into the 60s. The air will be cold enough that some forecast models also show the potential for accumulating snow over parts of the Rockies followed by the Upper Midwest (see final image). To put this system in some historical perspective, the Minneapolis-St. Paul area has not seen measurable snow in May since 1991.
We're starting a very warm week in California, and conditions will be about as summer-like as they get in San Francisco. As a strong ridge of high pressure strengthens over the West Coast, temperatures will warm and offshore winds will keep the marine layer out of the Bay Area. For much of the week daily high temperatures in San Francisco will reach the low- to mid-80s, well above normal, and many locations in the region will likely set new daily record highs over this period. The image on the right shows forecast highs for Friday, but similar temperatures can be expected Wednesday and Thursday as well. The dry, offshore winds will also result in fire concerns, and the NWS has issued a Red Flag Warning for the North and East Bay hills. Any unattended fires could quickly get out of control given the hot, dry, windy conditions and abnormally dry vegetation for this time of year.
In the central and eastern U.S., temperatures have finally warmed up to near normal after a cool March and most of April. However, the warm up is short lived as anomalously deep upper level trough moves into the region. The images on the right are forecast 500 mb heights, winds, and vorticity for Tuesday night and then Friday morning. On Tuesday, a strong trough is noted over the western Plains region. However, instead of progressing quickly eastward as would typically be expected, this trough closes off and detaches from the steering flow (or jet stream). Without the upper level steering, this closed low will be left to drift across the central Plains and will only slowly move east. The system will bring unseasonably cold temperatures, with highs only in the 40s for many locations where average highs are well into the 60s. The air will be cold enough that some forecast models also show the potential for accumulating snow over parts of the Rockies followed by the Upper Midwest (see final image). To put this system in some historical perspective, the Minneapolis-St. Paul area has not seen measurable snow in May since 1991.
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