Over the past month, the large-scale pattern has featured a persistent trough along the Pacific Northwest coast and a high-amplitude upper-level ridge (a.k.a. the "death ridge") centered over Texas, as shown in the 30-day mean 500-mb height analysis for 17 July – 15 Aug 2011.
However, a subtle but important shift in this pattern is presently underway. Over the past week, troughing over the Pacific Northwest has weakened and the upper-level ridge has built westward into the Intermountain West.
This has brought the longest stretch of days with a maximum temperature above 90F this month and minimum temperatures over the past four days of 70F or greater.
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| Source: National Weather Service |
So, the heat is on and we expect maximum temperatures at KSLC to head into the mid–upper 90s by for today, Wednesday and Thursday.
When does the first storm of Autumn come into the picture? Or is that still too far away to tell? Also, Paradise SNOTEL still had 10.0 inches SWE at midnight on 8/23.
ReplyDeleteJim,
ReplyDeleteI have to say that those first two images seem nearly identical to me, especially with regards to heights over the Great Basin. I do agree that the trough off the PacNW Coast has weakened, but to me the effects seem minimal.
Could it be possible that the warming trend the past few days is more closely associated with a scouring out of moisture? (http://gpsmet.noaa.gov/)
Perhaps the diminished PW values and cloud cover, as well as isolated thunderstorms, from 3-4 days ago, is playing a significant role.
Jon:
ReplyDeleteOne person's signal is another person's noise. I agree that the changes are subtle. The first image is the 30-day mean for the past month, the second is the 7-day mean for the past week. The weakening PacNW trough is the primary difference, but this opens the door for the ridge to build westward.
Jim