There was some storm activity over southeastern Arizona yesterday afternoon (see radar image for 6:15 MST above). These storms developed mostly at higher elevations in the zone between terribly hot and dry northwesterly flow from the Sonoran Desert and the more moist, recycled low-level air that had seeped into Arizona, east and south of Tucson, from New Mexico. For the eighth consecutive day there was essentially no precipitation measured across all of eastern Pima County (at sunset I could see a light shower to the distant northeast). The moist, low-level subtropical air over Mexico remains over Mexico, as if there were an impermeable fence along the Border!
There was relatively little convective activity over Sonora yesterday evening and last night, so that, without other features in play, there remains little forcing to push this air northward. Values for precipitable water remain at 1 to 1 ¼” this morning across all of southern Arizona.
The morning soundings at Phoenix and Tucson continue to paint a dismal situation with very deep afternoon boundary layers indicated; just a sliver of elevated CAPE; and desiccating northwesterly winds below 700 mb. The wind filed is very chopped up in the lower-troposphere and the winds in upper-troposphere are west to southwesterly around the cutoff low west of California. Storms this afternoon will tend to be over higher terrain to the east and south, as per yesterday, with high bases and gusty outflows. I note that Safford had a gust to 52 mph and dust yesterday afternoon but no rain, Guthrie RAWS had gusts to 46 mph and 0.09”, and Columbine RAWS on Mt. Graham had 0.94” of rain.
The 500 mb chart this morning indicates that there are two circulation centers for the anticyclone: one over the White Mountains of Arizona and one over southern Sonora. There is a weak trough separating these centers. Previous NAM runs (until last evening’s) had forecast this trough to consolidate and swing westward across southeastern Arizona. This morning’s NAM forecast indicates this feature shifting eastward to the Big Bend of Texas and not playing a role in today’s local weather – so not much model consistency in this weak summer pattern. At 200 mb a huge and intense anticyclone continues, centered over north central Mexico.
There is hope for an intrusion of better low-level moisture and some real CAPE for much of southern Arizona at mid-week as the 500 mb cutoff pushes ashore in California. This increases southerly winds briefly, before the cutoff in effect establishes a mean trough over the western U. S.
There was relatively little convective activity over Sonora yesterday evening and last night, so that, without other features in play, there remains little forcing to push this air northward. Values for precipitable water remain at 1 to 1 ¼” this morning across all of southern Arizona.
The morning soundings at Phoenix and Tucson continue to paint a dismal situation with very deep afternoon boundary layers indicated; just a sliver of elevated CAPE; and desiccating northwesterly winds below 700 mb. The wind filed is very chopped up in the lower-troposphere and the winds in upper-troposphere are west to southwesterly around the cutoff low west of California. Storms this afternoon will tend to be over higher terrain to the east and south, as per yesterday, with high bases and gusty outflows. I note that Safford had a gust to 52 mph and dust yesterday afternoon but no rain, Guthrie RAWS had gusts to 46 mph and 0.09”, and Columbine RAWS on Mt. Graham had 0.94” of rain.
The 500 mb chart this morning indicates that there are two circulation centers for the anticyclone: one over the White Mountains of Arizona and one over southern Sonora. There is a weak trough separating these centers. Previous NAM runs (until last evening’s) had forecast this trough to consolidate and swing westward across southeastern Arizona. This morning’s NAM forecast indicates this feature shifting eastward to the Big Bend of Texas and not playing a role in today’s local weather – so not much model consistency in this weak summer pattern. At 200 mb a huge and intense anticyclone continues, centered over north central Mexico.
There is hope for an intrusion of better low-level moisture and some real CAPE for much of southern Arizona at mid-week as the 500 mb cutoff pushes ashore in California. This increases southerly winds briefly, before the cutoff in effect establishes a mean trough over the western U. S.
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