Monday, June 22, 2015

Humid Morning

We've been in the Sacramento area of California during past four days, so I'm a bit out of touch with what's been happening here in southeastern Arizona. But, low-level moisture has definitely increased since we left, coming in during Saturday evening/night. The surface observation time-series at TUS continues to have temporal drop-outs, but at DM AFB the dewpoint temperature jumped from 27 to 57 F during a period of only 45 minutes before midnight. This appears to have been outflow from MCSs in northern Sonora, even though the initial wind shift was to the west-southwest. Low-level moisture has remained relatively high since then. Time series below is of GPS-inferred PW values, with the increase depicted clearly at Tucson (on campus) and a bit earlier out west at Tohono O'odham Community College (also shows up more weakly at Bisbee/FHU).

The CIRA (Colorado State University) blended PW analysis for 5:00 am MST this morning (above) has lots of data drop-out areas but shows higher PW extending from Sonora across all of southern Arizona - note the small patch of values greater than an inch over eastern Pima County. The morning TWC sounding (from SPC - below) shows elevated low-level moisture below 700 mb (PW is a bit over an inch) and an old, elevated boundary layer (BL) from 700 to 500 mb. The SPC analysis indicates some CAPE but also considerable CIN. Typically a sounding like this will evolve with a new surface-based BL developing, keeping an inversion between the new and old BLs - sometimes, with intense heating, the two BLs merge into a single, very deep BL.

The forecast sounding above (from the 06 UTC WRF-NAM, valid at 5:00 pm MST this afternoon) indicates that the two BLs remain separate today. The forecast sounding has much reduced PW relative to this morning's observation (only 16 mm, although the forecast PW for 12 UTC was quite close to what was observed), apparently due to drying from the northwest. The forecast sounding has absolutely no CAPE, which is quite a bit different than the modified SPC analysis would indicate - probably will see something evolve that falls between the two.

The plot of CG flashes below (from Vaisala and Atmo through midnight last night) shows thunderstorm activity in northern Sonora that stayed well south of the border. The WRF forecasts for this evening bring the storm activity closer to the border, but still keep it in Mexico. By Wednesday an inverted trough in the middle-levels brushes into southeastern Arizona, increasing chances for an early start to our summer thunderstorm season.

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