Bit More On Morning Cold Spots

First, the morning low (am on November 25th) here, near the Rillito Wash, was 23 F. This makes 7 of last 8 mornings having temperatures here down in the 20s (other morning came in at 30 F). Plot below of morning low temperatures for the 25th, from MesoWest, is centered on the San Pedro Riparian Area - where lows have been very cold the last two mornings (9 F yesterday at station east of Tombstone and 11 F this morning).

Russ Scott provided the following:

Hi Bob.

Following up on yesterday’s low temp along the San Pedro:

Here’s a plot (above) of yesterday’s low at my research site along the San Pedro River.  This mesquite bosque site is quite close,  5 km south, of the Fairbank station shown on your Mesonet.  The San Pedro temp in the plot below is actually measured at 8 m height, at mid-canopy position, so a temp measurement at the standard screen height would be even colder than this.

The second plot (below) shows how effective these hard freezes, which started more than a week ago, are on damping latent heat (water vapor) fluxes by putting an end to the mesquite transpiration for the year.  Because it is so cold at these bottom land locations, the mesquite here don’t leaf out till late-April and don’t start transpiring until mid- May.

Russ

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Art Douglas noted: "El Ninos frequently bring early cold and we are sure doing that this year in some parts of the SW. Attached is this morning's low temp map for Mexico (below)."