Cold And Very Dry

Statement from the TUS NWS regarding forecast low temperatures for yesterday (Black Friday) morning:
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First freezing temperature of 2010 likely Friday morning at Tucson International airport

Although a good portion of the Tucson metro area has already recorded a freeze this year, either last winter or earlier this month, the official temperature site for the area, Tucson International Airport, has not. The lowest reading at the airport so far in 2010 has been 33 degrees on January 24th. The official NWS forecast calls for the airport to be near 29 degrees Friday morning as an Arctic air mass moves in. With the first freeze of 2010 at the airport likely to occur on Friday, this would rank as the 2nd latest first occurrence of 32 degrees or colder in a calendar year on record. The average first freeze date in a calendar year is January 9th.

Top 5 latest 1st occurrences of 32 degrees or colder in a calendar year at Tucson International Airport

November 27, 1980

November 26, 2010 ** (based on current forecast)

February 7, 1986

February 6, 2007

February 2, 1956

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The low at TUS yesterday morning was 30F - so, the airport measured its first freezing or below temperature for the entire year of 2010 on Friday, as per above statement. Low here at house (inside Tucson city limits) was 21F. At the house, yesterday was the 43rd morning low of 2010 with freezing, or below, temperatures! The 21F yesterday was the coldest morning of 2010, so far. If you're a gardener, there appear to be at least three plant hardiness climate zones within the Tucson city limits (perhaps four, but there are not enough observational data to determine the zones precisely).

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This morning (Saturday November 27th) the low at the house was 24F, while the airport official low was a relatively balmy 37F. Also of interest was the strong reversal between low (cold) areas and the mountain peaks (mild) this morning. For example, the Rincon RAWS (8209 ft MSL) site recorded a low of 37F, same as the airport, while the Mt. Hopkins RAWS (7120 ft MSL) site recorded a low of only 44F this morning.

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Finally, the RH has fallen to miserable, skin-cracking values, with dewpoints in the single digits or below zero. The graphic above shows the GPS and TWC raob comparisons of PW for the last 30 days. The RRS RAOB has been consistently too dry during the past month, but note that the last three comparisons have been very close and right around a ridiculously low 2 mm. Prime conditions for static electricity and also nose bleeds.