AM Showers Again - Freeze Watch For?

Early morning showers again, mostly across northern portions of the metro area. This event has been widespread across eastern Pima County but ALERT network shows that amounts were mostly around 0.15" or less, except up in the Catalinas. There has been some thunderstorm activity, as indicated by the 24-hour CG flash density plot below valid through 6:15 am MST this morning (from weather.graphics and Vaisala). Thunderstorms avoided most of Pima and Santa Cruz Counties.

Here at the house there were three periods of light showers yesterday, ending around 3:00 pm - total rain for yesterday was 0.14". This morning's showers have added 0.04" at this time. The Catalina sector of the ALERT data (second below - for 24-hours ending at 6:00 am), indicates another substantial event for the mountains. The 06 UTC run of the WRF-NAM model at Atmo indicated showers ending mid-day to early afternoon, as the cold trough sweeps by.

I will gripe again here about the imprecise character of some of the graphics used by the NWS. 

First, I should say that freezes are important to a number of folks locally - whether they are landscapers, gardeners, citrus growers, or even homeless and on the streets (the NWS forecasts trigger whether or not many shelters will open on cold nights).

The current NWS graphic above indicates a freeze watch across the entire metro area, and the early am forecast grid for TUS (the airport grid box) shown below indicates that the freeze watch is valid at the airport.

However, the text products from the NWS confuse the situation, as per (note I've added some highlighting):
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  AREA FORECAST DISCUSSION 

  NATIONAL WEATHER SERVICE TUCSON AZ 

  333 AM MST MON NOV 16 2015

   -------------------------------------------------------

THE WHITE MOUNTAINS...GENERALLY IN THE 3-7" RANGE OTHERWISE THE MAIN

  STORY WILL BE THE MUCH COLDER OVERNIGHT LOW TEMPERATURES ESPECIALLY

  ACROSS THE LOWER ELEVATIONS OF PIMA AND PINAL COUNTIES. STILL SOME

  UNCERTAINTY ON AREAL EXTENT OF FREEZING TEMPERATURES...THUS DECIDED

  TO NOT EXTEND CURRENT FREEZE WATCH OR CONVERT TO A WARNING. WILL LET DAY SHIFT EVALUATE FURTHER.

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The 3:33 am forecast discussion above seems to indicate that the freeze watch has not been continued due to uncertainties. However, the 5:00 am MST text for the freeze watch (below) indicates that the watch continues, but that much of the metro area is not included. I can not find any graphics that show the actual, current delineations of the freeze watch area. Additionally, the statement emphasizes that the Catalina foothills (generally north of the Rillito Wash extending up to Federal lands) are in the watch area. But, this zone is known as a "banana belt" for its warmer morning temperatures during the winter. 

So, to me, the situation seems generally confusing, aggravated by imprecise graphics. If you're concerned about low temperatures the next couple of mornings, you have to rely mainly upon local experience during similar events. Here at our location, I know that it will be below freezing the next couple of mornings, probably well below, and if I had bougainvillea blooming in the yard, I'd take action to protect them. Finally, graphic at bottom is from the 06 UTC forecast from the WRF-NAM model and shows 2-m temperatures forecast for 7:00 am tomorrow morning. The model has picked up on both the Rillito cold zone, as well the foothills banana belt.

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505 AM MST MON NOV 16 2015

...FREEZE WATCH REMAINS IN EFFECT FROM LATE TONIGHT THROUGH

TUESDAY MORNING...

* TEMPERATURES...LOW TEMPERATURES GENERALLY RANGING FROM 29 TO

  32 DEGREES ARE FORECAST TO OCCUR IN THE WATCH AREA. FREEZING

  TEMPERATURES ARE EXPECTED MAINLY ACROSS THE CATALINA FOOTHILLS

  AND THE FAR EASTERN AND SOUTHERN PORTIONS OF THE TUCSON METRO

  AREA. A SUBSTANTIAL PORTION OF THE TUCSON METRO AREA IS NOT

  INCLUDED IN THE FREEZE WATCH AT THIS TIME.