Area forecast discussion 
National Weather Service Tucson Arizona 
330 PM MST Monday may 20 2013 


Synopsis...a weak upper level ridge will move across the state 
Tuesday another quiet weather day Tuesday. A deep upper level low 
moving into the Pacific northwest Tuesday will deepen along the 
entire West Coast and linger over the region well into next week. 
This will result in a prolonged period of dry southwest flow across 
southern Arizona with above normal afternoon temperatures and a few 
gusty afternoons. 


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Discussion...winds continued to diminish in speed late this 
evening. That said...the red flag warning was allowed to expire on 
time. Lighter winds compared to today can be anticipated Tuesday. 
Current forecast looked on track...so please refer to the additional 
information in this product. 


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Aviation...sky clear through tonight..with a thickening high cloud trend 
Tuesday. Surface wind less than 10 kts overnight with Tuesday afternoon 
winds lighter than today...mainly in the 10-15 knots range. Aviation 
discussion not updated for taf amendments. 


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Fire weather...lighter...meaning more normal diurnal winds...and 
warmer temperatures are forecast Tuesday under high pressure. As a 
large area of low pressure sets up along the West Coast...somewhat 
stronger southwest winds are forecast to begin Wednesday through the 
Holiday weekend yielding occasional critical fire weather conditions 
across Southeast Arizona as dry weather persists...kd 


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Climate...Tucson will make another run toward the first 100 degree 
day of 2013 on Wednesday. Most of the temperature guidance that we 
access to...from MOS guidance to bias-corrected guidance to GFS 
ensembles guidance...are not forecasting 100 for Tucson this week. 
However the ec and UKMET 850-700 mb thickness values on Wednesday 
are continuing to show either 99 or 100 for Tucson. So there is a 
slight chance that Tucson will hit 100 this week. At this point I 
will continue to keep forecast high on Wednesday at 98. If the 
first 100 doesn't occur on Wednesday...we will likely have to wait 
until next Monday for our next shot. 


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Previous discussion...the broad upper level trough that has maintained 
the dry northwest flow across the area which has held temperatures near 
normal levels is moving out into the Central Plains and will no 
longer be a direct player in our weather. A short wave ridge will 
pass across the area Tuesday having a limited affect on the sensible 
weather other than allowing temperatures to be a degree or two 
warmer and slightly less wind than this afternoon. But the passing 
of its axis will open the door to the influence of the deep late 
season upper low/trough that will settle in along the West Coast and 
remain in that generally area in one form or another well into next 
week. 


The first hint of that trough influence will be the high clouds that 
will spread across the area later Tuesday into Tuesday night. They 
will clear out during the day Wednesday but from the look of things 
bands of high level moisture will stream across Arizona from time to 
time from Wednesday night into next week. Due to the position of 
the low and flow direction I am not seeing any potential for 
precipitation over our neck of the Woods. The greatest impact for 
our area from this setup will be the occasional breezy/windy periods 
that we will get especially as features rotate around the base of 
the trough. The basic idea is dry...somewhat warmer than normal 
with gusty afternoon winds now and then Thursday into early next 
week which is more of a fire weather concern than a concern for the 
general public. Cerniglia 


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Twc watches/warnings/advisories...none. 


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