Area forecast discussion 
National Weather Service Tucson Arizona 
935 am MST Tuesday may 31 2016 


Synopsis...a weak low pressure system will bring isolated to 
scattered showers and thunderstorms especially near the mountains 
into this evening and again Wednesday. A slight chance of showers 
and thunderstorms exists near the New Mexico border Thursday. 
Otherwise, much hotter daytime temperatures will prevail Thursday 
into early next week. Highs will be around 110 degrees near and west 
of Tucson this weekend. 


&& 


Discussion...a few cumuloform clouds were across the White 
Mountains and mainly across the Chiricahua Mountains in eastern 
Cochise County at this time. A few lightning strikes were detected 
just southeast of this forecast area across far northwest Chihuahua 
Mexico. Otherwise, clear skies prevailed across Southeast Arizona. 
Dewpoints at lower elevations valid 16z generally west of a Safford- 
Sierra Vista line were mainly in the mid teens to 20s. These temps 
were about 15-35 degs lower versus 24 hours ago. However, kdug 
dewpoint was 48 degs valid 16z. 


31/12z ktwc sounding total precip water value of 0.34 inch was 0.21 
inch lower versus 24 hours ago. The profile exhibited the bulk of 
drying in the surface-675 mb layer. 31/12z upper air plots depicted a 
573 dm low centered adjacent the international border southwest of 
Tucson. High pressure aloft was centered just west of the northern 
California coast with a ridge axis extending north into British 
Columbia. Light sly to wly flow aloft prevailed across Southeast 
Arizona. 


Based on several hrrr solutions as well as the 31/12z NAM/GFS and 
the univ of Arizona WRF-NAM, opted to make a few adjustments to the 
inherited pops for this afternoon/evening. The first adjustment was 
to remove isolated thunderstorms and patchy blowing dust for locales 
west of Tucson. The second adjustment was to increase pops slightly 
for locales south of Tucson late this afternoon and evening. The hi- 
res models were quite similar with depicting the best chance of 
measurable precip to occur mainly near the mountains northeast of 
Tucson into this evening. However, they have also been similar with 
depicting the potential for showers/tstms to occur from just of 
Tucson southward toward Nogales. 


Given the aforementioned very dry surface regime across much of the 
area, the main concern associated with any showers/tstms will be the 
potential of gusty outflows producing blowing dust capable of 
reducing visibilities substantially. The bulk of any showers/tstms 
should end by around midnight tonight. However, the univ of Arizona WRF- 
NAM suggest the potential for some showers to linger across eastern 
sections late tonight. Am leaning toward at least increasing cloud 
values late tonight across eastern sections. The best chance for 
showers/tstms Wednesday appears to be east of Tucson as per the 
inherited forecast. 


&& 


Aviation...valid through 01/18z. 
Isolated to scattered -tsra/-shra will occur mainly near the 
mountains east of ktus to the New Mexico border this afternoon and 
evening. A few -tsra/-shra may develop this afternoon and evening 
south of ktus, and perhaps in the vicinity of kols. The main threat 
from any -tsra/-shra given the very dry surface environment will be 
the potential for wind gusts to near 40-45 kts or so. Otherwise, a 
few clouds around 12k ft msl this morning will become sct-bkn clouds 
this afternoon and continue into Wednesday morning. Surface wind 
this afternoon and evening will be swly/wly at 10-20 kts with gusts 
to near 25 kts. Surface wind will be less than 10 kts at other times. 
Aviation discussion not updated for taf ammendments. 


&& 


Fire weather...isolated to scattered showers and thunderstorms are 
forecast to occur this afternoon and evening mainly near the 
mountains east of Tucson to the New Mexico border. Isolated showers 
and thunderstorms also exists late this afternoon and evening south 
of Tucson. Scattered showers and thunderstorms will then occur east 
of Tucson Wednesday, and a slight chance of showers and 
thunderstorms continues Thursday mainly near the New Mexico border. 
Expect strong, gusty and erratic winds with these showers and 
thunderstorms. Thereafter, dry conditions with very hot daytime 
temperatures and generally light winds will prevail Friday into early 
next week. 


&& 


Previous discussion /227 am MST/...we will hang on to mostly mountain 
showers/thunderstorms again on Wednesday, mainly between Tucson and 
the New Mexico border. Once the system exits the region late 
Wednesday, ridging will begin to build in from the west during the 
latter part of the week and remain in place through early next week. 
Enough lingering moisture to our east to justify slight chances for 
the White Mountains nearly each day through the remainder of the 
forecast period. 


As a result of the building high pressure, expect considerable 
warming of temperatures late this week and weekend. The first 100 
degree day for Tucson may occur on Thursday. However, if we miss 
that elusive 100 degree mark again on that day, we will easily 
surpass that threshold each day Friday through early next week, when 
highs will range from 105 to near 110 for the far western deserts. A 
bit early for headlines at this point, but day shift may want to 
consider an excessive heat watch for mainly central and western 
parts of the forecast area for this weekend, if guidance temps 
remain high. 


For Tucson, high temps will generally range from 2 to 4 degs below 
normal today and Wednesday, then around 2 to 4 degs above normal for 
Thursday. Thereafter, highs will range from 7 to 10 degs above 
normal, although the hottest days will occur this weekend. Low temps 
will be near normal Wednesday morning, then 4 to 5 degs above normal 
Thursday and Friday and 7 to 9 degs above normal this weekend into 
early next week. 


&& 


Twc watches/warnings/advisories...none. 


&& 


$$ 


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Francis 
previous discussion...mollere 



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