Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 231243

Area Forecast Discussion
National Weather Service Phoenix AZ
543 AM MST Wed May 23 2018

.UPDATE...Updated Aviation Discussion.


Quiet weather is expected across the area through next week with
near normal temperatures and dry conditions in the forecast.
Breezy conditions are likely Friday and Saturday as a low pressure
system moves into northern Arizona. This system will hang around
through the weekend keeping high temperatures in the 90s. Warmer
temperatures are likely for the first part of next week with highs
just over 100 degrees.


A large upper level trough centered over northern Utah continues
to slowly track to the north northeast with the southern extent of
the trough exiting Arizona by this afternoon. Southwesterly flow
aloft will remain dominant across the Desert Southwest over the
next couple days with heights slowly rising and temperatures
climbing back to above normals by Thursday. The large scale
troughing pattern over the Western U.S. still looks to be the main
influence through next week with two systems forecast to affect
the Southwestern U.S.

The first upper level low will start to take shape tonight off the
California coast, becoming a closed low on Thursday and tracking
east into central California by late Friday. High amplitude
ridging will set up over at least the eastern portion of the
Desert Southwest Thursday and Friday before the low finally moves
inland on Saturday. Winds will increase ahead of the low on Friday
and Saturday with the strongest wind gusts of 25-30 mph on
Saturday. Southwestern Imperial County will see wind gusts closer
to 40 mph Friday night and again Saturday evening with some patchy
blowing dust a possibility. The stronger winds and continued dry
conditions on Saturday should result in another day of enhanced
fire danger, but for now it looks like winds will fall short of
Red Flag criteria.

Cooler air will move in from the west this weekend as the low
moves into the Desert Southwest. This will drop highs on Saturday
down to around 90 degrees across southeast California and into the
middle 90s over the south-central Arizona deserts. Models remain
in good agreement tracking the low across northern Arizona
Saturday night before stalling the low over the Great Basin
Sunday and Monday. This will keep temperatures a few degrees below
normals on Sunday, but as the low weakens and shifts a bit
further north on Monday, highs should again be flirting with the
100 degree mark.

A similar scenario seems likely for the latter half of next week
with a brief ridging taking hold before another Pacific low
potentially nears the region. This would bring a warming trend
through the middle of next week and temperatures likely topping
100 degrees starting next Tuesday. Much higher model spread come
into play thereafter as this next Pacific low develops off the
West Coast. Ensemble means from the GEFS and European both show
the low approaching the West Coast sometime late next week, very
similar to the previous couple troughs. This preferred solution
would cool temperatures back down closer to normals at some point
late next week.


South-Central Arizona including KPHX, KIWA, and KSDL...
Southeast California/Southwest Arizona including KIPL and KBLH:

A weakening low pressure system will continue to retreat across
the Great Basin. Nevertheless, a weak southerly component to the
flow will persist across the area. For the Phoenix area, winds
will gradually veer to westerly during the late afternoon, while
generally remaining less than 10 kt. Onset of the downslope
easterly flow is anticipated around 08-09z at KIWA/KPHX.


Friday through Tuesday:
Dry conditions will prevail across the districts through the
holiday weekend with temperatures a couple degrees above normal
Thursday and Friday cooling back near normals over the weekend.
Afternoon minimum humidity levels will mostly fall in a 5-10%
range with generally poor overnight recoveries. Wind speeds will
begin to increase Friday across SE California, then across the
remainder of the districts on Saturday. Wind gusts approaching a
25-30 mph range will be likely and would lead to an elevated fire
danger, particularly on Saturday.


Spotter activation will not be needed.




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