Scientific Forecaster Discussion
fxus65 kpsr 200535 aaa
Area forecast discussion
National Weather Service Phoenix Arizona
1035 PM MST Thu Oct 19 2017
Update...updated aviation discussion...
a weak upper disturbance will shift eastward out of Arizona this
evening, with drier air overspreading the region from west to
east. Winds will increase as a cold front moves eastward tonight
and tomorrow, bringing cooler temperatures this weekend. High
pressure will rebuild over the region into early next week
leading to well above normal temperatures.
satellite imagery from this afternoon shows a narrow band of
ascent focused over Gila County into east-central Arizona,
accompanying a weak shortwave disturbance moving through the
region. Showers and a few thunderstorms have been observed since
early this morning, but with the leading edge of drier air aloft
spreading eastward, should continue to see rapid west-east clearing
through this evening.
A weak cold front will move through the region tomorrow afternoon,
resulting in increasing westerly winds across the entire area.
Sustained speeds around 15-20 mph, with some gusts to 30 mph,
across the lower deserts of south-central and southwest Arizona
will be possible. Even stronger winds are expected locally across
parts of southeast California, and a Wind Advisory has been
issued for southwest Imperial County (including a segment of I-8)
beginning this evening through late Friday evening. Patchy blowing
sand and blowing dust will also be possible mainly across
Imperial County tomorrow afternoon. Winds will weaken into
Saturday while turning out of the north across the lower Colorado
River valley, as high pressure builds over the Great Basin.
Locally gusty winds will still be possible here, while even drier
low-level air continues to spread into the southwest.
The other more pleasant effect on our weather will be the modest
cooling trend that will take place, as high temperatures in the
upper 80s to lower 90s are likely tomorrow, and mid-80s for high
temperatures on Saturday. Unfortunately, this will be short-lived,
as pattern amplification occurs in response to a very strong ridge
of high pressure building just east of the Pacific coast. Well
above-normal temperatures will return by Monday, approaching
record levels on Tuesday. The heat will moderate slightly later
in the week in response to northern rockies upper trough, but
highs will still remain in the 90s at most Lower Desert locations.
South-central Arizona including kphx, kiwa, and ksdl:
After a period of typical easterly drainage winds through the
remainder of tonight and early Friday morning, westerly winds are
expected to develop earlier than normal as a Pacific weather system
approaches from the west , during the mid-morning hours on Friday.
Stronger breezes are likely during the afternoon and early evening
hours Friday, with these westerly winds persisting well into the
night. Cloudiness will be limited to few-scattered high cirrus layers
during the entire taf period.
Southeast California/southwest Arizona including kipl and kblh:
A Pacific weather system approaching from the west will bring
gradually increasing westerly winds to kblh and increasing
southwesterly winds at kipl. Wind gusts as high as 30 kts are
possible by late morning/early afternoon at both taf sites. There is
also a chance for some blowing dust, but confidence is too low to
include dust in the tafs at this time. Cloudiness will be limited to
few-scattered high cirrus layers during the entire taf period.
Sunday through wednesday:
a warming trend begins Sunday with temperatures rebounding close
to 10f above normal on Monday and Tuesday. Minimum humidities will
remain below 15% (even at higher terrain locations) and overnight
recovery will be fair to good (at best). Winds will be light
overall (favoring north and northwest directions during the
daytime) except for breezy easterly winds on Wednesday.
Spotter information statement...
spotters should follow Standard reporting procedures.
California...Wind Advisory until 11 PM PDT Friday for caz562.