Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 200456
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
956 PM MST Thu Apr 19 2018

.UPDATE...Updated aviation discussion

&&

.SYNOPSIS...
A strong, but mostly dry weather system will affect the Desert
Southwest into Friday bringing a return of windy and critical
fire conditions across the eastern half of Arizona. A significant
warming trend is expected this weekend into early next week with
high temperatures eventually returning into the middle to upper
90s over the lower deserts.

&&

.DISCUSSION...
At 2 pm this afternoon, a strong Pacific upper low was moving east
and through the desert southwest, centered over far southern Nevada.
The surface cold front was pushing east and into the far
southwestern AZ deserts. This is a dry system and will bring little
if any chance for precip to the area tonight into Friday. IR imagery
showed a prefrontal band of high clouds moving through the central
deserts, with skies elsewhere sunny to partly sunny. Surface
dewpoints over the central deserts were low, ranging from the low
teens to low 20, and even out west the values were on the low side
with Blythe reading just 26 degrees. Biggest impact with this system
has been wind - we saw west winds gust over 40kt in the Imperial
valley earlier in the morning, and when best mixing kicks in this
afternoon, winds should pick up over most of the area, reaching wind
advisory levels over favored areas in far SE California as well as
higher terrain of southern Gila County. Some of the lower deserts
could see gusts approach 35 mph at times later today but for the
most part winds should remain below advisory criteria. Ahead of the
front, in south central AZ, temps today were running a few degrees
warmer than 24 hours ago as mixing and low level warm air advection
ahead of the front allowed temps to climb into the low to mid 80s.
Phoenix has already reached 85 this afternoon...but we should
certainly see some cooling by Friday in the wake of a departing cold
front. Look for Phoenix to fall into the upper 70s to around 80 on
Friday with temps starting to rebound into the mid 80s over the
warmer western deserts.

Main issue for the rest of today will be the continuing wind
advisories which will stay in effect thru 02z. A Red Flag Warning is
also in effect through 8 pm over the southwest and south central
Arizona with the main threat being from central Phoenix east into
southern Gila County. Areas of blowing dust are still expected this
afternoon given the gusty winds and we will continue to monitor in
case blowing dust advisories are needed.

Upper level ridging will take hold behind the exiting trough for
Saturday with 500mb heights quickly rebounding to around 580dm.
Models are still showing a weak shortwave coming off the Pacific
through Baja Saturday night, eventually into northern Mexico on
Sunday. This feature will bring a period of high clouds into the
Desert Southwest Saturday night into Sunday, but it should not
disrupt the warming trend over the region. Highs Saturday should
fall around 90 degrees while Sunday looks to be closer to 95
degrees.

Weak southwesterly flow aloft will remain across the Southwest
U.S. into early next week with 500mb heights hovering around
580-582dm. This will keep temperatures around 7-10 degrees above
normal through at least Tuesday. Model spread increases for the
middle of next week with another potential Pacific low approaching
the West Coast. This feature may help to amplify the ridge over
the Interior West if it becomes mostly cut-off from the northern
jet stream as indicated by the warmer European. The GFS is farther
north with the trough, more progressive and thus keeps
temperatures a bit cooler. Given this system is a week away, a
blend was used for forecast temperatures yielding highs mostly in
the middle 90s.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:

Slantwise visibilities are reduced this evening from the windy
conditions and lofted dust that occurred this past afternoon but
are expected to improve throughout the night. Winds will continue
to taper off tonight with easterlies returning late tonight.
Westerlies return early Friday morning but will be much weaker
with gusts up to 15 kts in the afternoon. Besides this, a few mid-
level clouds (~10 kft) may drift over the terminals tonight but
clear skies are expected by morning. No other aviation concerns.

Southeast California/Southwest Arizona including KIPL and KBLH:

Winds will continue to weaken overnight as a weather system moves
off to our east. Westerly flow will prevail through our TAF period
with winds favoring the northwest on Friday. Speeds will be much
weaker tomorrow with gusts up to 15 kts in the afternoon. Besides
this, clear skies will prevail with no other aviation concerns.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Sunday through Thursday...

As high pressure begins to build back in from the west expect a
warming trend together with very dry conditions. Above normal max
temps will reach mid 90s over warmer deserts Sunday, and will climb
to the upper 90s by the middle of next week. Min RH values near 6-10
percent are also expected to last throughout the period. Breezy to
windy conditions will develop late in the period as a low pressure
system approaches from the west. Overnight recovery is expected to
be poor to fair.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters are encouraged to report dense blowing dust.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...CB/Kuhlman
AVIATION...Wilson
FIRE WEATHER...Sawtelle


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