Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 232144

Area Forecast Discussion
National Weather Service Phoenix AZ
244 PM MST Thu Mar 23 2017

A strong low pressure system will continue to move through the
region today, exiting Arizona later tonight. Shower activity today
will develop mainly from Phoenix eastward. High pressure will build
back into the region Friday, however another Pacific disturbance
will move into the region Saturday. The Saturday system will remain
dry, but a larger and colder weather system next Tuesday and
Wednesday may bring another period of showers.


Isolated showers and thunderstorms have developed across northern
Maricopa into southern Gila County within a narrow band of ascent
accompany a mid-level vort max moving east-southeastward across
central Arizona. SPC mesoanalysis shows modest destabilization has
occurred (MLCAPE values exceeding 250 J/kg) amidst steepening
mid-level lapse rates and cold temperatures aloft. Vertical wind
shear has been sufficient to support some low-topped and briefly
organized showers and thunderstorms capable of producing small
hail and gusty winds, but weak low-level convergence with
generally veered westerly surface flow has tended to limit storm
duration. This activity should decrease this evening with the loss
of diurnal heating as the mid-level vort max shifts east of the
region. Breezy westerly winds are also occurring along the western
fringe of large-scale cyclonic flow at the surface, in response
to deepening low pressure over the central High Plains.

Drier and more quiescent conditions are in store tomorrow into the
weekend as transient ridging aloft builds over the region. This
will usher in a warming trend with temperatures near seasonal
normals for the next several days. A second low-amplitude
shortwave trough is forecast to glance the region late Saturday
and Sunday, with the highest precipitation chances expected to
remain north of the region. Some increase in westerly surface
winds will also occur once again, with the strongest winds across
southeast California, but the current forecast suggests speeds
should remain shy of advisory levels.

Yet another storm system, potentially more significant, is
forecast to deepen over the Southwest by Monday. Deterministic
model guidance has come more in line developing a cut off low
early next week. However, precipitation chances will still remain
sensitive to the availability of rich moisture and the exact
track of the low, so will only maintain slight chance PoPs Monday
and Tuesday. The higher confidence impact remains the the
potential for gusty winds on Monday.


South-Central Arizona Including KPHX, KIWA, and KSDL:

Showers have mostly left the terminal area although there may be a
lingering shower or two. Most of the rain and thunderstorms over the
higher terrain north and east of Phoenix. The winds will remain
westerly through the afternoon with occasional gusts upwards of 20
to 30 kts. The winds should follow their diurnal The ceilings
generally should not be a problem although there may be some
temporary passing broken decks between 3 to 5k feet. The lowest
ceilings will impact the areas north and east of Phoenix to possibly
include SDL.

Southeast California/Southwest Arizona Including KIPL and KBLH:

The major aviation weather concern through this afternoon and
evening will be stronger westerly winds. Wind speeds will generally
stay around 15 kts although there may be some stronger gusts.
Otherwise, skies will be generally clear with no other major weather

Aviation discussion not updated for amended TAFs.


Saturday through Wednesday...
Temperatures will moderate back towards the seasonal normal over
the weekend as high pressure and dry weather build back into the
region. Breezy weather will be common through most of the
districts, especially Saturday and Monday afternoon. Despite the
stronger winds and drying trend, humidity levels will be
manageable only falling into a 15-30 percent range. Overnight
recovery will be good to excellent. Periods of stronger winds may
lead to a locally elevated fire danger at times, but critical
conditions should not be breached. An active storm pattern will
remain over the Southwest states, leading to periods of cooler and
windy weather through the end of the month.


Spotter reports will not be needed through the weekend.




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