Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 150820

Area Forecast Discussion
National Weather Service Phoenix AZ
120 AM MST Thu Apr 15 2021

Temperatures will show minor up and down fluctuations through the
weekend as the region remains under the influence of a broad but
mostly dry weather system anchored over the Great Basin. Periods
of high clouds and increased winds will also continue. There will
be a window for a few showers Sunday across northern and eastern
Arizona as a smaller but more robust weather system rotates around
the larger one. Temperatures will increase early next week as the
influence of the weather system wanes, likely reaching into the
90s for lower desert communities and 80s for surrounding mountain
and foothill spots.



Residual westerly winds continue across our forecast area early
this morning as the overall weather pattern remains generally the
same as the past few days. An upper level low remains parked over
the Great Basin, more or less, with a persistent subtropical jet
along its southern periphery pushing along intermittent patches of
dense cirrus. This pattern doesn`t look to change much today into
tomorrow, though though the parade of high clouds tracking along
the US-MEX border will likely come to an end tomorrow morning as a
more robust vort max pushes through and the upper level jet streak
moves off to the east. Lift is not particularly strong with the
Friday system but the juxtaposition with the right- entrance
region of a modest jet and condensational pressure deficits at
warmer/higher isentropic levels of <5 mb could yield some light
radar echoes across southern Arizona. A limiting factor is a
persistent dry subcloud layer as the saturated air is generally
above 600 mb.

Saturday into Monday, attention turns to a vort max/PV anomaly
that will develop/consolidate and rotate from northern Utah toward
west Texas. There is a low end potential for a few showers to
develop along the elevated terrain of northern Arizona, mainly
Sunday, as the vort max focuses vertical ascent and enough
moisture is in place to saturate upper levels. Currently depicting
low end (20%) chance of showers of eastern Gila County. There will
still be somewhat dry low levels in place, so potential for
wetting rains (0.10" or more) are extremely low (<1%).

Winds will continue to be off-and-on through this period, with
enhanced breezes again today and again Sunday. There will be
somewhat of an elevated fire weather threat for our eastern CWA
today (captured well in the SPC Day 1 Fire Weather Outlook). The
EPS is suggesting the potential for somewhat stronger northerly
winds along the Lower Colorado River Valley on Sunday, which could
also bring another round of elevated fire weather conditions.

Temperatures through the weekend will show some up and down
fluctuations but overall remain fairly typical for mid April.
Heading into next week, a short wave ridge will move over the
region allowing temperatures to tick back up into the 90s. There
is still a modest amount of spread within the global model
ensemble families as to the degree of ridging but ultimately good
agreement on warmer and continued breezy afternoons.


.AVIATION...Updated at 0551Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Southwest and west winds above the surface through a very deep
layer are moderate to strong due to an upper low pressure system
centered over the Great Basin. An approaching weather disturbance
embedded within that system will lead to some strengthening
(mainly above FL100) overnight. At the surface, westerly winds
have weakened and will continue to do so. Anticipate a period of
light and variable roughly between 09Z-16Z before southwest and
west directions prevail by mid morning with some gustiness in the
afternoon. Anticipate weakening again during the evening. Aloft,
directions will trend toward northwesterly beginning late
Thursday afternoon (more noticeably AOB FL100). As for sky cover,
thick cirrus will begin to decrease after 09Z. Anticipate some
pockets of virga with the thickest cloud cover. Otherwise, cirrus
thins out quite a bit by midday Thursday.

Southeast California/Southwest Arizona including KIPL and KBLH:

Moderate to strong westerly flow is in place through the depth of
the troposphere due to an upper low pressure system centered over
the Great Basin. An approaching weather disturbance embedded
within that system will lead to some additional strengthening of
the winds above the surface tonight. This will be followed by some
weakening AOB FL100 and a turn toward northwesterly directions
beginning Thursday morning. At the surface, southwest and
westerly winds have weakened and will continue to do so but
otherwise continue through the night and into the morning.
Northwest winds are anticipated to develop by late morning before
beginning to trend toward westerly late Thursday afternoon. As for
sky cover, cirrus has thinned quite a bit but anticipate there
will be a resumption of at least thin broken cirrus overnight
before decreasing again during the day Thursday.


Saturday through Wednesday: Continuation of breezy afternoons and
gradually warming temperatures are expected through the period.
Sunday could see an enhanced period of northerly winds down the
Lower Colorado River Valley. There will be a low (20%) chance of
light rain for eastern Gila County, though wetting rains are quite
unlikely. For the most part, slight downward RH trends are
expected. They will remain quite low (10-20%) during the
afternoons with overnight recovery very location dependent -
30-50% in and around the Imperial Valley, 30-60% for Gila County,
and 20-30% elsewhere.


Spotters should follow standard reporting procedures.


CA...Wind Advisory until 2 AM PDT early this morning for CAZ562.



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