Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 141055

Area Forecast Discussion
National Weather Service Phoenix AZ
355 AM MST Fri Dec 14 2018

.UPDATE...Updated Aviation and Fire Weather Discussions.


Pleasant weather will continue through the weekend
with temperatures a few degrees above seasonal norms. There will
be off and on periods of thicker high clouds through Tuesday with
a slight chance of showers developing early next week. High
pressure will then build back over the region for the latter half
of the work week.


Today: High pressure will dominate today, with the ridge axis
currently stretching from Yuma northward into Montana.
Southwesterly flow behind the ridge axis is aiding in advecting a
batch of thicker high clouds associated with the next weather
system (currently situated over the western Pacific). As the
ridge axis continues to shift eastward, we can expect cloud cover
to continue to increase from west to east with mostly cloudy skies
expected by this evening across the forecast area. High
temperatures today will be a few degrees above normal approaching
the upper 60s/ low 70s. Due to enhanced cloud cover overnight,
lows will stay slightly elevated, only dropping into the mid to
upper 40s along the lower deserts.

Weekend through Tuesday: A wave in the western Pacific will move
eastward across the region on Saturday, with the southern portion
of it separating itself and becoming a closed low Saturday
afternoon just as it moves over the northern Baja California
Peninsula. The center of this low will then slowly track
northeastward, centering itself over northern Mexico by late
Sunday evening. Monday morning, this low will weaken and get
absorbed into the main trough and quickly move off the northeast
just as the main trough axis is entering our western forecast
area. This trough will then quickly move east Monday evening
through Tuesday morning and sweep a weak cold front across the
region. Through these series of events, moisture values increase
a decent amount, with PWs increasing from less than .2 inches
today to close to half an inch by Tuesday morning. However,
compared to yesterday`s model runs there has been a decrease in
atmospheric moisture, and due to this QPF amounts have dropped off
a good amount with areas out west now maybe getting up to .01
inches and areas out east getting maybe up to .05 inches. Because
of this downtrend, POPs were lowered a bit, with the greatest POPs
still expected Monday night through Tuesday morning across our
eastern CWA, especially over the higher terrain. Although we may
not see much rainfall from this, we can expect to see off and on
thicker clouds moving through the region this weekend through
early next week. Temperatures Saturday and Sunday will be in the
low 70s, but on Monday and Tuesday we can expect a little bit of a
cool down, with highs in the upper 60s/ low 70s in the lower
deserts. Overnight temperatures won`t change much, with lows only
expected to drop down into the 40s across lower elevation
locations each night.

Wednesday through Friday: High pressure starts to build back over
the region Tuesday night and persist through the work week before
another low pressure system meanders it`s way towards our area
Saturday morning. This will result in a slight warming trend
during the latter half of the week with highs approaching the low
to mid 70s each day.


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

Mostly clear skies early this morning will give way to increasing
high clouds by mid morning moving in from the west across the area.
Expect high cloud CIGS near 25kft by mid to late morning to
gradually thicken and lower to 15-17kft by later tonight. Otherwise
expect light to moderate to light and variable winds near 5-10kt
favoring the east through late afternoon. A relatively late
westerly switch over is then anticipated at about 00Z.

Southeast California/Southwest Arizona including KIPL and KBLH:

High clouds CIGS near 25kft are expected this morning to
gradually thicken and lower to 15-17kft by this evening. Light and
variable winds will begin to favor the north at KIPL by midday,
and the northwest at KBLH early tonight and remain light through
the period.

Aviation Discussion not updated for amended TAFs.


Sunday through Thursday:

With an unsettled weather pattern in place through Tuesday and
increasing moisture early in the period there are few fire weather
concerns. Min RH near 15-23 percent on Sunday will increase to
above 20 percent by Monday and stay above to well above that level
through the end of the period. Expect some breezy northerly winds
to develop on Tuesday and into Wednesday in SE CA and SW AZ. High
pressure will build into the area on Wednesday as highs
increase into the low 70s. Overnight recoveries will be good to


Spotters should follow standard reporting procedures.




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