Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 271016

Area Forecast Discussion
National Weather Service Phoenix AZ
316 AM MST Thu Apr 27 2017

Deepening low pressure over the Four Corners area on Friday will
bring windy conditions across Arizona including high fire danger.
There will be a chance of showers and possibly a thunderstorm
during the day Friday across the high terrain east of Phoenix.
Much cooler conditions will then move in behind the system on
Saturday, but high temperatures will quickly climb back well into
the 90s for next week.


Broad troughing remains a prominent feature across much of the
U.S. with a building Pacific ridge off the West Coast. As the
Pacific ridge amplifies through tonight, a strong upper level jet
max will dig southward along the western periphery of the trough
allowing for the intensification of the upper low as it pushes
southward into the Four Corners area late Friday. Before this
occurs, the Desert Southwest will remain under northwest flow
today with gradually falling heights aloft starting today. Today`s
highs will gain a couple degrees over Wednesday`s highs, but
cooler air will be heading our way starting Friday.

As the closed low digs south toward the area on Friday, surface
pressure will rapidly fall over New Mexico creating a strong west
to east pressure gradient. The main impacts on Friday will be the
windy conditions and the dangerous fire danger conditions
developing late in the afternoon across much of southern Arizona.
Strong mixing to above 700mb will likely result in wind gusts
reaching 40 mph across portions of south-central Arizona, but
more likely over eastern Arizona. Some blowing dust across the
lower deserts is likely, but much of it will remain fairly lofted.
As the cold front sweeps southward Friday afternoon and evening,
we should see some scattered showers and possibly a few
thunderstorms east of Phoenix, but limited moisture will keep most
areas dry. Very dry air will usher in behind the cold front Friday
afternoon allowing for surface dew points to crater, likely
bottoming out in the single digits early Friday evening. The
windy conditions and the very dry surface conditions will promote
high fire danger which has prompted widespread Red Flag Warnings
across southern Arizona Friday afternoon through the middle of
the evening.

The closed low will slowly progress southeastward through New
Mexico on Saturday leaving a breezy but cooler day for the area
on Saturday. The strong Pacific ridge off the West Coast will
begin sliding into our region on Saturday, but especially going
into next week. Models have finally come into better consensus
showing this ridge slowly sliding right through the Western U.S.
next week. The previous model runs showing another potential
trough digging into the Desert Southwest now have this trough much
farther to the northeast completely bypassing our region. This
will result in a warmer forecast for next week as highs will
climb into the middle 90s as early as Monday followed by some of
the warmest deserts likely reaching 100 degrees for the middle of
next week.


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

Once they develop (at or shortly after midnight), typical easterly
diurnal winds (in  the 7-10 kt range) are expected to persist
through midday on Thursday, then switch to westerly on Thursday
afternoon, with sustained winds rising into the 10-12 knot range
during the late afternoon/early evening hours.  Lighter westerly
winds to persist well into Thu night. SCT-BKN decks mainly aoa 25
kft to persist through the taf period.

Southeast California/Southwest Arizona Including KIPL and KBLH:

Westerly to northwesterly winds to persist through the taf period at
both SE CA taf sites, with speeds remaining mainly in the 7-10 kt
range. SCT to BKN decks primarily aoa 25 kft persist through the
TAF period as well

Aviation discussion not updated for amended TAFs.


Saturday through Wednesday:

A sharp cooling trend will settle into the region as a mostly dry
storm system sweeps through the Great Basin and down through the
Southwest Friday into Saturday. On Saturday, breezy conditions from
the north will persist over the western deserts and with minimum RH
values to stay mostly below 10 percent area-wide, we can expect
continued dangerous fire weather conditions out west during the
afternoon hours.

Dry and warmer conditions are expected Sunday into Monday

Less wind is expected today as compared to yesterday with speeds
mostly below 12 kts over the next 24 hours at both TAF sites. At
KIPL, light and variable winds will persist until about 20Z when
the winds will then shift to southeast. After sunset, near 02Z,
winds will shift back to the west-northwest. At KBLH, light and
variable winds will continue this morning before shifting to the
west early this afternoon near 20Z.  as high
pressure builds into the area from the west. By Monday high
temperatures over the deserts will climb into the mid 90s for the
most part with minimum RH values to stay mostly in the single
digits. Less wind is expected although we should see continued
afternoon and early evening breezes across much of the area,
favoring the west. Another weather system will push across the
region Tuesday/Wednesday, bringing breezy conditions back to the
area and a very very slight chance of rain on Wednesday to the
higher terrain of southern Gila county.


Spotter activation will not be needed through the middle of next


AZ...Red Flag Warning from 11 AM to 9 PM MST Friday for AZZ132.

     Red Flag Warning from 3 PM to 9 PM MST Friday for AZZ133.

     Red Flag Warning from 10 AM to 3 PM MST Friday for AZZ131.

CA...Red Flag Warning from 10 AM to 3 PM PDT Friday for CAZ231.



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