Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 131732

Area Forecast Discussion
National Weather Service Phoenix AZ
1032 AM MST Sun Oct 13 2019

.UPDATE...Updated aviation discussion.


A generally quiet and dry weather pattern will persist across the
region through the coming week. Temperatures will remain near to
slightly above normal for most of the coming week with highs
mostly in the upper 80s to lower 90s across the lower deserts.


Clear skies under weak ridging aloft still resides across the
Desert Southwest, but a weak trough approaching from the northwest
is forecast to move through on Monday. Additionally, a tropical
wave near the southern tip of the Baja will shift farther
northeastward today, but will still ultimately dissipate well
south of Arizona as it moves inland across northern Mexico.
However, the last few model runs have been gradually increasing
the amount of low level moisture advecting northward into the
Lower Colorado River Valley late tonight and eventually through
the rest of southern Arizona on Monday. The moisture advection
will also coincide with weak lift out ahead of the advancing
shortwave trough bringing the possibility of some light showers or
sprinkles to mainly southwest Arizona Monday morning. By Monday
afternoon, the weakening shortwave may bring a few isolated
showers to the central and eastern Arizona high terrain, but
chances for measurable rain look to be quite low.

High and low temperatures today through Tuesday will be near
steady state and right around seasonal normals. The increase in
low level moisture early this week should be noticeable as RHs
increase roughly 10-20%. Heights aloft will rebuild across the
region Tuesday into Wednesday out ahead of another weak Pacific
trough, this one approaching from the southwest. The increased
heights should allow temperatures to warm into Wednesday with
highs possibly approaching 95 degrees across the deserts, but
increasing high cirrus out ahead of the approaching trough may
hold back temperatures slightly. This second trough also looks to
be in a weakening stage as it passes through our region on
Thursday while moisture levels do not look all that sufficient to
support rain chances. Only a few ensemble members have any QPF
across our area on Thursday, so at this point rain chances look
quite low. This trough should at least bring slightly cooler air
into the region late this week with highs dropping back to around
90 degrees by Friday.

Higher model spread and greater forecast uncertainty is seen into
the weekend as the overall model consensus shows a deeper Pacific
trough moving into the Northwestern U.S., possibly as far south
as our region late in the weekend. Compared to yesterday`s model
runs, the system has trended farther to the northeast. This shift
in the track would keep Arizona dry, but it should continue the
cooling trend.


.AVIATION...Updated at 1105Z

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

Dry southwest flow aloft will keep skies generally clear at the TAF
sites for the next 24 hours. Winds will be on the light side, mostly
6kt or below, weakly favoring typical diurnal tendencies. Some
increase in mid-level cumulus is possible Monday morning and
afternoon, with bases expected to remain above 6k ft with only
FEW-SCT coverage expected. No aviation concerns expected for the
next 24 hours at least.

Southeast California/Southwest Arizona including KIPL and KBLH:

Dry southwest flow aloft will keep skies clear at the terminals for
the next 24 hours. Winds will increase from the south at around 10
kt this afternoon at KBLH into the early evening, before becoming
light and variable overnight. An increase in low-level clouds is
possible overnight into Monday morning, especially at KBLH, as
moisture moves north through the lower Colorado River Valley. Have
introduced SCT coverage at FL040 for KBLH after 13Z. Will have to
monitor for potentially thicker cloud coverage during this period.

Aviation Discussion not updated for amended TAFs.


Tuesday through Saturday:
A quiet and dry weather pattern with slightly above normal high
temperatures will prevail during most of the period. Min RH values
should range in the 11-20 percent range. Expect mainly light to
occasionally moderate diurnally driven winds through Friday with a
chance of breezy to very breezy northwesterly winds moving in across
the region Saturday afternoon. Mainly fair overnight recoveries will
gradually improve to mostly good by Friday night.


Spotters should follow standard reporting procedures.




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