Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 232152 CCA

Area Forecast Discussion
National Weather Service Phoenix AZ
250 PM MST Mon Oct 23 2017

Well above normal temperatures will persist Tuesday as strong high
pressure prevails across the western states. This high pressure
system will diminish in strength throughout the week resulting in a
gradual cooling trend, though temperatures will continue to remain
above normal. Dry conditions will also persist with no chance of
rain through the end of the month.


The afternoon WV satellite and objective analysis shows a highly
amplified and anomalous pattern locked over the Conus. Pronounced
troughing and several notable shortwaves combining in a negative
tilt fashion over the eastern half of the country will promote
intense cyclogenesis over the Great Lakes. Meanwhile, upstream east
Pacific ridging will translate into near record temperatures over
the southwest and renewed Santa Ana concerns along coastal
California. 12Z regional sounding data sampled widespread 594dm H5
heights and H7 temperatures in a +12C to +14C range. Both measures
are records for the date at all regional sites (TWC, FGZ, and VEF),
and in some cases are flirting with all-time records for the month
of October.

Influenced by the deepening and highly anomalous eastern Conus
trough, ridging through the southwest will begin to retrograde into
northern California and northeast Pacific effectively dampening
heights/temperatures aloft. However despite the weak cold advection
through central Arizona, a deep easterly fetch will be translated
into a compressional downslope component. These opposing features
should partially offset each other resulting in readings Tuesday
afternoon not terribly far from today. Otherwise, gusty ridge top
LLJ winds will eventually mix to the surface in central AZ though
speeds should be reserved enough to prevent much blowing dust or
other detrimental impacts.

A discernible cooling trend will commence Wednesday as the
aforementioned ridge weakens and retrogrades further; and a
shortwave drops south through the Rockies and fills into the western
periphery of the larger eastern trough. Trends in the operational
GFS continue to indicate the trough will only have a glancing blow
on the region with temperatures remaining well above average into
the weekend despite the passage of a backdoor cold front. ECMWF
trends still wish to dig somewhat lower heights further west versus
other models while bringing a stronger frontal push into the region.
Ensemble members decidedly agree with the GFS trends and have
maintained temperatures for the latter half of the week only some 5F
cooler than current.

Operational models and corresponding ensembles generally remain in
good agreement that another amplified ridge will build across the
intermountain West in the wake of the trough repositioning back
east of the Rockies. This will generate renewed dry northerly flow
and a continuation of the above normal temperatures into next week.
PoPs remain at 0 percent through next week and October will almost
certainly finish with 0.00 inches of precipitation at Sky Harbor
Airport. Although this is obviously well below normal, it is not
unprecedented (has occurred 10 times in the past 122 years, as well
as another 15 instances of only a trace of rain in October). The
last time a trace of precipitation was recorded was only 4 years
ago; however, it hasn`t been since 1999 that October was completely
rain free.


South-Central Arizona including KPHX, KIWA, and KSDL:
West winds will continue for the terminals into the early evening
before becoming calm/variable. Typical switch to easterly will occur
for most of the terminals with elevated northeasterly winds picking
up just off the surface near sunrise. KPHX may be presented with a
period of calm or southwest light winds at the sfc with 15-20kt NE
winds above 1500ft. Conditions may develop into localized LLWS for a
few hours into the AM, but confidence is not high enough for this to
develop to include mention of it in the TAFs. Clear skies will

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will follow typical diurnal headings - between west and
northwesterly for KIPL and northerly for KBLH for the TAF period.
Elevated speeds are likely for KBLH with some gusts into the teens
at times. Clear skies will prevail.

Aviation discussion not updated for amended TAFs.



Thursday through Monday:

Somewhat cooler temperatures will descend into the districts for the
second half of the week though readings will still remain several
degrees above average. The airmass will remain very dry ensuring
clear skies and no chance of rain. This will also lead to afternoon
minimum humidity levels falling into a 10-15% range following only
fair overnight recovery. After some gusty winds Wednesday, wind
speeds should not pose any threat towards enhanced fire behavior the
remainder of the week.


PHOENIX    NormalRecord
Mon Oct 2386100 in 2003
Tue Oct 248596 in 2014
Wed Oct 25      85          96 in 2014

YUMA     NormalRecord
Mon Oct 23      87          102 in 1959
Tue Oct 24      87          105 in 1959
Wed Oct 25      87          100 in 1959


Spotters should follow standard reporting procedures.





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