Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 252343

Area Forecast Discussion
National Weather Service Phoenix AZ
443 PM MST Tue Jun 25 2019

.UPDATE...Updated aviation forecast discussion.


High pressure will continue to gradually build across the Desert
Southwest this week resulting in steadily warming temperatures, and
slightly above normal readings returning by the end of the week. Dry
weather will also continue along with occasionally breezy
conditions, but signs of rainfall in the immediate future.


Subtropical ridging remains supplanted well into Mexico this
afternoon as pronounced troughing and deep negative height anomalies
are positioned off the Pacific NW coast. Within the extension of the
west coast trough, a weak PV anomaly and jet streak were supporting
a slug of upper level moisture streaming into the region. Otherwise,
better quality boundary layer moisture is far removed from the
region with deep convection even lacking through northern and
central Mexico.

For the remainder of the week, a more amplified Conus pattern will
develop in response to approaching western trough and downstream
Atlantic blocking. Strong positive height anomalies will build into
the southern and central plains with a nearly stationary ridge axis
extending back into SE Arizona. H5 heights will steadily increase
through the weekend peaking somewhere in a 591-594dm range. Guidance
output range is very narrow yielding excellent confidence
temperatures will languish near average heading into the weekend,
then only potentially edge slightly above average during the
weekend. There is a notable wildcard during the weekend as the
operational GFS suggests extensive mid and upper tropospheric
moisture flowing into the region (likely blow off from an East
Pacific tropical disturbance). Should this come to fruition, the
diurnal range may be narrowed in spite of warming temperatures
aloft. Regardless, the orientation of the ridge axis ensure dry SW
flow within the boundary layer and higher theta-e air trapped along
the New Mexico border (and even limited moisture into Sonora).

By the middle of next week, the operational GFS shifts the
subtropical high a little further to the northwest across the Desert
Southwest with some semblance of inverted troughing over Texas.
There are indications in this model of boundary layer moisture and
total column PWAT increases, especially for SE AZ; though closer to
south-central AZ, forecast soundings indicate little more than
meager 7 g/kg mixing ratios. However, this operational member is
largely an outlier as compared to the majority of NAEFS members and
recent operational ECMWF iterations where the H5 high center drifts
back towards Sonora. The most likely outcome points towards
persistence of dry westerly flow across the majority, if not
entirety CWA with only a marginally better setup for deep convection
over the White Mountains and far SE Arizona. Eventually, outflows
and moisture seeps will foster better 8-10 g/kg boundary layer
mixing ratios, but the convergence of evidence points towards this
not happening until the end of next week at the earliest.


.AVIATION...Updated at 2345 UTC.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
There are no major aviation weather concerns. For tonight, winds
will follow typical diurnal directional patterns becoming lighter
after sunset and easterly overnight. Expect a similar diurnal
pattern tomorrow although there may be a few hours of southerly
breezes with some gusts (most likely below 20 kts) between 18Z-22Z
before becoming westerly in the afternoon. Smoke from nearby
wildfires east of Phoenix are not likely to create any slantwise
visibility issues.

Southeast California/Southwest Arizona including KIPL and KBLH:
There are no major aviation weather concerns. The winds will
follow typical diurnal trends at KIPL with some evening breezes.
Southerly winds with some breezes will continue into tonight for
KBLH and other terminals along the Colorado River.

Aviation Discussion not updated for amended TAFs.


Friday through Tuesday:
Seasonably warm and dry weather will persist over all the districts
through the beginning of next week. Ridge top and gap winds will
occasionally be breezy during the afternoon hours with SW gusts
around 25 mph common. Minimum relative humidity values will mostly
fall into a 10-15% range with generally poor (locally fair)
overnight recovery. The winds and humidity combined with very dry
fuels will frequently result in elevated fire weather conditions
during this period.


Spotter activation is not expected.




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