Scientific Forecaster Discussion
fxus65 kpsr 142330
Area forecast discussion
National Weather Service Phoenix Arizona
430 PM MST Thu Nov 14 2019
Update...updated aviation discussion.
warm and dry conditions will continue through the coming weekend
and into early next week. A strong storm system is poised to
affect the region late Tuesday through Thursday, bringing
increasing chances for rain and cooler temperatures.
a relatively quiet day weather-wise across the southwest as
shortwave ridging remains parked over the eastern Great Basin
southward towards the Gulf of California. Scattered upper-level
cloudiness is spreading eastward from the Pacific across Southern
California. Temperatures are running several degrees above normal
this afternoon, and are expected to top out in the lower 80s. A
shortwave trough approaching the Pacific coast is associated with
an extensive area of cloudiness on satellite. This feature will
become significant later next week as the large-scale pattern
undergoes a change.
Meanwhile, little day-to-day change of weather conditions can be
expected through Tuesday, with high temperatures topping out in
the lower 80s each day - roughly 6-10 degrees above normal. During
this period, the aforementioned shortwave trough will evolve into
a prominent closed upper low off the coast of northern Baja
California, and remain nearly stationary from Sunday through
Tuesday as upper ridging rebuilds over the western Continental U.S.. as this
occurs, an elongated period of south/southeasterly flow to the
east of the closed low will tap into moisture deep in the tropics
over the eastern Pacific.
More substantial changes to the large-scale pattern occur by
Tuesday as a cold upper trough evolves over the Pacific northwest.
This trough will interact and eventually phase with the southern-
stream closed low off of baja while digging southward, and bring
an increasing amount of moisture from the south-southwest into
southeast California and Arizona. Precipitation chances will
likely increase beginning Tuesday night and especially on
Wednesday as the closed low quickly evolves into a lead open wave
ahead of the primary trough. Still some uncertainty in the exact
evolution of the upper trough and associated cold-core low, but
the general track will be across Arizona Thursday into Friday, and
bring much cooler temperatures. Ensemble forecasts, including the
gefs and eps, have generally trended higher with quantitative precipitation forecast amounts. In
particular, the eps now has an ensemble-mean quantitative precipitation forecast value near 1.6
inches, while the gefs just remains shy of 1 inch for Phoenix.
Have adjusted quantitative precipitation forecast upward slightly from the nbm mean, with around 1
inch of quantitative precipitation forecast officially forecast for the Phoenix area. As is
typical, higher amounts are likely north and east of Phoenix. Much
less rain is currently forecast across southwest Arizona and
southeast California, with only one-quarter of an inch or less
generally expected. There is the possibility of some convection
as well on Thursday as the strongest forcing for ascent
accompanying the trough spreads eastward across south-central Arizona.
At this time, it appears this will be more of a long-duration
event with periods of light to moderate rain, although brief
periods of heavy rain are still not out of the question across
south-central Arizona. However, will still have to monitor trends
in case a heavier rain scenario becomes more apparent, given the
climatologically high amount of moisture and some eps/gefs members
showing more than 2 inches of rainfall for Phoenix. High
temperatures in the 60s are also probable by Thursday.
Aviation...updated at 2300z.
South-central Arizona including kphx, kiwa, ksdl, and kdvt:
Nearly calm winds will shift to easterly from 03-05z. Easterly
flow is expected to strengthen Friday morning but should remain
below 15 knots. The wind speed will weaken by mid afternoon and may
go calm for a few hours, but at this time is not expected to go
westerly. High clouds will continue to move through the region
with generally scattered coverage near 25k feet.
Southeast California/southwest Arizona including kipl and kblh:
Very light winds can be expected today and tonight, generally 5 kt
or less at both kipl and kblh. Skies will be partly cloudy with
Sunday through thursday:
conditions will remain dry and warm on Sunday and into early next
week. Outside of some enhanced winds Sunday, no significant winds
or changes in humidity levels are expected. Changes are expected
to begin Tuesday, with humidity levels creeping up as temperatures
gradually dip. Chances for wetting rains east of the lower
Colorado River will increase significantly Wednesday and Thursday,
with much higher humidities and cooler temperatures forecast.
Spotter information statement...
spotters should follow Standard reporting procedures.