Scientific Forecaster Discussion
fxus65 kpsr 202354
Area forecast discussion
National Weather Service Phoenix Arizona
454 PM MST sun Oct 20 2019
updated 00z aviation discussion.
dry and generally sunny conditions will persist across the Desert
Southwest through the week. High pressure will build across the
intermountain west early this week, resulting in a warming trend.
Temperatures will peak midweek with highs in the lower 90s across
the lower deserts. A return to below normal temperatures is possible
late in the week as a low pressure system drops southward through
a well-defined short-wave trough is evident on water vapor imagery
across The Rockies with the tail end of the system extending
back towards The Four Corners. Behind this trough, temperatures and
dewpoints across the region have been running a few degrees lower
than they were yesterday. Earlier this morning, the minimum
temperature at Sky Harbor Airport reached 58 degrees, which is the
coolest reading since may 23th. Low-level northerly flow has also
been funneled down the Colorado River valley in response to the
surface high across the Great Basin. Peak gusts reached 30-35
mph earlier today generally north of Blythe, California. Latest href
indicates winds will continue to subside as the pressure gradient
weakens through late afternoon.
A ridge in the eastern Pacific will build eastward early this week.
Subsequent increase in low-level thicknesses will yield some warming
Monday, but the more noticeable jump in temperatures will occur
Tuesday. Latest guidance indicates that high temperatures in the
lower deserts will peak in the lower 90s Tuesday/Wednesday and remain
well below daily records.
Uncertainty still remains quite high beginning Thursday. Models
are in good agreement the flow will amplify across the intermountain
west, with the ridge across the eastern Pacific and a
longwave trough situated across the central Continental U.S.. along the
interface of these two systems, a strong jet stream will develop, but
its positioning and evolution remain difficult to pin down. This
could mean the difference between a return to near normal
temperatures or much cooler conditions in the wake of a developing
shortwave trough to our east. Given the high variability in both the
gefs and European model (ecmwf) eps, the forecast has again been weighted heavily
towards National blend, which captures the cool down behind the
trough Friday. Regardless of what scenario materializes, conditions
will remain seasonably dry with no chance of precipitation.
Aviation...updated at 2354z
South-central Arizona including kphx, kiwa, ksdl, and kdvt; and
southeast California/southwest Arizona including kipl and kblh:
Minimal aviation concerns are expected through the taf period as
clear skies and light winds will prevail once brief 15-20 knot
gusts end by 02z at kblh and isolated Phoenix terminals. Westerly
winds at the Phoenix terminals will become northerly or light and
variable by 03-04z with the strongest northerly winds at kdvt.
Winds should become easterly or light and variable by sunrise
before switching to westerly around 19-20z at the Phoenix
terminals. Winds will generally stay out of the north-northwest across
southeast California and Southeast Arizona aside from downsloping
westerlies at kipl later this evening through late Monday morning.
Aviation discussion not updated for amended tafs.
Wednesday through sunday:
above normal temperatures are expected Wednesday, followed by a late
week cooling trend as an area of low pressure moves through the
southern rockies. No rain is expected with this system, though
breezy/windy conditions will be possible Thursday/Friday. Forecast
uncertainty remains quite high through the weekend.
Spotter information statement...
spotters should follow Standard reporting procedures.