Scientific Forecaster Discussion
fxus65 kpsr 090006
Area forecast discussion
National Weather Service Phoenix Arizona
506 PM MST sun Dec 8 2019
updated 00z aviation discussion.
abundant moisture will continue to bring cloudy skies with
isolated showers across the lower deserts this afternoon.
Additional isolated to scattered showers are possible again Monday
morning and afternoon. Afterwards, drier conditions with near to
slightly above normal temperatures are then expected for the rest
of the week.
water vapor imagery shows an upper level low centered over
California with a strong subtropical jet that continues to funnel
abundant moisture into the southwest. Thick overcast clouds and
generally moist conditions will keep temperatures cooler than
normal with highs struggling to reach the mid 60s. Shower
activity on radar has quieted somewhat over the last hour with
just a few weak showers in the forecast area.
For this afternoon and evening, several models indicate showers
redeveloping along the higher terrain north and east of Phoenix
and south of the valley over Pinal County. The Phoenix area may
see some isolated activity but the areal extent of rainfall will
be less compared to yesterday. During the overnight and into
Monday afternoon, convectively enhanced showers are possible as
instability increases when the cold core of the low moves
overhead. These showers may produce locally heavy downpours and
some locations may see a few more tenths of additional rainfall.
While thunderstorms are not anticipated, there may be enough
instability to support an isolated cell or two capable of
producing small hail on Monday afternoon. Farther west, tightening
of the pressure gradient will create breezy conditions across
southeast California and along the lower Colorado River. By Monday
night, the low will be southeast of the forecast area and our
conditions will begin to dry.
A dry disturbance will pass to our north keeping atmospheric
heights suppressed through midweek. As such, daytime temperatures
will remain near seasonal normal values before a ridging takes
hold later in the week allowing the 70s to return.
Aviation...updated at 0006z.
South-central Arizona including kphx, kiwa, ksdl, and kdvt:
Light shower activity will generally remain east of the terminals
through the evening hours as scattered-broken ceilings lift above 6 kft
with an overcast deck around 10 kft. Isolated to scattered
showers should return overnight after 09z with broken-overcast ceilings
lowering to 4-6 kft. MVFR ceilings and visibilities will be
possible with any heavier showers or patchy fog, particularly at
kiwa. Ceilings will gradually lift tomorrow morning as we
experience another lull in shower activity after 13-14z until
another round of isolated convection occurs with a weak front
early Monday afternoon. Very isolated thunderstorms will also be
possible due to elevated instability associated with the cold core
low aloft, but confidence is too low to include those chances in
the tafs at this time. Winds will generally be light and variable
before becoming westerly at 5-10 knots behind the front early
Monday afternoon before becoming easterly Monday evening.
Southeast California/southwest Arizona including kipl and kblh:
VFR conditions should generally prevail through the taf period as
midlevel cloud decks lift and clear out behind a weak cold front
that will push through the region overnight into Monday morning.
Light and variable winds across the region will gradually become
westerly this evening, with downsloping westerly 10-15 knot winds
expected at kipl tonight. Isolated showers are expected to develop
overnight along the front as it pushes into the Colorado River
valley and southwest Arizona, with the best chances between
09-12z at kblh. Skies should gradually clear behind the front on
Monday morning, with northwest winds gusting to 20-25 knots
expected at kblh with weaker winds expected at kipl.
Tuesday through saturday:
dry conditions will prevail under high pressure aloft. Minimum
humidity levels initially will be around 30-40% early in the
period, but will fall to 25-30% beginning Thursday. Overnight
recovery will still be good to excellent. Winds through the entire
period with be fairly light with little to no breeziness.
Spotter information statement...
spotters should follow Standard reporting procedures.
Arizona...Flash Flood Watch through Tuesday afternoon for azz556.