Scientific Forecaster Discussion
fxus65 kpsr 252240
Area forecast discussion
National Weather Service Phoenix Arizona
340 PM MST Tue Jul 25 2017
drier air moving into the region will result in a much lower
chance of storms for much of the work week a slight chance of
storms lingering for today. Decreasing cloudiness and moisture
will support a warming trend through Thursday with near normal
highs. An increase in moisture beginning Thursday will usher in a
increased chance of storms from west to east from Thursday night
through the weekend. Similarly, high temperatures decrease as
well...most noticeably over south- central Arizona.
after starting out today with dewpoints in the low to mid 70s and
maxrh values reaching the mid 60s to near 80 percent range across
much of the region, a drying trend is now underway with dewpoints
having already dropped 12 to 15 degrees since this morning.
Current radar is painting some very isolated and relatively small
showers and thunderstorms from the greater Phoenix valley to S.
Gila County moving northeast. Satellite shows cumulus and cumulonimbus cloud
fields over these same areas as well as La Paz County and southeast
California. Storm motion towards the northeast, as well as the VAD
wind profile from kiwa radar showing west-southwest to SW flow from the
surface and boundary layer up to near 10kft, indicate the drying
trend is now well underway (in spite of the semi-continuous
boundary layer Gulf of California seepage indicated by models
through much of this week). So today is still expected to remain
a "low grade" monsoon day. Operational models and ensembles are
in good agreement on the drying and increased stability through
early Thursday with almost no cape expected after this evening.
Later this week the south side of the high pressure system to our
east will begin to yield to several inverted troughs and
disturbances along with a return of increased moisture advection
from the south and southeast, putting an end to the drying trend
by sometime Thursday. The resulting increase in precipitable water and mixing
ratios will initially increase pops, first in the east, and then
gradually to the west beginning Friday afternoon and evening and
into the weekend. Then continued moisture advection through the
weekend will support the return of significant unstable
conditions in the lower deserts beginning Saturday and the return
of monsoon storms chances. The increased monsoon moisture this
weekend will also be accompanied by below normal high temps
south-central Arizona including kphx, kiwa, and ksdl:
scattered cumulus clouds have developed this afternoon as low-
level moisture remains rich, but a general drying trend is
occurring with winds aloft exhibiting a stronger westerly
component. Scattered showers and a few thunderstorms have
developed mainly east of the Phoenix area. Cannot rule out one or
two short-lived showers developing over parts of the Phoenix area,
but most should remain over the higher terrain. Otherwise, winds
are expected to be light and diurnal in nature through tomorrow
afternoon, with periods of mid-level clouds and diurnal cumulus
Southeast California/southwest Arizona including kipl and kblh:
The only potential weather concern will be thunderstorms
developing northward across far western Imperial County, and any
associated eastward-moving outflows across the Imperial Valley.
While kipl is not expected to be affected by precipitation, low
confidence in areas of blowing dust exists this afternoon which
could affect visibilities. Otherwise, quiet conditions with
periods of mid-high level clouds.
Aviation discussion not updated for amended tafs.
Friday through tuesday:
humidities and storm chances begin to increase into this weekend
with chances reaching southeast California by Saturday.
Temperatures will decrease to near to slightly below normal late
this week. Apart from thunderstorms, winds will follow familiar
warm season patterns.
Spotter information statement...
spotters should follow Standard reporting procedures.
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