Area Forecast Discussion
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FXUS65 KPSR 281046
Area Forecast Discussion
National Weather Service Phoenix AZ
346 AM MST TUE JUN 28 2016
High pressure will move somewhat north and east of Arizona this week
allowing warm temperatures to prevail, but also bring a couple of
weather disturbances through the state. An increase in monsoon
moisture will accompany these weather systems providing a threat of
afternoon and evening showers and thunderstorms the remainder of
Numerous circulations and a few outflows are present on this AM`s
IR/WV imagery, fairly typical this time of year between inverted wave
advection, remnant convective meso-lows and gravity waves. Lingering
light shower activity has exited the forecast area to the northwest,
heading into Mohave and Yavapai Counties this early AM. Widely
isolated showers are still drifting westward on Tucson`s radar near
a localized meso-low and along the northwestern flank and deformation
zone of a larger inverted wave over Chihuahua and Sonora sampled
best at the 500mb level. Vertically speaking, the anticyclonic
circulation placement throughout the significant levels (i.e. 700mb,
500mb, 300mb) is really all over the map, with the 700mb circ east of
the Rockies, 500mb over the Great Basin and the UL centers well to
our south over Mexico.
The upper difluence observed last evening over N AZ doesn`t appear
to be as great tonight however advection of favorable ML lapse rates
down along portions of the Rim are part of today`s set-up. Several
Hi-Res models develop storms over the Rim again today with several
solns pointing to a more organized outflow intrusion from the
northeast around or post 29/00z (5 pm local) into Phoenix. While
always a concern during the Monsoon, northeasterly outflows into
Phoenix aren`t typical dust producers. What could lead to blowing
dust later into the evening would be the propagation of storm
activity along intersecting outflows surviving into the lower desert
elevations. PoP chances go as far west as the Colorado River Valley
and Southwest AZ Deserts, with drier conditions in terms of PoPs but
not much by way of humidities for the western forecast zones. Broader
anticyclonic flow and a drier atmospheric column will support much
warmer-than-normal temperatures for portions of southeast CA,
especially for the Imperial Valley today and Wednesday. Conditions
look to just escape Excessive Heat Warning criteria today, but may
develop for Wednesday. It`s tricky this time of year to gauge if
long-traveling outflows or MCVs could import moisture or cloud cover
to limit the diurnal curve, so will hold off as upstream moisture and
convective activity today over AZ could work in SE CA`s favor for
Increasing Monsoon moisture levels and persistent inverted wave
breaking through the 700-500mb level will introduce deeper moisture
and additional dynamics to promote better chances for showers and
storms over the lower AZ deserts each day through the end of the work
week. Peak of the moisture and wave activity looks to be Thursday
into Friday, with significant enough cloud cover and potential for
rain-cooled air to cool forecast highs Friday across the south-
central AZ deserts into the upper 90s to low 100s. Gridded sky cover
guidance and several moisture fields (mixing ratio, humidities,
dewpoints) indicate a tight gradient lying in the vicinity of the CO
River Valley. While debris clouds are possible, increasing
southwesterly flow may prevent significant cloud cover development
west of the River and keep temperatures near normals through the end
of the week.
Beginning Saturday, low pressure will take shape over the Pac NW,
shifting the 500mb circulation further to our east/southeast and
allowing for stronger southwesterly steering flow to transition
through the area. Dry air advection from the Pacific results,
relegating the slight chances for the precip to the eastern AZ
mountains and out of the lower desert elevations. Under clearing
skies temperatures will see a warm-up, compared to those observed at
the end of the work week, and return to normal and seasonable values
by the Fourth of the July holiday.
South-Central Arizona including KPHX, KIWA, and KSDL:
Lower confidence forecast as several competing outflow boundaries
will create frequent wind shifts through the evening, before
settling on a predominant easterly direction overnight. There is a
fairly low chance of blowing dust making it into the Phoenix
terminals and lesser chance of actual storms impacting the terminal
sites. Easterly sfc winds should prevail much longer into the late
afternoon Tuesday than is typical.
Southeast California/Southwest Arizona including KIPL and KBLH:
Wind shifts will be the main forecast challenge in SE CA through
tonight as outflow boundaries move into the region from AZ. Brief
gusts will be possible at KBLH, but likely minimal impact at KIPL.
Periods of variability in sfc winds will be likely overnight, then
favor a southerly component Tuesday afternoon. Periodic cloud decks
12K-15K ft will be common across the region.
Aviation discussion not updated for amended TAFs.
Thursday through Monday...
Temperatures will continue to cool with highs in the 100-110F range
by Sunday. Monsoon moisture levels continue to increase over the
region with slight chances for isolated afternoon thunderstorms. The
best chances for convective weather remains over the mountains in
central and eastern Arizona. Any storms that develop have the
ability to produce lightning, gusty winds, and wetting rains.
Daytime relative humidities will drop to 15-25 percent but will have
nighttime recoveries. Otherwise, winds will be relatively normal in
the 5 to 15 mph outside of any storm influenced winds.
.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected.
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