Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Phoenix Arizona
912 PM MST sun Jul 27 2014
a relatively active monsoon pattern will last through Monday as a
series of disturbances move northward through southern Arizona and
southeast California...increasing the threat for thunderstorms across the
region. Monsoon moisture will likely remain across the region
through the early part of this week...with a chance for afternoon
and evening showers and thunderstorms each day. Some reduction in
monsoon activity is possible by the middle of the week as westerly
flow aloft brings somewhat drier air into the region.
a rather complex weather picture exists across the region this
evening with two strong middle-level circulations affecting monsoon
activity. Water vapor imagery has shown one circulation moving
northward across the Baja California peninsula with little to no active storms
associated with the feature. The other more compact circulation
moved through Southeast Arizona and southwest New Mexico this
afternoon and continues to progress to the north northwest along the
Arizona/New Mexico state line. This feature prompted several
clusters of thunderstorms...but most have just clipped our far
eastern zones. In between these features...an area of subsidence has
suppressed any storm development across from the lower Colorado
River valley through much of south-central Arizona. Current radar
imagery shows another cluster of showers and thunderstorms tracking
north northwest across Southeast Arizona.
00z Phoenix radiosonde observation was not too promising to allow for storms to
propagate through much of the lower deserts...but the Tucson radiosonde observation
showed much more instability...especially in the middle levels. The
way the cluster of storms has been propagating over the past couple
hours...the cold pool doesn/T seem to be impressively strong...so
outflows are not overly robust and further storm development along
outflows has been limited. Expect these showers and storms to
continue northwestward into the eastern Phoenix area late this
evening with the possibility of some strong gusty winds. Have
dramatically trimmed probability of precipitation for late this evening and the overnight
period from Phoenix westward...but have kept at least slight chance
probability of precipitation areawide.
Decent moisture will remain in the area through Monday with
continued storm chances...but models indicate a drying westerly flow
will set up starting Tuesday. Tuesday may be a bit of a transition
day with storms mainly focused across higher terrain areas...but
can/T rule out a few storms across the lower deserts. Latest model
runs have definitely been trending toward a somewhat drier middle week
period with 1000-700mb mixing ratios dropping into the 6-8 g/kg
range and precipitable waters dropping to between 1.0 and 1.5 inches. At this
moment...it looks like any monsoon activity for Wednesday and
Thursday will likely be confined to far eastern Arizona. Models then
point toward a bit of moisture resurgence for Friday into next
Temperatures for the period should fall within a small temperature
range of right around seasonal normals. Some areas may approach the
110 degree mark for highs on Wednesday and Thursday as drier air
allows for a bump in temperatures.
south-central Arizona including kphx...kiwa...and ksdl...
showers and storms over the higher terrain east and southeast of
Phoenix is expected to propagate towards kphx-kiwa-ksdl through late
this evening. Storm outflows should switch winds to an easterly
direction between 05-07z...with a modest gusty wind potential. Some
isolated to scattered showers and storms should make their way into
the Phoenix area...but coverage should be limited enough to not
mention in kphx and ksdl tafs.
Southeast California and southwest Arizona including kipl and kblh...
mostly clear skies expected at least into the early overnight with a
relatively low thunderstorm chance starting late tonight into Monday
morning. Background winds will remain light through the period...but
a small chance of storm outflows and gusty winds are possible with
any storms that develop tonight into Monday.
Aviation discussion not updated for amended tafs.
Tuesday through Saturday...
near normal temperatures and higher relative humidity levels are
expected. Minimum relative humidity levels will range from 15 to 25
percent and recover overnight to 35 to 45 percent. There will be a
daily threat of afternoon and evening thunderstorms...but these will
be mainly confined to the higher terrain of south-central Arizona.
Winds will be generally less than 15 miles per hour...except in the vicinity of
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