Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Phoenix Arizona
855 am MST Sat may 27 2017
very typical Memorial Day Holiday weather will persist through the
weekend with afternoon high temperatures climbing into the 90s and
lower 100s. Temperatures will peak on Monday and Tuesday before
minor cooling starts beyond the middle of next week. Some scattered
mountain storms will also be possible by the middle of the week.
very typical weather for Arizona this morning as a dry westerly flow
aloft was in place across the area, easily seen in the morning plot
and raob data. Infrared imagery at 9 am showed sunny skies area wide. The
12z 500mb plot data depicted very little change in the height field
and as such we do not expect much change in the high temperatures
for today. Highs will remain slightly below seasonal normals and in
the mid to upper 90s across the central deserts. Phoenix should top
out a degree or so higher than yesterday and at about 97 degrees.
Otherwise we can expect sunny skies and relatively light winds for
the rest of today. Current forecasts look to be in fine shape and no
updates are needed.
lower than normal heights aloft persist this morning from southern
Canada into The Rockies as a trough axis shifts into the plains and
the overall pattern temporarily becomes progressive. Into early next
week, a split flow type of pattern will materialize over the western
conus as high amplitude ridging extends into western Canada while an
active subtropical jet undercuts this ridge into the southwest. The
initial influence of this ridge will be a rapidly warming of the
atmospheric column, however the introduction of subtropical waves
will allow moisture and clouds to restrict any additional warmth
while also creating an environment supportive of mountain storms
over eastern Arizona.
Low level thermal profiles will rebound beginning today as nearly
steady state 500 mb heights near 579dm this morning slowly increase to
near 585dm by Monday. Temperature guidance spreads are very narrow
through the weekend providing very good confidence 100f temperatures
will be breached Sunday followed by the warmest day of the week on
Monday. While certainly no where near record breaking, highs some 5f
above normal appear very likely Monday and a day typically filled
with more outdoor activities and sun/heat exposure.
Through at least the first half of next week, an active subtropical
jet will bring several lower amplitude disturbance into the
southwest domain. The details regarding depth/intensity and moisture
availability remain varied among operational and ensemble member
output. The 00z operational GFS remains on the more aggressive side
bringing lower heights and somewhat stronger forcing mechanisms
further south. Ensemble means more closely resemble the 00z European model (ecmwf)
and CMC though impacts on end result sensible weather forecasts are
minimal and limited.
Regardless, ahead of these series of waves, substantial backing of
winds in the h9-700 mb layer will occur through the Rio Grande Valley
and Four Corners. Almost all model output suggests notable moisture
advection up the Rio Grande Valley and juxtaposed with weakly forced
ascent associated with the shortwaves, isold/sct thunderstorms will
be possible along the rim, White Mountains, and portions of southern
Gila County. The largest uncertainty lies with the areal extent and
westward push of the best quality moisture plume. Initial look at
sref probabilities suggest good chances of storms, however
deterministic model quantitative precipitation forecast is quite underwhelming. This may be a case
of more elevated echoes and lightning versus accumulating rainfall.
The forecast for the latter half of next week still remains quite
uncertain with model spread growing in a partially blocked flow
pattern. The operational 00z GFS still remains a more aggressive
outlier though has backed off the most unlikely outcome of a deep
closed low. The 00z European model (ecmwf) and Gem continue to look far more
agreeable when compared to other medium range guidance keeping an
ill defined height weakness and troughing signature lingering
through the SW conus. Moisture will mostly be relegated to New
Mexico in persistent westerly flow (i.E. Little to no chance of
rain), though the general weak cyclonic flow pattern will favor
temperatures hovering close to climatology.
south-central Arizona including kphx, kiwa, and ksdl,
and southeast California/southwest Arizona including kipl and kblh:
Few aviation weather concerns for Saturday. The winds will remain
light at 5 to 10 knots and follow typical diurnal directional
shifts. Skies will remain clear with no other major concerns.
Aviation discussion not updated for amended tafs.
Monday through friday:
generally warm with mostly dry conditions for the period. However,
a weather system will bring a slight chance for isolated
thunderstorms Tuesday and Wednesday in the higher elevations to
the north and east of Phoenix. Rainfall amounts with any storms
looks minimal but a threat of dry lightning will exist for both
days. Outside of thunderstorms, the winds will be the breezy
Wednesday and Thursday with gusts up to 20-25 mph. Otherwise,
minimum relative humidities will bottom at 10 to 20 percent with
fair overnight recoveries.
Spotter information statement...
spotter reports will not be needed through the middle of next week.
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