Scientific Forecaster Discussion
fxus65 kpsr 232050
Area forecast discussion
National Weather Service Phoenix Arizona
150 PM MST Tue may 23 2017
high pressure moving across the region will bring one more day of
well-above normal temperatures on Wednesday, with high temperatures
once again rising well above 100 degrees at many Lower Desert
locations. Cooler temperatures will return by the latter portion of
the week and into the upcoming weekend as low pressure once again
moves into, and across the western US.
Tonight through Wednesday...
Strong ridging over the Desert Southwest, that is bringing some very
warm temperatures to the region today, is expected to begin to shift
slowly to the east on Wednesday as long-wave trofing begins to dig
back southward into the western US. Current 500mb heights in the 586-
588dm are expected to begin to slowly fall on Wednesday. However,
increasing low-level southerly flow is expected to keep temperatures
elevated through the lower levels of the atmosphere through
Wednesday afternoon. Current numerical model output is indicating
that most Lower Desert locations will see highs once again rising
into the 105-110 degree range on Wednesday (hottest in the lower
Colorado River valley). However, it still looks like heatrisk levels
will be slightly lower than what we are seeing today, mainly due to
somewhat lower dewpoints. However, the usual precautions should
still be taken if outdoor activity is planned during the daylight
Thursday through next Tuesday...
Overnight Wednesday into Thursday, ridge heights will be flattened
as strong Pacific low pressure moves into the pac northwest. Trough
heights will continue to trail southward through the
intermountain west, introducing height falls as early as Wednesday
but most noticeably late Wednesday into Thursday on the order of
3 to 5 dam. High pressure ridge will move to our east drawing a
local enhancement of the sub-tropical jet across Southern California and
into the southwest late Wednesday into Thursday. Forecast 250mb
jet winds Sample 80-90kts with surface winds forecasts nudging
into the 90th to 95th percentile gefs reforecast ranges. Advisory
conditions may develop as early as Wednesday, but look likely for
Thursday over the peninsular ranges between San Diego and el
centro with gusts of 45 mph or greater possible. Ridgetop winds
will eventually mix and expand down into the lower elevations
during the day Thursday with gusts for the western deserts ranging
30 to 35 mph. Gusts across southwest and south-central Arizona
could range 20 to 30 mph. Visibility and air quality impacts are
anticipated in the dust/sand prone areas, especially across
southeast California. Elevated winds and dry advection into the
region could also add localized fire weather concerns to the mix
for Thursday. With all the wind and height falls transitioning
into the area, high temperatures cool into the upper 90s to near
100 for Thursday and fall further for the end of the work week.
Temperatures look likely to stay below triple digit readings
through the weekend as longwave troughing holds over the region,
keeping elevated thicknesses and warmth removed from the area. A
gradual warming trend will begin Sunday and into early next week
and Pacific ridging returns warmth to the area from the west.
south-central Arizona including kphx, kiwa, and ksdl, and southeast
California/southwest Arizona including kipl and kblh:
Mostly clear skies and light winds following typical diurnal wind
patterns can be expected through Wednesday morning. Somewhat
stronger westerly winds can then be expected on Wednesday afternoon
as low pressure dropping into the western US begins to increase
winds aloft. No significant aviation concerns through the taf period.
Aviation discussion not updated for amended tafs.
Friday through tuesday: breezy southwesterly winds, with sustained
speeds ranging from 10-20 mph, can be expected area-wide on Friday.
A few gusts to 30 mph will also be possible. Temperatures will be
slightly below-normal as highs only reach the low 90s, but dry
conditions will still result in minimum relative humidity values of 10-15 percent.
As a result, at least low-end elevated fire weather conditions look
High pressure will build over the Great Basin this weekend into
early next week, and will result in weakening winds and warmer
temperatures. High temperatures of 100-105 are forecast across the
lower deserts on Monday and Tuesday. A weak low pressure system
may also develop off the Southern California coast early next
week, and advect modest amounts of moisture into eastern Arizona.
Will have to monitor for the potential for isolated thunderstorms
across the higher terrain of southern Gila County on Tuesday
afternoon, but at this point lightning potential appears low.
Spotter information statement...
spotter reports should not be needed.
Arizona...excessive heat warning until 8 PM MST this evening for azz532-
California...excessive heat warning until 8 PM PDT this evening for caz566-