Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus65 kpsr 291603 

Area forecast discussion
National Weather Service Phoenix Arizona
903 am MST Mon may 29 2017

very typical Memorial Day Holiday weather will continue with
afternoon high temperatures climbing into the 90s and lower 100s.
Temperatures will peak today and Tuesday before some cooling
starts during the middle of the week. Scattered mountain storms
will also be possible, mostly for Tuesday and Wednesday.


upper level ridge axis will slowly move across Arizona today with
fairly weak flow aloft. We will further realize more warming
today as afternoon highs easily top 100 degrees across the lower
deserts with the warmest locations topping 105 degrees. The first
hints at a southeasterly semi-moist mid level flow can be seen
barely entering extreme southeastern Arizona from New Mexico. Both
the GFS and European show moisture values between 4-6g/kg
1000-700mb mixing ratios by this afternoon which may give rise to
a few high based thunderstorms, but generally east of Gila County.
A weak trough nearing the California coast this morning will
spread some high cirrus across the Desert Southwest through this
evening, but should have little to no impact on daytime high
temps. No updates to the current forecast are needed at this time.


Previous discussion...
a quiet weather pattern continues for the Desert Southwest with dry
westerly flow aloft. Regional height rises will continue into Monday
with models indicating 500 mb heights between 582 to 585dm. This will
translate into very warm temperatures 5 to 8 degrees above seasonal
normals. Memorial Day will have a moderate heat risk for much of the
area including Phoenix Metro, Yuma, and el centro.

Nevertheless, a trough currently located off the California coast
will begin to make its presence known with increasing clouds and
moisture into the area by late Monday evening. The chance for
elevated thunderstorms Monday evening is not substantial but the
threat is greater than zero. Model soundings indicate some
convective available potential energy (cape) over the highest
terrain features north and east of Phoenix while ncar ensemble
forecasts show isolated pockets of reflectivity over the Mogollon

Tuesday and Wednesday look to be the best days for elevated
thunderstorms. Increased southeasterly winds in the lowest half of
the atmosphere will draw additional moisture into the area. GFS and
NAM model soundings indicate a range of 200 to 600 j/kg of cape
over the higher terrain including the rim, White Mountains, and
the Pinal Mountains. Any thunderstorms that do develop will have
the potential for lightning strikes and producing outflow winds
that may pose fire weather concerns for ongoing fire suppression
operations and potential for new fires. Unfortunately,
precipitation amounts with any storms leaves much to be desired
with most model outputs indicating 0.01 of an inch or less of
rain. Additionally, the surface pressure gradient will tighten as
the trough progresses through California which will lead to breezy
conditions for Wednesday afternoon. Gusts 15-25 mph will be
possible, especially along the lower Colorado River area and over
the higher elevations in Gila County.

Otherwise, temperatures will drop to near seasonal normals for the
middle part of the week before gradually warming as 500 mb heights
recover. The gefs indicates 500 mb heights will return to the 582-586dm
range by the weekend. As such, the temperature forecast was weighted
more towards the upper half of the available guidance.


south-central Arizona including kphx, kiwa, and ksdl, and
southeast California/southwest Arizona including kipl and kblh:

Little to no aviation impacts through Tuesday morning with only
periodic cirrus cigs spreading into the region. Sfc winds will
remain light (under 15kt), though the daily wind shift around the
Phoenix terminals will likely occur about an hour later than the
past couple days.

Aviation discussion not updated for amended tafs.


Fire weather...
Wednesday through sunday:
with temperatures hovering not terribly far from the early June
average, the greatest fire weather threat will be isolated
thunderstorms with little to no measurable rainfall Wednesday over
parts of southern Gila County. Drier air will move back over the
districts starting Thursday ending the thunderstorm/lightning
threat. Winds will obtain the typical late afternoon breeziness
Wednesday and Thursday with somewhat lighter winds through the
weekend. Minimum humidity levels will fall to around 10% except in a
15-20% range over higher terrain of Gila County, as well as lower
elevations of southeast California. Overnight recovery will
generally be fair.


Spotter information statement...
spotter reports should not be needed this week.


Psr watches/warnings/advisories...


Visit US on facebook, twitter, and at weather.Gov/Phoenix

National Weather Service Glossary of Abbreviations