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Area forecast discussion 
National Weather Service Phoenix Arizona
835 am MST Sat Apr 18 2015

mostly clear skies and warming temperatures are expected today
through the remainder of the weekend. High temperatures in the lower
deserts will climb back above 90 by this afternoon. Look for dry and
warm weather to persist into the middle of next week. Big changes
are possible Wednesday into an approaching storm system
brings cooler temperatures and a slight chance of showers into the


Discussion... 12z plot data as well as vapor imagery showed the
sluggish upper level low pressure system finally starting to shift
off towards the east...with the main low center moving across south
central Colorado at 8 am. Middle level moisture as well as vorticity spokes
continued to rotate around the back side of the low resulting in
periods of clouds moving across southern Gila County over the past 24
hours. Current infrared imagery showed an area of thick middle cloud drifting
across areas east of Globe...with flat out clear skies from Phoenix
westward. No issues expected for the rest of the the low
will keep moving east and dry northwest flow aloft will keep skies
sunny over the lower deserts. Any threat for precipitation will stay to the
east of zone skies become mostly sunny over southern Gila County
by this afternoon. At 8 am temperatures over the central deserts were
running 2-9 degrees warmer than 24 hours ago...and as the airmass
continues to modify and warm in the boundary layer...high temperatures
today will corresponding climb to above normal levels. Warmer
central deserts will rise into the middle 80s to about 90...with warmer
western deserts climbing into the low 90s under sunny skies. Current
forecasts look to be in good shape and no updates are needed.

Previous discussion...
satellite this morning shows dry air over the region...with mostly
clear skies over the entire forecast area. Some clouds continue to
wrap around the upper level low pressure located over
south-central Colorado. Clouds were clipping our higher terrain
earlier in the evening...but now have moved east of the region. Have
decided to keep some single digit probability of precipitation in zone couple of
periods due to some residual moisture...though really am not
expecting anything to develop.

Today will see noticeable warming from heights begin
rising in the wake of the exiting low and trough. Readings will climb
above normal and above the 90 degree mark in the lower deserts...the
warmest it has been in a couple of days. This dry and warm pattern
will persist through the middle of next week. Highest temperature
right now look to be on Monday...when Lower Desert locations will
see the Mercury rise to around 93 degrees.

Models continue to advertise big changes for the later half of the
week. Significant cooling is likely...with some model guidance
indicating highs will remain in the upper 70s across much of the
area on Thursday. There is also greater confidence of rainfall
across the region. Climatologically speaking...very little rain
normally falls during the month of April. Last year only a trace
fell at Phoenix Sky Harbor and in 2013 and 2012 only .06 and .05
inches fell respectively. Slightly over a quarter of an inch fell in
2011...but you have to go all the way back to 2004 to find any
significant rainfall. That year we measured .68 inches. This far out
there still is quite a bit of uncertainty...but some models are
indicating totals up to half an inch are possible in northern
Maricopa County. The bulk of this is expected to fall Thursday
afternoon into Friday morning. Did make some adjustments to our probability of precipitation
in these periods...with increases to account for greater confidence
of rainfall.


Aviation... south-central Arizona including kphx...kiwa...and
ksdl...southeast California and southwest Arizona including kipl and

Clear skies with no aviation impacts through the period. Winds will
follow typical diurnal directions with some occasional afternoon
gusts to around 15-20 knots mostly for Phoenix area terminals.

Aviation discussion not updated for amended tafs.


Fire weather...
Monday through Wednesday...
temperatures will remain on the warm side as high pressure builds
into the area for the short term. Afternoon temperatures on the
deserts will warm into the lower 90s this weekend. Minimum
humidities will range from 5 to 10 percent each day and daytime
southwesterly breeziness can be expected. A Pacific low pressure
system will approach the western states by Wednesday and will result
in gusty southwest winds area-wide each afternoon and significantly
cooler temperatures. Minimum humidities will increase a bit starting
Wednesday with values mainly in the teens.


Psr watches/warnings/advisories...




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previous discussion...McLane
fire weather...waters/Kuhlman

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