Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Phoenix Arizona
1030 PM MST Thursday Mar 5 2015
Update...updated aviation discussion.
dry conditions with a warming trend will prevail through the middle
of next week. Most Lower Desert locales will warm into the middle to
upper 80s by next Tuesday. Somewhat cooler weather is the expected
for the end of next week as westerly flow aloft begins to push
inland over the region.
Discussion... a strong high pressure ridge aloft was in place along
the West Coast this evening...bringing dry subsident northeasterly flow aloft
to the region. Precipitable water values over Arizona were well below one quarter
of an inch...and most of the surface dewpoints in the central
deserts ranged from the teens to upper 20s at 8 PM. Infrared imagery
showed clear skies across the region. For the rest of tonight expect
clear skies...mild overnight temperatures and light winds. Current
forecasts are in good shape and no updates are needed.
Previous discussion...a West Coast ridge will be the dominant
feature through early next week with dry northerly flow aloft likely
continuing through the middle of next week. However...water vapor
and upper height analysis shows a weak closed low off the northern
Baja California coast. Models are in good agreement showing this low eventually
drifting back to the east northeast into southern Arizona by Friday
night into Saturday. Low level winds will remain easterly ahead of
this low while a slight bit of moisture gets pulled into far eastern
Arizona...but GFS 1000-700mb mixing ratios only show 2-3 g/kg and 3-
5 g/kg via the European. As the pv anomaly and 90 knots upper jet
traverses Southeast Arizona during the day Saturday...we may have
enough support and moisture for a few showers and maybe a
thunderstorm. Have increased probability of precipitation across our far eastern zones
Saturday with some light end slight chances now across far eastern
Temperatures will get a good boost starting Friday as upper heights
increase and 850mb temperatures rise from around 10c today to near
14c from Friday and into the weekend. Highs will near 80 degrees in
the warmest spots Friday with lower 80s commonplace for this
weekend. Once the closed low and a secondary weak shortwave that
passes through The Four Corners region on Monday exits to the
east...the Pacific Ridge will build in over the Desert Southwest.
This will lead to even warmer temperatures for the middle of next
week as 850mb temperatures possibly reach around 18c. Some
approaching middle level moisture may hinder high temperatures somewhat
for the middle of next week...but many Lower Desert spots should
reach into the middle 80s for next Wednesday and Thursday. There is
fairly high confidence we will see dry conditions from Sunday
through the middle of next week with some uncertainty and a
potential weak weather system for the end of next week.
south-central Arizona including kphx...kiwa...ksdl...southeast
California and southwest Arizona including kipl and kblh...
High pressure aloft centered along the California coast will keep skies
generally clear next 24 hours at least across all of the taf sites.
Sufficient low/middle level NE-SW gradient to keeps winds favoring the
east across the central deserts...and favoring the north/northeast
down the lower Colorado River valley. May see a few gusts to around 20kt
at kphx/kiwa taf sites on Friday...mainly in the 16z through 22z
window. A few northerly gusts to 20kt are also possible at kblh Friday afternoon.
Otherwise no aviation concerns at the taf sites for the next 24
hours and beyond.
Aviation discussion not updated for amended tafs.
Saturday through Thursday...high pressure will generally maintain
its grip over the district through the middle of next week.
Abnormally warm and dry conditions will prevail with afternoon
humidity levels typically falling into a 15 to 25 percent
range...followed by fair to good overnight recovery. Winds will
remain light and favor an easterly or northerly direction...though
some component of a diurnal upslope/drainage cycle will be evident.
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