Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Phoenix Arizona
1004 PM MST Thu Feb 23 2017
dry weather with below normal temperatures will continue through
Saturday. However, two fast moving weather disturbances are forecast
to move into the region Sunday and again Monday night. The weather
system Monday night will have better potential for spreading rain
showers across the region. Drier and eventually warmer weather will
return to the area by the middle of next week.
much drier and cooler conditions continue to settle in over the
region in the wake of yesterday's cool frontal passage. Area
dewpoints are ranging from 15 to near 30 degrees drier than this
time last evening and daytimes also reflected the cooler airmass
advection coming in 8 to 10 degrees below readings from Wednesday.
Save for still elevated westerly breezes in a few foothill locales
and across some area ridgetops, winds have scaled back from their
daytime speeds with gustiness ceasing with the loss of diurnal
heating. Enhanced sundowner winds into the Imperial Valley as well
as some breezy mid-slope winds will highlight the evening wind
speeds this evening with most other Lower Desert locales feeling
speeds fall below 10kts mostly. Nighttime skies will remain mostly
clear and more sheltered locations/those that see winds calm will
experience a fairly cool morning in comparison to most this month
with upper 30s and low 40s possible across the deserts. No updates
planned for the near-term grids tonight; forecasts are trending
with current observations.
Previous discussion /issued at 222 PM MST/...
tonight through Saturday...
in the wake of a dry cold front last night, a cooler airmass will
continue to settle over the region through Saturday. Under mostly
clear skies and much lower dewpoints, temperatures will be much
cooler than normal, but a little warmer on Saturday. Light winds.
Sunday through Tuesday...
a couple of Pacific storms are still forecast to move into the
region this period, generally one Sunday and another Monday night.
However, a very complex Rex block pattern continues over the
eastern Pacific, so daily model run solutions for Sunday and
Monday night continue to waver slightly, with adjustments to
timing, intensity and precipitation amounts. For example, the
European model is now much wetter than the GFS for Monday night in
south central AZ, including Phoenix. And, what complicates precip
forecasts in south central Arizona is the increasingly moist southern
branch jet stream, from just north of Hawaii, that is forecast to
merge with the northern branch jetstream over the area.
For now the Sunday system will be relatively dry, but a good chance
of showers will continue generally from the Colorado River valley
eastward on Monday night.
Wednesday and Thursday...
Dry weather with near normal temperatures are forecast this period.
south-central Arizona including kphx, kiwa,and ksdl:
southeast California/southwest Arizona including kipl and kblh:
Dry northwest flow will keep skies mostly clear and still elevated
overnight westerly winds in the early hours of the 06z taf. West
winds will eventually wane for the Phoenix area terminals,
transitioning to the usual southeasterly winds in the early Friday
am hours. Northwest to west winds will persist for kipl and kblh
Aviation discussion not updated for amended tafs.
Saturday through Wednesday...
dry conditions, but increasing clouds are expected for most areas
through early Sunday as a mostly dry weather system passes by to
the north. A second weather system is likely for Monday into
Tuesday with better chances of wetting rains, especially across
the high terrain of Arizona. Below normal temperatures are
expected through the entire period. Breezy conditions early Sunday
and again on Monday are expected in most areas with breezy
conditions persisting down the lower Colorado River each afternoon
through Wednesday. Humidities will start out dry on Saturday, but
improve through early next week with minimum readings as high 35
to 40% on Monday. Gradual drying thereafter will lead to afternoon
readings closer to 20% on Wednesday.
Spotter information statement...
spotter reports will not be needed through the weekend.
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