000 
fxus65 kpsr 192117 
afdpsr 


Area forecast discussion 
National Weather Service Phoenix Arizona 
217 PM MST sun Feb 19 2017 


Synopsis... 
an exiting Pacific weather system will leave lingering showers 
into early this evening and clouds through much of the night 
across the eastern half of Arizona. Drier conditions will 
gradually move into the region through the middle part of this 
week as above normal temperatures return to the area Tuesday and 
Wednesday amidst a significant warming trend. A mainly dry cold 
front will move through the region Thursday, with temperatures 
returning to near normal. A more potent storm system may affect 
the region next Sunday. 


&& 


Discussion... 
scattered instability type showers across south-central and 
eastern Arizona will gradually diminish starting late this 
afternoon with most of the activity coming to an end early this 
evening. Soggy conditions in the wake of the exiting Pacific low 
will persist into tonight with low stratus likely continuing 
across much of south-central and eastern Arizona. Areas west of 
Phoenix through the lower Colorado River valley should mostly 
clear out by midnight leaving a brief window before high clouds 
stream in from the west. Fog formation is possible tonight with 
the clearing skies, lingering boundary layer moisture, and light 
winds, but thinking it will mostly be localized and situated 
across southern Maricopa and Yuma counties. Have added patchy fog 
mention to these areas late tonight through early Monday morning. 


A substantial warming trend begins on Monday and especially 
Tuesday, as midlevel ridging builds over the southwest. High 
temperatures are expected to be just shy of 80 degrees across many 
Lower Desert locations on both Tuesday and Wednesday. A 
significant, but mostly dry, cold front will move through the area 
on Thursday, bringing high temperatures back into the upper 60s 
to lower 70s for the remainder of the week. This will be 
associated with a fast moving storm system that will glance 
central Arizona. 


Model guidance continues to advertise a more significant upper 
trough developing next weekend near the Pacific coast, but with 
significant timing/evolution differences still remaining. The 
most probable solution at this point reflects the storm system 
affecting southeast California as early as late Saturday evening, 
and the remainder of western/central Arizona on Sunday. This storm 
system does not appear to be as moisture-rich as more recent 
events, but still could see an uptick in precipitation chances for 
Sunday/Monday. However, given the uncertainty, only slight chance 
pops are currently forecast. Below-normal temperatures are also 
possible by Sunday, with high temperatures forecast to be in the 
mid-upper 60s. 


&& 


Aviation... 
south-central Arizona including kphx, kiwa,and ksdl: 


Upper low slowly exiting to the east with scattered to numerous 
light showers persisting across the central deserts. Expect light 
rain/rain showers through early afternoon before dissipating and as 
such will keep -ra in the tafs thru 21z, after that may see vcsh 
into the late afternoon as cold air aloft will lead to isolated 
instability showers. Otherwise main concern will be low ceilings; 
much guidance suggests ceilings in the 2-3k ballpark thru at least 21z 
with a few lower ceilings down to around 1k feet. From mid aftn thru 
early evening should still see ceilings 3-5k feet widespread. Do not 
expect significant visibility issues this afternoon, maybe 5-6sm at 
times in mist/drizzle but as showers decrease visible values should 
generally stay above 6sm. Any ceilings after 03z should genly be 
above 6k feet. Winds not an issue, following mostly diurnal 
tendencies aob 12kt. 


Southeast California/southwest Arizona including kipl and kblh: 


Fog in the Imperial Valley should be over by 19z and no longer 
affect the kipl taf. Otherwise expect few-sct lower cloud decks in 
the 3-5k foot ballpark through the afternoon. May see some increase 
in high clouds overnight tonight into Monday morning. At kblh should 
see few-sct low decks this afternoon mostly above 3k feet with 
additional decks near 8k feet, clouds becoming few at best by 03z. 
Again, may see scattered-broken high cloud decks develop tonight into Monday 
morning. Winds will be rather light, favoring the south at kblh and 
the west at kipl with speeds mostly below 12kt, over the next 24 
hours. 


Aviation discussion not updated for amended tafs. 


&& 


Fire weather... 
Tuesday through Saturday...dry conditions are expected for most 
areas through Saturday. Above normal temperatures can be expected 
Tuesday and Wednesday. A low pressure system passing mainly to 
the north Wednesday night and Thursday will lead to cooler 
temperatures and locally breezy conditions. Rain chances with the 
midweek system will be limited to the higher terrain of south- 
central Arizona. Anticipate slight warming Friday and Saturday. 
Minimum humidities will trend downward through the workweek (especially 
on thursday) with most lower elevations in the 15-20% range by 
Friday. Overnight recovery though will remain good. 


&& 


Spotter information statement... 
spotters should follow Standard reporting procedures. 


&& 


Psr watches/warnings/advisories... 
Arizona...none. 
California...none. 
&& 


$$ 






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