Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 251651

Area Forecast Discussion
National Weather Service Flagstaff AZ
951 AM MST Sat Feb 25 2017

.SYNOPSIS...Cool and dry conditions will continue today. An
unsettled pattern will arrive on Sunday and last into early next
week, with breezy and cool conditions along with a good chance for
rain and snow showers.


.UPDATE...No major updates were required to the ongoing forecast.
Only the sky grids were adjusted to show a little more dramatic
increase in cloud cover later today and tonight.

The forecast focus continues on the Monday-Tuesday weather
system. There is still the potential for significant precipitation
accumulations. Forecast models were initially wet, then scaled
back, and now are looping back to a wet solution again. The run to
run inconsistency has led to a low confidence forecast for the
Monday-Tuesday period. Hopefully the 12z runs of the models this
morning trend towards a consensus for the afternoon forecast.
Stay tuned.


.PREV DISCUSSION /354 AM MST/... Temperatures will continue to
warm slightly across the area as another day of breezy dry
westerly flow continues over Northern Arizona. Some locations may
see gusts around 30 mph this afternoon ahead of the next
approaching system.

By Sunday morning increasing clouds and some shower activity is
expected to develop mainly over the high country as a quick moving
shortwave trough crosses Arizona. Models continue to show a
decrease in available moisture, which will ultimately be the
limiting factor for precipitation amounts with this system. Due to
the dry nature of this shortwave, showers will be scattered with
the majority of precipitation occurring over the higher peaks. No
significant accumulations are expected. Snow levels will remain
relatively low between 4500-5500 feet. Which will allow for some
light accumulations of snow to occur, however no significant
accumulations are anticipated this weekend.  As the system exits
the region Sunday night, breezy zonal flow will develop again over
Northern Arizona in its wake, however another trough of low
pressure is expected to impact the area possibly bringing a more
significant amount of precipitation to Northern Arizona Monday
afternoon through Tuesday Night. Models have for the time being
come into agreement over a decent transport of moisture from the
Pacific Ocean of the Coast of Northern Baja California directly
into Arizona.

Model guidance from the operational runs of the GFS and ECMWF
show efficient moisture transport that will allow for up to 2
inches of precipitation to fall over the Mogollon Rim Monday
Afternoon through Tuesday evening. While Confidence is low
concerning this solution, it should be noted that at least amongst
the GEFS ensemble, the operational forecast is only slightly
above the average of the ensemble members at the moment.
Confidence will increase if subsequent runs continue to show this
return to a wetter solution. For the time being probability of
precipitation, along with quantitative precipitation forecasts,
and subsequent snowfall amounts have been increased to account for
this change towards a wetter start to next week. Snow levels look
to be around 5500-6000 for this current solution, so some winter
weather impacts look possible at this time for the higher
elevations above the Mogollon Rim. Interested parties should
continue to monitor the forecast for additional updates as this
second of two systems looks to impact the region.

As the second system moves out of the area Tuesday night a ridge
of high pressure looks to dominate the forecast through the
remainder of the period. Temperatures are expected to climb back
above seasonal averages by the end of the work week as dry
conditions dominate.



.AVIATION...For the 18Z package...Expect VFR conditions for the next
18 hours. High to mid-level clouds will be on the increase today and
this evening in advance of an approaching storm system. Look for
afternoon southwest surface winds of 10-25 knots. Sunday morning,
clouds will continue to increase with areas of MVFR ceilings and
showers forming across the high terrain of northern Arizona by 18Z.
The snow level will be around 4000 feet MSL. Aviation discussion not
updated for TAF amendments.






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