Weather Service Report


413 
FXUS65 KFGZ 172111
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
209 PM MST Sat Feb 17 2018

.SYNOPSIS...Expect fair weather tonight. Gusty southwest winds to
develop Sunday afternoon and persist Sunday night as a powerful 
cold front approaches. Rain and snow showers to develop late 
Sunday along the Mogollon Rim. The cold front to cross the area 
Monday with very strong winds for all, and good chance of rain and
snow showers along and north of the Mogollon rim. Tuesday could 
be the coldest day so far this season.

&&

.DISCUSSION...
Progs in good agreement showing a very strong cold front to cross
northern Arizona on Monday. Satellite shows this system is moving
into the pac NW this afternoon. Also seen on sat images is the
pool of precipitable water values of 0.90 inch plus not to far
south of the AZ Mexico border and extending off the Baja coast.  

Expect fair weather tonight. Progs continue to show southwest 
wind speeds increasing at all levels Sunday afternoon and thus
have issued a Wind Advisory for much of the area, with gusts to 
45 mph forecast.   

Sunday night - We still expect moisture to move northward as 
southwest flow increases further, leading to upslope shower 
development well ahead of the main cold front. We did issue a 
Winter Storm Watch for areas above 6500 feet from the Kaibab
Plateau through the Mogollon Rim and White Mountains. This watch
to cover the strong southwest winds and precipitation. The wind
advisory will continue overnight for areas below 6500' as GFS 
shows wind speeds from its ground to 2kft agl increasing into the
30-45 kt range. 

On Monday, strong southwest winds will cover much of the region. 
We have issued a High Wind Watch for Monday for the northeast 
quarter of the state, with sustained speeds in the 35-45 mph range
with widespread gusts of 55-65 mph. Travel in this area is not 
looking awesome. Daytime Monday looks to be the period of heaviest
precip. Upslope shower activity will continue and rain and snow 
showers will attend the cold front, with accumulating snow above 
5500 feet. Finally, much colder and unstable air will trail the 
front, with instability showers lingering into Monday night. The 
forecast hourly temp trends looked good showing cooling values for 
much of the daylight hours. This will be a very cold system and snow 
ratios will be high. 

At this time we feel very confident in the wind forecasts and
products. We have blended this mornings official QPF with the 
latest WPC forecasts which increased accumulations over the 
favored upslope areas a bit. 

Tuesday looks very cold with highs in the 20s in the high country
to the 40s in the Verde valley. There is a chance of showers due 
to instability as 500mb temps to be in the -25C to -35C range. 
All are encourage to monitor the latest forecasts. 

.Long Term (Tuesday night through Saturday)...

Chances for rain and snow showers dwindle Tuesday 
evening, with clearing skies forecast for Tuesday night. As a 
result, expect a round of very cold temperatures Wednesday morning, 
possibly the coldest of the next 7 days. The current forecast calls 
for low temperatures ranging from the teens to single digits across 
much of Arizona's High Country.

Model spread increases beginning Wednesday, but generally agree that 
northern Arizona will remain under the influence of a longwave 
trough into the weekend. This will result in a period of below 
normal temperatures, with potential for periods of increased cloud 
cover and chances for showers. The operational ECMWF predicts light 
showers across portions of northern Arizona late Friday. However, 
the GFS remains dry. With that said, neither suite of models 
suggests a stout ridge over the West Coast, which is a significant 
departure from the overall weather pattern that had been in place 
across the United States for much of this winter season.

&&

.AVIATION...For the 00Z Package...Upper level cloud cover will 
increase overnight as a winter weather system approaches from the 
northwest. After 17Z Sunday, wind speeds will increase across the 
area, strongest along and north of the Mogollon Rim. In general, 
expect southwest winds from 20 to 30 knots with gusts into the 35 to 
45 knot range. Aviation discussion not updated for amendments.

&&

.FIRE WEATHER...On Sunday, gusty southwest winds return as a strong 
cold front approaches from the northwest. The strongest winds will 
be along and north of the Mogollon Rim, where wind gusts as high as 
50 mph will be possible. On Monday, even stronger winds are forecast 
as a stout cold front sweeps across the area. The strongest winds 
will likely occur east of Flagstaff, where wind gusts as high as 60 
mph will be possible. In addition, rain and high elevation snow 
showers will accompany the front as it moves across the area from 
the northwest to the southeast.

Tuesday through Thursday...Chances for snow showers linger into 
Tuesday. Dry conditions along with a continuation of below normal 
temperatures are forecast for Wednesday and Thursday.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...Wind Advisory from 2 PM Sunday 
to midnight MST Sunday night FOR AZZ038.

Wind Advisory from 2 PM Sunday to 7 AM MST Monday FOR AZZ004>017-
039-040.

High Wind Watch from Monday morning through Monday afternoon FOR 
AZZ005-009>014-039-040.

Winter Storm Watch from late Sunday night through Monday evening 
FOR AZZ004-007-015>017.


&&

$$

PUBLIC...DL
AVIATION...RR
FIRE WEATHER...RR


For Northern Arizona weather information visit
weather.gov/flagstaff

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Western Regional Climate Center, wrcc@dri.edu