Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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095
FXUS65 KFGZ 201722
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
1022 AM MST Fri Jan 20 2017

.SYNOPSIS...A series of winter storms will affect the region
through early next week. These will be cold systems, with heavy
accumulations of snow across the high country. Hazardous driving
conditions should be anticipated for the next several days. Expect
precipitation to wind down Tuesday with very cold temperatures
through Thursday.

&&

.UPDATE...
The first disturbance that moved across the area last night
brought snow ratios of about 14:1 to areas above 6500. We
have massaged snow ratios for tonights system towards this value
for areas above 6500 feet and increased overnight QPF an
additional .10-.20 for upslope areas along and south of the
Mogollon Rim from Williams through the White Mtns. Thus additional
snowfall from noon today through noon Saturday is up a few inches,
now generally 12-18 inches for areas above 6500 feet with 18-24
new above 7500 feet. Snowfall rates at times tonight in the high
country should be in the 1-2 inch per hour range.

Radars across the SW U.S. show increasing coverage of light
showers already into Yavapai county. Expect steady precip to
redevelop across areas west of a Page to Payson line this
afternoon and spread eastward overnight.

&&

.PREV DISCUSSION /600 AM MST/...The first in a series of winter
storms arrived late Thursday afternoon and brought rain and snow
to much of the area overnight. This storm moved well east of the
state this morning. However, the saturated layer remains unstable
and upslope showers have persisted. This regime will continue for
much of the morning before deeper moisture and forcing arrives
arrives ahead of our next storm, still located in the eastern
Pacific.

There may be a brief period between 6AM-8AM MST where the upslope
showers along the Mogollon Rim are enhanced by a seeder-feeder
process. This process is driven by a small area of mid-level warm
advection, noted ahead of the next low.

This next storm has a much larger wavelength and longer fetch of
unstable and moist air compared to the system last night. We
expect a larger area to be affected and QPF values to be on the
order of 2 to 3 times what was observed overnight.

Rain and snow amounts will be prolific tonight and the Winter
Storm Warning will continue. This is a dangerous storm, only
travel if absolutely necessary.

Precipitation will slowly taper off from west to east during the
day Saturday. There will likely be another unstable and saturated
upslope layer to contend with, which will prolong some shower
activity in the higher terrain. We have extended the Winter Storm
Warning all the way through Saturday in the eastern zones as a
result.

Hghts rise Saturday night and early Sunday ahead of yet another
Pacific storm system due late Sunday and Monday. Details are now
becoming more clear concerning this system and it looks like it
will be just as serious as the storm approaching for tonight.

The is some debate concerning the development of warm advection
precipitation ahead of the low Sunday afternoon, but by Sunday
night and Monday, most models now agree on moderate to high levels
of QPF and strong winds. We have boosted POPs and snow amounts,
stay tuned.

A cold and unstable airmass will trail the third storm well into
the middle of next week. Expect a drying trend with some mountain
snow showers by this time, with very cold temperatures.

&&

.AVIATION...For the 18Z package...A passing weather system will
cause widespread MVFR conditions and areas of IFR/LIFR conditions
through the next 24 hours. The lowest ceilings and visibilities are
expected in association with a north to south oriented band of
precipitation currently draped across southern California. This band
is forecast to cross northern Arizona from west to east from this
afternoon through the overnight hours. LIFR visibilities and
ceilings are likely in heavy rain and snow along this band -
especially for locations above 5500 feet, and on south facing slopes
along and south of the Mogollon Rim. In addition, expect south to
southwest winds with gusts into the 25 to 35 knot range.

Conditions may begin to improve from west to east after 15Z
Saturday, but periods of MVFR/IFR ceilings and visibilities are
expected to continue over higher terrain in showers behind the
system. Aviation discussion not updated for TAF amendments.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...Winter Storm Warning until noon MST Saturday FOR AZZ004-006>008-
015-038.

Winter Storm Warning until 6 PM MST Saturday FOR AZZ016>018.


&&

$$

PUBLIC...DL/Peterson
AVIATION...RR


For Northern Arizona weather information visit
weather.gov/flagstaff



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