Weather

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afdfgz 


Area forecast discussion 
National Weather Service Flagstaff Arizona 
850 am MST Sat Oct 11 2008 


Synopsis...a strong cold front will move through northern Arizona 
today. Very windy conditions are expected through sunset. Wind gusts 
up to 70 miles per hour are forecast for the Mogollon Rim...Navajo 
and Apache counties. This storm system will bring sharply colder 
temperatures...with areas of rain and thunderstorms east of 
Flagstaff today...and a chance of rain or snow showers northwest of 
Flagstaff. Cold temperatures will remain Sunday and Monday. A 
gradual improvement in the weather is expected starting Tuesday. 
&& 


Discussion...at 8 am MST...the surface cold front appears to be 
along a line from Page to Flagstaff to Black Canyon City. Areas east 
of this line will see wind gusts from 55 to 70 miles per hour today. The 
sustained wind forecasts today of 35 to 45 miles per hour for Apache and Navajo 
counties looks good. The Winslow Airport reported a gust to 61 miles per hour 
at 820 this morning. Winds from this mornings sounding are 39 knots 
at 9000 feet mean sea level and 70 knot at 14000 feet mean sea level. 


Severe thunderstorms are possible through middle afternoon for areas 
east of a line from Payson to Window Rock. There are thunderstorms 
occurring in this area now...with storm motions to the northeast 
from 45 to 55 miles per hour. Damaging wind and hail are the main threats. 
Current grids and products are in good shape. 


Previous discussion 350 am...infrared satellite loop is showing 
increasing cloud cover and cooling tops across northern Arizona this 
morning...especially over northern Gila County and the White 
Mountains. Surface dewpoints across the entire forecast area have 
gone up over the past six hours or so. However...out to the west dry 
air is beginning to push eastward as surface dewpoints are starting 
to come down across Needles and Blythe. Winds have stayed up all 
night and have hovered near Wind Advisory criteria across the high 
terrain. 


Water vapor imagery showing large upper low over east central 
California and western Nevada at this time. To the south off the tip 
of Baja California is Hurricane Norbert. Some moisture from this tropical 
system is being pulled northeastward and across southeastern 
Arizona. Already showers and thunderstorms have formed over tucson's 
County Warning Area and current radar shows convective activity starting across 
northern Gila County and the whites with a few lightning strikes 
noted near Mount Baldy peak. 


This strong area of low pressure is forecast to move northeast 
across the Great Basin today. Strong southwest winds being generated 
by this system will result in very windy conditions across northern 
Arizona this morning and afternoon. 700 mb winds are forecast to be 
in the 50 to 75 knot range during this time period...with the 
strongest winds being felt from the Mogollon Rim along to the whites 
and north to the Utah border. A High Wind Warning has already been 
issued by earlier shifts and this will be continued. For areas 
west...a Wind Advisory was also issued. For a more detailed 
description on these wind products...please see phxnpwfgz. 


One of the main issues for today will be the strength of the 
convective gusts. Because of the very strong winds aloft...any 
shower or thunderstorm could bring down these strong winds. The High 
Wind Warning will handle this over the White Mountains...and we 
probably go back and add damaging wind wording to northern Gila 
County. 


The best chances for precipitation will be across the high terrain 
in the southeast part of the forecast area where the moisture will 
be most concentrated. A secondary area of chance probability of precipitation are over the 
Kaibab Plateau for today as cold air aloft associated with 
the upper trough swings through that area. 


The system is anticipated to move across northern Utah this evening 
with its effects over the Northland waning. Winds will gradually 
diminish and skies will eventually clear as dry air from the west 
filters in. As a result...a hard freeze is likely for most areas 
above 4500-5000 feet Saturday night and Sunday night...the first of 
the season at some locations. Expect warmer temperatures for Monday 
through most of next week as the storm system moves away from the 
state. There is a possibility of some moisture moving in from the 
southeast by midweek...and a low chance of showers has been included 
in the forecast. 


&& 


Aviation...for the 12z package...a strong low pressure system will 
bring very strong winds to northern Arizona today. Expect southwest 
winds of 15 to 30 kts early...increasing through the day. The 
strongest winds will occur along and north of the Mogollon 
Rim...where afternoon gusts will reach 50 kts in many places and 
possibly as high as 60 kts east of Flagstaff. Winds will weaken 
after sunset. In addition...clouds and showers will bring periods of 
MVFR conditions to portions of east central Arizona today and 
tonight. Elsewhere across northern Arizona...VFR conditions are 
anticipated. Aviation discussion not updated for amendments. 


&& 


Fgz watches/warnings/advisories... 


Severe Thunderstorm Watch in effect until 2 PM MST this afternoon 
for azz016-018. 


High Wind Warning in effect until 6 PM MST this evening for 
azz009>018-039-040 


Wind Advisory until 4 PM MST this afternoon for azz004>008-037-038. 


&& 


$$ 


Public.........42 
aviation.......McCollum 


Visit weather.Gov/Flagstaff for northern Arizona weather information.