Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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000
FXUS65 KFGZ 312043
AFDFGZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
143 PM MST MON AUG 31 2015

.SYNOPSIS...EXPECT ANOTHER ROUND OF SCATTERED TO NUMEROUS SHOWERS
AND THUNDERSTORMS TODAY. SOME STORMS TODAY MAY CONTAIN LARGE HAIL
AND TORRENTIAL RAINFALL...AS WELL AS DAMAGING WINDS. STORM
ACTIVITY WILL SLOWLY MOVE EAST THROUGH THE WEEK...WITH WESTERN
YAVAPAI AND COCONINO COUNTIES LIKELY DRYING OUT.

&&

.DISCUSSION...THIS MORNING`S WATER VAPOR IMAGERY REVEALS NORTHERN
ARIZONA IS CURRENTLY LOCATED BETWEEN A WEST COAST TROUGH AND A
RIDGE OF HIGH PRESSURE EXTENDING FROM NORTH MEXICO NORTHEASTWARD
THROUGH THE CENTRAL PLAINS. BETWEEN THESE FEATURES SITS AN
ENHANCED BELT OF UPPER LEVEL WINDS, WITH A PAIR OF JET MAXIMA, AND
ASSOCIATED SHORTWAVE TROUGHS, PROPAGATING THROUGH THE FLOW.
OBSERVATIONS REVEAL SURFACE DEW POINTS REMAIN ELEVATED ACROSS
NORTHERN ARIZONA. VALUES RANGE FROM THE LOW 50`S TO THE MID 60`S,
WITH THE GREATEST DEW POINTS IN THE LOW DESERTS OF YAVAPAI COUNTY.

THIS MORNINGS UPPER AIR SOUNDING FROM NEAR FLAGSTAFF REVEALS
SLIGHTLY STRONGER WINDS THROUGHOUT THE DEPTH OF THE ATMOSPHERE AS
COMPARED TO YESTERDAY MORNINGS VALUES. THIS IS NOT SURPRISING
GIVEN THE TIGHTENING GRADIENTS BETWEEN THE TROUGH TO OUR WEST AND
RIDGE TO OUR EAST. AS A RESULT, DEEP LAYER SHEAR VALUES HAVE
INCREASED, WITH AROUND 20 KNOTS INDICATED BY THE SOUNDING. IN
ADDITION, ATMOSPHERIC INSTABILITY HAS INCREASED A BIT AS
TEMPERATURES HAVE SLIGHTLY COOLED ABOVE 500 MB. MODIFIED OBSERVED
AND FORECAST SOUNDINGS INDICATE OVER 1000 J/KG OF MIXED LAYER
CAPE MAY DEVELOP ALONG THE WESTERN MOGOLLON RIM TODAY. STORM
MOTION WILL GENERALLY BE FROM THE SOUTHWEST OR WEST AROUND 15
KNOTS.

HI-RES MODEL RUNS FROM THE UNIVERSITY OF ARIZONA FORECAST ANOTHER
CONVECTIVELY ACTIVE DAY, WITH THE MOST WIDESPREAD ACTIVITY
OCCURRING FROM THE MOGOLLON RIM NORTHWARD. IN ADDITION, THEY
INDICATE THE POTENTIAL FOR INCREASING ACTIVITY SOUTH OF THE RIM IN
THE LATE AFTERNOON AND EVENING GENERATED BY OUTFLOWS FROM PRIOR
CONVECTION. THIS TREND APPEARS TO CAPTURED IN THE EVOLUTION OF THE
SREF POP FORECAST AS WELL, BUT EXTENDING FURTHER NORTH INTO WESTERN
COCONINO COUNTY. THIS SEEMS PLAUSIBLE GIVEN THE PRESENCE OF A
WEAKENING JET MAXIMA AND SHORTWAVE TROUGH FORECAST TO MOVE
ACROSS NORTHWEST ARIZONA FROM TODAY THROUGH THE OVERNIGHT HOURS.

SO, FOR TODAY`S FORECAST, EXPECT ANOTHER ROUND OF SCATTERED TO
NUMEROUS SHOWERS AND THUNDERSTORMS. UNLIKE YESTERDAY, INCREASED
SHEAR MEANS WE COULD SEE A FEW ROTATING STORMS. FREQUENT
LIGHTNING AND FLOODING FROM HEAVY RAINFALL WILL BE THE PRIMARY
HAZARD, BUT LARGE HAIL AND STRONG DOWNBURST WINDS CANNOT BE RULED
OUT.

&&

.PREV DISCUSSION /415 AM MST/...MODELS CONTINUE TO INSIST THAT
DRIER AND MORE STABLE AIR WILL PUSH EAST ACROSS THE REGION THROUGH
THE WEEK. HOWEVER...TRENDS INDICATE THAT TUESDAY WILL LIKELY BE
MORE ACTIVE FROM WHAT WAS PREVIOUSLY THOUGHT AND THE DRYING TREND
WILL LIKELY BE STUBBORN TO MOVE EAST. EVENTUALLY...AS A STRONG
EARLY SEASON TROUGH PUSHES INTO THE PACIFIC NORTHWEST...THE DRIER
AIR MAY WIN OUT. HOWEVER...CONFIDENCE IS DECREASING ON THIS...POPS
MAY NEED TO BE RAISED LATER THIS WEEK.

&&

.AVIATION...FOR THE 18Z PACKAGE...SCT TO NMRS SHRA/TSRA ARE FORECAST
TODAY...MOST NUMEROUS TO THE NORTHEAST OF A LINE FROM
KGCN...KFLG...KPAN. STORMS WILL LIKELY PERSIST UNTIL 05Z TUESDAY.
LCL IFR CONDITIONS WILL OCCUR WITH THE STRONGER STORMS...WITH STRONG
SURFACE WINDS. EXPECT ISOLD -TSRA AFT 05Z TUE. AVIATION DISCUSSION
NOT UPDATED FOR TAF AMENDMENTS.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

PUBLIC...RR/PETERSON
AVIATION...BAK


FOR NORTHERN ARIZONA WEATHER INFORMATION VISIT
WEATHER.GOV/FLAGSTAFF


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