Severe Thunderstorm Warning 2, NWS Flagstaff, AZ

AREA FORECAST DISCUSSION...UPDATED FOR ISOLD WIND THREAT
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
1040 AM MST SAT MAY 30 2009

.SYNOPSIS...SEASONABLE TEMPERATURES...LIGHT WINDS AND SCATTERED
AFTERNOON THUNDERSTORMS WILL CONTINUE THROUGH THE WEEKEND. DRIER AND
WARMER WEATHER IS EXPECTED NEXT WEEK...WITH ONLY A SLIGHT CHANCE OF
AFTERNOON THUNDERSTORMS OVER THE MOUNTAINS.

&&

.DISCUSSION...UPPER LOW CURRENTLY (900 AM MST) CENTERED SOUTH OF LAS
VEGAS ALONG THE COLORADO RIVER WITH STORMS ALREADY OCCURRING UNDER
THE COLD POOL -16C 500 MB AIR AND WEAK DIFFLUENCE ALOFT TO THE NORTH
AND EAST OF THE UPPER LOW CENTER. ANOTHER LINE OF STORMS ARE
ORGANIZING FROM BLACK CANYON CITY NORTHWEST TO 20 MILES SOUTHWEST OF
SELIGMAN. BEST MOISTURE AND DYNAMICS WITH THIS SYSTEM IS HEADED FOR
NAVAJO AND APACHE COUNTIES AND EASTERN COCONINO COUNTIES FOR THIS
AFTERNOON. EXPECTING AN ISOLD WIND THREAT IN A FEW STRONG STORMS
ALONG WITH SOME HAIL WITH THE POSSIBILITY OF ISOLD HEAVY RAIN MAINLY
EAST OF FLAGSTAFF TO THE NEW MEXICO BORDER. THE GRIDDED FORECASTS
HAVE BEEN UPDATED TO INCREASE PRECIPITATION CHANCE THIS AFTERNOON
EAST OF FLAGSTAFF. THE ZONE FORECASTS WILL BE UPDATED SHORTLY.

&&
.PREVIOUS DISCUSSION /245 AM MST/...A WEAK LOW PRESSURE SYSTEM
CURRENTLY LOCATED ACROSS SOUTHERN CALIFORNIA WILL LIFT INTO WESTERN
ARIZONA THIS AFTERNOON AND EVENING...THEN INTO NORTHEAST ARIZONA FOR
SUNDAY. SFC DEWPOINTS THIS MORNING ARE AROUND 40F FOR OUR FORECAST
AREA...A BIT HIGHER THAN MODEL FORECASTS. WITH THE MOISTURE IN
PLACE...EXPECT SCATTERED THUNDERSTORMS BY MID DAY ALONG THE
MOUNTAINS...MOVING GENERALLY NORTHWARD AT 10-15 MPH. WE HAVE BOOSTED
STORM CHANCES UP FOR TODAY...INTO THE 30-50 PCT RANGE FOR MOST
AREAS. DRIER LOW-LEVEL AIR IS NOTED ACROSS SOUTHWEST ARIZONA WHICH
MAY AFFECT YAVAPAI COUNTY LATER TODAY...SO KEPT POPS IN THE 20-30
PCT RANGE THERE. A FEW ISOLATED STRONGER STORMS ARE POSSIBLE AS THE
LOW-LEVEL SHEAR WILL INCREASE WITH THE APPROACH OF THE LOW PRESSURE
SYSTEM. THE CHANCE OF THUNDERSTORMS WILL CONTINUE ON SUNDAY...WITH
THE BEST CHANCE SHIFTING TO THE NORTHERN THIRD OF ARIZONA NEAR THE
LOW PRESSURE SYSTEM.

FOR NEXT WEEK...A DRIER SOUTHWESTERLY FLOW WILL DEVELOP IN ADVANCE
OF A CUTOFF LOW WEST OF CALIFORNIA. A WARMING TREND IS
EXPECTED...WITH JUST ENOUGH MOISTURE LINGERING FOR A SLIGHT CHANCE
OF HIGH-BASED AFTERNOON STORMS OVER THE MOUNTAINS. TOWARD THE END OF
THE WEEK...THE CUTOFF LOW MAY MOVE CLOSE ENOUGH TO THE STATE TO
PRODUCE SOME GUSTY SOUTHWEST WINDS.

&&

.AVIATION...FOR THE 18Z PACKAGE...THROUGH 03Z SUNDAY BKN-OVC CLOUDS
TO RETURN WITH BASES AT OR ABOVE 13 KFT MSL. SCATTERED SHOWERS AND
THUNDERSTORMS WILL DEVELOP...WITH LOCAL MVFR CONDITIONS
LIKELY...PRIMARILY ACROSS COCONINO COUNTY AND THE MOGOLLON RIM.
AFTER 03Z SUNDAY PRECIPITATION TO DIMINISH...WITH SCT-BKN CLOUDS AT
OR ABOVE 14 KFT MSL REMAINING. AVIATION DISCUSSION NOT UPDATED FOR
AMENDMENTS.

&&

.FIRE WEATHER...FOR THE WEEKEND...A LOW PRESSURE SYSTEM OVER
SOUTHWEST ARIZONA THIS MORNING WILL KEEP MOISTURE AND ATMOSPHERIC
INSTABILITY OVER THE NORTHLAND...WITH SCATTERED DAYTIME SHOWERS AND
THUNDERSTORMS DEVELOPING AFTER 1000L TODAY. LIGHTNING ACTIVITY
LEVELS HAVE BEEN BUMPED TO 4 FOR NEARLY ALL OF COCONINO COUNTY AND
THE MOGOLLON RIM FROM LAKE MARY TO THE WHITE MOUNTAINS. WINDS WILL
BE LIGHT THROUGHOUT THE PERIOD EXCEPT NEAR THUNDERSTORMS.

MONDAY THROUGH WEDNESDAY...A GENERAL REDUCTION IN MOISTURE IS
ANTICIPATED...BUT ENOUGH WILL LINGER TO JUSTIFY KEEPING A SLIGHT
CHANCE OF AFTERNOON SHOWERS AND THUNDERSTORMS THROUGH THE PERIOD.

&&

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

&&

PUBLIC.....................TC/JJ
AVIATION/FIRE WEATHER......DL

VISIT WEATHER.GOV/FLAGSTAFF FOR NORTHERN ARIZONA WEATHER
INFORMATION.