Heavy Rain in Arizona, September 23, 2007

AZZ020>028-CAZ030>033-231800-

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
230 AM MST SUN SEP 23 2007

.SYNOPSIS...
STRONG PACIFIC LOW IS OVER NEVADA AND QUICKLY SWEEPING OUT OF THE
REGION. SOME LINGERING LINES OF SHOWERS AND THUNDERSTORMS ARE STILL
FORMING OVER CENTRAL AND SOUTHERN ARIZONA. THESE SHOULD DIMINISH AS
THE LOW MOVES FURTHER TO THE NORTHEAST AND LOSES SOME OF ITS
STRENGTH. WITH ITS DEPARTURE WE CAN EXPECT TO SEE DRYING OUT AND A
SLOW RETURN TO NORMAL TEMPERATURES WITH LITTLE CHANCE OF RAIN BY
MONDAY.

&&

.SHORT TERM...
TODAY THROUGH TUESDAY...
WATER VAPOR IMAGERY SHOWS THE UPPER LEVEL LOW THAT HAS BEEN SITUATED
OFF THE SOUTHERN CALIFORNIA COAST OVER THE LAST COUPLE DAYS IS
FINALLY KICKING OUT TO THE NE AND WEAKENING. THE MOISTURE PLUME FROM
DYING TROP STORM IVO THAT BROUGHT IN AMPLE TPW ON SATURDAY IS NOW
DIMINISHING. SOME SHOWER/TSTM LINES STILL EXIST IN ERN AZ BUT ARE
BECOMING FEWER AS THE LOW LOSES STEAM AND CONTINUES MOVING AWAY TO
THE NE. EXPECT THE REMAINING SHOWER/TSTM LINES TO CONTINUE MOVG E
AND SHOULD BE OUT OF AZ...MOVG INTO SW CO AND NW NM.

RIDGE WILL BUILD BACK IN OVER CWA ON SUNDAY WITH VERY DRY CONDITIONS
AND TEMPS SLOWLY INCHING BACK UP TO NORMAL OR A BIT ABOVE.

&&

.LONG TERM...
TUESDAY NIGHT THROUGH SATURDAY...
ECMWF AND GFS IN GOOD AGREEMENT WITH THE TROF MOVING THROUGH THE
PLAINS MID WEEK...WITH A DRIER WESTERLY FLOW OVER SE CA AND AZ.
HEIGHTS WILL RISE THE LATTER PART OF THE WEEK FOR INCREASING TEMPS.
ECMWF INDICATING ANOTHER TROF TO SWING THROUGH THE ROCKIES FRI/SAT
...WHILE THE GFS DEPICTS A MORE ZONAL FLOW. BY SAT AFTERNOON...WE
SEE BIG DIFFERENCES BETWEEN THE ECMWF AND THE GFS. THE GFS STARTS TO
INDICATE A WEAK LOW DEVELOPING OVER THE PAC...WITH RIDGING OVER THE
WRN CONUS. ECMWF PRETTY MUCH THE OPPOSITE OF THE GFS...WITH RIDGING
ALONG THE PAC NW COAST AND A FAIRLY AMPLIFIED TROF MOVING THROUGH
THE ROCKIES. UNTIL THE MED RANGE BEGIN TO MERGE ON THE SAME SCENARIO
(OR AT LEAST SOMETHING CLOSER THAN WHAT WE ARE SEEING NOW)...TRENDS
WILL BE DIFFICULT TO CALL. FOR NOW...FEEL FAIRLY CONFIDENT IN THE
WARMING AND DRYING TREND THE FIRST PART OF THE EXTENDED...AND WELL
CALL FOR LITTLE CHANGE THU/FRI/SAT...WITH TEMPS ACROSS THE WARMEST
DESERT LOCALES NEAR 100.

&&

.AVIATION...
SEPTEMBER 23 0400 UTC (SEPTEMBER 22 2100 MST)

DRIER AIR WILL CONTINUE TO MOVE INTO SOUTHEAST CALIFORNIA AND THE
SOUTHWEST DESERTS OF ARIZONA TONIGHT AS THE UPPER LEVEL LOW OVER
SOUTHERN CALIFORNIA MOVES NORTHEAST INTO THE NORTHERN ROCKIES. SKIES
WILL CLEAR FROM THE WEST OVER IMPERIAL...YUMA AND BLYTHE BY 06Z.
PARTIAL CLEARING IS EXPECTED OVER KPHX/KIWA AND SATELLITE AIRFIELDS
BY 09Z...WITH LOCAL CEILINGS GENERALLY AT OR ABOVE 12K FEET. AREAS
OF LOWER CIGS DOWN TO 8000 FEET EXPECTED TO PERSIST OVER THE HIGHER
TERRAIN EAST OF PHOENIX...ALONG WITH ISOLATED THUNDERSTORM ACTIVITY
ACROSS PORTIONS OF EASTERN ARIZONA THROUGH 12Z.

SEE TAFS PHXTAFPHX...PHXTAFIWA...PHXTAFYUM...LAXTAFBLH AND LAXTAFIPL
FOR MORE DETAILED INFORMATION.

AVIATION DISCUSSION IS NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SEPTEMBER 22 2130 UTC (SEPTEMBER 22 1430 MST)

LARGE UPPER LEVEL LOW WILL DRIFT ACROSS UTAH BY MONDAY WITH A DRY
WESTERLY FLOW ALOFT SPREADING ACROSS SOUTHEAST CALIFORNIA AND INTO
SOUTHWEST ARIZONA. A SLOW WARMING TREND IS ALSO EXPECTED WITH RH
VALUES ON THE DESERTS DROPPING INTO THE TEENS EACH DAY FOR TUESDAY
THROUGH FRIDAY. WINDS DURING THIS PERIOD WILL GENERALLY REMAIN WELL
BELOW CRITICAL LEVELS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

SHORT TERM...WATERS
LONG TERM...WANEK
AVIATION...MEYERS
FIRE WX...SIPPLE