FXUS65 KPSR 120500 AAA
AFDPSR

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PHOENIX AZ
1000 PM MST SUN MAY 11 2008

SOUTH-CENTRAL AND SOUTHWEST ARIZONA...AND SOUTHEAST CALIFORNIA
FORECAST DISCUSSION

.UPDATE...
UPDATED AVIATION DISCUSSION.

&&

.SYNOPSIS...
A LOW PRESSURE SYSTEM WILL MOVE SOUTHEAST FROM WASHINGTON ACROSS
IDAHO LATE TONIGHT AND MONDAY...UTAH MONDAY NIGHT...AND ARIZONA
TUESDAY. THIS SYSTEM WILL BRING SOME BREEZINESS INTO THIS EVENING...
THEN WINDY WEATHER MONDAY AND TUESDAY. TEMPERATURES WILL BEGIN TO
DROP BACK MONDAY WITH MUCH COOLER WEATHER TUESDAY. THERE IS ALSO A
CHANCE OF SHOWERS AND THUNDERSTORMS EAST OF THE GREATER PHOENIX AREA
TUESDAY AFTERNOON AND EVENING. STRONG HIGH PRESSURE ALOFT FROM THE
PACIFIC WILL BRING SIGNIFICANTLY WARMER WEATHER DURING THE LAST HALF
OF THE WEEK. THE FIRST 100 DEGREE WEATHER OF THE YEAR IS EXPECTED IN
MANY DESERT LOCATIONS INCLUDING PHOENIX BY THE END OF THE WEEK.

&&

.DISCUSSION...
UPPER LEVEL HIGH PRESSURE RIDGE OVER ARIZONA...WHICH LED TO VERY
WARM MAX TEMPS TODAY...SUCH AS 98 AT PHOENIX AND 102 AT CASA
GRANDE...STARTING TO WEAKEN AND SHIFT EAST AHEAD OF A DEVELOPING PAC
NW TROF. 00Z 500MB PLOTS INDICATED AROUND 20M HEIGHT FALLS ACROSS
AZ...WITH THE MOST SIGNIFICANT FALLS WELL TO OUR NORTHWEST...SUCH AS
80M AT BOISE. AIRMASS OVER ARIZONA CURRENTLY VERY DRY...WITH PWAT
VALUES ONLY AROUND 0.10 INCH...AND EXCEPT FOR A FEW HIGH CLOUDS
SPREADING INTO SERN AZ...SKIES WERE GENLY CLEAR AT 8 PM PER THE
LATEST IR IMAGERY. LATEST SHORT RANGE PROGS IN AGREEMENT THAT
DEVELOPING TROF OVER THE PAC NW WILL SLOWLY SHIFT SEWD TONIGHT...AND
LEAD TO A STEADY TIGHTENING OF THE LOW/MID LEVEL GRADIENTS. WIND
SHOULD NOT BE TOO MUCH OF A PROBLEM THOUGH...AS THE ATMOSPHERE WILL
MOSTLY DECOUPLE UNDER CLEAR SKIES...AND WINDS SHOULD STAY BELOW 15
MPH MOST PLACES. STRONGEST WINDS THIS EVE HAVE OCCURRED OVER SERN
CA...MAINLY IMPERIAL COUNTY...WHERE SURFACE GRADIENT HAS BEEN THE
TIGHTEST. WEST WINDS HAVE GUSTED TO AROUND 30 MPH...BUT WINDS THERE
SHOULD LOWER BELOW 15 MPH BY MIDNIGHT AS THE GRADIENT BEGINS TO
RELAX A BIT. FOR THE REST OF TONIGHT...SKIES SHOULD REMAIN CLEAR FOR
THE MOST PART...WITH JUST A FEW HIGH CLOUDS SPREADING OVER THE ERN
ZONES. FORECASTS APPEAR IN GOOD SHAPE AND NO UPDATES ARE NEEDED
ATTM. REST OF THE DISCUSSION IS FROM THE PREVIOUS DAY SHIFT.

.PREVIOUS DISCUSSION...
HIGH PRESSURE ALOFT MOVING EAST JUST EAST OF OUR AREA RESULTED IN
WARMER WEATHER TODAY WITH EARLY AFTERNOON TEMPERATURES GENERALLY 2
TO 5 DEGREES WARMER THAN YESTERDAY.

A LOW PRESSURE SYSTEM THAT WAS MOVING SOUTHEAST OVER WASHINGTON
TODAY WILL MOVE OVER IDAHO LATE TONIGHT AND MONDAY...UTAH MONDAY
NIGHT...AND ARIZONA TUESDAY. THIS SYSTEM WILL BRING SOME BREEZINESS
INTO THIS EVENING...THEN WINDY WEATHER MONDAY AND CONTINUED WINDY
WEATHER DOWN THE LOWER COLORADO RIVER VALLEY TUESDAY.

A FIRE WEATHER WATCH IS IN EFFECT FOR SOUTHEAST CALIFORNIA AND THE
LOWER COLORADO RIVER VALLEY FOR MONDAY AFTERNOON AND EVENING FROM 2
PM TO 8 PM MST/PDT AND MAY BE NEEDED AGAIN DOWN THE LOWER COLORADO
RIVER VALLEY FOR TUESDAY FROM LATE MORNING THROUGH THE AFTERNOON AND
EVENING. A WIND ADVISORY MAY ALSO HAVE TO BE ISSUED FOR IMPERIAL
COUNTY MONDAY AFTERNOON AND EVENING.

TEMPERATURES WILL BEGIN TO DROP BACK MONDAY WITH MUCH COOLER WEATHER
TUESDAY AS THE LOW PRESSURE SYSTEM MOVES ACROSS THE AREA. ENOUGH
MOISTURE IS EXPECTED FOR A CHANCE OF SHOWERS AND THUNDERSTORMS EAST
OF THE GREATER PHOENIX AREA TUESDAY MAINLY OVER THE HIGHER TERRAIN
IN THE AFTERNOON AND EVENING. OTHERWISE...SOME CLOUDINESS IS EXPECTED
TO MOVE SOUTHEAST MAINLY ACROSS SOUTH-CENTRAL ARIZONA TUESDAY. OTHER
THAN THAT...MOSTLY CLEAR NIGHTS AND SUNNY DAYS ARE EXPECTED TO
CONTINUE THIS WEEK.

STRONG HIGH PRESSURE ALOFT WILL MOVE EAST FROM THE EASTERN PACIFIC
OVER THE WEST COAST INTO THE WESTERN UNITED STATES...AND BRING
SIGNIFICANTLY WARMER WEATHER TO OUR AREA DURING THE LAST HALF OF THE
WEEK. THE FIRST 100 DEGREE WEATHER OF THE YEAR IS EXPECTED IN MANY
DESERT LOCATIONS INCLUDING PHOENIX BY THE END OF THE WEEK.

&&

.AVIATION...
AS AN UPPER LEVEL DISTURBANCE APPROACHES THE SOUTHWEST UNITED STATES
TONIGHT...SURFACE AND MID LEVEL GRADIENTS WILL CONTINUE TO TIGHTEN.
WEST WINDS FROM 10-20 MPH AT KPHX/KIWA SHOULD GRADUALLY TAPER OFF
AND SWITCH TO THE SE BY 09Z. STRONGEST WINDS THIS EVE LIKELY TO BE
AT KIPL...WHERE SW TO W WINDS WILL LIKELY GUST TO NEAR 30 MPH THRU
06Z...THEN LOWER TO BELOW 15 MPH AFTER MIDNIGHT. PERSISTENT
SOUTHERLY WINDS ALONG THE LOWER COLORADO RIVER VALLEY EXPECTED
THROUGH THE NEXT 24 HOURS WITH GUSTS TO AROUND 22 KNOTS POSSIBLE
THRU MIDNIGHT. CLEAR SKIES EXPECTED ALL LOCALES TONIGHT THRU MONDAY
AFTERNOON...WITH SOME INCREASE IN MID/HI CLOUDS OUT WEST AFTER 21Z.

WINDS WILL INCREASE LATER MONDAY AT ALL SITES AS A COLD FRONT
APPROACHES...WHERE SUSTAINED SPEEDS WILL RANGE FROM 15-20 KTS/GUSTS
TO 25 KTS IN CENTRAL ARIZONA AND THE LOWER COLORADO RIVER
VALLEY...TO 20-25 KTS/GUSTS TO NEAR 35 KTS IN SOUTHEAST
CALIFORNIA...INCLUDING KIPL. STRONGEST GUSTS AT BOTH KIPL AND KBLH
WILL DEVELOP BY AROUND 22Z AND CONTINUE UNTIL 03-04Z TUESDAY.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
AN INCREASE IN WINDS IS EXPECTED LATER THIS AFTERNOON INTO THIS
EVENING IN SOUTHEAST CALIFORNIA AND THE LOWER COLORADO RIVER
VALLEY...AHEAD OF A LOW PRESSURE SYSTEM APPROACHING THE SOUTHWEST.
GUSTS TO AROUND 25 MPH WILL BE POSSIBLE THIS EVENING. A MORE NOTABLE
INCREASE IN WINDS IS EXPECTED MONDAY...ESPECIALLY IN SOUTHEAST
CALIFORNIA AND THE LOWER COLORADO RIVER VALLEY. THE FIRE WEATHER
WATCH FOR MONDAY WILL CONTINUE FOR THIS AREA. WIDESPREAD GUSTS TO 35
MPH WILL BE POSSIBLE...PARTICULARLY IN IMPERIAL COUNTY. THE
COMBINATION OF STRONG WINDS WITH VERY DRY AIR AND LOW RELATIVE
HUMIDITY MAY CREATE HAZARDOUS FIRE WEATHER CONDITIONS. A DECISION TO
UPGRADE THIS WATCH WILL BE PASSED ON TO LATER SHIFTS.

IN SOUTHWEST/CENTRAL ARIZONA...EXPECTING A BREEZY DAY HERE AS WELL
MONDAY...ALTHOUGH THE WINDS WILL NOT BE QUITE AS STRONG AS SOUTHEAST
CALIFORNIA. SOME AREAS MAY EXPERIENCE SUSTAINED WINDS NEAR 20 MPH
WITH GUSTS TO 30 MPH. ISOLATED MOUNTAIN TOP LOCATIONS MAY SEE EVEN
STRONGER WINDS. PARTS OF LA PAZ COUNTY MAY APPROACH CRITICAL FIRE
WEATHER CONDITIONS IN THE LATE AFTERNOON MONDAY. HOWEVER...THE
DURATION AND AREAL COVERAGE OF CRITICAL CONDITIONS MAKE THIS A
MARGINAL EVENT.

BY TUESDAY...THE LOW PRESSURE SYSTEM IS EXPECTED TO BE CENTERED OVER
CENTRAL ARIZONA...WHICH WILL LEAD TO COOLER CONDITIONS...LIGHTER
WINDS...AND A SLIGHT INCREASE IN RELATIVE HUMIDITIES. BREEZY TO
WINDY CONDITIONS CAN STILL BE EXPECTED ALONG THE LOWER COLORADO RIVER
VALLEY AS A NORTH WIND TAKES HOLD ON THE BACK SIDE OF THE LOW. LATER
IN THE WEEK...A RIDGE OF HIGH PRESSURE BUILDS AS TEMPERATURES WILL
WARM QUICKLY TO SLIGHTLY ABOVE SEASONAL NORMALS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...FIRE WEATHER WATCH FOR THE LOWER COLORADO RIVER VALLEY...
     FIRE WEATHER ZONE 131...FROM 2 PM TO 8 PM MST MONDAY.

CA...FIRE WEATHER WATCH FOR JOSHUA TREE NATIONAL PARK...EASTERN
     RIVERSIDE COUNTY AND IMPERIAL COUNTY INCLUDING THE LOWER
     COLORADO RIVER VALLEY...FIRE WEATHER ZONES 230...231...AND 232
     FROM 2 TO 8 PM PDT MONDAY.

&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX

DISCUSSION...CB/ELLIS
AVIATION...CB
FIRE WEATHER...ROGERS