Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 301625
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
925 AM MST TUE SEP 30 2014

.SYNOPSIS...
DRY NORTHWEST FLOW WILL ESTABLISH ITSELF OVER THE AREA THIS
WEEK...KEEPING SKIES MOSTLY CLEAR AND RAINFALL CHANCES NIL.
TEMPERATURES WILL BEGIN THE WEEK SLIGHTLY BELOW NORMAL AND GRADUALLY
WARM THROUGH THE WEEK AS HIGH PRESSURE STRENGTHENS OVER THE WEST.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS THE WEATHER SYSTEM WE HAD THIS PAST
WEEKEND NOW MOVING FROM THE ROCKIES ONTO THE CENTRAL AND NORTHERN
GREAT PLAINS. WEST OF THAT A WEAKER SYSTEM IS MOVING THROUGH THE
PACIFIC NORTHWEST AND GREAT BASIN. FURTHER WEST...THERE IS A RIDGE
OF HIGH PRESSURE OVER THE NORTHEAST PACIFIC. THIS LEAVES DRY
NORTHWESTERLY FLOW OVER OUR FORECAST AREA. RAOB TRENDS OVER THE PAST
24 HOURS SHOW VERY LITTLE WARMING IN THE LOWER LEVELS AT TWC WITH
INCREASING WARMING FURTHER WEST...ESPECIALLY AT NKX. FORECAST HIGHS
FOR TODAY REFLECT THIS THOUGH SOME TWEAKS WERE MADE. THE UPPER
TROUGH TO OUR NORTHWEST WILL BRUSH ARIZONA WEDNESDAY KEEPING
TEMPERATURE TRENDS PRETTY FLAT. MORE LATER.

&&

.PREVIOUS DISCUSSION ISSUED 307 AM...
LARGE UPPER LOW RESPONSIBLE FOR THIS WEEKEND`S WEATHER EVENT ACROSS
THE SOUTHWEST STATES NOW IS CIRCULATING INTO THE PLAINS STATES...WITH
DRY NORTHWEST FLOW DRAPED ACROSS MUCH OF THE WESTERN CONUS THIS AM.
NEARLY CLOUDLESS SKIES OBSERVED ACROSS SOUTHEAST CA AND MUCH OF
AZ...SAVE FOR SOME MID-LEVEL STRATUS DECKS SKIRTING THE NORTHERN AZ
BORDER NEAR PAGE. GENERALLY LITTLE CHANGE NOTED ON AREA TEMPERATURES
THIS MORNING COMPARED TO MONDAY...WITH LOW 60S TO LOW 70S OBSERVED AT
MOST SITES. WHILE THE BROADER DEWPOINT TREND HAS BEEN DRIER THROUGH
THIS EARLY WEEK...OBSERVED VALUES HAVE WIDELY VARIED DURING THE
OVERNIGHT HOURS OVER MANY OF THE LOWER DESERT ELEVATIONS. EXPECT
THIS TO CONTINUE THE NEXT FEW MORNINGS AS SURFACE CONDITIONS STILL
HOLD SOME MOISTURE FROM RECENT RAINFALL AND TEMPERATURES HAVEN`T
BEEN TOO WARM TO HELP EVAPORATE THIS MOISTURE AWAY. WHERE THE
MORNINGS WILL HAVE A WIDE RANGE OF VALUES... AFTERNOON MIXING FOR
THE NEXT FEW DAYS SHOULD DROP READINGS INTO THE UPPER 30S TO LOW
40S...POSSIBLY EVEN DRIER OVER PORTIONS OF SOUTHEAST CA.

DRY NORTHWEST FLOW WILL PERSIST THROUGH THURSDAY OVER MUCH OF THE
WEST...WITH ANOTHER SWIFT SHORTWAVE DISTURBANCE DROPPING OUT OF
BRITISH COLUMBIA CANADA AND INTO THE GREAT BASIN STATES LATE
WEDNESDAY INTO THURSDAY. 850MB TEMPERATURE PLOTS AND MSLP ANALYSIS
SHOW THE FRONT STALLING OVER NORTHERN AZ...WITH NORTH TO
NORTHEASTERLY FLOW FILTERING DOWN THE COLORADO RIVER VALLEY AND
THROUGH THE MOGOLLON RIM. NOTICEABLY BREEZY CONDITIONS WILL DEVELOP
ALONG THE COLORADO RIVER OF 10 TO 15 MPH WITH SOME PERIODS OF
ENHANCED GUSTINESS POSSIBLE THURSDAY INTO FRIDAY. WITH LOWERED
SHORTWAVE HEIGHTS TO THE NORTH/NORTHEAST OF PHOENIX...NEAR OR JUST
BELOW NORMAL TEMPERATURES (LOW 90S) WILL HOLD THROUGH THURSDAY. THE
WESTERN FORECAST AREA BEING JUST OUT OF RANGE OF THE THERMAL PROFILE
OF THE FRONT WILL SEE SLIGHTLY WARMER CONDITIONS IN THE MID TO UPPER
90S.

PACIFIC RIDGING WILL QUICKLY BUILD INTO THE SOUTHWEST DESERTS
BEGINNING EARLY FRIDAY. TEMPERATURES UNDER THIS PATTERN LOOK TO PEAK
ON SATURDAY WITH THE WARMER WESTERN DESERTS IN THE 100-105F RANGE AND
94-99F FOR THE LOWER AZ DESERTS WITH MOSTLY CLEAR SKIES AND LIGHT
WINDS. BY THE SUNDAY-MONDAY PERIOD...THE UPPER RIDGE CIRCULATION
CENTER WILL TRANSITION TO OUR EAST/SOUTHEAST AS BROAD
TROUGHING/SHORTWAVE ENERGY FROM OVER THE GREAT LAKES EXPANDS BACK
INTO THE CENTRAL PORTIONS OF THE COUNTRY AND ANOTHER AREA OF WEAK
TROUGHING/LOWER HEIGHT ANOMALY MOVES IN ALONG 30N IN THE EASTERN
PACIFIC.

ACTIVITY FROM THE EASTERN PACIFIC TROPICS COULD PLAY A ROLE IN THE
EXTENDED PERIOD BY THE MIDDLE PART OF NEXT WEEK. LATEST NHC FORECAST
HAS AN AREA WELL SOUTH OF ACAPULCO, MEXICO PROGGED FOR TROPICAL
CYCLONE FORMATION AT 90 PERCENT WITHIN THE NEXT 5 DAYS. BOTH THE GFS
AND ECMWF PICK UP ON THE POTENTIAL TROPICAL SYSTEM...THE NEXT NAME ON
THE CYCLONE LIST IS SIMON...AS IT MOVES FURTHER INTO THE PACIFIC
WATERS AND EVENTUALLY TURNING NORTHWESTWARD. WHILE IT IS FAR TOO
EARLY TO HANG A HAT ON ANY ONE MODEL SOLUTION...STORM PATH OR STORM
EVOLUTION...THE REPOSITIONING OF THE UPPER RIDGE TO OUR
EAST/SOUTHEAST COULD TRANSPORT SOME ELEVATED MOISTURE FIELDS THAT
WORK UP THE GULF OF CALIFORNIA BACK INTO NORTHERN MEXICO AND THE
SOUTHWEST STATES. WITH UPPER RIDGE HEIGHTS REMOVED FROM THE AREA
DURING THIS PERIOD...TEMPERATURES WILL SCALE BACK TO MORE NORMAL
READINGS AND POSSIBLY COOLER IF ELEVATED DEWPOINTS AND HUMIDITIES
MAKE SOME SORT OF A COMEBACK.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...AND
SOUTHWEST ARIZONA AND SOUTHEAST CALIFORNIA INCLUDING KIPL AND KBLH...

LIGHT DIURNAL WINDS AND MAINLY CLEAR SKIES WILL PREDOMINATE AT ALL
TAF SITES THROUGH WEDNESDAY. NO AVIATION WEATHER IMPACTS ANTICIPATED.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
WITH VIRTUALLY NO CHANCE OF RAINFALL THROUGH THE
PERIOD...TEMPERATURES WILL BE MAINTAINED IN A SLIGHTLY ABOVE AVERAGE
CATEGORY. MINIMUM HUMIDITY LEVELS WILL REMAIN RELATIVELY STEADY
THROUGHOUT THE PERIOD...DROPPING INTO THE TEENS ACROSS LOWER
ELEVATIONS. OVERNIGHT RECOVERY WILL BE GOOD. WINDS WILL BE
UNSEASONABLY LIGHT WITH OCCASIONAL AFTERNOON BREEZINESS IN UPSLOPE
AREAS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX

DISCUSSION...AJ
PREVIOUS DISCUSSION...NOLTE
AVIATION...HIRSCH
FIRE WEATHER...MO






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