Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 192111
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
210 PM MST SAT APR 19 2014

.SYNOPSIS...
A PACIFIC LOW PRESSURE SYSTEM MOVING EAST ACROSS ARIZONA WILL LEAD
TO A LINGERING SLIGHT CHANCE OF SHOWERS OR THUNDERSTORMS ACROSS
SOUTH CENTRAL ARIZONA THIS EVENING. HIGH PRESSURE ALOFT WILL BUILD
INTO THE AREA SUNDAY INTO EARLY NEXT WEEK BEHIND THE EXITING
LOW...AND LEAD TO SUNNY DAYS AND CLEAR NIGHTS ALONG WITH SHARPLY
WARMING HIGH TEMPERATURES. BREEZY TO WINDY CONDITIONS ARE EXPECTED
NEXT TUESDAY INTO WEDNESDAY AS A DRY WEATHER SYSTEM PASSES BY TO OUR
NORTH. THE PASSING SYSTEM WILL LEAD TO COOLER WEATHER...WITH HIGH
TEMPERATURES FALLING TO NEAR SEASONAL NORMALS ON WEDNESDAY. HIGHER
PRESSURE WILL RETURN FOR THE LATTER PART OF THE NEXT WORK WEEK...
BRINGING ANOTHER WARMING TREND AND GENERALLY SUNNY SKIES.

&&

.DISCUSSION...
UPPER LEVEL PACIFIC LOW CONTINUED TO PUSH EASTWARD ACROSS THE DESERT
SOUTHWEST EARLY THIS AFTERNOON WITH THE MAIN LOW CENTER SHIFTED INTO
FAR SOUTH CENTRAL ARIZONA. MOST OF THE DYNAMICS/Q FORCING HAS
SHIFTED INTO FAR EASTERN OR SOUTHEAST ARIZONA...TO THE SOUTHEAST OF
OUR CWA...AND THE ASSOCIATED CONVECTION HAS SHIFTED SOUTHEAST OF OUR
AREA AS WELL. ONE OF THE MAIN VORT MAXES ROTATING THRU THE BASE OF
THE TROF...AND CLEARLY SEEN IN THE VAPOR IMAGERY...WAS TREKKING
ALONG THE SRN AZ/MEXICAN BORDER EARLY THIS EVENING...AND THE PVA
INDUCED CONVECTION AHEAD OF IT WAS PUSHING THRU FAR SERN AZ...WELL
SOUTHEAST OF THE GREATER PHOENIX AREA.

OTHERWISE...IR IMAGERY INDICATED PARTLY CLOUDY SKIES ACROSS MUCH OF
THE THE CWA...AS THE COLD AIR ALOFT MOVING OVER THE DESERTS HELPED
GENERATE VARIABLE AMOUNTS OF CU ALONG WITH A FEW INSTABILITY
SHOWERS. MADE A ZONE UPDATE FOR THIS AFTERNOON TO INCLUDE SLIGHT
CHANCES OF SHOWERS AND THUNDERSTORMS ACROSS THE SOUTHWEST DESERTS OF
ARIZONA...BASED ON INCREASING ECHO ON RADAR AS WELL AS INCREASING
AND THICKENING INSTABILITY CUMULUS. FOR LATER THIS AFTERNOON AND
INTO THE EVENING HOURS...THE LOW WILL CONTINUE TO SHIFT EAST
ALLOWING DRIER AND MORE SUBSIDENT AIR TO OVERSPREAD THE LOWER
DESERTS. THERE WILL BE A LINGERING SLIGHT CHANCE OF SHOWERS OR
THUNDERSTORMS FROM THE GREATER PHOENIX AREA EASTWARD...WITH THE BEST
THREAT FOR ANY CONVECTION OVER HIGHER TERRAIN AREAS WELL TO THE EAST
OF PHOENIX...AND MAINLY EAST OF GLOBE. BY MIDNIGHT EXPECT MOST OF
THE CONVECTION TO HAVE ENDED...AND SKIES ACROSS MOST OF THE CWA TO
BECOME MOSTLY CLEAR.

FOR SUNDAY...TROF AXIS WILL SHIFT INTO NEW MEXICO...AND HIGH
PRESSURE ALOFT WILL BUILD INTO THE DESERTS FROM THE WEST. THERE WILL
BE A BIT OF LINGERING MOISTURE AND INSTABILITY OVER THE HIGHER
TERRAIN EAST OF PHOENIX...AND AS SUCH WE WILL KEEP AROUND A 10
PERCENT CHANCE OF INSTABILITY STORMS GOING EAST OF GLOBE DURING THE
AFTERNOON HOURS. OTHERWISE EXPECT MOSTLY SUNNY SKIES ALONG WITH
WARMING HIGH TEMPERATURES. HIGH TEMPS WILL RISE SEVERAL DEGREES AND
INTO THE LOW TO MID 90S ACROSS THE WARMEST LOWER DESERTS. HIGH
PRESSURE ALOFT WILL BUILD FURTHER ON MONDAY...LEADING TO SOME
ADDITIONAL WARMING UNDER GENERALLY SUNNY SKIES.

FOR TUESDAY INTO WEDNESDAY...BOTH THE GFS AND ECMWF CONTINUE TO CALL
FOR A RATHER VIGOROUS PACIFIC UPPER TROF TO MOVE EAST THROUGH THE
DESERT SOUTHWEST...BRINGING CONSIDERABLE WIND TO THE AREA TUESDAY
AFTERNOON AND EVENING...AND LEADING TO SOME CONCERNS REGARDING
POTENTIAL FOR DANGEROUS FIRE WEATHER CONDITIONS. TOO EARLY AT THIS
TIME TO ISSUE A FIRE WEATHER WATCH...BUT THIS MAY BE NEEDED SOMETIME
IN THE NEXT DAY OR SO SHOULD CONFIDENCE IN THE EVENT CONTINUE TO
CLIMB. OTHERWISE THIS WILL BE A TYPICAL APRIL SYSTEM FOR OUR
CWA...BRINGING WIND AND COOLING AND NO PRECIP. IT APPEARS TO BE A
VERY DRY SYSTEM AND SKIES SHOULD BE MOSTLY SUNNY FOR THE MOST PART
BOTH DAYS. DESPITE THE WIND POTENTIAL...THIS TROF WILL LIKELY PASS
TO FAR TO OUR NORTH TO BRING SIGNIFICANT COOLING...AND HIGH TEMPS
ARE FORECAST TO DROP BACK TO NEAR SEASONAL NORMALS ON
WEDNESDAY...WITH THE WARMER DESERTS FALLING INTO THE MID TO UPPER
80S. FLAT UPPER RIDGING...AND DRY WESTERLY FLOW ALOFT...WILL FOLLOW
ON THURSDAY FOR MOSTLY SUNNY SKIES AND A BIT OF WARMING WITH THE
WARMER DESERTS CLIMBING BACK INTO THE LOWER 90S.

OPERATIONAL AND ENSEMBLE MODEL SPREAD IS SOMEWHAT HIGHER THAN SEEN
RECENTLY FOR THE END OF NEXT WEEK...HOWEVER STILL REMAINS RELATIVELY
SMALL IN A SEASONAL SENSE. FLAT RIDGING AND/OR QUASI-ZONAL FLOW
SHOULD PREDOMINATE THE GENERAL PATTERN FOR THE MAJORITY OF TIME WITH
H5 HEIGHTS HOVERING NOT FAR FROM 576DM. THIS MODEL AVERAGE SOLUTION
FOR HEIGHTS ALOFT IS SLIGHTLY HIGHER THAN PREVIOUS MODEL
ITERATIONS...AND CONSEQUENTLY HAVE EDGED FORECAST HIGHS SLIGHTLY
WARMER TO JUST ABOVE CLIMATOLOGICAL LEVELS. THERE IS STILL NO
EVIDENCE SUPPORTING ANY PRECIPITATION MUCH OF NEXT WEEK...WITH ONLY
VERY LIMITED OPPORTUNITY POSSIBLY ARRIVING NEXT WEEKEND.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
A LOW PRESSURE SYSTEM WILL TRACK EAST ACROSS CENTRAL AZ THIS PERIOD.
EXPECT LIGHT WINDS AND SCATTERED CLOUD DECKS GENERALLY AOA 10KFT
WITH ISOLATED SHOWERS/THUNDERSTORMS THIS AFTERNOON MAINLY EAST OF
KPHX-KIWA-KSDL. THERE IS STILL THE POSSIBILITY OF STRONG GUSTY
ERRATIC WINDS POSSIBLE NEAR VIRGA SHAFTS AND STORMS. SKIES IMPROVE
AND CLEAR OUT LATER THIS EVENING AFTER 03Z AS LOW MOVES EAST.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
LIGHT WINDS AND FEW TO SCATTERED CLOUD DECKS AOA 12KFT EXPECTED
THROUGH THIS AFTERNOON. SKIES CLEAR OUT BY EARLY EVENING FOR MOSTLY
CLEAR SKIES THE REMAINDER OF THE TAF PERIOD.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
TUESDAY THROUGH SATURDAY...
WESTERLY FLOW ALOFT WILL BRING WARM AND DRY CONDITIONS FOR TUESDAY
WITH WELL ABOVE SEASONAL NORMAL HIGH TEMPERATURES. A COOLING TREND
ENSUES WEDNESDAY AND THURSDAY AS A LOW PRESSURE SYSTEM MOVES INTO
THE GREAT BASIN AND THE PACIFIC NORTHWEST. THE BIGGEST IMPACT WITH
THIS SYSTEM WILL BE AN INCREASE IN WIND AREA-WIDE TUESDAY INTO
WEDNESDAY...WITH GUSTS UP TO 35 MPH POSSIBLE...AND EVEN STRONGER
GUSTS EXPECTED ACROSS SOUTHEAST CALIFORNIA AND PORTIONS OF THE LOWER
COLORADO RIVER VALLEY. MINIMUM HUMIDITY LEVELS ALSO BOTTOM OUT IN
THE SINGLE DIGITS DURING THIS TIME FRAME OF STRONG
WINDS...PRESENTING AN INCREASED FIRE DANGER THREAT AND THE POSSIBLE
ISSUANCE OF RED FLAG WARNINGS IN SOME AREAS. LIGHT WINDS...WITH DRY
AND WARMER CONDITIONS ARE ON TAP THURSDAY THROUGH SATURDAY AS
HIGH PRESSURE ALOFT BUILDS BACK INTO THE AREA.


&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...CB/MO
AVIATION...MEYERS/KUHLMAN
FIRE WEATHER...MEYERS/KUHLMAN












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