Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 311622
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
922 AM MST SAT JAN 31 2015

.SYNOPSIS...
RAIN SHOWER CHANCES WILL CONTINUE FOR MUCH OF THE DAY
TODAY...ESPECIALLY ACROSS SOUTH CENTRAL ARIZONA...BEFORE DIMINISHING
TONIGHT. TEMPERATURES WILL REMAIN ON THE COOL SIDE OVER THE CENTRAL
DESERTS...WARMING TO NEAR 70 ACROSS SOUTHEAST CALIFORNIA. A RETURN
TO DRY WEATHER AND A SLOW WARMING TREND WILL BEGIN SUNDAY AND
CONTINUE THROUGH THE END OF THE NEXT WORK WEEK.

&&

.DISCUSSION...
A RATHER COMPLEX WEATHER SCENARIO CURRENTLY ACROSS THE DESERT
SOUTHWEST INVOLVING THE LARGESCALE UPPER LEVEL LOW AND MULTIPLE VORT
MAXES WITHIN THE UPPER LEVEL TROUGH. THE TWO MOST SIGNIFICANT VORT
MAXES ARE SITUATED OVER SOUTHERN NEVADA AND ANOTHER OVER THE
NORTHERN GULF OF CALIFORNIA. THE SOUTHERN ONE IS LOCATED IN THE
BETTER VERTICAL ASCENT AREA AND IS PROVIDING A GOOD AMOUNT OF
ENHANCED LIFT TO KEEP AN AREA OF RAIN GOING ACROSS SOUTHERN ARIZONA.
CURRENT RADAR RETURNS SHOW SHOWERS MAINLY FROM GILA BEND INTO
SOUTHERN MARICOPA COUNTY WITH SLOW NORTHWARD MOVEMENT. VERY MOIST
BOUNDARY LAYER CONDITIONS AND CALM TO LIGHT WINDS HAS ALLOWED FOR
SOME PATCHY DENSE FOG FORMATION ACROSS NORTHERN PINAL COUNTY
PROMPTING A DENSE FOG ADVISORY THROUGH 18Z.

THE MAIN IMPACT TODAY WILL BE THE SHOWERS ON THE NORTHERN PERIPHERY
OF THE VORT MAX SITUATED TO OUR SOUTH...HOW FAR NORTH THESE SHOWERS
WILL MAKE IT AND HOW MUCH THEY WILL AFFECT THE PHOENIX METRO AREA.
LATEST 12Z MODEL GUIDANCE SHOWS THIS AREA OF RAIN MAKING INTO AT
LEAST THE SOUTHERN PHOENIX AREA AND POSSIBLY INTO CENTRAL PHOENIX BY
NOON. HOWEVER...THE OVERALL MOVEMENT OF THE VORT MAX IS TO THE
SOUTHEAST AND EVENTUALLY THE NORTHERN FRINGE OF THE SHOWERS STILL
STOP ITS NORTHWARD PROGRESSION AND THEN PIVOT BACK TO THE SOUTHEAST
THIS AFTERNOON. WE ALSO CAN EXPECT SOME ISOLATED TO SCATTERED
INSTABILITY SHOWER DEVELOPMENT DURING THE AFTERNOON HOURS MAINLY
FROM PHOENIX EASTWARD. WE COULD SEE A FEW THUNDERSTORMS...BUT DUE TO
VERY LITTLE INSTABILITY...THE POTENTIAL FOR THUNDERSTORMS WILL
REMAIN LIMITED UNLESS WE SEE ENOUGH BREAKS IN THE CLOUDS WHICH IS
UNLIKELY. HAVE ADJUSTED POPS THROUGH THIS EVENING TO LOWER CHANCES
ACROSS SOUTHWEST ARIZONA AND TO INCREASE CHANCES TO THE SOUTH AND
EAST OF PHOENIX.

WILL LOOK AT THE POTENTIAL FOR FOG OVERNIGHT TONIGHT AND EARLY
SUNDAY AND LIKELY ADD IN SOME AREAS OF DENSE FOG ACROSS NORTHERN
PINAL COUNTY AS CONDITIONS WILL BE VERY SIMILAR TO THAT OF THIS
MORNINGS.

&&

.PREVIOUS DISCUSSION...
A DEEP AND WET UPPER LEVEL LOW PRESSURE SYSTEM REMAINED SITUATED
ACROSS THE DESERT SOUTHWEST AS WELL AS NRN BAJA/NWRN MEXICO EARLY
THIS MORNING. MAIN UPPER LOW CENTER APPEARED TO BE SPINNING OVER FAR
SRN NEVADA...AS SEEN IN THE LATEST VAPOR IMAGERY...WHILE AT THE SAME
TIME A SERIES OF VORT LOBES/DISTURBANCES ROTATED AROUND THE MAIN LOW
MAINLY SKIRTING THE SRN CA COAST AND MOVING INTO NRN BAJA AND FAR
SRN AZ. RADAR AT 2 AM SHOWED SCATTERED TO NUMEROUS SHOWERS MOVING
NORTHEASTWARD ACROSS CENTRAL AND SERN AZ...WITH MUCH LESS ECHO
PRESENT OVER THE WESTERN DESERTS AND OVER SERN CA. AIRMASS IS VERY
MOIST ACROSS THE LOWER DESERT WITH PWAT VALUES RUNNING AROUND 1
INCH. HOWEVER...IT IS NOT PARTICULARLY UNSTABLE...AS H5 TEMPS ARE ON
THE WARM SIDE RUNNING AROUND MINUS 15-16C PER THE LATEST PLOT DATA.
A FEW LIGHTNING STRIKES HAVE BEEN SEEN OVERNIGHT...BUT MAINLY TO THE
SOUTH OF ARIZONA.

AS THE DAY PROGRESSES...PROGS CONTINUE TO CALL FOR THE MAIN LOW TO
START SHIFTING OFF TO THE SOUTHEAST...AND MOST OF THE VORT LOBES OR
DISTURBANCES WILL MOSTLY SKIRT BY TO OUR SOUTH AS THE LOW MOVES
ALONG. THE MAIN UPPER JET HAS ALREADY MOVED EAST OF OUR AREA AND
WINDS ALOFT WILL BECOME QUITE LIGHT FOR THE REST OF THE DAY. AS
DYNAMICS CONTINUE TO TAPER OFF...BUT MOISTURE REMAINS VERY HIGH...WE
WILL BE PRIMED FOR CONTINUED INSTABILITY SHOWERS ACROSS THE
DESERTS...MOST NUMEROUS ACROSS SOUTH CENTRAL ARIZONA. POPS WILL
REMAIN IN THE CHANCE TO LIKELY CATEGORY EAST OF THE LOWER CO RIVER
VALLEY FOR MOST OF THE DAY...WITH THE HIGHEST VALUES OVER SRN GILA
COUNTY. DO NOT EXPECT MUCH IN TERMS OF QPF TODAY...MOST NEW RAINFALL
TOTALS SHOULD STAY LESS THAN ONE QUARTER OF AN INCH. WE WILL STILL
CALL FOR A SLIGHT CHANCE OF MAINLY AFTERNOON THUNDERSTORMS OVER THE
CENTRAL DESERTS...AND SHOULD A STORM DEVELOP...RAINFALL TOTALS COULD
QUICKLY APPROACH ONE HALF INCH OVER SMALL AREAS. TEMPS TODAY WILL
STAY WELL BELOW SEASONAL NORMALS GIVEN THE CLOUDY MOIST
ATMOSPHERE...AND WE SHOULD SEE HIGHS IN THE GREATER PHOENIX AREA
HOVER IN THE LOW TO MID 60S FOR THE MOST PART.

OVERNIGHT TONIGHT...THE LOW WILL CONTINUE TO PUSH OFF TO THE
SOUTHEAST...AND AS SUCH A DRIER AND MORE SUBSIDENT NORTHEAST FLOW
ALOFT WILL SPREAD INTO THE AREA. WE CAN EXPECT A LINGERING SLIGHT
CHANCE FOR MAINLY EVENING SHOWERS OVER THE CENTRAL DESERTS...WITH
LOW END CHANCES ACROSS SRN GILA COUNTY...AND BY SUNDAY MORNING THERE
WILL BE JUST SOME LINGERING LOW/MID CLOUDINESS ACROSS SOUTH CENTRAL
AZ INCLUDING THE GREATER PHOENIX AREA. PATCHY FOG IS LIKELY EAST OF
THE LOWER CO RIVER VALLEY SUNDAY MORNING...AND WILL BE MENTIONED IN
THE FORECAST PACKAGE...BUT LINGERING CLOUDS WILL LIMIT THE AMOUNT OF
RADIATIONAL COOLING AND REDUCE THE DENSITY AND COVERAGE OF FOG THAT
DOES DEVELOP. OTHERWISE EXPECT PARTLY TO MOSTLY SUNNY SKIES DURING
THE DAY SUNDAY ALONG WITH SOMEWHAT WARMER HIGH TEMPS. LOOK FOR
CENTRAL DESERT HIGHS CLIMBING INTO THE MID TO UPPER 60S ON
SUNDAY...REACHING TO NEAR SEASONAL NORMALS.

MONDAY THROUGH FRIDAY...
THE RIDGE SLOWLY BUILDS INTO THE WEST MONDAY THROUGH FRIDAY FOR A
GRADUAL WARMING TREND...AND WE CAN EXPECT DESERT HIGHS TO REACH BACK
INTO THE LOW TO MID 70S BY NEXT WEDNESDAY...WITH THE WARMER WESTERN
DESERTS RISING TO NEAR 80 BY NEXT THURSDAY...WITH LITTLE CHANGE ON
FRIDAY.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL...SCATTERED
SHOWERS HAVE BEEN ERODING AS THEY MOVE INTO SW MARICOPA COUNTY
APPROACHING THE PHOENIX METROPOLITAN AREA. CEILINGS HAVE BEEN
EXTREMELY VARIABLE WITH BASES GENERALLY RANGING FROM 2500 TO 7KFT.
SATELLITE SHOWS ADDITIONAL SHORT-WAVES UP-STREAM AND MODELS INDICATE
ADDITIONAL THREAT OF SHOWERS SATURDAY MORNING THROUGH AFTERNOON.
THIS WILL KEEP LOW VFR MVFR CEILINGS IN THE AREA FOR MUCH OF TODAY.
TIMING OF THE SHOWERS IS DIFFICULT TO PIN DOWN SO HAVE ELECTED TO
ONLY INCLUDE VCNTY WORDING AT THIS TIME. THERE IS A CHANCE
VISIBILITIES WILL RESTRICT AT TIMES BELOW 6SM WITH FOG...THOUGH
EXPECT THIS TO BE TEMPORARY AND PREVAILING VSBY MOST OF THE FORECAST
PERIOD TO BE GREATER THAN 6SM. WINDS BE LIGHT AND VARIABLE THIS
MORNING...BECOMING MORE WESTERLY BY AFTERNOON.

AN ISOLATED THUNDERSTORM COULD DEVELOP THIS AFTERNOON...THOUGH
CONFIDENCE IS NOT HIGH ENOUGH TO WARRANT INCLUSION IN TAFS.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
CEILINGS WILL RANGE FROM 5 TO 7 KFT THROUGH EARLY EVENING AND THEN
SKIES WILL BEGIN SCATTERING OVERNIGHT. SHOWERS FOR THE MOST PART
SHOULD REMAIN EAST OF THE COLORADO RIVER...THOUGH SOME SHOWER
ACTIVITY COULD DEVELOP IN THE VCNTY OF KBLH THROUGH 18Z. WINDS WILL
BEGIN VEERING FROM THE SOUTHWEST TO THE NORTH THROUGH THE DAY...WITH
GUSTS UP TO 18 KTS POSSIBLE AT KBLH THIS AFTERNOON.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
DRIER AND SIGNIFICANTLY WARMER WEATHER IS EXPECTED...AS HIGH
PRESSURE BEGINS BUILDING BACK INTO THE REGION. HIGH TEMPERATURES IN
THE LOWER DESERTS WILL START OUT NEAR 70 ON MONDAY AND GRADUALLY
CLIMB TO AROUND 80 BY FRIDAY. LOW LEVEL MOISTURE WILL GRADUALLY
DECREASE THROUGH THE PERIOD...WITH MINIMUM AFTERNOON HUMIDITIES
DECREASING TO AROUND 25 PERCENT BY FRIDAY. WINDS ARE EXPECTED TO BE
LIGHT AND VARIABLE FOR MOST OF THE FORECAST PERIOD.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...KUHLMAN
PREVIOUS DISCUSSION...CB
AVIATION...MCLANE
FIRE WEATHER...MCLANE















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