Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 312113
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
213 PM MST SAT JAN 31 2015

.SYNOPSIS...
AN EXITING LOW PRESSURE SYSTEM WILL BRING LINGERING RAIN CHANCES
INTO EARLY TONIGHT TO THE EAST AND SOUTHWEST OF THE PHOENIX AREA.
AREAS OF FOG...POTENTIALLY DENSE ACROSS NORTHERN PINAL
COUNTY...WILL BE POSSIBLE LATE TONIGHT THROUGH SUNDAY MID MORNING
DUE TO ABUNDANT LOW LEVEL MOISTURE AND CLEARING SKIES. HIGH PRESSURE
WILL QUICKLY PUSH IN STARTING SUNDAY BRINGING CLEARING
SKIES...DRYING CONDITIONS...AND WARMER TEMPERATURES. THE DRY
CONDITIONS WILL PERSIST THROUGH THE NEXT WEEK WHILE A SLOW WARMING
TREND ALLOWS FOR HIGHS REACHING NEAR 80 ACROSS THE LOWER DESERTS BY
NEXT FRIDAY.

&&

.DISCUSSION...
THE LATEST SATELLITE AND UPPER HEIGHT ANALYSIS SHOWS THE UPPER
TROUGH STARTING TO PICK UP SOME SPEED MOVING TO THE SOUTHEAST. TWO
DISTINCT CIRCULATION CENTERS CONTINUE TO BE EVIDENT ON WATER VAPOR
IMAGERY...ONE THAT IS QUICKLY WEAKENING AS IT MOVES INTO SOUTHERN
CALIFORNIA AND ANOTHER WELL SOUTH OF THE AREA...CENTERED NEAR
29.7N/114.2W. THE SOUTHERN VORTICITY MAX IS STILL HELPING TO BRING
SCATTERED SHOWERS ACROSS SOUTHEAST AND SOUTH-CENTRAL ARIZONA...WHILE
A FEW MESO-VORTICIES CAN BE SEEN WITHIN RADAR IMAGERY...ONE OVER
SOUTHERN MARICOPA COUNTY AND TWO OTHERS OVER SOUTHERN PINAL COUNTY.
AREAS OF SHOWERS...SOME PRODUCING MODERATE RAIN AT TIMES...ARE
FOCUSED NEAR THESE MESO-VORTICIES...WHILE MORE WIDELY ISOLATED
SHOWERS HAVE BEEN MOVING WESTWARD ACROSS NORTHWEST MARICOPA COUNTY
IN AN AREA OF SLIGHT ENHANCED INSTABILITY FROM SOME PEAKS OF SUN.
THE LATEST HRRR AND WRF4KM HI-RES DATA SHOWS SHOWERS LASTING THROUGH
MID AFTERNOON BEFORE GRADUALLY DIMINISHING BY EARLY EVENING. THIS
SEEMS LIKE A VERY REASONABLE SOLUTION AS THE LARGE SCALE TROUGH
CONTINUES TO DRIFT SOUTHEASTWARD OUT OF THE AREA AND WE SHOULD SEE
ANY OVERLAYING LARGE SCALE ASCENT MOVE OUT OF THE CWA.

ONCE SHOWERS END SOMETIME THIS EVENING...FOCUS THEN TURNS TOWARD THE
POTENTIAL FOR FOG TONIGHT AND SUNDAY MORNING. THE SETUP FOR FOG IS
NOT QUITE IDEAL AS WE SHOULD HAVE SOME LINGERING LOW STRATUS HANGING
AROUND THROUGH FOR THE FIRST OF TONIGHT. HOWEVER...VERY MOIST
SURFACE CONDITIONS WITH SURFACE DEW POINTS IN THE LOW TO MID 50S AND
LIGHT WINDS SHOULD DEFINITELY ALLOW FOR SOME FOG FORMATION ACROSS
THE AREA BY 12Z SUNDAY. MODEL RH FIELDS SHOW DRY AIR WORKING IN
ALOFT FROM THE NORTH AFTER MIDNIGHT...BUT BOUNDARY LAYER CONDITIONS
WILL REMAIN MOIST THROUGH SUNDAY AND POTENTIALLY MONDAY MORNING. THE
POTENTIAL FOR WIDESPREAD FOG AND ANY DENSE FOG WILL MOSTLY RELY ON
HOW MUCH CLEARING HAPPENS TONIGHT. CONFIDENCE IS HIGH THAT WE WILL
SEE FOG IN AT LEAST LOW LYING AND RURAL AREAS ACROSS MARICOPA AND
ESPECIALLY PINAL COUNTY...BUT STILL NOT VERY CONFIDENT ON THE EXTENT
OF ANY FOG IN THE PHOENIX METRO AREA AND FOR ANY DENSE FOG POTENTIAL.

SKIES WILL EVENTUALLY CLEAR OUT BY NOON SUNDAY IF THEY DIDN/T
ALREADY...AND WITH RIDGING AND DRYING ALOFT MOVING IN FROM THE
NORTH...WE WILL BEGIN TO SEE SOME WARMING. WE SHOULD SEE NEAR NORMAL
HIGHS FOR SUNDAY AND THEN A FEW MORE DEGREES FOR MONDAY. THE PACIFIC
RIDGE WILL STAY TO OUR WEST THROUGH THE MIDDLE OF THE WEEK GIVING US
500MB HEIGHTS GENERALLY BETWEEN 574-576DM...BUT MODELS THEN SHIFT
THE RIDGE OVERHEAD BY LATE IN THE WEEK POINTING AT HEIGHTS NEARING
580DM. THIS WILL TRANSLATE INTO A NICE WARM-UP WITH LOWER DESERT
HIGHS APPROACHING 80S DEGREES BY NEXT THURSDAY AND FRIDAY.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL...SCATTERED
SHOWERS CONTINUE TO ROTATE EASTWARD ACROSS THE GREATER PHX AREA AT
THIS HOUR...WITH HAVE RESULTED IN CIGS VARYING BETWEEN 3K FT AND 7
KT FT AT THE TERMINALS THIS AFTERNOON...WITH VISIBILITIES DROPPING
BRIEFLY DOWN TO AS LOW AS 5SM IN THE HEAVIER SHOWERS. THE LATEST
HI-RES MODEL RUNS ARE CONSISTENT WITH EARLIER RUNS...GRADUALLY
DIMINISHING THIS SHOWER ACTIVITY THROUGH THE REMAINDER OF THE
AFTERNOON AND EARLY EVENING AS THE UPPER LOW CONTINUES TO SLIDE TO
THE SOUTH...AND AWAY FROM OUR REGION...WITH SHOWER ACTIVITY PRETTY
MUCH ENDING AROUND/SHORTLY AFTER SUNSET. MID-LEVEL CLOUD LAYERS ARE
THEN EXPECTED TO PERSIST THROUGH MUCH OF TONIGHT. FOG COULD BE A
PROBLEM BY MORNING DUE TO A COMBINATION OF LIGHT WINDS AND AMPLE
LOW-LEVEL MOISTURE. HOWEVER...THE AFOREMENTIONED MID-LEVEL
CLOUDINESS WILL,LIKELY KEEP OVERNIGHT LOW TEMPS UP A BIT...WHICH
SHOULD KEEP ANY FOG THAT ACTUALLY FORMS FROM BECOMING TOO DENSE.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
DRIER AIR MOVING INTO THE REGION FROM THE NORTH IS EXPECTED TO ALLOW
SKIES TO CLEAR AT BOTH TERMINALS THROUGH THE EVENING AND OVERNIGHT
HOURS...WITH MAINLY CLEAR SKIES EXPECTED ON SUNDAY. NORTHERLY TO
NORTHWESTERLY WINDS ARE EXPECTED AT BOTH TERMINALS THROUGH THE TAF
PERIOD...GRADUALLY DIMINISHING AS THE SFC PRESSURE GRADIENT RELAXES.

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
AVIATION...PERCHA
FIRE WEATHER...MCLANE


















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