046
FXUS65 KPSR 292015
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
115 PM MST MON DEC 29 2025
KEY MESSAGES
- HIGH PRESSURE WILL RESULT IN DRY AND LOCALLY BREEZY CONDITIONS
WITH TEMPERATURES SLIGHTLY ABOVE NORMAL THROUGH TUESDAY.
- AN UNSETTLED WEATHER REGIME MOVING INTO THE REGION DURING THE
MIDDLE AND LATTER HALF OF THE WEEK WILL LEAD TO PERIODS OF INCREASED
LIGHT RAIN CHANCES.
- DRIER WEATHER SHOULD RETURN DURING THE WEEKEND WITH TEMPERATURES
STILL HOVERING NEAR TO SLIGHTLY ABOVE NORMAL.
SHORT TERM /TODAY THROUGH WEDNESDAY/
A REX BLOCKING PATTERN HAS BECOME ESTABLISHED OVER THE EAST
PACIFIC/WESTERN CONUS WITH STRONG RIDGING FOLDING INTO THE PACIFIC
NW WHILE A DEEP CYCLONIC CIRCULATION SPINS WELL WEST OF THE BAJA
PENINSULA. MEANWHILE, WV IMAGERY DEPICTS A MORE SUBTLE VORTICTY
CENTER RETROGRADING THROUGH CENTRAL/SOUTHERN CALIFORNIA POISED TO
BECOME ABSORBED BY THE AFOREMENTIONED SOUTHERN GYRE, AND EVENTUALLY
PROVIDING THE IMPETUS FOR THIS SYSTEM TO EJECT INTO THE SW CONUS
LATER THIS WEEK. THE CURRENT PATTERN CONFIGURATION CONTINUES TO
PROMOTE STRONG SFC PRESSURE RISES FROM THE GREAT BASIN THROUGH HIGH
PLAINS IMPOSING MODESTLY STRONG E/NE H9-H7 WIND SPEEDS. AS A RESULT,
GUSTY WINDS WITH ENHANCED MIXING HAVE BEEN NOTED THROUGH THE LOWER
COLORADO RIVER VALLEY AND RIDGE TOPS OF SOUTH-CENTRAL ARIZONA. THIS
TIGHT PRESSURE GRADIENT WILL RESULT IN DEEPER THAN USUAL MIXING AND
TRANSLATION OF GUSTY WINDS TO LOWER ELEVATIONS, HOWEVER WILL WEAKEN
OVER THE NEXT 36 HOURS. OTHERWISE, FORECAST CONFIDENCE IS VERY GOOD
THAT TEMPERATURES 4F-8F ABOVE NORMAL WILL BE COMMON THE NEXT
SEVERAL DAYS.
ON WEDNESDAY, SHORTWAVE ENERGY WILL BEGIN PROPAGATING TOWARDS
SOUTHERN CALIFORNIA AS JET ENERGY SHIFTS TO THE EASTERN PERIPHERY OF
THE CUTOFF LOW COMPRISING THE REX BLOCK. WHILE THE NEGATIVE HEIGHT
ANOMALY WILL BE STEADY WEAKENING AS IT OPENS AND CRESTS OVER A
SHORTWAVE RIDGE, ROBUST SOUTHERLY FLOW WILL DEVELOP ACROSS NORTHERN
MEXICO EVENTUALLY SENDING MOISTURE NORTHWARD INTO ARIZONA WITH PWATS
QUICKLY RISING TO 250-300% OF NORMAL BY WEDNESDAY EVENING. UPPER
LEVEL MOISTURE (H7-H5 LAYER) WILL BE FIRST TO SPREAD INTO THE
SOUTHWEST CREATING CLOUDY SKIES AND A TOP DOWN SATURATION PROCESS.
HOWEVER, LOWER LEVEL MOISTURE AROUND THE H8 LAYER WILL SURGE ACROSS
THE INTERNATIONAL BORDER WITH NOTABLE THETA-E ADVECTION INCREASING
WEDNESDAY AFTERNOON. LARGER SYNOPTIC SCALE FORCING WILL INITIALLY BE
FAIRLY WEAK, AND THE GREATER FORECAST UNCERTAINTY LIES WITH THE
HASTE AT WHICH THESE TOP DOWN AND MOISTURE ADVECTIVE PROCESSES CAN
OVERCOME THE DRIER EASTERLY FLOW AND PROGRESS BEYOND JUST VIRGA AND
SPRINKLES INTO ACCUMULATING RAINFALL. MOST MODEL GUIDANCE INDICATES
THIS BEING ACCOMPLISHED VERY LATE AFTERNOON, THOUGH HISTORICALLY
THIS PROCESS CAN OCCUR FAR MORE ABRUPTLY. REGARDLESS, SHOWERS SHOULD
READILY BLOSSOM AND EXPAND THROUGH MUCH OF THE CWA BY EARLY
WEDNESDAY EVENING, ALBEIT WITH RAINFALL AMOUNTS LIKELY LIMITED, AND
POTENTIALLY BECOMING MORE TIED TO OROGRAPHIC INFLUENCES HEADING INTO
THE OVERNIGHT.
LONG TERM /THURSDAY THROUGH MONDAY/
THE MAIN FORECAST CONCERN FOR THE LATTER HALF OF THE WEEK WILL BE
THE EVOLUTION OF THIS DRAMATIC MOISTURE INCREASE AND ENHANCED RAIN
CHANCES FOLLOWED BY A DRYING TREND SOMETIME LATER IN THE WEEK. THE
PEAK OF THE COMBINED FORCED ASCENT AND MOISTURE ANOMALY SHOULD OCCUR
THURSDAY WITH PERIODIC RAIN CHANCES THROUGH MUCH OF THE DAY, AND
PARTICULARLY PRONOUNCED NORTH AND EAST OF PHOENIX. SHOWER CHANCES
SHOULD DIMINISH ACROSS THE WESTERN DESERTS BY THURSDAY EVENING, THEN
THROUGHOUT MUCH OF THE ARIZONA ZONES DURING THE OVERNIGHT HOURS.
RAINFALL AMOUNTS ARE STILL A BIT UNCERTAIN, BUT DUE TO THE OVERALL
WEAK FORCING MOST LOWER DESERT AREAS SHOULD STAY BETWEEN 0.01-0.25"
WHILE SOME ISOLATED AREAS AND THE MORE FAVORED UPSLOPE AREAS NORTH
AND EAST OF PHOENIX MAY RECEIVE 0.25-0.75". UPPER LEVEL RIDGING IS
FORECAST TO MOVE OVER THE REGION THURSDAY NIGHT INTO FRIDAY WITH
CONSIDERABLE DRYING OCCURRING ALOFT. SOME LINGERING LIGHT SHOWER
CHANCES MAY STICK AROUND INTO FRIDAY ACROSS THE EASTERN ARIZONA HIGH
TERRAIN, BUT THIS SHOULD RESULT IN LITTLE, IF ANY ADDITIONAL
ACCUMULATION.
GUIDANCE SHOWS ANOTHER UPPER LEVEL TROUGH APPROACHING THE WEST COAST
OF CALIFORNIA LATER ON FRIDAY, BUT THE CURRENT TRACK IS LIKELY TO
MOSTLY BYPASS THE FORECAST AREA WELL TO THE NORTHWEST OVER THE
WEEKEND. THE NBM IS STILL TRYING TO SUGGEST THIS MAY BRING ANOTHER
ROUND OF RAIN CHANCES, BUT THAT SEEMS TO BE A STRETCH, SO POPS HAVE
BEEN REDUCED SATURDAY AND SUNDAY. FORECAST HIGH TEMPERATURES ARE
EXPECTED TO DIP LATER THIS WEEK, BUT READINGS ARE LIKELY TO STAY 3-5
DEGREES ABOVE NORMAL MOST DAYS. OVERNIGHT TEMPERATURES WILL BECOME
QUITE MILD STARTING MIDWEEK WITH LOWS MOSTLY IN THE 50S DUE TO THE
THE CLOUDY SKIES.
AVIATION
UPDATED AT 1740Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
NO MAJOR AVIATION WEATHER CONCERNS EXPECTED THROUGH THE TAF PERIOD.
ELEVATED E/NE WINDS ARE EXPECTED THIS AFTERNOON, WITH GUSTS INTO THE
UPPER TEENS TO AROUND 20 KT EXPECTED. WINDS WILL RELAX SLIGHTLY
AFTER SUNSET, BUT REMAIN GENERALLY AOB 10 KT THROUGH THE REMAINDER
OF THE PERIOD. SCT HIGH CIRRUS CLOUDS ARE EXPECTED THROUGH THE
PERIOD.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO MAJOR AVIATION CONCERNS ARE EXPECTED THROUGH THE TAF PERIOD.
WINDS AT KBLH ARE EXPECTED TO MAINTAIN A NORTHERLY COMPONENT THROUGH
THE PERIOD, WITH SPEEDS GENERALLY AOB 10 KT, WITH SOME GUSTS UP
AROUND 20-25 KT THIS AFTERNOON. AT KIPL, NORTHERLY WINDS ARE
EXPECTED THROUGH THIS AFTERNOON, THEN THIS EVENING (~04Z) WINDS WILL
GO WESTERLY. SPEEDS AT KIPL, WILL GENERALLY BE AOB 8 KT THROUGH THE
PERIOD. INCREASING MID AND HIGH LEVEL CLOUDS ARE EXPECTED THROUGH
THE PERIOD.
FIRE WEATHER
DRY WEATHER WITH SLIGHTLY ABOVE NORMAL TEMPERATURES WILL BE SEEN
EARLY THIS WEEK WITH MINIMUM HUMIDITY LEVELS IN A 20-30% RANGE.
ENHANCED NORTH TO NORTHEAST WINDS WILL BE COMMON THROUGH TUESDAY,
PARTICULARLY ACROSS RIDGE TOPS OF EASTERN DISTRICTS WHERE GUSTS OF
20-30 MPH ARE EXPECTED TODAY. MOISTURE WILL BEGIN TO SEEP BACK INTO
THE REGION BY WEDNESDAY RAISING HUMIDITIES AND BRINGING RAIN CHANCES
LATE WEDNESDAY AND THURSDAY.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
SHORT TERM...18
LONG TERM...KUHLMAN/18
AVIATION...BERISLAVICH
FIRE WEATHER...KUHLMAN
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