110
FXUS65 KPSR 262021
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
120 PM MST FRI DEC 26 2025
KEY MESSAGES
- A WEAK WEATHER DISTURBANCE WILL MOVE ACROSS THE REGION LATE THIS
WEEK RESULTING IN A FEW HIGHER TERRAIN SHOWERS AND TEMPERATURES
SETTLING CLOSER TO THE SEASONAL NORMAL.
- DRY WEATHER WITH LOCALLY BREEZY CONDITIONS WILL RETURN DURING THE
FIRST HALF OF NEXT WEEK BEFORE RAIN CHANCES RETURN BY NEXT WEDNESDAY
AND THURSDAY.
SHORT TERM /TODAY THROUGH SUNDAY/
ELONGATED TROUGHING ALONG THE WEST COAST OF NORTH AMERICA WILL
GRADUALLY PROGRESS INLAND, WHILE SIGNIFICANTLY WEAKENING AND
OBTAINING A POSITIVE TILT ORIENTATION OVER THE NEXT 48 HOURS.
SHALLOW MOISTURE OVER SOUTH-CENTRAL ARIZONA REMAINS ABUNDANT WITH
SFC-H8 MIXING RATIOS NEAR 9 G/KG, ALBEIT WITH A SUBSTANTIAL DRY
LAYER AROUND H7. MODELING CONTINUES IN GOOD AGREEMENT BRINGING A
DECAYING FRONT INLAND AHEAD OF THIS TROUGH AND COLD CORE LATER
TONIGHT, ALBEIT ACCOMPANIED WITH LIMITED ASCENT STRUCTURE, AND PER
FORECAST SOUNDINGS INCOMPLETE TOP DOWN SATURATION. HOWEVER, DEEP SW
FLOW SHOULD PROMOTE A PERIOD OF MOIST, OROGRAPHIC LIFT WITH MINOR
RAINFALL ACCUMULATIONS PRIMARILY FOCUSED OVER FOOTHILLS AND
MOUNTAINS NORTH AND EAST OF PHOENIX. WHILE NOT PRECLUDING A BRIEF
SHOWER ACROSS LOWER ELEVATION COMMUNITIES THROUGH SATURDAY MORNING,
THE PREPONDERANCE OF GUIDANCE SUGGESTS AT MOST 10-15% CHANCE OF
ACCUMULATING RAINFALL OUTSIDE OF PREFERRED UPSLOPE AREAS.
AS THE TROUGH AXIS SHIFTS THROUGH THE FORECAST AREA OVER THE WEEKEND
AND H5 HEIGHTS DESCEND INTO A 564-568DM RANGE, TEMPERATURES
THROUGHOUT MUCH OF THE LOWER/MIDDLE TROPOSPHERE WILL COOL MARKEDLY
WITH SFC READINGS FALLING CLOSER TO THE DAILY NORMALS. ENSEMBLE
GUIDANCE SPREAD IS SOMEWHAT LARGER THAN WOULD BE ANTICIPATED WITH
OFFICIAL NBM OUTPUT FALLING TOWARDS THE LOWER END (25TH PERCENTILE)
OF THE GUIDANCE ENVELOP. WITH SUBSIDENCE AND A DIRER AIRMASS
FILTERING INTO THE REGION, THIS MAKE SENSE WITH RESPECT TO LOW
TEMPERATURES, HOWEVER FORECAST BUFR SOUNDINGS SUGGEST ANY PROLONGED
PERIOD OF AFTERNOON INSOLATION COULD FORCE HIGHS A FEW DEGREES ABOVE
THE MANDATED NBM FORECAST. OTHERWISE, BUILDING HIGH PRESSURE NORTH
OF THE CWA WILL PROMOTE INCREASING NORTHERLY WINDS SUNDAY AFTERNOON
WITH THE INITIAL PUSH OF STRONGER GUSTS FUNNELING DOWN THE LOWER
COLORADO RIVER VALLEY (TYPICAL FOR THIS TIME OF YEAR), BUT JUST
SHORT OF ADVISORY CRITERIA.
LONG TERM /MONDAY THROUGH FRIDAY/
ONCE THE TROUGH EXITS INTO NEW MEXICO SUNDAY, SHARP UPSTREAM RIDGING
WILL CONTINUE TO PROMOTE STRONG SFC PRESSURE RISES OVER THE GREAT
BASIN RESULTING IN VERY DRY NORTHERLY FLOW SWEEPING THROUGH THE
REGION. SURFACE DEW POINTS PLUNGING INTO THE TEENS AND 20S (AND
POSSIBLY LOWER) WILL BE COMMON BY SUNDAY NIGHT WITH A STRONG
PRESSURE GRADIENT TRANSLATING EASTWARD INTO ARIZONA. BREEZY
CONDITIONS SHOULD EXPAND ACROSS RIDGE TOPS NORTH AND EAST OF PHOENIX
MONDAY MORNING WITH SHELTERED VALLEY LOCATIONS POTENTIALLY
EXPERIENCING READINGS FLIRTING WITH FREEZING. THIS OUTCOME WOULD BE
MOST LIKELY IN RURAL, LOWER DESERT AREAS OF LA PAZ AND MARICOPA
COUNTIES (I.E. SALOME, BOUSE, ETC.) WHERE LOWS FALLING BELOW
FREEZING COULD OCCUR FOR THE FIRST TIME THIS WINTER. UNCERTAINTY
WITH RESPECT TO IMPACTS OF WINDS MIXING THE BOUNDARY LAYER EVEN IN
VALLEYS, ALONG WITH FORECAST READINGS ONLY MARGINALLY BELOW FREEZING
PER NBM OUTPUT PRECLUDES A WATCH ISSUANCE AT THIS TIME, HOWEVER AT
LEAST LOCAL MINOR FREEZE ISSUES WILL NEED TO BE MONITORED.
THE WEATHER PATTERN IS LIKELY TO GET COMPLICATED MID/LATE NEXT WEEK
AS GUIDANCE IS STILL DEPICTING A CUTOFF LOW LURKING WELL WEST OF THE
BAJA PENINSULA. AN ELONGATED RIDGE IS ALSO EXPECTED TO SET UP ACROSS
CALIFORNIA THROUGH THE GREAT BASIN AND SOUTHWEST BY TUESDAY, FORMING
A TEMPORARY EAST PACIFIC REX BLOCK. THIS RIDGE SHOULD BOOST
TEMPERATURES SLIGHTLY MIDWEEK, BUT EVENTUALLY GUIDANCE SHOWS A
STRONG MOISTURE PUSH AHEAD OF THE CUTOFF LOW BY LATE WEDNESDAY INTO
THURSDAY. DEPENDING ON THE AMOUNT OF MOISTURE, UPPER LEVEL JET
FORCING, AND THE POSITIONING OF THE CUTOFF LOW, WE MAY SEE RAIN
CHANCES ENTER THE PICTURE AS EARLY AS WEDNESDAY LATE AFTERNOON, BUT
MORE LIKELY THURSDAY INTO FRIDAY. UNCERTAINTY REMAINS VERY HIGH WITH
THE EVOLUTION OF THIS NEXT WEATHER SYSTEM AND OVERALL FLOW PATTERN
GIVEN MASSIVE NORTH ATLANTIC BLOCKING AND MODEL DIFFERENCES IN
RECTIFYING THE UPSTREAM RESPONSE.
AVIATION
UPDATED AT 1740Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
NO MAJOR AVIATION CONCERNS ARE EXPECTED THROUGH THE TAF PERIOD.
WINDS WILL BE AOB 5-10KTS AND WILL MAINTAIN AN EASTERLY COMPONENT
THROUGH THE LATE MORNING HOURS BEFORE RESUMING TYPICAL DIURNAL
TRENDS THIS AFTERNOON. HOWEVER, BEFORE THE WESTERLY SHIFT THIS
AFTERNOON FULLY DEVELOPS A SOUTHERLY COMPONENT CAN BE EXPECTED
DURING THE TRANSITION PERIOD. EXPECT MOSTLY SCT TO BKN MID TO HIGH
LEVEL CLOUDS THIS AFTERNOON AND EVENING WHICH WILL PROGRESSIVELY
THICKENING TO OVC WITH CEILINGS DROPPING TO AOB 7-10 KFT BY THE END
OF THE TAF PERIOD.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO MAJOR AVIATION CONCERN ARE EXPECTED THROUGH THE TAF PERIOD.
MOSTLY HIGH LEVEL CLOUDS WITH SOME MID LEVEL CLOUDS EXPECTED TO
ENTER THE AREA BY THIS AFTERNOON. WINDS AT KIPL WILL MAINTAIN A
WESTERLY DIRECTION WITH SPEEDS AROUND 5-10 KTS AND KBLH WILL FAVOR A
SOUTHERLY TO SOUTHWESTERLY DIRECTION WITH SIMILAR SPEEDS.
FIRE WEATHER
A WEAKENING WEATHER SYSTEM WILL GRADUALLY SHIFT THROUGH THE REGION
THROUGH SATURDAY. THIS WILL BRING COOLER TEMPERATURES, ELEVATED
HUMIDITIES, AND ADDITIONAL CHANCES FOR LIGHT RAIN MAINLY OVER THE
HIGH TERRAIN OF THE EASTERN DISTRICTS TONIGHT INTO SATURDAY. MINRHS
WILL REMAIN AROUND 40-60% AREAWIDE THROUGH SATURDAY BEFORE LOWERING
TO CLOSE TO 20% STARTING SUNDAY. ANTICIPATE WINDS TO REMAIN FAIRLY
LIGHT AREAWIDE, GENERALLY 15 MPH OR LESS, THEN BREEZY CONDITIONS
ARRIVE SUNDAY INTO EARLY NEXT WEEK AS A DRY COLD FRONT IS LIKELY TO
SWEEP THE AREA FROM THE NORTH.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
SHORT TERM...18
LONG TERM...KUHLMAN/18
AVIATION...KUHLMAN/95
FIRE WEATHER...KUHLMAN
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