795
FXUS65 KPSR 180530
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1030 PM MST SAT OCT 17 2026
UPDATE
06Z AVIATION DISCUSSION
KEY MESSAGES
- CHANCES FOR LIGHT RAIN WILL HEIGHTEN OVER ARIZONA THIS WEEKEND
WITH THE BEST CHANCES FOR ACCUMULATIONS FOCUSED OVER HIGHER TERRAIN
LOCATIONS.
- TEMPERATURES WILL GRADUALLY WARM CLOSER TO THE SEASONAL NORMAL
THROUGH THE MIDDLE OF NEXT WEEK.
- A PACIFIC LOW PRESSURE SYSTEM MOVING INTO THE SOUTHWEST DURING THE
MIDDLE AND END OF NEXT WEEK WILL RESULT IN MUCH BETTER RAINFALL
CHANCES WITH THE POSSIBILITY OF A FEW EMBEDDED THUNDERSTORMS, AS
WELL AS COOLER TEMPERATURES
SHORT TERM /TODAY THROUGH SUNDAY/
PRONOUNCED REX BLOCKING CURRENTLY OVER THE WESTERN CONUS WILL
TRANSITION INTO A MORE PROGRESSIVE PATTERN OVER THE NEXT 48 HOURS AS
STRONG JET ENERGY ENTERING THE EAST PACIFIC ACTS TO DEAMPLIFY THE
RIDGE AXIS WHILE ALSO FORCING THE ABSORPTION THE ASSOCIATED SOUTHERN
STREAM CUTOFF LOW INTO THE MEAN WESTERLY FLOW ALOFT. THE LATTER OF
THESE TWO PROCESSES WILL TAKE MUCH LONGER FOR COMPLETION RESULTING
IN A PROLONGED PERIOD OF SOUTHERLY MOIST ADVECTION THROUGH THE H7-H5
LAYER YIELDING TOTAL COLUMN PWATS IN EXCESS OF 1" ACROSS MUCH OF THE
CWA. THIS PATTERN CONFIGURATION WILL ALSO PLACE SOUTH-CENTRAL ARIZONA
WITHIN A FAVORABLE ASCENT POSITION IN RELATION TO AN UPPER LEVEL JET
STREAK ABLE TO TAP SOME OF THIS THICK MIDLEVEL MOISTURE. HOWEVER,
THE SFC-H8 LAYER REMAIN EXCEPTIONALLY DRY DUE TO PERSISTENT
DOWNSLOPING EASTERLY WINDS, AND THIS DEEP SUB-CLOUD DRY LAYER WILL
NEED TO BE AT LEAST PARTIALLY MOISTENED BEFORE MORE NOTABLE CHANCES
OF MEASURABLE RAIN CAN BE ACHIEVED. BASED ON THE SYNOPTIC ASCENT
STRUCTURE, A WEAKENING EASTERLY LOW LEVEL GRADIENT, AND TRENDS IN
REGIONAL WV IMAGERY, FEEL THIS EVOLUTION WILL BE MORE EFFECTIVE THAN
SUGGESTED BY BASE NBM POPS, AND HAVE BOOSTED THE CHANCES FOR LIGHT
ACCUMULATIONS THROUGH SUNDAY MORNING.
FORECAST UNCERTAINTY SUNDAY AFTERNOON AND EVENING IS GREATER THAN
USUAL FOR A 24-48 TIME FRAME WITH SOME MEASURE OF MIDLEVEL CYCLONIC
FLOW HOVERING OVER SOUTH-CENTRAL ARIZONA AS THE UPPER WAVE ONLY
SLOWLY GETS STRETCHED AND DEAMPLIFIES. MOISTURE SHOULD GRADUALLY
BECOME SCOURED FROM THE CLOUD LAYER AS WINDS VEER MORE
SOUTHWESTERLY, BUT THE PROCESS MAY BE MORE DELAYED WITH THE SLOW
TRANSITION. THUS, ITS NOT OUT OF THE QUESTION A FEW LIGHT SHOWERS
LINGER THROUGHOUT THE DAY, THOUGH BECOMING PRIMARILY FOCUSED IN
OROGRAPHICALLY FAVORED AREAS EAST OF PHOENIX. BY SUNDAY EVENING, THE
UPPER LOW WILL FINALLY BEGIN EJECTING INTO NORTHERN ARIZONA, BUT
EVEN SO, MOIST UPSLOPE THROUGH GILA COUNTY COULD STILL SUPPORT A
COUPLE ISOLATED LIGHT SHOWERS INTO MONDAY MORNING.
LONG TERM /MONDAY THROUGH FRIDAY/
BY EARLY NEXT WEEK, HIGH PRESSURE WILL BE WELL ESTABLISHED OVER NE
CONUS, WHILE THE AFOREMENTIONED WAVE BECOMES ABSORBED INTO THE MEAN
SW FLOW HEAD OF THE NEXT INCOMING LOW PRESSURE SYSTEM DIVING DOWN
THE WEST COAST. ANOTHER LOW CHANCE (20-30%) OF SHOWERS MAY BE
MANIFESTED MONDAY MORNING ACROSS THE HIGHER TERRAIN OF SOUTH-CENTRAL
ARIZONA , HOWEVER IF ANYTHING DOES DEVELOP, TOTAL ACCUMULATIONS ARE
EXPECTED TO BE MINIMAL. BY TUESDAY, DEEP TROUGHING AND STRONG
NEGATIVE HEIGHT ANOMALIES WILL AMPLIFY AND INTENSIFY ALONG THE WEST
COAST, HOWEVER CONFIDENCE IN THE TIMING AND DEPTH OF THIS FEATURE
REMAINS LOW TO MODERATE. THE DETERMINISTIC ECMWF FORECASTS A SLOWER
AND DEEPER SOLUTION YIELDING A MORE ROBUST RAINFALL SCENARIO, WHILE
THE GFS DETERMINISTIC PROVIDES A FASTER OUTCOME LIFTING THE COLD
CORE INTO SOUTHERN UTAH RESULTING IN A MORE TEMPERED RAINFALL
POTENTIAL. REGARDLESS, THE TIMING OF THE BEST RAINFALL POTENTIAL IS
HIGHLIGHTING THE WEDNESDAY AND THURSDAY TIME FRAME WHILE PATTERN
RECOGNITION AND SOME INSTABILITY PARAMETERS SUGGEST THE POTENTIAL FOR
STRONG THUNDERSTORMS AHEAD OF THE SHORTWAVE PASSAGE. ADDITIONALLY,
WITH THE UNCERTAINTY OF THIS NEXT SYSTEM, A WIDE SPREAD IN NBM
TEMPERATURES HAVE PRESENTED THEMSELVES THROUGHOUT THE WEEK, THOUGH
BELOW NORMAL HIGHS ARE MOST LIKELY.
AVIATION
UPDATED AT 0530Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
NO MAJOR AVIATION CONCERNS ARE EXPECTED DURING THE TAF PERIOD.
WINDS WILL CONTINUE TO FAVOR AN E'RLY COMPONENT THROUGH SUNDAY
EVENING, WITH PERHAPS SOME ISOLATED GUSTS DURING THE MID TO LATE
MORNING HOURS. KSDL WOULD BE MOST LIKELY TO SEE THESE OCCASIONAL
BREEZY CONDITIONS DUE TO THEIR PROXIMITY TO TERRAIN FEATURES. VCSH
WILL CONTINUE TO MOVE OVER THE REGION TONIGHT, BUT OUTSIDE OF
INSTANCES OF ERRATIC WINDS, OPERATIONAL IMPACTS FROM THIS ACTIVITY
ARE NOT ANTICIPATED. CURRENT TAFS HAVE SHRA EXITING THE METRO BY
14-15Z AT THE LATEST, BUT TIMING MAY NEED TO BE ADJUSTED IN
SUBSEQUENT AMENDMENTS IF DIFFERENT FORECAST TRENDS ARE REALIZED.
ABUNDANT CLOUD COVER WILL BE PRESENT THROUGH SUNDAY MORNING BUT
SHOULD BEGIN TO SCATTER OUT LATER IN THE FORECAST WINDOW.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO MAJOR AVIATION CONCERNS ARE EXPECTED DURING THE NEXT 24 HOURS.
OUTSIDE OF EXTENDED PERIODS OF LIGHT AND VRB CONDITIONS, WINDS
WILL CONTAIN A W'RLY COMPONENT AT KIPL, WHILE KBLH EXPERIENCES
OSCILLATIONS BETWEEN NW AND NE. CLOUD COVER WILL BEGIN TO SCATTER
OUT OVERNIGHT, WITH MOSTLY CLEAR SKIES RETURNING BY THE BACK-HALF
OF THE FORECAST WINDOW.
FIRE WEATHER
WIND SPEEDS THROUGH THE BEGINNING OF NEXT WEEK WILL BE MUCH WEAKER
THAN THE PAST SEVERAL DAYS WITH MINIMAL GUSTINESS. LIGHT SHOWERS
WILL AFFECT MUCH OF THE ARIZONA DISTRICTS THIS WEEKEND, AND
PARTICULARLY OVER EASTERN DISTRICTS, BUT THE CHANCE FOR WETTING RAIN
IS LOW (~10%). MINIMUM HUMIDITY LEVELS WILL IMPROVE CLOSER TO A 30-
50% RANGE DURING THE FIRST HALF OF NEXT WEEK, THEN LIKELY RISE
FURTHER DURING THE LATTER HALF OF THE WEEK. OVERNIGHT RECOVERY
SHOULD BE GOOD TO EXCELLENT. A PACIFIC WEATHER DISTURBANCE WILL
BRING INCREASED CHANCES OF WETTING RAINFALL, BREEZY WINDS, AND
COOLER TEMPERATURES DURING THE LATTER HALF OF NEXT WEEK.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
SHORT TERM...18
LONG TERM...18/RYAN
AVIATION...RW
FIRE WEATHER...18/RYAN
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