680
FXUS65 KPSR 181815
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1115 AM MST SUN OCT 18 2026
UPDATE...UPDATED 18Z 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 MONDAY/
THE REX BLOCK PATTERN THAT WAS POSITIONED OVER WEST CONUS HAS
ALREADY BEGUN TO BREAK DOWN AS THE HIGH PRESSURE IS NOW OVER THE
NORTHERN PLAIN STATES. THE HIGH PRESSURE WILL CONTINUE TO QUICKLY
MOVE INTO NE CONUS BY LATE THIS EVENING. MEANWHILE THE CUT OFF LOW
TO OUR SW HAS ALREADY BEGUN TO LOOSEN INTO AN OPEN WAVE. AS THE
LOW CONTINUES TO OPEN AND BEGIN TO BE ABSORBED INTO THE MAIN
WESTERLY FLOW ALOFT DECENT MOISTURE ADVECTION THROUGH THE MID
LEVELS WILL OCCUR, LEADING TO PWATS IN EXCESS OF 1" ACROSS MUCH OF
THE CWA. THIS IS NEAR 200-225% OF NORMAL, OR ABOVE THE 90TH
PERCENTILE OF NAEFS MEAN PRECIPITABLE WATER, VERY UNUSUAL FOR THIS
TIME OF YEAR. ADDITIONALLY, AS THE LOW OPENS IT WILL PLACE SOUTH
CENTRAL AZ IN A FAVORABLE POSITION FOR ASSOCIATED POSITIVE
VORTICITY, AIDING IN THE ASCENT OF THE AFOREMENTIONED MOISTURE. AS
A RESULT SLIGHT CHANCES FOR ISOLATED SHOWERS WILL CONTINUE TO
LINGER, WITH POPS BETWEEN 15-30% STRETCHING BETWEEN SOUTHERN
MARICOPA COUNTY THROUGH PINAL COUNTY AND INTO THE HIGHER TERRAIN
EAST OF THE PHOENIX METRO THROUGH THE MORNING HOURS INTO THE
AFTERNOON. BY THIS 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. BY MONDAY AFTERNOON MOST OF THE LOWER DESERTS
POPS ARE <10% WHILE 20-30% PERSIST OVER THE EASTERN HIGH TERRAIN,
HOWEVER IF ANYTHING DOES DEVELOP, TOTAL ACCUMULATIONS ARE
EXPECTED TO BE MINIMAL.
LARGE SPREAD IN NBM TEMPERATURES REMAIN FOR TODAY AND MONDAY WITH
THE UNCERTAINTY OF SHOWERS, AND DEPTH OF H5 HEIGHTS ASSOCIATED WITH
THE LOW. REGARDLESS, HIGH TEMPERATURES TODAY ARE FORECASTED TO BE IN
THE MID 80S ACROSS THE LOWER DESERTS. BY MONDAY, AHEAD OF THE NEXT
LOW PRESSURE SYSTEM, H5 HEIGHTS WILL INCREASE AS A RIDGE BUILDS OVER
EASTERN CONUS, IN TURN HEIGHTS ALOFT INCREASE SLIGHTLY OVER THE
DESERT SW RAISING TEMPERATURES A FEW DEGREES INTO THE MID TO UPPER 80S
THROUGH MID-WEEK.
LONG TERM /TUESDAY THROUGH SATURDAY/
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 CONTINUES TO BE
LOW TO MODERATE. THE DETERMINISTIC'S HAVE STARTED TO COME INTO
BETTER AGREEMENT COMPARED TO 24 HRS AGO BUT STILL SHOW KEY
DIFFERENCES. THE ECMWF FORECAST CONTINUES TO SHOW A SLIGHTLY
SLOWER SYSTEM HOWEVER MUCH SHALLOWER THAN BEFORE. MEANWHILE THE
GFS DETERMINISTIC REMAINS MOSTLY UNCHANGED, WITH THE EXCEPTION OF
NOW LEANING TOWARDS A MORE POSITIVELY TILTED TROUGH THAN COMPARED
TO THE ECMWF, AND THE PREVIOUS GFS RUNS, SPREADING OUT ANY
VORTICITY ADVECTION AND HINDERING BETTER CHANCES FOR STORM
DEVELOPMENT. EVEN WITH THESE DIFFERENCES COMPARED TO PREVIOUS
RUNS, THE ECMWF CONTINUES TO FORECAST A MORE MORE ROBUST RAINFALL
SCENARIO IN COMPARISON TO THE GFS. EITHER WAY, WEDNESDAY AND
THURSDAY CONTINUE TO BE THE BEST WINDOW FOR RAINFALL POTENTIAL,
WHILE PATTERN RECOGNITION AND SOME INSTABILITY PARAMETERS SUGGEST
THE POTENTIAL FOR STRONG THUNDERSTORMS AHEAD OF THE SHORTWAVE
PASSAGE. LINGERING POPS CONTINUE INTO FRIDAY MORNING BEFORE
EXPECTING TO DRY OUT BY THE WEEKEND.
ADDITIONALLY, WITH THE UNCERTAINTY OF THIS NEXT SYSTEM REMAINING,
A WIDE SPREAD IN NBM TEMPERATURES CONTINUE THROUGHOUT THE WEEK,
MOST NOTABLY ON THURSDAY WITH A SPREAD OF 11 DEGREES BETWEEN THE
25TH AND 75TH PERCENTILE. EVEN WITH THIS LARGE OF SPREAD BELOW
NORMAL HIGHS ARE LIKELY LATE THIS WEEK HEADING INTO THE WEEKEND.
AVIATION
UPDATED AT 1815Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
NO MAJOR AVIATION WEATHER CONCERNS ARE EXPECTED THROUGHOUT THE TAF
PERIOD. AREAS OF LIGHT SHOWERS AND VIRGA CONTINUE TO MOVE THROUGH
PORTIONS OF THE PHOENIX METRO, WITH MOST OF THE ACTIVITY LOCATED
WEST OF THE METRO. WITH THE SHOWERS CONTINUING VCSH HAS BEEN
EXTENDED IN THE TAFS THROUGH 20-21Z THIS AFTERNOON. OPERATIONAL
IMPACTS WILL REMAIN MINIMAL WITH THIS ACTIVITY. WIND DIRECTIONS
WILL OVERALL EXHIBIT AN EASTERLY COMPONENT THROUGH THE MAJORITY OF
THE TAF PERIOD. A PERIOD OF WESTERLY WINDS IS POSSIBLE THIS
EVENING (23-08Z), BUT WINDS MAY JUST BE LIGHT AND VARIABLE DURING
THIS WINDOW BEFORE THEY REESTABLISH THE EASTERLY COMPONENT
OVERNIGHT. SO, VRB WINDS HAS BEEN ADDED TO THE KPHX AND KIWA TAFS
FOR THIS WINDOW. WINDS AT KSDL AND KDVT WILL BE LIGHT AND VARIABLE
BEGINNING AROUND 00Z THROUGH THE END OF THE TAF PACKAGE. WIND
SPEEDS THROUGH THE EARLY AFTERNOON WILL BE AROUND 10-15 KT BEFORE
DECREASING TO AOB 8 KT THE REST OF THE PERIOD. ABUNDANT MID-LEVEL
CLOUDS WILL REMAIN IN PLACE THROUGH THE EARLY AFTERNOON HOURS
BEFORE SCATTERING OUT HEADING INTO THE EVENING.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO MAJOR AVIATION CONCERNS ARE EXPECTED THROUGHOUT THE TAF PERIOD
WITH MOSTLY CLEAR SKIES. BOTH TAF SITES WILL HAVE LIGHT AND
VARIABLE WINDS THROUGH THE PERIOD WITH SPEEDS AOB 5 KT. WHILE
WINDS WILL BE LIGHT AND VARIABLE, WINDS AT KIPL WILL TEND TO
EXHIBIT MORE OF A W/NW COMPONENT AND WINDS AT KBLH WILL TEND TO
EXHIBIT MORE OF A NE/NW COMPONENT.
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...RYAN
LONG TERM...RYAN
AVIATION...BERISLAVICH
FIRE WEATHER...18/RYAN
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