112
FXUS65 KPSR 212011
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
110 PM MST MON SEP 21 2026
KEY MESSAGES
- DRY AND TRANQUIL CONDITIONS, ALONG WITH NEAR NORMAL TEMPERATURES
WILL CONTINUE THROUGH AT LEAST THE MIDDLE OF THE WEEK.
- RAIN CHANCES WILL RETURN TO PORTIONS OF ARIZONA OVER THE NEXT FEW
DAYS, ALTHOUGH FOCUSED PRIMARILY OVER FOOTHILL AND HIGH TERRAIN
AREAS.
- LOWER DESERT RAINFALL CHANCES WILL BE HEIGHTENED SOMEWHAT DURING
THE LATTER HALF OF THE WEEK.
SHORT TERM /TODAY THROUGH WEDNESDAY/
A SEASONALLY STRONG TROUGH WAS MOVING ONSHORE IN SOUTHERN CALIFORNIA
EARLY THIS AFTERNOON WITH A JET STREAK TRANSLATING DOWNSTREAM OF THE
COLD CORE FORCING DEAMPLIFICATION AND LIFTING OF THE CYCLONIC
CIRCULATION TOWARDS THE GREAT BASIN. HOWEVER, JET FORCED ASCENT HAS
COMBINED WITH A NARROW BAND OF MIDLEVEL MOISTURE TO PRODUCE A SMALL
AREA OF ELEVATED CONVECTION ALONG THE LOWER COLORADO RIVER VALLEY
EARLIER TODAY. THIS FEATURE WILL CONTINUE TO EXIT THE FORECAST AREA
BY THIS EVENING ALTHOUGH RESIDUAL, ELONGATED TROUGHING WILL LINGER
ACROSS SOUTHERN CALIFORNIA/NEVADA. THIS WILL CREATE A DEEPLY
MERIDIONAL FLOW PATTERN OVER THE NEXT 72 HOURS CAPABLE OF IMPORTING
SHEARED VORTICITY CENTERS FROM THE SOUTH, AS WELL AS PERIODICALLY
BETTER LOW LEVEL MOISTURE PROFILES. H5 HEIGHTS WILL REMAIN NEARLY
STEADY STATE IN A 580-584DM RANGE ENSURING A CONTINUATION OF NEAR
NORMAL TEMPERATURES THE NEXT SEVERAL DAYS.
BOTH GLOBAL AND HREF MODELING SUGGESTS A LOW AMPLITUDE VORTICITY
CENTER (LIKELY CONVECTIVELY ENHANCED OVER NORTHERN MEXICO) STREAMING
INTO EASTERN ARIZONA TUESDAY AFTERNOON. ALONG WITH A SMALL JET
SEGMENT FEEDING INTO THE RIGHT REAR QUADRANT OF THE NORTHERN STREAM,
ASCENT STRUCTURE TAPPING MARGINALLY BETTER MOISTURE IN SE ARIZONA
WILL BECOME VERY FAVORABLE FOR DEEP CONVECTIVE DEVELOPMENT OVER
HIGHER TERRAIN LOCATIONS. WHILE LOWER ELEVATIONS IN THE CWA WILL NOT
INITIALLY HAVE SUFFICIENT MOISTURE FOR THUNDERSTORM SUSTENANCE,
GUSTY SOUTHEAST OUTFLOW WINDS SEEM MORE LIKELY, FOSTERED BY DCAPE
VALUES NEAR 1500 J/KG ALLOWING BETTER BOUNDARY LAYER MOISTURE TO
SURGE NORTHWEST THROUGH THE FORECAST AREA. AS A RESULT, INSTABILITY
PARAMETERS WILL REACH MUCH HIGHER LEVELS WEDNESDAY (I.E. MLCAPE 1000-
1500 J/KG), THOUGH STRONGER CINH AND LACK OF A TRIGGERING MECHANISM
MAY PRECLUDE MORE THAN ISOLATED MOUNTAIN STORMS AS THE REGION MAY
FALL UNDER SHORTWAVE RIDGING AND SUBSIDENCE BEHIND THE TUESDAY
VORTICITY CENTER EXITING THE REGION.
LONG TERM /THURSDAY THROUGH SUNDAY/
BY THE LATTER HALF OF THE WEEK, THE INFLUENCE OF THE WEAKENING
SOUTHWESTERN LOW WILL ALL BUT DISAPPEAR. THE FOCUS WILL SHIFT TOWARD
THE INTERPLAY BETWEEN LARGE SCALE TROUGHING OVER THE EASTERN
PACIFIC/WEST COAST AND THE SUBTROPICAL HIGH OVER THE SOUTHERN PLAINS
AND NORTHERN MEXICO. GLOBAL ENSEMBLES FAVOR RETROGRESSION TOWARD THE
DESERT SOUTHWEST APPROACHING THE WEEKEND. THIS EVOLUTION WOULD NOT
COMPLETELY SCOUR RESIDUAL MOISTURE IMMEDIATELY, SO RAIN CHANCES WILL
LIKELY LINGER INTO THURSDAY. CURRENT POPS SHOW 30-50% CHANCES FOR
FOOTHILL AND MOUNTAIN AREAS AND 10-30% PROBABILITIES FOR THE SOUTH-
CENTRAL ARIZONA DESERTS. BEYOND THAT, PERSISTENT SOUTHWESTERLY FLOW
WOULD EVENTUALLY DRY US OUT ENOUGH TO LIMIT RAIN CHANCES HEADING
INTO THE WEEKEND. ANOTHER INFLUX OF MOISTURE BY THE END OF THE SEVEN
DAY PERIOD MAY BRING RAIN CHANCES BACK ONCE AGAIN, BUT MAX CHANCES
AT THIS TIME ONLY RANGE BETWEEN 20-30%.
EVEN WITH THE COMPETING AIRMASSES, REGIONAL TEMPERATURES WILL ONLY
FLUCTUATE WITHIN A FEW DEGREES THROUGH THE WEEKEND. WHILE THE RIDGE
KEEPS ANOTHER SHORTWAVE FROM PROGRESSING TOWARD THE REGION, AS
MENTIONED PREVIOUSLY, IN RETURN, THE LARGE SCALE TROUGHING TO OUR
WEST WILL KEEP THE HIGH FROM BECOMING TOO AMPLIFIED, PREVENTING ANY
FURTHER DISCUSSION OF ABNORMAL HEAT, AT LEAST DURING THIS FORECAST
PERIOD. TEMPERATURES FOR THE LOWER DESERTS THURSDAY THROUGH SUNDAY
WILL RANGE GENERALLY BETWEEN 94-106 DEGREES, WHILE OVERNIGHT LOWS
HOVER NEAR 70-82 DEGREES.
AVIATION
UPDATED AT 1740Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
NO MAJOR AVIATION WEATHER CONCERNS WILL EXIST THROUGH TUESDAY
AFTERNOON UNDER PERIODS OF SCT-BKN MID AND HIGH CLOUD DECKS WITH
BASES REMAINING AOA 8K FT AGL. WINDS WILL VEER OUT OF THE SSE/S AND
MAINTAIN THIS DIRECTION THROUGH MUCH OF THE AFTERNOON, PRESENTING A
MINOR CONCERN WITH A SOUTHERLY CROSS-RUNWAY COMPONENT AT KPHX AND
KDVT. HOWEVER, ONLY OCCASIONAL GUSTS TO AROUND 15 KTS ARE EXPECTED
THROUGH THE AFTERNOON WITH SPEEDS REMAINING MOSTLY AOB 10 KTS. BY
THIS EVENING, A MUCH LATER THAN USUAL WESTERLY WIND SWITCH IS
ANTICIPATED. A FAMILIAR PATTERN WILL TAKE SHAPE TONIGHT AND TUESDAY
MORNING, WITH E/SE NOCTURNAL DRAINAGE WINDS ESTABLISHING FOLLOWED BY
WINDS VEERING OUT OF THE SSE TUESDAY MORNING. CHANCES FOR SHRA/TSRA
IN THE PHOENIX AIRSPACE REMAIN BELOW 10% THROUGH TUESDAY AFTERNOON,
WITH MOST ACTIVITY REMAINING WELL TO THE EAST AND SOUTHEAST,
HOWEVER, SOME PERIODS WITH VIRGA SHOWERS IN THE VICINITY CANNOT BE
RULED OUT.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
SHRA/TSRA WILL CLEAR KBLH WITHIN THE NEXT HOUR. OUTSIDE OF THIS
ACTIVITY, NO MAJOR IMPACTS ARE ANTICIPATED THROUGH THE NEXT 24 HOURS
WITH PERIODS OF SCT MID AND CLOUD DECKS BECOMING CLEAR BY THIS
EVENING. WINDS WILL FAVOR W/NW AT KIPL, WITH A PERIOD OF GUSTS TO 20-
25 KTS EXPECTED THIS EVENING. AT KBLH, WINDS WILL FAVOR S THROUGH
THE DAY WITH AFTERNOON GUSTS BETWEEN 15-20 KTS LIKELY, FOLLOWED BY
SW-W WINDS THIS EVENING INTO THE OVERNIGHT HOURS.
FIRE WEATHER
NEAR TO SLIGHTLY ABOVE NORMAL TEMPERATURES WILL PREVAIL OVER THE
NEXT SEVERAL DAYS, WITH MINIMAL DAY-TO-DAY FLUCTUATIONS. DRY
CONDITIONS WITH NO CHANCES FOR RAIN CONTINUE THROUGH TODAY AHEAD
RETURNING HIGH TERRAIN RAIN CHANCES FOR FOOTHILL AND HIGH TERRAIN
AREAS STARTING TUESDAY. MINRHS BETWEEN 15-30% WILL BE COMMON ACROSS
THE REGION, WITH EVEN HIGHER READINGS (35-50%) FOR THE FAR EASTERN
DISTRICTS. MAXRHS WILL RANGE FROM FAIR TO GOOD OVER THE WESTERN AND
CENTRAL DISTRICTS, TO GOOD AND EXCELLENT FOR THE EASTERN DISTRICTS
INTO THE WEEKEND. OUTSIDE OF SOME MARGINAL BREEZINESS CAUSED BY AN
APPROACHING WEATHER SYSTEM, WINDS WILL FOLLOW FAMILIAR DIURNAL
TRENDS WITH TYPICAL TERRAIN INDUCED AFTERNOON GUSTS AROUND 15-25
MPH.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
SHORT TERM...18
LONG TERM...RW
AVIATION...WHITTOCK
FIRE WEATHER...RW
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