620
FXUS65 KPSR 290957
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
ISSUED BY NATIONAL WEATHER SERVICE TUCSON AZ
257 AM MST TUE APR 29 2025
SYNOPSIS
DRY CONDITIONS WILL PERSIST THROUGH THIS WEEK AS TEMPERATURES WARM
FROM NEAR TO ABOVE NORMAL TEMPERATURES HEADING THROUGH THE MIDDLE
AND LATTER PORTIONS OF THIS WEEK. A WEATHER DISTURBANCE MOVING
INTO REGION THIS WEEKEND WILL BRING ANOTHER ROUND OF BREEZY TO
WINDY CONDITIONS AND MUCH COOLER TEMPERATURES GOING INTO EARLY
NEXT WEEK.
DISCUSSION
RESIDUAL TROUGHING CONTINUE TO PERSIST ACROSS THE DESERT SOUTHWEST
EARLY THIS MORNING, AS THE LOW CIRCULATION HAS MIGRATED INTO
NORTHERN ARIZONA. THIS LOW CIRCULATION WILL CONTINUE TO MIGRATE
SOUTHWARD TODAY, RESULTING IN SOME INCREASING CLOUDINESS AND MAYBE
EVEN SPARK A FEW VIRGA SHOWERS OVER HIGHER TERRAIN AREAS AS MID-
LEVEL MOISTURE MAY BE SUFFICIENT TO PRODUCE SOME FALLING
PRECIPITATION. OTHERWISE, TROUGHING OVER THE REGION WILL KEEP
TEMPERATURES NEAR NORMAL LEVELS, AS A WARMING TREND WILL BEGIN
TODAY AS LONGWAVE TROUGHING WEAKENS AND EVENTUALLY SHIFTS EAST OF
ARIZONA BY TOMORROW.
MORE OF A TRANSITORY WEATHER PATTERN WILL CONTINUE THROUGH THE
MIDDLE AND LATTER PORTIONS OF THE WEEK, AS MID-LEVEL HEIGHTS BUILD
GRADUALLY, WARMING TEMPERATURES TO ABOVE NORMAL LEVELS WEDNESDAY
AND INTO THE WEEKEND. A WEAK REX BLOCK PATTERN WILL CAUSE ANOTHER
TROUGHING FEATURE TO DIP SOUTHWARD FROM THE PACIFIC NORTHWEST AS
DOWNSTREAM RIDGING BUILDS NORTH OF THIS TROUGHING FEATURE THAT
WILL SETTLE NEAR THE SOUTHERN CALIFORNIA COAST BY THURSDAY. THESE
WEAK NEGATIVE HEIGHT ANOMALIES WILL THEN GRADUALLY MIGRATE INTO
SOUTHERN ARIZONA BY FRIDAY, WHERE NEUTRAL TO WEAKLY NEGATIVE
HEIGHT ANOMALIES WILL PREVENT HIGH TEMPERATURES FROM REACHING WELL
ABOVE NORMAL LEVELS. THE RIDGING THAT BUILT INTO THE PACIFIC
NORTHWEST WILL BE CENTERED OVER THE INTERMOUNTAIN WEST AHEAD OF
THE NEXT IMPACTFUL WEATHER FEATURE THAT WILL BRING ANOTHER CHANGE
TO THE SENSIBLE WEATHER TO ARIZONA AND SOUTHEASTERN CALIFORNIA
THIS WEEKEND.
THE EVOLUTION OF THIS TROUGHING PATTERN HEADING INTO THIS WEEKEND
IS COMING MORE INTO FOCUS AS ENSEMBLES ARE NOW HONING IN BETTER ON
HOW DEEP AND INTENSE THIS TROUGHING FEATURE WILL BECOME. ALL
ENSEMBLE MEMBERS NOW DEPICT SOME VERSION OF A CUTOFF LOW
DEVELOPING BY SUNDAY AS THIS TROUGH DEEPENS INTO THE DESERT
SOUTHWEST, WITH JUST MINOR POSITIONAL AND MID-LEVEL NEGATIVE HEIGHT
ANOMALY DIFFERENCES THROUGH SUNDAY. THUS, THE REGION CAN EXPECT
THE SENSIBLE WEATHER CONDITIONS TO TRANSITION STARTING SATURDAY,
WHERE BREEZY TO WINDY CONDITIONS FILTER IN FROM WEST TO EAST
THROUGH SUNDAY. SHOULD THE CONDITIONS LINE UP RIGHT, AT LEAST
ELEVATED FIRE WEATHER CONDITIONS MAY BECOME A CONCERN ON SATURDAY
DUE TO THE LINGERING LOW RELATIVE HUMIDITIES AND STRONGER WINDS
FOR HIGHER TERRAIN AREAS OF SOUTH-CENTRAL ARIZONA.
DUE TO THE POSITION OF THIS CUTOFF LOW REMAINING WEST OF THE
REGION ON SATURDAY, ABOVE NORMAL TEMPERATURES ARE EXPECTED TO
REMAIN IN PLACE PRIOR TO A DRAMATIC COOLDOWN ON SUNDAY, ON THE
ORDER 10-20 DEGREES, DEPENDING ON HOW STRONG THIS LOW BECOMES.
WIDESPREAD WINDY CONDITIONS MAY BECOME A FACTOR ON SUNDAY AS A
RESULT, ALTHOUGH PRECIPITATION CHANCES CONTINUE TO REMAIN MINIMAL
TO NONE. DESPITE THE PESSIMISM ON PRECIPITATION CHANCES, THERE ARE
A COUPLE OF ENSEMBLE CLUSTERS (REPRESENTING 10-15% OF THE
MEMBERSHIP) THAT PAINT SOME LIGHT ACCUMULATIONS ACROSS SOME LOWER
DESERT LOCATIONS ON SUNDAY SHOULD THE TROUGH AMPLIFY ENOUGH TO
ADVECT MORE SUFFICIENT MOISTURE INTO SOUTH- CENTRAL ARIZONA.
HOWEVER, CURRENT NBM POP'S STILL REASONABLY REMAIN AT 10% OR LOWER
SUNDAY ONWARD AT THIS TIME. AS MENTIONED, TEMPERATURES ARE
EXPECTED TO DIP TO BELOW TO WELL BELOW NORMAL LEVELS (STILL A 5-10
DEGREES INTERQUARTILE RANGE) BEGINNING ON SUNDAY AND EXTENDING
INTO EARLY NEXT WEEK.
AVIATION
UPDATED AT 0450Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, KDVT:
WINDS WILL TEND TO FOLLOW THEIR TYPICAL DIURNAL PATTERNS. WIND
SPEEDS WILL GENERALLY REMAIN UNDER 10 KTS WITH THE EXCEPTION OF SOME
OCCASIONAL WESTERLY GUSTS INTO THE UPPER TEENS TOMORROW AFTERNOON.
SKIES WILL REMAIN MOSTLY CLEAR WITH FEW HIGH CLOUDS TOMORROW
AFTERNOON.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
WIND DIRECTIONS WILL PRIMARILY FAVOR THE W TO NW AT BOTH TERMINALS
WITH SPEEDS GENERALLY AOB 8 KT. SOME OCCASIONAL NW'RLY GUSTS INTO
THE UPPER TEENS ARE POSSIBLE AT KBLH TOMORROW AFTERNOON. SKIES WILL
REMAIN MOSTLY CLEAR.
FIRE WEATHER
WARMING AND DRYING CONDITIONS WILL COMMENCE TODAY, RESULTING IN
DEGRADING RH'S GOING THROUGH THE REST OF THE WEEK. EXPECT MINIMUM
RH'S OF 10-20% TO DIP TO 7-15% BY THE MIDDLE OF THE WEEK, WITH
OVERNIGHT RECOVERIES WORSENING TO AROUND 25-40%. WINDS WILL
MAINTAIN SEASONALLY TYPICAL UPSLOPE GUSTINESS IN THE AFTERNOON
THROUGH THE ENTIRE WEEK WITH LIKELY STRONGER GUSTS ARRIVING THIS
WEEKEND. A COOL WEATHER SYSTEM WILL THEN APPROACH AND MOVE THROUGH
THE REGION THIS WEEKEND. THIS WILL BRING MINIMUM RH VALUES BACK
ABOVE CRITICAL LEVELS. HOWEVER, THIS SYSTEM WILL ALSO BRING
INCREASED GRADIENT WINDS ACROSS THE AREA AND IT LOOKS AS THOUGH
THERE WILL BE A PERIOD OF AT LEAST ELEVATED FIRE WEATHER
CONDITIONS FOR SOUTH- CENTRAL AZ SATURDAY AFTERNOON. PREDICTIVE
SERVICES STILL SHOW ERCS ARE BELOW THE 75TH PERCENTILE, WHICH
SHOULD HELP LIMIT THE LARGE FIRE RISK.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
DISCUSSION...YOUNG
AVIATION...WHITTOCK/RYAN
FIRE WEATHER...YOUNG/BENEDICT
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page