803
FXUS65 KPSR 151729
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1029 AM MST MON JUL 15 2019
UPDATE
UPDATED AVIATION DISCUSSION.
SYNOPSIS
STRONG HIGH PRESSURE WILL REMAIN PARKED OVER THE REGION THROUGH
TOMORROW AND PROVIDE AN EXTENDED PERIOD OF HOT WEATHER. AN
EXCESSIVE HEAT WARNING IS IN EFFECT TODAY THROUGH TUESDAY EVENING
FOR MANY LOWER DESERT LOCATIONS. DRIER AIR WILL MOVE INTO THE
REGION THROUGH TUESDAY AND LIMIT THE THREAT OF THUNDERSTORMS TO
HIGH TERRAIN AREAS IN NORTH/EAST/SOUTHEAST ARIZONA. AN UPTICK IN
MONSOON ACTIVITY LOOKS POSSIBLE WEDNESDAY THROUGH EARLY NEXT WEEK,
WITH THE GREATEST CHANCES THIS WEEKEND INTO EARLY NEXT WEEK.
DISCUSSION
THE SUBTROPICAL HIGH HAS NUDGED A LITTLE FURTHER SOUTH AND IS
SITUATED OVER THE ARIZONA/NEW MEXICO BORDER. THE CENTER OF THIS
HIGH WILL SLOWLY SHIFT TO THE EAST TODAY AS A PACIFIC TROUGH DIGS
SOUTH ALONG THE WESTERN CONUS. THIS WILL GRADUALLY SHIFT THE WINDS
ALOFT TO THE SOUTHWEST AND ADVECT DRIER MID-LEVEL AIR INTO THE
REGION. SKIES TODAY WILL REMAIN MOSTLY SUNNY WITH A FEW MID-LEVEL
CLOUDS FROM TIME TO TIME. WITH MOISTURE SLOWLY BEING PUSHED NORTH
AND EAST, THE GREATEST THUNDERSTORM CHANCES WILL BE ACROSS HIGH
TERRAIN AREAS IN NORTH/EAST/SOUTHEAST ARIZONA. WITH THUNDERSTORMS
DEVELOPING AROUND OUR EASTERN FORECAST AREA TODAY, IT IS POSSIBLE
THAT WE COULD SEE AN OUTFLOW BOUNDARY MAKE IT'S WAY INTO THE LOWER
DESERTS, HOWEVER INSTABILITY WILL BE LIMITED AND REGENERATION OF
STORMS IN THE LOWER DESERTS REMAINS VERY UNLIKELY. THE MAIN STORY
TODAY WILL BE THE HEAT. WITH 592-594 DM HEIGHTS OVERHEAD AND A
DRIER ATMOSPHERE IN PLACE, TEMPERATURES WILL HAVE NO TROUBLE
SOARING INTO THE 110-115 DEGREE RANGE THIS AFTERNOON. DUE TO THIS,
AN EXCESSIVE HEAT WARNING IS IN EFFECT FOR MANY LOWER DESERT
LOCATIONS (GO TO THE PSR WATCHES/WARNINGS/ADVISORIES SECTION BELOW
FOR MORE INFORMATION).
ON TUESDAY, THE AFOREMENTIONED PACIFIC TROUGH DIGS FURTHER SOUTH
AND EAST, PUSHING THE SUBTROPICAL RIDGE AND ASSOCIATED MONSOON
MOISTURE A LITTLE FURTHER SOUTHEAST. THIS WILL RESULT IN EVEN
LOWER PRECIPITATION CHANCES WITH THE BEST COVERAGE IN SOUTHEAST
ARIZONA. WITH SIMILAR HEIGHTS IN PLACE ON TUESDAY AND AN EVEN
DRIER ATMOSPHERE, EXPECT TEMPERATURES TO BE THE SAME OR MAYBE A
DEGREE WARMER. THIS WILL KEEP THE EXCESSIVE HEAT WARNING IN
EFFECT THROUGH TUESDAY EVENING FOR SIMILAR LOCATIONS. TUESDAY
NIGHT, GUIDANCE CONTINUES TO SHOW A DECENT GULF SURGE FROM STORMS
IN NORTHERN MEXICO. THIS WILL ADVECT MOISTURE INTO THE LOWER
DESERTS ON WEDNESDAY AND POSSIBLY LEAD TO AN UPTICK IN MONSOON
ACTIVITY WEDNESDAY EVENING. THIS INCREASE IN ATMOSPHERIC MOISTURE
WILL ALSO LEAD TO A DECREASE IN HIGH TEMPERATURES (AROUND 5
DEGREES) WEDNESDAY AFTERNOON.
THURSDAY THROUGH MONDAY, THE SUBTROPICAL HIGH EXPANDS INTO THE
EASTERN CONUS AND GRADUALLY SHIFTS WINDS ALOFT TO THE SOUTH AND
THEN SOUTHEAST. THIS WILL CONTINUE TO ADVECT MONSOON MOISTURE
INTO THE REGION. IN ADDITION, MODELS CONTINUE TO DEPICT A SERIES
OF WAVES PROPAGATING AROUND THE SUBTROPICAL HIGH AND ACROSS THE
REGION, ESPECIALLY THIS WEEKEND INTO MONDAY. THESE WAVES COULD
SERVE AS AN EXTRA MECHANISM FOR STORM DEVELOPMENT IN THE LOWER
DESERTS. UNFORTUNATELY, CONFIDENCE STILL REMAINS LOW ON EXACT
TIMING, SO IT'S HARD TO SAY WHICH DAYS WILL BE MORE ACTIVE THAN
OTHERS, BUT RIGHT NOW IT LOOKS LIKE THE BEST CHANCES ARE THIS
WEEKEND AND EARLY NEXT WEEK. THE GOOD NEWS IS, THE GRADUAL
INCREASE IN MOISTURE THROUGH EARLY NEXT WEEK WILL CAUSE A
DOWNWARD TREND IN TEMPERATURES, WITH HIGHS FALLING AROUND OR JUST
BELOW AVERAGE SUNDAY AND NEXT MONDAY.
AVIATION
UPDATED AT 1730 UTC
SOUTH-CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
WINDS WILL FOLLOW THE TYPICAL DIURNAL DIRECTIONAL TENDENCIES WITH
THE WESTWARD SHIFT OCCURRING WITHIN THE NEXT HOUR OR SO. THERE IS
NO CHANCE FOR THUNDERSTORMS IN THE TERMINAL AREA AND THE CHANCE
FOR ANY OUTFLOWS IS LOW. OTHERWISE, EXPECT OCCASIONAL AFTERNOON
BREEZES.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
WINDS WILL BECOME PREDOMINANTLY WESTERLY-SOUTHWESTERLY AT BOTH
SITES WITH OCCASIONAL AFTERNOON GUSTS. THE WINDS WILL BECOME VERY
LIGHT AND VARIABLE IN DIRECTION LATE TONIGHT. NO STORMS OR
OUTFLOWS ARE EXPECTED ANYWHERE NEAR THE TERMINAL AREA.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
FIRE WEATHER
WEDNESDAY THROUGH SUNDAY:
TEMPERATURES WILL BECOME MORE SEASONAL, ALTHOUGH STILL HOT DURING
THE DAYTIME. MINIMUM RH VALUES WILL STRUGGLE TO STAY ABOVE 15%
THROUGH SATURDAY (THOUGH HIGHER TERRAIN EASTERN DISTRICTS WILL
LIKELY BE A LITTLE MORE SATURATED). ON SUNDAY, MINIMUM RH VALUES
INCREASE INTO THE UPPER TEENS/LOW 20S. OVERNIGHT RECOVERIES
THROUGH SATURDAY WILL RANGE FROM 25-40% AT LOWER ELEVATIONS AND
SUBSTANTIALLY HIGHER IN EASTERN DISTRICTS. SATURDAY NIGHT INTO
SUNDAY MORNING, MINIMUM RH VALUES WILL INCREASE INTO THE 40S AND
50S. WINDS WILL REMAIN FAIRLY LIGHT WITH SOME AFTERNOON BREEZES
FAVORING TYPICAL DIURNAL TENDENCIES. THERE WILL BE SLIGHT CHANCES
FOR STORMS, MAINLY ALONG THE HIGHER TERRAIN NORTH/EAST/SOUTHEAST
OF PHOENIX. HOWEVER, PERIODIC OUTFLOW BOUNDARIES WITH ERRATIC
SHIFTING WINDS WILL BE POSSIBLE. THE BEST STORM CHANCES IN THE
LOWER DESERTS LOOK TO BE THIS WEEKEND.
SPOTTER INFORMATION STATEMENT
SPOTTERS SHOULD FOLLOW STANDARD REPORTING PROCEDURES.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...EXCESSIVE HEAT WARNING UNTIL 8 PM MST TUESDAY FOR AZZ532-534-
536>544-546-548>551-553>556-559.
CA...EXCESSIVE HEAT WARNING UNTIL 8 PM PDT TUESDAY FOR CAZ566>568.
DISCUSSION...HERNANDEZ
AVIATION...DEEMS
FIRE WEATHER...HERNANDEZ
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