832
FXUS65 KTWC 310930
AFDTWC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
230 AM MST SAT MAY 31 2025
SYNOPSIS
TEMPERATURES WILL BE AROUND NORMAL TODAY THEN COOL TO
BELOW NORMAL AS A WEATHER SYSTEM MOVES THROUGH THIS WEEKEND INTO
EARLY NEXT WEEK. IT WILL BRING A SUBSTANTIAL MOISTURE INCREASE
INTO THE REGION, INITIALLY WITH A SLIGHT CHANCE OF MAINLY DRY
THUNDERSTORMS SOUTH AND EAST OF TUCSON TODAY. WIDESPREAD SHOWERS
AND ISOLATED THUNDERSTORMS WILL OCCUR SUNDAY INTO EARLY MONDAY
WITH DRY CONDITIONS RETURNING THEREAFTER.
DISCUSSION
WATER VAPOR IMAGERY SHOWS A CLOSED LOW CENTERED OFF
THE MIDDLE COAST OF BAJA CALIFORNIA WITH RIDGING TO ITS NORTH.
TROPICAL STORM ALVIN IS ABOUT 250 MILES SOUTH OF BAJA CALIFORNIA,
AND WILL CONTINUE TO MOVE NORTHWARD THANKS TO THE PLACEMENT OF THE
UPPER LEVEL LOW. SOUTHERLY FLOW ALONG THE EASTERN EDGE OF THE LOW
HAS ADVECTED TROPICAL MOISTURE INTO SOUTHERN SONORA WHERE PWAT
VALUES ARE AROUND 1.5". THIS TROPICAL MOISTURE PLUME WILL CONTINUE
ITS NORTHWARD MOVEMENT TODAY WITH PWAT VALUES IN SOUTHEAST
ARIZONA RANGING FROM 0.8-1.0" BY THIS EVENING. THIS WILL BE ENOUGH
MOISTURE TO MAYBE GET ISOLATED DRY THUNDERSTORMS OVER THE HIGHER
TERRAIN SOUTH AND EAST OF TUCSON. HREF MEMBERS AREN'T TERRIBLY
EXCITED, BUT DO SHOW A FEW WEAK, DRY STORMS FORMING THIS
AFTERNOON. THE MAIN THREATS WILL BE GUSTY WINDS FROM EVAPORATING
DOWNDRAFTS AND LIGHTNING THAT COULD IGNITE NEW FIRES.
TONIGHT THE UPPER LEVEL LOW BEGINS TO SLOWLY MOVE EASTWARD AND
BEGINS TO OPEN UP. AT THE SAME TIME MOISTURE VALUES INCREASE
FURTHER ESPECIALLY OVER CENTRAL AND WESTERN PIMA COUNTY. BY SUNDAY
MORNING ENSEMBLE MEAN PWAT VALUES RANGE FROM 1.2"-1.5" FROM TUCSON
WESTWARD. EAST OF TUCSON PWAT VALUES ARE 1" OR LESS. HREF MEMBERS
SHOW SCATTERED SHOWER ACTIVITY WEST OF TUCSON BEGINNING AFTER
MIDNIGHT AND CONTINUING INTO SUNDAY MORNING. AS THE LOW
PROGRESSES EASTWARD, SHOWER ACTIVITY INCREASES EASTWARD AS WELL,
WITH WIDESPREAD SHOWERS AND EMBEDDED THUNDERSTORMS EXPECTED OVER
MOST OF SOUTHEAST ARIZONA SUNDAY AFTERNOON INTO THE EVENING. BY
THIS POINT PWAT VALUES WILL BE 250-300 PERCENT OF NORMAL.
RAINFALL AMOUNTS IN VALLEY LOCATIONS LOOK TO GENERALLY BE
0.2"-0.6" AND UP TO 1" IN THE MOUNTAINS. THE BULK OF THIS RAINFALL
WILL LIKELY FALL SUNDAY AFTERNOON AND EVENING. LOCALIZED AREAS
COULD ALSO SEE 1" OR MORE. ONE SUCH AREA COULD BE THE TOHONO
O'ODHAM NATION. THE 31/00Z HREF SHOWS 30-60 PERCENT PROBABILITIES
OF 1" OR GREATER OF QPF FROM SANTA ROSA DOWN TO THE INTERNATIONAL
BORDER THROUGH SUNDAY EVENING. THIS WILL BE AN AREA TO WATCH FOR
LOCALIZED FLOODING ISSUES ESPECIALLY BECAUSE HIGH RUNOFF IS
EXPECTED DUE TO THE PAST FEW MONTHS OF VERY DRY CONDITIONS. AREA
BURN SCARS WILL ALSO BE UNDER THREAT FOR POSSIBLE DEBRIS FLOWS
FROM STRONGER STORMS OR TRAINING STORMS. WPC HAS ALL OF SOUTHEAST
ARIZONA UNDER A MARGINAL THREAT FOR FLASH FLOODING.
SHOWERS THEN CONTINUE OVERNIGHT AND DECREASE FROM WEST TO EAST
MONDAY MORNING INTO THE AFTERNOON. THE LOW WILL LIKELY BE AN OPEN
WAVE BY MONDAY AFTERNOON AND WILL BE MOVING INTO THE FOUR CORNERS
REGION. MOISTURE WILL QUICKLY DECREASE BEHIND THE LOW LEADING TO
PRECIP BEING ON THE LIGHTER SIDE MONDAY. ANOTHER CLOSED LOW
FOLLOWS IN BEHIND TUESDAY LEADING TO JUST A SLIGHT CHANCE FOR
PRECIP EAST OF TUCSON AND BREEZY WINDS. FOR THE REMAINDER OF THE
WORK WEEK SOUTHEAST ARIZONA STAYS UNDER DRY SOUTHWEST FLOW WITH
HIGH PRESSURE BECOMING CENTERED OVER NORTHERN MEXICO AND A
SHORTWAVE MAKING ITS WAY DOWN THE WEST COAST.
TEMPERATURES WILL BE BELOW NORMAL THROUGH WEDNESDAY WITH HIGHS
POTENTIALLY BELOW 90 DEGREES SUNDAY AND MONDAY IN TUCSON. AFTER
WEDNESDAY HIGHS RETURN TO NORMAL OR A FEW DEGREES ABOVE NORMAL.
AVIATION
VALID THROUGH 01/12Z.
CLOUDS GENERALLY BKN 10K-14K THROUGH THE PERIOD. ISOLATED DRY
THUNDERSTORMS WILL BE POSSIBLE OVER THE HIGHER TERRAIN SOUTH AND
EAST OF TUCSON THIS AFTERNOON. TOWARDS THE VERY END OF THE PERIOD
-SHRA WILL BE POSSIBLE FROM KTUS-KOLS WESTWARD. WINDS WILL BE
SLY/SELY THIS MORNING LESS THAN 10 KTS BECOMING NWLY AT KTUS THIS
AFTERNOON 5-10 KTS. ELSEWHERE WINDS STAY SLY. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.
FIRE WEATHER
A DRY THUNDERSTORM THREAT EXISTS TODAY SOUTH AND
EAST OF TUCSON MAINLY OVER THE HIGHER TERRAIN. MINIMUM HUMIDITY
VALUES WILL BE 12 TO 22 PERCENT. TROPICAL MOISTURE THEN BEGINS TO
MOVE IN WHICH WILL LEAD TO WIDESPREAD SHOWERS AND THUNDERSTORMS
SUNDAY INTO MONDAY. RAIN COULD BE HEAVY AT TIMES LEADING TO
POSSIBLE DEBRIS FLOWS OVER NEW AREA BURN SCARS. OVERALL WINDS
REMAIN LIGHT BUT GUSTY AND ERRATIC WINDS WOULD OCCUR WITH ANY
THUNDERSTORM ACTIVITY. ANOTHER WEATHER SYSTEM MOVES THROUGH
TUESDAY WITH A SLIGHT CHANCE FOR PRECIP EAST OF TUCSON ALONG WITH
BREEZY WINDS. THEREAFTER EXPECT DRY AND WARMING CONDITIONS.
TWC WATCHES/WARNINGS/ADVISORIES
NONE.
HARDIN
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