504
FXUS65 KTWC 180817
AFDTWC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
117 AM MST FRI SEP 18 2026
SYNOPSIS
THERE WILL BE A SLIGHT CHANCE OF SHOWERS AND
THUNDERSTORMS ALONG THE ARIZONA/NEW MEXICO STATE LINE AND IN THE
WHITE MOUNTAINS THIS AFTERNOON AND EVENING. OTHERWISE, DRIER AIR
WILL MOVE ACROSS SOUTHEAST ARIZONA OVER THE WEEKEND INTO EARLY NEXT
WEEK. MOISTURE THEN SPREADS BACK ACROSS PORTIONS OF SOUTHEAST
ARIZONA NEXT WEEK FOR A CHANCE OF SHOWERS AND THUNDERSTORMS, MAINLY
EAST OF TUCSON. HIGH TEMPERATURES WILL BE NEAR NORMAL THROUGH NEXT
WEEK.
DISCUSSION
ON THE LARGE SCALE, AN UPPER LOW WAS CENTERED ALONG
THE NEVADA/OREGON STATE LINE, WITH A TROUGH AXIS EXTENDING SOUTHWARD
THROUGH CALIFORNIA AND HIGH PRESSURE ALOFT WAS CENTERED OVER FAR
EASTERN TEXAS. THE UPPER LOW WILL MOVE SLOWLY EAST INTO WESTERN
WYOMING BY LATE SATURDAY, WITH THE TROUGH AXIS SLIDING ACROSS THE
GREAT BASIN AND NORTHERN ARIZONA. A SECONDARY LOW MOVES INTO THE
CENTRAL CALIFORNIA COAST LATE SUNDAY INTO MONDAY. THIS SECONDARY LOW
WILL THEN LIFT NORTHEAST THROUGH THE INTERMOUNTAIN WEST EARLY TO MID
NEXT WEEK, AS HIGH PRESSURE ALOFT SHIFTS WESTWARD INTO FAR SOUTHERN
TEXAS.
SATELLITE LAYER BLENDED TOTAL PRECIPITABLE WATER IMAGERY INDICATES
PWATS WERE CURRENTLY IN THE 1.0"-1.2" RANGE ACROSS SOUTHEAST
ARIZONA, WITH LOWER VALUES OF 0.50"-0.75" TO OUR WEST ACROSS
SOUTHERN CALIFORNIA AND NORTHERN BAJA. THIS DRIER AIR WILL BEGIN TO
MOVE INTO THE REGION FROM THE WEST TODAY AS THE UPPER LOW AND TROUGH
AXIS SHIFT EASTWARD. THERE WILL STILL BE ENOUGH MOISTURE FOR A
SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS ALONG THE NEW MEXICO
STATE LINE AND IN THE WHITE MOUNTAINS THIS AFTERNOON/EVENING.
MODELED PWATS INDICATE VALUES LOWERING TO NEAR 0.75" BY EARLY THIS
EVENING.
SATURDAY LOOKS TO BE THE 'DRIEST' DAY WITH MODEL PW VALUES AROUND
0.50" ACROSS THE FORECAST AREA AND ARIZONA ON THE BACK SIDE OF THE
AFOREMENTIONED TROUGH AXIS. BY SUNDAY, MODEL PW VALUES START TO
INCREASE BACK TO NEAR 0.75" AS THE SECONDARY UPPER LOW MOVES INTO
THE CALIFORNIA COAST AND DEEPER MOISTURE STARTS WORKING BACK
NORTHWARD THROUGH EASTERN SONORA. WHILE THE FORECAST ACROSS
SOUTHEAST ARIZONA REMAINS DRY ON SUNDAY, WE WILL HAVE TO MONITOR ANY
CONVECTIVE OUTFLOW BOUNDARIES OVER SONORA WHICH MAY PUSH CONVECTION
NORTHWARD ALONG THE INTERNATIONAL BORDER IN COCHISE COUNTY.
BY EARLY TO MID NEXT WEEK THE LOW LIFTS ACROSS THE INTERMOUNTAIN
WEST AND THE UPPER HIGH BEGINS TO SHIFT WESTWARD BACK ACROSS TEXAS,
AND INCREASING AMOUNTS OF MOISTURE MOVE BACK INTO SOUTHEAST ARIZONA
FROM THE EAST AND SOUTH. THE LATEST POP GRIDS SHOW A SLIGHT CHANCE
OF SHOWERS AND THUNDERSTORMS ACROSS COCHISE COUNTY ON MONDAY, WITH A
SLIGHT CHANCE/CHANCE OF SHOWERS AND THUNDERSTORMS MAINLY EAST OF
TUCSON ON TUESDAY AND THEN A CHANCE OF SHOWERS AND THUNDERSTORMS
FROM TUCSON EASTWARD WEDNESDAY THROUGH FRIDAY OF NEXT WEEK. MODELED
PW VALUES BY MID TO LATE NEXT WEEK ARE BACK UP INTO THE 1.0"-1.25"
RANGE ACROSS SOUTHEAST ARIZONA.
OTHERWISE, HIGH TEMPERATURES THROUGH NEXT FRIDAY ARE WITHIN A DEGREE
OR TWO OF NORMAL, WITH HIGHS IN THE MID 90S IN THE TUCSON METRO, TO
NEAR 100 DEGREES ACROSS THE WESTERN DESERTS AND IN THE MID 80S TO
LOWER 90S ACROSS THE VALLEY LOCATIONS OF SANTA CRUZ, COCHISE, GRAHAM
AND SOUTHERN GREENLEE COUNTIES.
AVIATION
VALID THRU 19/12Z.
MAINLY CLEAR SKIES/SKC CONDITIONS WEST OF KTUS THRU THE FORECAST
PERIOD. FROM KTUS EASTWARD, FEW-SCT CLOUDS AT 8K-11K FT AGL AND SCT
(LOCALLY BKN CLOUDS) AOA 20K FT AGL BETWEEN 18/17Z AND 19/04Z. A
SLIGHT CHANCE OF -TSRA/-SHRA ALONG THE NEW MEXICO STATE LINE AND IN
THE WHITE MOUNTAINS BETWEEN 19/19Z AND 20/03Z. SFC WIND LESS THAN 12
KTS THRU THE FORECAST PERIOD, FAVORING A SWLY/WLY DIRECTION DURING
THE AFTERNOON/EARLY EVENING HOURS AND VARIABLE IN DIRECTION AT OTHER
TIMES. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.
FIRE WEATHER
THERE WILL BE A SLIGHT CHANCE OF SHOWERS AND
THUNDERSTORMS ALONG THE ARIZONA/NEW MEXICO STATE LINE AND IN THE
WHITE MOUNTAINS THIS AFTERNOON AND EVENING. OTHERWISE, MAINLY DRY
CONDITIONS INTO MONDAY. MOISTURE THEN SPREADS BACK ACROSS PORTIONS
OF SOUTHEAST ARIZONA NEXT WEEK FOR A CHANCE OF SHOWERS AND
THUNDERSTORMS, MAINLY EAST OF TUCSON. HIGH TEMPERATURES WILL BE NEAR
NORMAL THROUGH NEXT WEEK. MIN RH VALUES WILL BE IN THE 12-17 PERCENT
RANGE WEST OF TUCSON THROUGH THE WEEKEND AND 17-27 PERCENT IN VALLEY
LOCATIONS EAST OF TUCSON (25-40 PERCENT IN THE MOUNTAINS). RH VALUES
THEN INCREASE 7-15+ PERCENT NEXT WEEK AS MOISTURE MOVES BACK INTO
SOUTHEAST ARIZONA. 20-FOOT WIND WILL BE LESS THAN 15 MPH INTO AT
LEAST THE MIDDLE OF NEXT WEEK. GUSTY AND ERRATIC WINDS WILL
ACCOMPANY ANY THUNDERSTORMS.
TWC WATCHES/WARNINGS/ADVISORIES
NONE.
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