289
FXUS65 KTWC 212027
AFDTWC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
127 PM MST SUN DEC 21 2025
SYNOPSIS
DRY AND WARM WEATHER CONTINUES THROUGH TUESDAY, WITH
THE POTENTIAL FOR RECORD HIGH TEMPERATURES AT A FEW LOCATIONS. AN
APPROACHING PACIFIC STORM SYSTEM WILL RESULT IN A CHANCE OF RAIN
SHOWERS TUESDAY NIGHT INTO NEXT WEEKEND. THIS SYSTEM WILL BRING
COOLER BUT STILL ABOVE NORMAL HIGH TEMPERATURES.
DISCUSSION
IN THE LARGE SCALE, HIGH PRESSURE ALOFT CURRENTLY
CENTERED OVER NORTHERN MEXICO WILL MOVE EAST INTO THE SOUTHERN
PLAINS BY LATE TUESDAY. WEST COAST TROUGHING THEN TAKES PLACE FROM
THE MIDDLE OF THE WEEK THROUGH NEXT WEEKEND.
UNSEASONABLY WARM HIGH TEMPERATURES AND DRY CONDITIONS WILL CONTINUE
THROUGH TUESDAY, WITH NEAR RECORD TO RECORD HIGH TEMPERATURES. HIGH
TEMPERATURES WILL TOP OUT 15-20 DEGREES ABOVE NORMAL TODAY THROUGH
TUESDAY.
AS THE PATTERN CHANGES TO A WEST COAST TROUGH THE LATTER HALF OF THE
WORK WEEK, HIGH TEMPERATURES LOWER 5-10 DEGREES WEDNESDAY THROUGH
FRIDAY. THIS STILL TRANSLATES INTO HIGH TEMPERATURES 10-13 DEGREES
ABOVE NORMAL, OR IN THE 70S FOR VALLEY LOCATIONS ACROSS SOUTHEAST
ARIZONA. ANOTHER 3-5 DEGREES OF COOLING TAKES PLACE NEXT WEEKEND AS
THE TROUGH AXIS DEEPENS AND A PACIFIC STORM SYSTEM DROPS INTO THE
BASE OF THE TROUGH. HIGHS WILL STILL BE 3-5 DEGREES ABOVE NORMAL,
WITH HIGHS TOPPING OUT IN THE MID 60S TO NEAR 70 DEGREES.
ALTHOUGH THERE ARE PRECIPITATION CHANCES ACROSS THE FORECAST AREA
TUESDAY NIGHT THROUGH NEXT WEEKEND, THERE APPEARS TO BE TWO MAIN
DISTINCT TIME FRAMES WITH THE HIGHEST PRECIPITATION CHANCES. THE
FIRST IS TUESDAY NIGHT INTO THURSDAY AND THE SECOND IS SATURDAY
NIGHT INTO MONDAY.
FOR THE TUESDAY NIGHT INTO THURSDAY PERIOD, THE MODELS ARE IN GOOD
AGREEMENT THAT A SUBTROPICAL MOISTURE PLUME WILL GET PULLED
NORTHEASTWARD ACROSS ARIZONA IN SOUTHWEST FLOW ALOFT AS THE WEST
COAST TROUGH SETS UP. ALTHOUGH POPS ARE CURRENTLY AT 20-50 PERCENT
(VALLEYS) AND 40-70 PERCENT (MOUNTAINS), RAINFALL AMOUNTS WILL BE
FAIRLY LIGHT, GENERALLY 0.15" OR LESS IN THE VALLEYS AND 0.20-0.40"
IN THE MOUNTAINS. SNOW LEVELS WILL BE ABOVE MOUNTAINTOP LEVELS.
THERE IS A HIGHER MODEL UNCERTAINTY FOR THE SATURDAY NIGHT INTO
MONDAY TIME FRAME, WITH THE DETERMINISTIC ECMWF EJECTING THE UPPER
LOW INTO NORTHERN ARIZONA LATE IN THE WEEKEND, WHILE THE GFS KEEPS
THE UPPER LOW OFF THE CALIFORNIA COAST THROUGH THE WEEKEND (BUT
STEERS ANOTHER SUBTROPICAL MOISTURE PLUME INTO ARIZONA). THE
ENSEMBLES TEND TO FAVOR KEEPING THE UPPER LOW TO OUR WEST. NBM
PRECIPITATION AMOUNTS ARE ON THE LIGHT SIDE, WITH AMOUNTS BETWEEN
0.10" AND 0.25". SNOW LEVELS LOWER INTO THE 8,500 TO 9,000 FOOT
RANGE SATURDAY NIGHT INTO MONDAY.
OVERALL, WHILE CONFIDENCE IS HIGH THAT THE PATTERN WILL GET MORE
ACTIVE THE SECOND HALF OF THIS WEEK INTO NEXT WEEKEND, CONFIDENCE
REMAINS LOW TO MODERATE ON PRECIPITATION TIMING/AMOUNTS ACROSS
SOUTHEAST ARIZONA DUE TO MODEL DIFFERENCES IN THE TRACK OF THE UPPER
LOW AND THE LACK OF AN OBVIOUS TRIGGER (LIFT/DYNAMICS VERSUS HIGH
PW/OROGRAPHIC LIFT) OVER THE FORECAST AREA.
AVIATION
VALID THROUGH 23/00Z.
GENERALLY CLEAR SKIES/SKC CONDIITONS THRU 22/18Z, THEN INCREASING
HIGH CIRRUS CLOUDS WITH SCT-BKN CLOUDS AOA 20K FT AGL BY END OF
FORECAST PERIOD. SFC WIND 10 KNOTS OR LESS, FAVORING A WLY/NWLY
DIRECTION IN THE AFTERNOON/EARLY EVENING AND VARIABLE IN DIRECTION
AT OTHER TIMES. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.
FIRE WEATHER
WARM AND DRY CONDITIONS CONTINUE THROUGH TUESDAY,
WITH HIGHS 15-20 DEGREES ABOVE NORMAL. A COOLING TREND STARTS ON
WEDNESDAY INTO NEXT WEEKEND, BUT HIGHS WILL STILL BE 5-10 DEGREES
ABOVE NORMAL. TROPICAL MOISTURE WILL STREAM NORTHWARD AHEAD OF A
PACIFIC STORM SYSTEM, RESULTING IN A CHANCE OF LIGHT PRECIPITATION
TUESDAY NIGHT INTO THURSDAY. ADDITIONAL PRECIPITATION CHANCES ARE
EXPECTED LATE NEXT WEEKEND. 20-FOOT WINDS WILL BE 15 MPH OR LESS AND
TERRAIN DRIVEN INTO NEXT WEEKEND. MIN RELATIVE HUMIDITY VALUES AT
ALL ELEVATIONS WILL BE IN THE 10-20 PERCENT RANGE THROUGH TUESDAY,
INCREASING TO 30-45 PERCENT (AND HIGHER IN THE MOUNTAINS) WEDNESDAY
INTO NEXT WEEKEND.
TWC WATCHES/WARNINGS/ADVISORIES
NONE.
ZELL
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