465
FXUS65 KTWC 050800
AFDTWC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
100 AM MST MON JAN 5 2026
SYNOPSIS
SEASONABLE TEMPERATURES CONTINUE TO START THE WORK WEEK WITH HIGH
CLOUDS STREAMING THROUGH THE REGION. A LOW PRESSURE SYSTEM IS
EXPECTED TO CROSS THE REGION WEDNESDAY INTO FRIDAY, BRINGING
CHANCES FOR RAIN AND HIGH ELEVATION MOUNTAIN SNOW. COOL
TEMPERATURES WILL FOLLOW INTO NEXT WEEKEND.
DISCUSSION
A DEEPENING TROUGH NOW OFF THE COAST OF NORTHERN CALIFORNIA WILL
GRADUALLY PUSH SOUTH OVER THE NEXT SEVERAL DAYS. THE RIDGE THAT
WAS IN PLACE YESTERDAY HAS FLATTENED AND BEGUN PUSHING EASTWARD
AS THE TROUGH DIGS FURTHER SOUTH. TO START THE WORK WEEK
TEMPERATURES ACROSS SOUTHEASTERN ARIZONA REMAIN NEAR TO JUST ABOVE
NORMAL.
THE PACIFIC TROUGH WILL CONTINUE TO EXTEND SOUTHWARD BECOMING A
CUT OFF LOW TUESDAY MORNING THEN PUSH EAST AND ONSHORE INTO
NORTHERN BAJA WEDNESDAY EVENING, KEEPING IT CLOSED, THEN QUICKLY
MOVE IT INTO TEXAS THURSDAY. THE SYSTEM WILL RESULT IN VALLEY
RAIN, HIGH LEVEL MOUNTAIN SNOW WITH SNOW LEVELS BETWEEN 7000-7500
FEET AND BELOW NORMAL TEMPERATURES. IT'S LOOKING INCREASINGLY
LIKELY A SECOND WAVE WILL DIVE IN FROM THE PACIFIC NORTHWEST
THURSDAY, CAUSING THE INITIAL WAVE TO OPEN AND KICK OUT WITHOUT
DELAYING PRECIPITATION CHANCES TERRIBLY LONG.
ENSEMBLES FOCUS THE BEST PRECIPITATION CHANCES TO BE FROM
WEDNESDAY AFTERNOON STARTING IN SOUTHWESTERN PIMA COUNTY THROUGH
FRIDAY MORNING FOR ARES NORTHEAST OF TUCSON. OVERALL
PRECIPITATION FORECAST REMAINS SIMILAR TO PREVIOUS SHIFTS WITH
AROUND 0.1"-0.25" ACROSS LOWER ELEVATIONS AND HIGHER ATOP
MOUNTAINS (WITH LESS IN WESTERN PIMA). SNOW TOTALS HAVE COME UP A
LITTLE BIT SINCE YESTERDAY NOW RANGING FROM 1"-6". WHILE THE
SECOND DISTURBANCE SEEMS TO STAY MORE NORTH, THERE IS A CHANCE IT
COULD DESCEND FURTHER SOUTH AND THAT WOULD LINGER LIGHT SNOW INTO
FRIDAY BRINGING ADDITIONAL ACCUMULATIONS. THERE ARE STILL
DISCREPANCIES BETWEEN THE MODELS ON HOW DEEP THE TROUGH AND
SECONDARY DISTURBANCE WILL DESCEND SOUTH AND HOW QUICKLY THE
SYSTEM EXITS THE REGION.
ONCE THE TROUGH PASSES, NORTH TO NORTHWEST FLOW ALOFT WILL SET IN
PLACE. A COLD AIR MASS WILL ASSOCIATE WITH THIS SYSTEM, LEADING TO
SUB- FREEZING MORNING LOWS LIKELY IN HISTORICALLY COOLER VALLEYS
EAST OF TUCSON STARTING FRIDAY MORNING. MEANWHILE FROM PINAL
THROUGH EASTERN PIMA AND SANTA CRUZ COUNTIES, THE COOLEST
TEMPERATURES OF THE SEASON SO FAR MAY OCCUR WITH THE TUCSON METRO
POTENTIALLY SEEING THE 30S FRIDAY MORNING THROUGH SUNDAY MORNING.
NBM PROBABILITIES FOR PARTS OF THE TUCSON METRO OBSERVING BELOW 32
DEGREES HAS INCREASED SOME SINCE YESTERDAY, NOW WITH A 35% CHANCE
SATURDAY MORNING. THIS COLD AIR WILL LOWER HIGH TEMPERATURE TO
BELOW NORMAL BY WEDNESDAY.
AVIATION
VALID THROUGH 06/12Z.
SKC-FEW CLOUDS AOA 18-20K FT AGL BECOMING FEW-SCT AFT 05/13Z AOA
15-20K FT AGL. CLOUDS INCREASE TO SCT-BKN BY 06/08Z PERSISTING
THROUGH THE END OF THE FORECAST PERIOD. SURFACE WINDS LIGHT AND
TERRAIN DRIVEN THROUGH THE FORECAST PERIOD. AVIATION DISCUSSION
NOT UPDATED FOR TAF AMENDMENTS.
FIRE WEATHER
LIGHT WINDS AND MINIMUM RELATIVE HUMIDITIES ABOVE 30 PERCENT
THROUGH WEDNESDAY. A SYSTEM WILL CROSS THE REGION WEDNESDAY INTO
FRIDAY, BRINGING CHANCES FOR RAIN AND HIGH ELEVATION MOUNTAIN
SNOW. TEMPERATURES ARE FORECAST TO FALL BELOW NORMAL WILL THIS
SYSTEM THURSDAY INTO THE WEEKEND.
TWC WATCHES/WARNINGS/ADVISORIES
NONE.
MALARKEY
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