519
FXUS65 KTWC 111018
AFDTWC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
318 AM MST TUE NOV 11 2025
SYNOPSIS
HIGH TEMPERATURES REMAIN SEVERAL DEGREES ABOVE AVERAGE THROUGH
THURSDAY. A LOW PRESSURE SYSTEM IS THEN EXPECTED TO CROSS THE
REGION FRIDAY THROUGH THE WEEKEND, BRINGING CHANCES FOR RAIN AND
HIGH ELEVATION MOUNTAIN SNOW, COOLER TEMPERATURES, AND WINDY
CONDITIONS.
DISCUSSION
AFTER A CHILLY MORNING IN THE EASTERN VALLEYS, TEMPERATURES BOUNCE
BACK UP TODAY TO ABOVE NORMAL AS AN UPPER LEVEL RIDGE DRIFTS OVER
THE REGION.
OVER THE COMING SEVERAL DAYS AN UPPER TROUGH CURRENTLY OVER THE
GULF OF ALASKA IS EXPECTED TO DIG SOUTH, LIKELY CROSSING THE WEST
COAST AND REACHING THE DESERT SOUTHWEST FRIDAY TO SATURDAY. GLOBAL
MODEL ENSEMBLE MEMBERS ARE SHOWING INCREASING CONSISTENCY IN
HANDLING THE EVOLUTION OF THE UPPER TROUGH, WITH MOST CLOSING OFF
THE BASE OF THE TROUGH AS IT BEGINS TO CROSS THE UPPER BAJA. A
CUTOFF LOW OFTEN PRESENTS CHALLENGES IN FORECASTING TIMING OR
PRECIPITATION TOTALS, AND IN THIS CASE THERE SHOULD REMAIN A
MEDIUM SIZED GRAIN OF SALT IN WHAT TO EXPECT FRIDAY THROUGH THE
WEEKEND. LOOKING AT WHAT THE 00Z DETERMINISTIC SUITE IS SHOWING
SYNOPTICALLY, AN UPSTREAM JET EJECTS A SPEED MAX THROUGH THE BASE
OF THE LOW AS IT APPROACHES. IN THAT OUTCOME IT'S REASONABLE TO
SEE HOW THAT JET STREAK ASSOCIATED WITH THE CROSSING LOW BRINGS
STRONG ASCENT TO PRODUCE NOTABLE PRECIPITATION CHANCES AND
POTENTIALLY PERIODS OF MODERATE RATES. HOWEVER THERE REMAINS THE
POTENTIAL FOR THE LOW TO DELAY ITS ARRIVAL OR ARRIVE WEAKER THAN
MANY ENSEMBLE MEMBERS ARE SHOWING, WHICH IS REASONABLE AS WELL
GIVEN THE LIKELIHOOD THAT IT CLOSES OFF.
THE ENSEMBLE SPREAD IN QPF AT ANY ONE LOCATION REMAINS FAIRLY
HIGH GIVEN THESE UNCERTAINTIES, RANGING FROM JUST VERY LIGHT
AMOUNTS TO OVER AN INCH (WITH AN EVEN GREATER VALUES AT
ELEVATION). THE HIGH END OF THE PROBABILISTIC ENVELOPE HAS
INCREASED IN RECENT MODEL RUNS AS MORE ENSEMBLES ARE LATCHING ONTO
THE SOLUTION THAT FEATURES A STRONGER LOW, WHICH DOES INTRODUCE
THE POSSIBILITY FOR MINOR FLOODING IMPACTS. SHORT- TERM RAINFALL
RATES AREN'T LIKELY TO CAUSE NOTABLE FLOODING CONCERNS ON THEIR
OWN, BUT AREAS UNDER THE EXIT REGION OF THE UPPER JET MAY SEE A
PROLONGED PERIOD OF MODERATE PRECIPITATION THAT COULD CAUSE STREET
PONDING AND RUNNING WATER THROUGH WASHES. CURRENTLY THE FAVORED
TRACK IS TENDING TO BRING HEAVIEST RAINFALL TOTALS NORTH OF TUCSON,
CLOSER TO PHOENIX AND NORTH...BUT PERIODS OF MODERATE
PRECIPITATION CAN'T BE RULED OUT FOR ANY LOCATION OF SOUTHEASTERN
ARIZONA. ACCUMULATING SNOW ATOP MOUNTAINS SHOULD ALSO ARRIVE WITH
THIS LOW, MAINLY ABOVE 7500 FEET. IF SUFFICIENT MOISTURE WRAP-
AROUND OCCURS AS THE LOW CROSSES LATE SATURDAY, SNOW LEVELS MAY
DROP A BIT LOWER. CURRENT FORECAST TOTALS REMAIN BELOW ADVISORY
CRITERIA BUT 6 INCH ACCUMULATIONS OR MORE CAN'T BE RULED OUT IN
THE WHITE MOUNTAINS.
TEMPERATURES WILL SIGNIFICANTLY DROP WITH THIS SYSTEM AND
SOUTHWEST WINDS WILL INCREASE FRIDAY INTO THE WEEKEND. HIGHS
SATURDAY WILL LIKELY FALL 10-15 DEGREES BELOW NORMAL AND
POTENTIALLY EVEN LOWER IN AREAS THAT SEE PROLONGED PRECIPITATION.
TEMPERATURES REMAIN BELOW NORMAL SUNDAY INTO EARLY NEXT WEEK WITH
JUST A MODEST REBOUND AS THE LOW EXITS. A RISK OF SUB- FREEZING
MORNING LOWS SUNDAY THROUGH TUESDAY WILL RETURN FOR VALLEYS EAST
OF TUCSON.
AVIATION
VALID THROUGH 12/12Z.
MAINLY SKC WITH A FEW HIGH LEVEL CIRRUS STREAMING THROUGH THE
AREA. WINDS LIGHT, TERRAIN DRIVEN, AND UNDER 10 KTS THROUGH THE
FORECAST PERIOD. AVIATION DISCUSSION NOT UPDATED FOR TAF
AMENDMENTS.
FIRE WEATHER
LIGHT TERRAIN DRIVEN WINDS MAINLY UNDER 12 MPH THROUGH WEDNESDAY
WITH MINIMUM RELATIVE HUMIDITIES OF 12 TO 22 PERCENT. A LOW
PRESSURE SYSTEM WILL LIKELY CROSS THE REGION FRIDAY THROUGH THE
WEEKEND. WINDS WILL BEGIN TO INCREASE AHEAD OF THIS SYSTEM
THURSDAY AND ESPECIALLY FRIDAY. WIDESPREAD RAIN AND HIGH ELEVATION MOUNTAIN
SNOW CHANCES OVERSPREAD THE REGION FRIDAY AND SATURDAY.
TEMPERATURES ARE EXPECTED TO BECOME WELL BELOW NORMAL OVER THE
WEEKEND.
TWC WATCHES/WARNINGS/ADVISORIES
FREEZE WARNING UNTIL 9 AM MST THIS MORNING FOR AZZ507>509.
PUBLIC...EDWARDS
AVIATION...EDWARDS
FIRE WEATHER....EDWARDS
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