317
FXUS65 KTWC 292127
AFDTWC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
227 PM MST THU MAY 29 2025
SYNOPSIS
TEMPERATURES WILL REMAIN SLIGHTLY ABOVE NORMAL THROUGH FRIDAY WITH
GENERALLY DRY CONDITIONS PREVAILING. A WEATHER SYSTEM
THIS WEEKEND WILL BRING A SUBSTANTIAL MOISTURE INCREASE INTO THE
REGION, INITIALLY WITH A SLIGHT CHANCE OF MAINLY DRY THUNDERSTORMS
EAST OF TUCSON FRIDAY, THEN SLIGHT CHANCES OF SHOWERS AND ISOLATED
THUNDERSTORMS SATURDAY. WIDESPREAD SHOWERS AND ISOLATED
THUNDERSTORMS WILL OCCUR SUNDAY INTO EARLY MONDAY WITH DRY
CONDITIONS RETURNING THEREAFTER. BELOW NORMAL TEMPERATURES RETURN
SUNDAY INTO EARLY NEXT WEEK.
DISCUSSION
IN THE UPPER LEVELS, DIVERGENT FLOW ALOFT ASSOCIATED WITH A CLOSING
LOW OVER NORTHWEST BAJA WAS RESPONSIBLE FOR THE WIDESPREAD HIGH
LEVEL CLOUDS OVER SOUTHERN ARIZONA THIS AFTERNOON AND EVENING.
WHILE CURRENTLY LACKING A MOISTURE FEED TO ADEQUATELY COMBAT THE
DRY LOW TO MID LEVELS, THIS WILL LIKELY CHANGE OVER THE COMING
DAYS AS RICHER MOISTURE MOVES IN FROM THE SOUTH AND EAST. TO THE
SOUTH, NOW NAMED TROPICAL STORM ALVIN WILL MOVE NORTH TOWARDS THE
BAJA PENINSULA THIS WEEKEND. WHILE THIS STORM IS EXPECTED TO
WEAKEN SOON, THE MOISTURE ASSOCIATED WITH IT WILL PLAY A LARGE
PART IN PROVIDING AN ANOMALOUSLY MOIST ENVIRONMENT OVER
SOUTHEASTERN ARIZONA BY SUNDAY. ADDITIONAL MOISTURE SHOULD MOVE
INTO FAR EASTERN LOCATIONS AS EARLY AS TOMORROW WITH SOUTHEASTERLY
FLOW SETTING UP OVER NORTHERN MEXICO AND NEW MEXICO. THE DEPTH OF
THIS SOUTHEASTERLY MOISTURE IS MORE QUESTIONABLE HOWEVER AND THE
PROBABILITY FOR RAINFALL IN FAR EASTERN AREAS OF SOUTHEASTERN
ARIZONA WILL INITIALLY BE LIMITED FOR THAT REASON. THE SYNOPTIC
PATTERN WILL ALSO LIMIT PRECIPITATION POTENTIAL AS THE UPPER LOW
TO THE WEST REMAINS CLOSED WHILE SITTING TO THE WEST. THIS OVERALL
SETUP WILL THEN LIKELY CHANGE ON SUNDAY AS THE UPPER LOW OPENS
AND KICKS OUT OVER THE REGION, OVERLAPPING WITH THE ARRIVAL OF
RICHER TROPICAL MOISTURE FROM THE SOUTH.
FRIDAY SHOULD SEE CLOUD BUILD-UPS OVER EASTERN HIGH-TERRAIN
LOCATIONS AS MODEST MID-LEVEL MOISTURE ARRIVES IN THE AFTERNOON
AND EVENING, PROVIDING AN ISOLATED RISK OF DRY THUNDERSTORMS AND
LIGHTNING. OTHERWISE THE WEATHER FORECAST FEATURES ABOVE NORMAL
TEMPERATURES WITH DESERT HIGHS RANGING FROM 95-100 DEGREES.
THE LEADING EDGE OF TROPICAL MOISTURE ARRIVES ON SATURDAY WITH
PRECIPITABLE WATER VALUES OF 0.6" TO NEAR ONE INCH MOVING IN FROM
THE SOUTH. THE UPPER LOW WILL STILL BE WELL TO THE WEST, KEEPING A
SHORTWAVE RIDGE OVER THE REGION. WHILE THIS DAMPENS NOTABLE
PRECIPITATION CHANCES, DIURNAL INSTABILITY SHOULD BE ABLE TO
DEVELOP FROM THIS MOISTURE IN THE AFTERNOON, WITH ISOLATED LIGHT
SHOWERS AND VERY ISOLATED THUNDERSTORMS IN THE AFTERNOON AND EARLY
EVENING.
AS MENTIONED ABOVE SUNDAY WILL LIKELY SEE THE COMBINATION OF A
CROSSING OF A NOW OPEN AND MORE PROGRESSIVE UPPER LEVEL TROUGH AS
WELL AS THE PUSH OF ANOMALOUS MOISTURE INTO SOUTHEASTERN ARIZONA.
NAEFS CLIMATOLOGICAL GUIDANCE PUTS THE FORECAST ATMOSPHERIC
MOISTURE AT THE 97TH-99TH PERCENTILE FOR THIS TIME OF YEAR. GIVEN
THE SYNOPTIC FORCING ASSOCIATED WITH THE CROSSING UPPER LEVEL JET
AND THE ANOMALOUS TROPICAL MOISTURE FEED, WIDESPREAD SHOWER AND
THUNDERSTORM CHANCES ARE EXPECTED SUNDAY INTO MONDAY. MODEL
GUIDANCE IS IN FAIR AGREEMENT WITH THE TIMING OF THE TROUGH
PASSAGE AND PRECIPITATION TIMING, WITH CHANCES SPREADING FROM WEST
TO EAST FROM SUNDAY MORNING IN WESTERN ARIZONA TO SUNDAY AFTERNON
AND NIGHT FURTHER EAST. THERE LIKELY IS SOME ROOM FOR ADJUSTMENT
IN THIS TIMING AS LEAD TIME DECREASES GIVEN NORMAL UNCERTAINTIES
IN HOW CLOSED LOWS OPEN AND PHASE WITH THE UPPER LEVEL FLOW. THE
OVERALL QPF RANGE IS FAIRLY CONSISTENT TO THE PREVIOUS FORECAST,
WITH VALLEY RANGES FROM 0.2" TO 0.5" AND HIGHER AMOUNTS IN
MOUNTAINS. THE HEAVIEST RAINFALL RATES SHOULD ARRIVE AS THE UPPER
JET CROSSES, LIKELY SUNDAY EVENING THROUGH EARLY MONDAY MORNING.
IN LOCATIONS THAT SEE MULTIPLE ROUNDS OF SHOWERS UNDER THIS PERIOD
OF STRONGER ASCENT ALOFT, AMOUNTS HIGHER THAN THE AFOREMENTIONED
RANGE ARE POSSIBLE (NBM PROBABILITIES OF 0.75" RANGE FROM AROUND
10-20 PERCENT WITH THIS SCENARIO). AGAIN, THERE REMAINS A
POSSIBILITY THE TRANSITION OF THE UPPER LOW TAKES A BIT LONGER
THAN FORECAST, DELAYING THESE PROBABILITIES A BIT MORE INTO
MONDAY.
MONDAY'S OUTLOOK WILL DEPEND ON THE EASTWARD PROGRESS OF THE UPPER
LOW AND WHETHER OR NOT PRECIPITATION CHANCES LINGER WITH A SLOWER
TRACK. ALONG AND BEHIND THIS LOW, TEMPERATURES SHOULD FALL BELOW
NORMAL, WITH CURRENTLY FORECAST HIGHS SUNDAY AND MONDAY AROUND 5-7
DEGREES BELOW NORMAL. IN AREAS THAT SEE PROLONGED SHOWERS AND
CLOUD COVER EVEN COOLER TEMPERATURES ARE LIKELY. WEST TO SOUTHWEST
BREEZY WINDS ARE LIKELY BEHIND THIS EXITING LOW, ESPECIALLY IF
ENHANCED BY A SECOND TROUGH DEPICTED BY GLOBAL MODELS ARRIVING
AROUND MID-WEEK. CURRENT ENSEMBLES FAVOR A MOSTLY DRY PASSAGE WITH
THIS SECOND WAVE HOWEVER AS IT STAYS A BIT NORTH AND ARRIVES
WEAKER THAN THE PREVIOUS WAVE.
AVIATION
SCT-BKN CLOUDS MAINLY AOA 15K FT THROUGH THE VALID PERIOD.
GENERALLY LIGHT AND TERRAIN DRIVEN WINDS LESS THAN 12 KTS THROUGH
THE FORECAST PERIOD WITH WLY/SWLY AFTERNOON GUSTS AROUND 15 KTS.
AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.
FIRE WEATHER
AN EVOLVING WEATHER PATTERN FRIDAY THROUGH THE WEEKEND BEGINS TO
DRAW MOISTURE INTO FAR EASTERN AREAS FRIDAY. THIS INITIAL
MOISTURE MAY CREATE SOME BUILD-UPS WITH DRY LIGHTNING FRIDAY
AFTERNOON AND EVENING. OVERALL MOISTURE NEAR THE SURFACE REMAINS
LOW FRIDAY AFTERNOON WITH MINIMUM RELATIVE HUMIDITY VALUES IN THE
SINGLE DIGITS TO 12 PERCENT. THEN ADDITIONAL MOISTURE PUSHES INTO
SOUTHEASTERN ARIZONA SATURDAY BRINGING MINIMUM HUMIDITY VALUES TO
12 TO 22 PERCENT. THIS MAY DEVELOP ANOTHER OPPORTUNITY FOR CLOUD
BUILD-UPS AND DRY LIGHTNING, ESPECIALLY SOUTH AND EAST OF TUCSON.
SUNDAY INTO MONDAY SHOULD FEATURE ADEQUATE MOISTURE FOR A HIGH
LIKELIHOOD OF WIDESPREAD WETTING RAIN OPPORTUNITIES. OVERALL WINDS
REMAIN LIGHT BUT GUSTY AND ERRATIC WINDS WOULD OCCUR WITH ANY
THUNDERSTORM ACTIVITY. DRY WEATHER RETURNS BY NEXT TUESDAY.
TWC WATCHES/WARNINGS/ADVISORIES
NONE.
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AVIATION...EDWARDS
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