467
FXUS65 KTWC 021013
AFDTWC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
313 AM MST FRI MAY 2 2025
SYNOPSIS
TEMPERATURES WILL BE A COUPLE DEGREES ABOVE NORMAL
INTO SATURDAY THEN COOL TO WELL BELOW NORMAL SUNDAY INTO EARLY
NEXT WEEK AS A STRONG PACIFIC WEATHER SYSTEM MOVES THROUGH.
ALTHOUGH THIS SYSTEM WILL BE GENERALLY DRY FOR SOUTHEAST
ARIZONA...IT WILL BRING STRONG AND GUSTY WINDS SUNDAY RESULTING
IN CRITICAL FIRE WEATHER CONDITIONS.
DISCUSSION
THE UPPER PATTERN THIS MORNING IS DEFINED BY A
STRONG RIDGE OF HIGH PRESSURE IN THE PACIFIC NORTHWEST WITH A
WEAK UPPER LOW TRAPPED SOUTH OF THIS FEATURE (CENTERED OVER FAR
SOUTHERN CALIFORNIA). DESPITE THE CLOSE PROXIMITY OF THE UPPER-
LOW, THE 850-700 MB THICKNESSES FOR KTUS ARE STILL PROGGED AOA
1630-1640M. ACCORDING TO OUR LOCAL EMPIRICALLY DRIVEN REGRESSION
EQUATION/STUDY WOULD PRODUCE A HIGH TEMPERATURE AT KTUS BETWEEN
88-91 DEGREES. DIFFLUENCE AROUND THE UPPER-LOW MAY BE ENOUGH TO
PRODUCE SOME LIGHT SHOWERS OVER THE WHITE MOUNATINS THE NEXT FEW
DAYS, WITH THE POTENTIAL FOR AN OCCASIONAL DRY LIGHTNING STRIKE AS
WELL. AIRMASS IS GENERALLY TOO DRY FOR ANYTHING MORE THAN A FEW
HUNDREDTHS OF AN INCH OF PCPN IN THE EAST-CENTRAL MOUNTAINS OF
ARIZONA.
THE BIGGEST FORECAST CHALLENGE TO THIS FORECAST PACKAGE IS THIS
WEEKEND AS A STRONG UPPER LOW MAKES ITS WAY FROM THE EASTERN
PACIFIC INTO ARIZONA. THIS IS AN ABNORMALLY STRONG FEATURE THAT IS
3 STANDARD DEVIATIONS FROM THE MEAN WITH REGARDS TO THE 500 MB
HEIGHTS. THE MAIN IMPACT WILL BE FROM THE STRONG AND GUSTY
SOUTHWEST WINDS SUNDAY. STRONG GRADIENT IN THE LOWER LEVELS WILL
DRIVE THE STRONG WINDS SUNDAY, WITH 50KT FLOW GENERALLY ABOVE 500
MB FOR THE EVENT. THIS WILL LIMIT THE HIGH-END GUSTS EXPECTED,
ESPECIALLY ALONG THE INTERNATIONAL AND ARIZONA/NEW MEXICO BORDERS
S AND SE OF TUCSON TO THE 40-45 MPH RANGE. MOISTURE PLUME WITH A
PWAT AROUND 0.75 INCHES WILL PUSH INTO INTO THE WESTERN PORTIONS
OF THE CWA AHEAD OF THE UPPER LOW SATURDAY NIGHT INTO SUNDAY
MORNING INCREASING DEWPOINTS AND RESULTING IN MINIMUM RH VALUES
AROUND 20-30 PERCENT WEST OF TUCSON ON SUNDAY. DESPITE THE CLOSE
PROXIMITY OF THIS MOISTURE, THE EASTERN HALF OF THE CWA WILL HOLD
ONTO DEWPOINTS IN THE LOWER 20S WHICH WOULD RESULT IN MINIMUM
HUMIDITIES IN THE 11-16 PERCENT RANGE. WHAT USUALLY HAPPENS IN
THIS TYPE OF PATTERN IS THAT THE UPPER LOW IS A TAD SLOWER THAN
PROGGED. THIS ESSENTIALLY KEEPS THE FEATURE FARTHER WEST,
RESULTING IN DRIER THAN EXPECTED CONDITIONS TO OUR EAST DURING
THE DAY. THIS BODES WELL FOR THE FIRE WEATHER WATCH IN EFFECT FOR
SUNDAY...BUT CONFIDENCE IS STILL NOT HIGH ENOUGH THAT THE MOISTURE
WILL BE HELD AT BAY TO CONVERT THE WATCH TO A RED FLAG WARNING AT
THIS TIME. I SUSPECT THAT THE WESTERN PORTIONS OF THE FIRE
WEATHER WATCH AREA MAY NEED TO BE TRIMMED AS THE TIMING IS
REFINED.
OTHERWISE, THE UPPER-LOW ISN'T TOO EXCITED TO DEPART THE REGION
LINGERING AROUND THE FOUR CORNERS THROUGH WEDNESDAY AS THE UPPER
RIDGE UPSTREAM POSITIVELY TILTS INTO THE PACIFIC NORTHWEST. WE
WILL REMAIN ON THE SOUTHERN PERIPHERY OF THIS SYSTEM LIMITING THE
POTENTIAL FOR PRECIPITATION ACROSS SOUTHEAST ARIZONA TO THE
NORTHERN PORTIONS OF THE FORECAST AREA. IN ANY EVENT, PCPN WILL BE
LIGHT. EXPECT AFTERNOON TEMPERATURES TO REMAIN BELOW NORMAL THE
FIRST HALF OF NEXT WEEK, WITH A WARMUP THE SECOND HALF OF THE WEEK
EXPECTED AS THE UPPER TROUGH IS REPLACED WITH A SHORTWAVE RIDGE.
AVIATION
VALID THROUGH 03/12Z. SKC THRU 02/18Z, THEN SCT 12-15K
FT AGL. AREAS TO THE NE OF KSAD WILL SEE SCT-BKN CLOUDS AOA 6-10K
FT AGL AFT 02/18Z. SFC WINDS LESS THAN 10 KTS THROUGH THE MORNING
HOURS, THEN WLY 8-12 KTS WITH GUSTS TO 20 KTS AFT 02/19Z. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.
FIRE WEATHER
WARM WITH SLIGHTLY ABOVE NORMAL TEMPERATURES THE
NEXT FEW DAYS. WINDS TODAY WILL GENERALLY BE SWLY/WLY 10-15 MPH
WITH OCCASIONAL AFTERNOON GUSTS TO 25 MPH. THERE WILL BE A SLIGHT
CHANCE FOR SHOWERS AND AN ISOLATED LIGHTNING STRIKE OR TWO IN THE
WHITE MOUNTAINS TODAY AND SATURDAY (AND SLIGHT CHANCES FOR DRY
LIGHTNING ELSEWHERE ACROSS GRAHAM AND GREENLEE COUNTY) AS A WEAK
WEATHER SYSTEM MOVES THROUGH. A STRONG PACIFIC STORM SYSTEM WILL
THEN MOVE INTO THE REGION THIS WEEKEND, RESULTING IN WINDY
CONDITIONS AND THE POTENTIAL FOR CRITICAL FIRE WEATHER CONCERNS
SUNDAY. A FIRE WEATHER WATCH REMAINS IN EFFECT SUNDAY FROM THE
TUCSON AREA AND POINTS EASTWARD.
TWC WATCHES/WARNINGS/ADVISORIES
FIRE WEATHER WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING
FOR AZZ150>153.
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