289
FXUS65 KFGZ 211015
AFDFGZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
315 AM MST WED OCT 21 2026
SYNOPSIS
A VERY ACTIVE PERIOD OF WEATHER IS ANTICIPATED OVER
THE NEXT TWO DAYS. A STRONG WEATHER SYSTEM IS BRINGING WIDESPREAD
SHOWERS AND THUNDERSTORMS THIS MORNING, AND WILL CONTINUING
THROUGH THURSDAY. THE PRIMARY CONCERNS ARE FLOODING AND FLASH
FLOODING, SEVERE THUNDERSTORMS, AND EVEN A FEW TORNADOES. DRIER
CONDITIONS WITH LINGERING SLIGHT CHANCES FOR SHOWERS ARE EXPECTED
BY FRIDAY INTO THE WEEKEND.
DISCUSSION
A CONCERNING SITUATION WILL EVOLVE ACROSS ARIZONA
OVER THE NEXT TWO DAYS, WITH THREATS OF FLOODING/FLASH FLOODING,
SEVERE THUNDERSTORMS, AND TORNADOES. A STRONG LOW PRESSURE SYSTEM
OFF THE CALIFORNIA COAST IS BEGINNING TO MOVE INLAND. THIS IS WELL
POSITIONED TO CARRY A DEEP MOISTURE SURGE OF TROPICAL AND
SUBTROPICAL ORIGINS, AS WELL AS PROVIDE AN IDEAL ENVIRONMENT FOR
SEVERE WEATHER. THE LOW EVENTUALLY LIFTS THROUGH THE GREAT BASIN
ON THURSDAY, DRAGGING A COLD FRONT THROUGH THE REGION LATE
THURSDAY INTO FRIDAY.
THIS MORNING...THE FIRST SURGE OF TROPICAL MOISTURE HAS ARRIVED, AND
ACTIVITY IS RAMPING UP QUICKLY EARLY THIS MORNING. CURRENT
MESOANALYSIS SHOWS A 50-55KT JET OVERHEAD AT 500MB, AS WELL AS A
STRENGTHENING SOUTHEASTERLY LOW-LEVEL JET ADVECTING WARM AIR AND
HIGH DEWPOINTS INTO NORTHERN AZ. THIS HAS ALLOWED FOR INCREASING
INSTABILITY SOUTH OF THE RIM DURING THE OVERNIGHT HOURS, WITH MLCAPE
VALUES CURRENTLY AROUND 250-500 J/KG IN YAVAPAI AND GILA COUNTIES.
COUPLED WITH BULK SHEAR AROUND 50KTS AND STORM RELATIVE HELICITY 100-
200 M2/S2, WE ARE SEEING SCATTERED DISCRETE SUPERCELL THUNDERSTORMS
INITIATING ALONG THE TERRAIN AS OF 2 AM MST. THIS IS EXPECTED TO
DECLINE IN EXTENT OVER THE NEXT FEW HOURS AS CONDITIONS BECOME
SLIGHTLY MORE UNFAVORABLE, HOWEVER CONTINUED THUNDERSTORMS ACTIVITY
IS EXPECTED ESPECIALLY FURTHER WEST. SEVERE THUNDERSTORMS BRINGING 1-
2 INCH HAIL HAVE REMAINED THE PRIMARY THREAT THUS FAR. A SECONDARY
THREAT OF FLASH FLOODING IS ALSO IN PLAY THIS MORNING GIVEN THE
ARRIVAL OF DEEP MOISTURE. HOWEVER FAST STORM MOTION AND SCATTERED
COVERAGE WILL ALLOW RAIN ACCUMULATIONS TO LIKELY REMAIN BELOW FLASH
FLOODING CONCERNS OUTSIDE OF SENSITIVE BURN SCARS.
TODAY THROUGH THURSDAY EVENING...THREATS OF FLASH FLOODING AND
SEVERE THUNDERSTORMS CONTINUE THROUGH THE PERIOD. FOR FLOODING,
WE WILL REMAIN IN A CONTINUOUS FETCH OF DEEP TROPICAL/SUBTROPICAL
MOISTURE WITH MODEST INSTABILITY AND ENHANCED LOW-LEVEL FLOW.
PRECIPITABLE WATER (A MEASURE OF ATMOSPHERIC MOISTURE) WILL RISE
TO 0.8-1.2 INCHES ACROSS MOST OF OUR AREA. THIS IS HIGHLY
ANOMALOUS FOR MID-OCTOBER. DESPITE THE FAST EXPECTED STORM
MOTION, PERIODS OF TRAINING OR BACK-BUILDING STORMS ARE POSSIBLE
AND COULD LEAD TO LOCALLY HEAVY RAINFALL RATES WITH FLASH FLOODING
CONCERNS. ALSO SEVERAL ROUNDS OF HEAVY RAIN ARE EXPECTED FOR
MOST, AND LONGER DURATION FLOODING OF RIVERS, STREAMS, NORMALLY
DRY WASHES, DRAINAGE BASINS, ETC IS POSSIBLE. THIS IS EXACERBATED
FURTHER BY VERY SATURATED SURFACE CONDITIONS FOR ALL OF NORTHERN
AZ. AS A RESULT, A FLOOD WATCH WILL BE IN EFFECT BEGINNING AT 5 AM
MST TODAY AND CONTINUING THROUGH 11 PM MST THURSDAY. THE THREAT
OF FLOODING ENDS ON THURSDAY EVENING AS A COLD FRONT SWEEPS FROM
WEST TO EAST AND BRINGS MUCH DRIER AIR IN ITS WAKE.
FOR THE SEVERE THREAT, AN UNSTABLE ENVIRONMENT WITH AN IMPRESSIVE
SHEAR PROFILE WILL BE MAINTAINED THROUGH THE PERIOD. THE JET AT
500MB WILL CONTINUE TO STRENGTHEN ON WEDNESDAY AS THE LOW PRESSURE
SYSTEM SLOWLY APPROACHES. DESPITE CLOUD COVER TO LIMIT
DESTABILIZATION, HI-RES GUIDANCE REMAINS ADAMANT THAT CAPE VALUES
UP TO 1000-1500 J/KG WILL DEVELOP BY WEDNESDAY AFTERNOON WITH
HELP FROM LOW-LEVEL MOISTURE ADVECTION AND STEEPENING MID-LEVEL
LAPSE RATES. SEVERAL ROUNDS OF SEVERE WEATHER ARE POSSIBLE, WITH
THE PEAK THREAT WINDOW BEGINNING LATE WEDNESDAY AFTERNOON THROUGH
EVENING. STRONGER SUPERCELL STORMS WILL BE CAPABLE OF LARGE 2+
INCH HAIL, DAMAGING WIND GUSTS, AND EVEN A FEW TORNADOES. SPC
MAINTAINS AN ENHANCED RISK (LEVEL 3 OUT OF 5) OF SEVERE WEATHER
CENTERED ALONG THE MOGOLLON RIM ON WEDNESDAY. INTO THURSDAY, THE
SEVERE THREAT LOOKS TO SHIFT A BIT FURTHER EAST TOWARDS THE
EASTERN MOGOLLON RIM AND WHITE MOUNTAINS WITH POTENTIAL FOR STRONG
STORMS ALONG THE PROPAGATING COLD FRONT.
BE PREPARED AND HAVE A WAY TO RECEIVE WARNINGS!
FRIDAY AND ONWARD...ACTIVITY IS EXPECTED TO TREND DOWNWARD BY FRIDAY
INTO THE WEEKEND AFTER THE MAIN TROUGH AXIS PUSHES PAST NORTHERN AZ
AND DRIER AIR MOVES IN. A CLOSED LOW MAY LINGER ACROSS WESTERN AZ,
AND SLIGHT CHANCES FOR SHOWERS AND THUNDERSTORMS REMAIN IN THE
FORECAST EACH DAY. EXPECT LIGHTER WINDS AND TEMPERATURES REMAINING
BELOW NORMAL OTHERWISE.
AVIATION...WEDNESDAY 21/06Z THROUGH THURSDAY 22/06Z
VFR TO
MVFR, ESPECIALLY NEAR HEAVIER SHOWERS OR THUNDERSTORMS. EXPECT
SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS TO DEVELOP AFTER
TONIGHT AND SPREAD NORTHWARD THROUGH WEDNESDAY MORNING. NUMEROUS
SHOWERS AND THUNDERSTORMS THROUGHOUT THE DAY WEDNESDAY AND
CONTINUING THROUGH WEDNESDAY NIGHT. THERE IS THE POTENTIAL THAT
SOME STORMS COULD BECOME SEVERE ON WEDNESDAY, PRODUCING LARGE HAIL
OR DAMAGING WIND. WINDS LIGHT AND VARIABLE OR TERRAIN DRIVEN
OVERNIGHT, BECOMING SE-S 10-20KTS WEDNESDAY. GUSTY AND ERRATIC
WINDS NEAR THUNDERSTORMS.
OUTLOOK...THURSDAY 22/06Z THROUGH SATURDAY 24/06Z...VFR TO MVFR
CONDITIONS, ESPECIALLY NEAR HEAVIER SHOWERS AND THUNDERSTORMS.
NUMEROUS SHOWERS AND THUNDERSTORMS THURSDAY, SOME MAY BE SEVERE
WITH DAMAGING WINDS AND LARGE HAIL. ACTIVITY DIMINISHES FROM WEST
TO EAST LATE THURSDAY NIGHT. A FEW SHOWERS OR THUNDERSTORMS MAY
LINGER ALONG THE ARIZONA/NEW MEXICO BORDER FRIDAY, WITH THE REST
OF THE REGION DRYING OUT. WINDS S-SW 10-20 KTS WITH GUSTS TO 30
KTS THURSDAY, SW-W 10-20KTS FRIDAY.
FIRE WEATHER...THIS MORNING THROUGH THURSDAY
INCREASING SHOWERS
AND THUNDERSTORMS THIS MORNING BECOMING WIDESPREAD ON WEDNESDAY AND
THURSDAY. SOME STORMS MAY PRODUCE VERY HEAVY RAINFALL LEADING TO
FLOODING OR FLASH FLOODING BOTH DAYS. SOME STRONGER STORMS MAY
PRODUCE STRONG WINDS AND LARGE HAIL. OUTSIDE OF STORMS, EXPECT SOUTH
WINDS 10-20 MPH WITH GUSTS 30-40 MPH ON WEDNESDAY, BECOMING SOUTH
THROUGH SOUTHWEST ON THURSDAY. DAYTIME TEMPERATURES NEAR TO BELOW
NORMAL.
FRIDAY THROUGH SUNDAY...ISOLATED SHOWERS AND THUNDERSTORMS ARE
EXPECTED FOR FRIDAY THROUGH SUNDAY. SOUTHWEST THROUGH WEST WINDS 10-
15 MPH WITH GUSTS TO 25 MPH ON FRIDAY, THEN LIGHT NORTHERLY WINDS 5-
15 MPH ON SATURDAY AND SUNDAY.
FGZ WATCHES/WARNINGS/ADVISORIES
FLOOD WATCH THROUGH THURSDAY EVENING FOR AZZ004>018-037>040.
PUBLIC...LEWANDOWSKI
AVIATION...BERNHART
FIRE WEATHER...LEWANDOWSKI
FOR NORTHERN ARIZONA WEATHER INFORMATION VISIT
WEATHER.GOV/FLAGSTAFF
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