598
FXUS65 KPSR 231923
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1223 PM MST TUE APR 23 2019
SYNOPSIS
A LOW PRESSURE SYSTEM HAS INCREASED SHOWER AND STORM CHANCES IN
SOUTH-CENTRAL ARIZONA THROUGH THIS EVENING. AS HIGH PRESSURE BUILDS
OVER THE REGION IN THE WAKE OF THE LOW, A WARMING TREND WILL BEGIN,
STARTING OVER SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA TODAY AND
THEN IN SOUTH-CENTRAL ARIZONA TOMORROW. THURSDAY THROUGH FRIDAY,
HIGHS IN THE LOWER DESERTS WILL BE APPROACHING OR EXCEEDING 100
DEGREES. ANTICIPATE COOLER TEMPERATURES BY LATE IN THE WEEKEND AND
EARLY NEXT WEEK.
DISCUSSION
THE UPPER LEVEL PATTERN SHOWS A PRONOUNCED UPPER LEVEL CLOSED LOW
PRESSURE SYSTEM CENTERED OVER NW MX AND THE SSE AZ BORDER WITH A WSW-
ENE ORIENTED RIDGE AXIS FROM N CA ACROSS THE INTERMOUNTAIN WEST AND
CENTRAL ROCKIES. IR SATELLITE AND WV IMAGERY IS SHOWING AN INCREASE
IN CLOUD COVER ACROSS THE REGION AS A PAIR OF VORT MAX DISTURBANCES
PUSH SOUTHWEST ACROSS THE AREA ALONG THE NORTHERN PERIPHERY OF THE
LOW. AS A RESULT, THE CHANCES FOR SHOWERS AND STORMS HAVE INCREASED
THIS AFTERNOON AND EARLY EVENING FROM PHOENIX AND CASA GRANDE
EASTWARD.
HIGH-RES MODELS AND HREF MEMBERS ARE FAIRLY BULLISH ON DEVELOPING
SCATTERED CONVECTIVE SHOWERS, STORMS AND OUTFLOW WINDS FOR GOOD
PORTIONS OF S GILA, PINAL AND E MARICOPA COUNTIES BEGINNING EARLY TO
MID AFTERNOON WITH THE ACTIVITY LINGERING INTO THE EVENING AND
TAPERING OFF BY/AFTER 01-03Z. SURFACE HEATING WITH WARM DAYTIME
TEMPERATURES COMBINED WITH COLD AIR ALOFT, NEAR -21C AT H5, WILL
CONTRIBUTE TO INCREASING INSTABILITY THIS AFTERNOON. HREF MEAN CAPE
BY MID AFTERNOON IS FORECAST IN THE LOW 100S J/KG WITH MAX CAPE
VALUES FORECAST AT 250-750 J/KG. MOISTURE ALSO CONTINUES TO INCREASE
THIS AFTERNOON WITH SPC MESOSCALE VALUES ALREADY ABOVE 0.5 IN. AS
THEY HEAD TOWARDS VALUES NEAR 0.75 IN.
THE MAIN IMPACTS FROM TODAY'S STORMS WILL BE GUSTY OUTFLOW AND
CONVECTIVE DOWNDRAFT WINDS AND DRY LIGHTNING WHICH WILL POTENTIALLY
IMPACT BOTH AVIATION AND FIRE WEATHER CONCERNS. THIS IS SUPPORTED BY
RELATIVELY DRY INVERTED V BOUNDARY LAYER PROFILE COMBINED WITH FORECAST
DCAPE VALUES NEAR 1400 J/KG BY 00Z. SUSTAINED EASTERLY COMPONENT
OUTFLOW BOUNDARY WINDS NEAR 15-20KT WILL LIKELY EXPERIENCE LOCAL
CONVECTIVE GUSTS TO 30-35KT CLOSER TO THE STORMS. OTHER NOTABLE
IMPACTS WILL INCLUDE ABRUPT WINDSHIFTS AND ERRATIC WINDS, ESPECIALLY
NEAR THE STORMS. DUE TO THE GUSTY WINDS, THERE IS ALSO A SLIGHT
CHANCE OF LOCALLY LOFTED DUST. RAINFALL AMOUNTS WITH TODAY'S STORMS
ARE ALSO FORECAST TO BE ISOLATED TO SPOTTY AND MOSTLY MODEST.
ALSO FOR TODAY A WARM UP WILL BEGIN ACROSS SE CA AND SW AZ WITH
TEMPERATURES CLIMBING INTO THE MID 90S IN THOSE AREAS. FOR WEDNESDAY
THROUGH THURSDAY THE WARMING TREND SPREADS EAST AS THE LOW PRESSURE
SYSTEM EXITS TO THE EAST AND HIGH PRESSURE EXPANDS AND BUILDS OVER
AZ AND THE WESTERN US. BY LATE THU. H5 HEIGHTS REACH NEAR 583-584
DAM. THE ASSOCIATED SUBSIDENCE AND WAA WILL ALLOW TEMPERATURES TO CLIMB INTO
TO THE UPPER 90S TO LOW 100S LATE IN THE WEEK ACROSS THE LOWER DESERTS.
LOCALIZED AREAS OF MODERATE HEAT RISK WILL SPREAD FROM SE CA ON
WEDNESDAY EAST INTO THE LOWER DESERTS AND PHOENIX ON THURSDAY AND
FRIDAY. THE HOTTEST DAY IN PHOENIX IS CURRENTLY EXPECTED ON FRIDAY
WHEN HIGHS WILL REACH WELL ABOVE NORMAL IN THE LOW 100S.
BY LATE IN THE WEEKEND AND EARLY NEXT WEEK, EXPECT LOWER TEMPERATURES
CLOSER TO SEASONAL NORMS AHEAD OF AND WITH A COMPACT PACIFIC LOW
PRESSURE SYSTEM THAT IS EXPECTED TO MOVE THROUGH S CA AND INTO AZ
AROUND MONDAY.
AVIATION
UPDATED AT 1746 UTC.
SOUTH-CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
SHOWERS AND THUNDERSTORMS OVER EASTERN AND NORTHERN GATES ALONG WITH
GUSTY OUTFLOW WINDS (20-30KT) AND ABRUPT WIND SHIFTS WILL BE A MAJOR
CONCERN FOR ALL PHOENIX AREA TERMINALS FROM MID AFTERNOON THROUGH
EARLY EVENING.
EAST WINDS SHOULD PREVAIL THROUGH THE LATE MORNING AS SHOWER
ACTIVITY REMAINS MOSTLY WELL REMOVED FROM AERODROME SITES (BOTH TO
THE SOUTHEAST AND NORTHEAST). AFTER A SWITCH TO A WESTERLY WIND
COMPONENT EARLY AFTERNOON, HIGH RESOLUTION MODELS CONTINUE TO BE IN
EXCELLENT AGREEMENT IN RAPIDLY DEVELOPING THUNDERSTORMS OVER HIGHER
TERRAIN EAST OF PHOENIX WITH STEERING FLOW BRINGING AGGRESSIVE
OUTFLOW BOUNDARIES INTO LOWER ELEVATIONS. A FEW TS COULD HOLD
TOGETHER AND DIRECTLY IMPACT AIRPORTS (MOST LIKELY AT KSDL AND
KDVT), THOUGH EASTERN APPROACHES WILL LIKELY BE IMPACTED
NONETHELESS. OUTFLOW BOUNDARIES COULD BRING ABRUPT WIND SHIFTS
(SOMEWHERE BETWEEN AN EAST AND NORTH-NORTHEAST WIND) AS EARLY AS
22Z, BUT COULD HOLD OFF UNTIL 00Z-01Z. THERE IS A POTENTIAL FOR
BRIEF WIND GUSTS AS HIGH AS 35 KTS AS OUTFLOWS FROM THE STRONGER
CELLS MIX STRONGER WINDS ALOFT DOWN TO THE SFC. AT THIS POINT,
POTENTIAL FOR SIGNIFICANT BLOWING DUST LOOKS LOW, WITH THE
SHOWERS/STORMS MOVING IN FROM A LESS FAVORABLE NORTHEASTERLY
DIRECTION. ALL ACTIVITY SHOULD DISSIPATE AFTER ABOUT 04Z.
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
LITTLE TO NO AVIATION CONCERNS THROUGH THE TAF PERIOD UNDER MOSTLY
CLEAR SKIES. WINDS TO REMAIN MOSTLY FROM A NORTHERLY TO
NORTHWESTERLY DIRECTION THROUGH EARLY EVENING BEFORE BECOMING MORE
WESTERLY AND DIMINISHING LATER TONIGHT AND WEDNESDAY. A FEW STRONGER
GUSTS IN EXCESS OF 20KT (PARTICULARLY AT KBLH) ARE LIKELY THROUGH
MID AFTERNOON BEFORE WEAKENING BY LATER IN THE AFTERNOON AND
EVENING.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
FIRE WEATHER
THURSDAY THROUGH MONDAY:
HIGH PRESSURE WILL BUILD INTO THE REGION THURSDAY, BRINGING A
SIGNIFICANT WARMING TREND WITH HIGHS ON THE LOW DESERTS WELL INTO
THE UPPER 90S TO NEAR 100 THURSDAY THROUGH SATURDAY. THE WARMEST
DAY LOOKS TO BE FRIDAY. ACCORDINGLY, HUMIDITIES DECLINE WITH
MINIMUM READINGS ON THE LOWER DESERTS HOVERING AROUND 10% AND
OVERNIGHT RECOVERY DECLINING TO FAIR. LATE IN THE WEEKEND AND
EARLY NEXT WEEK, A LOW PRESSURE SYSTEM IS EXPECTED TO BRING COOLER
TEMPERATURES. AS THE SYSTEM APPROACHES, ANTICIPATE MORE
NOTICEABLE BREEZINESS DURING THE LATTER PART OF THE WEEK. AT THIS
TIME, CRITICAL FIRE WEATHER THRESHOLDS ARE NOT ANTICIPATED.
SPOTTER INFORMATION STATEMENT
SPOTTER ACTIVATION IS NOT EXPECTED FOR THE NEXT 7 DAYS.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
DISCUSSION...SAWTELLE
AVIATION...PERCHA/MO
FIRE WEATHER...ROGERS/AJ
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