881
FXUS65 KPSR 152342
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
442 PM MST THU MAY 15 2025
UPDATE
UPDATED AVIATION DISCUSSION.
KEY MESSAGES
1) GUSTY WINDS OVER THE WEEKEND RESULTING IN A LOCALLY ELEVATED
FIRE DANGER
2) INCREASED ODDS FOR ABOVE NORMAL TEMPERATURES AND WIDESPREAD
MODERATE HEATRISK RETURNING LATE NEXT WEEK...
DISCUSSION
WEATHER PATTERN OVERVIEW:
BROAD, WEAKLY CYCLONIC FLOW LINGERS OVER THE SW CONUS AS A CLOSED,
OCCLUDED LOW PRESSURE SYSTEM LIFTS INTO THE UPPER MIDWEST. THE
WEAKNESS LEFT IN THE MIDTROPOSPHERIC FLOW OVER THE FORECAST AREA
FROM THIS EXITING SYSTEM WILL QUICKLY BE FILLED OVER THE WEEKEND BY
A SERIES OF PACIFIC NEGATIVE HEIGHT ANOMALIES INTENSIFYING INTO AN
AMPLIFIED LONGWAVE WESTERN TROUGH. THE MAGNITUDE OF THE ATTENDANT
PACIFIC JET DURING THIS MERIDIONAL TRANSITION WILL ENSURE ROBUST
SHORTWAVE ENERGY AND NOTABLE HEIGHT FALLS MIGRATE INTO MUCH OF
ARIZONA. THE TIMING AND JUXTAPOSITION OF HEIGHT FALLS AND JET CORE
CARVING OUT THE TROUGH BASE WILL SUPPORT VERY GUSTY WINDS THROUGHOUT
THE WEEKEND, BUT PARTICULARLY SATURDAY AFTERNOON/EVENING ACROSS SE
CALIFORNIA WHERE PARAMETERS ALIGN NEARLY OPTIMALLY. AS SUCH,
ADVISORIES WILL ALMOST CERTAINLY BE NECESSARY IN THE TYPICAL WIND
PRONE LOCATIONS OF IMPERIAL COUNTY. THESE GUSTY WINDS COMBINED WITH
SEASONALLY LOW HUMIDITY VALUES WILL ALSO RESULT IN AN ELEVATED FIRE
DANGER, THOUGH MORE LIMITED WIND SPEEDS IN SOUTH-CENTRAL ARIZONA
SATURDAY AND HIGHER MOISTURE SWEEPING THROUGH THE REGION SUNDAY MAY
PRECLUDE MORE CRITICAL CONDITIONS.
ENSEMBLE MEMBERSHIP REMAINS IN GOOD AGREEMENT DEPICTING SEVERAL
VORTICITY CENTERS PIVOTING THROUGH THE LONGWAVE TROUGH WITH ONE
NOTABLE AND FINAL TRAILING WAVE DIGGING INTO NORTHERN ARIZONA
MONDAY. GIVEN THE INLAND TRAJECTORY OF THIS ENTIRE SERIES OF
SHORTWAVES, MOISTURE WILL BE EXTREMELY LIMITED WITH BOUNDARY LAYER
MIXING RATIOS NEVER EXCEEDING 5 G/KG. HOWEVER, GIVEN THE UNUSUAL
DEPTH OF THE TROUGH AND MAGNITUDE OF THE COLD CORE, A FEW SHOWERS
MAY BE SQUEEZED OUT OVER HIGHER TERRAIN AREAS. ON THE OTHER HAND,
RECENT OPERATIONAL MODELS HAVE SHIFTED THE JET STREAK AND COLD CORE
SLIGHTLY FURTHER NORTH RESULTING IN A FORECAST OF A LARGE MIDLEVEL
CAPPING INVERSION LOCKED OVER THE SOUTHERN HALF OF ARIZONA. IF THIS
MODEL TREND COMES TO FRUITION, IT WOULD BE ALL BUT IMPOSSIBLE FOR
ANYTHING OTHER THAN OUTFLOW WINDS TO PROPAGATE INTO LOWER
ELEVATIONS.
WHILE SOME SUBTLE MIDLEVEL WEAKNESS IN THE HEIGHT FIELD MAY HOLD
OVER THE SOUTHWEST DURING THE LATTER HALF OF THE WEEK, ENSEMBLES ARE
FAR MORE RESOLUTE IN BUILDING STRONGER RIDGING OVER NORTHERN MEXICO
AND SW CONUS. SOME OF THE MORE EXTREME MEMBERS HAVE BEEN
HIGHLIGHTING H5 HEIGHTS AROUND 594DM, HOWEVER THE PREPONDERANCE OF
OUTPUT SUGGESTS HEIGHTS CLOSER TO 588DM. AS A RESULT, WIDESPREAD
MODERATE HEATRISK SHOULD EVOLVE TOWARDS THE END OF NEXT WEEK WITH
TEMPERATURES NEARLY 10F ABOVE NORMAL. SHOULD ANY OF THE MORE
ANOMALOUS SOLUTIONS BE REALIZED (AND IT COULD BE ARGUED THAT WOULD
BE A LIKELY OUTCOME GIVEN THE PATTERN PROGRESSION), THIS COULD BE
THE FIRST VESTIGES OF MAJOR HEATRISK WITH TEMPERATURES 15F ABOVE
NORMAL YIELDING EXTREME HEATRISK OVER THE HOLIDAY WEEKEND.
FORECAST CONFIDENCE & DEVIATIONS:
GOOD CONFIDENCE IN TEMPERATURE FORECASTS EXISTS THE NEXT COUPLE
DAYS, BUT THEN DETERIORATES SIGNIFICANTLY EARLY NEXT WEEK DEPENDING
ON HOW FAR SOUTH THE COLD CORE MIGRATES. MANDATED NBM FORECASTS HAVE
BUMPED WARMER BASED MAINLY ON CHANGES IN THE OPERATIONAL MEMBERS,
BUT COULD FLIP FLOP BACK BASED ON FUTURE MODEL ITERATIONS. FEEL THE
AUTOMATED NBM WINDS OVER THE WEEKEND ARE SOMEWHAT UNDERFORECAST AND
HAVE MADE SOME MINOR INCREASES DURING PEAK MIXING HOURS. SPURIOUS
POP AND QPF GRIDS WERE SUBSTANTIALLY REDUCED THIS CYCLE, HOWEVER DID
HAVE TO MAKE SOME MINOR ADJUSTMENTS BASED ON UNREALISTIC MODEL
ARTIFACTS. AVERAGE CONFIDENCE EXISTS WITH RESPECT TO TEMPERATURES
TOWARDS THE END OF THIS FORECAST PERIOD, BUT WOULD NOT BE SURPRISED
IF ACTUAL READINGS WERE EVEN WARMER THAN THE CURRENT AUTOMATED NBM
OUTPUT.
AVIATION
UPDATED AT 2341Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, KDVT;
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO AVIATION IMPACTS ARE EXPECTED THROUGH THE NEXT 24 HOURS. WINDS
AT ALL TERMINALS WILL FOLLOW TYPICAL DIURNAL TRENDS, WITH SPEEDS
REMAINING AT OR BELOW 10 KTS THROUGH MOST OF THE TAF PERIOD.
AFTERNOON GUSTINESS CAN BE EXPECTED IN THE PHOENIX AREA, WITH
GUSTS UP TO 15-20 KTS AT TIMES. CLEAR SKIES WILL PREVAIL.
FIRE WEATHER
WITH DRY CONDITIONS PREVAILING THROUGH NEXT WEEK, WINDS WILL
INCREASE IN SPEED OVER THE WEEKEND YIELDING AN ELEVATED FIRE DANGER
WITH LOCALLY NEAR CRITICAL CONDITIONS. MINRHS WILL MOSTLY FALL IN A
10-15% RANGE THROUGH SATURDAY BEFORE A COOLER AND SOMEWHAT MORE
MOIST AIRMASS KEEP MINIMUM READINGS IN A 15-25% RANGE SUNDAY AND
MONDAY. POOR TO FAIR OVERNIGHT RECOVERY OF 20-50% WILL IMPROVE
CLOSER TO A 35-60% RANGE EARLY NEXT WEEK. WINDS WILL BE MOST
PRONOUNCED IN WESTERN DISTRICTS SATURDAY WITH GUSTS 30-40 MPH, THEN
TRANSLATING INTO EASTERN DISTRICTS SUNDAY ALBEIT WITH SOMEWHAT
WEAKER SPEEDS. VERY WARM AND DRY WEATHER WILL RETURN DURING THE
MIDDLE OF NEXT WEEK, HOWEVER WIND SPEEDS WILL BE MUCH WEAKER AS HIGH
PRESSURE STARTS BUILDING INTO THE REGION.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
DISCUSSION...18
AVIATION...BENEDICT
FIRE WEATHER...18
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