Weather Service Report


604 
FXUS65 KPSR 280336
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
835 PM MST TUE JAN 27 2015

.SYNOPSIS...
SOME PATCHY FOG IS POSSIBLE TONIGHT AND TOMORROW MORNING BUT 
OTHERWISE ANTICIPATE DRY CONDITIONS WITH JUST SOME HIGH CLOUDS 
WEDNESDAY. ANOTHER LOW PRESSURE SYSTEM APPROACHES THURSDAY FOR 
INCREASED CLOUDINESS DURING THE DAY. RAIN CHANCES GO UP DRAMATICALLY 
THURSDAY NIGHT AND CONTINUE INTO SATURDAY...MAINLY EAST OF THE LOWER 
COLORADO RIVER VALLEY. SNOW LEVELS WILL REMAIN HIGH...LOWERING TO 
NEAR 7000 FEET BY SATURDAY MORNING. ANTICIPATE COOLER HIGH 
TEMPERATURES AS WELL. DRY CONDITIONS TAKE OVER SUNDAY THROUGH 
TUESDAY. 

&&

.DISCUSSION...
JUST SOME HIGH CLOUD COVER ACROSS THE REGION THIS EVENING AS WEAK 
SHORTWAVE RIDGING ALOFT HAS SETTLED ACROSS THE AREA. THE LOW/MID 
CLOUDS FROM EARLIER THIS AFTERNOON HAVE DISSIPATED AND THE CIRRUS TO 
THE SOUTH IS ASSOCIATED WITH OUR FAST APPROACHING LATE-WEEK SYSTEM. 
MID EVENING TEMPERATURES WERE GENERALLY IN THE MID 60S WITH LIGHT 
WINDS ACROSS THE REGION.

THE PRIMARY CONCERN FOR THE REST OF THE EVENING/OVERNIGHT IS FOG 
POTENTIAL. COMPARING CROSSOVER TEMPERATURES TO FORECAST MIN TEMPS 
YIELDS A PRETTY WIDESPREAD AREA OF PATCHY FOG ACROSS THE 
AREA...EXCEPT FOR A DONUT HOLE AROUND THE PHOENIX AREA AND PORTIONS 
OF PINAL COUNTY. THE INCREASING CLOUD COVER IS VERY CONCERNING BUT A 
LONG ENOUGH SATELLITE LOOP SUGGESTS CLOUDS WILL INCREASE THROUGH 
MIDNIGHT...THEN CLEAR OUT SHORTLY THEREAFTER UNTIL AT LEAST DAYBREAK 
WEDNESDAY. I WILL KEEP A MENTION OF PATCHY FOG IN PLACE IN THE 
FORECAST WITH THE CAVEAT THAT THE MOST LIKELY LOCATIONS TO SEE FOG 
WILL BE THE NORMALLY COOLER/PROTECTED AREAS IN THE OPEN DESERTS. 21Z 
SREF PROBS OF VSBYS LESS THAN 6SM ARE AROUND 15-20 PERCENT IN THE 
PHOENIX METRO AND SINCE I CAN'T ENTIRELY DISMISS THE 
POSSIBILITY...FEEL IT PRUDENT TO KEEP THE MENTION OF FOG IN PLACE.

OTHERWISE...JUST SOME MINOR ADJUSTMENTS TO OVERNIGHT MINS AND 
WINDS/CLOUDS BASED ON OBSERVATIONAL TRENDS. NOTHING MAJOR. 

&&

.PREVIOUS DISCUSSION...
WEDNESDAY...
OTHERWISE THERE WILL ONLY BE SOME HIGH CLOUDS WEDNESDAY WITH A WEAK 
PASSING IMPULSE. TEMPERATURES WILL REMAIN MILD. 

THURSDAY THROUGH SATURDAY...
THE NEXT SYSTEM TO AFFECT OUR AREA IS CURRENTLY WELL OFF SHORE WITH 
THE SOUTHERN END OF IT CENTERED WELL WEST OF SOUTHERN BAJA. 
CURRENTLY THERE IS A FAIRLY SHARP GRADIENT OF PRECIPITABLE WATER IN 
THE AREA WHERE THE SOUTHERN END IS LOCATED...20N-30N LATITUDE...WITH 
OVER 1.5 INCHES IN THE SOUTHERN END AND ABOUT TWO-THIRDS OF AN INCH 
AT THE NORTHERN END. THERE IS GOOD MODEL AGREEMENT THE SYSTEM WILL 
ADVECT A NEW BATCH OF DEEP MOISTURE INTO THE AREA...CLOSER TO 1 INCH 
PRECIPITABLE WATER. THIS STARTS THURSDAY AS THE SYSTEM MOVES 
NORTHEASTWARD AND INCREASING HIGH CLOUDS OVER THE AREA DURING THE 
DAY...WITH SLIGHT CHANCES OF SHOWERS DEVELOPING OVER THE HIGHER 
TERRAIN IN THE AFTERNOON. PRECIPITATION CHANCES GO UP DRAMATICALLY 
THURSDAY NIGHT AND PEAK ON FRIDAY...GENERALLY 60-80 PERCENT OVER 
SOUTH-CENTRAL ARIZONA INCLUDING PHOENIX AND LESS SO FURTHER WEST. 
BEST DYNAMICAL LIFT LOOKS TO BE FRIDAY MORNING...THOUGH IT IS 
MODEST. THE LOW DEEPENS FRIDAY BECOMING CENTERED OVER THE LOWER 
COLORADO RIVER VALLEY. AS A RESULT...A LITTLE BIT OF CAPE DEVELOPS 
FRIDAY AFTERNOON. MODELS DEPICT CAPE TO BE MAINLY OVER SOUTHEAST 
ARIZONA BUT SPILLING INTO SOUTH-CENTRAL ARIZONA. THIS IS LIKELY DUE 
TO A BIT WARMER LOWER LEVELS/STEEPER LAPSE RATES OVER OUR EASTERN 
AREAS COMPARED TO OUR WESTERN AREAS. THUS INSERTED A MENTION FOR 
SLIGHT CHANCE OF THUNDER FRIDAY AFTERNOON FOR SOUTH-CENTRAL ARIZONA 
BUT MAY NEED TO EXPAND THAT FURTHER WEST. DYNAMICAL LIFT PRETTY MUCH 
GOES AWAY FRIDAY NIGHT AND SATURDAY WE ARE LEFT WITH THE LOW CENTER 
AND A MOISTURE RICH AIRMASS. THUS SHOWERS LIKELY TO BE BECOME 
LIGHTER AND MORE SPOTTY FRIDAY NIGHT AND SATURDAY. QPF FOR PHOENIX 
AREA THURSDAY NIGHT AND FRIDAY RANGES FROM HALF TO TWO-THIRDS OF AN 
INCH. ANTICIPATE ANOTHER TWO TO THREE TENTHS OF AN INCH IN THE 
FRIDAY NIGHT THROUGH SATURDAY TIME FRAME. 

SUNDAY THROUGH TUESDAY...
SUNDAY LOOKS TO BE A DRY DAY WITH TEMPERATURES RISING BACK TO NEAR 
NORMAL AS AN UPPER LEVEL RIDGE MOVES IN ACROSS THE STATE. WITH THE 
UPPER RIDGE TAKING OVER FOR EARLY NEXT WEEK...WILL LIKELY SEE 
CONTINUED DRY CONDITIONS AND HIGH TEMPERATURES BACK INTO THE 
70S.      

&&

.AVIATION... 
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL...
MID LEVEL CLOUDS HAVE EXITED THE REGION AND ONLY SOME HIGH LEVEL 
CEILINGS ARE REMAINING. THESE WILL LIKELY CLEAR OUT AFTER 06-09Z 
YIELDING SEVERAL HOURS WHERE FOG COULD FORM. FEEL THE BEST LOCATION 
WOULD BE KIWA OR KSDL GIVEN THEIR COOLER TEMPERATURES BUT CONFIDENCE 
TOO LOW TO GO WITH MUCH LOWER THAN 6SM AT THIS POINT. OTHERWISE 
AVIATION IMPACTS THROUGH LATE WEDNESDAY APPEAR MINIMAL. EXPECT 
LIGHT/DIURNALLY DRIVEN WINDS AT ALL SITES. 

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
JUST SOME HIGH CLOUDS LEFT TO CONTEND WITH ACROSS SE CA. SREF VSBY 
PROBABILITIES SUGGEST MVFR CONDITIONS ARE POSSIBLE AT BLH AND I WILL 
MAKE SLIGHT DOWNWARD ADJUSTMENTS TO THEIR VSBY FORECAST IN THE 06Z 
TAF. IPL CHANCES APPEAR LOWER PER 21Z SREF BUT DEWPOINT DEPRESSIONS 
ARE ALREADY NARROWING AND I WILL ALSO MENTION MVFR THERE AS WELL. 
CONDITIONS SHOULD IMPROVE RAPIDLY AFTER 16Z WITH INCREASED BL MIXING 
AND HEATING. AS FOR WINDS...LIGHT/DIURNALLY DRIVEN AT BOTH SITES. 

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER... 
THURSDAY THROUGH MONDAY...
ABOVE NORMAL TEMPERATURES AND RELATIVELY MOIST CONDITIONS WILL 
PREVAIL THURSDAY AS A RIDGE PREDOMINATES ACROSS MEXICO. ANOTHER LOW 
PRESSURE SYSTEM WILL RESULT IN INCREASING RAIN CHANCES AND 
COOLER TEMPERATURES THURSDAY NIGHT THROUGH SATURDAY. A WARMING AND 
DRYING TREND IS EXPECTED SUNDAY/MONDAY AS A RIDGE BUILDS ACROSS 
CALIFORNIA.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX

DISCUSSION...LEINS/AJ/KUHLMAN
AVIATION...LEINS
FIRE WEATHER...HIRSCH



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