Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 300328
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
827 PM MST THU JAN 29 2015

...SIGNIFICANT RAIN EVENT DEVELOPING TONIGHT GOING INTO SATURDAY...

.SYNOPSIS...
A PACIFIC LOW PRESSURE SYSTEM WILL LEAD TO A SIGNIFICANT RAIN EVENT
ACROSS THE REGION STARTING TONIGHT AND GOING INTO SATURDAY.
ANTICIPATE RAINFALL TO BE MOST WIDESPREAD ON FRIDAY WITH MORE HIT
AND MISS SHOWERS ON SATURDAY. SNOW LEVELS WILL REMAIN
HIGH...LOWERING TO AROUND 7000-7500 FEET BY SATURDAY MORNING. DRY
WEATHER AND A SLOW WARMING TREND BEGINS SUNDAY AND CONTINUES THROUGH
THURSDAY.

&&

.DISCUSSION...
LOW PRESSURE CONTINUES TO SLOWLY APPROACH THE AREA AND WAS JUST WEST
OF THE BAJA PENINSULA AS OF 03Z THIS EVENING. MEANWHILE...COPIOUS
MOISTURE HAS MOVED INTO ARIZONA AND KTUS 00Z SOUNDING INDICATED A
PWAT OF 1.07 INCHES...5TH HIGHEST VALUE ON RECORD FOR JANUARY. NOT
SURPRISINGLY THE COMBINATION OF NEAR RECORD MOISTURE AND STRONG
ISENTROPIC ASCENT AHEAD OF THE INITIAL SHORTWAVE TROUGH HAS RESULTED
IN RAPID DEVELOPMENT OF SHOWERS ACROSS THE AREA. SHOWERS BEGAN
AROUND 00Z AND MOST LOCATIONS ACROSS THE PHOENIX METRO AND POINTS
EAST HAVE ALREADY SEEN A FEW HUNDREDTHS OF AN INCH OF RAINFALL.
LOCALLY HIGHER AMOUNTS WERE NOTED NORTH/EAST OF PHOENIX...GENERALLY
0.15 TO 0.2 INCHES THROUGH 0320Z.

WITH ADDITIONAL RAINFALL ALREADY ON RADAR TO OUR SOUTH AND EVERY
AVAILABLE OPERATIONAL MODEL /AND ENSEMBLES/ INDICATING ADDITIONAL
RAINFALL OVERNIGHT...POPS WERE BUMPED TO 100 PERCENT ACROSS MOST OF
THE AREA. SOUTHEAST CALIFORNIA WILL BE MUCH MORE HIT AND MISS
THROUGH MIDNIGHT BUT EVEN THESE LOCATIONS STAND A GOOD CHANCE OF
SEEING RAINFALL OVERNIGHT. QPF REMAINS ON TARGET...INHERITED VALUES
ARE WELL IN LINE WITH 21Z SREF QPF MEAN.

MADE SOME ADJUSTMENTS TO TEMPS AND DEWPOINTS AS WELL. WITH MOST
LOCATIONS ALREADY AT THEIR WET BULB TEMPERATURES...LOOK FOR STEADY
TEMPS FOR THE REST OF THE EVENING AND OVERNIGHT HOURS. SOUTHEAST
CALIFORNIA LOCALES COULD DROP A FEW MORE DEGREES ESPECIALLY AT THE
ONSET OF RAIN WITH EVAPORATIONAL COOLING BUT NONETHELESS TEMPS
AREN`T GOING TO BE DROPPING OFF MUCH AT ALL TONIGHT.

SHOWERS WILL PERSIST INTO FRIDAY MORNING AS WELL BEFORE DECREASING
SLIGHTLY FRIDAY AFTERNOON AND EVENING. COVERAGE/FREQUENCY OF SHOWERS
WILL TREND DOWN FRIDAY NIGHT WITH MORE HIT AND MISS TYPE SHOWERS
SATURDAY. RAINFALL OVER OUR FORECAST AREA WILL BE BEST OVER SOUTHERN
GILA...NORTHERN MARICOPA...NORTHERN PINAL...AND LA PAZ COUNTIES WITH
LESS RAINFALL OVER YUMA AND RIVERSIDE COUNTIES AND LEAST OVER
IMPERIAL COUNTY. THE AMOUNT OF ATMOSPHERIC MOISTURE CONTENT BEING
ADVECTED BY THIS SYSTEM...CURRENTLY CENTERED NEAR 30N/120W...IS
QUITE IMPRESSIVE. BLENDED TPW IMAGERY THIS AFTERNOON SHOWS VALUES
NEAR 1.0 INCHES NEAR THE MEXICO BORDER AND VALUES NEARING 1.5 INCHES
APPROACHING THE BAJA SPUR. THE 00Z BASED NAEFS FORECASTS PWATER
ANOMALIES OF 4-4.5 STANDARD DEVIATIONS ABOVE NORMAL TONIGHT AND
FRIDAY...TRENDING DOWNWARD FRIDAY NIGHT AND SATURDAY. THERE REMAINS
A SLIGHT CHANCE OF THUNDERSTORMS FRIDAY AFTERNOON AND EVENING THEN
AGAIN SATURDAY AFTERNOON ACROSS THE FORECAST AREA. THE AMOUNT OF
MODEL CAPE LOOKS QUITE MODEST PER A WIDE ARRAY OF MODELS...AS WOULD
BE EXPECTED WITH A MILD SYSTEM. CAPE MAY BE A BIT BETTER ON SATURDAY
THAN ON FRIDAY...BUT STILL LOW END VALUES. HOWEVER...IF ANY MANAGE
TO FORM THEY COULD PRODUCE BRIEF VERY HEAVY RAIN AND MAYBE SOME
SMALL HAIL. RAINFALL COULD BE HEAVY ENOUGH TO PRODUCE RUNOFF IN
WASHES...MAINLY HIGHER TERRAIN AND FOOTHILLS...AND FOR SURE SOME
NUISANCE STREET FLOODING. AT THIS TIME...ANTICIPATE THAT IT WILL NOT
BE INTENSE ENOUGH TO MERIT THE ISSUANCE OF A FLASH FLOOD WATCH.
SINCE THE SYSTEM IS ORIGINATING FROM LOWER LATITUDES...TEMPS WILL BE
MILD FOR A WINTERTIME SYSTEM. ACCORDINGLY SNOW LEVELS WILL BE
HIGH...BOTTOMING OUT IN THE 7000-7500 FEET LEVEL SATURDAY MORNING.

SUNDAY THROUGH WEDNESDAY...
SUNDAY LOOKS TO BE A DRY. PATCHY FOG IS A POSSIBILITY BUT THERE MAY
BE ENOUGH LINGERING CLOUDS TO HINDER THE RADIATIONAL COOLING
NECESSARY.  THE RIDGE SLOWLY BUILDS INTO THE WEST MONDAY THROUGH
WEDNESDAY FOR A GRADUAL WARMING TREND...AND WE CAN EXPECT DESERT
HIGHS TO REACH BACK INTO THE LOW TO MID 70S BY NEXT WEDNESDAY.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL...
RAIN IS ONGOING ACROSS THE METRO AS OF 03Z WITH A FEW BREAKS NOTED
ACROSS THE EAST VALLEY. CONDITIONS REMAIN VFR BUT HAVE STEADILY
DECREASED ALL EVENING. SHOWERS WILL PERSIST FOR SEVERAL MORE
HOURS...WELL INTO THE DAY FRIDAY. RAIN WILL INCREASE OVERNIGHT WITH
THE WORST PERIOD EXPECTED TO BE BETWEEN 11Z-18Z. WIDESPREAD CEILINGS
BETWEEN 800-1500FT ARE EXPECTED ACROSS THE ENTIRE PHOENIX METRO
DURING THIS PERIOD ALONG WITH PERIODIC VSBYS AROUND 5SM WITH THE
HEAVIEST SHOWERS. SOME SUBTLE IMPROVEMENT IN CONDITIONS IS EXPECTED
BY EARLY AFTERNOON ALTHOUGH THIS COULD RESULT IN SOME
DESTABILIZATION AND AN OCCASIONAL RUMBLE OF THUNDER. CONFIDENCE WAY
TOO LOW TO MENTION THUNDER OUTRIGHT IN THE TAFS BUT THERE IS A
POSSIBILITY. GIVEN MOIST ADIABATIC PROFILES IT WOULD BE HARD FOR ANY
STORM TO REACH SEVERE LIMITS.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
NO RAIN ACROSS THE SOUTHEAST CALIFORNIA TERMINALS AS OF 03Z BUT
RADAR IS BEGINNING TO FILL IN ACROSS THE SOUTH.  FOR THE MOST PART
IPL WILL ONLY SEE STEADY LIGHT RAIN AND OCCASIONAL 5KFT
CEILINGS...BUT BLH WILL BE MUCH MORE NEGATIVELY IMPACTED WITH
CONDITIONS APPROACHING IFR THRESHOLDS EARLY FRIDAY MORNING. SIMILAR
TO PHOENIX THERE WILL LIKELY BE A PERIOD WHERE CONDITIONS IMPROVE
SLIGHTLY...THUS THERE WOULD ALSO BE A CHANCE OF THUNDER AROUND THE
COLORADO RIVER TOO. SAME ARGUMENTS AS ABOVE...WILL BE VERY MOIST AND
WILL BE DIFFICULT TO GET MUCH IN THE WAY OF SEVERE WEATHER.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
RAIN SHOWERS WILL LINGER OVER PORTIONS OF THE REGION THROUGH
SATURDAY. GREATEST LIKELIHOOD FOR SHOWERS WILL BE OVER SOUTH-CENTRAL
ARIZONA...PARTICULARLY OVER THE HIGHER TERRAIN NORTH AND EAST OF THE
PHOENIX METROPOLITAN AREA. THERE IS A SLIGHT CHANCE OF
THUNDERSTORMS...MAINLY SATURDAY AFTERNOON. NORTHWEST WINDS WILL ALSO
PREVAIL OVER THE REGION ON SATURDAY...KEEPING TEMPERATURES SEVERAL
DEGREES COOLER THAN BELOW NORMAL. A WARMING AND DRYING TREND IS THEN
EXPECTED SUNDAY THROUGH WEDNESDAY...AS A RIDGE BUILDS BACK IN ACROSS
THE EASTERN PACIFIC.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...LEINS/AJ/CB
AVIATION...LEINS
FIRE WEATHER...MCLANE





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