Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 292236
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
335 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...
SCATTERED SPRINKLES HAVE STARTED THIS AFTERNOON. THE TREND OF
THICKENING CLOUDS AND SHOWER COVERAGE WILL CONTINUE WITH MEASURABLE
SHOWERS BECOMING MORE COMMON AS THE EVENING PROGRESSES. ANTICIPATE
MORE WIDESPREAD RAINFALL DEVELOPING AFTER MIDNIGHT WITH FREQUENT
SHOWERS DURING THE DAY FRIDAY. 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...

A PACIFIC LOW PRESSURE SYSTEM WILL MOVE INTO THE REGION FROM THE
SOUTHWEST...IMPORTING A SIGNIFICANT AMOUNT OF SUBTROPICAL MOISTURE
AND RAIN INTO THE GREATER PHOENIX AREA TONIGHT AND FRIDAY. POSSIBLE
THUNDERSTORMS FRIDAY AFTERNOON BETWEEN 18Z FRI AND 23Z FRI. CIGS
LOWERING WITH RAIN THROUGH THE PERIOD BECOMING 8 THSD OVC BY 00Z
FRI...6 THSD OVC BY 06Z FRI...AND WIDE-SPREAD 2-3 THSD BY 12Z FRI.


SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...

A PACIFIC LOW PRESSURE SYSTEM WILL MOVE INTO THE REGION FROM THE
SOUTHWEST...IMPORTING A SIGNIFICANT AMOUNT OF SUBTROPICAL MOISTURE
AND RAIN MAINLY INTO AZ TONIGHT AND FRIDAY...BUT SPILLING INTO
SOUTHEAST CA AND THE COLORADO RIVER VALLEY. CIGS LOWERING WITH
SHOWERS THROUGH THE PERIOD BECOMING 8 THSD OVC BY 00Z FRI...6 THSD
OVC BY 06Z FRI...AND BKN 3 THSD OVC BY 12Z FRI.

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...AJ/CB
AVIATION...VASQUEZ
FIRE WEATHER...MCLANE





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