Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 301835
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1140 AM MST FRI JAN 30 2015

.UPDATE...UPDATED AVIATION WEATHER DISCUSSION.

&&


.SYNOPSIS...
A PACIFIC LOW PRESSURE SYSTEM WILL LEAD TO A SIGNIFICANT RAIN EVENT
ACROSS THE REGION TODAY AND CONTINUING INTO SATURDAY. WE ANTICIPATE
RAINFALL TO BE MOST WIDESPREAD TODAY 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 NEXT THURSDAY.

&&

.DISCUSSION...
COVERAGE OF SHOWERS THIS MORNING HAS TRENDED DOWN OVER SOUTHWEST
ARIZONA AND SOUTHEAST CALIFORNIA. ACTIVITY HAS ALSO BECOME LESS
WIDESPREAD OVER METRO PHOENIX BUT REMAINS MORE WIDESPREAD OVER GILA
COUNTY. THE DOWNTREND LOOKS TO BE ASSOCIATED WITH THE EXIT OF A VORT
MAX NOW CENTERED ROUGHLY NEAR THE CAL-NEV-ARI BORDERS. THE MAIN
UPPER TROUGH IS CHANGING SHAPE DUE TO THE VARIOUS VORT LOBES
DUMBELLING AROUND. OTHER AREAS OF INTEREST WITHIN THE TROUGH INCLUDE
THE SOUTHERN END NEAR/WEST OF THE BAJA SPUR AND ANOTHER LOBE/VORT
MAX CENTERED ALONG THE CENTRAL CALIFORNIA COAST. THERE MAY BE
ANOTHER VORT MAX TO MOVE THROUGH THE FORECAST AREA LATER
TODAY/TONIGHT BUT OVERALL...THE PREVIOUSLY MENTIONED VORT LOBES WILL
LARGELY MISS OUR FORECAST AREA FOR THE DURATION OF THE EVENT...PER
LATEST MODELS. HOWEVER...DYNAMICAL FORCING WILL CONTINUE TO AFFECT
SOUTHEAST ARIZONA AND ADVECTION OF THOSE SHOWERS INTO OUR AREA MAY
OCCUR SATURDAY MORNING. AS FOR THUNDERSTORM POTENTIAL...MODEL CAPE
FOR THIS AFTERNOON CONTINUES TO LOOK QUITE MEAGER FROM THE GFS AND
BETTER FROM THE NAM. RAP IS EVEN BETTER THAN THE NAM BUT STILL UNDER
200 J/KG. HRRR SHOWS SOME ISOLATED WEAK CONVECTION AS WELL. THUS
WILL HOLD ON THE SLIGHT CHANCES. NAM SHOWS A NOTABLE INCREASE IN
CAPE FOR SATURDAY WHILE THE GFS IS STILL MEAGER. AS FOR CHANGES TO
THE FORECAST IN THE SHORT TERM...MAY NEED TO MAKE SOME DOWNWARD
ADJUSTMENTS TO POPS...MORE NOTICEABLY IN OUR WESTERN AREAS. MORE
LATER.

&&

.PREVIOUS DISCUSSION ISSUED 255 AM MST/155 AM PST...
AT 2 AM...VIGOROUS UPPER LEVEL LOW CONTINUED TO SPIN JUST OFF THE
NRN BAJA COAST...SPREADING COPIOUS AMOUNTS OF MOISTURE NORTHWARD
INTO ARIZONA AND PORTIONS OF FAR SERN CA. CURRENT BLENDED TOTAL
PRECIP WATER IMAGERY SHOWED 1.25-1.5 INCHES OF PWAT MOVING NORTH
ACROSS CENTRAL BAJA...POISED TO MOVE NORTH INTO ARIZONA DURING THE
DAY TODAY. IR IMAGERY AT 2 AM SHOWED AN IMPRESSIVE STREAM OF CLOUDS
OVERSPREADING THE AREA FROM THE SOUTH...AND THE LATEST 1.3 DEG RADAR
LOOP SHOWED WIDESPREAD SHOWERS SPREADING NORTH ACROSS MUCH OF
CENTRAL/SOUTH CENTRAL AZ WITH AREAL COVERAGE VIRTUALLY 100 PERCENT.
OVER THE PAST 6 HOURS...VIRTUALLY EVERY MARICOPA COUNTY FLOOD
CONTROL DISTRICT GAGE HAS PICKED UP MEASURABLE RAIN...WITH MOST
TOTALS BETWEEN ONE TENTH AND ONE THIRD OF AN INCH. PHOENIX HAS
PICKED UP 0.36 INCHES SO FAR WITH THIS EVENT...AND THE PERIODS OF
EXPECTED HEAVIEST RAINFALL HAVE YET TO OCCUR.

MODEL GUIDANCE HAS BEEN REMARKABLY CONSISTENT OVER THE PAST FEW DAYS
REGARDING THE EVOLUTION OF THIS WET WEATHER SYSTEM...INCLUDING
DETAILS SUCH AS TIMING AND QPF AMOUNTS. ALL GUIDANCE CALLS FOR AN
UPPER CLOSED LOW TO FORM OVER FAR SERN CA BY LATER THIS AFTERNOON...
AND AS THE LOW SPINS UP THE MOST SIGNIFICANT PRECIP IS EXPECTED TO
OCCUR OVER THE AREA...ESPECIALLY ACROSS SOUTH CENTRAL AZ. POPS WILL
STAY VERY HIGH TODAY...LIKELY OUT WEST AND CATEGORICAL OVER OUR
EASTERN FORECAST ZONES...WITH BASICALLY A 100 PERCENT CHANCE OF RAIN
CONTINUING FOR THE GREATER PHOENIX AREA. QPF AMOUNTS SHOULD RANGE
BETWEEN ONE QUARTER AND ONE HALF INCH TODAY ACROSS SOUTH CENTRAL
AZ...WITH LOCALLY HIGHER AMOUNTS OVER HIGHER TERRAIN AREAS TO THE
NORTH AND EAST OF PHOENIX. THERE WILL BE MODEST INSTABILITY OVER THE
CENTRAL DESERTS TODAY SO WE WILL CONTINUE TO CALL FOR A SLIGHT
CHANCE OF AFTN/EVE THUNDERSTORMS BASICALLY FROM THE LOWER CO RIVER
VALLEY EASTWARD. SHOULD A STORM DEVELOP...RAINFALL TOTALS WILL
BECOME ENHANCED. GIVEN ALL OF THE CLOUDS AND SHOWERS...HIGH TEMPS
TODAY WILL STAY WELL BELOW SEASONAL NORMALS WITH HIGHS OVER SOUTH
CENTRAL AZ TO HOVER IN THE UPPER 50S TO LOW 60S.

FOR TONIGHT THROUGH THE EVENING ON SATURDAY...THE UPPER LOW IS
PROGGED TO VERY SLOWLY TRANSLATE TO THE EAST/SOUTHEAST AND AS IT
DOES SO THERE WILL BE PERIODS OF ENHANCED LIFT/UVV AS VORT
SPOKES/LOBES ROTATE AROUND THE MAIN UPPER LOW. WITH MOISTURE OVER
THE LOWER DESERTS EXPECTED TO REMAIN VERY HIGH THROUGH SATURDAY...
PWAT VALUES REMAINING BETWEEN 0.75 AND 1.00 INCH...THE CONTINUED
DYNAMICS FROM THE VORT LOBES WILL KEEP SHOWERS GOING OVER MOST THE
REGION AND POPS WILL STAY ELEVATED. CHANCE TO LIKELY POPS WILL
REMAIN ACROSS SOUTH CENTRAL AZ TONIGHT AND SATURDAY...WITH POPS
DROPPING INTO THE SLIGHT CHANCE CATEGORY OVER SERN CA DURING THE DAY
ON SATURDAY.

OVERALL...WE ARE LOOKING AT STORM TOTAL AMOUNTS ENDING SATURDAY
EVENING RANGING FROM ONE QUARTER TO ONE HALF INCH OVER THE WESTERN
DESERTS...TO OVER ONE INCH ACROSS THE CENTRAL DESERTS INCLUDING THE
GREATER PHOENIX AREA. HIGHER AMOUNTS...1.25 TO NEARLY 2 INCHES...ARE
POSSIBLE IN THE HIGHER TERRAIN AREAS NORTH AND EAST OF PHOENIX. FOR
NOW WE EXPECT RAIN TO BE CONTINUAL AND NOT LOCALLY HEAVY OR INTENSE
ENOUGH TO WARRANT FLASH FLOODING CONCERNS. THERE MAY BE AREAS THAT
EXPERIENCE SOME URBAN OR SMALL STREAM FLOODING AS TIME WEARS ON AND
WE CAN SIMPLY ISSUE FLOOD ADVISORY PRODUCTS AS NEEDED TO COVER THIS
CONTINGENCY.

HIGH TEMPS SATURDAY WILL REMAIN WELL BELOW NORMAL AND WILL CHANGE
LITTLE FROM TODAYS EXPECTED READINGS. HIGHS SATURDAY IN THE GREATER
PHOENIX AREA WILL STAY IN THE UPPER 50S TO LOW 60S...NEARLY 10
DEGREES BELOW SEASONAL NORMALS.

SUNDAY THROUGH THURSDAY...
SUNDAY LOOKS TO BE A DRY AND WARMER DAY. PATCHY MORNING 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 THURSDAY FOR A GRADUAL WARMING TREND...AND WE
CAN EXPECT DESERT HIGHS TO REACH BACK INTO THE LOW TO MID 70S BY
NEXT WEDNESDAY...WITH THE WARMER WESTERN DESERTS RISING TO NEAR 80
BY NEXT THURSDAY.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL...
PERIODS OF RAIN WILL CONTINUE THROUGH 20Z WITH OCCASIONAL IFR CIGS
AND VSBYS AS A WEATHER DISTURBANCE MOVES THROUGH THE AREA FROM THE
SOUTH.  IN THE WAKE OF THE WEATHER DISTURBANCE...CIGS SHOULD LIFT TO
BETWEEN 25-35 HUNDRED FT (WIDESPREAD MVFR) WITH VSBYS BETWEEN 3-5
MILES AS RAIN DIMINISHES TO LIGHT SCT SHWRS. MVFR CONDITIONS WILL
CONTINUE OVERNIGHT FRIDAY...HOWEVER ANOTHER BOUT OF RAIN IS EXPECTED
SATURDAY MORNING WITH WIDESPREAD MVFR AND OCCASIONAL IFR CONDITIONS
IN CIGS/VSBYS (BETWEEN 10Z AND 17Z SAT).


SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
WIDESPREAD CIGS BETWEEN 6-8 THSD AGL WITH ISOLATED RAIN SHWRS
THROUGH 12Z SAT.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SUNDAY THROUGH THURSDAY...
DRIER AND SIGNIFICANTLY WARMER WEATHER IS EXPECTED...AS HIGH
PRESSURE BEGINS BUILDING BACK INTO THE REGION. HIGH TEMPERATURES IN
THE LOWER DESERTS WILL START OUT IN THE UPPER 60S ON SUNDAY AND
GRADUALLY CLIMB INTO THE UPPER 70S BY THURSDAY. WINDS ARE EXPECTED
TO BE LIGHT AND VARIABLE FOR MOST OF THE FORECAST PERIOD.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...AJ
PREVIOUS DISCUSSION...CB
AVIATION...VASQUEZ
FIRE WEATHER...MCLANE









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