Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 201530
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
830 AM MST SUN APR 20 2014

.SYNOPSIS...
HIGH PRESSURE WILL BUILD INTO THE AREA EARLY THIS WEEK LEADING TO
SUNNY DAYS...CLEAR NIGHTS...AND SHARPLY WARMER AFTERNOON HIGH
TEMPERATURES. BREEZY TO WINDY CONDITIONS WILL DEVELOP OVER MUCH OF
THE AREA TUESDAY AFTERNOON INTO WEDNESDAY AS A DRY WEATHER SYSTEM
PASSES TO THE NORTH. TEMPERATURES WILL FALL ONLY SLIGHT IN RESPONSE
TO THIS WEATHER SYSTEM...CLOSER TO SEASONAL NORMALS FOR THE
REMAINDER OF THE WEEK.

&&

.DISCUSSION...
UPPER LEVEL LOW HAS SHIFTED WELL TO THE EAST OF ARIZONA THIS MORNING
LEAVING A DRIER SUBSIDENT NWLY FLOW ALOFT IN PLACE ACROSS THE STATE.
H5 PLOTS SHOWED A 30M HEIGHT RISE STATEWIDE...WITH PWAT VALUES DOWN
TO LESS THAN ONE HALF INCH AT FLG...AND DOWN TO 0.63 AT TUS. IR
IMAGERY AT 8 AM SHOWED CLEAR SKIES ACROSS SERN CA AND MOST OF AZ
INCLUDING THE LOWER SRN DESERT. SURFACE DEWPOINTS REMAINED A BIT
ELEVATED AND WERE MOSTLY IN THE 40S THIS MORNING ACROSS THE LOWER
CENTRAL DESERT. DESPITE THE UPPER LOW NOW WELL EAST OF
PHOENIX...PLOTS DID SHOW MODEST CYCLONIC FLOW ALOFT ACROSS EASTERN
AZ...AND WITH BOUNDARY LAYER MOISTURE STILL LINGERING...EXPECT SOME
CU TO DEVELOP DURING THE AFTERNOON HOURS LEADING TO MOSTLY SUNNY
SKIES. ALSO...LIFTED INDEX AT FLG THIS MORNING WAS MINUS 2.5...AND
AS SUCH IT IS LIKELY THAT SOME CONVECTION WILL FORM ALONG THE
EASTERN RIM AND WHITE MOUNTAINS TODAY. THUS...WE MAY SEE AN ISOLATED
STORM DEVELOP EAST OF GLOBE THIS AFTERNOON AND WE WILL KEEP THE VERY
SLIGHT CHANCE POPS IN PLACE ACROSS THE EASTERN PORTION OF ZONE 24
THIS AFTERNOON. OTHERWISE...HIGH TEMPS WILL LIKELY RISE A FEW
DEGREES TODAY GIVEN THE AMPLE SUNSHINE IN PLACE...AND SUBTLE WARMING
OF THE LOW/MID LEVEL AIRMASS. CURRENT FORECASTS LOOK TO BE IN GOOD
SHAPE AND NO UPDATES ARE NEEDED AT THIS TIME.

.PREVIOUS DISCUSSION...
EARLY MORNING WV IMAGERY SHOWS THE CIRCULATION CENTER WHICH PASSED
THROUGH THE ERN PARTS OF THE FORECAST AREA YESTERDAY HAS MOVED INTO
CNTRL NEW MEXICO. OBJECTIVE ANALYSIS STILL DEPICTS A PORTION OF THE
COLD CORE ALOFT LINGERING OVER THE ERN PART OF ARIZONA...AND ONE CAN
INFER SOME WEAKLY SHEARED VORTICITY AND DEFORMATION STILL PRESENT
WITH IN THE WRN PERIPHERY OF THE LARGER SCALE CIRCULATION. GIVEN
THESE DYNAMICS AND SOME RESIDUAL MIDLEVEL MOISTURE...BOTH HIGH
RESOLUTION AND GLOBAL SCALE MODELS SUGGEST SOME AMOUNT OF
INSTABILITY/CONVECTIVE DEVELOPMENT OVER THE WHITE MOUNTAINS THIS
AFTERNOON. FOR THE MOST PART...ANY ACTIVITY SHOULD REMAIN TO THE
EAST OF THE FORECAST AREA...HOWEVER STEERING FLOW COULD CONCEIVABLY
SWING AN ARM OF VORTICITY BACK TO THE SOUTHWEST AND CLIP THE FAR
SERN PARTS OF GILA COUNTY (THOUGH CHANCES HARDLY SUPPORT ANYTHING
MUCH OVER 10 PERCENT PROBABILITY OUTCOME).

BY AND LARGE...THE STORY OVER THE NEXT COUPLE DAYS WILL BE THE
SIGNIFICANTLY WARMER TEMPERATURES. RIDGING WILL BEGIN TO BUILD OVER
THE FORECAST AREA TODAY CHARACTERIZED BY H5 HEIGHT RISES ON THE
ORDER OF 4-6DM. HEIGHTS ALOFT WILL BECOME MAXIMIZED MONDAY AFTERNOON
WITH THE H5 LEVEL AROUND 582DM...AND RESULTANT SFC-H7 TEMPERATURES
INCREASING SOME 2C-3C EACH SUCCESSIVE DAY. BASED ON BEST PERFORMING
GUIDANCE DURING THE PREVIOUS TWO WARM EPISODES EARLIER THIS MONTH
(8TH-11TH AND 15TH-17TH)...AFTERNOON HIGHS AT LOWER ELEVATION
POPULATION CENTERS SHOULD REACH INTO THE LOW/MID 90S TODAY...AND
MID/UPPER 90S MONDAY (SOME OF THE PREFERRED LOCATIONS SURROUNDING
THE COLORADO RIVER VALLEY LIKELY ECLIPSING THE 100 DEGREE
THRESHOLD).

MODELS REMAIN VERY CONSISTENT IN THE TIMING AND LOCATION OF A
SEASONALLY STRONG PROGRESSIVE OPEN WAVE BREAKING INTO THE WRN CONUS
TUESDAY. THE JET BASE OF THIS TROUGH SHOULD CROSS THE SIERRA CHAIN
TUESDAY AFTERNOON...EXPANDING INTO THE GREAT BASIN ON WEDNESDAY.
WHILE THE 00Z OPERATIONAL GFS IS DISPLACED SOMEWHAT FURTHER SOUTH
WITH LOWER HEIGHTS THAN THE ECMWF...DIFFERENCES ARE MINOR AND THE
PRIMARY RESULT WILL BE A TIGHTENING OF THE PRESSURE GRADIENT AND
INCREASED WINDS ALONG AND BEHIND THE LOW LEVEL FRONTAL BOUNDARY
TUESDAY AFTERNOON AND EVENING. WHILE THE MOST SIGNIFICANT WIND GUSTS
WILL BE IN THE IMMEDIATE LEE OF THE SAN DIEGO MOUNTAINS ACROSS WRN
IMPERIAL AND RIVERSIDE COUNTIES...THE ENTIRE CWA WILL NOTICE
PROLONGED STRONGER WINDS. THE GREATEST IMPACT WILL LIE WITH FIRE
WEATHER CONCERNS GIVEN THE ANTECEDENT DRY CONDITIONS AND FUELS
COMBINED WITH THESE WEATHER CONDITIONS (SEE FIRE WEATHER DISCUSSION
AND PLANNING FORECASTS).

OTHERWISE...THE LOW LEVEL FRONTAL PASSAGE SHOULD CLEAR THE FORECAST
AREA WEDNESDAY MORNING...WITH MODEST HEIGHT FALLS AND SFC-H7 CAA.
THIS WILL ONLY BE SUFFICIENT TO COOL THE REGION BACK TOWARDS THE
CLIMATOLOGICAL NORMAL WEDNESDAY AFTERNOON...WITH SHORTWAVE RIDGING
AND H5 HEIGHTS REBOUNDING AOA 576DM BY THURSDAY AND FRIDAY. ENSEMBLE
SPREAD CONTINUES TO GROW FOR THE WEEKEND TIME FRAME WITH EACH
FORECAST ITERATION. THE MODEL TREND OF NEGATIVE HEIGHT ANOMALIES
COVERING THE NORTHEAST PACIFIC BASIN REMAINS CONSISTENT...HOWEVER
THE SUBSEQUENT PROGRESSION OF SHORTWAVES INTO THE WRN/CNTRL CONUS IS
HIGHLY UNCERTAIN.

OPERATIONAL MEMBERS HAVE RETAINED GOOD RUN TO RUN CONTINUITY...WITH
THE GFS BODILY DEEPENING A SIGNIFICANT SINGLE WAVE INTO THE SWRN
CONUS OVER THE WEEKEND...WHILE THE ECMWF EJECTS SEVERAL WEAKER LEAD
WAVES THROUGH THE DOWNSTREAM QUASI-ZONAL FLOW WHILE MAINTAINING
GENERAL EAST PACIFIC TROUGHING. THE OPERATIONAL GEM IS SOMEWHAT OF
A COMPROMISE OF THESE TWO EXTREMES...BUT TENDS TO EVENTUALLY FAVOR
SOME MEASURE OF DEEPER TROUGHING NEAR THE FORECAST AREA. ENSEMBLE
MEMBERS EXHIBIT A VAST ARRAY OF POSSIBLE OUTCOMES...RESULTING IN
VERY LOW FORECAST CONFIDENCE NEXT WEEKEND. AT THIS TIME...UNLESS THE
SYSTEM DIGS EVEN DEEPER TO THE WEST OF CALIFORNIA...COULD NOT ARGUE
FOR HIGHER PRECIPITATION CHANCES WITH THE CURRENT SHORTWAVE
PROPAGATION TRAJECTORIES (THATS NOT TO SAY IT COULDN/T HAPPEN...JUST
VERY DIFFICULT THIS TIME OF YEAR). RATHER...THE PRIMARY FORECAST
CHALLENGE WILL BE DETERMINING IF/WHEN PRONOUNCED COOLING AFFECTS THE
REGION.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...

MOSTLY CLEAR SKIES AND LIGHT WINDS LESS THAN 10KT EXPECTED AT ALL
TAF SITES THROUGH AT LEAST 12Z MONDAY MORNING.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
TUESDAY THROUGH SATURDAY...
A LOW PRESSURE SYSTEM MOVES INTO THE GREAT BASIN...THE PRESSURE
GRADIENT TIGHTENING FOR AN INCREASE IN WIND AREA-WIDE LATE TUESDAY
AFTERNOON AND EVENING...WITH GUSTS UP TO 35 MPH POSSIBLE...AND EVEN
STRONGER WIND GUSTS EXPECTED ACROSS SOUTHEAST CALIFORNIA AND
PORTIONS OF THE LOWER COLORADO RIVER VALLEY INTO THE EVENING HOURS.
MINIMUM HUMIDITY LEVELS BOTTOM OUT IN THE SINGLE DIGITS DURING THIS
TIME FRAME...PRESENTING AN INCREASED FIRE DANGER THREAT AND THE
POSSIBLE ISSUANCE OF A WATCH OR RED FLAG WARNINGS IN SOME
AREAS...MUCH WILL BE PREDICATED ON HOW QUICKLY HUMIDITY LEVELS
RECOVER AND IF THE STRONGEST WINDS REMAIN ALOFT DURING THE EVENING
HOURS. WIDESPREAD BREEZY CONDITIONS PERSIST WEDNESDAY...WITH THE
STRONGER WIND FIELD THIS TIME FOCUSED ACROSS SOUTHEAST AND EASTERN
ARIZONA. MUCH LIGHTER WINDS AND DRY AND WARMER CONDITIONS ARE ON TAP
THURSDAY THROUGH SATURDAY AS HIGH PRESSURE ESTABLISHES OVER THE
REGION.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...CB
PREVIOUS DISCUSSION...MO
AVIATION...MEYERS
FIRE WEATHER...MEYERS






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