Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 201648
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
945 AM MST THU NOV 20 2014

.SYNOPSIS...DRY CONDITIONS WITH SEASONABLE DAYTIME TEMPERATURES WILL
CONTINUE TODAY. A LOW PRESSURE SYSTEM WILL THEN BRING ISOLATED TO
SCATTERED VALLEY RAIN AND MOUNTAIN SNOW SHOWERS FRIDAY AFTERNOON AND
FRIDAY NIGHT. ONLY LIGHT PRECIPITATION AMOUNTS ARE EXPECTED. DRY
CONDITIONS WITH A SLOW WARMING TREND WILL THEN PREVAIL SATURDAY
THROUGH WEDNESDAY.

&&

.DISCUSSION...IR/VISIBLE SATELLITE IMAGERY AND SURFACE OBSERVATIONS
INDICATE CLEAR SKIES ACROSS SE AZ AT THIS TIME. A VERY DRY REGIME
CONTINUES WITH DEWPOINTS VALID 16Z RANGING FROM THE UPPER SINGLE
DIGITS TO THE LOWER 20S. 20/12Z KTWC SOUNDING TOTAL PRECIP WATER
VALUE WAS 0.25 INCH. 20/12Z UPPER AIR PLOTS DEPICTED A RIDGE AXIS
EXTENDING FROM WRN NEW MEXICO NWD INTO WRN MONTANA...A DEEP TROUGH
OVER THE ERN CONUS...AND A 551 DM LOW CENTERED OFF THE OREGON COAST
VICINITY OF 43N/130W. MODERATE TO STRONG WLY FLOW ABOVE 700 MB
PREVAILED ACROSS SE AZ.

BASED ON SATELLITE TRENDS AS WELL AS THE 20/12Z NAM...HAVE TRENDED
THE GRIDDED DATA SKY VALUES DOWNWARD TODAY. THUS...EXPECT CLEAR
SKIES ACROSS MUCH OF THE AREA THIS MORNING...THEN SOME INCREASE IN
THIN CIRRIFORM CLOUDS MAINLY NW OF TUCSON THIS AFTERNOON. HIGH TEMPS
THIS AFTERNOON FOR MOST LOCALES WILL BE WITHIN A DEGREE-OR-TWO OF
TEMPS ACHIEVED THUR.

HAVE NOTED THAT THE 20/12Z NAM/GFS POPS SUGGEST THAT INCREASED POP
VALUES MAY BE NECESSARY FRI AFTERNOON/EVENING. WILL AWAIT THE FULL
RECEIPT OF THE 20/12Z ECMWF BEFORE MAKING THIS CHANGE TO THE
INHERITED OFFICIAL FORECAST. THIS NOTION WILL BE ADDRESSED IN THE
AFTERNOON DISCUSSION. PLEASE REFER TO THE ADDITIONAL SECTIONS FOR
FURTHER DETAIL.

&&

.AVIATION...VALID THRU 21/12Z.
CLEAR SKIES FOR MUCH OF SE AZ TODAY THEN GRADUALLY INCREASING CLOUDS
ABOVE 20K FT AGL THIS EVENING INTO EARLY FRIDAY MORNING AS A LOW
PRESSURE SYSTEM APPROACHES FROM THE WEST. SURFACE WIND THRU EARLY
FRIDAY MORNING WILL GENERALLY BE LESS THAN 10 KTS. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...DRY CONDITIONS WITH LIGHT TERRAIN DRIVEN WINDS WILL
PREVAIL TODAY. A LOW PRESSURE SYSTEM WILL BRING ISOLATED TO
SCATTERED RAIN SHOWERS WITH PERHAPS A FEW MOUNTAIN SNOW SHOWERS LATE
FRIDAY AFTERNOON AND FRIDAY NIGHT. DRY CONDITIONS WILL THEN CONTINUE
THROUGH THE MIDDLE OF NEXT WEEK. ANOTHER LOW PRESSURE SYSTEM PASSING
TO THE NORTH OF THE REGION SUNDAY WILL BRING GUSTY WEST TO NORTHWEST
WINDS TO THE AREA. THE UPPER GILA VALLEY MAY SEE WINDS OF 10-15 MPH
WITH GUSTS OF 25-30 MPH. SLIGHTLY ELEVATED EASTERLY WINDS ARE
EXPECTED OVERNIGHT MONDAY AND INTO TUESDAY MORNING.

&&

.PREV DISCUSSION...OUR NEXT WEATHER MAKER IS SEEN OVER THE EASTERN
PACIFIC WATERS WEST OF THE OREGON AND NORTHERN CALIFORNIA COASTS AND
IS MOVING EAST SOUTHEAST. THIS SYSTEM IS EXPECTED TO MOVE ONSHORE
INTO NORTHERN CALIFORNIA THIS AFTERNOON AND THEN DIVE SOUTHEAST
THROUGH CENTRAL AND SOUTHERN CALIFORNIA LATE TONIGHT/EARLY FRIDAY
BEFORE MAKING ITS WAY INTO WESTERN ARIZONA AND NORTHWESTERN SONORA
ON FRIDAY. MODELS INDICATE THAT THIS SYSTEM WILL HAVE ENOUGH
ASSOCIATED MOISTURE TO JUSTIFY SLIGHT CHANCE POPS FOR DESERT/VALLEY
LOCATIONS AND LOW END CHANCE CATEGORY POPS FOR THE MOUNTAINS. THE
BEST TIMING FOR PRECIP WITH THIS SYSTEM SEEMS TO BE LATE FRIDAY
AFTERNOON AND INTO THE EVENING HOURS. THAT SAID...I MADE SOME
ADJUSTMENTS TO THE POP FORECAST TO REFLECT THIS NOTION. RAINFALL
AMOUNTS WITH THIS SYSTEM ARE EXPECTED TO BE VERY LIGHT...GENERALLY
RANGING FROM JUST A TRACE ON THE LOW END TO PERHAPS A THIRD OF AN
INCH ON THE HIGH END. SNOWFALL LEVELS EXPECTED TO FALL TO AROUND 7K
FEET AS THIS SYSTEM MOVES THROUGH...SO ANY SNOW ON MOUNTAIN TOPS
WILL BE VERY LIGHT WITH LITTLE TO NO ACCUMULATION EXPECTED.

ONCE THIS SYSTEM EXITS TO THE EAST EARLY SATURDAY...ANOTHER LOW
PRESSURE SYSTEM WILL BE MOVING THROUGH THE PACIFIC NORTHWEST AND
INTERMOUNTAIN WEST WITH THE TAIL END OF THIS SYSTEM BRUSHING THROUGH
THE FOUR CORNERS REGION EARLY SUNDAY AND INTO NEW MEXICO BY LATE IN
THE DAY. SOME MOISTURE WILL ACCOMPANY THIS SYSTEM...BUT IT SHOULD
REMAIN TO THE NORTH OF MY FORECAST AREA...SO FOR NOW I HAVE NO
MENTION OF POPS IN THE TEXT PRODUCTS OF THE FORECAST...BUT DO SHOW
THE `SILENT` SINGLE DIGIT POPS IN THE GRIDS.

ONCE THIS SYSTEM EXITS QUICKLY TO THE EAST...RIDGING WILL BUILD IN
FROM THE WEST FOR A WARMUP IN TEMPERATURES FOR EARLY TO MIDDLE OF
NEXT WEEK. ECWMF SHOWS A TROUGH OF LOW PRESSURE MOVING ACROSS
ARIZONA ON THANKSGIVING DAY...WHILE THE GFS SHOW A HIGHLY AMPLIFIED
RIDGE EXTENDING FROM ARIZONA INTO THE PACIFIC NORTHWEST. GFS
ENSEMBLE MEMBERS ALL SHOWED RIDGING DURING THIS TIME WITH JUST ONE
MEMBER SHOWING A TROUGH. HOWEVER...THIS IS ONE DAY BEYOND MY
OFFICIAL FORECAST PERIOD...SO STAY TUNED TO SUBSEQUENT FORECASTS TO
SEE WHAT THE MODELS WANT TO DO LATE NEXT WEEK.

FOR TUCSON...HIGH TEMPERATURES GENERALLY NEAR TO SLIGHTLY ABOVE
NORMAL TODAY...THEN 2 TO 3 DEGS BELOW NORMAL FRIDAY THROUGH
MONDAY...WITH THE COOLEST DAY OCCURRING ON FRIDAY. ABOVE NORMAL
HIGHS FOR TUESDAY AND WEDNESDAY OF NEXT WEEK. LOW TEMPERATURES WILL
HOVER WITHIN A DEGREE OR TWO EITHER SIDE OF NORMAL THROUGH NEXT
WEDNESDAY.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

VISIT US ON FACEBOOK...TWITTER...YOUTUBE...AND AT WEATHER.GOV/TUCSON

FRANCIS
PREVIOUS DISCUSSION...MOLLERE





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