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548
FXUS65 KTWC 260335 CCA
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
835 PM MST SUN JAN 25 2015

.SYNOPSIS...INCREASING MOISTURE FROM THE SOUTH WILL BRING
THICKENING CLOUDS AND SHOWERS TO SOUTHERN ARIZONA MONDAY INTO EARLY
TUESDAY. DRY AND WARMER MID WEEK BEFORE A STRONGER PACIFIC SYSTEM
BRINGS VALLEY RAIN AND MOUNTAIN SNOW TO THE AREA FRIDAY AND SATURDAY.

&&

.DISCUSSION...MOISTURE INCREASING FROM THE SOUTH THIS EVENING WITH
SURFACE DEW POINTS IN THE UPPER 20S ALONG THE BORDER (UP ABOUT 15
DEGREES COMPARED TO 24 HRS AGO) AND THE 00Z KTWC SOUNDING
PRECIPITABLE WATER (PW) AT 0.28 INCH (DOUBLE YESTERDAY`S VALUES). 1
INCH PW SHOWING UP IN CENTRAL TO NORTHERN SONORA AS WELL AS CENTRAL
TO NORTHER PORTIONS OF THE GULF OF CALIFORNIA ON SATELLITE BLENDED
TOTAL PW ESTIMATES. WE ARE ON TRACK FOR RAIN TOMORROW AND TOMORROW
NIGHT.

STILL SOME TIMING ISSUES AS THE NAM CONTINUES TO BE SLOWEST IN
SPREADING SHOWERS NORTH TOMORROW MORNING. SOME SLIGHTLY SLOWER 18Z
TRENDS WITH OTHER MODELS AS WELL...SO WE MADE A FEW TWEAKS TO THE
FORECAST THIS EVENING. FIRST WE INCREASED DEW POINTS A LITTLE
EARLIER FROM THE SOUTH AND ADJUSTED CLOUD COVER FOR FIRST PERIOD
TRENDS. SECONDLY WE SPLIT THE POP AND WEATHER GRIDS INTO 3 HOUR
INCREMENTS TO SHOW A SLOWER SPREAD NORTHWARD OF SHOWERS TOMORROW
MORNING AS PER LATER MODEL TRENDS AND CURRENT HI RES RAPID REFRESH
OUTPUT. FINALLY...WE INCREASED STORM TOTAL QPF VALUES IN MOUNTAINS
TO BETTER REFLECT POTENTIAL OROGRAPHIC EFFECTS WITH MORE EXTREME
PRECIPITABLE WATER VALUES. COULD SEE NEAR RECORD PW VALUES FOR
JANUARY. THE RECORD IS 1.12 INCHES AND WE ARE ALMOST GUARANTEED TO
SEE VALUES OVER 1 INCH.

&&

.AVIATION...VALID THRU 27/06Z.
CLOUDS AND SHOWERS INCREASING FROM THE SOUTH OVER THE NEXT 24 HOURS.
MID AND HIGH CLOUDS INCREASING OVERNIGHT. AFTER 26/14Z...LOWERING
CLOUDS ARE EXPECTED THRU THE REST OF THE DAY...WITH SCT-BKN CLOUDS
AT 4-8K FT AGL AND BKN-OVC CLOUDS AT 10-15K FT AGL. CHANCE OF
SHOWERS AFT 26/16Z. ELY/SELY SURFACE WIND AT 10-15 KTS. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...EAST TO SOUTHEAST WINDS WILL OCCUR ACROSS MUCH OF
THE AREA OVER THE NEXT COUPLE OF DAYS. WIND SPEED WILL BE IN THE
10-15 MPH RANGE...WITH A FEW HIGHER GUSTS. THERE WILL BE A CHANCE OF
SHOWERS MONDAY INTO TUESDAY. THE BEST CHANCE FOR SHOWERS WILL BE
MONDAY AFTERNOON AND MONDAY NIGHT. DRY WEATHER WILL RETURN TUESDAY
AFTERNOON THROUGH THURSDAY BEFORE ANOTHER DISTURBANCE BRINGS A GOOD
CHANCE OF SHOWERS LATE NEXT WEEK AND INTO NEXT WEEKEND.

&&

.PREV DISCUSSION...NOT MUCH HAS CHANGED FROM THIS MORNINGS
DISCUSSION. HIGH CLOUD COVER SHOULD PERSIST THROUGH THE NIGHT. LOWER
LEVEL CLOUDS SHOULD DEVELOP LATER THIS EVENING AS MID LEVEL MOISTURE
ADVECTS INTO SOUTHERN AZ FROM THE PACIFIC. THIS WILL SET THE STAGE
FOR OUR APPROACHING PRECIPITATION EVENT. MODELS ARE A BIT MIXED ON
THE START TIME FOR PRECIP...BUT GENERALLY AGREE THAT PRECIP WILL
BEGIN ALONG THE BORDER MONDAY MORNING...WITH THE MOST WIDESPREAD
PRECIP DURING THE EVENING MONDAY INTO TUESDAY MORNING. CURRENT
SATELLITE IMAGERY HINTS THAT THE UPPER LOW IS MOVING SLIGHTLY
FURTHER WEST THAN ORIGINALLY ANTICIPATED...SO THAT FAVORS THE
HEAVIEST PRECIP CHANCES GENERALLY ACROSS PIMA AND PINAL COUNTIES.

AS FOR SNOW CHANCES...THE SNOW LEVELS WILL BE FAIRLY HIGH IN THIS
EVENT...UPWARDS OF 9000 FEET. THAT LIMITS THE SNOW MAINLY TO THE
WHITE MOUNTAINS. AGAIN...WITH THE FURTHER WEST PUSH OF THE UPPER
LOW...SNOW TOTALS SHOULD BE HELD IN THE 1 TO MAYBE 5 INCH RANGE.

ONCE THIS SYSTEM EXITS THE AREA TUESDAY...THE UPPER RIDGE OVER THE
WESTERN US REAMPLIFIES AND YET ANOTHER CUT OFF LOW DEVELOPS FIRST
OVER NEVADA...AND THEN SETTLES NEAR SOUTHERN CALIFORNIA OR THE BAJA
PENINSULA SATURDAY. THIS SYSTEM APPEARS TO BE MUCH WETTER THAN OUR
MONDAY SYSTEM. MODELS SHOW SIMILAR MOISTURE METRICS...LIKE PRECIP
WATER OR LAYER RELATIVE HUMIDITY...BUT NEXT WEEKENDS SYSTEM HAS THE
POTENTIAL TO BRING PRECIP FOR A LONGER PERIOD OF TIME. THE
ECMWF...FOR EXAMPLE...PRODUCES PRECIP FOR WELL OVER 24 HOURS ACROSS
SE ARIZONA. THE GFS IS SLIGHTLY LESS OPTIMISTIC...BUT GIVEN THE
TRENDS HAVE BEEN FAIRLY CONSISTENT FOR THE LAST FEW DAYS...I DECIDED
TO INCREASE PRECIP CHANCES FOR THE END OF THE WEEK.

SNOW LEVELS WILL STILL BE HIGH NEXT WEEKEND...BUT MAY COME IN 1000
FEET OR SO LOWER THAN MONDAY. BEST ESTIMATE RIGHT NOW IS THAT SNOW
LEVELS WILL TO SIT AROUND 8000 FEET.

THE MAIN CONCERN WITH NEXT WEEKS SYSTEM...IN ADDITION TO THE RAIN
AND SNOW...WILL BE TRAVEL IMPACTS FOR THOSE HEADING NORTH FOR A
HIGHLY ATTENDED SPORTING EVENT. SLICK ROADS WILL BE COMMON FRIDAY
AND SATURDAY...SO DRIVERS SHOULD BE PREPARED.

JJB

&&

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

&&

$$

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MEYER/BROST/ZELL







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