Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 300438
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
940 PM MST THU JAN 29 2015

.SYNOPSIS...A STORM SYSTEM WILL BRING VALLEY RAIN AND MOUNTAIN SNOW
ESPECIALLY TONIGHT INTO SATURDAY. MINOR FLOODING MAY OCCUR DUE TO
PERIODS OF HEAVY RAINFALL. THE MOST SIGNIFICANT SNOWFALL WILL BE
ABOVE 8000 FEET...OR ACROSS THE HIGHEST PEAKS. EXPECT MUCH COOLER
DAYTIME TEMPERATURES FRIDAY INTO THIS WEEKEND. DRY CONDITIONS WITH A
WARMING TREND WILL THEN OCCUR EARLY NEXT WEEK.

&&

.DISCUSSION...SCATTERED TO WIDESPREAD SHOWERS WERE OCCURRING THIS
EVENING ACROSS SE AZ. SINCE THESE SHOWERS ARE MOVING AROUND 25 TO 35
MPH TO THE NE...RAINFALL AMOUNTS HAVE GENERALLY BEEN LIGHT LESS THAN
A TENTH OF AN INCH...WITH LOCALIZED AMOUNTS BETWEEN 0.25" AND 0.35".
SNOW LEVEL STILL ABOVE THE TIPS WITH TEMPERATURES AT THE HIGHEST
PEAKS IN THE MID TO UPPER 30S. THE TUCSON AFTERNOON SOUNDING CAME IN
WITH A PRECIPITABLE WATER VALUE OF 1.07" WHICH RANKS AS THE 5TH
HIGHEST JANUARY VALUE ON RECORD. AS OF 8 PM...PRECIPITABLE WATER
VALUES ACROSS THE AREA...BASED ON VARIOUS SOURCES...RANGED FROM
0.65" IN THE WHITES TO 1.10" OVER WESTERN PIMA COUNTY.

UPPER LOW OFF NRN BAJA COAST CONTINUES TO SPREAD MOISTURE NORTH INTO
SOUTHERN ARIZONA. RAINFALL RATES WILL BE ON THE INCREASE TONIGHT AS
SEVERAL DISTURBANCES CAUGHT IN THE SOUTHERLY FLOW MOVES ACROSS THE
AREA. LATEST 00Z QPF FORECASTS BY NAM AND GFS HAVE PUSHED THE
HIGHEST QPF TOTALS A LITTLE FURTHER WEST VERSUS PREVIOUS RUNS BUT
DISAGREE SLIGHTLY ON PLACEMENT. OVERALL STILL IN LINE IN WHAT WE
HAVE CURRENTLY IN THE FORECAST.

WILL MAKE SOME SHORT TERM FORECAST TWEAKS IN EVENING UPDATE.

CHECK PREVIOUS DISCUSSION BELOW FOR FURTHER DETAILS.

&&

.AVIATION...VALID THRU 31/00Z.
A PACIFIC LOW PRESSURE SYSTEM WILL MOVE EASTWARD INTO SOUTHEAST
ARIZONA INTO FRIDAY. THIS SYSTEM WILL BRING A SIGNIFICANT AMOUNT AND
MOISTURE RESULTING IN WIDESPREAD VALLEY RAIN AND MOUNTAIN SNOW.
THERE IS ALSO A SLIGHT CHANCE OF THUNDERSTORMS ACROSS MUCH OF THE
AREA FRIDAY AFTERNOON. CLOUD DECKS EARLY THIS EVENING WILL GENERALLY
BE AT 6-10K FT AGL...THEN LOWER TO GENERALLY 2-3K FT AGL BY FRIDAY
MORNING. HIGHER TERRAIN WILL BE OBSCURED FRIDAY IN CLOUDS AND
PRECIPITATION. SURFACE WIND WILL GENERALLY BE SELY/SLY AT 5-15 KTS
THRU THE PERIOD. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...EXPECT WIDESPREAD VALLEY RAIN AND MOUNTAIN SNOW
TONIGHT INTO SATURDAY. THE MOST SIGNIFICANT SNOWFALL WILL OCCUR
ACROSS THE HIGHEST PEAKS OF THE WHITE MOUNTAINS...MOUNT GRAHAM...AND
THE CATALINA AND RINCON MOUNTAINS NEAR TUCSON. A FEW LINGERING
SHOWERS WILL OCCUR MAINLY EAST TO SOUTH OF TUCSON SUNDAY...THEN DRY
CONDITIONS WILL PREVAIL SUNDAY NIGHT THROUGH THURSDAY.

&&

.PREV DISCUSSION...RAINFALL INTENSITY SHOULD DECREASE PERHAPS AS
EARLY AS FRI EVENING...BUT MORE LIKELY LATE FRI NIGHT AND ESPECIALLY
SAT. HOWEVER...AMPLE MOISTURE CONTINUING ACROSS THE AREA IN
COMBINATION WITH WEAK SYNOPTIC SCALE ASCENT DUE TO THE PRESENCE OF
THE UPPER LOW WILL LEAD TO WIDESPREAD SHOWER COVERAGE. A SLIGHT
CHANCE OF THUNDERSTORMS WILL CONTINUE SAT AFTERNOON DUE TO AN
ENVIRONMENT OF WEAK AOB 300 J/KG MUCAPE. THE UPPER LOW THAT IS
PROGGED TO BE CENTERED OVER THE LOWER COLORADO RIVER VALLEY MIDDAY
SAT IS PROGGED TO MOVE SWD INTO THE NRN GULF OF CALIFORNIA SAT
NIGHT...THEN MOVE SLOWLY SEWD ACROSS SONORA MEXICO SUN. THERE SHOULD
BE ENOUGH MOISTURE TO MAINTAIN A SLIGHT CHANCE OF SHOWERS FROM
TUCSON EWD/SWD SUN.

STORM TOTAL LIQUID AMOUNTS ARE FORECAST TO GENERALLY RANGE FROM 0.50
TO 1.50 INCHES IN THE VALLEYS...WITH SOME AMOUNTS IN EXCESS OF 2.00
INCHES POSSIBLE. LIQUID AMOUNTS ACROSS THE MOUNTAINS WILL GENERALLY
RANGE FROM 1.00 - 2.00 INCHES. HOWEVER...LIQUID AMOUNTS IN EXCESS OF
2 INCHES SHOULD OCCUR ACROSS SOME MOUNTAINS...PARTICULARLY FROM THE
CATALINA/RINCON MOUNTAINS NEAR TUCSON NEWD TO THE WHITE MOUNTAINS.

SNOW LEVELS FRI MORNING WILL BE AROUND 9000 FEET. SNOW LEVELS WILL
THEN LOWER TO AROUND 8000 FEET FRIDAY EVENING...AND CONTINUE TO
LOWER TO NEAR 7500 FEET BY MIDDAY SATURDAY. STORM TOTAL SNOW
ACCUMULATIONS SHOULD APPROACH OR EVEN EXCEED 2 FEET IN THE WHITE
MOUNTAINS ABOVE 7000 FEET...WITH 18-22 INCHES OF SNOWFALL ABOVE 7000
FEET FURTHER SWWD ACROSS THE PINALENO MOUNTAINS INCLUDING MOUNT
GRAHAM. STORM TOTAL SNOW ACCUMULATIONS ARE FORECAST TO RANGE BETWEEN
12-16 INCHES ACROSS THE CATALINA/RINCON MOUNTAINS ABOVE 7000 FEET.

DRY CONDITIONS WILL THEN PREVAIL SUN NIGHT-THUR. MUCH COOLER TEMPS
WILL OCCUR FRI AND SAT...WITH HIGH TEMPS ACROSS THE AREA TO AVERAGE
ABOUT 5-10 DEGS F BELOW NORMAL. A WARMING TREND WILL THEN OCCUR
SUN-THUR.

&&

.CLIMATE...POSTED DAILY RAINFALL RECORDS FOR JANUARY 30TH AND 31ST
FOR SELECTED LOCATIONS ON OUR WEBSITE...TWITTER AND FACEBOOK.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
  WINTER STORM WARNING FROM 5 AM FRIDAY TO NOON MST SATURDAY FOR
   AZZ510-511 ABOVE 7000 FEET.
  WINTER STORM WARNING FROM 11 AM FRIDAY TO NOON MST SATURDAY FOR
   AZZ514 ABOVE 7000 FEET.

&&

$$

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





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