Area Forecast Discussion
Issued by NWS Tucson, AZ

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS65 KTWC 251647
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
945 AM MST THU DEC 25 2014

.SYNOPSIS...EXPECT BREEZY TO WINDY CONDITIONS TODAY FOLLOWED BY A
GOOD CHANCE OF VALLEY RAIN AND MOUNTAIN SNOW LATE THIS AFTERNOON
INTO TONIGHT. A FEW LINGERING SHOWERS WILL OCCUR ACROSS EASTERN
SECTIONS FRIDAY...THEN DRY CONDITIONS WILL PREVAIL THIS WEEKEND AND
EARLY NEXT WEEK. WIDESPREAD FREEZING TEMPERATURES APPEAR TO BE
INCREASINGLY LIKELY FRIDAY NIGHT AND EARLY SATURDAY MORNING.

&&

.DISCUSSION...CLEAR SKIES PREVAIL ACROSS WRN PIMA COUNTY WITH PARTLY
CLOUDY SKIES ELSEWHERE AT THIS TIME. A VERY DRY SURFACE REGIME WAS
ONGOING WITH DEWPOINTS AT LOWER ELEVATIONS VALID 16Z RANGING FROM
THE SINGLE DIGITS TO LOWER 20S F. SURFACE TEMPS VALID 16Z WERE
NEARLY 5-20 DEGS F WARMER VERSUS 24 HOURS AGO. 25/12Z KTWC SOUNDING
TOTAL PRECIP WATER VALUE WAS 0.41 INCH...AN INCREASE OF 0.25 INCH
VERSUS THIS TIME WED. THE COLUMN DEPICTED A DRY SURFACE-600 MB
LAYER...BUT WAS NEARLY SATURATED ABOVE 500 MB. STRONG GENERALLY WLY
WINDS PREVAILED THROUGHOUT MUCH OF THE COLUMN.

DEEP UPPER TROUGH OVER THE INTERMOUNTAIN WEST AND SWRN CONUS WITH
539 DM LOW CENTERED NEAR SALT LAKE CITY THIS MORNING WILL PROGRESS
EWD INTO THE CENTRAL/SRN ROCKIES FRI. BASED ON VARIOUS 25/12Z NWP
MODEL SOLUTIONS...SOME ADJUSTMENTS WERE MADE TO THE INHERITED
GRIDDED DATA POP FIELDS FOR LATER TODAY INTO TONIGHT. THE OVERALL
SCENARIO OF SHOWERS DEVELOPING EARLY THIS AFTERNOON MAINLY WEST TO
NORTH OF TUCSON APPEARS REASONABLE. VALLEY RAIN AND MOUNTAIN SNOW
SHOWERS WILL THEN SPREAD EWD AND SHOULD ENCOMPASS MOST LOCALES FROM
TUCSON EWD TO THE NEW MEXICO BORDER TONIGHT.

THE MOST SIGNIFICANT CHANGES WERE TO INCREASE POPS FOR ERN PIMA
COUNTY INCLUDING TUCSON AND SOUTHEAST PINAL COUNTY LATE THIS
AFTERNOON. OPTED TO REDUCE POPS ACROSS THE TUCSON METRO AREA LATE
TONIGHT...BUT STILL MAINTAINED ISOLATED SHOWERS FOR ERN PIMA COUNTY.
A SLIGHT CHANCE OF SHOWERS WILL CONTINUE ACROSS ERN SECTIONS FRI
MORNING...AND A FEW LINGERING SHOWERS MAY YET CONTINUE NEAR THE NEW
MEXICO BORDER FRI AFTERNOON.

STORM TOTAL LIQUID AMOUNTS AND SNOW ACCUMULATIONS REMAIN UNCHANGED.
THUS...AMOUNTS GENERALLY BETWEEN ONE TENTH OF AN INCH AND ONE THIRD
OF AN INCH SHOULD OCCUR...WITH SNOW ACCUMULATIONS OF 2-5 INCHES
ABOVE 7000 FEET.

BASED MAINLY ON THE 25/12Z NAM/GFS...ALSO OPTED TO CHANGE THE
EXPIRATION TIME OF THE INHERITED WIND ADVISORY FROM 9 PM MST TO 7 PM
MST. 25/12Z KTWC SOUNDING WINDS OF 35-55 KTS IN THE 700-500 MB LAYER
CONTINUE TO JUSTIFY WIND ADVISORY CRITERIA SPEEDS LATER TODAY FOR
LOCALES MOSTLY SE OF TUCSON.

FINALLY...VARIOUS 25/12Z GUIDANCE CONTINUE TO SUPPORT THE LIKELY
OCCURRENCE OF WIDESPREAD FREEZING TEMPS FOR MUCH OF THE AREA FRI
NIGHT AND EARLY SAT MORNING. WILL LIKELY ISSUE A FREEZE WATCH LATER
TODAY THAT WOULD INCLUDE THE TUCSON METRO AREA AS WELL AS AT LEAST
PORTIONS OF SOUTH CENTRAL/SOUTHEAST PINAL COUNTY. THE POTENTIAL
EXISTS FOR A HARD FREEZE TO OCCUR FOR THE TUCSON METRO AREA...
PERHAPS FOR A FEW HOURS OR SO.

PLEASE REFER TO THE ADDITIONAL SECTIONS FOR FURTHER DETAIL.

&&

.AVIATION...VALID THRU 26/18Z.
A LOW PRESSURE SYSTEM MOVING ACROSS THE FOUR CORNERS REGION WILL
BRING A SLIGHT CHANCE OF -SHRA THIS AFTERNOON FROM KTUS NORTHWARD
AND WESTWARD INTO CENTRAL PIMA COUNTY. SCATTERED TO NUMEROUS -SHRA
AND HIGHER TERRAIN -SHSN WILL THEN OCCUR TONIGHT. MVFR CONDITIONS
WILL OCCUR ESPECIALLY ACROSS HIGHER TERRAIN. ISOLATED -SHRA AND
HIGHER TERRAIN -SHSN WILL PREVAIL EAST OF TUCSON FRIDAY MORNING.
SURFACE WIND FROM LATE THIS MORNING INTO THIS EVENING WILL GENERALLY
BE SWLY/WLY AT 15-30 KTS WITH GUSTS TO AROUND 40 KTS. SURFACE WIND
LATE TONIGHT AND FRIDAY MORNING WILL DIMINISH TO GENERALLY LESS THAN
15 KTS. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...WINDY CONDITIONS WILL OCCUR TODAY ESPECIALLY SOUTH
TO SOUTHEAST OF TUCSON. THERE IS A SLIGHT CHANCE OF SHOWERS MAINLY
FROM TUCSON NORTHWARD THIS AFTERNOON FOLLOWED BY A GOOD CHANCE OF
VALLEY RAIN AND MOUNTAIN SNOW TONIGHT. A SLIGHT CHANCE OF SHOWERS
WILL OCCUR MAINLY NEAR THE NEW MEXICO BORDER FRIDAY FOLLOWED BY DRY
CONDITIONS THIS WEEKEND AND EARLY NEXT WEEK.

&&

.PREV DISCUSSION...BY EARLY SATURDAY THE TROUGH WILL LINGER ACROSS
THE CENTRAL PLAINS INTO THE EXTREME SOUTHEAST CORNER OF ARIZONA.
COLD AIR BEHIND THIS SYSTEM WILL RESULT IN A COLD START TO THE
MORNING ON SATURDAY WITH READINGS WELL BELOW FREEZING FOR MOST
LOCATIONS...WITH THE EXCEPTION OF THE FAR WESTERN DESERTS OF PIMA
COUNTY NEAR ORGAN PIPE AND AJO. SIMILAR TEMPS FOR SUNDAY MORNING...
ALBEIT A DEGREE OR TWO WARMER...BUT STILL BELOW FREEZING FOR MOST
LOCATIONS.

BRIEF SHORTWAVE RIDGING WILL BUILD IN BEHIND THE SYSTEM ON SATURDAY
BEFORE ANOTHER PACIFIC SYSTEM DROPS TO THE SOUTHEAST ACROSS THE
PACIFIC NORTHWEST LATE SATURDAY AND EARLY SUNDAY. THIS SYSTEM IS
THEN EXPECTED TO DEVELOP INTO A CLOSED LOW OVER NORTHERN PORTIONS OF
THE GREAT BASIN AND NORTHERN ROCKIES BY LATE MONDAY. IT WILL THEN
SWING INTO THE GREAT BASIN AND CENTRAL CALIFORNIA ON TUESDAY...WITH
THE CENTER OF CIRCULATION OVER SOUTHERN NEVADA AND SOUTHEAST
CALIFORNIA LATE TUESDAY/EARLY WEDNESDAY AND WILL BE BODILY OVER
ARIZONA ON WEDNESDAY. THE MODELS ARE IN PRETTY GOOD AGREEMENT WITH
THE GFS/ECMWF AND CANADIAN MODELS ALL SHOWING A SIMILAR SCENARIO
WITH REGARD TO THE TIMING...POSITION AND STRENGTH OF THIS LOW.
MODELS ARE ALSO SUGGESTING THAT THIS STORM WILL BE COLD WITH HIGH
TEMPERATURES POTENTIALLY IN THE LOWER 50S AND PERHAPS A BIT COLDER
BASED ON 850-700MB THICKNESS VALUES. THAT SAID...I INCREASED POPS
FOR THE TUESDAY NIGHT INTO WEDNESDAY TIME FRAME BASED ON RECENT
MODEL SOLUTIONS...AS WELL AS TO BLEND WITH THE SURROUNDING OFFICES.
FOR NOW THE POPS ARE ONLY IN THE SLIGHT CHANCE TO CHANCE CATEGORY...
BUT IF THE SYSTEM DEVELOPS WITH THE KIND OF MOS POP VALUES THAT ARE
CURRENTLY BEING ADVERTISED...THEN MY FORECAST WOULD BE ON THE LOW
SIDE. IN ADDITION...SNOW COULD END UP REACHING THE VALLEY FLOORS FOR
COCHISE AND GRAHAM COUNTIES WEDNESDAY NIGHT OF NEXT WEEK. OF COURSE
THIS IS A LONG WAY OFF...SO STAY TUNED.

FOR TUCSON...HIGH TEMPERATURES GENERALLY A COUPLE OF DEGREES ABOVE
NORMAL TODAY...THEN 10 TO 15 DEGS BELOW NORMAL FOR FRIDAY AND
SATURDAY. FOR THE PERIOD SUNDAY THROUGH WEDNESDAY...HIGHS BELOW
NORMAL EACH DAY...BUT THE COLDEST DAY WILL OCCUR ON WEDNESDAY WHEN
HIGHS COULD BE AROUND 10 DEGS BELOW NORMAL. LOW TEMPS WILL BE BELOW
NORMAL THROUGH THE FORECAST PERIOD...BUT THE COLDEST MORNINGS WILL
OCCUR SATURDAY AND SUNDAY WHEN LOWS WILL RANGE FROM 8 TO 10 DEGS
BELOW NORMAL.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
    WIND ADVISORY UNTIL 7 PM MST THIS EVENING FOR AZZ503-507-508-
    512-513.

&&

$$

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

FRANCIS
PREVIOUS DISCUSSION...MOLLERE




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.