Area Forecast Discussion
Issued by NWS Tucson, AZ

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
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 161543
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
843 AM MST TUE DEC 16 2014

.SYNOPSIS...EXPECT DRY CONDITIONS WITH TEMPERATURES A FEW DEGREES
ABOVE NORMAL TODAY. A PACIFIC STORM SYSTEM WILL BRING VALLEY RAIN...
MOUNTAIN SNOW AND COOLER TEMPERATURES WEDNESDAY THROUGH THURSDAY.
DRY CONDITIONS WILL THEN PREVAIL FRIDAY INTO EARLY NEXT WEEK.

&&

.DISCUSSION...DENSE HIGH CLOUD COVER WILL CONTINUE TODAY AHEAD OF A
SERIES OF SHORTWAVE TROUGHS. THE MAIN FOCUS WILL BE ON PRECIPITATION
WITH THESE WAVES. GUIDANCE CONTINUES TO SHOW SHOWERS BEGINNING
WEDNESDAY MID MORNING AND CONTINUING INTO THURSDAY. WILL SEE 700 MB
TEMPS FALLING QUICKLY AS THE FIRST WAVE PUSHES THRU. THIS WILL ALLOW
FOR SNOW SHOWERS TO DEVELOP ACROSS ELEVATIONS ABOVE 7000 FT. THESE
CONDITIONS WILL GENERALLY BE IN PLACE SO DON`T FORESEE MUCH IN THE
WAY OF LOWERING OF SNOW LEVELS THRU THIS EVENT. CURRENT FORECAST
SEEMS ON TRACK SO NO UPDATES NEEDED AT THIS TIME.

&&

.PREV DISCUSSION/ISSUED AT 415 AM MST/...A DEEP UPPER TROUGH WAS
OVER THE ERN PACIFIC AND WRN CONUS WITH UPPER RIDGE OVER THE ROCKIES
EARLY THIS MORNING. SEVERAL IMPULSES WILL ADVANCE THRU THE BASE OF
THE LONGWAVE TROUGH OVER THE SWRN CONUS INTO THUR. AMPLE MOISTURE
ABOVE 500 MB WILL MAINTAIN PRECIP-FREE CONDITIONS WITH MOSTLY CLOUDY
SKIES INTO THIS EVENING. THE FIRST IN THE SERIES OF IMPULSES IN
COMBINATION WITH INCREASING LOWER LEVEL MOISTURE WILL BRING A SLIGHT
CHANCE OF SHOWERS LATE TONIGHT...ESPECIALLY WEST OF TUCSON. ISOLATED
TO SCATTERED SHOWERS PRODUCING LIGHT RAINFALL AMOUNTS SHOULD THEN
OCCUR WED MORNING.

THERE ARE THREE FAIRLY SIGNIFICANT CHANGES TO THIS OFFICIAL FORECAST
ISSUANCE VERSUS SUBSEQUENT FORECASTS. THE FIRST CHANGE IS THE ONSET
FOR SHOWERS AS NOTED ABOVE. THE ECMWF WAS PARTICULARLY FASTER WITH
STARTING PRECIP TONIGHT...WHEREAS PREVIOUS NWP MODELS DEPICTED DRY
CONDITIONS TO CONTINUE ACROSS SE AZ THRU TONIGHT. THUS...OPTED FOR A
SLIGHT CHANCE OF SHOWERS LATE TONIGHT MAINLY WEST-TO-NORTH OF TUCSON.

THE SECOND CHANGE TO THE FORECAST IS THE FAIRLY SIGNIFICANT
REDUCTION OF QPF/S WED-THUR AS DEPICTED BY THE 16/00Z NAM/GFS/ECMWF/
CANADIAN. A DEEPER IMPULSE IS STILL PROGGED TO MOVE EWD ACROSS THIS
FORECAST AREA LATE WED AFTERNOON INTO THUR. ALTHOUGH THE EXPECTED
RAINFALL AMOUNTS AND SNOW ACCUMULATIONS HAVE BEEN REDUCED...THE
EXPECTED PRECIP COVERAGE IS SIMILAR TO PREVIOUS OFFICIAL FORECASTS.
THUS...THERE CONTINUES TO BE A GOOD CHANCE OF SHOWERS WED AFTERNOON
ESPECIALLY FROM TUCSON NWD. NUMEROUS SHOWERS SHOULD OCCUR WED
NIGHT...THEN SHOWERS WILL DECREASE FROM WEST-TO-EAST THUR. THERE IS
A SLIGHT CHANCE OF SHOWERS EAST OF TUCSON THUR EVENING FOLLOWED BY
DRY CONDITIONS AREA-WIDE LATE THUR NIGHT-FRI.

THE REVISED STORM TOTAL LIQUID AMOUNTS ARE FORECAST TO RANGE FROM
0.10 - 0.50 INCH IN THE VALLEYS...WITH LIQUID AMOUNTS UP TO AROUND
0.75 INCH ACROSS THE HIGHER PEAKS. SNOW LEVELS MIDDAY WED WILL
GENERALLY RANGE FROM 6500-7000 FEET...THEN SNOW LEVELS ARE FORECAST
TO LOWER TO 5500-6000 FEET BY MIDDAY THUR. GIVEN THE REDUCED LIQUID
AMOUNTS...THE STORM TOTAL SNOW ACCUMULATIONS HAVE BEEN REVISED
DOWNWARD AS WELL.

STORM TOTAL SNOW ACCUMULATIONS ARE NOW EXPECTED TO RANGE FROM 4-8
INCHES ABOVE 7000 FEET ACROSS THE CATALINA/RINCON MOUNTAINS NEAR
TUCSON...THE PINALENO MOUNTAINS INCLUDING MT. GRAHAM SOUTHWEST OF
SAFFORD...AND NEWD TO THE WHITE MOUNTAINS. ONLY VERY MINOR SNOW
ACCUMULATIONS...IF ANY...WILL OCCUR ELSEWHERE.

FINALLY...THE THIRD CHANGE OF SIGNIFICANCE REGARDING THIS FORECAST
ISSUANCE IS THE REMOVAL OF PRECIP CHANCES THIS WEEKEND. THE ECMWF
WAS NEARLY IDENTICAL TO THE GFS WITH THE DEPICTION OF A POSITIVE-
TILTED OPEN WAVE TROUGH TO MOVE SEWD ACROSS THE AREA SAT NIGHT
FOLLOWED BY AN AMPLIFYING HIGH PRESSURE SYSTEM ALOFT WEST OF THE SRN
CALIFORNIA COAST SUN-MON.

HIGH TEMPS THIS AFTERNOON WILL BE A FEW DEGS ABOVE NORMAL FOLLOWED
BY 5 DEGS F OR SO OF DAILY COOLING WED-THUR. A WARMING TREND WILL
THEN OCCUR FRI-SAT...THEN NEAR NORMAL DAYTIME TEMPS WILL PREVAIL
SUN-MON.

&&

.AVIATION...VALID THRU 17/18Z.
SCT-BKN HIGH CLOUDS WILL CONTINUE TO STREAM INTO THE AREA. WILL SEE
A LOWERING OF CLOUD DECKS THIS EVENING AHEAD OF A SHORTWAVE TROUGH
MOVING INTO THE AREA. THIS TROUGH WILL BRING SOME SHOWERS TOMORROW.
DON`T EXPECT MUCH ACTIVITY AT ANY OF THE TERMINALS DURING THIS
FORECAST PERIOD...THOUGH SHOULD BEGIN TO SEE SOME AFTER 18Z/17.
AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...EXPECT DRY CONDITIONS WITH GENERALLY LIGHT WINDS
TODAY. THEN A COUPLE OF STORM SYSTEMS WILL BRING A FEW PERIODS OF
VALLEY RAIN AND MOUNTAIN SNOW WEDNESDAY THROUGH THURSDAY. BREEZY
SOUTHERLY WINDS ARE EXPECTED WEDNESDAY AT 10 TO 20 MPH EASING AND
BECOMING WESTERLY THURSDAY. THEREAFTER...MOSTLY DRY WEATHER IS
EXPECTED THROUGH THE COMING WEEKEND WITH PLENTY OF PASSING HIGHER
CLOUDS. POTENTIALLY BREEZY NW WINDS COULD DEVELOP DURING THE
AFTERNOON HOURS SATURDAY AND SUNDAY.

&&

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

&&

$$

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

DISCUSSION...FRANCIS
AVIATION/FIRE WEATHER...CERNIGLIA







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