Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 221601
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
901 AM MST THU JAN 22 2015

.SYNOPSIS...AN UPPER LOW WILL DROP SOUTH ALONG THE NEW MEXICO BORDER
THROUGH THIS EVENING GENERATING A FEW SHOWERS ALONG THE BORDER AND
FORCING COLDER ACROSS THE STATE ON NORTHERLY BREEZES.  DRY AND
MILDER WEATHER WILL RETURN THIS WEEKEND BEFORE A LOW WEST OF BAJA
DIRECTS MOISTURE NORTH AND BRINGS A THREAT OF SHOWERS TO SOUTHERN
ARIZONA SUNDAY NIGHT INTO TUESDAY.

&&

.DISCUSSION...THERE ARE FEW CHANGES FROM THE OVERNIGHT DISCUSSION.
THE UPPER LEVEL LOW PRESSURE SYSTEM EVIDENT ON SATELLITE ALONG THE
ARIZONA AND NEW MEXICO BORDER CONTINUES TO PUSH SOUTH. MOST OF
SOUTHERN ARIZONA WILL REMAIN IN THE DRY COMPONENT OF THIS
SYSTEM...WITH THE EXCEPTION OF THE WHITE MOUNTAINS AND EXTREME
SOUTHEAST ARIZONA. CLOUD COVER AND A FEW SNOW FLAKES IN THE HIGH
TERRAIN OR RAIN DROPS IN THE VALLEYS ARE POSSIBLE THROUGH THE
AFTERNOON...BUT SHOULD NOT RESULT IN ANY MAJOR IMPACTS.

THE MORE NOTICEABLE RESULT FROM THIS LOW PRESSURE SYSTEM WILL BE AN
INCREASE IN WIND SPEEDS TODAY FROM THE NORTH AND EAST. PLUS THE
COOLER AIR ASSOCIATED WITH THIS SYSTEM WILL KEEP HIGH TEMPERATURES
TODAY 10 TO ALMOST 20 DEGREES BELOW THE LAST FEW DAYS...OR ABOUT 10
DEGREES BELOW AVERAGE CONDITIONS FOR LATE JANUARY. OVERNIGHT LOWS
WILL ALSO FALL BELOW OUR RECENT OBSERVATIONS...BUT WE ARE NOT
EXPECTING WIDESPREAD FREEZING CONDITIONS IN THE LOWER ELEVATIONS OF
PIMA AND PINAL COUNTIES. COLDER AIR...BELOW FREEZING...WILL FILTER
INTO THE LOWER ELEVATIONS OF COCHISE...GRAHAM AND GREENLEE COUNTIES
TONIGHT AND AGAIN SATURDAY MORNING.

&&

.AVIATION...VALID THRU 23/12Z.
THERE WILL BE A SLIGHT CHANCE OF -SHRA E OF KTUS AS LOW PRESSURE
DROP S ALONG AZ/NM BORDER. OTHERWISE VFR CONDS WILL PREVAIL. LIGHT
SURFACE WIND THIS MORNING BECOMING GUSTY OUT OF THE NORTH-NORTHEAST
AT 10-15 KTS WITH GUSTS TO 25 KTS LATE THIS MORNING INTO THIS
AFTERNOON. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.
GLUECK

&&

.FIRE WEATHER...UPPER LEVEL LOW PRESSURE WILL DROP SOUTH ALONG THE
ARIZONA/NEW MEXICO BORDER TODAY...BRINGING A SLIGHT CHANCE OF VALLEY
RAIN AND MOUNTAIN SNOW SHOWERS TO AREAS EAST OF A MT GRAHAM-BISBEE
LINE. MUCH COOLER TODAY WITH GUSTY NORTHERLY WINDS DEVELOPING.
REMAINING COOL ON FRIDAY BUT DRY. DRY AND WARMER THIS WEEKEND. A
PERSISTENT EASTERLY WIND WILL SET UP TONIGHT INTO THE WEEKEND WITH
LOCALLY GUSTY CONDITIONS NEAR FAVORED MOUNTAIN GAPS.

MOISTURE WILL BE ON THE INCREASE EARLY NEXT WEEK AS LOW PRESSURE OFF
BAJA COAST LIFTS N. STILL SOME UNCERTAINTY ON WHERE THE BEST CHANCES
FOR PRECIPITATION WILL OCCUR. AT THIS TIME WILL GO WITH A SLIGHT
CHANCE OF SHOWERS.  GLUECK

&&

.PREV DISCUSSION...WATER VAPOR IMAGERY SHOWING THE UPPER LOW
DEVELOPING OVER FAR NW NEW MEXICO THIS HOUR...RIGHT ON SCHEDULE.
THIS SYSTEM WILL DROP NEARLY DUE SOUTH THROUGH THE DAY AND BRING A
SMALL THREAT OF SNOW SHOWERS TO THE WHITE MOUNTAINS AND RAIN AND
HIGHER ELEVATION SHOW SHOWERS TO AREAS ALL ALONG THE NEW MEXICO
BORDER...MAINLY THROUGH EARLY AFTERNOON.  RATHER STRONG COLD
ADVECTION FROM ABOUT 700 MBS ON DOWN OCCURRING ON THE WEST SIDE OF
THIS SYSTEM WHICH WILL KEEP A LID ON MUCH WARMING TODAY.  HIGH
TEMPERATURES TODAY WILL BE 8-14 DEGREES COOLER THAN YESTERDAY AND
NOT CLIMBING OUT OF THE 50S MOST AREAS.  THE EXPECTED BREEZES WILL
ADD A BIT OF ADDITIONAL CHILL AS WELL.

TONIGHT THROUGH FRIDAY SKIES WILL BE CLEAR WITH COOLER THAN NORMAL
TEMPERATURES AND AN EASTERLY BREEZE.  LOW TEMPERATURES WILL BE
SOMEWHAT TRICKY AS BREEZY AREAS WILL NOT COOL OFF AS MUCH AS
SHELTERED LOCATIONS.  OVERALL...FRIDAY MORNING LOWS WILL RANGE FROM
THE LOW TO MID 20S SHELTERED AREAS OF COCHISE...GRAHAM AND GREENLEE
COUNTIES TO THE MID 30S TO AROUND 40 WESTERN DESERTS.

SOMEWHAT TEMPORARY REX PATTERN DEVELOPS BY LATE IN THE WEEKEND WITH
THE TRANSITION ALLOWING FOR DRY AND MILDER CONDITIONS FOR THE
WEEKEND.  WHILE I TRIMMED AFTERNOON TEMPS BACK A FEW DEGREES
SATURDAY AND SUNDAY...THEY ARE STILL 3-6 DEGREES WARMER THAN
NORMAL.

THEN THINGS GET MORE INTERESTING.  THE REX PATTERN...TYPICALLY MORE
OF A BLOCKING PATTERN...WILL BE TRANSITORY ALLOWING THE LOW CENTER
WELL TO THE SW TO BEGIN MOVING NORTH WHICH WILL SPREAD MOISTURE UP
ACROSS THE REGION EARLY IN THE WEEK.  THE CURRENT FORECAST RELIES
HEAVILY ON THE 00Z GFS...00Z CANADIAN AND 12Z ECMWF IDEA.  THE 00Z
ECMWF WAS TOSSED DUE TO IT BEING SIGNIFICANTLY DIFFERENT THAN ITS
EARLIER RUNS AND THE OTHER MODELS/ENSEMBLES IN GENERAL.  TIMING IS A
BIT SUSPECT STILL...BUT THE BASIC IDEA IS THAT LATE SUNDAY NIGHT
INTO MONDAY THERE DEVELOPS A CHANCE OF SHOWERS WHICH REMAINS WITH US
THROUGH TUESDAY AS THE LOW MOVES NORTH...WEST OF BAJA AND UP THROUGH
SOUTHERN CALIFORNIA TUESDAY.  WITH THE WARM SOUTHERLY FLOW...EXPECT
TEMPERATURES TO REMAIN WARMER THAN NORMAL DESPITE THE EXPECTED CLOUD
COVER THROUGH THE PERIOD.  AS THE TIME DRAWS CLOSER DETAILS WILL
COME INTO BETTER FOCUS.

FOR WEDNESDAY ONWARD THE REGION REMAINS IN A SW FLOW PATTERN THAT
HAS A FAIR AMOUNT OF MID AND HIGH LEVEL MOISTURE.  AT THIS TIME IS
LOOKS DRY WEDNESDAY AND THURSDAY BUT I TWEAKED CLOUD COVER UP A
BIT.  LONGER RANGE MODELS SUGGEST A THREAT OF SHOWERS AGAIN NEXT
FRIDAY ONWARD.  CERNIGLIA

&&

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

&&

$$

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