Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 230409
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
909 PM 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...EASTERLY SURFACE FLOW WILL CONTINUE THROUGH TOMORROW
AFTERNOON FOR MOST LOCATIONS. SURFACE GRADIENT WILL RELAX SOME
DURING THE DAY...WHICH WILL ALLOW WINDS TO DIMINISH SOME.
STILL...EXPECT ELEVATED EASTERLY WINDS TO PERSIST OVER THE NEXT
FEW DAYS. THEN FOCUS TURNS TO THE PROGGED CUTOFF LOW OFF WESTERN
BAJA COAST. THIS SYSTEM WILL ADVECT MOISTURE INTO THE AREA BRING
BACK THE POTENTIAL FOR PRECIPITATION EARLY NEXT WEEK. SEE PREV
DISCUSSION FOR FURTHER DETAILS. ALL IN ALL...CURRENT FORECAST IS
IN GOOD SHAPE SO NO UPDATES NEEDED AT THIS TIME.

&&

.AVIATION...VALID THRU 24/06Z.
VFR CONDITIONS WILL PREVAIL IN AND AROUND THE TERMINALS OVER THE
NEXT 24 HOURS. LOWER CEILINGS ARE POSSIBLE EAST OF KDUG AS AN AREA
OF LOW PRESSURE MOVES EAST OF THE AREA. LOW CLOUDS MAY OBSCURE
TERRAIN AT TIMES IN AND AROUND THE CHIRICAHUA MOUNTAINS. EAST
WINDS WILL IMPACT MOST AREAS OVERNIGHT WITH GUSTS AS HIGH AS 25
MPH. AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...BRISK EAST WINDS WILL IMPACT MOST AREAS OVERNIGHT.
WIND GUSTS AS HIGH AS 25 MPH WILL BE POSSIBLE. DRY AND STABLE
WEATHER WILL BUILD BACK IN WITH WARMING TEMPERATURES THROUGH THE
WEEKEND.

MOISTURE WILL BE ON THE INCREASE EARLY NEXT WEEK AS LOW PRESSURE OFF
BAJA COAST LIFTS NORTH. SHOWER POTENTIAL WILL BE ON THE
INCREASE...WITH THE BEST CHANCE OVER WESTERN PORTIONS OF PIMA
COUNTY.

&&

.PREV DISCUSSION... /ISSUED 254 PM MST THU JAN 22 2015/

DISCUSSION...PRIMARY CONCERN FOR THE NEXT WEEK IS THE POTENTIAL FOR
SHOWERS...AND POSSIBLY A FEW THUNDERSTORMS...MONDAY AND TUESDAY.
MORE ON THAT IN A MOMENT.

CURRENTLY...VISIBLE SATELLITE IMAGERY AND SURFACE OBSERVATIONS SHOW
THE LOW CLOUDS AND LIGHT PRECIP ONGOING JUST ALONG THE AZ AND NEW
MEXICO BORDER. IN ADDITION...THE TIGHT PRESSURE GRADIENT IN PLACE
ACROSS SOUTHEAST AZ IS RESULTING IN GUSTY SURFACE WINDS. FOR
TONIGHT...WRF AND HRRR OUTPUT SUGGESTS EASTERLY LOW LEVEL FLOW WILL
CONTINUE THROUGH THE MORNING HOURS. THE RESULTING DOWNSLOPE WINDS
SHOULD KEEP LOW TEMPERATURES A FEW DEGREES HIGHER THAN MOS GUIDANCE
SUGGESTS IN VALLEY LOCATIONS TO THE WEST OF MOUNTAIN RANGES...THIS
INCLUDES LOCATIONS SUCH AS TUCSON AND SAFFORD.

THE UPPER LEVEL PATTERN MOVES INTO A TRANSITIONAL PHASE STARTING
TOMORROW AS THE UPPER LEVEL LOW PRESSURE SYSTEM IN NEW MEXICO SWEEPS
TO THE EAST...AND HIGH PRESSURE BUILDS OVER THE WESTERN U.S.. A
PRONOUNCED SHORT WAVE TROUGH EMBEDDED IN THE UPPER RIDGE DIVES SOUTH
TOWARD ARIZONA TOMORROW MORNING. THIS SHORT WAVE EVENTUALLY DIGS
SOUTHWEST...INTENSIFIES...AND BECOMES CUT OFF FROM THE MAIN PATTERN
JUST OFF THE COAST OF BAJA CALIFORNIA. THIS RESULTS IN AN UPPER
LEVEL REX BLOCK PATTERN WHERE WITH THE INTENSE HIGH PRESSURE RIDGE
EXTENDING OVER THE PACIFIC NORTHWEST AND THE CUT OFF LOW OFF THE
BAJA PENINSULA. THIS PATTERN SHOULD STICK AROUND FOR A FEW DAYS AND
WHILE THE PACIFIC NORTHWEST HEATS UP TO NEAR RECORD LEVELS...THOSE
OF US IN THE SOUTHWEST WILL SEE TEMPERATURES WARM UP A FEW DEGREES
ABOVE AVERAGE. IN ADDITION...MOIST AIR FROM THE PACIFIC WILL BE
TRANSPORTED BY THE LOW PRESSURE SYSTEM INTO SOUTHERN ARIZONA. BY
TUESDAY MORNING...PRECIPITABLE WATER VALUES WILL SKYROCKET TO AROUND
1 INCH...WHICH DOES NOT SEEM HIGH...BUT IS ACTUALLY NEAR THE 99TH
PERCENTILE FOR MID JANUARY.

ONCE THE CUT OFF LOW DISLODGES FROM THE BLOCKING PATTERN ON
MONDAY...IT WILL PUSH NORTH AND BING THE MOISTURE...ALONG WITH
PLENTY OF LIFT...TO SUPPORT PRECIPITATION ACROSS SOUTHEAST ARIZONA.
RIGHT NOW...IT APPEARS THE BEST SHOT FOR PRECIPITATION WILL TAKE
PLACE TUESDAY MORNING THROUGH THE AFTERNOON HOURS. SNOW LEVELS
SHOULD REMAIN FAIRLY HIGH AS THIS SYSTEM WILL BE RELATIVELY WARM FOR
MID JANUARY GIVEN ITS TIME SPENT OFF THE BAJA PENINSULA. RIGHT
NOW...WE ARE THINKING SNOW LEVELS MAY FALL TO AROUND 8000 FEET OR
SO. THEIR SHOULD BE SUFFICIENT COLD AIR ALOFT...AND WARM LOW LEVEL
AIR...TO SUPPORT A LIGHTNING STRIKE OR TWO. THE CURRENT FORECAST
DOES NOT MENTION THUNDERSTORMS AS I AM NOT CONFIDENT ON EXACTLY
WHERE THUNDER IS MOST LIKELY...BUT THE FAVORED AREA IS PIMA COUNTY
TO THE WEST. RAINFALL AMOUNTS ARE STILL UP IN THE AIR...BUT WE COULD
SEE A FEW TENTHS WITH A ISOLATED AMOUNTS NEAR ONE HALF INCH.

FOLLOWING THE EARLY WEEK SYSTEM...THE UPPER PATTERN BECOMES MORE
PROGRESSIVE AND GIVES WAY TO SHORT TERM RIDGING THROUGH MID
WEEK...FOLLOWED BY ANOTHER LOW PRESSURE SYSTEM BY NEXT WEEKEND.  THE
ECMWF EVEN SUGGESTS ANOTHER REX BLOCK PATTERN STARTING NEXT
FRIDAY...WHILE THE GFS IS MORE PROGRESSIVE AND BRINGS A TROUGH
THROUGH BY SATURDAY. EITHER WAY...THE LONG TERM FORECAST IS FAIRLY
UNSETTLED AT THIS POINT.

&&

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

$$

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