Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 290951
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
251 AM MST THU JAN 29 2015

.SYNOPSIS...A STORM SYSTEM WILL BRING VALLEY RAIN AND MOUNTAIN SNOW
MAINLY THURSDAY NIGHT INTO SATURDAY. THE MOST SIGNIFICANT SNOWFALL
WILL BE ABOVE 8000 FEET OR ACROSS THE HIGHEST PEAKS. EXPECT MUCH
COOLER DAYTIME TEMPERATURES WITH THIS SYSTEM. DRY CONDITIONS WILL
RETURN EARLY NEXT WEEK ALONG WITH A WARMING TREND.

&&

.DISCUSSION...SURFACE RIDGING WILL SETTLE IN OVER THE PLAINS TODAY.
THIS WILL TIGHTEN THE PRESSURE GRADIENT OUT EAST...WHICH WILL
ELEVATE WINDS THIS AFTERNOON...ESPECIALLY OVER THE GILA RIVER AND
SAN SIMON VALLEYS. THIS PRESSURE GRADIENT WILL GENERALLY STAY IN
PLACE UNTIL FRIDAY EVENING...SO WINDS WILL LIKELY REMAIN ELEVATED
THROUGH THIS TIME AS WELL.

DURING THE SAME TIME PERIOD THE UPPER LEVEL TROUGH OFF THE BAJA
COAST THIS MORNING WILL DEEPEN AND MOVE ONSHORE. THE CENTER OF THE
LOW IS PROGGED TO BE OVER SOUTHERN CALIFORNIA BY FRIDAY EVENING.
THIS TRAJECTORY VERY GOOD FOR DEEP MOISTURE ADVECTION FOR THE
AREA...AS HAS BEEN ADVERTISED FOR SEVERAL DAYS.

GUIDANCE HAS CONTINUED TO SHOW SOME INSTABILITY FRIDAY AND
SATURDAY DURING DAYLIGHT HOURS. THIS ENHANCES THE UNCERTAINTY
WITH RESPECT TO QPF AND SNOW TOTALS...ESPECIALLY ACROSS THE
SOUTHERN TIER OF ZONES. NEVERTHELESS...EXPECT WIDESPREAD 1-2
INCHES OF TOTAL LIQUID TO BE MEASURED ACROSS MOST LOCATIONS
THROUGHOUT THE EVENT...WITH LOCALLY HEAVIER AMOUNTS POSSIBLE.

ACROSS THE HIGHER TERRAIN OF THE WHITE MOUNTAINS EXPECT
PRECIPITATION TYPE TO QUICKLY BE DOMINATED BY SNOW. OTHER
LOCATIONS WILL HAVE TO WAIT FOR SNOW LEVELS TO BEGIN TO FALL.
INITIALLY...SNOW LEVELS WILL BE AROUND 9000 FT...THOUGH BY LATE
FRIDAY EXPECT THEM TO BE MORE AROUND 8000 FT. FOR THIS REASON HAVE
DELAYED THE START OFF SNOW FOR THE SANTA CATALINA MOUNTAINS BY
6 HOURS COMPARED TO THE PINALENO AND WHITE MOUNTAINS. THAT BEING
SAID...IF A CONVECTIVELY ENHANCED SHOWER MOVES IN EARLY FRIDAY
LOCALIZED SNOW CAN/T BE RULED OUT...THOUGH CONFIDENCE REMAINS TOO
LOW TO MENTION AT THIS TIME.

FRIDAY EVENING THE AFOREMENTIONED TROUGH WILL BEGIN TO DIG SOUTH
WHILE LIFTING...WHICH WILL ALLOW THE INTENSITY OF THE SHOWERS TO
RELAX FOR THE MOST PART. THOUGH...STILL EXPECTING WIDESPREAD
SHOWERS ACROSS THE AREA INTO SATURDAY.

BY SATURDAY EVENING THE TROUGH AXIS IS EXPECTED TO SPAN FROM
CENTRAL GULF OF CALIFORNIA INTO NORTHEASTERN NEW MEXICO.
SO...EXPECT SHOWER ACTIVITY TO BEGIN TO DIMINISH FROM NORTHWEST TO
SOUTHEAST THROUGH SUNDAY EVENING WHEN TROUGH REACHES SOUTHERN
BAJA. THIS WILL ALLOW FOR UPPER LEVEL RIDGING TO SLIDE OVERHEAD BY
THE END OF THE FORECAST.

SNOW TOTALS THROUGHOUT THE EVENT COULD REACH TWO FEET FOR THE
WHITE MOUNTAINS AND NEAR THAT MUCH FOR THE PINALENO MOUNTAINS /MT
GRAHAM. AS FOR THE SANTA CATALINA MOUNTAINS AND MORE SPECIFICALLY
MT. LEMMON EXPECT AROUND A FOOT. AGAIN THERE IS POTENTIAL FOR
HIGHER TOTALS WITH CONVECTION.

&&

.AVIATION...VALID THRU 30/12Z.
AS A STRONG LOW PRESSURE SYSTEM...WHICH IS CURRENTLY JUST OFF THE
CALIFORNIA COAST MAKES ITS WAY EASTWARD OVER THE NEXT FEW DAYS...
FLYING CONDITIONS WILL RAPIDLY DETERIORATE WITH INCREASING CLOUDS
MAINLY ABOVE 12K FT AGL EARLY THIS MORNING FOLLOWED BY FEW TO
SCATTERED CLOUDS AROUND 6-10K FT AGL AND OVERCAST CLOUD DECKS ABOVE
12K FT AGL BY THIS EVENING. A FEW -SHRA MAY DEVELOP EAST AND SOUTH
OF KTUS THIS AFTERNOON...WITH SCT TO NMRS -SHRA DEVELOPING AFTER
AROUND 30/06Z. CIGS AND VSBYS WILL DECREASE EVEN FURTHER DURING THIS
PERIOD WITH MVFR CONDITIONS POSSIBLE IN SOME LOCATIONS BEFORE
SUNRISE FRIDAY. SURFACE WIND WILL BE MOSTLY LESS THAN 12 KTS THIS
MORNING...THEN BECOMING SELY/SLY AT 10-15 KTS THIS AFTERNOON WITH
THE STRONGEST AND GUSTIEST WINDS ALONG THE NEW MEXICO BORDER AND
ALONG THE GILA RIVER VALLEY. WINDS WILL REMAIN FROM THE SOUTHEAST
OVERNIGHT INTO EARLY FRIDAY...ESPECIALLY ALONG THE NEW MEXICO BORDER
AND GILA RIVER VALLEY WHERE WINDS WILL BE SUSTAINED AT 15 TO 20 MPH
WITH HIGHER GUSTS DURING THE LATE EVENING AND OVERNIGHT HOURS.
AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...A STORM SYSTEM WILL BRING WIDESPREAD VALLEY RAIN AND
MOUNTAIN SNOW MAINLY 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. A
FEW LINGERING SHOWERS WILL OCCUR MAINLY EAST TO SOUTH OF TUCSON
SUNDAY...THEN DRY CONDITIONS WILL PREVAIL MONDAY THROUGH WEDNESDAY.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM LATE TONIGHT THROUGH SATURDAY MORNING
FOR AZZ510-511-514.

&&

$$

DISCUSSION...MEADOWS
FIRE WEATHER/AVIATION...88

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