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000
FXUS65 KGJT 010301
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
801 PM MST SAT FEB 28 2015

.UPDATE...
ISSUED AT 801 PM MST SAT FEB 28 2015

COMPLEX SYNOPTIC PICTURE THIS EVENING AS THERE ARE TWO REGIONS OF
PCPN WITH A THIN DRY SLOT (COINCIDING WITH I70) THAT SPLITS THE
FORECAST AREA. STRONG JET WILL CUT ACROSS SW COLORADO
OVERNIGHT...COMBINED WITH OROGRAPHICS AND POTENTIAL
INSTABILITY...WILL CONTINUE TO GENERATE SNOWFALL OVER THE SAN
JUANS AND UNCOMPAHGRE PLATEAU. SOME OF THIS WILL SPILL OVER INTO
THE VALLEYS AND BELIEVE THAT ACCUMULATING SNOW WILL OCCUR IN THE
MONTROSE VICINITY. WINTER WEATHER ADVISORY ISSUED TONIGHT FOR
ZONE 11...BUT SHORT TERM MODELS SHOW THAT SNOW WILL BE ENDING
TOWARD DAYBREAK BEFORE THE NEXT MOISTURE SURGE.

ON THE BIGGER PICTURE...CURRENT FORECASTS ON TRACK ALTHOUGH THE
SHORT TERM IS CHALLENGING GIVEN THE CONVECTIVE COMPONENT.

&&

.SHORT TERM...(TONIGHT THROUGH SUNDAY NIGHT)
ISSUED AT 326 PM MST SAT FEB 28 2015

CONVECTION OR INSTABILITY IS DEFINITELY BECOMING A FACTOR IN THIS
STORM AS WE HAD REPORTS OF ALMOST 4 INCH PER HOUR RATES NEAR CORTEZ
EARLIER THIS MORNING. THIS AREA OF INSTABILITY...DRIVEN BY DYNAMIC
TROP ALOFT...IS RUNNING JUST NORTH OF JET CORE. SEVERAL OBSERVING
SITES UNDER THIS FLOW HAVE SEEN AN INCREASE IN SNOW RATES WITH VSBYS
DOWN TO 1/4 OF A MILE AT TIMES. IT WILL BE INTERESTING TO SEE
REPORTS ROLL IN THROUGH THE EVENING. LOOKING AT AREA WEB CAMS
HOWEVER ROADS BELOW 10000 FEET ARE HANDLING THIS SNOWFALL WELL FOR
THE MOST PART. THAT IS LIKELY TO CHANGE TONIGHT AS TEMPERATURES COOL
AND HAZARDOUS DRIVING CONDITIONS WILL SPREAD TO LOWER ELEVATIONS.

TONIGHT THE JET WILL BE LIFTING NORTHWARD AS THE UPPER LOW AND
ATTENDANT TROUGH DIGS FARTHER SOUTH ALONG THE SOUTHERN CALIFORNIA
COAST. THIS BACKS THE UPPER FLOW TO THE SOUTHWEST OVER OUR REGION.
MODELS HAVE BEEN FAIRLY CONSISTENT THE PAST FEW DAYS ARCING AN AREA
OF ENHANCED PRECIPITATION FROM SOUTHEAST UTAH INTO CENTRAL COLORADO
NEAR THIS JET AXIS. THEY HAVE ALSO BEEN CONSISTENT SHOWING A
DOWNWARD TREND IN THE SOUTHERN VALLEYS. OROGRAPHICS IN THIS FLOW
SHOULD CONTINUE TO FORCE SNOW SHOWERS INTO THE HIGHER TERRAIN OF
THE SOUTHERN AND EASTERN SAN JUANS SO HIGH POPS CONTINUE THERE.
WOULD THINK AT LEAST ANOTHER 4 TO 8 (FOOT NEAR WOLF CREEK) INCHES
ARE LIKELY. IN THE VALLEYS MODELS ARE DRYING THE DENDRITIC LAYER
WHICH LIMIT THE POTENTIAL. HOWEVER THIS DRYING IS AN INDICATION OF
INSTABILITY ALOFT AND COINCIDES WITH THE UPSTREAM ACTIVITY
CURRENTLY OVER NORTHERN ARIZONA. AS THIS SLIDES OVER TONIGHT THINK
SNOW SHOWERS WILL AGAIN BE HIGHLY LIKELY SO LEFT POPS ON HIGH END
FOR NOW WITH ACCUMS IN THE 2-4 INCH RANGE CLOSER TO THE FOOTHILLS.
CONVECTION IS LIKELY TO BRING IN SOME HIGHER AMOUNTS. TO THE NORTH
CONFIDENCE NOT HIGH ENOUGH FOR ADDING ANY VALLEYS TO THE CURRENT
HEADLINES BUT SOME SNOW IN THE GUNNISON...AND GRAND VALLEYS ARE
LIKELY. CLOSER TO THE BORDER UPGLIDE SHOULD ALSO BRING LIGHT SNOW
ALONG THE YAMPA RIVER VALLEY BY THE LATE EVENING HOURS.

EXPECT SOME DOWNTURN IN PRECIPITATION ACTIVITY SUNDAY WITH SOME
DRYING INDICATED ACROSS THE CENTRAL SECTION AND A ONLY MODICUM OF QG
LIFT BETWEEN WAVES AS THE MAIN UPPER LOW SITS OVER SRN CA. MODELS
CONTINUE TO FOCUS BEST SNOWFALL INTO THE SWRN SAN JUANS AND ARCHULETA
COUNTY IN THE SW FLOW ACROSS THE FOUR CORNERS. 700 MB TEMP ADVECTION
LOOKS PRETTY NEUTRAL MUCH OF THE DAY...BUT WARM ADVECTION REDEVELOPS
SUNDAY NIGHT PROVIDING SOME FRONTOGENETIC LIFT ACROSS THE SOUTH AS
THE 700 MB TEMP GRADIENT TIGHTENS FOR INCREASED SNOW ACCUMS. SW WINDS
BEGIN TO STRENGTHEN AT MTN TOP LEVEL SUNDAY NIGHT SO ADDED AREAS
OF BLOWING SNOW TO THE SAN JUANS/LA SALS/ABAJO MTNS AFTER MIDNIGHT.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 326 PM MST SAT FEB 28 2015

THE SRN CA UPPER LOW GETS KICKED OUT TO THE NORTHEAST MONDAY BY AN
UPSTREAM SHORTWAVE TROUGH DROPPING DOWN THE WEST COAST TO REPLACE
IT. EXPECT TO SEE PRECIPITATION BACK ON THE INCREASE MONDAY AS
THE EJECTING LOW REACHES OUR AREA MONDAY EVENING AS AN OPEN WAVE.
700 MB WINDS CONTINUE TO STRENGTHEN FOR AREAS OF BLOWING SNOW OVER
THE CENTRAL AND NRN MTNS. 700 MB BAROCLINIC ZONE SHIFTS NORTH TO
ABOUT THE TAVAPUTS/ROAN PLATEAUS AS A WARM FRONT FOR SOME RAIN OR
RAIN/SNOW MIX IN THE LOWER VALLEY MONDAY AS MODELS SHOW A SURFACE
LOW DEVELOPING OVER OUR AREA. 12Z NAM KEEPS THIS SFC LOW OVER SWRN
CO WHILE THE 12Z GFS AND ECMWF PLACE MORE OVER NWRN CO...WHICH
COULD HAVE SOME RAMIFICATIONS FOR PRECIPITATION COVERAGE AND
AMOUNTS. WILL KEEP THE WINTER STORM WATCH BEGINNING MONDAY FOR THE
NORTHERN VALLEYS IN PLACE.

FLOW TURNS WEST TO NORTHWEST MONDAY NIGHT AND TUESDAY BEHIND THE
WAVE WITH COLDER AIR SWEEPING IN FOR TUE. DISTURBANCES IN THE
NORTHERN STREAM SHOULD BECOME MORE INFLUENTIAL AND SHIFT THE FOCUS
OF THE PRECIPITATION TO THE CENTRAL AND NORTHERN MTNS...THOUGH THE
NAM12 AND ECMWF ALSO FAVOR THE NWRN SAN JUANS. THE WINTER HIGHLIGHTS
ACROSS THE NORTH EXTEND INTO WED MORNING...BUT FOLLOWED MODEL
GUIDANCE OF DECREASING POPS TUE NIGHT INTO WED FOR NOW. PLENTY OF
TIME FOR THINGS TO STILL CHANGE WITH THE DYNAMIC NATURE OF THIS
STORM HOWEVER...AND TRAILING NWLY FLOW IN COLD ADVECTION WOULD
FAVOR THE NRN MTNS AS HINTED AT BY THE GFS THOUGH NOT THE ECMWF.

UNSETTLED FLOW SHOULD PERSIST ON THURSDAY BUT WITH SURFACE HIGH
PRESSURE IN PLACE AND LIMITED MOISTURE WILL KEEP THE FORECAST DRY.
MODELS SHOW THE PACIFIC RIDGE TRYING TO BUILD INLAND LATE NEXT
WEEK BUT ALSO SOME ENERGY MOVING ALONG THE US/MEXICO BORDER
UNDERCUTTING IT. FOLLOWED THE BLENDED MODEL FOR DRY WEATHER AND
WARMING TEMPS FRI AND SAT.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 634 PM MST SAT FEB 28 2015

WIDESPREAD SNOW IS EXPECTED AT MOUNTAIN AIRFIELDS THROUGH THE
PERIOD...PLUS KDRO (DURANGO). LULL PERIODS MAY EXIST BETWEEN 12Z-
18Z WITH BRIEF CLEARING...BUT CONFIDENCE IN FORECASTING THESE
BREAKS IS POOR. EXPECT CIGS/VIS TO LOWER AT KMTJ OVERNIGHT WITH
PERIODS OF -SN THROUGH THE NIGHT.

CURRENT LOCATIONS THAT HAVE VFR CONDITIONS MAY DETERIORATE AND
BECOME MVFR/IFR AS SNOW BANDS MOVE IN AND OUT.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER STORM WARNING UNTIL 9 AM MST WEDNESDAY FOR COZ003-013.

     WINTER STORM WATCH FROM LATE SUNDAY NIGHT THROUGH WEDNESDAY
     MORNING FOR COZ001-002-004-005.

     WINTER STORM WARNING UNTIL 8 PM MST MONDAY FOR COZ009-010-012-
     017>019-021>023.

     WINTER WEATHER ADVISORY UNTIL 8 PM MST MONDAY FOR COZ014.

     WINTER WEATHER ADVISORY UNTIL 6 AM MST SUNDAY FOR COZ011.

     WINTER WEATHER ADVISORY UNTIL 8 AM MST MONDAY FOR COZ008.

UT...WINTER STORM WARNING UNTIL 9 AM MST WEDNESDAY FOR UTZ025.

     WINTER STORM WATCH FROM LATE SUNDAY NIGHT THROUGH WEDNESDAY
     MORNING FOR UTZ023-024.

     WINTER STORM WARNING UNTIL 8 PM MST MONDAY FOR UTZ028.

&&

$$

UPDATE...PF
SHORT TERM...15/JAD
LONG TERM...JAD
AVIATION...PF