Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 291145
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
445 AM MST THU JAN 29 2015

.SHORT TERM...(TODAY THROUGH FRIDAY)
ISSUED AT 445 AM MST THU JAN 29 2015

A MID LEVEL CLOUD DECK PERSISTS NORTH OF THE TAVAPUTS/FLATTOPS EARLY
THIS MORNING. EXPECT THIS CLOUD DECK WILL GRADUALLY ERODE BY
MIDDAY OR EARLY AFTERNOON. HIGH CLOUDS HAVE SPREAD ACROSS THE
REGION FROM THE SOUTH AND WEST AND WILL CONTINUE TO STREAM ACROSS
THE FORECAST AREA TODAY. THE THICKEST CLOUDS WILL BE OVER THE
SOUTHERN HALF...AND WILL LOWER THROUGH THE AFTERNOON. THIS
MOISTURE IS BEING CARRIED INTO THE SOUTHWEST CONUS BY THE SOUTH-
SOUTHWEST FLOW AHEAD OF A LOW PRESSURE CIRCULATION OFF THE BAJA
COAST. BY THE AFTERNOON A FEW SHOWERS WILL BEGIN TO DEVELOP OVER
THE SOUTHERN MOUNTAINS AS THE MOISTURE DEEPENS...AND ISENTROPIC
UPGLIDE PROVIDES SOME SYNOPTIC SCALE LIFT. IN SPITE OF THE CLOUDY
SKIES...TEMPERATURES WILL REMAIN WELL ABOVE NORMAL FOR LATE
JANUARY.

ISENTROPIC UPGLIDE WILL CONTINUE TONIGHT AND INTO FRIDAY AS THE
PACIFIC LOW MOVES ONSHORE EARLY FRIDAY. MOISTURE WILL DEEPEN
ACROSS THE REGION OVERNIGHT AS THE FLOW CONTINUES TO TAP INTO A
GOOD SUBTROPICAL MOISTURE FETCH. BY LATE TONIGHT PRECIPITATION
WILL BEGIN TO RAMP UP OVER THE FOUR CORNERS REGION...AND
ESPECIALLY OVER THE SOUTHWEST SLOPES OF THE SAN JUANS AND ABAJO
MOUNTAINS. THIS WILL KEEP OVERNIGHT LOW TEMPERATURES VERY
MILD...ESPECIALLY IN THE SOUTHERN AND CENTRAL VALLEYS.

MOISTURE CONTINUES TO DEEPEN ON FRIDAY AS THE LOW STRENGTHENS OVER
SOUTHERN CALIFORNIA. AS A RESULT...PRECIPITATION WILL SPREAD
NORTHWARD BY THE AFTERNOON AND INCREASE OVER THE SOUTH. THE WARM
NATURE OF THIS FLOW WILL KEEP SNOW LEVELS ON THE HIGH SIDE. AGREE
WITH THE PREVIOUS FORECAST THAT THE BEST ACCUMULATIONS WILL STAY
ABOVE 9000 FEET IN THE SOUTHERN MOUNTAINS. PRECIPITATION SHOULD
START OUT AS SNOW LATE TONIGHT IN THE SOUTHERN VALLEYS...BUT
EXPECT IT WILL SWITCH OVER TO A RAIN/SNOW MIX...OR ALL RAIN DURING
THE DAY ON FRIDAY. WILL CONTINUE TO KEEP AN EYE ON THIS AS LOWER
SNOW LEVELS COULD HAVE BIG RAMIFICATIONS. FOR OTHER AREAS...VALLEY
RAIN AND MOUNTAIN SNOW WILL SPREAD FROM THE SOUTH-SOUTHWEST TO THE
NORTHEAST FRIDAY THROUGH SATURDAY. EXPECT TEMPERATURES WILL BE
COOLER ON FRIDAY DUE TO PRECIPITATION AND LOWER CLOUDS...ESPECIALLY
OVER THE SOUTH.

FOR NOW WILL NOT CHANGE THE WINTER STORM WATCH FOR THE SOUTHWEST
SAN JUAN MOUNTAINS. THERE CONTINUES TO BE SOME DIFFERENCES IN THE
MODELS WITH THE GFS ON THE WEAKER SIDE.

.LONG TERM...(FRIDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 445 AM MST THU JAN 29 2015

CLOSED LOW CENTERED OVER THE SRN COLORADO RIVER BASIN CONTINUES TO
SEND WAVES OF MOISTURE INTO FOUR CORNERS AREA. FORECASTS REMAIN A
BIT TRICKY WITH RESPECT TO HOW MUCH QPF...SNOW LEVELS AND SNOW
AMOUNTS. ISENTROPIC UPGLIDE CONTINUES THROUGH FRIDAY NIGHT BEFORE
TRANSITIONING TO COLD ADVECTION. IN SPITE OF THE WARM MOIST
ADVECTION AND RELATIVELY WARM SYSTEM...MAIN SURFACE LOW STAYS
SOUTH OF THE SRN UTAH/COLORADO BORDER AND RESULTS IN A LOW LEVEL
EASTERLY COMPONENT OVER THE SWRN COLORADO VALLEYS. SURFACE WARM
ADVECTION MAY BE LACKING AND COULD BE THE REASON WHY GFS MOS
GUIADANCE HAS A PREFERENCE FOR SNOW AT BLANDING AND DURANGO. NAM
SOUNDINGS SHOW AN ISOTHERMAL LAYER ABOVE THE SURFACE WHICH
SUPPORTS THIS IDEA. THE EASTERLY COMPONENT IS ALSO PROBLEMATIC FOR
HEAVY SNOWFALL IN THE SAN JUAN MOUNTAINS...COULD BE A SITUATION
WHERE THE FOOTHILLS (LIKE VALLECITO RESERVOIR) RECEIVE MORE SNOW
THAN PLACES LIKE SILVERTON AND MOLAS/RED MOUNTAIN PASSES.

WHILE THE PRIMARY FOCUS IS ON SW COLORADO...PRECIPITATION SHIELD
SHOULD EXTEND AS FAR NORTH AS ROUTE HIGHWAY 40 (VERNAL TO STEAMBOAT
SPRINGS). THE CENTRAL MOUNTAINS HAVE A SHOT OF RECEIVEING LOWER
END ADVISORY SNOW AMOUNTS (I.E. 4-8 INCHES). DRIER NORTHWEST FLOW
INCREASES BY SATURDAY AFTERNOON AND PUSHES THE MOIST AIR MASS TO
THE SOUTHEAST AND RAIN/SNOW WILL BE ENDING BY SATURDAY EVENING.

THE REMAINDER OF THE LONG TERM PERIOD LOOK UNEVENTFUL WITH
NORTHWEST FLOW PREVAILING. THE JET AXIS IS NORTH OF COLORADO...BUT
EMBEDDED SHORT WAVES BRING A CHANCE OF OROGRAPHIC LIGHT SNOW TO
THE PARK RANGE. DOES NOT APPEAR TO BE ANY SIGNIFICANT EPISODES IN
THIS PATTERN...BUT SOMETIMES A SHORT WAVE IS MORE AMPLIFIED THAN
EXPECTED AND SNOWFALL EXCEEDS EXPECTATIONS. RIGHT NOW...THIS SEEMS
TO BE A REMOTE POSSIBILITY. MUCH OF THE REGION WILL HAVE MILD
CONDITIONS FOR EARLY FEBRUARY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 445 AM MST THU JAN 29 2015

CLOUDS WILL BE ON THE INCREASE TODAY WITH A TREND OF LOWER CIGS
TONIGHT. ALL TAF SITES WILL HAVE VFR CONDITIONS TODAY...BUT SLOWLY
DETEORIATING CONDITIONS CAN BE EXPECTED TONIGHT. AREAS OF LIGHT SNOW
OVER THE SOUTH WILL BE EXPANDING NORTHWARD TONIGHT. CIGS WILL
LOWER AND BECOME LOCALLY IFR IN LIGHT SNOW AND FOG. TAF SITES THAT
STAND THE BEST CHANCE FOR SNOW ARE KTEX AND KDRO.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER STORM WATCH FROM FRIDAY MORNING THROUGH SATURDAY
     AFTERNOON FOR COZ019.

UT...NONE.
&&

$$

SHORT TERM...EH
LONG TERM...PF
AVIATION...PF



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