Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 271714
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1014 AM MST TUE JAN 27 2015

.UPDATE...
ISSUED AT 1006 AM MST TUE JAN 27 2015

BAND OF MID AND HIGH LEVEL CLOUDS CONTINUES TO WORK NORTH ACROSS
THE FORECAST AREA THIS MORNING. BAND BEING LIFTED NORTH BY UPPER
LEVEL LOW OVER NEVADA THAT WILL BE LIFTING NORTH INTO IDAHO OVER
THE NEXT 18 HOURS AND THEN SLIDING EAST ACROSS WYOMING. WILL BE
KNOCKING POPS DOWN FOR THE REMAINDER OF THE DAY WITH SOME TWEAKS
TO TEMPS AS WELL.

&&

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 410 AM MST TUE JAN 27 2015

THE REX BLOCK HAS BEEN ERADICATED FROM THE WESTERN UPPER AIR
PATTERN. THE RIDGE AXIS ON THE 00Z H5 HAND ANALYSIS MAP IS NOW
ORIENTED FROM WEST TEXAS TO WESTERN OREGON WHILE THE UPPER LOW
CIRCULATION IS PUSHING ONSHORE IN CENTRAL CALIFORNIA. MOISTURE
FEEDING INTO THE LOW FROM THE SUBTROPICS IS FEEDING A RATHER LARGE
AREA OF PRECIPITATION FROM SOUTHERN CALIFORNIA ACROSS SOUTHERN
NEVADA...SW. UTAH AND MUCH OF ARIZONA. FARTHER EAST...AWAY FROM
THE SYSTEM DYNAMICS...RADAR RETURNS ARE MORE SPARSE AND PROBABLY
NOT MUCH OF THIS IS REACHING THE GROUND. 00Z KGJT SOUNDING SHOWED
A LARGE ARE OF DRY AIR TO OVERCOME. THE STRENGTH OF THIS RIDGE
WILL BE STRONG ENOUGH TO FORCE THE CALIFORNIA STORM NORTHWARD INTO
IDAHO BEFORE IT SWINGS EASTWARD TONIGHT. DO NOT THINK THIS BODES
WELL FOR PRECIPITATION OVER OUR CWA TODAY. IN THIS WARM REGIME THE
DENDRITIC LAYER IS QUITE HIGH AND SHOULD NOT BE SATURATED AS
MOISTURE FROM THE SOUTH ENCOUNTERS THE DRY AIR UNDER THE RIDGE.
THE BEST CHANCES APPEAR TO BE ALONG OUR FAR WESTERN BORDER. THERE
WILL LIKELY BE VIRGA PASSING OVERHEAD THROUGH THE DAY AND SOME OF
THE HIGHER TERRAIN MAY SEE A FEW SPRINKLES OR LIGHT SHOWER BUT
NOTHING SIGNIFICANT. HAVE LITTLE CONFIDENCE LOWER ELEVATIONS WILL
GET MORE THAN A TRACE IF ANY. FORCING IMPROVES TONIGHT INTO
WEDNESDAY AS THE SYSTEM BEGINS TO ACCELERATE EASTWARD AND FORCING
FROM THE SOUTHERN JET MOVES OVER THE CENTRAL COLORADO MOUNTAINS.
TEMPERATURES ARE WARM INITIALLY TONIGHT NEAR MINUS 1C AT H7 BUT
BEGIN TO FALL AFTER MIDNIGHT AS THE STORM AXIS PASSES THROUGH
CENTRAL WYOMING. STILL DO NOT LIKE DENDRITIC PROFILES WHICH STAY
MAINLY UNSATURATED SOUTH OF THE WY BORDER. CROSS SECTIONS DO SHOW
MOISTURE AT MOUNTAIN LEVEL ALONG WITH INSTABILITY SO OROGRAPHICS
SHOULD BE ENOUGH TO POPS SHOWERS LATE THIS EVENING INTO WEDNESDAY
AFTERNOON. BEST FOCUS FOR NOW APPEARS TO BE FLAT TOPS TO THE PARK
RANGE FOR 2-4 AT BEST ABOVE 9500 FEET. NORTHWEST FLOW/CAA ON
WEDNESDAY MAY SUPPORT SNOW GETTING DOWN TO THE LOWER VALLEYS BUT
NOT REALLY ACCUMULATING WITH TEMPERATURES GETTING ABOVE FREEZING.
THE CHANGE IN FLOW WILL HELP THE VAIL PASS AND ELK RANGES SEE SOME
SNOW WEDNESDAY BUT AGAIN LOOKS ONLY AND INCH OR TWO. TEMPERATURES
STAY ABOVE NORMAL THE NEXT FEW DAYS AS WELL WITH POLAR JET
REMAINING WELL TO THE NORTH.

.LONG TERM...(WEDNESDAY NIGHT THROUGH MONDAY)
ISSUED AT 410 AM MST TUE JAN 27 2015

PROGRESSIVE RIDGE AXIS TRANSLATES ACROSS UTAH AND COLORADO WEDNESDAY
NIGHT AND THURSDAY...THEN THINGS GET INTERESTING. WINTER MAY RETURN
TO THE FORECAST AREA THURSDAY NIGHT THROUGH SATURDAY...ALBEIT FROM
AN UNCONVENTIONAL DIRECTION WITH THE SRN HALF BEING THE PRIMARY
TARGET AREA.

MODELS SHOW TWO DISTINCT CIRCULATIONS ASSOCIATED WITH THE STRENGTHENING
TROUGH AS IT PUSHES INTO THE INTERIOR WEST. THE NRN CIRCULATION IS
CENTERED OVER CENTRAL CALIFORNIA WEDNESDAY NIGHT AND EVOLVES INTO
A CLOSED LOW OVER NEVADA/UTAH BY THURSDAY AFTERNOON. FARTHER SOUTH
OFF THE BAJA CALIFORNIA COAST IS THE SECONDARY CIRCULATION THAT
SENDS A DEEP MOISTURE PLUME INTO ARIZONA AND NEW MEXICO. THIS
SECONDARY FEATURE BECOMES THE DOMINANT PLAYER AND EVOLVES INTO A
CLOSED LOW CIRCULATION OVER THE FOUR CORNERS BY SATURDAY MORNING.
AHEAD OF THESE FEATURES IS WARM ISENTROPIC UPGLIDE THAT RESULTS IN
A RAPIDLY EXPANDING CLOUD/PRECIPITATION SHIELD OVER MUCH OF THE
FOUR CORNER STATES. QG DIAGNOSTICS SHOW WIDESPREAD ASCENT (ALTHOUGH
NOT OVERLY IMPRESSIVE) BUT PROMINENT WHEN COMBINED WITH
ISENTROPIC UPGLIDE. MODELS SHOW SURFACE CYCLOGENESIS ACROSS THE
DESERT SOUTHWEST...WITH THE 00Z GFS MODEL SHOWING THE SURFACE LOW
REACHING DURANGO. MODEL DISCREPANCIES DO EXIST BETWEEN THE GFS AND
ECMWF...BUT THE BIGGER PICTURE AND MODEL TRENDS INDICATE THE
POTENTIAL FOR A SIGNIFICANT PRECIPITATION EVENT FOR THE SRN HALF
OF THE FORECAST AREA (WITH LIGHTER AMOUNTS ACROSS THE NRN HALF).

FORECASTING SNOW LEVELS AT THIS POINT IS CHALLENGING GIVEN THE
LOWER RESOLUTION MODELS TO EXAMINE THIS POTENTIAL EVENT. WET BULB
ZERO TEMPERATURES SUGGEST A SNOW LEVEL BETWEEN 7500 TO 8500 FEET
OVER THE SAN JUAN MOUNTAINS (MAY BE BRIEFLY AT THE VALLEY FLOORS
AT THE ONSET OF THE STORM FRIDAY MORNING). SNOW LEVELS WILL BE
DEPENDENT WHERE THE CYCLOGENETICAL SURFACE LOW FORMS AND WHERE/HOW
IT TRACKS EASTWARD. BOTTOM LINE...HEAVY SNOW THAT LEANS TOWARD THE
SIERRA CEMENT VARIETY IS POSSIBLE OVER THE SOUTHERN MOUNTAINS ON
FRIDAY AND SATURDAY.

IMPROVING CONDITIONS FROM THE NORTHWEST IS EXPECTED ON SUNDAY AS
THE TROUGH MOVES DOWNSTREAM. THIS WILL LEAD TO A DRIER MONDAY AND
TEMPS AT OR SLIGHTLY ABOVE NORMAL.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1006 AM MST TUE JAN 27 2015

VFR CONDITIONS EXPECTED TO PERSIST AT TERMINAL SITES THROUGH
MIDDAY WEDNESDAY. HOWEVER...ISOLATED TO SCATTERED SHOWERS ARE
EXPECTED TO DEVELOP OVERNIGHT...MAINLY EAST OF A LINE FROM KCAG
TO KRIL TO KGUC. EARLIER FORECAST OF SHOWERS APPROACHING THE
VICINITY OF KEGE AND KASE REMAINS ON TRACK AND TAFS WILL REFLECT
THIS POSSIBILITY LATER TONIGHT THROUGH 15Z WEDNESDAY MORNING.
MOUNTAINS WILL BE OCCASIONALLY OBSCURED AFTER 06Z THIS EVENING.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...NONE.
UT...NONE.
&&

$$

UPDATE...JDC
SHORT TERM...15
LONG TERM...PF
AVIATION...JDC


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