Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 020728
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1228 AM MST MON MAR 2 2015

.UPDATE...
ISSUED AT 1226 AM MST MON MAR 2 2015

UPDATED TO END THE ADVISORY FOR THE GUNNISON BASIN WHERE SNOW
ACCUMULATION IS EXPECTED TO BE LIMITED.

UPDATE ISSUED AT 922 PM MST SUN MAR 1 2015

SOME INTERESTING WEATHER TO START THE NEW WEEK. ONE OF THE COLDEST
SYSTEMS OF THE WINTER WILL WORK ITS WAY THROUGH THIS FORECAST AREA
MONDAY AFTERNOON THROUGH TUESDAY NIGHT.

SUNDAY EVENING THE CALIFORNIA LOW IS SHOWING SOME DUMBBELLING
ELONGATING TO THE SW WHILE A COLDER SYSTEM DROPS SOUTH THROUGH THE
PACIFIC NW. HEIGHTS ARE CLIMBING LOCALLY AND THE JET IS
STRENGTHENING.

FOR TONIGHT WARM ADVECTION WILL BRING A MILD NIGHT ACROSS THE
REGION WITH MORNING LOWS NOT A LOT DIFFERENT THAN 9PM READINGS.
DEWPOINTS HAVE RISEN TO ABOVE FREEZING FOR ALL THE SOUTHERN
VALLEYS EFFECTIVELY ELIMINATING SNOW THERE. SNOW LEVELS ARE
COMPLEX WITH BOTH TELLURIDE AT 9000FT AND MONTROSE AT 5700FT
REPORTING 33 DEGREES AND SNOW. BUT GENERALLY SNOW ACCUMULATION
LEVELS LOOK TO STAY ABOVE 8000FT SOUTH TONIGHT...RISING TO ABOUT
6000FT NORTH. THE JET STRENGTHENS TONIGHT FROM 120KT TO 150KT BY
MONDAY AFTERNOON. ALREADY THIS EVENING WINDS IN THE MOUNTAINS OF
SE UTAH AND SW CO ARE GUSTING ABOVE 50MPH OVER EXPOSED TERRAIN AND
THAT WILL INCREASE INTO MONDAY. MOUNTAIN PASS GUSTS TO 75MPH
SHOULD BE EXPECTED.

MONDAY THE SURFACE LOW WORKS INTO SE UTAH BY MIDDAY AND LIFTS INTO
NW CO IN THE AFTERNOON DEEPENING AS IT GOES. SO FRONTAL PASSAGE
STARTS MIDDAY IN SE UTAH AND THROUGH ALL OF WESTERN COLORADO SOON
AFTER DARK. 700MB WINDS OF 50KTS MAY BE MIXED DOWN INTO THE
VALLEYS AT TIMES NEAR THE FRONT. SHOWERS WILL ADD TO THAT NUMBER.

SNOW ACCUMULATIONS THROUGH MONDAY REMAIN IN THE 6-12 INCH RANGE
FOR THE MOUNTAINS...WITH THE NW CO PLATEAU PROGGED TO GET 3-6
INCHES.

COLD AIR POURS IN MONDAY NIGHT THROUGH TUESDAY NIGHT WHEN THE -36C
COLD CORE FINALLY PASSES ACROSS THE PARK RANGE IN NW CO. THIS NEW
AIR MASS IS CONSIDERABLY DRIER AND SNOW WILL BECOME MUCH LESS
DENSE.

&&

.SHORT TERM...(TONIGHT THROUGH MONDAY NIGHT)
ISSUED AT 336 PM MST SUN MAR 1 2015

H5 UPPER AIR HAND ANALYSIS AT 12Z HAD THE POSITIVELY TILTED
WESTERN LOW CENTERED OVER THE SOUTHERN SAN JOAQUIN VALLEY.
LIGHTNING BEING SEEN IN THE LOW THIS AFTERNOON BUT SO FAR NONE IN
THE SOUTHWEST. HOWEVER THE INSTABILITY IS THERE AND APPARENT ON
RADAR AND SATELLITE IMAGERY. ANOTHER IMPORTANT FEATURE IS THE
KICKER WAVE DROPPING DOWN THE WESTERN BRITISH COLUMBIA COASTLINE
THIS AFTERNOON. DERIVED GOES IMAGERY SHOWS SOME INTERESTING BLOBS
OF ANOMALOUSLY HIGH PRECIPITABLE WATER OVER NORTHERN NEW MEXICO
AND OVER CENTRAL UTAH. THIS IS WHERE PWATS ARE 180 TO 250 PERCENT
SOGGIER THAN NORMAL. FEEDING ACROSS THE CENTRAL BAJA IS THE SUB-
TROPICAL TAP...WHICH AGAIN THE 295K-300K THETA SURFACES HAVE SHOWN
BEING TRANSPORTED INTO THIS SYSTEM. AS SUCH SURFACE DEW POINTS
HAVE RISEN ABOVE THE 32 DEGREE MARK OVER MANY OF THE SOUTHERN
VALLEYS. THIS IS NOT GOOD FOR MAKING SNOW STICK IF IT MAKES IT TO
THE GROUND...WHICH LOW LEVEL PROFILES SHOW IS UNLIKELY. AS SUCH
RAIN HAS BECOME THE PREDOMINANT PTYPE AND COULD NOT JUSTIFY THE
LONG TERM WARNING. AREAS ABOVE 7500 FEET WILL REMAIN SNOW BUT FOR
THE MOST PART ACCUMULATIONS...EXCEPT AT THE HIGHEST ELEVATIONS AND
UNDER CONVECTIVE BANDS...HAS BEEN LIGHT WITH SNOW TO LIQUID RATIOS
PROBABLY PUSHING ABOVE CLIMO OF 13:1.

THE `KICKER WAVE` BEGINS TO INTERACT WITH THE WESTERN LOW AFTER
MIDNIGHT...AND EVENTUALLY REPLACES IT BY MONDAY EVENING. THIS
INTERACTION CREATES A STRENGTHENING THERMAL GRADIENT OVER OUR REGION
TONIGHT AS THE UPPER LOW BEGINS TO DEFORM...WHICH IN RESPONSE
INDUCES A MID LEVEL JET ACROSS THE FOUR CORNERS REGION. THIS JET IN
TURN WILL PUSH A LOW LEVEL WARM FRONT FEATURE INTO THE NORTHERN CWA
VALLEYS BY SUNRISE. THIS FRONT ALONG WITH STRONG UPGLIDE WILL FOCUS
THE HEAVIER PRECIPITATION OVER OUR CENTRAL AND NORTHERN
TERRAIN..WITH SNOW LIKELY RETURNING TO THE UPPER PORTION OF THE
I-70 CORRIDOR TO VAIL PASS. FARTHER SOUTH THE DENDRITIC LAYER
WILL BE DISRUPTED BY THIS JET AND THIS SHOULD PRODUCE A GENERAL
LULL WITH JUST THE OCCASIONAL PASSING SHOWER. HEAVY SNOW IN THESE
SHOWERS NOT OUT OF QUESTION BUT WHEN AND WHERE TO HARD TO
PREDICT...SO JUST A DOWNTREND IN POPS/QPF/SNOW IN PLACE FOR NOW IN
THE LOW ELEVATIONS. GENERAL MOIST SOUTHERLY FLOW SHOULD KEEP SNOW
GOING OVER THE HIGHEST TERRAIN WITH AMOUNTS IN THE 4-8 INCH RANGE
AT PASS LEVEL. HIGHER AMOUNTS UP TOP AND LOWER AT MOUNTAIN BASES.
MILD NIGHT IN STORE WITH CLOUD AND WARM FRONT LIFTING THROUGH.

MONDAY AND MONDAY NIGHT...THE TROUGH IS EXPECTED TO SHIFT EASTWARD
ACROSS THE GREAT BASIN MONDAY. A COLD FRONT DRIVEN BY THE TROUGH
WILL PUSH INTO EASTERN UTAH LATE IN THE MORNING...ACROSS WESTERN
COLORADO DURING THE AFTERNOON...THEN EAST OF THE CONTINENTAL
DIVIDE MONDAY EVENING. WARM AIR AHEAD OF THE FRONT (7H TEMPS OF -2
TO -3 DEGS IN THE MORNING AND NEAR 0 DEGS DURING THE AFTERNOON)
WILL KEEP SNOW LEVELS ELEVATED ACROSS THE SOUTH SO WILL NOT
INCLUDE HILITES FOR ELEVATIONS BELOW ROUGHLY 7000 FEET ON MONDAY.
IN CONTRAST...MOISTURE OVERRUNNING A WARM FRONT SHOULD BRING
PERSISTENT SNOWFALL TO THE LOWER ELEVATIONS OF NORTHWEST COLORADO.
MEANWHILE...DEEP MOISTURE (7H SPECIFIC HUMIDITY OF 4 TO 4.3 G/KG)
WILL CONTINUE TO GENERATE HEAVY SNOW OVER THE HIGHER ELEVATIONS
DUE TO BOTH OROGRAPHIC AND DYNAMIC LIFT. BANDS OF HEAVY SNOW ARE
LIKELY ALONG THE COLD FRONT AS IT MOVES THROUGH THE AREA. STRONG
WINDS ALOFT WILL RESULT IN AREAS OF SNOW AND BLOWING SNOW OVER THE
HIGHER TERRAIN.

WINDS SHIFT TO THE WEST WITH TROFPA MONDAY NIGHT AND SNOW LEVELS
WILL LOWER AS 7H TEMPERATURES DECREASE IN ITS WAKE. MODELS SUGGEST
A DECREASE IN SNOWFALL RATES ACROSS WESTERN COLORADO WITH A LULL
IN ACTIVITY POSSIBLE OVER EASTERN UTAH. GUIDANCE NUMBERS FOR MONDAY
AFTERNOON HIGHS CAME IN PRETTY MILD SO BOOSTED HIGHS A BIT. CLOUDS
AND WIND WILL MODERATE LOWS MONDAY NIGHT WHICH APPEARED WELL
REPRESENTED IN PREVIOUS FORECAST.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 336 PM MST SUN MAR 1 2015

A SECONDARY TROUGH ROLLS ACROSS THE REGION TUESDAY DRIVING ANOTHER
COLD FRONT...THIS ONE MUCH COLDER THAN THE FIRST...NORTH TO SOUTH
ACROSS THE AREA. 7H TEMPS AS LOW AS -20 DEG C WERE INDICATED BY
MODELS ACROSS THE NORTH BY MIDNIGHT TUESDAY. DYNAMIC AND OROGRAPHIC
LIFT COMBINED WITH STEEP LAPSE RATES WILL CAUSE SNOWFALL TO
INCREASE IN BOTH AREAL COVERAGE AND INTENSITY. CONSEQUENTLY...
APPEARS REASONABLE TO CONTINUE HILITES ACROSS WESTERN COLORADO
THROUGH TUESDAY AFTERNOON. MODELS A BIT DIVIDED ON HOW LONG SNOW
WILL CONTINUE INTO TUESDAY NIGHT ACROSS NORTHERN COLORADO SO WILL
NOT MAKE ANY CHANGES TO HILITES FOR THAT AREA AT THIS TIME. BEFORE
THIS IS ALL OVER...STILL LOOKING AT FEET OF SNOW FOR A NUMBER OF
MOUNTAIN AREAS THROUGHOUT EASTERN UTAH AND WESTERN COLORADO.

RESIDUAL MOISTURE WILL FUEL LINGERING SNOW SHOWERS ALONG THE
DIVIDE WEDNESDAY WITH SNOW FINALLY ENDING WEDNESDAY NIGHT.
THEREAFTER FOLLOWS A PERIOD OF DRY NORTHWEST FLOW WHICH SHOULD
LAST UNTIL SATURDAY AFTERNOON. EC AND GFS DIFFER WITH ENERGY
ASSOCIATED WITH A SHORTWAVE DROPPING OUT OF THE NORTHWEST SATURDAY
AFTERNOON WITH MORE AMPLIFIED EC GENERATING SNOWFALL ACROSS MUCH
OF THE NORTH AND DIVIDE MOUNTAINS FROM THROUGH SATURDAY NIGHT. THE
GFS...ON THE OTHER HAND...INDICATED A MUCH WEAKER SYSTEM PROVIDING
ONLY A GLANCING BLOW TO THE DIVIDE MOUNTAINS DURING THIS PERIOD.
BOTH INDICATED A DRY SUNDAY HOWEVER.

EXPECT UNSEASONABLY COOL TEMPERATURES TO SLOWLY MODERATE TOWARD
NEAR NORMAL LEVELS BY THE WEEKEND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1057 PM MST SUN MAR 1 2015

WIDESPREAD RAIN AND SNOW WITH THE SNOW LEVEL AROUND 6500 FEET
(EXCEPT NEAR THE VALLEY FLOOR NORTH OF I70) WILL BE STEADY THROUGH
00Z TUESDAY. MOUNTAIN TAF SITES WILL BE WELL BELOW ILS BREAKPOINTS
AND AIRFIELDS BELOW MINIMUMS WILL BE COMMON. FOR THE LOWER
VALLEYS...CIGS WILL TREND LOWER WITH VFR BECOMING MVFR. SOUTHWEST
WINDS INCREASE MONDAY AFTERNOON WITH G25KTS. MODERATE MECHANICAL
TURBULENCE WILL OCCUR.

AFTER 22Z MONDAY...THE HIGHEST SNOWFALL OR RAINFALL RATES OCCUR
DURING THIS TIME AS A STRONG COLD FRONT MOVES ACROSS WRN COLORADO.
GUST WINDS TO 25-30KTS WILL ACCOMPANY THE FRONT...LOCALIZED G40KTS
ABOVE 7000 FEET. DURING THE FRONTAL PASSAGE...ALL TAF SITE WILL
HAVE VIS BLO 3SM BR IN RAIN OR SNOW (SNOW LEVEL LOWERING TO NEAR
THE VALLEY FLOORS) WITH CIGS BELOW ILS BREAKPOINTS.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER STORM WARNING UNTIL 5 PM MST TUESDAY FOR COZ001-002-009-
     010-012-017>019.

     WINTER STORM WARNING UNTIL 9 AM MST WEDNESDAY FOR COZ003>005-013.

UT...WINTER STORM WARNING UNTIL 5 PM MST TUESDAY FOR UTZ023-025-028.

&&

$$

UPDATES...JOE
SHORT TERM...15/NL
LONG TERM...NL
AVIATION...PF



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