Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 130820
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
220 AM MDT SUN APR 13 2014

.UPDATE...
ISSUED AT 214 AM MDT SUN APR 13 2014

SNOTELS HAVE MEASURED ONLY ABOUT AN INCH OR TWO AT MOUNTAIN SITES
ALONG NORTHERN UT AND CO SINCE YESTERDAY AFTERNOON.
HOWEVER...SHOWERS ARE BECOMING MORE STEADY THIS MORNING OVER NE
UTAH AND NW CO. A WELL ORGANIZED LINE ON SLC RADAR WILL REACH
EASTERN UTAH INCLUDING VERNAL AND THE UINTAS WITHIN AN HOUR TO AN
HOUR AND A HALF. DECIDED TO ISSUE WINTER WX ADVISORY FOR ZONE 3
SINCE THEY APPEAR TO BE IN THE FIRING ZONE AND LOCATIONS ABOVE
8000 FT ARE LIKELY TO ACCUMULATE 5+ INCHES OF SNOW BY TONIGHT. THE
FRONT IS ON TRACK TO REACH THE REGION MID MORNING/LATE MORNING AND
WILL ALLOW COLD ADVECTIVE SNOW IN NORTHERLY FLOW TO CONTINUE
THROUGH THIS EVENING OVER NORTHWEST COLORADO.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 341 PM MDT SAT APR 12 2014

SRN STREAM SHORT WAVE WILL SKIRT ACROSS THE SRN PORTION OF THE
FORECAST AREA THIS EVENING BEFORE SLIDING EAST. ENOUGH
MOISTURE FOR THUNDERSTORMS BUT MOSTLY OF THE GUSTY WIND VARIETY AS
SURFACE DEW POINTS ARE BARELY IN THE 30S. GIVEN ITS EARLY SEASON
AND THE UPPER LEVEL SHORT WAVE MOVES EAST...ISOLATED EVENING
STORMS SHOULD END BY MID EVENING.

ATTENTION FOCUSES ON THE UPSTREAM POTENT WAVE OVER THE NRN
ROCKIES. LOOKS LIKE A CLASSIC SPRINGTIME SNOWSTORM FOR THE
COLORADO ROCKIES. LINGERING MOISTURE AND INSTABILITY FROM TODAYS
CONVECTION GETS LIFTED AHEAD OF THE MAIN TROUGH...KEEPING A FEW
NOCTURNAL SHOWERS ONGOING THROUGH THE NIGHT. BUT THESE SHOWERS
WILL BE EXPANDING TOWARD DAYBREAK AS LARGE SCALE ASCENT INCREASES.

TIGHT CIRCULATION FORMS OVER UTAH SUNDAY MORNING BEFORE
STRENGTHENING OVER THE WRN SLOPE IN THE AFTERNOON...THEN MOVES
DOWNSTREAM LATE IN THE SHORT TERM PERIOD.  INTENSE THERMAL
GRADIENT OVER WYOMING DROPS INTO NW COLORADO AS THE MID LEVEL
CIRCULATION TIGHTENS. NICE COUPLET ON THE QG DIAGNOSTICS THAT
INDICATE A WELL STRUCTURED. DEEP LAYERED ASCENT COINCIDES WITH
POTENTIAL INSTABILITY DUE TO STRONG MID LEVEL COLD ADVECTION.
WHILE SNOW LEVELS WILL BE HIGH IN THE EARLY STAGES OF THIS
EVENT...700 MB TEMPS BECOME COLDER THAN -10C ALONG THE DIVIDE.
THIS IS COLD ENOUGH FOR SIGNIFICANT ACCUMULATIONS IN THE HIGH
COUNTRY...AND IT WILL FALL FAST AND FURIOUS AND POSSIBLE HIGH
IMPACTS TO TRAVEL OVER MOUNTAIN PASSES DUE TO WET HEAVY SLUSH.
ELECTED TO UPGRADE THE WINTER WEATHER ADVISORY TO WARNINGS (EXCEPT
FOR THE SWRN SAN JUANS THAT HAVE AN UNFAVORABLE OROGRAPHIC
COMPONENT.)

QPF FORECAST IS CHALLENGING GIVEN THE STRONG CONVECTIVE COMPONENT.
USED THE WPC QPF GUIDANCE AS MY BASE FORECAST...BUT BLENDED WITH
THE HIGHER RESOLUTION WRF MODELS TO PICK UP THE FINER DETAILS.
THIS WILL NOT BE CLOSE TO PERFECT AS CONVECTIVE SPRING SNOWSTORMS
PICK THEIR OWN BULLSEYE. WITH THE MID LEVEL CIRCULATION TRACKING
DIRECTLY OVERHEAD...SNOWFALL AMOUNTS WILL BE GENEROUS WITH
LOCALIZED HEAVY AMOUNTS.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 341 PM MDT SAT APR 12 2014

THE WEATHER PATTERN DURING THE UPCOMING WEEK LOOKS TO BE A BIT MORE
PROGRESSIVE AS THE AMPLIFIED WESTERN RIDGE WILL NOT HAVE A CHANCE TO
RE-ESTABLISH ITSELF. THIS WILL BRING A MORE SEASONABLE REGIME BACK
TO THE REGION AND TEMPERATURES WILL GENERALLY HOVER NEAR NORMAL.
THERE WILL BE SOME FLUCTUATIONS IN TEMPERATURES EITHER WAY AS A MORE
DEFINED SYSTEM WORKS THROUGH MID-WEEK...BUT OTHERWISE DRY
CONDITIONS LOOK ON TAP.

FOR MONDAY THIS SPRING STORM WILL BE MOVING QUICKLY OUT BY SUNRISE
WITH CLEARING EXPECTED THROUGH THE DAY. COOL AIR LEFT BEHIND THE
PASSAGE OF THE COLD FRONT WILL BE DROPPING TEMPERATURES 20 TO 25
LOWER THAN TODAY/S ABOVE NORMAL READINGS. A FLATTENING...TRANSITORY
RIDGE WORKS ACROSS THE ROCKIES MONDAY NIGHT AND TUESDAY BEING PUSHED
EAST BY THE NEXT PACIFIC NORTHWEST TROUGH. MODEL DIVERGENCE STILL IN
PLACE IN THE HANDLING OF THIS TROUGH AS IT DROPS ACROSS THE CENTRAL
ROCKIES ON WEDNESDAY. THE GFS A BIT MORE BULLISH AND VERY SIMILAR TO
THIS SYSTEM BY TAKING A CLOSED CIRCULATION ACROSS OUR NORTHERN
MOUNTAINS. THE EURO IS MORE OPEN AND THEREFORE PROGRESSIVE WITH THIS
WAVE...FOCUSING MORE OF THE PRECIPITATION EAST OF THE ROCKIES WHERE
ANOTHER SHOT OF COLD AIR WILL BE HEADING. SOME OF THE ENSEMBLES ARE
LEANING TOWARD THE GFS SOLUTION...BUT POPS WILL REMAIN ON THE LOW
SIDE FOR NOW UNTIL SOME BETTER CONSENSUS DEVELOPS WITH THE
OPERATIONAL MODELS. BEHIND THIS WAVE A RATHER FLAT PATTERN SETS UP
WITH LOW PRESSURE TRACKING ALONG THE SOUTHWEST CONUS BORDER.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1017 PM MDT SAT APR 12 2014

SHOWERS HAVE BECOME FOCUSED NORTH OF THE I-70 CORRIDOR AS THE
STRONGER PART OF THIS WEATHER SYSTEM APPROACHES FROM THE
NORTHWEST. A COLD FRONT ASSOCIATED WITH THIS SYSTEM IS EXPECTED TO
REACH THE NORTHERN CO/UT BORDER AROUND 12Z...THEN ON TO THE I-70
CORRIDOR AROUND 18Z...AND FINALLY INTO THE FOUR CORNERS REGION BY
00Z/SUNDAY EVENING.

IN THE WAKE OF THE FRONT THE SNOW LEVEL WILL DROP TO MOUNTAIN
BASES RESULTING IN WIDESPREAD OBSCURATION OF THE HIGHER TERRAIN.
THE NORTHWEST AND CENTRAL COLORADO VALLEY AIRPORTS ARE LIKELY TO
EXPERIENCE PERIODS OF MVFR CIGS AND VSBY IN SNOW FROM 15Z ONWARD
AS THE COLDER AIR CONTINUES TO FILTER ACROSS THE AREA.

CLEARING WILL BEGIN OVER EASTERN UTAH AND NW COLORADO BETWEEN 03Z
AND 06Z SUNDAY NIGHT.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER WEATHER ADVISORY FROM 6 AM THIS MORNING TO 3 AM MDT
     MONDAY FOR COZ019.

     WINTER STORM WARNING FROM 6 AM THIS MORNING TO 6 AM MDT MONDAY
     FOR COZ012-018.

     WINTER STORM WARNING UNTIL 3 AM MDT MONDAY FOR COZ004-009-010-
     013.

     WINTER WEATHER ADVISORY UNTIL 9 PM MDT THIS EVENING FOR COZ003.

UT...WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING FOR UTZ023.

&&

$$

UPDATE...JAM
SHORT TERM...PF
LONG TERM...15
AVIATION...TGJT



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