Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 170331
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
931 PM MDT SAT MAY 16 2015

.UPDATE...
ISSUED AT 931 PM MDT SAT MAY 16 2015

UPDATED THE FORECAST TO INCREASE PRECIPITATION ACROSS NORTHWEST
COLORADO DUE TO UPPER LEVEL SHORTWAVE ROTATING THROUGH THE BASE
OF THE TROUGH AS 00Z MODELS ARE CONSISTENT IN SHOWING THIS WITH
THE VALLEYS SEEING RAIN AND MOUNTAINS DOWN TO THE GRAND MESA AND
WEST ELKS AND ELKS SHOWING A PERIOD OF MODERATE TO HEAVY WET
SNOWFALL PICKING UP AFTER MIDNIGHT THROUGH ABOUT 6 AM.

UPDATE ISSUED AT 558 PM MDT SAT MAY 16 2015

LATEST SATELLITE IMAGERY AND RADAR SHOWS CONVECTIVE DEVELOPMENT
JUST WEST AND ALONG THE GREEN RIVER IN EASTERN UTAH ON THE LEADING
EDGE OF A SHORTWAVE ROTATING DOWN THE BACKSIDE OF THE UPPER LEVEL
LOW. THIS LINE OF CONVECTIVE ACTIVITY EXTENDS FROM SOUTH OF VERNAL
THROUGH MOAB AND CANYONLANDS NP SOUTH TOWARDS LAKE POWELL. THE RAP
MODEL IS PICKING UP ON THIS ACTIVITY VERY WELL AND HAS THIS
ACTIVITY PROGRESSING EASTWARD THROUGH THE GRAND VALLEY AROUND
02Z/8PM MDT AND THROUGH MONTROSE AND DURANGO BY 06Z/MIDNIGHT.
BOOSTED POPS TO REFLECT THIS. WILL TAKE A CLOSER LOOK AT THE
OVERNIGHT HOURS AS SOME SHORT TERM MODELS INDICATE AREAS NORTH OF
I-70 PICKING UP MORE SHOWERS AS THE SHORTWAVE ON THE BACKSIDE OF
THE LOW MOVES THROUGH. MAY NEED TO INCREASE POPS IN THE NORTHERN
VALLEYS. REMAINING HIGHLIGHTS ALSO REMAIN ON TRACK AND WILL LET
THE SAN JUANS EXPIRE AT 6 PM.

&&

.SHORT TERM...(TONIGHT THROUGH SUNDAY NIGHT)
ISSUED AT 243 PM MDT SAT MAY 16 2015

AS THE SOUTH CENTRAL COLORADO SHORT WAVE DEPARTS EAST LATE THIS
AFTERNOON...THE NEXT ONE OVER ERN IDAHO/NRN UTAH DROPS INTO THE
WESTERN SLOPE TONIGHT. UPSTREAM SHORT WAVE DOES NOT GENERATE
DYNAMICAL QG LIFT...BUT STILL WILL HAVE FAVORABLE OROGRAPHICS IN A
MOIST LOW STATIC STABILITY ENVIRONMENT. MID LEVEL COLD ADVECTION
IS WEAK...BUT DOES EXIST FOR A FEW HOURS FOR ACCUMULATING SNOWFALL
OVER THE MOUNTAIN PASSES. HIGH RESOLUTION MODELS SUGGEST THAT 2-4
INCHES MAY STILL FALL OVER THE PARK/GORE RANGES...AND POSSIBLY AS
FAR SOUTH AS THE ELK/WEST ELK RANGES.

THE SAN JUAN MOUNTAINS WILL BE ON THE SRN FRINGE OF THIS SHORT
WAVE...AND THE NWRN SAN JUANS MAY GET 1-2 INCHES FROM THIS
FEATURE. DID NOT FEEL THIS JUSTIFIES THE WINTER STORM WARNING
THROUGH EARLY SUNDAY MORNING...SO SHORTENED THE TIMING THROUGH
6 PM THIS EVENING (TO MATCH WITH WFO PUB). OBSERVATIONS AND WEB
CAMS SHOW ONGOING SNOW SHOWERS OVER THE SRN MOUNTAINS WITH WET
MOUNTAIN HIGHWAYS.

A DEFINITE DRYING TREND WILL BE SEEN ACROSS THE CWA ON
SUNDAY AS THIS STORM EXITS AND A TRANSITORY RIDGE BUILDS IN FROM THE
SOUTHWEST. A BIT OF LINGERING MOISTURE ON THE BACK SIDE OF THE
SYSTEM WILL KEEP SOME SHOWER ACTIVITY OVER THE NORTHERN
MOUNTAINS...THOUGH THIS SHOULD BE MAINLY ISOLATED IN
NATURE...SUNSHINE SHOULD BE PLENTIFUL IN THE SOUTHERN VALLEYS. THE
RIDGE AXIS SHIFTS ACROSS OUR CWA SUNDAY NIGHT. ELEVATED INSTABILITY
WILL EXIST ON THE NOSE OF THE DEVELOPING WARM AIR ADVECTION PATTERN
AND THIS COULD LEAD TO SOME ISOLATED SHOWERS OR THUNDERSTORMS
DURING THE EARLY MORNING HOURS. HOWEVER MOISTURE IS QUITE LIMITED
AND THIS WILL MOST LIKELY STAY IN THE FORM OF PASSING MID LEVEL
ACCAS. TEMPERATURES WILL BEGIN TO REBOUND AS WELL WITH HIGHS ON
SUNDAY WARMING SOME 7 TO 10 DEGREES...BUT STILL BELOW SEASONAL
NORMALS.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 243 PM MDT SAT MAY 16 2015

STRONG BLOCKING IN THE CENTRAL ATLANTIC AND A REX PRODUCING RIDGE
OVER WESTERN CANADA PROMISES TO KEEP THE PACIFIC STORM TRACK AIMED
AT OUR REGION. THE NEXT STORM DIVING DOWN THE LEFT COAST OF NOAM
SWINGS INLAND NEAR SAN FRAN BAY BY EARLY MONDAY. THE SOUTHERLY
GRADIENT AHEAD OF THIS SYSTEM TIGHTENS OVER EASTERN UTAH THROUGH
THE DAY AS THE LOW SHIFTS FARTHER INLAND. CAPPING OVERHEAD SHOULD
KEEP MUCH OF THE THUNDERSTORM ACTIVITY IN CHECK UNTIL THE
AFTERNOON AND BACKED OFF THE EARLY DAY POPS. 310K THETA SURFACES
SHOW SOME MOISTURE BEING DRAWN NORTHWARD FROM THE PACIFIC SYSTEM.
THE NOSE OF THE UPPER JET WILL BE CURVING INTO THE 4 CORNER IN THE
AFTERNOON AND THE LIFT PRODUCED WILL BE SUFFICIENT ENOUGH TO
INITIATE SCATTERED CONVECTION ACROSS OUR CWA. IN THE WEST...STORM
MOVEMENT AND INVERTED V PROFILES SUGGEST SOME OF THE STORMS WILL
BE CAPABLE OF STRONG OUTFLOW WINDS...COMPARABLE TO THE PREVIOUS
SYSTEM. THE MODELS ARE THEN INDICATING BETTER MOISTURE ADVECTION
ARRIVING ON THE WARM CONVEYOR BELT...ORIGINATING FROM THE GULF OF
MEXICO. THE ENSEMBLE ANOMALY PAGE HINTS AT THIS AS WELL WITH
WETTER THAN NORMAL PWAT ARCING FROM THE NEW MEXICO PLAINS INTO
SOUTHWEST COLORADO BY EARLY TUESDAY. COMBINING THIS MOISTURE WITH
MASSIVE ASCENT FORMED BY THE EXIT REGION OF THE JET MAX AND THE
ENERGY FROM THE TROUGH WILL BRING ANOTHER VERY WET DAY. THE
COLDEST PART OF THIS SYSTEM WILL NOT MOVE OVER OUR CWA UNTIL IT
HAS MODIFIED BUT SNOW LEVELS STILL LOOK TO DROP TO NEAR PASS
LEVEL MONDAY NIGHT AND TUESDAY AND MORE WINTER HEADLINES NOT OUT
OF THE QUESTION. WILL ALSO HAVE TO MONITOR HYDROLOGY ASPECTS OF
THIS STORM AS IT STRENGTHENS ACROSS THE SOUTHERN CWA TUESDAY
MORNING...WITH THE HIGH PWAT...RUNOFF AND POSSIBLY RAIN ON SOME OF
THE NEW SNOWPACK. TEMPERATURES TAKE A HIT BACK TO 10 TO 15 DEGREES
BELOW NORMAL ON TUESDAY UNDER THIS PRECIPITATION EVENT. THE LOW
LIFTS NORTHWARD THROUGH THE DAY AND FORCES THE MAIN PRECIPITATION
SHIELD INTO OUR NORTHERN ZONES IN THE AFTERNOON AND EVENING.
SOUTHWEST FLOW THEN DOMINATES THE PATTERN FOR THE REMAINDER OF
THE WEEK WITH A DRIER AND WARMER OUTCOME EXPECTED. THERE WILL BE
POCKETS OF ENERGY AND MOISTURE LIFTING THROUGH PRODUCING AFTERNOON
CONVECTION...BUT NOT AS WIDESPREAD AS THE PAST FEW STORMS. THE
NEXT PACIFIC STORM ARRIVES ALONG THE COAST BY LATE IN THE WEEK
AND WE APPEAR TO BE HEADING TO A SIMILAR SOLUTION THE PAST SEVERAL
STORMS WITH ANOTHER WET WEEKEND POSSIBLE.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 601 PM MDT SAT MAY 16 2015

SHOWERS AND ISOLATED THUNDERSTORMS WILL CONTINUE TO MOVE THROUGH
THE REGION OVER THE NEXT 24 HOURS. KTEX WILL CONTINUE TO SEE
PERIODS OF LIFR AND IFR CIGS/VSBYS AS SNOW SHOWERS MOVE THROUGH.
OTHERWISE...VFR CONDS EXPECTED TO HOLD AT THE REMAINING TERMINAL
SITES...WITH BRIEF PERIOD OF MVFR TO IFR CIGS/VSBYS AS SHOWERS
MOVE THROUGH. THE SHOWERS WILL BE DIMINISHING AFTER 00Z SUNDAY
EVENING.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER WEATHER ADVISORY UNTIL 9 AM MDT SUNDAY FOR COZ004-009-010-
     012-013.

UT...NONE.
&&

$$

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



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