Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 200513
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1113 PM MDT SUN APR 19 2015

.UPDATE...
ISSUED AT 807 PM MDT SUN APR 19 2015

PAIR OF WAVES SHOWING UP NICELY IN THE 1.5 PVU PLOTS THIS EVENING.
ONE HAS BEEN MARCHING OUT OF UTAH INTO COLORADO THIS EVENING AND
SPREADING SHOWERS AND A FEW THUNDERSTORMS ACROSS THE PLATEAUS AND
ADJACENT VALLEYS. HAVE BEEN UPDATING THE FORECAST IN OUR WESTERN
CWA AS IT PLUGS ALONG. EXPECT A DOWNTURN IN COVERAGE NOW THAT
SUNSET HAS ARRIVED BUT HAVE EXTENDED POPS TO THE SOUTH THOUGH THE
EARLY MORNING HOURS FOR SOME LIGHT PRECIPITATION DRIVEN BY THE
PASSING WAVE. THE SECOND WAVE IS DROPPING ACROSS SOUTHERN WYOMING
AND WILL BE IMPACTING OUR NORTHEAST ZONES FROM ABOUT 04Z ONWARD.
THIS IS FAIRLY QUICK MOVING SYSTEM AND ALSO COMPACT. DO NOT
ANTICIPATE MUCH PROBLEM WITH THIS BUT WILL CONTINUE TO WATCH
UPSTREAM TRENDS THE NEXT FEW HOURS.

&&

.SHORT TERM...(TONIGHT THROUGH MONDAY NIGHT)
ISSUED AT 227 PM MDT SUN APR 19 2015

MODELS CONTINUE TO DEPICT IMPULSES OF ENERGY MOVING OVER THE CWA
THROUGH THE SHORT TERM PERIOD. THIS IS BEING BORNE OUT WITH OBS
SHOWING SOME LIGHT PRECIP ACROSS THE AREA WHILE THE RADAR MOSAIC
SHOWS SOME CONVECTIVE DEVELOPMENT UNDER THE IMPULSES. BUMPED UP
POPS TO ACCOUNT FOR THIS AND ALSO EXPANDED STORM COVERAGE. NO
LIGHTNING STRIKES YET BUT STEEP LAPSE RATES...CAPE...AND AVAILABLE
MOISTURE MAY LEND THEMSELVES YET TO SOME THUNDER. NAM12 AND GFS
KEEP PRECIP IN THE PICTURE PICKING UP AFTER MIDNIGHT. HARD TO SEE
IF ONE IMPULSE OR TWO...LEANING TOWARDS TWO IMPULSES BUT IF
SO...THERE`S HARDLY A BREAK BETWEEN THEM. WHETHER IT`S ONE OR TWO
THE END RESULT IS THE SAME...SPOTTY SHOWERS WITH POSSIBLE THUNDER
THIS AFTN/EVENING BECOMING MORE ISOLD/SCTD IN NATURE OVERNIGHT.

A PERTURBED NORTHWEST FLOW WILL CONTINUE OVER THE AREA THROUGH
MONDAY NIGHT...BETWEEN HIGH PRESSURE OVER THE WEST COAST AND LOW
PRESSURE ACROSS THE EASTERN HALF OF THE CONUS. LINGERING MOISTURE
AND WARMER DAYTIME TEMPERATURES WILL ALLOW SOME AFTERNOON
CONVECTION CONFINED MAINLY TO THE HIGHER TERRAIN. MOISTURE AND
GENERALLY WEAK NORTHWEST OROGRAPHICS WILL FAVOR THE NORTH...SO
EXPECT BETTER COVERAGE FROM THE MOUNTAINS NEAR ASPEN AND
NORTHWARD. THE FLOW WEAKENS OVERNIGHT AND HIGH PRESSURE SHIFTS
OVER THE AREA. THE WARMING TREND WILL CONTINUE.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 227 PM MDT SUN APR 19 2015

THE BIG PICTURE ACROSS NORTH AMERICA WILL BE DOMINATED BY STRONG LOW
PRESSURE OVER THE GREAT LAKES TO QUEBEC...AND A LESS STABLE MEAN
TROUGH ALONG THE WEST COAST. FOR US AN UNSETTLED SPRING PATTERN WILL
PERSIST THROUGH NEXT WEEKEND. PACIFIC MOISTURE AND A SERIES OF
DISTURBANCES ORIGINATING FROM THE WESTERN TROUGH WILL MOVE ACROSS
THE REGION. FOR NOW THE DETAILS REMAIN ELUSIVE. HOWEVER MODELS
AGREE THAT A SPLIT PATTERN WILL PERSIST ALONG THE PACIFIC
COAST...WITH A COUPLE OF SOUTHERN LOWS SET TO IMPACT THE DESERT
SOUTHWEST TO THE SOUTH AND CENTRAL ROCKIES.

IT APPEARS THAT THE FIRST AND WEAKER OF THE TWO LOWS WILL BEGIN TO
LIFT OUT TUE. A SECOND TROUGH DEVELOPS ALONG THE WEST COAST AND
CLOSES OFF A LOW WEST OF THE SO CA/NO BAJA COAST BY WED. AHEAD OF
THE FIRST LOW...MOISTURE WILL CONTINUE TO STREAM INTO OUR
AREA...WHICH WILL BE DOMINATED BY A SOUTHEAST TO NORTHWEST LEANING
RIDGE OF HIGH PRESSURE. IN SPITE OF THE RIDGE OVERHEAD...SOME
DIURNAL SHOWERS WILL BE POSSIBLE AS THE REMNANTS OF THE FIRST LOW
PROVIDES A LITTLE ENERGY AS IT MOVES INTO THE SOUTHERN GREAT
BASIN.

THE STRONGER LOW THEN MOVES INLAND AND OPENS UP PUMPING MOISTURE
INTO THE REGION. MODELS STILL SHOW DIFFERENCES IN ITS HANDLING
AND TIMING. BUT IT SEEMS THIS STORM SYSTEM HAS A THE POTENTIAL TO
BRING WIDESPREAD PRECIPITATION TO OUR FORECAST AREA. FOR NOW IT
APPEARS THAT THE BEST CHANCE OF PRECIPITATION WILL BE LATE THU AND
FRI. SNOW LEVELS WILL BE VERY HIGH AS MODELS KEEP 700MB TEMPS
MOSTLY ABOVE ZERO C DEGREES INTO SAT.

WITH LESS CONFIDENCE THE ECMWF SHOWS ANOTHER PACIFIC TROUGH MOVING
ACROSS THE PACIFIC NORTHWEST AND INTO OUR REGION SAT AND SUN.
HOWEVER THE 12Z SOLUTION IS MUCH FARTHER NORTH AS COMPARED TO THE
PREVIOUS RUN...AND KEEPS THE BEST ACTION WELL TO OUR NORTH. THE
LATER RUN IS ALSO A LITTLE FASTER. ON THE FLIP SIDE THE GFS SHOWS
RIDGING.


&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1104 PM MDT SUN APR 19 2015

A DISTURBANCE CONTINUES TO MOVE SOUTHEAST ACROSS THE FORECAST AREA
OVERNIGHT. EXPECT SNOW SHOWERS OVER THE HIGHER TERRAIN WITH RAIN
SHOWERS OVER THE LOWER ELEVATIONS. AREAS OF MOUNTAIN OBSCURATION WITH
SNOW AND RAIN SHOWERS WILL RESULT IN MVFR CIGS AND VSBY...WITH
BRIEF IFR CONDITIONS IN THE HEAVIER SNOW SHOWERS. THE MOST
IMPACTED TAF SITES WILL ASPEN AND EAGLE WHERE SHOWER ACTIVITY IS
MOST LIKELY. SHOWER ACTIVITY WILL DIMINISH BY 1300 UTC. ISOLATED
TO SCATTERED SHOWERS WILL REDEVELOP BY MONDAY AFTERNOON MAINLY
OVER THE HIGHER TERRAIN RESULTING IN MVFR CONDITIONS. VFR
CONDITIONS ARE EXPECTED AT ALL TAF SITES.

&&

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

$$

UPDATE...15
SHORT TERM...TGR/EH
LONG TERM...EH
AVIATION...MPM



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