Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 301708
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1108 AM MDT THU APR 30 2015

.SHORT TERM...(TODAY THROUGH FRIDAY)
ISSUED AT 357 AM MDT THU APR 30 2015

UPPER PATTERN NOT MUCH DIFFERENT THAN 24 HOURS AGO OTHER THAN THE
FEATURES HAVE SHIFTED EASTWARD. THE WEST COAST SYSTEM HAS MOVED ON
SHORE AND THE AMPLIFIED RIDGE IS HOLDING STRONG FROM THE DESERT
SOUTHWEST TO THE NORTHERN PLAINS AND CANADIAN PRAIRIES. WATER VAPOR
IS SHOWING TWO SHEAR ZONES TO OUR WEST...A STRONGER MORE DEFINED
ONE ASSOCIATED WITH THE MAIN TROUGH AND AND A WEAKER ONE
EXTENDING FROM CENTRAL NEVADA TO EASTERN MONTANA. IT IS THIS
WEAKER AREA OF CHANNELIZED VORTICITY THAT WILL BE STRETCHED ACROSS
OUR NORTHERN CWA LATE THIS AFTERNOON. A DEFINED COLD FRONT IS
MOVING AHEAD OF THE TROUGH EARLY THIS MORNING...BUT AS HEATING OF
THE DAY TAKES SHAPE AND THIS FRONT MOVES FARTHER INTO THE
RIDGE...IT WILL WEAKEN. MODELS SHOW IT LIMPING INTO OUR NORTHWEST
ZONES BY MID AFTERNOON AND SETTLING ALONG THE HIGH PLATEAUS BY
LATE AFTERNOON. THE MAIN FORCING FOR LARGE SCALE ASCENT STAYS
ACROSS THE NORTHERN ROCKIES TODAY WHERE THE MAIN ENERGY IN THE
TROUGH WILL BE SWINGING THROUGH. THIS WILL FORCE MOISTURE DOWN
INTO OUR REGION WHERE HEATING OF THE DAY WILL INCREASE MID LEVEL
DELTA T. THIS INSTABILITY AGAIN WILL BE MAINLY RELEASED FROM
OROGRAPHIC LIFT AND HIGHEST POPS WILL BE ON THE WITH SLIGHTLY
BETTER FOCUS NEAR AND BEHIND THE COLD FRONT TO THE NORTH. THIS
HANDLED WELL IN GRIDS AND ONLY SMALL TWEAKS TO GOING FORECAST.
MOISTURE REMAINS STUCK OVER OUR CWA THROUGH THE END OF THE WEEK.
FORCING REMAINS WEAK AND UNORGANIZED SO AGAIN EXPECT CONVECTION TO
FIRE MAINLY ON THE TERRAIN FRIDAY. THE FRONT WILL HAVE LITTLE
IMPACT ON TEMPERATURES AND WE CAN EXPECT ANOTHER DAY WITH
TEMPERATURES NEAR 10 DEGREES ABOVE NORMAL ON FRIDAY.

$$

.LONG TERM...(FRIDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 357 AM MDT THU APR 30 2015

WEAK SHORT WAVE ENERGY...CURRENTLY ALONG THE SRN CALIFORNIA AND
BAJA COAST...WILL BE TRACKING ACROSS THE DESERT SOUTHWEST ON
SATURDAY. THIS WAVE REACHES THE COLORADO ROCKIES BY SUNDAY
MORNING. GIVEN THE DIFLUENT CHARACTER OF THIS TROUGH...DYNAMICAL
FORCING IS NONEXISTANT...BUT ELEVATED MOISTURE WILL FUEL DIURNAL
AND TERRAIN DRIVEN CONVECTIVE SHOWERS (AND GUSTY WINDS DUE TO THE
DRIER BOUNDARY LAYER ENVIRONMENT) THIS WEEKEND. STEERING FLOW IS
SUFFICIENT THAT A FEW OF THESE SHOWERS WILL TRACK OVER THE WRN
COLORADO VALLEYS...ALTHOUGH NOT MUCH RAINFALL IS EXPECTED.

A MORE PROMINENT CLOSED LOW CIRCULATION IS EXPECTED TO TRACK
ACROSS NRN BAJA INTO ARIZONA ON MONDAY...THEN LIFT NORTHEAST INTO
COLORADO ON TUESDAY. SIMILAR CONDITIONS WOULD EXIST ON MONDAY...BUT
AN EXPANSION OF SHOWERS WITH A FEW MORE THUNDERSTORMS WOULD BE
EXPECTED ON TUESDAY. WITH THE INCREASED CLOUD COVER...TEMPS SHOULD
FALL A FEW DEGREES. THERE IS SOME MODEL SPREAD BY NEXT TUESDAY
WHICH LOWERS THE CONFIDENCE LEVEL TO AVERAGE...BUT THE TREND IS
FOR AN INCREASE OF UNSETTLED WEATHER NEXT WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1105 AM MDT THU APR 30 2015

VFR CONDITIONS ARE EXPECTED AT ALL TAF SITES THE NEXT 24 HOURS.
A SLIGHT INCREASE IN HIGHER LEVEL MOISTURE WILL ALLOW A FEW
MORE HIGH-BASED SHOWERS AND THUNDERSTORMS TO FORM AFTER 21Z THIS
AFTERNOON AND CONTINUE UNTIL 02Z. EXPECT LOCALLY GUSTY WINDS
NEAR THESE SHOWERS. A WEAK COLD FRONT WILL MOVE GRADUALLY
THROUGH THE AREA FROM NORTHWEST TO SOUTHEAST LATE THIS AFTERNOON
AND TONIGHT. NOT SIGNIFICANT IMPACT ON FLIGHT CONDITIONS IS
EXPECTED THROUGH FRIDAY MORNING.

&&

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

$$

SHORT TERM...15
LONG TERM...PF
AVIATION...CC


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