Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 021034
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
434 AM MDT WED SEP 2 2015

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 434 AM MDT WED SEP 2 2015

A WEAK DISTURBANCE WILL REACH THE FOUR CORNERS EARLY THIS
AFTERNOON ENHANCING SHOWER AND THUNDERSTORM ACTIVITY NEAR THE
FOUR CORNERS TODAY. WITH THE H5 VORT MAX PUSHING NORTH INTO SE
UTAH AND SW COLORADO LATE IN THE DAY AND NEAR 1 INCH PRECIPITABLE
WATER...ISOLATED SHOWERS ARE BOUND TO CONTINUE THROUGH THE
OVERNIGHT HOURS DESPITE THE LACK OF JET SUPPORT ALOFT. PULSES OF
ENERGY WILL CONTINUE AS A STREAM OF MOISTURE CONTINUES TO FILTER
INTO THE FOUR CORNERS FROM THE SOUTH THROUGH THURSDAY.

AN UPPER LEVEL TROUGH WILL PLUNGE INTO THE PACIFIC NW ON THURSDAY
...STRENGTHENING THE PRESSURE GRADIENT BETWEEN THIS TROUGH AND THE
EXISTING HIGH PRESSURE OVER THE CENTRAL US. WINDS WILL INCREASE
FROM THE SOUTHWEST ON THURSDAY ACROSS NE UTAH AND NW COLORADO DUE
TO THE CLASH IN AIRMASSES.

.LONG TERM...(THURSDAY NIGHT THROUGH TUESDAY)
ISSUED AT 434 AM MDT WED SEP 2 2015

PERSISTENT SOUTHWEST FLOW CONTINUES INTO THE THURSDAY NIGHT AS THE
REGION REMAINS SANDWICHED BETWEEN THE TROUGH OVER THE PACIFIC
NORTHWEST AND HIGH PRESSURE OVER TEXAS. LATEST MODELS INDICATED A
90 KT SUBTROPICAL JET STREAK WILL PUSH INTO THE FOUR CORNERS LATE
THURSDAY NIGHT REIGNITING SHOWER ACTIVITY ACROSS THE SOUTH WITH
THE SAN JUANS FAVORED.

PER PREVIOUS DISCUSSIONS...SOME OF THE MOISTURE ORIGINATING FROM
TROPICAL DEPRESSION FOURTEEN-E WILL SWEEP OVER THE FORECAST AREA
ON FRIDAY. THIS WILL DRIVE PRECIPITABLE WATER VALUES TO BETWEEN 1
INCH OVER THE FOUR CORNERS...TO AROUND 0.80 OF AN INCH ACROSS THE
NORTH. DAYTIME HEATING COMBINED WITH DIVERGENCE ASSOCIATED WITH
THE SUBTROPICAL JET WILL GENERATE INCREASED SHOWERS AND
THUNDERSTORMS WITH HEAVY RAIN BECOMING MORE PREVALENT. MODELS WERE
CONSISTENT IN KEEPING THE NORTHWEST QUADRANT OF THE FORECAST AREA
WEST OF THE MOISTURE PLUME SO THUNDERSTORMS WILL BE SCARCE.

THE ECMWF HAS COME AROUND TO THE GFS SOLUTION FOR SATURDAY WHICH
WAS DRIER...RELATIVELY SPEAKING...THAN FRIDAY. MODELS ROTATE A
SHORTWAVE TROUGH THROUGH THE BASE OF THE MEAN PACIFIC TROUGH
CAUSING THE MOISTURE PLUME A BIT TO THE EAST. PW VALUES FALL AS A
RESULT SO...WITH LESS FUEL AVAILABLE...STORM COVERAGE WILL BE
REDUCED. THE DRYING TREND CONTINUES SUNDAY AS THE SHORTWAVE
PUSHES OFF TO THE NORTHERN PLAINS AND FLOW BECOMES MORE ZONAL
DRAWING FROM ARID AIR OVER THE WEST. DRIER CONDITIONS PERSIST INTO
MONDAY...THOUGH MONSOON MOISTURE BEGINS TO AMASS SOUTH OF THE
FORECAST AREA. BOTH MODELS INDICATED A SECOND TROUGH PASSAGE
MONDAY NIGHT INTO TUESDAY. ACCORDING TO THE EC...THIS WILL KEEP
MONSOON MOISTURE SOUTH OF THE FORECAST AREA. IN CONTRAST...THE
SHORTWAVE DEPICTED BY THE GFS WAS SHALLOWER IN DEPTH WHICH FAILS
TO KEEP MOISTURE AT BAY. THIS SOLUTION ALLOWS FOR SOME MOISTURE
RETURN INTO THE SAN JUANS TO FUEL AFTERNOON SHOWERS AND
THUNDERSTORMS.

PER PREVIOUS DISCUSSIONS...TEMPERATURES WILL BE SUBDUED BY CLOUDS
AND SHOWERS THROUGH SATURDAY AND WILL GENERALLY FALL SEVERAL
DEGREES BELOW NORMAL DURING THIS PERIOD. A COLD FRONT PUSHES
ACROSS THE NORTH SUNDAY WHICH WILL DRIVE TEMPERATURES DOWN A FEW
MORE DEGREES FOR LOCATIONS NORTH OF THE I-70 CORRIDOR. HOWEVER...
TEMPERATURES SHOULD REBOUND TO NEAR NORMAL LEVELS EARLY NEXT WEEK
IN RESPONSE TO INCREASED SUNSHINE.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 434 AM MDT WED SEP 2 2015

VFR CONDITIONS WILL PERSIST THROUGH 18Z. DAYTIME HEATING WORKING
ON LINGERING MOISTURE ACROSS THE AREA WILL GENERATE SCATTERED
THUNDERSTORMS OVER THE MOUNTAINS FROM 18Z THROUGH 03Z/THU. THERE
IS A SLIGHT CHANCE OF THUNDERSTORMS MOVING OVER AIRPORTS FROM
LATE AFTERNOON INTO THE EARLY EVENING. ITS UNLIKELY THAT CIGS WILL
DROP BELOW ILS BREAKPOINTS...HOWEVER...GUSTY OUTFLOW WINDS TO 30
TO 35 MPH ARE POSSIBLE. SHOWERS AND THUNDERSTORMS WILL DECREASE
AFTER 03Z...BUY MAY LINGER OVER THE SOUTHERN MOUNTAINS PAST
MIDNIGHT. AFTER 09Z...A DISTURBANCE APPROACHING FROM THE SOUTH IS
EXPECTED TO GENERATE ADDITIONAL SHOWER ACTIVITY ACROSS THE FOUR
CORNERS REGION. A FEW EMBEDDED THUNDERSTORMS ARE POSSIBLE.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...NONE.
UT...NONE.

&&

$$

SHORT TERM...JAM
LONG TERM...NL
AVIATION...NL


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