Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 120253
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
853 PM MDT THU SEP 11 2014

.UPDATE...
ISSUED AT 842 PM MDT THU SEP 11 2014

COLD FRONT CONTINUES TO DROP SOUTH ACROSS NORTHWEST COLORADO AND
LOOKS LIKE IT WILL JUMP THE BOOKCLIFFS SHORTLY SENDING COOLER
CONDITIONS THROUGH THE INTERSTATE 70 CORRIDOR. IN ADDITION...ISOLATED
SHOWERS HANGING ON ALONG INTERSTATE 70 FROM GLENWOOD TO VAIL
PASS. GUSTY WINDS AND LIGHT RAIN WILL BE THE PRIMARY CONCERN WITH
THESE DECAYING SHOWERS. GRIDS HAVE BEEN MODIFIED AND NEW ZONES
SENT.

UPDATE ISSUED AT 502 PM MDT THU SEP 11 2014

SHOWERS HAVE JUMPED UP A BIT IN INTENSITY ACROSS THE FLAT TOPS
NORTH OF INTERSTATE 70. AS DISCUSSED BELOW...DOWNSCALED MODELS
PICKING UP ON THIS ACTIVITY WITH THE HRRR ALSO JOINING IN. HAVE
NUDGED POPS UP A BIT ACROSS THE FLAT TOPS AND ACROSS PORTIONS OF
MOFFAT AND ROUTT COUNTIES THROUGH EARLY THIS EVENING. THIS
ACTIVITY WILL QUICKLY DIMINISH BY SUNSET WITH CLEAR AND COLD
CONDITIONS ON TAP OVERNIGHT.

&&

.SHORT TERM...(TONIGHT THROUGH FRIDAY NIGHT)
ISSUED AT 300 PM MDT THU SEP 11 2014

TIGHTENING PRESSURE GRADIENT OVER NW COLORADO IS PRODUCING SOME
OROGRAPHIC CLOUD AND GUSTY SURFACE WINDS TO 25 KTS. DOWNSCALED
NAMDNG25 AND RAP13 PAINTS A THIN RIBBON OF LIGHT SHOWERS FROM
BOOKCLIFFS TO THE FLAT TOPS BY LATE AFTERNOON. VISUAL SATELLITE
IMAGES DO SHOW LOW TOP CONVECTION IS FORMING OVER THE HIGHER
TERRAIN OF NW AND WC COLORADO...SO SCENARIO APPEARS TO BE IN PLAY.
ANY LIGHT SHOWERS WILL DISSIPATE WITH SUNSET.

SURFACE COLD FRONT FROM WYOMING DROPS INTO NW COLORADO EARLY THIS
EVENING AND SPREADS SOUTHWARD. APPEARS THIS FRONT REACHES THE I70
CORRIDOR LATE THIS EVENING...BUT DOES NOT GO MUCH FARTHER SOUTH.
MINIMAL MOISTURE WITH THE FRONT AND NOT EXPECTING ANY WEATHER
EXCEPT FOR A WIND SHIFT TO N-NE. DRIER AIR MASS FILTERING INTO NW
COLORADO WILL ALLOW TEMPS TO FALL BELOW FREEZING ALONG THE RIVER
VALLEYS AND LOW LYING SPOTS. CONFIDENCE IS HIGH THIS WILL OCCUR
WITH MID TO UPPER 20S IN THE YAMPA AND WHITE RIVER BASINS. WILL
UPGRADE THE FREEZE WATCH TO FREEZE WARNING AND INCLUDE STEAMBOAT
SPRINGS VICINITY.

GRADIENT FLOW RELAXES ON FRIDAY AS COLD TROUGH MOVES ACROSS THE
CENTRAL PLAINS. AIR MASS WILL BE SIGNIFICANTLY DRIER AND WILL MEAN
MORE SUNSHINE FOR THE ENTIRE REGION. COOLER MAX TEMPS ACROSS THE
NORTH...BUT NEAR PERSISTENCE FOR THE SOUTHERN HALF.

INTERESTINGLY MODEL DATA SHOWS A LITTLE MOISTURE FILTERING INTO
ARCHULETA COUNTY ON FRIDAY NIGHT. NOT CONVINCED THAT LIGHT PCPN
WILL FORM DURING THE NOCTURNAL HOURS...WILL KEEP THE DRY FORECAST
ONGOING. IF NOTHING ELSE...SOME SHALLOW UPSLOPE FLOW MAY PRODUCE
SCATTERED CLOUDS. OTHERWISE BENIGN WEATHER CONDITIONS PERSIST
THROUGH FRIDAY NIGHT.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 300 PM MDT THU SEP 11 2014

THE LAST IN A SERIES OF TROUGHS WORKS THROUGH THE NORTHERN TIER OF
STATES ON SATURDAY. THIS ALLOWS THE SUBTROPICAL HIGH...THAT HAS
BEEN SQUASHED ALONG THE GULF COAST STATES...TO BEGIN TO AMPLIFY
WESTWARD INTO THE DESERT SW. DAYTIME TEMPERATURES REBOUND TO NEAR
NORMAL AFTER FRIDAY/S COOL DOWN. ALSO MOISTURE WILL BEGIN TO
PERCOLATE NORTH THROUGH AZ-NM INTO THIS FORECAST AREA. MARGINAL
MOISTURE OVER THE WEEKEND WILL PRODUCE MAINLY AFTERNOON MOUNTAIN
THUNDERSTORMS PRODUCING MORE WIND THAN RAIN.

MOISTURE INCREASES EARLY NEXT WEEK AS HIGH PRESSURE AMPLIFIES
NORTHWARD ALONG THE SPINE OF THE ROCKIES. NO ORGANIZED FORCING
SEEN FOR NOW...SO EXPECT SCATTERED AFTERNOON TO EARLY EVENING
STORMS AND SOME CHANCE OF LOCALLY HEAVIER SHOWERS DUE TO SLOW
STORM MOTION.

FOR WEDNESDAY INTO THURSDAY WE ARE WATCHING TROPICAL STORM ODILE
THAT MAY MAKE HURRICANE STATUS AS IT WORKS ITS WAY UP ALONG THE
MEXICAN WEST COAST. THE MORE PROGRESSIVE GFS PULLS ODILE MOISTURE
INTO THE REGION AS A PACIFIC TROUGH SWEEPS THE WEST. THE EC KEEPS
THE ROCKIES RIDGE IN PLACE WHICH FORCES ODILE OUT TO SEA.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY EVENING) ISSUED
AT 847 PM MDT THU SEP 11 2014

A COLD FRONT WILL SLIDE SOUTH OF INTERSTATE 70 THIS MORNING WITH
CLEARING AND COLD CONDITIONS EXPECTED OVERNIGHT. DECAYING SHOWERS
ALONG INTERSTATE 70 FROM GLENWOOD SPRINGS TO VAIL PASS WILL
DIMINISH BY 07Z. GUSTY OUTFLOW WINDS TO 30 MPH AND LIGHT RAIN
WILL ACCOMPANY THE SHOWERS. OTHERWISE...VFR CONDITIONS ARE
EXPECTED THROUGHOUT THE PERIOD.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...FREEZE WARNING FROM 2 AM TO 9 AM MDT FRIDAY FOR COZ002-005.

UT...NONE.
&&

$$

UPDATE...JDC
SHORT TERM...PF
LONG TERM...JOE
AVIATION...JDC



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