Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 240340
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
940 PM MDT SAT AUG 23 2014

.SHORT TERM...(TONIGHT THROUGH SUNDAY NIGHT)
ISSUED AT 311 PM MDT SAT AUG 23 2014

THE STRONG VORTICITY MAXIMA IN THE BOTTOM OF THE TROUGH OVER
SOUTHERN WYOMING IS BEGINNING TO LIFT NE THIS AFTERNOON. THIS
WILL DIMINISH THE FORCING OVER THIS FORECAST AREA INTO THE EVENING
HOURS. 12Z MODELS SHOW SOME RESULTING MID LEVEL DRYING AND
DECREASING INSTABILITY INTO THE EVENING. AN ASSOCIATED WEAK
FRONTAL BOUNDARY HAD DUG TO A LINE STRETCHED FROM THE SOUTHERN ELK
MTNS SW TO THE ABAJO MTNS IN SE UTAH. ISOLATED LIGHTNING STRIKES
WERE OCCURRING ALONG THIS BOUNDARY WHILE SHOWERS FURTHER NORTH
ARE LIGHTNING FREE. PRECIPITABLE WATER VALUES REMAIN BETWEEN 0.6
AND 0.8 INCH THROUGH THESE PERIODS.

TONIGHT IN THE NORTHERN AIR MASS MODELS CONTINUE TO SHOW WEAK
DISTURBANCES PASSING ALONG AND NORTH OF I70. THIS WILL LIKELY KEEP
SOME SHOWERS OCCURRING WITH SOME LIGHTNING POTENTIAL. STORMS WILL
STILL BE MOVING QUICKLY TO THE NE AT AROUND 30 MPH. IN AREAS THAT
HAVE RECEIVED SUBSTANTIAL RAINFALL THE LAST 24 HOURS...PATCHY FOG
MAY FORM OVERNIGHT.

SUNDAY IS THE IN-BETWEEN DAY AS TODAY/S LOW LIFTS INTO NORTH
DAKOTA AND THE NEXT TROUGH DIGS SOUTH THROUGH CENTRAL WYOMING.
WINDS ALOFT BACK FROM W TO SW. SOME WEAK SHEARED VORTICITY ACROSS
THE NORTH WITH A 60KT JET OVER NE UTAH. LIGHT SHOWERS AND ISOLATED
STORMS WILL FAVOR THE NORTH.

SUNDAY NIGHT THE NEXT LOW DIGS TO SOUTHERN OREGON-IDAHO. THE JET
SAGS INTO THE CENTRAL CWA PRODUCING SOME DEFORMATION DIAGONALLY
FROM MOAB TO STEAMBOAT. ISOLATED TO LOW SCATTERED STORMS EXPECTED
ALONG THIS BOUNDARY.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 311 PM MDT SAT AUG 23 2014

ONE AREA OF LOW PRESSURE WILL BE LIFTING INTO THE CANADIAN
PRAIRIES WHILE ANOTHER CIRCULATION DIVES SOUTHWARD ACROSS THE
PACIFIC NORTHWEST EARLY MONDAY. THIS WILL CAUSE THE WESTERN TROF
TO AMPLIFY POSITIVELY ACROSS THE WESTERN STATES AND INCREASE THE
SOUTHWEST FLOW OVER OUR CWA. INTERESTINGLY THERE ARE TWO TROPICAL
SYSTEMS IN THE EASTERN PACIFIC DURING THIS TIME. THETA SURFACES
SUGGEST BOTH OF THESE SYSTEMS WILL BE INTERJECTING MOISTURE INTO
THE DESERT SOUTHWEST ON MONDAY...WHICH WILL BE PULLED NORTHWARD BY
TUESDAY. THE QUESTION INITIALLY ON MONDAY MORNING WILL BE HOW
SIGNIFICANT THE CURRENT BOUNDARY OVER OUR SOUTHERN CWA WILL BE AS
IT IS LIFTED NORTH BY BACKING FLOW ALOFT. BOTH SHORT TERM MODELS
SUGGEST SOME SHOWER ACTIVITY LIFTING OUT OF OUR NORTHERN CWA
MONDAY MORNING SO HAVE ADJUSTED POPS ACCORDINGLY. WITH THE JET
CORE SHIFTING NORTHEAST AND A TEMPORARY TAP OF DRIER AIR
ALOFT...MAINLY TERRAIN BASED STORMS ARE ANTICIPATED WHICH LOOK TO
BE FAVORED OVER THE SOUTHERN AND CENTRAL DIVIDE MOUNTAINS.

COME TUESDAY THROUGH THURSDAY THE MODELS ARE STILL IN A BIT OF
DISAGREEMENT WITH THE PROGRESSIVE NATURE OF THE TROUGH SWINGING
ACROSS THE ROCKIES INTO THE PLAINS. AGAIN 315K SURFACES SHOW A
STRONG INFLUX OF MOISTURE BEGINNING MONDAY EVENING AS DOWNSTREAM
FLOW FROM THE WESTERN TROUGH MERGES WITH THE ANTICYCLONIC FLOW
AROUND THE PLAINS SUBTROPICAL HIGH. PWATS RESPOND BY PUSHING BACK
TO NEAR AN INCH BY TUESDAY MORNING. LARGE SCALE ASCENT FROM THE
WESTERN TROUGH AND THE JET FORMING ALOFT DUE TO CONFLUENCE WILL
AID INSTABILITY FOR ANOTHER ACTIVE DAY ON TUESDAY. HAVE RAISED
POPS AND TRENDED TEMPERATURES DOWNWARD. BY 00Z WEDNESDAY THE GFS
ALREADY APPEARS TO BE A FAST OUTLIER IN PUSHING THE TROUGH AXIS
EASTWARD. THIS TREND CONTINUES AND IS MAGNIFIED BY 00Z THURSDAY.
SO THE DRYING TREND IN THE GFS IS GIVEN LITTLE CONFIDENCE AND THE
TREND IN POPS WILL BE INCREASING FOR WEDNESDAY. ENSEMBLES HELP
CONFIDENCE WITH THE PUSHING THE TROUGH EAST OF THE ROCKIES BY
THURSDAY MORNING WITH DRIER NORTHERLY FLOW MOVING IN TO CLOSE OUT
THE FORECAST. THIS SHOULD ALSO BRING A BUMP IN TEMPERATURES BACK
TOWARD NORMAL OR ABOVE.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 923 PM MDT SAT AUG 23 2014

A WIDE BAND OF MID LEVEL CLOUDS AND SCATTERED SHOWERS/ISOLATED
THUNDERSTORMS SHOULD PERSIST THROUGH MUCH OF TONIGHT IN SE UTAH
AND SW COLORADO UP INTO CENTRAL MOUNTAINS OF COLORADO WHERE LOCAL
MOUNTAIN OBSCURATION CAN BE EXPECTED IN VICINITY OF SHOWERS.
ADDITIONALLY...LESSER AMOUNTS OF MID LEVEL CLOUDS AND ISOLATED
SHOWERS WILL LIKELY PERSIST TONIGHT IN PORTIONS OF NORTHWEST
COLORADO.

PATCHY FOG HAS ALREADY FORMED IN SOME LOCATIONS AND WILL LIKELY
OCCUR IN OTHER AREAS LATER TONIGHT WHERE SIGNIFICANT RAIN FELL
TODAY. LOCAL IFR CEILINGS AND VSBYS POSSIBLE IN FOG. AIRPORTS AT
ELEVATIONS ABOVE THE 7000 FOOT LEVEL MOST VULNERABLE TO PATCHY FOG
FORMATION. ANY FOG THAT DEVELOPS TONIGHT SHOULD DISSIPATE WITHIN
AN HOUR OR SO AFTER SUNRISE ON SUNDAY.

BY 13Z SUNDAY...EXPECT WIDESPREAD VFR ACROSS THE FORECAST AREA AS
MOST OF THE CLOUDS SHOULD THIN OUT BY THEN WITH ONLY ISOLATED
LINGERING SHOWERS. DAYTIME HEATING ON SUNDAY SHOULD RESULT IN A
FEW AFTERNOON/EVENING SHOWERS AND THUNDERSTORMS OVER THE
MOUNTAINS.

&&

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

$$

SHORT TERM...JOE
LONG TERM...15
AVIATION...JRP



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