Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 200434
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1034 PM MDT TUE AUG 19 2014

.UPDATE...
ISSUED AT 947 PM MDT TUE AUG 19 2014

MAINLY STRATIFORM PRECIPITATION CONTINUES THIS EVENING WITH A FEW
RUMBLES OF THUNDER THANKS TO EMBEDDED CONVECTION. LATEST NAM12 RUN
NOT INTIALIZING WELL...NOR IS THE GFS WITH BOTH SHOWING WIDESPREAD
AND HEAVY PRECIP OVERNIGHT WHILE HRRR IS CAPTURING PRECIP IN OUR
AREA PRETTY WELL. HRRR ALSO SHOWS SOME SHOWERY ACTIVITY
CONTINUING OVERNIGHT BUT COVERAGE IS ISOLATED AT BEST. LOOKING
UPSTREAM...RADAR MOSAIC SHOWING CONVECTION OVER EXTREME WRN UT/ERN
NV WITH NOT MUCH IN BETWEEN. IR IMAGERY IS ALSO SHOWING WARMING
CLOUD TOPS ACROSS OUR CWA INDICATING STRONGEST CONVECTION HAVING
ENDED. DO HAVE SOME CONCERN THAT UPPER LEVEL JET MOVING OVERHEAD
MAY FIRE OFF MORE CONVECTION OVERNIGHT BUT WITH DIVERGENCE
WEAKENING...WILL GO WITH MORE SCT TO ISOLD COVERAGE.

&&

.SHORT TERM...(TONIGHT THROUGH WEDNESDAY NIGHT)
ISSUED AT 344 PM MDT TUE AUG 19 2014

CURRENT IR SATELLITE SHOWS TWO PRECIPITATION HOT SPOTS - ONE WEST
OF VERNAL AND THE OTHER DOWN BY THE FOUR CORNERS. RADAR RETURNS
SHOW THE OUTER PERIPHERY OF THE ENHANCEMENT AT BLANDING UTAH AT
315PM. THIS RAIN WILL EXPAND TO THE NORTHEAST THROUGH THE LATE
AFTERNOON AND EVENING AS PRECIPITABLE WATER VALUES REACH THEIR
MAXIMUM OF ONE INCH TO 1.2 INCHES ACROSS THE REGION. A SERIES OF
H5 VORT MAXES ALONG WITH AN APPROACHING H3 50KT JET WILL MOVE
INTO THE AREA THIS EVENING...HELPING TO SUSTAIN SHOWERS AND
OCCASIONAL EMBEDDED THUNDERSTORMS. STORM MOTION STILL LOOKS TO BE
20 TO 30 KTS WITH MINIMAL TRAINING OCCURRING SO FAR.

SOME SUBSIDENCE OVER THE REGION TOMORROW WILL HINDER HIGH
LIKELIHOOD OF SHOWERS AND THUNDERSTORMS...HOWEVER FORECAST CIN IS
LOW OR NONEXISTENT BY THE AFTERNOON...AND AMPLE MOISTURE AND
BREAKS IN THE CLOUDS WILL BE IN PLACE TO INITIATE
ISOLATED/SCATTERED CONVECTION IN THE AFTERNOON. STEERING FLOW WILL
SLOW BY MIDDAY TO 10 TO 15 KTS. EXPECTING ACTIVITY TO OCCUR
EARLIER IN THE AFTERNOON AND TAPER OFF FOR THE MOST PART IN THE
EVENING.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 344 PM MDT TUE AUG 19 2014

WEATHER THE LAST HALF OF THE WEEK DEPENDS LARGELY ON THE UPPER LOW
CURRENTLY DROPPING SOUTH ALONG THE CA COAST. MODELS CONTINUE TO
HAVE SOME DIFFICULTY HANDLING THIS LOW. THE GFS REMAINS THE MOST
PROGRESSIVE...SWINGING IT IN INLAND ACROSS SRN CA THU AND UP
THROUGH ERN UT/WRN CO THU NIGHT. THE NAM AND ECMWF ARE SLOWER BY
ABOUT 12-24 HRS ON A TRACK A LITTLE FARTHER SOUTH. NUDGED POPS
UPWARD THU-FRI BUT REMAINED CONSERVATIVE DUE TO THE TIMING
DIFFERENCES.

SOME STORMS COULD BE RATHER STRONG THU-FRI GIVEN THAT THE DEEP LAYER
Q-G FORCING MAXIMA MOVES ACROSS THE AREA...AND 0-6KM VERTICAL WIND
SHEAR INCREASES WITH TROUGH PASSAGE...REGARDLESS OF MODEL. MODELS
ALSO HINT AT BRIEF ENTRAINMENT OF SOME MOISTURE FROM TROPICAL
STORM LOWELL...REFLECTED MORE IN THE 320K/325K ISENTROPIC SURFACE
HUMIDITY THAN PRECIPITABLE WATER FORECAST.

CONCURRENTLY...SHORTWAVE ENERGY SHARPENS AN UPPER TROUGH OVER THE
PAC NW AND NRN ROCKIES LATE IN THE WEEK. THIS TROUGH THEN SLOWLY
MIGRATES EASTWARD TO THE NORTHERN PLAINS AND SOUTHERN CANADA BY
MONDAY AFTERNOON. THIS SHOULD RESULT IN SOMEWHAT DRIER WESTERLY FLOW
ACROSS OUR AREA BY SUNDAY FOR A DOWNTURN IN SHOWER AND STORM
ACTIVITY THIS WEEKEND THROUGH EARLY NEXT WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 947 PM MDT TUE AUG 19 2014

-RA BEING REPORTED ALONG AND N OF I-70 THIS EVENING WITH KRIL
COMING IN WITH SOME MVFR CIGS WHILE REMAINING TAF SITES REPORTING
CIGS AROUND 6 TO 7K. AS THIS PRECIP CONTINUES SHIFTING TO THE NE...VFR
CONDITIONS ARE EXPECTED WITH BKN TO OVC SKIES. LATEST GUIDANCE
SHOWING MORE OF A DOWN DAY TOMORROW WITH SOME ISOLD CONVECTION TO
CONTEND WITH ACROSS THE CWA WITH MTN TAF SITES AND POSSIBLY SOME
VALLEY SITES SEEING SOME -RA...VCTS...OR A PASSING -TSRA.

&&

.HYDROLOGY...
ISSUED AT 344 PM MDT TUE AUG 19 2014

MONSOONAL MOISTURE IS RETURNING THIS EVENING AS AN UPPER LEVEL
LOW OVER CALIFORNIA PULLS DEEP SUBTROPICAL MOISTURE INTO THE
REGION. SHOWERS AND THUNDERSTORMS WILL INCREASE IN COVERAGE FROM
WEST TO EAST THIS EVENING...PEAKING THIS EVENING THEN CONTINUING
OVERNIGHT INTO WEDNESDAY MORNING. EXPECT SOME SMALL STREAM AND
ARROYO FLOOD ISSUES BY WEDNESDAY MORNING IN THE USUAL PROBLEM
AREAS. HOWEVER...DO NOT EXPECT SUFFICIENTLY WIDESPREAD COVERAGE OF
TORRENTIAL DOWNPOURS TO WARRANT FLASH FLOOD WATCH.

&&

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

$$

UPDATE...TGR
SHORT TERM...JAM
LONG TERM...JAD
AVIATION...TGR
HYDROLOGY...NL/JAM


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