Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 182323
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
523 PM MDT MON AUG 18 2014

.SHORT TERM...(TONIGHT THROUGH TUESDAY NIGHT)
ISSUED AT 333 PM MDT MON AUG 18 2014

BIG CHANGES WILL OCCUR OVER THE NEXT 24 HOURS AS AN UNSEASONABLY
STRONG AND NEARLY VERTICALLY STACKED TROUGH...CURRENTLY OVER
CALIFORNIA...MOVES EAST INTO THE GREAT BASIN. THIS BRINGS EASTERN
UTAH AND WESTERN COLORADO INTO IDEAL POSITION FOR DEEP
SUBTROPICAL MOISTURE TO ADVECT INTO THE REGION. PRECIPITABLE
WATER VALUES OF 1 TO 1.3 INCH ARE EXPECTED TO COVER EASTERN UTAH
AND EVEN EXTREME WESTERN COLORADO BY LATE TUESDAY AFTERNOON. THIS
IS ALMOST 2 STANDARD DEVIATIONS ABOVE NORMAL FOR THIS TIME OF
YEAR.

MODELS ARE FORECASTING MULTIPLE VORT MAXES TO REACH THE UT/CO
BORDER THROUGHOUT THE DAY FROM NOON TO MIDNIGHT. THERE IS SOME
UNCERTAINTY ON THE TIMING OF H3 JET SUPPORT OF 60KTS REACHING THE
AREA...WHICH WILL HELP TO PROVIDE ASCENT IN THE UNIMPRESSIVE CAPE
AND SHEAR ENVIRONMENT. EXPECTING CLOUD COVER TO HINDER INSTABILITY
DURING THE DAY...HOWEVER THIS SCENARIO COULD CHANGE IF SUFFICIENT
CLEAR AIR IS ABOUND BY LATE MORNING. THE RAP SHOWS JET SUPPORT
INCHING INTO EASTERN UTAH AND SOUTHWEST COLORADO DURING THE
MORNING ON TUESDAY...HOWEVER THE NAM AND GFS SHOW THE BEST JET
SUPPORT ON TUESDAY NIGHT AND WEDNESDAY MORNING. STORM MOTION WILL
BE DECENT FOR TUESDAY - ABOUT 20 TO 30 KTS...SO COULD NOT JUSTIFY
A FLASH FLOOD WATCH AT THIS TIME. IT WILL RAIN IN MANY LOCATIONS
BY TUESDAY NIGHT...BUT ONLY EXPECTING MODERATE TO HEAVY RAIN
MULTICELLULAR STORMS CAUSING NUISANCE/SMALL STREAM FLOODING AT
THIS TIME. SEE HYDRO SECTION FOR MORE.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 333 PM MDT MON AUG 18 2014

THE FORECAST AREA REMAINS UNDER SW FLOW WED-THU WITH THE JET AXIS
OVERHEAD. MONSOONAL MOISTURE PLUME WEAKENS WITH PRECIPITABLE WATER
VALUES DROPPING UNDER 1 INCH. NAM/GFS SHOW A WEAK 300 MB JET MAX
ARRIVING ON WED FOR POTENTIAL SUPPORT AND INCREASED VERTICAL
SHEAR....AND SHOULD IT ENTRAIN SOME DRIER MIDLEVEL AIR OVER HIGHER
MOISTURE NEAR THE SURFACE...IT COULD LEAD TO SOME STRONGER STORMS
WED AFTERNOON.

MODELS STILL HAVING TROUBLE HANDLING THE UPPER LOW THAT IS
CURRENTLY DROPPING SOUTH ALONG THE NRN CA COAST...WHICH LOWERS
FORECAST CONFIDENCE AFTER MIDWEEK. BUT AT LEAST THE GFS AND ECWMF
NOW BOTH BRING THE 500 MB LOW INLAND...JUST TIMING AND TRACK ARE
DIFFERENT. THE 12Z GFS SWINGS THE LOW INLAND ACROSS SRN CA WED AND
THEN LIFTS IT NE ACROSS UT AS AN OPEN WAVE ON THU. THIS COULD ADD
SOME DYNAMIC PUNCH TO STORM DEVELOPMENT ON THU. THE 12Z ECMWF IS
SLOWER BRINGING IT INLAND AND TRACKS IT FARTHER SOUTH ACROSS AZ
AND NWRN NM. THE 12Z CANADIAN HAS IT SHEARING OUT ALONG THE SRN CA
COAST THU-FRI. MODELS ALSO SHOW ENERGY DROPPING OUT OF THE GULF OF
AK LATE IN THE WEEK THAT SHOULD MAINTAIN TROUGHING OVER THE PAC
NW/NRN ROCKIES.

FOR NOW...WITH FOLLOW THE CONSENSUS MODEL TREND...WHICH SHOWS A
LESSENING OF STORM COVERAGE THE LAST HALF OF THE WEEK BUT NOT A
COMPLETE CESSATION. LOWER LEVEL MOISTURE LIKELY TO LINGER WITH SOME
SMALLER EMBEDDED WAVES IN THE FLOW THAT COULD TRIGGER ISOLATED-
SCATTERED ACTIVITY ABOUT EACH DAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 519 PM MDT MON AUG 18 2014

MOST CONVECTION IS EXPECTED TO DIE DOWN OVERNIGHT THOUGH SOME
LINGERING SHOWERS...MAYBE A QUICK RUMBLE OF THUNDER...IS POSSIBLE
THROUGH 09Z. FLYING CONDITIONS WILL DETERIORATE TOMORROW AS A
DISTURBANCE MOVES OVERHEAD WITH MID LEVEL BKN TO OCCNL OVC CIGS
EXPECTED FROM 18Z ONWARDS. MANY AREAS WILL SEE VCSH BECOMING VCTS
AS THE AFTERNOON PROGRESSES. THE STRONGER CELLS WILL PRODUCE MVFR
TO POSSIBLY IFR VIS AT TIMES DUE TO LOWERED VISIBILITIES. GUSTY
OUTFLOW WINDS ARE ALSO POSSIBLE REACHING 40+ MPH IN THE AFTERNOON
AND EVENING HOURS. MTN TOPS WILL LIKELY BE OBSCURED FOR MOST OF
THE FORECAST AREA. CONVECTION IS EXPECTED TO CONTINUE OVERNIGHT
THOUGH COVERAGE WILL LESS THAN SEEN DURING THE DAY.

&&

.HYDROLOGY...
ISSUED AT 333 PM MDT MON AUG 18 2014

MONSOONAL MOISTURE WILL RETURN TOMORROW 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 THROUGHOUT THE AFTERNOON AND PEAK DURING THE LATE HOURS OF
THE DAY AND OVERNIGHT INTO WEDNESDAY MORNING. EXPECTING TO HAVE
SMALL STREAM AND ARROYO FLOOD ISSUES BY WEDNESDAY MORNING IN THE
USUAL PROBLEM AREAS...BUT AT THIS NOT EXPECTING HIGH COVERAGE OF
TORRENTIAL DOWNPOURS DUE TO THUNDERSTORMS. THEREFORE...NO WATCHES
HAVE BEEN ISSUED AT THIS TIME.

&&

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

$$

SHORT TERM...JAM
LONG TERM...JAD
AVIATION...TGR
HYDROLOGY...JAM



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