Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 250443
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1043 PM MDT SUN AUG 24 2014

.UPDATE...
ISSUED AT 1036 PM MDT SUN AUG 24 2014

CONVECTION CONTINUES TO EXPAND IN AREAL COVERAGE ALONG AND NORTH
OF UPPER LEVEL JET LIFTING NORTHEAST ACROSS THE FORECAST AREA
LATE THIS EVENING. FEW STRONGER CELLS DEVELOPING WITH NUMEROUS
OUTFLOW BOUNDARIES KICKING UP STRONGER SFC WINDS. LATEST HRRR RUNS
INDICATE THIS WILL CONTINUE THROUGH THE REMAINDER OF THE NIGHT AND
HAVE MADE SIGNIFICANT ADJUSTMENTS TO POPS GRIDS TO FIT CURRENT
TRENDS AND EXPECTED CONDITIONS FOR THE REMAINDER OF THE NIGHT.
OUTFLOW GUSTS TO 40 MPH POSSIBLE TONIGHT ALONG WITH SMALL HAIL
NEAR THE STRONGER CELLS. OTHERWISE...MORE MUCH NEEDED RAIN FOR THE
NORTHERN PORTIONS OF OUR FORECAST AREA.

UPDATE ISSUED AT 550 PM MDT SUN AUG 24 2014

SHORT TERM UPDATE WILL BE REQUIRED EARLY THIS EVENING AS
CONVECTION HAS INCREASED ACROSS EAST CENTRAL UTAH. THIS ACTIVITY
MAY EXPAND INTO NW COLORADO...POSSIBLY AS FAR AS A LINE FROM MOAB
TO ASPEN. THIS ACTIVITY IS IN RESPONSE TO EMBEDDED DISTURBANCE
ALONG A SHEAR AXIS THAT CUTS ACROSS THE FORECAST AREA THIS
EVENING. RAP AND HRRR MODELS INDICATE THAT SHOWERS AND STORMS
LASTING WELL BEYOND SUNSET WILL OCCUR FROM VERNAL TO ROUTT COUNTY.
IT APPEARS THAT THE LOWER RESOLUTION SUCH AS THE GFS40 IS
SUGGESTING NOCTURNAL CONVECTION AS WELL. UPDATE WILL BE COMING AND
WILL BE LEANING TOWARDS THE RAP/HRRR MODELS.

&&

.SHORT TERM...(TONIGHT THROUGH MONDAY NIGHT)
ISSUED AT 255 PM MDT SUN AUG 24 2014

12Z H5 HAND ANALYSIS SHOWING A BLOCKING RIDGE EXTENDING FROM THE
GULF STATES UP INTO THE CANADIAN MARITIME REGION. AS SUCH LOW
PRESSURE WILL BE ANCHORING IN THE WESTERN STATES TO START OUT THE
NEW WEEK. THE MORE IMPRESSIVE FEATURES SHOWING UP IN WATER VAPOR
THIS AFTERNOON ARE THE PAIR OF LOWS ROTATING AROUND EACH OTHER OVER
MONTANA AND WASHINGTON THIS AFTERNOON. THE FORMER RETREATING
NORTHEASTWARD AND THE LATTER DROPPING SOUTHWARD WHERE IT WILL CARVE
OUT A FAIRLY AMPLIFIED TROUGH THROUGH THE GREAT BASIN BY EARLY
TUESDAY. DERIVED IMAGERY AND RAOB DATA SHOWS A SIGNIFICANT DECREASE
IN MOISTURE THE PAST 24 HOURS AS THE MONSOONAL PLUME HAS BEEN
DIRECTED INTO THE EASTERN PLAINS. AT GJT AND UPSTREAM PWATS ARE
BELOW NORMAL FOR THIS TIME OF YEAR. THERE ARE SOME RETURNS SHOWING
UP ON RADAR WITH LOW LEVEL MOISTURE...MOUNTAIN CIRCULATIONS AND
INSTABILITY BEING ENHANCED BY A JET ALOFT. THE FOCUS FOR OVERNIGHT
SHOULD MAINLY BE ACROSS THE NORTH WHERE VEERING MID LEVEL PROFILES
AND THE PASSING JET MAXIMA WILL ADD JUST ENOUGH ASCENT TO KEEP
NOCTURNAL CONVECTION FIRING. HAVE THROWN OUT THE AGGRESSIVE GFS
QPF OUTPUT ATTM WITH IT NOT VERIFYING SO FAR THIS AFTERNOON. THETA
SURFACES NEAR 315K SHOW DECENT UPGLIDE NORTH OF INTERSTATE 70
TONIGHT WHILE ALSO HINT AT SOME TAP TO THE TROPICAL MOISTURE LEFT
OVER FROM WHAT IS LEFT OF MARIE. THIS TAP DOES NOT LOOK TO GREATLY
ENHANCE THE MOISTURE ADVECTION TONIGHT BUT MAY PLAY SOME ROLE IN
STORM FORMATION OVER THE EASTERN DIVIDE MOUNTAINS FOR MONDAY.
AGAIN MONDAY LOOKS TO BE SOMEWHAT OF A DOWN DAY AS THE JET ALOFT
WEAKENS AND OVERALL PWATS REMAIN BELOW NORMAL. A SMALL RIBBON OF
THE MOISTURE MENTIONED ABOVE LOOKS TO FAVOR CONVECTION OVER THE
CENTRAL DIVIDE MOUNTAINS UNDER CONFLUENT FLOW ALOFT. THIS ALL
HANDLED WELL IN THE GOING GRID FORECAST SO ONLY SMALL TWEAKS
NEEDED. TEMPERATURES SHOULD BE A BIT MORE MILD OVERNIGHT UNDER WAA
AND PUSH SOME 3 TO 7 DEGREES UPWARD FOR TUESDAY. TUESDAY NIGHT THE
FLOW BACKS MORE SOUTHERLY ALOFT AS THE MAIN TROF AXIS BECOME
ORIENTED MORE MERIDIONALLY. MONSOON AND TROPICAL MOISTURE LOOK TO
BE FORCED NORTHWARD IN THIS FLOW AND THERE SHOULD BE AN INCREASE
IN CONVECTION FROM MIDNIGHT TOWARD SUNRISE...SETTING UP A MORE
ACTIVE DAY FOR TUESDAY.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 255 PM MDT SUN AUG 24 2014

THE CHALLENGE OF THESE PERIODS HAS BEEN THE TIMING AND THEREFORE
THE PLACEMENT OF THE UPPER LOW THAT WILL DIG OVER THE REGION. THE
EC AND NAM ARE IN GOOD AGREEMENT WITH A SLOWER SOLUTION. THE GFS
AND CANADIAN PRODUCE A FASTER PROGRESSION BUT THE GFS IS SLOWER
THAN ITS PREVIOUS RUNS. AS THE UPPER LOW IS DECOUPLED FROM THE
POLAR FRONT JET...THE SLOWEST EC SOLUTION IS PREFERRED. SO
INCREASED STORM COVERAGE AND COOLER TEMPS ARE EXPECTED THROUGH
THURSDAY.

TUESDAY...THE UPPER LOW DUG INTO EASTERN NEVADA ENHANCING A 75KT
JET OVER THIS CWA. MOISTURE SURGES TO OVER AN INCH PRECIPITABLE
WATER VALUES IN SE UTAH. WEDNESDAY THE UPPER LOW SLOWLY PROGRESSES
INTO NE UTAH LOSING JET SUPPORT BUT GAINING CYCLONIC AND DIVERGENT
FLOW ALOFT. PRECIP WATER VALUES REMAIN NEAR ONE INCH. STORM MOTION
ALSO REMAINS BRISKLY TO THE NE AT 20 KTS LIMITING RAINFALL FORM
ANY SINGLE STORM. BY THURSDAY THE LOW CENTER AMBLES TO THE
CONTINENTAL DIVIDE WITH WRAP-AROUND DYNAMICS ACROSS THE NORTHERN
CWA AND THE UPPER FLOW SWITCHING TO NW. SOME NOCTURNAL STORMS ARE
EXPECTED THROUGH THESE PERIODS.

BY FRIDAY THE EC PROGRESSES THE OPENING LOW ONTO THE EASTERN
PLAINS WITH A RIDGE BUILDING IN FROM THE WEST. FRIDAY STORM
ACTIVITY WILL LINGER ALONG THE CONTINENTAL DIVIDE...THEN A DRYING
AND WARMING TREND INTO THE WEEKEND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1036 PM MDT SUN AUG 24 2014

SHOWERS AND THUNDERSTORMS WILL CONTINUE ACROSS NORTHEAST UTAH AND
NORTHWEST COLORADO THROUGH 15Z MONDAY MORNING. GUSTY WINDS TO 40
MPH AND SMALL HAIL WILL OCCUR NEAR THE STRONGEST STORMS. LOCAL
MVFR CIGS POSSIBLE WITH MOUNTAINS BECOMING OBSCURED AT TIMES.
SOUTH OF INTERSTATE 70...VFR CONDITIONS EXPECTED TO PERSIST
THROUGH MIDDAY MONDAY.

AFTER 18Z...SCATTERED SHOWERS AND THUNDERSTORMS WILL REDEVELOP
OVER THE MOUNTAINS WITH ACTIVITY TRANSITIONING OUT OVER THE
VALLEYS AFTER 00Z MONDAY EVENING. WITH ANY STORMS...GUSTY
WINDS...HAIL AND LOWERED CIGS SHOULD BE EXPECTED...WITH MOUNTAIN
TOPS BECOMING OBSCURED.

&&

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

$$

UPDATE...JDC
SHORT TERM...15
LONG TERM...JOE
AVIATION...JDC



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