Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 201641
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1041 AM MDT WED AUG 20 2014

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 357 AM MDT WED AUG 20 2014

LIGHT SHOWERS CONTINUED OVER PORTIONS OF CENTRAL AND NORTHWEST
COLORADO AND NORTHEAST UTAH EARLY THIS MORNING. LIFT ASSOCIATED
WITH THE LEFT EXIT REGION OF A JET STREAK ON THE EASTERN SIDE OF
A CLOSED LOW CIRCULATION OFF THE SOUTHERN CALIFORNIA COAST
APPEARED TO BE RESPONSIBLE FOR SUSTAINING MOIST CONVECTION.

THE INFLUENCE OF JET LEVEL DIVERGENCE DIMINISHES LATE TONIGHT INTO
WEDNESDAY MORNING. THEREAFTER...A SHORTWAVE WHICH WAS OVER WEST-
CENTRAL UTAH EARLY THIS MORNING WILL BECOME ENTRAINED IN THE
NORTHERLY STREAM...MOVING ACROSS NORTHEAST UTAH INTO NORTHWEST
COLORADO THIS MORNING. CONSEQUENTLY...SHOWERS AND EMBEDDED
THUNDERSTORMS WILL BE FAVORED ACROSS THE NORTH BEFORE NOON. A
MORE SHEARED SECONDARY WAVE WILL MOVE ALONG THE NORTHERN BORDER
AREA DURING THE AFTERNOON CONTINUING TO FOCUS SHOWERS AND
THUNDERSTORMS ACROSS THAT PORTION OF THE FORECAST AREA.

ELSEWHERE...DAYTIME WARMING WILL SPARK SCATTERED SHOWERS AND
THUNDERSTORMS...MAINLY OVER THE HIGHER TERRAIN. CLOUD COVER WILL
REMAIN PRETTY EXPANSIVE LIMITING INSOLATION AND IN TURN...STORM
STRENGTH. PRECIPITABLE WATER VALUES WILL BE FALLING BELOW AN INCH
AS DRIER MID-LEVEL FLOW MOVES IN. THIS...COMBINED WITH STEERING
WINDS STILL AVERAGING NEAR 20 KTS WILL LIMIT THE THREAT OF
EXCESSIVE RAINFALL AND FLOODING. HOWEVER...LOCALIZED FLOODING
CANNOT BE COMPLETELY RULED OUT. CLOUD COVER AND SHOWERS WILL
CONTINUE TO BRING COOLER THAN NORMAL AFTERNOON HIGHS AND MOS
GUIDANCE SEEMED TO CAPTURE THIS WELL.

THE UPPER LOW OVER SOUTHERN CALIFORNIA WILL BEGIN TO WEAKEN AND
SHIFT INLAND LATE TONIGHT THROUGH THU. THIS KEEPS THE AREA UNDER
A SOUTH-SOUTHWEST FLOW. WHILE THIS FLOW REGIME IS FAVORABLE FOR
KEEPING THE SUB-TROPICAL TAP OPEN...IT DOES LOOK LIKE THERE WILL
BE A MODEST DOWNTURN IN MOISTURE THROUGH THURSDAY. PWAT VALUES
WILL BE MOSTLY BETWEEN HALF AND THREE QUARTERS INCH. AFTER THE
DIURNAL ACTIVITY DIMINISHES THIS EVENING...EXPECT A FEW NOCTURNAL
SHOWERS AND THUNDERSTORMS OVERNIGHT TONIGHT. THEN WITH DAYTIME
HEATING ON THU...MOSTLY SCATTERED SHOWERS AND THUNDERSTORMS WILL
DEVELOP IN THE AFTERNOON FOR THE MOUNTAINS...WITH LESS COVERAGE
IN THE VALLEYS.

.LONG TERM...(THURSDAY NIGHT THROUGH TUESDAY)
ISSUED AT 357 AM MDT WED AUG 20 2014

THERE ARE STILL SOME DIFFERENCES IN THE TIMING OF WHEN THE
WEAKENED SOUTHERN CALIFORNIA LOW WILL PASS OVER THE AREA. THE
FASTER GFS SHOWS IT OVER THE FOUR CORNERS AT 12Z/6AM MDT
FRI...WITH THE NAM/EC ABOUT 9-12 HOURS LATER. MODELS ALSO
INDICATED THAT SOME MOISTURE FROM TROPICAL STORM LOWELL COULD GET
ENTRAINED IN THE SOUTHWEST FLOW AHEAD OF THE LOW. ESPECIALLY IF
THE GFS VERIFIES...THU NIGHT COULD BE RELATIVELY ACTIVE WITH
NIGHTTIME CONVECTION INCREASING AFTER MIDNIGHT. BUT EVEN THE
SLOWER NAM/EC SOLUTIONS WOULD ENHANCE INSTABILITY TOWARDS MORNING.
THEN DAYTIME HEATING WILL ADD TO THE MIX ON FRI...FOR BETTER
AFTERNOON SHOWERS AND THUNDERSTORMS. TEMPERATURES WILL REMAIN
BELOW NORMAL.

THE UNSEASONABLE LONG-WAVE TROUGH REMAINS OVER THE ROCKIES FROM
SATURDAY INTO TUESDAY WITH A SERIES OF SHORTWAVES MOVING THROUGH
DURING THIS TIME FRAME. LITTLE SKILL IN TIMING OF THOSE
DISTURBANCES THIS FAR OUT...SO WILL CONTINUE TO FORECAST MAINLY
DIURNAL SHOWERS AND THUNDERSTORMS...FAVORING THE MOUNTAINS...THIS
WEEKEND THROUGH EARLY NEXT WEEK. MOISTURE DEPTH AND STORM MOTION
NOT FAVORABLE FOR SIGNIFICANT HEAVY RAIN. STAGNANT PATTERN FAVORS
LITTLE CHANGE IN TEMPERATURES WHICH SHOULD REMAIN COOL DURING
THIS PERIOD.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1031 AM MDT WED AUG 20 2014

A DISTURBANCE ALOFT WILL CONTINUE SWEEPING ACROSS NW CO AND NE UT
AND GENERATE SCATTERED SHOWERS AND THUNDERSTORMS THROUGH EARLY THIS
AFTERNOON...GENERALLY NORTH OF THE I-70 CORRIDOR. HIGH MOISTURE
CONTENT AND GENERALLY THICK LOW AND MID LEVEL CLOUD COVER WILL
SUPPRESS STORM DEVELOPMENT OVER MUCH OF THE AREA UNTIL ABOUT
20Z. THEN CLEARING SKIES WILL SPREAD FROM THE SW TO NE...ALLOWING
STORM COVERAGE AND INTENSITY TO INCREASE. MOUNTAINS WILL BE
OBSCURED AT TIMES. TAF SITES ALONG THE I-70 CORRIDOR FACE A GOOD
CHANCE FOR THUNDERSTORM ACTIVITY WITH BRIEF MVFR/IFR VSBY POSSIBLE
IN HEAVY RAIN. THERE IS ONLY A SLIGHT CHANCE THAT THE REMAINDER OF
THE TAF SITES WILL BE DIRECTLY IMPACTED BY THUNDERSTORMS...THOUGH
THERE IS A GOOD CHANCE THAT THUNDERSTORMS WILL BE IN THE VICINITY
THROUGHOUT THE AFTERNOON AND INTO THE EVENING. SHOWERS AND
THUNDERSTORMS WILL LARGELY DIMINISH THIS EVENING WITH VFR
CONDITIONS RETURNING REGION WIDE.

&&

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

$$

SHORT TERM...NL/EH
LONG TERM...EH/NL
AVIATION...CC



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