Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 042349
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
549 PM MDT SAT JUL 4 2015

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 308 PM MDT SAT JUL 4 2015

AN UPPER LEVEL RIDGE OF HIGH PRESSURE CENTERED OVER THE FOUR
CORNERS THIS AFTERNOON WILL SHIFT SOUTHEAST TONIGHT AND SUNDAY.
WEAK TROUGHS OF LOW PRESSURE WILL MOVE AROUND THE NORTHERN
PERIPHERY OF THE RIDGE AND OVER NORTHEAST UTAH AND WESTERN
COLORADO LATE TONIGHT AND SUNDAY. CONVECTIVE ACTIVITY THIS
AFTERNOON AND EVENING WILL BE LOCALLY DRIVEN BY TERRAIN FORCING
AND OUTFLOWS...AND MAY VERY WELL CONTINUE WELL INTO THE EVENING.
INSTABILITY JUST NOT THAT GREAT...BUT SLOW MOVING STORMS WILL POSE
A FLOODING THREAT AND WILL BE MONITORED CLOSELY

A FEW SUBTLE CHANGES TO NOTE FOR THIS FORECAST PACKAGE.
FIRST...THE INITIAL SHORTWAVE ENERGY RIDING AROUND THE WESTERN
SIDE OF THE RIDGE IS EXPECTED TO PASS OVER THE FORECAST AREA
BETWEEN 6 AM AND NOON SUNDAY...A LITTLE EARLIER THAN PREVIOUSLY
EXPECTED. MID LEVEL THETA-E ADVECTION OCCURS IN ADVANCE OF THIS
WAVE...SO AM EXPECTING A SURGE OF SHOWERS/THUNDERSTORMS TO MOVE
NORTHEAST ACROSS EASTERN UT AND WESTERN CO LATE TONIGHT AND SUNDAY
MORNING. EVENTUAL COVERAGE IS STILL UNCERTAIN THOUGH...SO POPS MAY
BE A LITTLE CONSERVATIVE. SECOND...THE NORTHERN STREAM TROUGH IS
NOT EXPECTED TO DIP AS FAR SOUTH AS EARLIER THOUGHT...NOW STAYING
MAINLY ACROSS MONTANA. SO MID LEVEL SPEED SHEAR AND SYNOPTIC
FORCING FROM THIS FEATURE IS NOT AS GREAT ON SUNDAY.
HOWEVER...THERE IS ANOTHER WEAK PERTURBATION IN THE DEVELOPING
WEST-NORTHWEST FLOW ALOFT THAT WILL CROSS THE REGION SUNDAY
AFTERNOON AND NIGHT. WHILE THE PEAK PRECIP WATER VALUES OCCUR
SUNDAY MORNING (1.3 TO 1.4 INCHES)...STILL PLENTY OF MOISTURE LATE
IN THE DAY FOR THIS WAVE TO ACT ON AND CAUSE ANOTHER ROUND OF
TERRAIN-FOCUSED SHOWERS/STORMS WHICH WILL MOVE OFF TO THE EAST AND
AFFECT ADJACENT VALLEYS. ACTIVITY WILL LIKELY LINGER WELL INTO
SUNDAY NIGHT. HIGHS SUNDAY SHOULD BE A FEW DEGREES BELOW NORMAL.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 308 PM MDT SAT JUL 4 2015

A WEAK SURFACE COLD FRONT WILL MOVE SOUTH THROUGH NORTHEAST UTAH
AND NORTHERN COLORADO SUNDAY NIGHT AND STALL OUT ACROSS SOUTHWEST
COLORADO LATE MONDAY. THOUGH FLOW ALOFT GOES BACK TO BEING MAINLY
ANTI-CYCLONIC AROUND HIGH PRESSURE CENTERED SOUTH OF NEW
MEXICO...STILL HAVE A TRAIN OF WEAK SHORTWAVES MOVING IN THE FLOW
OVER OUR FORECAST AREA RIGHT ON THROUGH THURSDAY. PRECIPITABLE
WATER VALUES DROP TO GENERALLY 0.75 TO 1 INCH...BUT STILL AMPLE TO
SUPPORT THE TYPICAL DIURNAL TRENDS OF SHOWERS/THUNDERSTORMS
IMPACTING MAINLY THE MOUNTAINS. CANNOT RULE OUT STORMS MOVING
OVER ADJACENT VALLEYS THOUGH. MEDIUM RANGE MODELS STILL SHOWING
MORE ROBUST DRYING OF THE ATMOSPHERE OVER OUR AREA OCCURRING DUE
TO DRY SOUTHWEST FLOW AHEAD OF LARGE CLOSED UPPER LEVEL LOW
PRESSURE SYSTEM MOVING INLAND ACROSS CA/NV FRIDAY AND SATURDAY.
EXPECT TEMPERATURES TO REMAIN SIMILAR DAY TO DAY...A FEW DEGREES
BELOW NORMAL.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 546 PM MDT SAT JUL 4 2015

SCATTERED SHOWERS AND THUNDERSTORMS WILL REMAIN IN THE FORECAST
THROUGH SUNDAY EVENING...WITH ACTIVITY INCREASING AFTER MIDNIGHT
TONIGHT. STORMS WILL PRODUCE HEAVY RAIN AND SMALL HAIL ALONG WITH
THE POTENTIAL FOR FREQUENT LIGHTNING. CIGS WILL BE DROPPING BELOW
ILS BREAKPOINTS AT TIMES AT ALL TERMINAL SITES AS STRONGER
SHOWERS AND THUNDERSTORMS MOVE THROUGH. THE BIGGEST IMPACTS WILL
OCCUR BETWEEN 08Z TONIGHT AND 16Z SUNDAY MORNING...AND AGAIN AFTER
19Z SUNDAY AFTERNOON.

&&

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

$$

SHORT TERM...BEN
LONG TERM...BEN
AVIATION...JDC



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