Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 201713
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1113 AM MDT SAT SEP 20 2014

.UPDATE...
ISSUED AT 1110 AM MDT SAT SEP 20 2014

THE MORNING MODELS YIELD NO SURPRISES. NAM MOS POPS HAVE TRENDED
UP AGAIN IN THIS MODEL RUN. THE TRANSIENT RIDGE AXIS IS OVER THE
REGION THIS MORNING WITH LITTLE DIURNAL CHANGE OF TEMPERATURES OR
DEWPOINTS. THE UPPER LOW ALONG THE SOUTHERN CALIFORNIA COAST IS
BEGINNING TO KICK INLAND AND WILL BRING A INCREASING SHOWERS
STARTING TONIGHT. ITS UPPER DIVERGENCE FORCING IS EVIDENT IN
SOUTHERN NV WHERE THUNDERSTORMS ARE VENTING THIS MORNING. THIS
AFTERNOON`S CONVECTION WILL BE CONFINED TO THE COLORADO EASTERN
MTNS MAINLY SOUTH OF I-70 AND THE SE UTAH MTNS WITH MID-LEVEL
SUBSIDENCE SUPPRESSING ELSEWHERE.

AS THE RIDGE AXIS SHIFTS ONTO THE PLAINS THIS EVENING THE FLOW
SHIFTS TO MOIST SOUTH. MODELS ARE IN GOOD AGREEMENT THAT PRECIP
WATER VALUES CLIMB TO 1.1 INCHES THROUGH EASTERN UTAH AND FAR
WESTERN COLORADO. THE NAM ROTATES FROM SSE TO NNW SOME DISTURBANCE
THAT IS PRODUCING ENHANCED PRECIP OVER THE SAN JUANS AFTER
MIDNIGHT TONIGHT. THE GFS AND SHORTER TERM MODELS DO NOT RESOLVE
THIS FEATURE. STILL SOME STORMS ARE LIKELY TO GO THROUGH THE NIGHT

SUNDAY THE UPPER LOW LIFTS THROUGH NV WITH ITS ASSOCIATED JET
STREAK PUSHING TOWARDS NE UTAH. SHOWERS ARE EXPECTED TO BE
WIDESPREAD BUT THE STRONGEST STORMS MAY OCCUR IN NE UTAH LATE
SUNDAY WITH A COMBINATION OF DEEP MOISTURE AND JET FORCING OVER
SURFACE CONVERGENCE. STORM MOTION TO THE NE AT 20-25 KTS WILL
LIMIT RUNOFF PROBLEMS EXCEPT WHERE MULTIPLE CELLS TRAIN OVER THE
SAME LOCATION. WE WILL ISSUE AN NON-SPECIFIC SPECIAL WEATHER
STATEMENT TO HANDLE THIS CHANGE TO A MUCH MORE MOIST PATTERN.

THE LOW OPENS AS IT LIFTS THROUGH WYOMING ON MONDAY. JET STREAK
WEAKENS BUT PERSISTS OVER NW CO SUNDAY NIGHT-MONDAY. MOISTURE
ERODES FROM SW TO NE THROUGH THESE PERIODS WITH MONDAY STORMS AND
SHOWERS LIMITED TO THE NORTHERN MTNS.

&&

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 357 AM MDT SAT SEP 20 2014

DRY AND STABLE CONDITIONS WILL PREVAIL AGAIN TODAY AS HIGH
PRESSURE AND LOW PRECIPITABLE WATER CONTINUE OVER THE AREA. THE
CLOSED LOW OFF THE SRN CA COAST WILL MOVE VERY SLOWLY INLAND OVER
SRN AND CENTRAL CA THIS AFTERNOON. A SHORTWAVE TROUGH ROTATING
AROUND THE EASTERN PORTION OF THIS STORM WILL HELP THE RIDGE TO
FUNNEL MOISTURE INTO THE AREA LATER THIS AFTERNOON...WITH A
RESULTING INCREASE IS SHOWER AND THUNDERSTORM DEVELOPMENT OVER SW
CO. FORECAST SOUNDINGS NEAR THE FOUR CORNERS SHOW THE PWAT
INCREASING TO OVER 0.75 INCHES AFTER 21Z AND CONTINUING TO
INCREASE THEREAFTER. HAVE INCREASED CLOUD COVER AND PRECIP CHANCES
OVER THE SOUTHERN HALF OF THE AREA THIS AFTERNOON.

THE CLOSED UPPER LOW TRACKS NORTHEAST ACROSS CENTRAL CA TONIGHT AND
CENTRAL NV ON SUNDAY. MOISTENING ISENTROPIC UPLIFT IN SOUTHERLY
UPSLOPE FLOW TONIGHT WILL BRING A CHANCE OF SHOWERS TO MAINLY SE
UT/SW CO LATE TONIGHT. THIS CHANCE SPREADS ACROSS MUCH OF OUR AREA
SUNDAY MORNING AS THIS BAND LIFTS NORTHWARD. SOME BRIEF CLEARING MAY
OCCUR ACROSS THE SOUTH AROUND MIDDAY PER THE 315K/320K ISENTROPIC
HUMIDITY FIELDS...BUT DAYTIME HEATING AND THE APPROACH OF A
WEAKENING 300 MB JET MAX SHOULD CAUSE SCATTERED SHOWERS AND STORMS
TO FILL IN SUNDAY AFTERNOON.

.LONG TERM...(SUNDAY NIGHT THROUGH FRIDAY)
ISSUED AT 357 AM MDT SAT SEP 20 2014

SUNDAY NIGHT COULD BE RATHER ACTIVE AS THE UPPER LOW MOVES ACROSS SE
ID/NW UT. THE WEAKENING UPPER JET SLIPS OVER SE UT/SW CO...WHILE A
500 MB VORTICITY LOBE SWINGS ACROSS NE UT/NW CO. THE LOSS OF HEATING
SUNDAY NIGHT WILL BE COMPENSATED FOR BY BETTER DYNAMICS. BEST
COMBINATION OF 0-6KM VERTICAL WIND SHEAR AND MUCAPE IS SHOWN SUNDAY
EVENING AND SUNDAY NIGHT FOR THE POTENTIAL OF A FEW STRONGER
STORMS...WITH STRONG GUSTY OUTFLOW WINDS AND HAIL POSSIBLE. WITH
PRECIPITABLE WATER VALUES NEAR AN INCH SUNDAY EVENING...LOCALLY
HEAVY RAIN ALSO IN THE MIX.

FLOW ALOFT SHIFTS FROM SOUTHERLY SUNDAY NIGHT TO WESTERLY ON MONDAY
AS THE UPPER LOW MOVES ACROSS WY. THIS SHOULD PULL IN SOME DRIER AIR
CONFINING SCATTERED SHOWERS/STORMS MAINLY THE NORTH. TEMPS A FEW
DEGREES COOLER ON MONDAY.

TUESDAY THROUGH FRIDAY...THE 500 MB TROUGH WILL BE WELL EAST OF CO
TUE MORNING WITH NW FLOW OVER THE AREA AND REMNANT MOISTURE AND
SHOWERS HUGGING THE NORTHERN AND CENTRAL CO MOUNTAINS. BY TUE
AFTERNOON MOST OF THESE SHOULD DISSIPATE AND/OR MOVE EAST OF THE
AREA AS MOISTURE ERODES QUICKLY.

A BIG RIDGE IS PROJECTED TO DOMINATE THE WEATHER ACROSS MUCH OF
THE WESTERN U.S. TUE AFTERNOON THROUGH THU MORNING. DRIER
CONDITIONS WITH A WARMING TREND ARE EXPECTED IN THIS TIME PERIOD.

THURSDAY AFTERNOON AND FRIDAY...THE MIDRANGE MODELS ARE COMING
INTO AGREEMENT ON THIS BEING A TRANSITION PERIOD. THE RIDGE IS
PROJECTED TO ERODE TO THE SOUTHEAST AND ANOTHER STRONG PACIFIC
TROUGH MOVES INLAND. AN IMPRESSIVE LOOKING STAND-UP COLD FRONT
WILL MOVE INTO WESTERN AND CENTRAL UT FRIDAY...AND APPROACH
EASTERN UT FRIDAY AFTERNOON. HAVE INCREASED CLOUDS AND PRECIP
CHANCES FROM WEST TO EAST FRIDAY AFTERNOON. AS THE SYSTEM ACROSS
THE GREAT BASIN FRIDAY...A STRONG JET ROUNDS THE BASE OF THE
TROUGH WITH GOOD DIVERGENCE ALOFT AND AMPLE MOISTURE OVER MUCH OF
UT. THIS COULD BE A VERY INTERESTING SYSTEM.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 1110 AM MDT SAT SEP 20 2014

ISOLATED SHOWERS AND THUNDERSTORMS WILL DEVELOP OVER THE
MOUNTAINS...WITH A SLIGHT CHANCE OF A THUNDERSTORM IN THE VICINITY
OF KTEX AFTER ABOUT 21Z. AFTER 03Z...SHOWERS AND THUNDERSTORMS
WILL INCREASE OVER SOUTHWEST CO AND SOUTHEAST UT. THERE IS A 30
PERCENT CHANCE OF MVFR VSBYS IN HEAVIER SHOWERS AT KDRO AND KTEX
THROUGH 06Z. THEN SCATTERED SHOWERS AND STORMS WILL BECOME
WIDESPREAD THROUGH 18Z SUNDAY WITH SHOWERS PRODUCING VIS DOWN TO
4SM AND CIG AT OR BLO 040.


&&

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

$$

UPDATE...JOE
SHORT TERM...CC/JAD
LONG TERM...JAD/CC
AVIATION...JOE



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