000
FXUS65 KGJT 302118 CCA
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
317 PM MDT FRI JUL 30 2010

CORRECTED TO ADD MISSING WORD IN LONG TERM SECTION

.SHORT TERM...TONIGHT THROUGH SUNDAY...

TWO AIR MASS REGIMES SPLITS THE FORECAST AREA WITH THE CURRENT
FLASH FLOOD WATCH HIGHLIGHTING WHERE THE BEST CONVECTIVE POTENTIAL
EXISTS.  THE MORNING 12Z KGJT SOUNDING SHOWED SIGNIFICANT DRYING
ABOVE 450 MB.  GRANTED THIS IS VERY HIGH...BUT THE HIGH LEVEL
SUBSIDENCE INVERSION SUPPRESSES DEEP CONVECTION.  CURRENTLY THIS IS
WHAT IS BEING OBSERVED WITH ISOLATED TERRAIN DRIVEN STORMS NORTH OF
I70.  DEEPER STRONGER CONVECTION OCCURRING OVER THE SOUTHERN
MOUNTAINS WITH SATELLITE INFRARED INDICATING CLOUD TOPS COLDER THAN
-60C.  SPOTTY HEAVER RAINERS HAVE BEEN OBSERVED OVER THE SAN JUAN
FOOTHILLS.  EXPECT THE AREAL COVERAGE OF STORMS TO INCREASE OVER
THE SRN AREAS INTO THE EARLY EVENING HOURS.

LATER TONIGHT OVER SOUTHWEST COLORADO...STEERING WINDS VEER AROUND
AND RETURN TO A SOUTHERLY COMPONENT.  CONVECTIVE DEBRIS FROM
EASTERLY WAVE OVER NEW MEXICO WILL SPREAD NORTH...POSSIBLY AS FAR
NORTH AS THE I70 CORRIDOR.  WHERE THE MOISTURE CONTENT IS HIGHEST...
THIS COULD KEEP SCATTERED SHOWERS WITH EMBEDDED STORMS ONGOING
THROUGH NIGHT...NOT THAT UNUSUAL DURING A MONSOONAL SURGE.  BOOSTED
OVERNIGHT POPS FOR THIS AREA AS THE SREF AND NAM12 MODELS SHOW THIS
TREND.

SATURDAY AND SATURDAY NIGHT...DEEPEST MOISTURE REMAINS OVER THE SRN
AREAS WITH DRIER AIR NORTH OF I70.  SIMILAR CONDITIONS SATURDAY
EXCEPT THAT SOUTHERLY FLOW WILL REACH WYOMING...ALTHOUGH 700 MB
FLOW IS ABOUT 10 KNOTS.  THIS IS SUFFICIENT FLOW THAT IMPROVES THE
CHANCES OF MERGING CELLS.  GIVEN THE HEAVY RAINERS THIS AFTERNOON
OVER THE SRN MOUNTAINS AND SLIGHTLY HIGHER CHANCE OF HEAVY RAINERS ON
SATURDAY...WILL GO AHEAD AND ISSUE A FLASH FLOOD WATCH FOR THE SAME
AREA.

SUNDAY...EASTERLY WAVE MAY SHEAR OUT ACROSS THE WESTERN SLOPE ON
SUNDAY...DEPENDING WHAT MODEL TO PICK.  THE NAM SHEARS THE WAVE
ACROSS THE SAN JUAN MOUNTAINS...BUT THE GFS IS A LITTLE FARTHER
WEST AND NORTH.  WILL NEED TO WATCH THIS...ALTHOUGH NEITHER MODEL
DOES NOT SHOW A SIGNIFICANT QPF INCREASE FROM SATURDAY TO SUNDAY.
BOTTOM LINE FOR THE NEXT TWO DAYS...HEAVY RAINERS FAVOR SOUTHWEST
COLORADO...WITH SOME STORMS SPREADING INTO SOUTHEAST UTAH...WITH
TERRAIN DRIVEN BUT SHORTER LIVED STORMS NORTH OF I70.

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...

UPPER LEVEL HIGH PRESSURE EXPECTED TO STRETCH FROM OCEAN TO OCEAN
ACROSS THE SOUTHERN USA THIS PERIOD. AN UPPER LEVEL TROUGH ALONG THE
PAC NW COAST MONDAY IS FORECAST TO EVENTUALLY MOVE INLAND AND SHOULD
BRING SOME DRIER AIR TO AT LEAST THE NORTH AFTER MIDWEEK.

BUT UNTIL THEN...EXPECT THE MONSOONAL MOISTURE PLUME TO REMAIN
ORIENTED SOUTHWEST TO NORTHEAST OVER SE UT AND THE 4 CORNERS MON-
WED. PRECIPITABLE WATER EXCEEDS 1 INCH ALONG THE MOISTURE AXIS.
TROPOPAUSE POTENTIAL VORTICITY CHARTS SHOW WAVE CURRENTLY NEAR THE
MEXICAN GULF COAST ROTATING UP INTO AZ EARLY NEXT WEEK AND THEN
SHEARING NORTHEAST ACROSS OUR FORECAST AREA WED AFTERNOON-NIGHT. THIS
WILL KEEP A DAILY CHANCE OF THUNDERSTORMS PRESENT MON-WED...MOST
NUMEROUS ACROSS THE SAN JUAN MTNS TO LEAST IN NE UT AND NW CO.
LOCALLY HEAVY RAIN POSSIBLE IN THE SOUTH. ANTICIPATE A DECREASE IN
SHOWER COVERAGE THU-FRI AS PLUME GETS SHUNTED EAST BY THE PAC NW
TROUGH MOVING EAST ACROSS THE NRN ROCKIES AND WY.

&&

.AVIATION...

NUMEROUS THUNDERSTORMS WITH LOCALLY HEAVY RAINFALL WILL BE COMMON
THROUGH TO 03Z TODAY.  STORMS WILL CREATE AREAS OF MOUNTAIN
OBSCURATION WITH MVFR CIGS AND VIS IN RAIN SHOWERS. LOCALIZED IFR
CIGS AND VIS ARE LIKELY IN THE HEAVY DOWNPOURS. SHOWERS AND
THUNDERSTORMS WILL SLOWLY TAPER OFF AFTER 03Z AND EXPECT ISOLATED
COVERAGE AFTER MIDNIGHT.  STORMS WILL QUICKLY REDEVELOP AFTER 18Z ON
SATURDAY.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...NONE
UT...NONE.

$$

SHORT TERM.....PF
LONG TERM......JAD
AVIATION.......TGJT

NWS GJT Office Area Forecast Discussion