Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 271646
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1046 AM MDT SUN JUL 27 2014

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 408 AM MDT SUN JUL 27 2014

HIGH PRESSURE WAS CENTERED ALONG THE SW CO/NW NM BORDER REGION
EARLY THIS MORNING...NOT FAR FROM WHERE IT WAS LOCATED YESTERDAY.
A WEAK SHORTWAVE ROTATING AROUND THE HIGH OVER EAST-CENTRAL UTAH
WAS RESPONSIBLE FOR PERSISTENT LIGHT SHOWERS OVER THE EASTERN
TAVAPUTS AND ROAN PLATEAUS. MEANWHILE...AN AREA OF DEFORMATION
BETWEEN THE HIGH CIRCULATION AND AN MCV OVER SOUTHEAST CO APPEARED
RESPONSIBLE FOR A WEAKENING SINGLE CELL STORM 30NM SOUTHWEST OF
KPSO AROUND 0830Z.

NAM APPEARED TO BEST HANDLE THESE FEATURES AND SUGGESTS THAT SOME
LIGHT CONVECTIVE ACTIVITY WILL CONTINUE OVER THE AFOREMENTIONED
AREAS PAST DAYBREAK. THE NORTHERN SHORTWAVE APPEARS TO LOSE SOME
ENERGY IN RESPONSE TO SHEARING FORCES...HOWEVER SHOULD STILL BE
CAPABLE OF GENERATING LATE MORNING SHOWERS AND AN EMBEDDED
THUNDERSTORM OVER PORTIONS OF NORTHWEST CO. ELSEWHERE...RESIDUAL
MONSOON MOISTURE AND DAYTIME HEATING WILL GENERATE SCATTERED
SHOWERS OVER THE MOUNTAINS FROM LATE MORNING THROUGH THE
AFTERNOON. 00Z/SUN KGJT SOUNDING PW VALUE DOWN CLOSE TO 0.1 INCHES
AS COMPARED TO YESTERDAY/S SOUNDING...BUT DOES NOT APPEAR THIS
WILL HAVE A PARTICULARLY NOTICEABLE IMPACT ON TODAY/S MOIST
CONVECTION. STORMS WILL CONTINUE TO BE SLOW MOVING AND CAPABLE OF
PRODUCING AREAS OF HEAVY RAIN WHICH MAY LEAD TO LOCALIZED FLASH
FLOODING OR MUD/DEBRIS FLOWS.

DECREASED ATMOSPHERIC MOISTURE WILL YIELD A BIT MORE SUNSHINE THAN
SATURDAY SO CONTINUED FORECAST FAVORING A FEW DEGREES OF WARMING
THIS AFTERNOON.

STORMS WILL LINGER THROUGH THE EVENING HOURS WITH ISOLATED HEAVY
RAINERS BEFORE WINDING DOWN BY MIDNIGHT WITH SOME OUTFLOW BOUNDARY
INTERACTIONS IN THE VALLEYS. A FEW ISOLATED STORMS MAY LINGER INTO
THE OVERNIGHT HOURS AS PRECIPITABLE WATER (PW) VALUES REMAIN NEAR
OR SLIGHTLY BELOW AN INCH WITH MINIMAL VALUES INDICATED ACROSS THE
NORTH WITH 0.8 INCHES. A DEEPER SURGE OF MONSOONAL MOISTURE
RETURNS FROM THE SOUTHWEST AROUND THE HIGH PRESSURE SITUATED OVER
NEW MEXICO...EAST OF THE FOUR CORNERS WHICH IS A PERFECT POSITION.
PW VALUES INCREASE WITH AN INCH TO 1.2 INCHES ACROSS MUCH OF THE
AREA. DEW POINTS ARE FORECAST TO BE IN THE UPPER 40S TO LOW 50S
WHICH IS NOT EXTREMELY HIGH BUT SUFFICIENT ENOUGH FOR AN INCREASE
IN SHOWER AND THUNDERSTORM DEVELOPMENT COMPARED TO SUNDAY. EXPECT
SCATTERED STORMS DEVELOPING FIRST OVER HIGHER TERRAIN AND DRIFTING
INTO VALLEYS LATER IN THE DAY WITH HEAVY RAIN EXPECTED AND
LOCALIZED FLOODING IN THE STRONGER STORMS. STEERING FLOW REMAINS
FAIRLY LIGHT SO NOT EXPECTING TO MUCH IN THE WAY OF MOVEMENT.

.LONG TERM...(MONDAY NIGHT THROUGH SATURDAY)
ISSUED AT 408 AM MDT SUN JUL 27 2014

...POTENTIAL FOR EXCESSIVE RAINFALL ON TUESDAY...

MONDAY NIGHT INTO TUESDAY IS WHEN THINGS GET VERY INTERESTING.  THE
MODELS HAVE BEEN VERY CONSISTENT OVER THE LAST 5 DAYS IN SHOWING AN
UPPER LEVEL WAVE OR SHORTWAVE TROUGH MOVING CLOCKWISE AROUND THE
AREA OF HIGH PRESSURE THROUGH THE FOUR CORNERS AND INTO EASTERN UTAH
AND WESTERN COLORADO DURING THE DAY ON TUESDAY.  THIS IS ALSO PAIRED
WITH A DEEPER SURGE OF MONSOONAL MOISTURE WITH PW VALUES ON AVERAGE
1.25 ACROSS THE REGION WITH THE HIGHEST AMOUNTS OVER LAKE POWELL
IN SE UTAH OF 1.5 INCHES. THIS UPPER LEVEL WAVE CAN CURRENTLY BE
SEEN ON WATER VAPOR IMAGERY AND IS VERY CLEARLY EVIDENT WHEN
LOOKING AT 5H-3H VORTICITY. THERE ARE TWO DISTINCT FEATURES ON
WATER VAPOR AS OF SUNDAY MORNING...A WAVE OVER EL PASO TEXAS
STRETCHING EAST TOWARDS THE OLD MEXICO-ARIZONA BORDER...AND
ANOTHER CYCLONIC CIRCULATION JUST OFF THE BAJA PENINSULA. 5H-3H
VORTICITY INDICATES THESE FEATURES MOVING FROM SOUTHWEST TO
NORTHEAST ACROSS ARIZONA AND MERGING OVER THE FOUR CORNERS MONDAY
NIGHT INTO TUESDAY MORNING. ON TUESDAY...THIS FEATURE MOVES
THROUGH NEVADA...UTAH AND WESTERN COLORADO.

SUFFICIENT MOISTURE IN PLACE COMBINED WITH THE SHORTWAVE TROUGH
MOVING THROUGH THE REGION WILL LEAD TO A VERY ACTIVE DAY IN TERMS OF
STORM DEVELOPMENT AS INSTABILITY ALSO REMAINS FAVORABLE.  DEW POINTS
ARE IN THE MID TO UPPER 50S AS WELL WHICH IS MORE THAN SUFFICIENT
FOR STRONGER STORMS AND VERY HEAVY RAIN POTENTIAL.  STEERING FLOW
AND SHEAR REMAIN FAIRLY LOW WITH STORM MOTION IN THE 5 TO 15 KT
RANGE.  BELIEVE MODELS ARE HAVING A TOUGH TIME WITH CONVECTION ON
THE LEADING EDGE OF THIS WAVE SO EXPECT STORMS TO CONTINUE THROUGH
MONDAY NIGHT IN ARIZONA AND NEAR THE FOUR CORNERS AND SPREAD
NORTHWARD AS THE WAVE MOVES THROUGH.  MAX TEMPERATURES WERE LOWERED
ON TUESDAY AS A RESULT OF INCREASED MOISTURE...CLOUD COVER AND
PRECIPITATION.  CONFIDENCE LEVEL IS FAIRLY HIGH WITH STRONGER STORMS
OCCURRING IN THIS ENVIRONMENT.  VERY HEAVY RAIN WITH POTENTIAL
DOWNPOURS AND FREQUENT LIGHTNING REMAIN THE BIGGEST THREATS.
THEREFORE...THERE IS A POSSIBILITY A FLASH FLOOD WATCH MAY BE
NEEDED ON TUESDAY AS STORM MOTION WILL ALSO BE FAIRLY MINIMAL. MUD
DEBRIS FLOWS AND ROCK SLIDES ARE POSSIBLE IN THE STEEPER TERRAIN.
CYCLING OF MOISTURE EXPECTED DURING THE REMAINDER OF THE WEEK WITH
MORE COMMONPLACE DIURNALLY DRIVEN SHOWERS AND THUNDERSTORMS EACH
DAY. TEMPERATURES EXPECTED TO TREND AT OR A LITTLE BELOW NORMAL
THROUGH SATURDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1046 AM MDT SUN JUL 27 2014

AN AREA OF SHOWERS HAS PERSISTED OVER THE EASTERN TAVAPUTS AND
ROAN PLATEAUS...AND WILL CONTINUE TO HOLD TOGETHER INTO THIS
AFTERNOON. AFTER 20Z STRONGER EMBEDDED CELLS MAY DEVELOP. OVER THE
REST OF THE FORECAST AREA...AFTERNOON HEATING WILL GENERATE
ANOTHER ROUND OF SCATTERED SHOWERS AND THUNDERSTORMS OVER THE
MOUNTAINS WHICH WILL DRIFT OVER ADJACENT VALLEYS DURING THE LATTER
PART OF THE AFTERNOON AND INTO THE EVENING. MONSOON MOISTURE IS
RATHER DEEP SO STORMS MOVING OVER TAF SITES WILL BRING BRIEF
PERIODS OF IFR VSBY AND POSSIBLY MVFR CIGS. MOUNTAIN OBSCURATIONS
WILL BE POSSIBLE IN SHOWERS AND LOW CLOUDS.

&&

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

$$

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



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