Winter Weather in Colorado, April 29 to 30, 2004

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
400 AM MDT THU APR 29 2004

.SHORT TERM (TODAY-FRIDAY)...STORM SYSTEM CENTERED OVER WESTERN
UTAH WILL CONTINUE TO DICTATE WEATHER FOR THE FORECAST AREA TODAY
THROUGH FRIDAY. UPPER CIRCULATION CENTERED OVER NORTHWEST UTAH EARLY
THIS MORNING WITH JET STREAMING NORTHEASTWARD ACROSS EASTERN UT AND
INTO WY. MEANWHILE...LATEST SATELLITE COMBINED WITH RUC SURFACE
ANALYSES AND STATION DATA DEPICTED THE SURFACE FRONT JUST SOUTH OF
PUB ON THE EASTERN PLAINS WEST TO GUC DRAPED ACROSS THE NORTHERN FACE
OF THE SAN JUAN MOUNTAINS TO SOUTH OF PGA IN NORTHEAST AZ. SATELLITE
AND RADAR INDICATED OVERRUNNING SITUATION ACROSS THE CENTRAL MTNS
WITH ISOLATED TO WIDELY SCATTERED LIGHT SHOWERS ONGOING. MOST
PERSISTENT SHOWER ACTIVITY WEST OF A LINE FROM RKS TO PUC BENEATH
VIGOROUS JET. SHOWERS OVER MUCH OF THE CWFA EARLY THIS MORNING WERE
LIGHT AND MUCH OF WHAT APPEARS IN RADAR IMAGERY APPEARED TO BE VIRGA
AS LOWER LEVELS DRY.

TODAY: MESOETA DEPICTED FRONTAL POSITION NICELY AT 06Z...SO MODEL
CONFIDENCE GOOD FOR THE EARLY PERIODS. GFS AND ETA BOTH INDICATE
UPPER LOW WILL SLOWLY FILL AS THE SYSTEM DROPS SOUTH ACROSS WESTERN
UTAH DURING THE DAY. BEST CHANCES FOR PRECIPITATION WILL CONTINUE
TO BE ALONG A LINE FROM PUC TO RKS THIS MORNING. CONSEQUENTLY...CUT
POPS BACK ACROSS MUCH OF WESTERN CO AND SOUTHEAST UTAH FOR THE
EARLY PART OF THE DAY. STRONG VORT LOBE ROTATING THROUGH THE BASE OF
THE TROF FROM MIDDAY THROUGH THE AFTERNOON WILL DRIVE THE COLD FRONT
EASTWARD ACROSS THE REMAINDER OF THE CWFA. STRONG 7H FLOW...TIGHT
SURFACE GRADIENT AND JET SWEEPING NORTHWARD OVERHEAD WILL RESULT IN
ADVISORY LEVEL WINDS AGAIN ACROSS THE SOUTHWEST CORNER OF THE CWFA
THIS AFTERNOON. WILL GO AHEAD WITH ADVISORY FOR UT ZONE 22 AND CO
ZONE 21. ELSEWHERE...DEEP MOISTURE NORTH COMBINED WITH UPPER LEVEL
FORCING AND GOOD NORTHEAST FLOW ENOUGH TO KEEP SNOW ACCUMULATING
ACROSS THE EASTERN UINTA MOUNTAINS AND WILL CONTINUE WWA ALREADY IN
EFFECT. MEANWHILE...WILL INCREASE POPS FOR THE REMAINDER OF THE CWFA
THIS AFTERNOON AS PVA...JET DIVERGENCE AND DIURNAL WARMING RESULT IN
INCREASED SHOWERS ACROSS THE AREA. WITH FRONT MOST OF THE WAY
THROUGH THE CWFA AND SHOWERS AND VIRGA INCREASING...EXPECT HIGHS TO
BE SIGNIFICANTLY LOWER THAN YESTERDAYS.

TONIGHT: VORT LOBE DISCUSSED ABOVE ROTATES ACROSS THE SAN JUAN
MOUNTAINS WHERE GOOD SOUTHERLY FLOW...PVA AND JET DIVERGENCE WILL
COMBINE TO BRING SNOW TO THE MOUNTAINS. COULD SEE A QUICK 3 TO 6
INCHES THIS EVENING WITH LIGHTER ACCUMS LATER TONIGHT. FOCUS FOR
SNOW SHIFTS NORTH AFTER MIDNIGHT...SO KEPT ACCUMS BELOW ADVISORY
CRITERIA AND WILL ENCOURAGE NEXT SHIFT TO TAKE A FRESH LOOK AT THIS
DEVELOPING SITUATION FOR POSSIBLE HIGHLIGHTS. UPPER LOW PUSHES
EASTWARD LATE WITH WRAP-AROUND BEGINNING TO AFFECT THE CENTRAL
MOUNTAINS AND NORTHERN PLATEAUS. AGAIN...QPF INDICATES POSSIBLE
ADVISORY LEVEL SNOW FOR THESE AREAS FROM MIDNIGHT THROUGH
MIDDAY FRIDAY. AGAIN...PUSHED SNOW ACCUMULATIONS TOWARD ADVISORY
LEVEL...BUT WILL LET LATER SHIFTS DETERMINE WEATHER ADVISORY IS
JUSTIFIED. CAA WILL CONTINUE OVERNIGHT...BUT CLOUDS AND MOISTURE
WILL MODERATE LOWS.

FRIDAY...AS ALLUDED TO ABOVE...WRAP-AROUND WILL KEEP BEST CHANCES
FOR SHOWERS ACROSS THE CENTRAL PORTION OF WESTERN COLORADO. LOW
CONTINUES TO TRACK EASTWARD...OPENING AND PUSHING EAST OF THE DIVIDE
LATE IN THE DAY. DRYING WILL WORK INTO THE NORTHWESTERN CORNER OF THE
CWFA...WHILE DRY AIR WRAPS INTO THE LOW ACROSS THE SOUTH.
TEMPERATURES WILL REMAIN COOL FOR THIS TIME OF YEAR.

.LONG TERM (FRIDAY NIGHT THROUGH WEDNESDAY)...AFTER A COOL FRIDAY
NIGHT...WARMER AND DRY  AS A BROAD RIDGE BUILDS OVER THE
REGION.

FRIDAY NIGHT...ANOTHER NIGHT OF POSSIBLE FROST DAMAGE...
MODELS IN GOOD AGREEMENT WITH THE CLOSED LOW PHASING WITH THE
NORTHERN BRANCH AND EXITING EAST. LOW POPS REMAIN NEAR THE
CONTINENTAL DIVIDE IN POSSIBLE WRAP-AROUND OR JET-INDUCED RIPPLES IN
NW FLOW. IN EASTERN UTAH AND FAR WESTERN COLORADO...CLEAR SKIES AND
SFC HIGH PRESSURE THREATEN TEMPERATURES APPROACHING FREEZING. SOME
EAST TO WEST SFC PRESSURE GRADIENT SUGGESTS DRAINAGE WINDS WILL
PROTECT ALL BUT THE VALLEY BOTTOMS.

SATURDAY...THE BACKSIDE JET NOSES INTO NW COLORADO. TEMPERATURE
ADVECTION REMAINS NEUTRAL BUT LOW POPS ARE WARRANTED IN THE
CONTINENTAL DIVIDE ZONES. TEMPERATURES WILL REMAIN BELOW NORMAL.

SUNDAY AND MONDAY...WEST COAST RIDGE WILL GRADUALLY APPROACH WITH
DRY AND MUCH WARMER CONDITIONS DEVELOPING. MAX TEMPS BY MONDAY WILL
REACH THE 80S OVER THE VALLEYS OF SE UTAH/SW COLORADO.

TUESDAY AND WEDNESDAY...MEDIUM RANGE MODELS SUGGEST A CHANGE IN THE
PATTERN BY MIDWEEK AS A PAC NW TROUGH MOVES INLAND. THE UPPER RIDGE
WILL SLIDE EAST OF THE AREA...INCREASING SOUTHWEST FLOW ACROSS THE
FORECAST AREA AND POTENTIALLY MID/HIGH LEVEL PACIFIC MOISTURE.
TEMPERATURES WILL ALSO COOL SEVERAL DEGREES FROM MONDAY. AT THIS
POINT...WILL KEEP THINGS DRY.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
.CO...WIND ADVISORY FOR COZ21.
.UT...WIND ADVISORY FOR UTZ22.
      WINTER WEATHER ADVISORY CONTINUES TODAY FOR UTZ23.

NL/DJN/JOE

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