Winter Storm in Colorado, May 4 to 5, 2001

SOUTH CENTRAL AND SOUTHEAST COLORADO AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PUEBLO COLORADO
230 PM MDT FRI MAY 4 2001

...MAIN PROBLEM IS SNOW POTENTIAL TONIGHT AND SATURDAY MORNING...

CURRENTLY...UPPER LOW SPINNING NEAR THE FOUR CORNERS WITH SOME
CONVECTION DEVELOPING AROUND THE UPPER LOW CENTER.  OVER OUR
SOUTHWEST AND CENTRAL MOUNTAINS...THE HEAVIER SNOW HAS ENDED WITH
SNOW SHOWERS REMAINING.  ECHO COVERAGE OVER THE EASTERN PLAINS IS
BEST NEAR THE EASTERN BORDER AND OVER THE PLAINS TO THE NORTH OF OUR
CWA.  SURFACE PRESSURE PATTERN IS SHOWING AN INVERTED TROUGH OVER
WESTERN KANSAS.  WINDS AT MOST PLAINS LOCATIONS ARE FROM THE
NORTHWEST.

THE MAJOR PROBLEM FOR TONIGHT AND INTO SATURDAY IS THE MOVEMENT OF
THE UPPER LOW AND THE EVOLUTION OF THE SURFACE FEATURES ON THE
PLAINS.  IN THE MOUNTAINS...THE 18Z RUC CONTINUES THE IDEA OF SOME
TYPE OF DEFORMATION BAND DEVELOPING SOMEWHERE AROUND THE SOUTHWEST
MOUNTAINS.  WHEN THE BAND DEVELOPS...THE 700MB WIND TURNS TO THE
EAST...WHICH IS UNFAVORABLE FOR THE SOUTHWEST MOUNTAINS. IN PAST
EXPERIENCES...I HAVE SEEN A LOCALIZED BAND OF SIGNIFICANT SNOW
OCCUR WITH THESE BANDS.  WITHOUT FAVORABLE OROGRAPHICS...IT IS
DIFFICULT TO GET WIDESPREAD SIGNIFICANT PRECIPITATION. IF
ANYTHING...WEAK NORTH TO NORTHWEST FLOW IS UNFAVORABLE FOR ZONES 60
AND 61. IN ZONES 58 THROUGH 61...I WILL CONTINUE SNOW SHOWER/PERIODS
OF SNOW THROUGH THE NIGHT WITH ACCUMULATIONS BELOW ADVISORY
CRITERIA.  I DO HAVE A LITTLE CONCERN FOR THE EAST SIDE OF THE SAN
LUIS VALLEY...WHICH SOMETIMES HAS UPSLOPE WITH DEEP EASTERLY FLOW.
FOR NOW...I WILL MENTION SOME ACCUMUALTIONS ESPECIALLY ON THE WEST
SIDE OF THE SAN LUIS VALLEY.

OVER THE EASTERN PLAINS AND SOUTHEAST MOUNTAINS...THE MAIN CONCERN
IS FOR SNOWFALL AMOUNTS ON THE EAST SLOPES OF THE MOUNTAINS.  THE
RUC IS CONTINUING THE TREND OF HAVING AN INVERTED TROUGH DEVELOP
OVER THE SOUTHEAST PLAINS OVERNIGHT.  THESE INVERTED TROUGHS TEND
TO DIMINISH THE PRECIPITATION AMOUNTS FOR EASTERLY OROGRAPHICS.  IN
ADDITION...THE RUC HAS WEAKER NORTHEAST FLOW THAN THE 12Z ETA AND
MESOETA.  I BELIEVE THE ETA PRECIPITATION FOR THE SOUTHEAST
MOUNTAINS MAY BE OVERDONE...ESPECIALLY FROM THE WET MOUNTAINS
SOUTHWARD.  ETA HAS ALMOST 1 INCH OVERNIGHT...WHILE THE MESOETA HAS
0.6 TO 0.8 INCHES.  ISENTROPIC UPGLIDE APPEARS TO BE BETTER FROM EL
PASO COUNTY NORTHWARD TONIGHT.  WITH THE APPARENT LESS FAVORABLE
CONDITIONS FURTHER SOUTH...I WILL MAINTAIN THE SNOW ADVISORY FOR
TONIGHT OVER THE WET MOUNTAINS AND SANGRE DE CRISTO MOUNTAINS.  EVEN
IF SOME LOCATIONS RECEIVE MORE THAN 8 INCHES...THE VERY WARM GROUND
WILL MINIMIZE THE EFFECT ESPECIALLY OVER ROAD SURFACES.  TELLER
COUNTY IS CLOSER TO THE BETTER DYNAMICS AND DEEPER NORTHEAST
FLOW...AND I WILL CONTINUE THE WARNING FOR TONIGHT.  IF THE UPPER
LOW SLOWS MORE THAN FORECAST...THE HIGHLIGHTS MAY HAVE TO BE
EXTENDED INTO THE MORNING.

ON SATURDAY...UPPER LOW WILL MOVE ACROSS THE SOUTHEAST PLAINS DURING
THE MORNING.  PLENTY OF MOISTURE ON THE BACK SIDE OF THE SYSTEM. ETA
IS PRINTING OUT A FAIR AMOUNT OF QPF.  TEMPERATURES ALOFT CONTINUE
TO WARM AND FLOW IS NOT FAVORABLE FOR OROGRAPHICS EXPECT FOR TELLER
COUNTY. OVER THE MOUNTAINS...NORTHERLY FLOW IS NOT THAT FAVORABLE
FOR ANY OF OUR MOUNTAIN RANGES.  I EXPECT PLENTY OF SNOW SHOWERS TO
CONTINUE OVER THE MOUNTAINS...BUT I DO NOT EXPECT WIDESPREAD AMOUNTS
ABOVE ADVISORY CRITERIA.  THE DEFORMATION BAND THAT DEVELOPS APPEARS
TO STAY NORTH AND WEST OF OUR FORECAST AREA.  SPC HAS SLIGHT RISK
EAST OF THE BORDER.  I WILL NOT MENTION ANY SEVERE IN THE ZONES.

FOR SATURDAY NIGHT AND SUNDAY...UPPER LOW IS SLOW TO LEAVE THE
REGION. MODEL SOUNDING STILL SUGGEST ENOUGH MOISTURE FOR SOME
SHOWERS ON THE PLAINS WITH SHOWERS IN THE MOUNTAINS.

IN THE EXTENDED...NORTHWEST FLOW WITH EMBEDDED DISTURBANCES WILL
CONTINUE THROUGH THE PERIOD.  NCEP THINKS THAT TIMING AND STRENGTH
OF DISTURBANCES IS VERY DIFFICULT GIVEN THE TRANSITIONAL PATTERN OF
THE FLOW.  CURRENT EXTENDED WITH SOME SHOWERS EACH DAY AND
LOOKS OK AND MATCHES MEX.

NOTE ON RIVERS...UPPER ARKANSAS RIVER VALLEY HAS 2 TO 4 INCHES
OF LIQUID FROM THIS PAST EVENT.  ABRFC RAN MODELS WITH CURRENT NCEP
TEMPERATURE FORECASTS.   IF COOL WEATHER WEATHER CONTINUES AS
EXPECTED...THEN NO MAJOR PROBLEMS ARE ANTICIPATED AT THIS TIME...BUT
STAYY TUNED FOR ANY CHANGES.

.PUB...SNOW ADVISORY TONIGHT...ZONES 65.66.70
       WINTER STORM WARNING TONIGHT FOR ZONE 67

WOLYN