Damaging Winds in Colorado, April 20, 2001

NORTHEAST AND NORTH CENTRAL COLORADO AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER COLORADO
230 PM MDT FRI APR 20 2001

SHORT TERM DISCUSSION:  TROF AXIS MOVING ACROSS THE MOUNTAINS NOW
WILL BRING AN END TO THE SHOWERS...BUT THERE WILL BE A BOUT OF
STRONG WEST WINDS IN ITS WAKE.  LACK OF ANY SOURCE OF WAVE
AMPLIFICATION PRECLUDES TOO MUCH OF A HIGH WIND THREAT.  THERE IS
ALREADY PLENTY OF WIND IN THE ZONES AND I WILL NOT CHANGE MUCH.
GUIDANCE TEMPS LOOK TOO LOW FOR A BREEZY NIGHT...THOUGH THE WINDS
WILL DROP OFF UNDER CLEAR SKIES AFTER MIDNIGHT.     GIMMESTAD

LONG TERM DISCUSSION:  LARGE SCALE PATTERN LOOKING SIMILAR TO PCPN
MAKERS OF THE PAST FEW WEEKS.  TIGHTLY WOUND MID-LVL CYCLONE DIVING
SEWRD JUST OFF NRN CA COAST HAS POTENTIAL TO BE A BIG SNOW MAKER FOR
PARTS OF OUR CWA DURING LATTER HALF OF WEEKEND.  ONCE AGAIN MODELS
PROVIDING CONFLICTING SIGNALS AS LATEST GLOBAL CANADIAN AND AVN
MODELS HV DELAYED ARRIVAL OF WEST COAST STORM SYSTEM BY AS MUCH AS
12 HRS. WHEREAS ETA AND NGM APPEAR LITTLE CHANGED FM PREVIOUS RUN.
OVERALL...MODELS TRACK H5 LOW ACRS SRN CA/AZ DURING THE DAY SAT WITH
U/A SWLY FLOW AHEAD OF LOW ON THE INCREASE.  TEMPS STAY ON THE MILD
SIDE IN THE HIGH COUNTRY SAT WITH PROGD H7 TEMP AT 00Z/SUN NR 0C
EQUATING TO MAX TEMPS IN THE 40S/LOWER 50S BEFORE AFTN SHWRS PUT AN
END TO HEATING.  ON THE PLAINS...SAT LOOKS COOLER WITH CLOUD COVER
AND THE ARRIVAL OF THE FIRST OF TWO COLD FRONTS.  FIRST COLD AIR
SURGE PROGD TO ARRIVE IN THE DEN METRO AREA AROUND 15Z/SAT. NOT MUCH
LOW LVL MOISTURE WITH ITS ARRIVAL BUT AS UPSLOPE FLOW DEEPENS
THROUGH THE DAY WITH SFC LOW FORMING IN SERN CO SHOULD SEE SNOWSHWRS
BLOOMING OVR THE MTNS AND FTHLS AND SCT RAIN SHWRS ON THE PLAINS
DURING THE AFTN.  THATS WHERE THE MODELS DIVERGE. 12Z/FRI ETA SHOWS
A REINFORCING SURGE OF COLD AIR ARRIVING IN THE DEN METRO AREA
AROUND 06Z/SUN WITH NELY SFC WINDS OF 15-30KTS ACRS NERN PLAINS.
ETA SHOWS RAIN ON THE PLAINS QUICKLY CHANGING TO SNOW SAT EVE WITH
COLD AIR RAMMING DOWN THE FRONT RNG.  BY LATE SUN AFTN ETA CRANKS
OUT AS MUCH AS 10 INCHES OF WET SNOW FOR PORTIONS OF FNT RNG FTHLS
AND URBAN CORRIDOR.  ON THE FLIP SIDE NGM A BIT SLOWER WITH ONSET OF
COLD AIR AND SNOWFALL.  STILL NGM SHOWS SOME PRETTY DECENT SNOW AMTS
FOR PARTS OF CWA BY 12Z/SUN.  WHEREAS AVN AND GLOBAL CANADIAN MODELS
DELAY ARRIVAL OF SNOW.  MATTER OF FACT...AVN NEVER REALLY COOLS SFC
TEMPS ENOUGH FOR SNOW ON THE PLAINS UNTIL MAYBE SUN AFTN AS STG ELY
UPSLOPE FLOW DVLPS WITH UPR LOW PASSES OVR SERN CO.  THIS IS A REAL
HEAD SCRATCHER.  SINCE MODELS LOOKING SO DIFFERENT...WILL MAKE ONLY
MINOR ADJUSTMENTS TO CURRENT FCST PACKAGE TO AVOID FLIP-FLOPPING.

IN THE EXTENDED PERIOD...DEPENDING ON WHEN THE WEEKEND STORM EXISTS
THE AREA SHOULD SEE DRIER CONDITIONS BY MON NGT WITH UPR-LVL TROF
OPENING UP AND MOVG EAST OF THE STATE.  WITH SKIES CLEARING AND SNOW
CVR COULD SEE A HARD FREEZE MON NGT.  TUE AND WED...SEE SLOW WARMING
WITH A SLGT CHC OF AFTN SHWRS TUE AFTN.  BAKER

.DEN...NONE.

COZ030>051-202000-

SIGNIFICANT WEATHER OUTLOOK FOR NORTHEAST AND NORTH CENTRAL COLORADO
NATIONAL WEATHER SERVICE DENVER CO
1215 PM MDT FRI APR 20 2001

THIS OUTLOOK PERTAINS TO THE FOLLOWING COLORADO COUNTIES

ADAMS     ARAPAHOE     BOULDER   CLEAR CREEK   DENVER       DOUGLAS
ELBERT    GILPIN       GRAND     JACKSON       JEFFERSON    LARIMER
LINCOLN   LOGAN        MORGAN    PARK          PHILLIPS     SEDGWICK
SUMMIT    WASHINGTON   WELD

SYNOPSIS:  A VIGOROUS SPRING WEATHER SYSTEM WILL MOVE ACROSS THE
AREA THIS AFTERNOON.  WIDESPREAD SHOWERS AND THUNDERSTORMS IN THE
MOUNTAINS WILL DECREASE BY LATE AFTERNOON.  ON THE PLAINS ISOLATED
SHOWERS AND THUNDERSTORMS ARE EXPECTED.  WINDS WILL INCREASE FROM
THE SOUTHWEST AND THEN SHIFT TO THE WEST BY THIS EVENING.  SPEEDS OF
20 TO 35 MPH WILL BE COMMON...WITH GUSTS TO 60 MPH ALONG THE EAST
SLOPES OF THE MOUNTAINS AND NEAR SOME OF THE THUNDERSTORMS.

OUTLOOK FOR SATURDAY:  SCATTERED AFTERNOON SHOWERS AND THUNDERSTORMS
BUT LESS WIND.

GIMMESTAD