Blizzard in Colorado, April 11, 2001

NORTHEAST AND NORTH CENTRAL COLORADO AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER COLORADO
315 AM MDT WED APR 11 2001...UPDATE

SHORT TERM DISCUSSION:  HAVE HAD JUST ABOUT EVERY KIND OF WX TO
DEAL WITH TNGT WITH TSTMS...GRAUPEL...RAIN...SNOW AND WIND.  ONLY
THING HAVENT HAD IS A NICE SUBTROPICAL TRADE WIND I COULD ENJOY
WHILE ON A VERANDA SIPPING SASPARILLA.  ALL THIS WX COURTESY OF A
DEEP AND NEARLY VERTICALLY STACKED LOW MOVING ACROSS SERN CO INTO
SWRN KS.  HAVE HAD SVRL CNVRGNC BANDS WITH EMBEDDED TSTMS ON RADAR
WHERE SNOW HAS BEEN DUMPED AT 2 INCHES PER HOUR.  OTHER AREAS ARE
GETTING 1/2 TO 1 INCH PER HOUR.  WITH CAA LOWERING FRZG LVL OVER FAR
NERN CO EXPECT RAIN TO CHNG OVER TO SNOW IN AKO AND POINTS E BY TIME
ZONES GO OUT.  MDLS ALL AGREE THAT SNOWFALL TO PICK UP IN NERN ZNS
WITH ANYWHERE FROM 3 TO 10 INCHES BTWN 12Z AND 00Z THIS AFTN. LESS
ACCUM ALG FNT RANGE AND IN FTHLS AS LOW LVL WINDS ALREADY FROM NW
WHICH IS DWNSLP.  WITH RECENT WARM TEMPS BLV GOOD AMOUNT OF MELTING
TO OCCUR SO WILL UNDERCUT THESE AMTS BUT STILL LOOKS LIKE 4-8 INCHES
POSSIBLE WHICH IS WITHIN THE CRITERIA FOR HVY SNOW ON PLAINS.

QUESTION IS WHAT TO DO ABOUT THE HIGHLIGHTS. SEE NO REASON TO DROP
WINTER STORM WARNING YET AS BEST SNOW AND STGST WINDS YET TO ARRIVE
OVER MOST OF PLAINS ZONES.  WITH NWLY WINDS NOW OBSERVED ALG THE
FTHLS AND I-25 CORRIDOR AS LOW PULLS INTO SWRN KS WILL LOWER SNOW
AMTS A LITTLE FOR THESE ZONES AND WILL PSBLY DOWNGRADE WRNG TO
SNOW/BLOWING SNOW ADVSY.  WILL WAIT TIL LAST MINUTE AND SEE WHAT
RADAR/METARS ARE SHOWING AT 4 AM. AS FOR MTNS INTERESTING THAT
RADAR DOES NOT SHOW MUCH ACTVTY...YET HAVE A GOOD COLD BACKWASH
CLOUD SHIELD IN PLACE OVER THAT AREA THAT SHUD BE PRODUCING A
DECENT AMT OF SNOW.  CALL TO EISENHOWER TUNNEL CONFIRMS MOD TO
HVY SNOW...THRFR WILL LEAVE WARNING IN PLACE FOR MTNS AS WELL.
SEE NO REASON TO LOWER WIND SPEEDS IN FCST.  TEMP FCSTS IN
BALLPARK WHICH MEANS MOS GDNC TEMPS ABT 10 DEGS TOO WARM.

UPON FURTHER REVIEW HAVE DECIDED TO DOWNGRADE TO SNOW AND BLOWING
SNOW ADVISORY FOR ZONES 38 AND 39 THIS MORNING.  SNOW ON THE
DECLINE AS WINDS IN THESE AREAS NOW BECOMING DOWNSLOPISH.
007

LONG TERM DISCUSSION...MODELS CONTINUE TO BE IN FAIRLY GOOD
AGREEMENT THROUGH THE MEDIUM RANGE.  WRAP AROUND MOISTURE WILL
PERSIST ACROSS THE NORTHEASTERN PLAINS THIS EVENING BEFORE WINDING
DOWN.  ELSEWHERE...SHORT WAVE H5 RIDGE WILL BE OVER THE AREA BUT
RESPITE IN THE WEATHER WILL BE BRIEF.  RIDGE WILL BE DIRTY AS
OVERRUNNING MOISTURE STARTS TO INCREASE AHEAD OF THE NEXT SYSTEM
WHICH IS EXPECTED TO MOVE ACROSS NORTHERN COLORADO THU AND THU
NIGHT.  THIS SYSTEM WILL NOT BE AS COLD OR AS POTENT AS THE ONE
TODAY.  FOR THE MOUNTAINS...SNOW WILL REDEVELOP TONIGHT AHEAD OF THE
TROUGH AND CONTINUE THROUGH THURSDAY NIGHT.  ALTHOUGH THIS SYSTEM IS
WEAKER...SEVERAL FACTORS SHOULD AMOUNT FOR SOME DECENT MOUNTAIN
SNOWFALL.  WEAK BUT PERSISTENT H7-H3 QG ASCENT...GOOD MID LEVEL
INSTBY (7-8C/KM) AND FAVORABLE OROGRAPHIC (DIRECTIONAL) COMPONENT.
WOULD NOT BE SURPRISED TO SEE SOME ADVISORY CRITERIA TYPE SNOW.  WL
LET LATER SHIFTS DEAL WITH THIS POTENTIAL PROBLEM.  IN THE PLAINS
...SFC WINDS BECOME MORE SOUTHEASTERLY WITH GOOD DENVER CYCLONE
DEVELOPING BY THU AFTERNOON.  LOW LEVEL THETA-A RIDGE ORIENTED OVER
MUCH OF EASTERN COLORADO AT 00Z FRI...THEN THIS AXIS SHIFTS EAST
THROUGH THE EVENING.  ETA SOUNDING FOR THIS TIME FRAME RANGE FROM
200-400 J/KG ALONG THE URBAN CORRIDOR TO 400-800 J/KG IN THE
PLAINS.  SO GOOD THUNDERSTORMS POTENTIAL THU AFTERNOON INTO THU
NIGHT.  AS FOR FRI...DRIER ZONAL FLOW WILL BE OVER THE AREA AS THE
SYSTEM SHIFTS NORTH.  A FAST MOVING SHORT WAVE EMBEDDED IN THIS FLOW
BRUSHES NORTHERN COLORADO SATURDAY SO WILL ADD A CHANCE OF SHOWERS
TO THE MOUNTAINS AT THAT TIME.  MRF DOES INDICATE A SURGE ALONG WITH
SOME PCPN MONDAY NIGHT INTO TUESDAY FOR THE PLAINS.  WL KEEP DRY FOR
NOW...BUT THIS MAY CHANGE IF NEXT RUN IS CONSISTENT WITH THIS
SOLUTION.  COOPER

.DEN...WINTER STORM WARNING THIS MORNING...40>45.
    ...WINTER STORM WARNING TODAY..ZNS 30..32>34..37.
    ...WINTER STORM WARNING TODAY..ZNS 46..48>50.
    ...SNOW AND BLOWING SNOW ADVISORY THIS MORNING...38 AND 39.