Severe Thunderstorm Warning 132, NWS Denver/Boulder, CO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
300 PM MDT THU AUG 14 2008

.SHORT TERM...NEXT SHORTWAVE AHEAD OF MAIN UPPER LOW OVER MONTANA
CURRENTLY MOVING INTO NORTHERN COLORADO. BEGINNING TO SEE COVECTION
ACROSS MOUNTAINS IN RESPONSE TO INCREASING QG ASCENT. ACROSS
PLAINS...LOW LEVEL MOISTURE HAS INCREASED FROM OVERNIGHT OUTFLOW
WITH DEWPOINTS MAINLY IN 50S. GPS INTEGRATED PRECIPITABLE WATER
VALUES HAVE INCREASED TO AROUND SEVEN TENTHS OF AN INCH. WEAK SURGE
CURRENTLY MOVING ACROSS AREA HAS SHIFTED THE LOW LEVEL WINDS TO THE
NORTHEAST. THIS HAS PROVIDED A BETTER WIND SHEAR PROFILE WITH THE
NORTHWEST FLOW ALOFT. THUS...SEVERE WEATHER THREAT IMPROVED SLIGHTLY
AS A RESULT. LAPS SURFACE ANALYSIS AS WELL AS ACARS SOUNDINGS
INDICATING CAPE VALUES HAVE INCREASED TO AROUND 1000 J/JG. BUT STILL
LARGE AREA OF CIN TO OVERCOME. APPROACHING WAVE SHOULD BE ENOUGH TO
OFFSET CIN AND GET STORMS GOING. A FEW STORMS COULD REACH SEVERE
LIMITS THIS EVENING...PRODUCING HAIL AND DAMAGING WIND. THE UPPER
LOW PROGGED TO MOVE INTO NORTHERN WYOMING AROUND MIDNIGHT...WHICH
WILL CONTINUE TO SATURATE AIRMASS AND INCREASE UPSLOPE. WITH
INCREASING UPSLOPE AND DYNAMICS...SHOULD SEE SHOWERS INCREASE IN
COVERAGE ACROSS PLAINS AFTER MIDNIGHT. CURRENT LIKELY POPS FOR
FOOTHILLS AND PLAINS STILL ON TRACK...WITH LOWER POPS OVER
MOUNTAINS. 7H TEMPERATURES COOL TO AROUND +4 DEGREES CELSIUS BY 12Z
FRIDAY...COULD STILL SEE SOME SNOW SHOWERS ACROSS THE HIGHER
MOUNTAINS ABOVE 11000 FEET. MODELS SIMILAR IN TRACKING THE LOW INTO
NORTHWEST COLORADO BY LATE AFTERNOON FRIDAY. THIS TREK WILL INCREASE
AND DEEPEN EASTERLY FLOW WITH FAVORABLE UPSLOPE FOR AREAS EAST OF
THE CONTINENTAL DIVIDE AS WELL AS INCREASING QG ASCENT. CURRENT
LIKELY POPS FOR FOOTHILLS AND PLAINS THROUGH THE DAY FRIDAY STILL ON
TRACK. GIVEN THE INCREASING UPSLOPE AND QG ASCENT...DECIDED TO
INCREASE POPS FOR THE MOUNTAINS EAST OF THE CONTINENTAL DIVIDE TO
LIKELY FOR THE AFTERNOON AND UP POPS TO JUST BELOW CATEGORICAL FOR
FOOTHILLS AND ADJACENT PLAINS. GUIDANCE SHOWING HIGHS IN THE UPPER
50S TO MID 60S ACROSS THE PLAINS. CURRENT TEMPERATURE GRIDS HAVE
HIGHS IN THE 60S...A FEW DEGREES WARMER THAN GUIDANCE. WILL LEAVE
TEMPERATURE GRIDS AS IS FOR NOW.

.LONG TERM...MODELS CONTINUE IN UNCHARACTERISTIC AGREEMENT.  THE
ECMWF...NAM...AND GFS ALL HAVE THE UPPER CLOSED LOW CENTER OVER THE
NORTHWESTERN CORNER OF COLORADO AT 12Z SATURDAY MORNING.  THEY ARE
ALL RIGHT ON TOP OF ONE ANOTHER WITH THE FEATURE...HARD TO BELIEVE
AT 48 HOURS OUT.  NOW...ALL THREE HAVE THE CENTER OVER SOUTH
CENTRAL/CENTRAL COLORADO AT 12Z SUNDAY MORNING.  BY 12Z MONDAY
MORNING...THE FEATURE IS OVER THE SOUTHEASTERN CORNER OF COLORADO
ACCORDING TO THE ECMWF AND GFS.  THE QG VERTICAL VELOCITY FIELDS
HAVE DECENT UPWARD MOTION PROGGED OVER THE FORECAST AREA FRIDAY
NIGHT THROUGH SUNDAY AFTERNOON.  THE BOUNDARY LAYER FLOW IS MAINLY
EAST-SOUTHEASTERLY THROUGH THE PERIODS.  THE CROSS SECTIONS NEVER
SHOW ANY DOWNSLOPING OFF THE MOUNTAINS THROUGH THE PERIODS.  FOR
MOISTURE...MODELS HAVE DEEP MOISTURE OVER MUCH OF THE FORECAST AREA
WELL INTO SUNDAY.  PRECIPITABLE WATER VALUES RANGE FROM ABOUT 0.80
TO 1.20 INCH THROUGH ALL THE PERIODS.  DEW POINTS STAY IN THE MID
40S TO MID 50S F FOR THE PLAINS AND FOOTHILLS FRIDAY NIGHT THROUGH
SUNDAY EVENING.  THE QPF GRIDS ARE LOADED WITH MEASURABLE RAINFALL
THROUGH SUNDAY.  LAPSE RATES ARE SHOWING THE LOWER LEVELS TO BE
PRETTY STABLE...BUT THE MID LEVELS ARE LESS CAPPED.  THE THETA-E
AXIS STAYS OVER CENTRAL COLORADO THROUGH THE PERIODS AFFECTIVE THE
WESTERN QUARTER OF THE FORECAST AREA ONLY.  THERE IS ONLY A BIT OF
CAPE OVER THE HIGH MOUNTAINS AND NORTHEAST CORNER FRIDAY EVENING
THROUGH SATURDAY NIGHT.  THERE IS MORE CAPE FOR LATE DAY SUNDAY OVER
MUCH OF THE FORECAST AREA...BUT NOTHING SUBSTANTIAL.  WILL KEEP POPS
HIGH AND WILL NEED MORE SATURDAY NIGHT WELL INTO SUNDAY.  CONCERNING
SNOW...FORECAST SOUNDINGS AGAIN SHOW THE WET BULB ZERO HEIGHTS LOW
ENOUGH TO WARRANT THE MENTION OF SNOW MIXED IN OVER THE HIGH
MOUNTAINS BOTH FRIDAY OVERNIGHT AND SATURDAY OVERNIGHT.  FOR
TEMPERATURES...SATURDAYS HIGHS ARE SIMILAR TO FRIDAYS.  SUNDAYS
HIGHS ARE 2-5 C WARMER THAN SUNDAYS.  FOR THE LATER DAYS...MONDAY
THROUGH THURSDAY...MODELS ARE SHOWING THE UPPER CLOSED LOW LINGERING
JUST TO OUR EAST-SOUTHEAST WELL INTO TUESDAY.  AN UPPER RIDGE MOVES
IN FROM THE WEST FOR THE LAST TWO DAYS.  IT CONTINUES TO LOOK DRIER
WITH WARMING TEMPERATURES TOWARDS THE END.  HOWEVER...NO TELLING HOW
LONG THE MODELS WILL CONTINUE TO STALL THE CLOSED LOW IN OUR
VICINITY?

&&

.AVIATION...SCATTERED THUNDERSTORMS EXPECTED THROUGH 06Z...COULD
AFFECT AREA AIRPORTS WITH GUSTY WINDS AND BRIEF HEAVY RAIN. SURFACE
WINDS TO REMAIN NORTH TO NORTHEASTERLY THROUGH FRIDAY. CONTINUED LOW
LEVEL MOISTURE WITH RAIN SHOWERS INCREASING IN COVERAGE AFTER 06Z
ALONG WITH ISOLATED THUNDERSTORMS...CONTINUING THROUGH THE DAY
FRIDAY. POTENTIAL FOR MVFR CONDITONS BETWEEN 06Z AND 15Z.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...NONE.

&&

D-L/RJK

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