Special Weather Statement, NWS Denver/Boulder, CO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
300 PM MDT THU APR 07 2011

.SHORT TERM...FOR THE NEXT 3-6 HOURS...WILL CONTINUE TO MONITOR THE
WEAK CONVECTIVE EXPECTED TO FORM AHEAD OF A SFC BASED INSTABILITY
AXIS CURRENTLY CREEPING EASTWARD ACROSS ERN ELBERT...ERN ADAMS AND
ERN ARAPAHOE COUNTIES. SFC DEWPTS NOT ALL THAT IMPRESSIVE AHEAD OF
THIS BNDRY THUS ACCOUNTING FOR THE LOW CAPE VALUES /100-200J/KG
RANGE/ IN THE AREA AS PER THE RUC. RUC SHOWS THIS AREA OF WEAK CAPE
BACKING NEWRD TOWARDS THE SRN FOOTHILLS AND METRO AREA EARLY THIS
EVENING WITH A SHIFT TO SELY WINDS OVER SRN PORTIONS OF THE I-25
CORRIDOR. AT THIS TIME...SUSPECT MOST IF NOT ALL OF THE CONVECTION
DURING THE NEXT 6 HRS WILL REMAIN CONFINED THE HIGH PLAINS TO THE
SOUTH AND EAST OF DENVER. OTHERWISE...SHOULD SEE SPOTTY CONVECTION
WINDING DOWN BY MID-EVENING WITH THE FORMATION OF A WEAK/MODERATE
SFC BASED INVERSION. FARTHER OUT ACROSS THE NERN CORNER OF THE STATE
10-20KT SELY BNDRY LAYER WINDS OVERNIGHT WILL AGAIN RESULT IN AREAS
OF FOG AND STRATUS BY AS EARLY AS MIDNIGHT. VSBYS IN SOME AREAS EAST
OF A BRIGGSDALE TO LIMON LINE COULD AGAIN FALL BELOW 1/4 MILE BEFORE
MORNING LIGHT.

IN THE HIGH COUNTRY...AS MID-LEVEL MOISTURE STREAMS INTO THE AREA
FROM THE SOUTHWEST SHOULD SEE SHOWERS INCREASING IN COVERAGE
OVERNIGHT WITH THE PASSAGE OF A WEAK MID-LEVEL IMPULSE. S-SWLY
RIDGETOP FLOW LESS THAN FAVORABLE FOR OROGRAPHIC PCPN...SO ANY
ACCUMULATION WILL BE LIMITED TO AREAS UP AROUND TIMBERLINE. ALTHOUGH
SNOW LEVELS SHOULD FALL BELOW 8000 FEET MSL WEST OF THE CONTINENTAL
DIVIDE BY MORNING.

ON FRIDAY...AS THE UPPER TROUGH MOVES CLOSER...SFC AND UPPER LEVEL
FLOW WILL STRENGTHEN. THE DRY SLOT EVIDENT ON SATELLITE OVER ARIZONA
AT THIS TIME IS PROGGED TO MIGRATE NEWRD OVER THE FCST AREA DURING
THE DAY. LOW LEVEL MOISTURE ON THE PLAINS /FOG AND STRATUS/ WILL
RETREAT EASTWARD DURING THE MORNING AS S-SWLY WINDS SPREAD OFF THE
FRONT RANGE AND PALMER DIVIDE. BY MIDDAY...SHOULD SEE S-SWLY SFC
WINDS BECOMING PRETTY GUSTY ON THE PALMER DIVIDE...SRN FOOTHILLS AND
ACROSS SOUTH PARK. THROUGH THE AFTERNOON SHOULD SEE THESE DRY...WARM
AND GUSTY DOWNSLOPING WINDS FANNING OUT ONTO THE PLAINS WHICH WILL
LIKELY CREATE CRITICAL WILDLAND FIRE DANGER CONDITIONS...
PARTICULARLY IN AREAS SOUTH OF INTERSTATE 76. THEREFORE THE
FIREWEATHER WATCH FOR THIS PORTION OF THE CWFA HAS BEEN UPGRADED TO
A RED FLAG WARNING BEGINNING AT 18Z. FURTHERMORE SHOULD SEE
TEMPERATURES TOMORROW AS MUCH AS 5-7C ABOVE AVERAGE FOR THE
DATE.

.LONG TERM...UPPER LEVEL TROUGH WILL BE OVER SOUTHERN CALIFORNIA AT
12Z SATURDAY. THIS WILL CAUSE FLOW ALOFT OVER EASTERN COLORADO TO BE
SOUTH-SOUTHWEST. DRY AND WARM AIR WILL BE TRANSPORTED NORTH UNDER
THIS PATTERN. DECREASED POPS OVER THE MOUNTAINS FRIDAY NIGHT AND
EARLY SATURDAY DUE TO THE DRY AIR OVER THE AREA. CROSS SECTION NOT
SHOWING MUCH IN THE WAY OF MOISTURE. PLUS WITH FLOW ALOFT BEING
NEARLY PARALLEL TO THE MOUNTAINS...DO NOT EXPECT ANY OROGRAPHIC
SHOWERS. WILL START TO SEE MOISTURE MOVE OVER THE HIGH COUNTRY
SATURDAY AFTERNOON AS LIFT FROM APPROACHING TROUGH MOVES OVER THE
STATE. HIGHS ON SATURDAY WILL BE 10-15 DEGREES ABOVE NORMAL.
SOUTHWEST WINDS WILL BECOME GUSTY WITH GUSTS TO 40 MPH. THESE WINDS
COMBINED WITH LOW RELATIVE HUMIDITIES WILL RESULT IN HIGH FIRE
DANGER. EXCEPT FOR THE NORTHERN FOOTHILLS AND LARIMER COUNTY WHERE
WINDS WILL BE WEAKER...WILL GO AHEAD AND ISSUE FIRE WEATHER WATCH
FOR THE ALL THE LOWER ELEVATIONS BELOW 8000 FEET AND ALSO INCLUDE
PARK COUNTY.

STILL A LOT OF UNCERTAINTY WITH THE FORECAST FOR SATURDAY NIGHT AND
SUNDAY AS THE UPPER LEVEL LOW MOVES FROM THE DESERT SOUTHWEST TO THE
CENTRAL PLAINS. THE NAM...GFS...ECMWF AND GEM ALL HAVE DIFFERENT
TRACKS FOR THE UPPER LEVEL LOW. GENERAL CONSENSUS AMONG THE MODELS
IS TO THE TAKE THE LOW ACROSS FAR SOUTHEAST COLORADO AND EJECT
NORTHEAST INTO THE CENTRAL PLAINS. WILL INCREASE POPS OVER THE
MOUNTAINS WHERE THE MAIN QUESTION IS NOT IF BUT HOW MUCH SNOW.
EXPECT QG LIFT AND OROGRAPHIC LIFT TO PRODUCE SNOW SATURDAY NIGHT
AND SUNDAY. PRECIPITATION WILL SPREAD EAST ACROSS URBAN CORRIDOR
LATE SATURDAY NIGHT AND SUNDAY. FOR FOOTHILLS AND AREAS WEST OF I-25
ONLY EXPECT A QUICK SHOT OF MOISTURE AS NORTHWEST DOWNSLOPE FLOW
WILL CAUSE THE PRECIPITATION TO COME TO AN END QUICKLY. BETTER
CHANCE FOR PRECIPITATION WILL BE OVER THE EASTERN PLAINS WHERE LIFT
WILL BE BETTER. THE NAM IS THE STRONGEST WITH THIS SYSTEM AND HAS
THE MOST FAVORABLE TRACK FOR EASTERN COLORADO TO RECEIVE
PRECIPITATION. IF THE NAM PANS OUT BLIZZARD CONDITIONS WILL BE
POSSIBLE OVER THE EASTERN PLAINS. THE GFS AND GEM ARE THE WEAKEST
AND WARMEST. THEY ONLY PRODUCE A BRIEF PERIOD OF RAIN OVER THE
EASTERN PLAINS. EITHER WAY IT APPEARS THE EASTERN PLAINS WILL
RECEIVE MOISTURE AND WILL BUMP POPS UP INTO THE LIKELY RANGE.

ANY LINGERING SHOWERS WILL COME TO AN END SUNDAY NIGHT AS THE LOW
EXITS THE REGION. AN UPPER LEVEL RIDGE WILL MOVE OVER COLORADO ON
MONDAY BRINGING MILD AND DRY CONDITIONS. NEXT SYSTEM WILL MOVE INTO
THE WESTERN U.S. TUESDAY. GFS SHOWING A FRONT PUSHING INTO NORTH
COLORADO TUESDAY WHILE THE ECMWF KEEPS A SOUTHERLY FLOW OVER THE
EASTERN PLAINS. WILL GO MIDDLE OF THE ROAD WITH TEMPERATURES AND
HAVE LOW POPS IN THE FORECAST. THE TROUGH WILL SLOWLY MOVE EASTWARD
AND FINALLY BE EAST OF THE STATE ON THURSDAY. WILL CONTINUE WITH THE
TREND OF LOW POPS FOR TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. NOT AN
IMPRESSIVE SYSTEM AT THIS TIME SO EXPECT PRECIPITATION AMOUNTS TO BE
ON THE LIGHT SIDE. WILL DRY OUT THE FORECAST THURSDAY AS RIDGING
STARTS TO BUILD OVER THE REGION.

&&

.AVIATION...DENVER AREA AIRPORTS WILL SEE PREVAILING CEILINGS ABOVE
10 THOUSAND FT AGL NEXT 24 HOURS. HOWEVER IN THE NEXT 2-5 HOURS
AIRPORTS COULD SEE OCCASIONAL ILS CEILINGS IN THE 5000-6000 FT AGL
RANGE WITH ISOLATED RAIN SHOWERS PASSING TO THE SOUTH AND EAST OF
THE DENVER METRO AREA. AFTER 04Z...SHOULD SEE A RETURN TO VFR
CONDITIONS WITH THE DEVELOPMENT OF TYPICAL S-SWLY DRAINAGE
WINDS.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING FROM NOON TO 8 PM MDT FRIDAY FOR
COZ214-216-239>241-245>247-249.

FIRE WEATHER WATCH FROM SATURDAY AFTERNOON THROUGH SATURDAY
EVENING FOR COZ214-216-239>251.

&&

SHORT TERM...BAKER
LONG TERM...MEIER
AVIATION...BAKER

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DENVER CO
356 PM MDT THU APR 7 2011

COZ041-045-072230-
CENTRAL AND EAST ADAMS AND ARAPAHOE COUNTIES CO-
ELBERT/CENTRAL AND EAST DOUGLAS COUNTIES ABOVE 6000 FEET CO-
356 PM MDT THU APR 7 2011

THE NATIONAL WEATHER SERVICE IN DENVER HAS ISSUED A SIGNIFICANT
WEATHER ADVISORY FOR

  CENTRAL ARAPAHOE COUNTY
  SOUTH CENTRAL ADAMS COUNTY

AT 356 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
THUNDERSTORM CAPABLE OF PRODUCING MARBLE SIZE HAIL.  THIS STORM WAS
LOCATED 11 MILES SOUTHWEST OF STRASBURG...OR 32 MILES EAST OF
DENVER...MOVING NORTHEAST AT 20 MPH.

LOCATIONS IN THE ADVISORY INCLUDE BUT ARE NOT LIMITED TO STRASBURG
AND BYERS.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

COPIOUS AMOUNTS OF HAIL ARE POSSIBLE WITH THIS STORM WHICH MAY COVER
ROADWAYS...LEADING TO HAZARDOUS DRIVING CONDITIONS...INCLUDING I-70
EAST OF BENNETT.

&&

LAT...LON 3988 10437 3978 10409 3956 10428 3957 10449
TIME...MOT...LOC 2156Z 208DEG 17KT 3961 10437

BARJENBRUCH