Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 171543
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
943 AM MDT FRI APR 17 2015

.UPDATE...
ISSUED AT 925 AM MDT FRI APR 17 2015

CENTER OF UPPER LEVEL LOW IS SLOWLY CREEPING EAST ACROSS FAR
SOUTHERN COLORADO. IT WILL LIFT NORTHEAST LATER TODAY AND TONIGHT
TO NEAR DENVER AND PULL DRIER AIR INTO EASTERN COLORADO TONIGHT.
BEFORE IT DOES...EASTERLY FLOW TO THE NORTH OF IT WILL CONTINUE TO
PUMP MOISTURE INTO NORTHEAST COLORADO AND PRODUCE WIDESPREAD RAIN
AND SNOW. SNOW LEVEL LOOKS TO BE AROUND 6000 FEET...COULD SEE SNOW
MIX DOWN TO 5500 FEET TO THE SOUTH OF DENVER WHERE THE COOLEST AIR
RESIDES. THIS AFTERNOON...SNOW LEVEL SHOULD RISE ABOVE 6000 FEET
AS WARM AIR ADVECTION CONTINUES. WILL KEEP THE ADVISORY GOING
THROUGH THE MORNING HOURS OVER THE PALMER DIVIDE...MAY BE ABLE TO
CANCEL IT THIS AFTERNOON AS THE SNOW CHANGES TO RAIN.

THERE HAVE BEEN THUNDERSTORMS FROM COLORADO SPRINGS TO PUEBLO
THIS MORNING. AS LOW LIFTS NORTHEAST...EXPECT THIS LIFT AND
INSTABILITY TO MOVE OVER NORTHEAST COLORADO. THERE HAVE BEEN A FEW
LIGHTNING FLASHES OVER JEFFERSON COUNTY THIS MORNING ALREADY.
THUNDERSTORMS SHOULD INCREASE OVER THE AREA LATER THIS MORNING AND
AFTERNOON. SURFACE BASED CAPES OF 500-1000 J/KG ARE EXPECTED TO
THE NORTHEAST OF A LINE FROM GREELEY TO LIMON. THERE WILL BE
ENOUGH INSTABILITY AND SHEAR FOR A CHANCE OF SEVERE STORMS. MAIN
THREAT WILL BE DAMAGING HAIL...THOUGH DAMAGING WINDS AND TORNADOES
WILL ALSO BE POSSIBLE.

ONCE CONVECTION DIES OFF AND MOVES OUT OF THE AREA...WIDESPREAD
PRECIPITATION SHOULD END. HOWEVER....EXPECT AN AREA OF PRECIPITATION
TO THE WEST OF THE LOW AS IT LIFTS NORTHEAST ACROSS THE AREA.

&&

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 507 AM MDT FRI APR 17 2015

UPPER LOW NOW WOBBLING AROUND DURANGO AND THERE IS DECENT MODEL
AGREEMENT ON IT MOVING SLOWLY EAST AND THEN NORTHEAST THROUGH
TONIGHT...COMING TOWARD DENVER BY LATE TONIGHT. SYSTEM IS
OCCLUDING OVER US...A RARE EVENT FOR THIS PART OF THE WORLD. DRIER
AIR ALOFT IS WRAPPING AROUND THE SYSTEM ACROSS THE PLAINS WITH A
SHOWER FILLED COMMA DEVELOPING OVER THE MOUNTAINS. SHOWERS AND
THUNDERSTORMS ALSO POPPING UP IN THE DRY SLOT WHERE WARMER MOIST
AIR IS FEEDING IN FROM THE EAST AT THE SURFACE. ALL THIS IS GOING
ABOUT AS PLANNED SO ONLY MINOR CHANGES AT THIS TIME.

FOR THE MOUNTAINS...THE WINTER STORM WARNING CONTINUES FOR THE
FRONT RANGE WHERE HEAVY SNOW WILL CONTINUE AT LEAST THROUGH THIS
MORNING. THE NORTHERN FRONT RANGE STILL LOOKS TO BE UNDER THE
PIVOT POINT FOR THE AREA OF HEAVY SNOW...THOUGH THE BEST SNOW
COULD SHIFT INTO SOUTHERN WYOMING FOR A WHILE THIS EVENING.
FURTHER SOUTH THE DURATION OF THE HEAVY SNOW WILL DEPEND ON THE
EXACT TRACK OF THE LOW AND THE SMALLER SCALE CONVECTIVE ELEMENTS
AS PARK COUNTY AND THE FOOTHILLS SOUTHWEST OF DENVER MAY BE ON THE
EDGE OF THE LARGE SCALE LIFT AT TIMES. BY LATER TONIGHT THE FLOW
WILL GO MORE NORTHERLY A DECREASE IN SNOW INTENSITY...ESPECIALLY
FOR THE SOUTHERN PART OF OUR AREA. I DID INCREASE POPS FOR AREAS
WEST OF THE FRONT RANGE WHICH WILL BE UNDER THE DEVELOPING BACK
SIDE DEFORMATION BAND. THE LOW LEVEL FLOW GENERALLY WILL NOT FAVOR
THESE AREAS...BUT THE LARGE SCALE LIFT SHOULD STILL PROVIDE SNOW.

FOR THE PLAINS THE LARGE SCALE PRECIPITATION BAND HAS LIFTED NORTH
OF THE AREA...BUT THE SATURATED BOUNDARY LAYER WILL CONTINUE TO
PRODUCE FAIRLY WIDESPREAD LIGHT PRECIPITATION. WARMER TEMPERATURES
HAVE ALMOST MADE IT TO DENVER...WITH 40S INTO SOUTHERN WELD
COUNTY...SO WE SHOULD HAVE NEARLY ALL RAIN DURING THE DAY TODAY
BELOW 6000 FEET...STILL A MIX BETWEEN 6000 AND 7000 FEET. EVEN
WITH THE LOW LEVEL WARMING...HIGHS TODAY STILL LOOKED TO
OPTIMISTIC GIVEN THE CLOUD COVER AND RAIN...SO I TRIMMED THEM
BACK A LITTLE.

AS TO THE SEVERE THUNDERSTORM THREAT...COOLER TEMPERATURES SHOULD
TAKE THE EDGE OFF OF THIS FOR MOST OF THE AREA. MODEL FORECAST
CAPES OF UP TO 2000 J/KG IN AREAS EAST OF AKRON LOOK A BIT
OVERDONE...MAYBE MORE LIKE 500 J/KG EAST OF DENVER AND 1000-1500
IN AKRON. BUT GIVEN THE WIND SHEAR AND COOL TEMPERATURES STILL
ENOUGH FOR SEVERE HAIL AND WIND DAMAGE. TORNADO RISK LIKELY
LIMITED TO THE CONVERGENCE LINE...OCCLUDED FRONT REALLY...THAT
WILL PROBABLY STRETCH FROM ABOUT NORTHERN WELD COUNTY ACROSS
WASHINGTON COUNTY. STORMS WILL BE MOVING TOWARD THE NORTHWEST OR
POSSIBLY EVEN WEST TODAY WITH THE BETTER MOISTURE COMING IN FROM
THE EAST AND THE CONVERGENCE FUELING ANY ORGANIZED STORMS. HRRR
SHOWS PRETTY WIDESPREAD CONVECTION AFTER ABOUT 20Z...AND THE
AMOUNT OF CONVECTION MAY ALSO LIMIT THE THREAT OF STRONGLY
ORGANIZED STORMS. BUT THE SPC OUTLOOK HIGHLIGHTING THE AREA WHERE
THE BEST CONVERGENCE WILL BE LOOKS GOOD.

LESS MODEL AGREEMENT ABOUT THE FATE OF THE WRAPAROUND
PRECIPITATION TONIGHT. I SHOWED A BIT MORE OF A GRADIENT WITH
HIGHER POPS TO THE NORTH AND LOWER SOUTH WITH THE LOW TRACKING
OVER US. THERE SHOULD BE A LITTLE COOLING AGAIN BUT IT REMAINS
VERY MOIST...SO THE SNOW LEVEL SHOULD NOT GET LOWER THAN IT WAS
OVERNIGHT. WILL HANG ON TO THE MENTION OF SOME SNOW MIXING IN
AGAIN FOR DENVER...BUT NOT LIKELY TO HAVE MUCH IF ANY
ACCUMULATION.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 507 AM MDT FRI APR 17 2015

AT 12Z SATURDAY MORNING...ALL THE MODELS HAVE THE UPPER CLOSED
LOW CENTERED OVER CENTRAL TO NORTHEASTERN COLORADO. BY 06Z
SATURDAY NIGHT THE CENTER IS OVER WESTERN KANSAS. THERE ARE 30-60
KNOT WEST-NORTHWESTERLY JET LEVEL WINDS OVER THE CWA SATURDAY
NIGHT THROUGH SUNDAY NIGHT. THERE IS SOME UPWARD SYNOPTIC SCALE
ENERGY FOR THE CWA ON SATURDAY...AT LEAST OVER THE EASTERN AND
NORTHERN CWA...THEN WEAK DOWNWARD MOTION IS INDICATED SATURDAY
NIGHT THROUGH SUNDAY NIGHT. THE BOUNDARY LAYER FLOW IS WEAK
SATURDAY MORNING...THEN DOWNSLOPING NORTHWESTERLY SATURDAY
AFTERNOON AND EVENING. AFTER MIDNIGHT...THE LOW LEVEL WINDS ARE
NORTHERLY AND THEY CONTINUE THROUGH THE DAY SUNDAY INTO THE NIGHT.
THERE IS SURGE OF COOLER AIR AND UPSLOPE SUNDAY MORNING. FOR
MOISTURE...MOST OF THE MODELS HAVE THE WESTERN CWA VERY MOIST ON
SATURDAY. THE PLAINS ARE DRIER. THE MOUNTAINS STAY MOIST SATURDAY
NIGHT... WITH INCREASING MOISTURE FOR THE PLAINS. SUNDAY AND
SUNDAY NIGHT ARE PRETTY MOIST FOR MUCH OF THE CWA. THERE IS
LIMITED CAPE OVER MUCH OF THE CWA LATE DAY SATURDAY...MUCH LESS
AND JUST OVER THE WESTERN CWA LATE DAY SUNDAY. THE LAPSE RATES ARE
PRETTY STEEP ON SATURDAY...BUT THERE IS A STRONG STABLE LAYER IN
THE MID LEVELS BY SUNDAY AFTERNOON. THE QPF FIELDS HAVE
MEASURABLE PRECIPITATION OVER MOST OF THE CWA SATURDAY INTO SUNDAY
MORNING...WITH THE HIGHER AMOUNTS IN THE MOUNTAINS AND FOOTHILLS.
ON SUNDAY AND SUNDAY NIGHT...THERE IS A TAD OF MEASURABLE
PRECIPITATION FOR THE MOUNTAINS AND PALMER RIDGE. FOR POPS WILL GO
WITH 30-60%S FOR ALL THE CWA SATURDAY AND SATURDAY NIGHT. WILL PUT
A BIT OF THUNDER IN SATURDAY AFTERNOON. FOR SUNDAY AND SUNDAY
NIGHT..."CHANCE"S IN THE HIGH COUNTRY...AND "SLIGHT CHANCES"S
OVER THE PLAINS. THERE COULD BE SOME SNOW ON THE PLAINS BOTH
SATURDAY NIGHT AND SUNDAY NIGHT...AT LEAST A MIXTURE. NO
HIGHLIGHTS. FOR TEMPERATURES...SATURDAY`S HIGHS ARE 1-3 C WARMER
THAN TODAY`S HIGHS. SUNDAY`S HIGHS COOL OFF 2-5 C FROM SATURDAY`S.
FOR THE LATER DAYS...MONDAY THROUGH THURSDAY...MODELS HAVE
NORTHWESTERLY FLOW ALOFT FOR THE CWA MONDAY INTO EARLY TUESDAY AS
AN UPPER RIDGE MOVES THIS WAY FROM THE WEST. THE UPPER RIDGE GETS
INTO COLORADO BY LATE TUESDAY AND THROUGH THE CWA BY WEDNESDAY
EARLY EVENING. THE MODELS DIVERGE ON THURSDAY. THE GFS BRINGS THE
NEXT UPPER TROUGH IN...BUT THE ECMWF IS SLOWER WITH IT.

&&

.AVIATION...(FOR THE TAFS THROUGH 18Z SATURDAY MORNING)
ISSUED AT 925 AM MDT FRI APR 17 2015

NOT LOOKING PROMISING FOR THE AIRPORTS TODAY WITH THE
DEFORMATION OF THE LOW TO THE SOUTH KEEPING A STEADY STREAM OF
MOISTURE MOVING INTO THE AIRPORT. LOW CLOUDS AND FOG WITH
SCATTERED LIGHT RAINSHOWERS WILL CONTINUE THROUGH THE DAY. NOT
EXPECTING SNOW TO RETURN WITH INCREASING TEMPERATURES. HOWEVER,
EVEN WITH SLIGHTLY WARMER TEMPS DO NOT EXPECT VISIBILITY OR
CEILINGS TO REACH ABOVE IFR UNTIL POSSIBLY THIS EVENING AS THE
DEWPOINTS CONTINUE TO STAY HIGH.

VARIOUS MODELS SHOWING IMPROVING CONDITIONS BETWEEN 20 AND 22Z AS
THE LOW CENTER CONTINUES TO MOVE NORTHEAST. SHOWERS WILL STILL
AFFECT THE AIRPORT BUT CEILINGS SHOW RAISE TO AT LEAST MVFR AND
POSSIBLY VFR LATER THIS EVENING AT KDEN AND KAPA. WINDS WILL BE
PREDOMINATELY FROM THE NORTH AS THE FLOW CONTINUES TO MOVE AROUND
THE LOW CENTER.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING FOR COZ037-
041.

WINTER STORM WARNING UNTIL 6 AM MDT SATURDAY FOR COZ033>036.

&&

$$

UPDATE...MEIER
SHORT TERM...GIMMESTAD
LONG TERM...RJK
AVIATION...MEIER



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