Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 211021
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
421 AM MDT THU MAY 21 2015

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 420 AM MDT THU MAY 21 2015

ANOTHER NIGHT OF STRATUS ON THE NORTHEAST PLAINS ALONG WITH PATCHY
FOG AND DRIZZLE ALONG THE FRONT RANGE. MOISTURE DEPTH BECOMES MORE
SHALLOW WITH TIME SO COULD SEE SOME PARTIAL CLEARING ON THE
PLAINS BY LATE MORNING. ALONG THE FRONT RANGE...DENVER CYCLONE
EXPECTED TO DEVELOP THIS AM WITH THE SOUTHEAST FLOW WHICH MAY HOLD
CLOUDS/FOG IN A BIT LONGER FOR LOCATIONS NORTH AND WEST OF
DENVER...PENDING EXACT LOCATION OF CONVERGENCE ZONE. GIVEN
ABUNDANT CLOUD COVER HAVE DROPPED HIGH TEMPERATURES A FEW DEGREES
ON THE PLAINS.

MAIN EVENT FOR NEXT 24 HOURS IS NEXT WAVE WHICH WILL EJECT
TOWARDS COLORADO LATER THIS AFTERNOON FROM THE PARENT LOW ACROSS
SOUTHERN CALIFORNIA. INCREASING QG ASCENT WITH STRONGEST FORCING
FROM THIS EVENING THROUGH 12Z FRIDAY. LATEST QPF FROM MODELS
INDICATE ANYWHERE FROM .25 TO .75 ON THE PLAINS AND UPWARDS OF AN
INCH IN THE MOUNTAINS. WILL CONTINUE TO INCREASE POPS ACROSS THE
BOARD. FOR THE MOUNTAINS...SNOW LEVEL WILL BE QUITE HIGH BUT
POTENTIAL FOR DECENT SNOWFALL OVER THE MOUNTAIN PASSES ABOVE 10500
FEET. HAVE OPTED TO ISSUE A WINTER WEATHER ADVISORY FOR 4-8 INCHES
OF SNOW FOR ZONE 34 WITH MAIN IMPACT OVER THE MOUNTAIN PASSES AND
VERY LITTLE SNOWFALL OVER VALLEY FLOORS. DECENT SOUTHEAST FLOW
WILL ENHANCE SNOWFALL ACROSS NORTHERN PARK COUNTY. HEAVIEST
SNOWFALL WILL BE FROM LATE AFTERNOON THROUGH TONIGHT.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 420 AM MDT THU MAY 21 2015

ON FRIDAY...BLOCKING LONGWAVE TROUGH WILL STILL BE OVER THE
INTERMOUNTAIN WEST WITH THE 500 MB LOW VICINITY OF LAS VEGAS AROUND
MIDDAY. STRONG SWLY FLOW ALOFT ROUNDING THE BOTTOM OF THE TROUGH IS
PROGGED TO BE CROSSING THE 4-CORNERS AND SRN COLORADO DURING THE
DAY. EMBEDDED IN THIS FLOW WAS A SHORTWAVE TROUGH WHICH MODELS SHOW
PASSING OVER NERN COLORADO EARLY IN THE MORNING. BEST MOISTURE AND
LIFT AHEAD OF THIS S/W SHOULD EXIT THE CWA AREA AS THE MORNING
PROGRESSES. HIGHER MTN PASSES COULD STILL PICK UP A COUPLE MORE
INCHES OF SNOW BY NOON. SHOULD ALSO SEE BACK EDGE OF SHOWERS ON THE
PLAINS EXITING THE AREA TO THE NORTHEAST WITH DRYING AND SUBSIDENCE
IN THE WAKE OF THE SHORTWAVE. HOWEVER...BY AFTERNOON WITH STRONG
SOLAR HEATING...INCREASING UPPER AIR DIFFLUENCE AND WET SOILS...
SHOULD SEE ANOTHER ROUND OF SHOWERS AND T-STORMS FORMING IN THE HIGH
COUNTRY AND ON THE ADJACENT HIGH PLAINS DURING THE AFTERNOON. WILL
STICK WITH 30-50 PCT PRECIP CHANCES ALREADY IN THE FCST FOR MOST
AREAS FRIDAY AFTERNOON. MOST OF THIS ACTIVITY SHOULD END DURING THE
EVENING. TEMPS ON FRIDAY LOOK TO BE 3-4 DEG C WARMER THAN THOSE ON
THURSDAY.

BY SATURDAY...THE MAIN UPPER TROUGH CONTINUES ITS SLOW EASTWARD
PROGRESSION WITH A MAJORITY OF THE DETERMINISTIC MODELS AND ENSEMBLE
MEMBERS SHOWING THE 500 MB LOW POSITIONED JUST NORTH OF THE 4-
CORNERS BY LATE AFTERNOON. SATURDAY LOOKS DRIER AND WARMER
PARTICULARLY EAST OF THE MTNS WITH MODELS SHOWING A DRY SOUTH-
SOUTHWESTERLY FLOW ALOFT OVER THE AREA. THEREFORE PRECIP CHANCES NOT
AS GREAT ON SATURDAY...ALTHOUGH STRONG DAYTIME HEATING AND MOIST
SOILS SHOULD AGAIN BE SUFFICIENT TO FUEL ISOLATED TO SCATTERED
SHOWERS AND ISOLATED TO SCATTERED T-STORMS MAINLY IN THE HIGH
COUNTRY AND ALONG THE NORTHERN AND EASTERN BORDERS OF THE CWA. THE
PROSPECT FOR SEVERE STORMS APPEARS LOW AT THIS TIME.

BY SUNDAY...MODELS SHOW THE UPPER TROUGH FINALLY MAKING ITS WAY
ACROSS THE THE REGION WHICH WILL INCREASE THE CHANCE FOR SHOWERS AND
T-STORMS FOR ALL AREAS BY MIDDAY IN THE HIGH COUNTRY AND BY LATER IN
THE AFTERNOON ON THE PLAINS AS IT LOOKS NOW. SFC CYCLOGENESIS UP NEAR
THE WY BORDER IN WELD COUNTY COULD ACT AS A FOCUS FOR A FEW STRONG
STORMS LATE AFTERNOON AND AND/OR EARLY IN THE EVENING. LOCALLY HEAVY
RAINFALL AND HAIL APPEARS TO BE THE MAIN THREATS. COULD SEE SHOWERS
LINGERING ALL NIGHT MAINLY EAST OF THE MTNS AS THE UPPER TROUGH
PASSES SLOWLY OVER THE AREA.

MEMORIAL DAY THROUGH WEDNESDAY...WILL REMAIN UNSETTLED AS A SERIES
OF WEAK SHORTWAVE DISTURBANCES IN A MOIST W-SWLY FLOW ALOFT MAKE
THEIR WAY ACRS THE REGION...APPROXIMATELY ONE A DAY. WILL KEEP DAILY
SHOWERS AND T-STORMS IN THE FCST THROUGH MID-WEEK AND TEMPERATURES
NEAR SEASONAL NORMS.

&&

.AVIATION...(FOR THE TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 420 AM MDT THU MAY 21 2015

IFR CIGS CONTINUE AT LOCAL TERMINALS. APPEARS DRIZZLE HAS ENDED AS
MOISTURE DEPTH BECOMES MORE SHALLOW. DENVER CYCLONE EXPECTED TO
DEVELOP THIS AM GIVEN THE SOUTHEAST LOW LEVEL FLOW ON THE PLAINS.
THIS MAY KEEP CLOUDS AND POTENTIAL FOR MORE FOG/DRIZZLE
LONGER...ESPECIALLY AT BJC THROUGH MUCH OF THE MORNING HOURS. NEXT
SYSTEM EXPECTED TO IMPACT TERMINALS MAINLY TONIGHT WITH SHOWERS
INCREASING IN AREAL EXTENT BY LATER THIS EVENING AND OVERNIGHT
WITH IFR/MVFR CIGS/VSBYS. COULD BE A FEW LIGHT SHOWERS DEVELOPING
AFTER 22Z.

&&

.HYDROLOGY...
ISSUED AT 420 AM MDT THU MAY 21 2015

FLOOD WARNINGS CONTINUE FOR THE SOUTH PLATTE FROM CENTRAL WELD
COUNTY INTO MORGAN AND NORTHWEST WASHINGTON COUNTIES. THE CREST
LOOKS TO HAVE PEAKED AT KERSEY TONIGHT AND WILL MOVE THROUGH EASTERN
WELD COUNTY TODAY...BEFORE PUSHING THROUGH CENTRAL MORGAN COUNTY
LATE THURSDAY NIGHT AND FRIDAY. AT THIS TIME...GENERALLY MINOR
FLOODING IS ANTICIPATED WITH WATER LEVELS BELOW LAST WEEKS CREST.
MINOR FLOODING ALSO ANTICIPATED ON THE CACHE LA POUDRE NEAR
GREELEY.

ANOTHER ORGANIZED SHORTWAVE WILL MOVE THROUGH THE REGION LATE
THIS AFTERNOON AND TONIGHT WITH MORE LIGHT TO MODERATE RAIN WITH
SOME EMBEDDED THUNDERSHOWERS. TOTAL LIQUID PRECIPITATION EXPECTED
TO RANGE FROM .25 TO .75 OF AN INCH ON THE PLAINS WITH UPWARDS OF
AN INCH OVER THE MOUNTAINS AND HIGHER FOOTHILLS. ALTHOUGH THESE
ARE NOT EXCEPTIONAL NUMBERS THE SATURATED GROUND CONDITIONS SHOULD
RESULT IN EFFICIENT RUNOFF. EXPECT THE CONTINUATION OF HIGH FLOWS
IN RIVERS AND STREAMS THAT ARE ALREADY HIGH... AND POSSIBLY THE
DEVELOPMENT OF BANKFULL OR MINOR FLOODING IN OTHER STREAM AND
RIVERS.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 6 AM MDT
FRIDAY FOR COZ034.

&&

$$

SHORT TERM...ENTREKIN
LONG TERM...BAKER
AVIATION...ENTREKIN
HYDROLOGY...ENTREKIN



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