Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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558
FXUS65 KBOU 262034
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
234 PM MDT TUE APR 26 2016

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 230 PM MDT TUE APR 26 2016

MODEL CONSENSUS IS FOR THE UPPER LOW OVER COLORADO TO ELONGATE
WITH THE NORTHERN PORTION FILLING OVERNIGHT AND TOMORROW WHILE A
SOUTHERN CENTER INTENSIFIES AND SCOOTS INTO KANSAS. AT THE SURFACE
WE ARE BEHIND A COLD FRONT AND NORTHERLY FLOW WILL CONTINUE.
LOWERED MAX TEMPS FOR THE REST OF THE THIS AFTERNOON BEHIND THE
FRONT. RAIN AND SNOW SHOWERS WILL CONTINUE TO EXPAND OVER THE
FOOTHILLS AND PALMER DIVIDE...ALONG WITH A FEW THUNDERSTORMS. A
FEW SHOWERS ARE ALSO EXPECTED TO REACH THE PLAINS...THESE WILL
LIKELY MIX WITH SNOW THIS EVENING. SNOW ACCUMULATIONS WILL LIKELY
REACH 1 TO 6 INCHES IN THE FOOTHILLS AND MOUNTAINS...AN INCH OR SO
OVER THE PALMER DIVIDE...AND A TRACE AT LOWER ELEVATIONS.

LATER TONIGHT BEHIND THE ELONGATED TROUGH DOWNSLOPE FLOW IS
EXPECTED TO BECOME ESTABLISHED...WITH A A DRYING TREND DEVELOPING
THAT WILL CONTINUE ON WEDNESDAY. THE DOWNSLOPE FLOW WILL AID
AFTERNOON TEMPERATURES ON WEDNESDAY...NEW GUIDANCE NUMBERS WERE
HIGHER THAN PREVIOUS FORECAST...SO BUMPED AFTERNOON TEMPERATURES
BY A COUPLE OF DEGREES ON THE PLAINS.  THERE WILL BE LINGERING
SHOWERS OVER THE NORTHEAST PLAINS WEDNESDAY ENDING LATE. OVER THE
MOUNTAINS THE NEXT SYSTEM WILL ALREADY BEGIN TO AFFECT THE STATE
WITH INCREASING SHOWERS SPREADING ACROSS THE HIGH COUNTRY ON
WEDNESDAY AFTERNOON.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 230 PM MDT TUE APR 26 2016

A SHORTWAVE UPPER RIDGE AND SOMEWHAT DRIER AIR OVER NERN COLORADO
WEDNESDAY NIGHT/EARLY THURSDAY MORNING IS PROGGED TO MOVE EAST OF
THE STATE BY AFTERNOON. A DIVERGENT SOUTHWESTERLY FLOW ALOFT ON THE
BACK SIDE OF THE RIDGE SETTING UP OVER THE STATE TRANSPORTS
INCREASING AMOUNTS OF MOISTURE FROM THE DESERT SOUTHWEST. QG ASCENT
FIELDS INDICATE A GRADUAL INCREASE IN SYNOPTIC SCALE LIFT
STARTING OVER THE MTNS DURING THE MORNING THEN OVER THE ADJACENT
PLAINS BY THE AFTERNOON. MODELS ALSO SHOW THE DEVELOPMENT OF
ANTICYCLONIC UPSLOPE FLOW ON THE PLAINS AND A STEADY DEEPENING OF
THIS FLOW INTO THE EVENING HOURS. MODELS DIFFER ON THE AMOUNT OF
PRECIP GENERATED BY THESE FEATURES...BUT OVERALL THE FOCUS APPEARS
TO BE OVER AND ALONG THE LEE SLOPE OF THE FRONT RANGE WHERE QPF
AMOUNTS RANGES ANYWHERE FROM A COUPLE TENTHS TO NEARLY THREE-
QUARTER INCH. FURTHERMORE MODEL WETBULB ZERO HTS GRADUALLY LOWER
THRU THE DAY WITH THE RAIN/SNOW LINE AROUND 7500 FT BY LATE
AFTERNOON RESULTING IN ALL SNOW IN THE FRONT RANGE.

OVERNIGHT...THE MEAN SNOW LEVEL BASED ON SEVERAL MODELS LOWERS TO
NEAR 5600 FT OVERNIGHT. SHOULD IT DROP BELOW THIS...THE LOWER
FTHLS AND NEARBY PLAINS INCLUDING THE PALMER DIVIDE COULD SEE
PRECIP GO OVER TO ALL SNOW. ACCUMULATIONS BIG QUESTION. COULD SEE
SEVERAL INCHES IN THE FOOTHILLS AND A FEW INCHES OF SOGGY WET
SNOW IN THE NEARBY PLAINS. HOWEVER...THE GFS INDICATED A NORTH-
SOUTH SNOW BAND OF 4-7 INCHES FROM DOUGLAS CTY NRN TO CNTRL WELD
CTY CLIPPING THE DEN METRO AREA BY 12Z/FRI...WITH 2-4 INCH AMTS
CLOSER TO THE FOOTHILLS. ON FRIDAY...THE AFOREMENTIONED UPPER
TROUGH PASSES OVER COLORADO WHICH APPEARS TO REINFORCE THE MOIST
UPSLOPE FLOW ON THE PLAINS. THE RAIN/SNOW LINE REMAINS UNCERTAIN
AS MODEL TEMPS DIFFER QUITE ABIT. STILL AREAS ABOVE 6500 TO 7000
FT SHOULD REMAIN COLD ENOUGH FOR SNOW THROUGHOUT THE DAY. COULD
END UP SEEING SIGNIFICANT ACCUMS IN AND NEAR THE FOOTHILLS BUT
WILL REFRAIN FROM GOING OVERBOARD WITH SNOW ACCUMS AT THIS TIME
DUE TO ONGOING UNCERTAINTY IN THE MODELS.

LOOKING AHEAD...TROUGH LIFTS OUT ON SATURDAY ALLOWS FOR SOME DRYING
WITH BRISK NWLY FLOW IN ITS WAKE. SHOULD SEE FURTHER DRYING AND
WARMING WITH PASSAGE OF A SHORTWAVE RIDGE SAT NIGHT/SUN MORNING.
THEN ANOTHER CLOSED LOW/UPPER TROUGH ORGANIZING OVER THE LOWER GREAT
BASIN TRACKS ACRS THE 4-CORNERS REGION DURING THE DAY AND EVENTUALLY
ACRS WYOMING/NRN COLORADO LATE SUNDAY AN MONDAY. SHOULD THIS LOW
TRACK FARTHER SOUTH THE CWA COULD END UP DEALING WITH ANOTHER
SIGNIFICANT PRECIP EVENT. FOR NOW WILL HANG ONTO LOW POPS...
GENERALLY IN THE 30-40 PCT RANGE ON THE PLAINS AND SOMEWHAT HIGHER
POPS FOR THE HIGH COUNTRY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 230 PM MDT TUE APR 26 2016

STRATUS WITH MVFR CEILINGS WILL PERSIST UNTIL AFTER MIDNIGHT...
AND SCATTERED SHOWERS MAY SPREAD ACROSS THE METRO AREA. LATER
TONIGHT DOWNSLOPE FLOW WILL HELP CLEAR OUT CLOUDINESS AND END
PRECIPITATION. SURFACE WINDS WILL BE MOSTLY NORTHERLY TODAY
THROUGH TOMORROW.


&&

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

$$

SHORT TERM...RTG
LONG TERM...BAKER
AVIATION...RTG



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