Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 180206
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
806 PM MDT SUN MAY 17 2015

.UPDATE...
ISSUED AT 805 PM MDT SUN MAY 17 2015

SHOWERS CONTINUE TO DRIFT ACROSS THE NORTHERN TIER OF COUNTIES
THIS EVENING...EXPECT THIS ACTIVITY TO DIMINISH AROUND MIDNIGHT.
SURFACE MAPS THIS EVENING SHOW A STRONG SURFACE HIGH IN MONTANA
AND STRONG PRESSURE RISES SUGGEST THAT IT WILL DROP TOWARDS THE
SOUTHEST TOWARDS EASTERN NEBRASKA...WITH THE WESTERN EDGE OF THE
AIRMASS INCREASING UPSLOPE CONDITIONS ACROSS EASTERN COLORADO.
LOWERED MINS A DEGREE OR SO TONIGHT AND MAX TEMPS A DEGREE OR SO
ON MONDAY...CLOSER TO GFS GUIDANCE.  IT IS ONLY MID 40S IN
NORTHEAST WYOMING...AND THAT AIR IS HEADING TOWARD US. WILL LEAVE
MENTION OF DRIZZLE AND FOG ALONG FOOTHILLS EARLY MONDAY...STILL
LOOKS LIKE A POSSIBILITY.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 330 PM MDT SUN MAY 17 2015

ISOLATED LIGHT RAIN SHOWERS CONTINUE TO DRIFT FROM WEST TO EAST
ACROSS THE AREA...MAINLY OVER MOUNTAINS...PALMER DIVIDE AND CYS
RIDGE. A BIT MORE COVERAGE THIS EVENING WITH SHALLOW UPSLOPE FLOW
HELPING TO AID SOME WEAK LIFT TO SHOWERS. A BIT TOO STABLE FOR
THUNDERSTORMS. STRONG SURFACE HIGH PRESSURE OVER MONTANA AND
NORTHERN WYOMING WILL SLIP SOUTHWARD TONIGHT AND ENHANCE THE
NORTHEAST LOW LEVEL FLOW AFTER MIDNIGHT. EXPECT STRATUS TO DEVELOP
OVER THE PLAINS AND FRONT RANGE LATER TNT AND EVEN SOME VERY LIGHT
RAIN/DRIZZLE AS LOW LEVELS MOISTEN UP.

FOR THE SYNOPTIC LARGE SCALE...THERE WILL A RIDGING ALOFT TNT AND
EARLY MONDAY BUT WILL BEGIN TO BECOME UNDER INFLUENCE OF BROAD
UPPER LOW MOVING INTO CALIFORNIA BY MONDAY AFTN. WEAK QG ASCENT
WILL SPREAD OVER COLORADO BY LATE MONDAY AFTERNOON AND EXPECT AN
INCREASE IN SHOWERS OVER MOUNTAINS. MAJORITY OF THE PLAINS WILL
STILL BE CAPPED BY INVERSION AND STATUS FOR MUCH OF MONDAY WITH
LITTLE IF ANY CHANCE OF SHOWERS.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 330 PM MDT SUN MAY 17 2015

PRETTY GOOD AGREEMENT IN THE MODELS FOR THE LOW MOVING ACROSS
COLORADO MONDAY NIGHT AND TUESDAY. THE MAIN FEATURE WILL BE A ZONE
OF MODERATE LIFT IN A DEEP SATURATED NEUTRAL ENVIRONMENT AHEAD OF
THE TROUGH. THIS ZONE WILL LIFT SLOWLY NORTHWARD ACROSS EASTERN
COLORADO MONDAY NIGHT INTO TUESDAY. MODEL QPFS HAVE TENDED A
LITTLE HIGHER...WITH AN AVERAGE OF 1 TO 1.5 INCHES OVER THE PLAINS
IN A 24 HOUR PERIOD. THERE WILL PROBABLY BE ENHANCED RAINFALL OVER
THE FOOTHILLS IN THE FIRST HALF OF THE EVENT WHEN THE LOW LEVEL
UPSLOPE IS THE STRONGEST...WITH THE HEAVIER RAIN SHIFTING TO THE
PLAINS DURING THE DAY ON MONDAY. BUMPED UP THE RAINFALL FORECAST
FOR THE FOOTHILLS TO 1 TO 2 INCHES. RELATIVELY GOOD AGREEMENT IN
THE MODEL PRECIP...ENSEMBLE MEMBERS ARE GENERALLY WITHIN PLUS OR
MINUS HALF AN INCH. ONE WRINKLE IS THAT BOTH THE 12Z NAM AND GFS
HAD A ZONE OF LIGHTER PRECIP OVER DENVER...ABOUT HALF OF WHAT
OTHER PLACES GET. PERHAPS A BREAK BETWEEN THE WARM ADVECTION
SHIELD OVER THE PLAINS AND THE UPSLOPE ENHANCEMENT. GIVEN THE
LARGE AREA OF LIFT...I HAVE SOME DOUBTS ABOUT WHETHER THAT WILL BE
TRUE. SNOW LEVEL REMAINS PRETTY HIGH...BUT THERE IS SOME COOLING
AND IT WILL LIKELY DROP FROM 10 THOUSAND FEET DOWN TO 9 OR
POSSIBLY EVEN 8 THOUSAND. LIKE PAST EVENTS THE WARM TEMPERATURES
WILL SERIOUSLY LIMIT THE IMPACT...BUT THAT ALSO MEANS THERE IS
PLENTY OF MOISTURE AVAILABLE WHERE IT IS COLD ENOUGH. MAIN IMPACT
WILL LIKELY BE SLUSHY ROADS DURING THE PERIOD OF HEAVIEST
SNOW...WITH QUICK IMPROVEMENT WHEN THE SNOW LETS UP.

DRIER AIR WORKS AROUND THE SOUTH SIDE OF THE SYSTEM LATER
TUESDAY EVENING...MODELS ARE TRENDING A BIT SLOWER WITH THIS BUT
WE SHOULD TRANSITION TO MORE OF A WEAK SHOWERY ENVIRONMENT TUESDAY
NIGHT. WEDNESDAY IS MOIST WITH COOL LOW LEVELS...STILL PROBABLY
SOME WEAK SHOWERS BUT IT MAY BE FAIRLY STABLE. THURSDAY FEATURES A
RIDGE WITH DRIER AIR ALOFT...BUT STILL LOW LEVEL MOISTURE AND
PERHAPS ENOUGH SUNSHINE/WARMING FOR MORE INSTABILITY. SO SEASONAL
POPS ARE STILL IN ORDER.

NEXT SYSTEM SCHEDULED FOR FRIDAY THROUGH SUNDAY...ANOTHER WEEKEND
LOW COMING OVER COLORADO. TOO EARLY TO PUMP IT TOO MUCH BUT MODELS
ARE FAIRLY CONSISTENT AND IT CERTAINLY COULD BE ANOTHER INCH OF
RAIN. EARLY INDICATIONS ARE THAT TEMPERATURES WILL BE RELATIVELY
WARM AGAIN...SO SNOW THREAT IS LIKELY LIMITED TO THE HIGHER
MOUNTAINS AGAIN.

&&

.AVIATION...(FOR THE TAFS THROUGH 00Z MONDAY LATE AFTERNOON)
ISSUED AT 805 PM MDT SUN MAY 17 2015

ISOLATED SHOWERS ARE STILL POSSIBLE THIS EVENING AT AREA AIRPORTS
WITH MAINLY WIND IMPACTS DUE TO OUFLOW WINDS. OVERNIGHT UPSLOPE
FLOW IS EXPECTED TO DEEPEN...AND THERE MAY BE SOME LOWER STRATUS
AND DRIZZLE...ESPECIALLY AT KBJC EARLY MONDAY MORNING. AS THE
UPPER LOW APPROACHES...SHOWERS AND THUNDERSTORMS BEGIN TO SPREAD
TO THE URBAN CORRIDOR VERY LATE MONDAY AFTERNOON OR EARLY EVENING.

&&

.HYDROLOGY...
ISSUED AT 330 PM MDT SUN MAY 17 2015

CURRENT FORECAST PRECIPITATION AMOUNTS FOR MONDAY NIGHT AND
TUESDAY OF 1 TO 1.5 INCHES OVER THE PLAINS AND 1.5 TO 2 INCHES
OVER THE MOUNTAINS WOULD LIKELY CAUSE SOME FLOODING AGAIN. RIVER
LEVELS REMAIN HIGH DUE TO GROUND WATER FROM THE RAINS OF THE LAST
TWO WEEKS. TEMPERATURES WILL BE COOL ENOUGH THAT SNOWMELT WILL NOT
BE A FACTOR...BUT WARM ENOUGH THAT THE MUCH OF THE FOOTHILLS
TERRAIN WILL RECEIVE SIGNIFICANT RAIN TO FLOW INTO THE FRONT RANGE
TRIBUTARIES TO THE SOUTH PLATTE. INTERESTS ALONG NORTHERN COLORADO
RIVERS...PARTICULARLY THE SOUTH PLATTE AND OTHER LOCATIONS THAT
HAVE FLOODED RECENTLY...SHOULD BE AWARE OF THE POSSIBILITY OF
RENEWED FLOODING AS EARLY AS TUESDAY IN THE HEADWATERS AND
DOWNSTREAM ON THE SOUTH PLATTE INTO NEXT WEEKEND.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM MONDAY EVENING THROUGH TUESDAY AFTERNOON
FOR COZ033-034.

&&

$$

UPDATE...RTG
SHORT TERM...ENTREKIN
LONG TERM...GIMMESTAD
AVIATION...ENTREKIN
HYDROLOGY...GIMMESTAD



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