Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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379
FXUS65 KBOU 151704
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
1104 AM MDT FRI MAY 15 2015

.UPDATE...
ISSUED AT 1039 AM MDT FRI MAY 15 2015

CONVECTION HAS STARTED ALREADY OVER THE MOUNTAINS...FOOTHILLS AND
PALMER RIDGE. THERE ARE A FEW BOUNDARIES FLOATING AROUND THE
PLAINS RIGHT NOW. THE MAIN ONE IS ALONG THE SOUTHERN CWA BORDER THEN
IT IS ORIENTED SOUTHWEST/NORTHEAST UP THROUGH ELBERT COUNTY INTO
EAST ARAPAHOE AND ADAMS. THE SOUTH-SOUTHEASTERLIES WINDS SOUTH OF
IT ARE COMING OFF THE HIGHER TERRAIN AND THE DOWNSLOPING HAS DRIED
OUT DEW POINTS INTO THE 30S F. MOST OF THE PLAINS OF THE CWA HAVE
DEW POINTS IN THE MID 40S TO LOWER 50S F RIGHT NOW. THAT BOUNDARY
IS MOVING NORTHWARD SLOWLY BUT SHOULD PROVIDE THE IMPETUS FOR
THUNDERSTORMS TO DEVELOP AT SOME POINT IN THE NEXT COUPLE OF
HOURS. WILL MAKE SOME ADJUSTMENTS TO POPS AND CLOUD COVER...BUT
NOTHING MAJOR.

&&

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 459 AM MDT FRI MAY 15 2015

COMPLEX SITUATION TODAY AS SOUTHERLY FLOW STRENGTHENS AHEAD OF
THE UPPER LOW OVER SOUTHERN NEVADA. BIGGEST QUESTION IS THE
POSITION OF LOW LEVEL FEATURES ON THE PLAINS THIS AFTERNOON AND
THE AMOUNT OF HEAT AND MOISTURE AVAILABLE FOR CONVECTION. SEVERAL
FACTORS ARE FAVORABLE FOR SEVERE WEATHER...MOST NOTABLY STRONG
SHEAR AND A PLUME OF MOISTURE PUSHING WESTWARD ON THE NORTH SIDE
OF A SURFACE LOW/TROUGH THAT WILL BE IN EASTERN COLORADO. IT IS
ALSO LOOKING LIKE THERE WILL BE ENOUGH DRY MID LEVEL AIR TO ALLOW
A FAIR AMOUNT OF SUN OVER NORTHEAST COLORADO TODAY...WHILE THE
WESTWARD EXTENT OF THE GOOD MOISTURE MAY BE A BIT MORE THAN
PREVIOUSLY EXPECTED. ALWAYS HARD TO SECOND GUESS JUST HOW MUCH
MIXING OUT OF THE MOISTURE THERE WILL BE...CERTAINLY WEST OF THE
DRY LINE THIS WILL HAPPEN...BUT ON THE NORTH SIDE OF THE LOW THE
PLUME OF MOISTURE WRAPPING AROUND WILL NOT MIX AS MUCH. BIGGEST
QUESTION IS PROBABLY THE SHARPNESS OF THE LOW/TROUGH FEATURE WHICH
IS OFTEN UNDERDONE IN THE MODELS. AT THIS HOUR THE HRRR IS SHOWING
A PLUME OF EAST WINDS HOLDING 50 DEGREE DEW POINTS AND CAPES
AROUND 2000 J/KG ALONG THE NORTHERN BORDER BACK AS FAR AS WELD
COUNTY. HOWEVER IT ALSO SCOURS OUT THE MOISTURE IN AREAS FURTHER
SOUTH...DRYING OUT WASHINGTON COUNTY BY MID AFTERNOON BEFORE THE
CONVECTION GETS GOING.

A NEGATIVE FACTOR MAY BE TOO MUCH SOUTHERLY WIND. THIS MAY HELP
DRY THINGS OUT AND PUSH THE BETTER MOISTURE TO THE NORTH...AND MAY
ALSO REDUCE THE SHEAR AND ESPECIALLY THE HELICITY IF THE WIND
PROFILE WINDS UP BEING PRETTY LINEAR. THERE SHOULD BE A SWEET SPOT
WITH THE LOW LEVEL WINDS BACKED TO EASTERLY...MOST LIKELY NEAR OUR
NORTHERN BORDER OR JUST INTO NEBRASKA. THIS AREA WOULD HAVE THE
BEST THREAT OF SEVERE WEATHER AND A DECENT TORNADO THREAT. WILL GO
WITH THIS IDEA AS THE MOST LIKELY SCENARIO...WITH STRONG STORMS
DEVELOPING IN THE MOISTURE ALONG THE DRY LINE AND/OR NORTH OF THE
LOW/TROUGH WHERE CAPES WILL BE 1500-2000 J/KG...THEN PROPAGATING
NORTH WITH THE SEVERE THREAT INCREASING NEAR OUR NORTHERN BORDER.
OTHER STORMS WILL FORM ON THE BACK EDGE OF THE DRY SLOT...NEAR THE
FRONT RANGE/CHEYENNE RIDGE BUT SHOULD BE WEAKER WITH CAPES OF 500
J/KG NEAR THE MOUNTAINS AND IMPROVING A BIT AS THEY MOVE EAST INTO
THE MOISTURE TONGUE. STILL COULD BE SOME SEVERE THREAT HERE AS
WELL...MAINLY IN NORTHERN WELD COUNTY. OF COURSE IF THE LOW WINDS
UP BEING BETTER DEFINED THERE WOULD BE A MUCH HIGHER THREAT OF
SEVERE WEATHER ON THE NORTH AND NORTHEAST SIDE OF THE LOW.

RAISED HIGHS A LITTLE EXPECTING MORE SUN...STILL A FEW DEGREES
BELOW GUIDANCE AND IF IT IS A LITTLE WARMER THAT WILL HELP AS
WELL. TRENDED POPS MORE TOWARD THE IDEA OF A GOOD BREAK IN THE DRY
SLOT MUCH OF TODAY...WITH STORMS MOVING IN FROM THE WEST AND
DEVELOPING IN THE NORTH AND EAST IN THE LATE AFTERNOON. BEST
COVERAGE PROBABLY IN THE EARLY EVENING ON THE PLAINS...BUT
INTESITY SHOULD BE LESS THEN. SOME CLOUDS AND WEAK SHOWERS HANG ON
OVERNIGHT WITH A LITTLE COOLING ALOFT AND OVERALL INCREASE IN
MOISTURE.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 459 AM MDT FRI MAY 15 2015

OVERALL TREND IN THE FORECAST IS THE SAME. THE NEXT SYSTEM WILL
IMPACT THE CWA ON SATURDAY. THE BROAD BUT CLOSED UPPER TROUGH WILL
STRETCH FROM THE NORTHERN ROCKIES TO THE DESERT SOUTHWEST AT 12Z
SATURDAY...WITH A MODERATE TO STRONG SLY FLOW OVER EASTERN
COLORADO. WEAK TO MODERATE MID AND UPPER LEVEL QG ASCENT WILL
REMAIN OVER NORTHEAST COLORADO THROUGH THE DAY...WITH PLENTY OF
MOISTURE IN PLACE. MAIN ISSUE WILL BE WHERE THE SFC LOW SETS UP
AND AT THIS TIME IT APPEARS TO BE ALONG THE EASTERN BORDER. IF
THIS OCCURS...THEN THE STRONG/SEVERE THUNDERSTORMS WILL LIKELY BE
EAST OF COLORADO...BUT CANNOT RULE OUT ONE OR TWO REACHING SEVERE
LEVELS ALONG THE BORDER WHERE THE BEST VERTICAL SHEAR WILL BE
PRESENT. IN AND AROUND DENVER FORECAST CAPES IN THE AFTERNOON NOT
BAD...800-900 J/KG. MOISTURE AOA 700 MB IN THE AFTN...BUT DRIER IN
THE LOWER LEVELS. IN THE MOUNTAINS...NO HIGHLIGHTS BUT COULD SEE
UP TO 5 INCHES ABOVE 10 KT THROUGH THE DAY SATURDAY.

SATURDAY NIGHT INTO SUNDAY...THE QG ASCENT SHIFTS TO THE NORTH AND
EAST WITH INCREASING QG DESCENT OVER THE REGION. THE MID LEVEL
TROUGH AXIS SLIDES EASTWARD SATURDAY EVENING...WITH SUBSIDENCE
IN PLACE AS A SHORT WAVE RIDGE PUSHES INTO THE STATE THROUGH
SUNDAY. SOME LINGERING SHOWERS IN THE HIGH COUNTRY WEST OF THE
CONTINENTAL DIVIDE...BUT DOWNSLOPE IN AND NEAR THE FRONT RANGE
FOOTHILLS SHOULD NEGATE MUCH OF THE PCPN IN THE 03Z-06Z WINDOW.
FOR SUNDAY AFTERNOON...SHOWERS AND A FEW STORMS ARE PROGGED TO
DEVELOP AS MID LEVEL MOISTURE AND AFTN HEATING WILL OFFSET THE
INFLUENCE OF THE RIDGE.

SUNDAY NIGHT...A SURFACE HIGH IS PROGGED TO PUSH A COLD FRONT INTO
THE FRONT RANGE IN THE EVENING. LINGERING SHOWERS AND ISOLATED
THUNDERSTORMS WILL LINGER THROUGH SUNDAY EVENING. NOT MUCH IN THE
WAY OF PCPN FM 06Z-18Z MONDAY. THE UPPER RIDGE WILL SHIFT TO THE
EAST WITH THE FLOW ALOFT BECOMING SOUTHWESTERLY AHEAD OF THE NEXT
DEVELOPING TROUGH. MUCH OF THE SHOWER/TSTM ACTIVITY ON MONDAY
AFTN WILL OCCUR IN THE HIGH COUNTRY. MDLS STILL PEG ANOTHER GOOD
CHC OF PCPN FOR MUCH OF THE CWA LATE MONDAY NIGHT THROUGH TUESDAY
EVENING. A MOIST SOUTHERLY FLOW ALOFT AHEAD OF THIS TROUGH...
OVERRUNNING AND STATIONARY FRONTAL BOUNDARY SITTING ALONG THE
FRONT RANGE/PALMER DIVIDE. THIS BROAD TROUGH IS PROGGED TO LIFT
NORTHWARD TUESDAY NIGHT...BUT NOT ENOUGH TO DRY THE REGION OUT ON
WEDNESDAY/THURSDAY. BEST CHC OF SHOWERS/TSTMS THOSE DAYS APPEAR TO
BE FROM THE FRONT RANGE EASTWARD WHERE THE BEST MOISTURE WILL BE.
OVERALL TEMPERATURES WL REMAIN COOLER THAN NORMAL...COLDEST ON
SATURDAY AND THEN TUESDAY/WEDNESDAY OF NEXT WEEK.

&&

.AVIATION...(FOR THE TAFS THROUGH 18Z SATURDAY MORNING)
ISSUED AT 1039 AM MDT FRI MAY 15 2015

AS MENTIONED ABOVE...THERE ARE A NUMBER OF BOUNDARIES FLOATING
AROUND WHICH WILL PLAY HAVOC WITH THE DIA WIND DIRECTIONS. THERE
IS A BOUNDARY WELL SOUTH OF DIA...STILL A FEW HOURS OUT OF BRING
SOUTHEASTERLIES TO THE AIRPORT. THERE IS CONVECTION STARTING IN
CENTRAL DOUGLAS COUNTY RIGHT WHICH MAY ACCELERATE THE ARRIVAL OF
THE SOUTHERLIES OR SOUTHEASTERLIES. WILL LEAVE THE NORTH-
NORTHWESTERLIES IN FOR NOW. WILL GO WITH A TEMPO FOR TSRA AFTER
19Z-20Z. NO CEILING ISSUES.

&&

.HYDROLOGY...
ISSUED AT 1039 AM MDT FRI MAY 15 2015

RIVER LEVELS ON THE SOUTH PLATTE WILL CONTINUE TO SLOWLY
RECEDE WITH THE EXCEPTION OF ITS COURSE THROUGH SEDGWICK. IT IS
STILL EXPECTED TO RISE IN SEDGWICK COUNTY INTO MID DAY SATURDAY
WITH THE CREST AT JULESBURG FORECAST TO BE BELOW FLOOD STAGE. IT
SHOULD START TO RECEDE AT JULESBURG BY SATURDAY AFTERNOON.

THE CACHE LA POUDRE RIVER IN WELD COUNTY IS JUST ABOVE FLOOD
STAGE AND THIS WILL CONTINUE INTO SATURDAY.

&&

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

$$

UPDATE...RJK
SHORT TERM...GIMMESTAD
LONG TERM...COOPER
AVIATION...RJK
HYDROLOGY...RJK



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