Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 310513
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
1013 PM MST FRI JAN 30 2015

.UPDATE...
ISSUED AT 1010 PM MST FRI JAN 30 2015

CLOSED UPPER LOW SPINNING OVER LAS VEGAS ATTM CONTINUES TO MAKE
SLOW EASTWARD PROGRESS THIS EVENING. MOISTURE RICH SOUTH-SOUTHWEST
FLOW IN ADVANCE OF THIS CYCLONE HAS ALSO CONTINUED TO STREAM UP
FROM THE DESERT SOUTHWEST AND OVER COLORADO QG VERTICAL VELOCITY
FIELDS INDICATE A WIDENING AREA OF LARGE SCALE ASCENT OVER
SOUTHERN COLORADO AND MOST OF KANSAS BUT LITTLE IN THE WAY OF LIFT
OVER NORTHEAST COLORADO AT THIS TIME. NWS RADAR NETWORK CONFIRM
THESE AREAS OF LIFT AS THEY INDICATE A WIDE AREA OF LIGHT TO
MODERATE PRECIP ACRS KANSAS AND THE SOUTHEAST CORNER OF COLORADO.
WHERE RADARS CAN`T GET TO SUCH AS THE SAN JUAN MTNS IN SWRN
COLORADO SFC OBS INDICATING LIGHT TO MODERATE SNOWFALL IN THE MTNS
AND RAIN/SNOW SHOWERS IN THE VALLEYS.

AROUND HERE...RADARS HAVE DETECTED A WIDENING BAND OF LIGHT PCPN
STRETCHING FROM THE HIGH TERRAIN UP AROUND LOVELAND AND BERTHOUD
PASSES E-SEWRD ACRS PARK...JEFFERSON AND DOUGLAS COUNTIES S-SW OF
DENVER. THIS AREA OF LIGHT PCPN...SNOW ROUGHLY ABV 6000 FT AGL...
RAIN AND SNOW BELOW THAT...WAS SHIFTING VERY SLOWLY NORTHWARD. SO
SLOW THAT THE START OF SNOW WITHIN THE DENVER AREA MAY NOT OCCUR
UNTIL MIDNIGHT OR EVEN AFTER THAT. LATEST MODEL SNOW GUIDANCE
CONTINUES TO SHRINK THE AREA OF MEASURABLE SNOWFALL...CONFINING
MOST OF IT TO THE MTNS...HIGH VALLEYS AND FOOTHILLS. EVEN THERE
HOURLY SNOWFALL RATES ON THE LIGHT SIDE.

THEREFORE HAVE MADE ADJUSTMENTS TO THE FORECAST GRIDS TO ACCOUNT
FOR LESS SNOW ON THE PLAINS TONIGHT. WIND...SKY COVER AND TEMP
GRIDS STILL LOOK GOOD.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 347 PM MST FRI JAN 30 2015

LIGHT SNOW MAKING ITS WAY NORTHEASTWARD TO ABOUT THE EISENHOWER
TUNNEL AT THIS TIME WITH A LARGE AREA OF PRETTY LIGHT
PRECIPITATION OVER WEST CENTRAL COLORADO. MOST VALLEY LOCATIONS
ARE SEEING SOME RAIN OR SNOW THOUGH...SO I WILL HANG ON TO THE
CHANCES OF LIGHT RAIN OR SNOW WE HAVE OVERNIGHT FOR DENVER WHICH
IS HIGHER THAN WHAT MODEL GUIDANCE INDICATES. EXPECTATION IS ONLY
FOR A FEW HUNDREDTHS OF AN INCH OF LIQUID THOUGH...DRIPPING RAIN
AND MAYBE A FRACTION OF AN INCH OF SNOW OVERNIGHT. TEMPERATURES
WILL STRUGGLE TO COOL WITH THE CLOUD COVER...BUT SOME EVAPORATIVE
COOLING WILL HELP...PROBABLY COLD ENOUGH FOR A CHANGEOVER TO SNOW
IN MOST PLACES BUT WITH THE PRECIP BEING LIGHT THERE COULD STILL
BE SOME RAIN. LEFT THE PREVIOUS FORECAST LOWS ALONE.

FOR SATURDAY...CURRENT BATCH OF LIFT SLIDES EAST OF US WITH SOME
DRYING...COULD SEE SOME BREAKS IN THE CLOUDS. THEN
ANOTHER...WEAKER...AREA OF WARM ADVECTION WILL PASS US BY TO THE
SOUTHEAST. PRECIPITATION WITH THIS WILL LIKELY STAY OVER SOUTHEAST
COLORADO INTO KANSAS...BUT I WILL KEEP SLIGHT CHANCES FOR OUR
AREA. I DID RAISE TEMPERATURES SLIGHTLY WITH A WARM START TO THE
DAY EXPECTED AND A LITTLE SUNSHINE OR AT LEAST THINNING OF THE
CLOUDS EXPECTED.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 347 PM MST FRI JAN 30 2015

|MODELS SHOW A SPLIT FLOW OVER THE WESTERN HALF OF THE UNITED STATES
SATURDAY NIGHT WITH A LARGE UPPER LOW OVER NORTHERN MEXICO AND A
DEVELOPING UPPER TROUGH OVER THE NORTHERN ROCKIES AND GREAT PLAINS
STATES. THIS TROUGH WILL SEND A SHORT WAVE AND ASSOCIATED COLD FRONT
INTO NORTHEASTERN COLORADO LATE SATURDAY EVENING. UPSLOPE FLOW
BEHIND THE FRONT COMBINED WITH SOME WEAK LIFT COULD PRODUCE SOME
SNOW SHOWERS ACROSS NORTHEASTERN COLORADO OVERNIGHT SUNDAY INTO
SUNDAY MORNING...WITH THE BEST CHANCE OVER THE PALMER DIVIDE AND
SOUTHERN FOOTHILLS. AT THIS TIME...SNOWFALL AMOUNTS WITH THIS SYSTEM
LOOK TO BE LIGHT WITH AMOUNTS FROM A TRACE TO ONE HALF INCH IN MOST
LOCATIONS.

BY MONDAY MORNING WIND AND SNOW INCREASE IN THE MOUNTAINS AS A MOIST
NORTHWESTERLY FLOW ALOFT DEVELOPS OVER COLORADO. THIS PATTERN SHOULD
BRING A GOOD CHANCE OF SNOW THROUGH WEDNESDAY. THERE ALSO LOOKS TO
BE THE POTENTIAL FOR HIGH WINDS IN THE MOUNTAINS AND FOOTHILLS ON
MONDAY AS A MOUNTAIN WAVE SETS UP. THE NAM CROSS SECTIONS SHOWS A
75+KTS CROSS MOUNTAIN FLOW JUST BELOW MOUNTAIN TOP LEVEL MONDAY
MORNING...WHICH WOULD KEEP THE STRONGEST WINDS OVER THE THE HIGHER
FOOTHILLS AND EASTERN SLOPES OF THE MOUNTAINS. IN ADDITION...THE
DOWNSLOPE FLOW SHOULD WARM TEMPERATURES TO ABOVE NORMAL VALUES ON
THE PLAINS...ESPECIALLY AREAS CLOSER TO THE FOOTHILLS.

BY WEDNESDAY...THERE IS SOME MODEL DIVERGENCE BETWEEN THE GFS AND
THE ECMWF. OVERALL THE PATTERN BETWEEN THE MODELS LOOK
SIMILAR...HOWEVER THE LOCATION OF THE UPPER LEVEL JET IS DIFFERENT.
AT 12Z WEDNESDAY...THE GFS HAS TWO JET STREAKS...ONE OVER NW
NEVADA...WITH ANOTHER STRETCHING FROM EASTERN WYOMING EASTWARD INTO
THE CENTRAL PLAINS. THIS PUTS NORTHERN COLORADO IN A FAVORABLE AREA
FOR LIFT. THIS LIFT COMBINED WITH PLENTY OF PLENTY OF MOISTURE AND
WEAK UPSLOPE WOULD PRODUCE PRECIPITATION FROM DENVER NORTH TO THE
WYOMING BORDER...WHICH IS DEPICTED BY THE MODEL. THE ECMWF SHOWS
THE JET OVER NORTHEAST WYOMING...WITH NOT MUCH LIFT OVER THE
REGION AND THE MAIN PRECIPITATION BAND FURTHER TO THE NORTH OVER
WYOMING. FOR NOW HAVE ONLY ADDED A CHANCE OF POPS IN THE NORTHERN
MOUNTAINS AND A SLIGHT CHANCE OVER THE PLAINS. WARMER AND DRIER
WEATHER IS EXPECTED ACROSS THE FRONT RANGE URBAN CORRIDOR LATE IN
THE WORK WEEK AS UPPER LEVEL HIGH PRESSURE COMBINES WITH DOWNSLOPE
FLOW.|

&&

.AVIATION...(FOR THE TAFS THROUGH 06Z SATURDAY EVENING)
ISSUED AT 1010 PM MST FRI JAN 30 2015

PRECIP HAS BEEN VERY SLOW TO DEVELOP IN THE DENVER AREA THIS
EVENING AND AS A RESULT CEILINGS HAVE BEEN SLOW TO FALL. DENVER
AREA TERMINALS STILL REPORTING VFR CONDITIONS AT THIS HOUR WITH
DRY CONDITIONS AND CIGS UP AROUND 8000 FT AGL. IT STILL APPEARS
CIGS WILL FALL AND AREAS OF LIGHT PRECIP WILL DEVELOP ACRS THE
METRO AREA. HOWEVER AT THIS TIME...IT APPEARS THE RISK OF
ACCUMULATING HAS DECREASED...AND ANY SNOWFALL MAY BE MIXED WITH
LIGHT RAIN OR DRIZZLE. DO NOT SEE ANY RISK OF FREEZING RAIN AND/OR
FREEZING DRIZZLE IN THE METRO AREA REST OF TONIGHT. AS FOR
WINDS...TERMINAL SHOULD SEE LIGHT NORTH-NORTHWEST WINDS...OR
PERHAPS CALM CONDITIONS FOR THE REMAINDER OF THE NIGHT.

&&

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

$$

UPDATE...BAKER
SHORT TERM...GIMMESTAD
LONG TERM...JK
AVIATION...BAKER



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