Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 121701
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
1101 AM MDT SAT APR 12 2014

.UPDATE...NOT PLANNING ON MANY CHANGES AT THIS POINT IN TIME.
CLOUD COVER IS RATHER EXTENSIVE WHICH MAY SHAVE A FEW DEGREES OFF
OF TODAY`S MAXIMUM TEMPERATURES AND LIMIT AFTERNOON CONVECTIVE
ACTIVITY AS WELL. FOR THE OVERNIGHT PERIOD SOME OF THE NEWER MODEL
DATA COMING IN SUGGESTS THAT PRECIPITATION MAY REMAIN LIQUID IN
MANY AREAS OVERNIGHT AND PERHAPS INTO TOMORROW MORNING AS WELL...
AT LEAST AT THE LOWER ELEVATIONS. THIS WILL HAVE AN IMPACT ON
OVERALL SNOW TOTALS AND SUBSEQUENT HIGHLIGHTS. WILL MULL THIS OVER
SOME MORE PRIOR TO UPGRADING ANYTHING.

&&

.AVIATION...PRETTY LOW WEATHER IMPACT DAY TODAY. WINDS SHOULD HOLD
ON TO SOME KIND OF WESTERLY COMPONENT THROUGHOUT THE DAY AND INTO
THE EVENING. PERHAPS A BIT OF CONVECTION DURING THE AFTERNOON AND
ATTENDANT VARIABLE/GUSTY WINDS BUT THREAT APPEARS LOW AT THIS
TIME. MORE SERIOUS ISSUES EXPECTED LATER TONIGHT AND SUNDAY WITH
ARRIVAL OF COLD FRONT AND UPPER TROUGH. 18Z TAFS WILL PROBABLY
REFLECT A LONGER PERIOD OF RAIN THAN THE PREVIOUS ISSUANCE.

&&

.PREV DISCUSSION... /ISSUED 515 AM MDT SAT APR 12 2014/

SHORT TERM...HIGH CLOUDS SPREADING OVER COLORADO BUT LOW LEVELS
ARE STILL DRY. MID LEVEL LAPSE RATES ARE A BIT STEEPER TODAY WHICH
COULD ALLOW FOR MORE CONVECTION...BUT THE DRY LOW LEVELS WILL
LIMIT CAPES TO LESS THAN 500 J/KG. IT MAY BE DIFFICULT TO GET
THUNDER...AND THE WEAK CONVECTION MAY PRODUCE MORE VIRGA THAN
RAIN. AT THIS POINT EXPECT THERE TO BE ENOUGH HOLES IN THE CLOUDS
TO ALLOW THE WARM TEMPERATURES WE ARE SHOWING...FORECAST AND
GUIDANCE ARE SIMILAR AND I WILL LEAVE THEM ALONE.

SOUTHERN STREAM SYSTEM PASSING UNDER US WILL MAINTAIN PRESSURE
FALLS TO THE SOUTH...THIS SHOULD PULL WINDS ON THE PLAINS MORE
NORTHERLY...BUT THIS WILL BE BATTLING THE MIXING NEAR THE
MOUNTAINS AND COULD MAINTAIN A CONVERGENCE ZONE OVER OUR PLAINS
WHICH COULD ALSO HELP CONVECTION A BIT.

NORTHERN STREAM SYSTEM WILL RACE THROUGH LATE TONIGHT WITH SHARP
COOLING. ENOUGH OF A TEMPERATURE GRADIENT THAT THE COLD FRONT MAY
GET OUT AHEAD OF THE UPPER WAVE A LITTLE BIT...BUT IT SHOULD ALL
BE THROUGH BY 12Z OR A FEW HOURS AFTER. GFS SHOWS PRETTY GOOD SNOW
FROM ABOUT BOULDER NORTHWARD BY 12Z WHILE OTHER MODELS HAVE IT
JUST DEVELOPING. LIGHT SHOWERS AHEAD OF THE FRONT MAY BE
RAIN...BUT I DO EXPECT SNOW PRETTY QUICKLY BEHIND THE
FRONT...MAYBE LESS CERTAIN OF THIS BELOW 5000 FEET.
OVERALL ONLY MINOR ADJUSTMENTS TO THE FORECASTS...MAINLY CLOUD
COVER TODAY. WINTER STORM WATCH WILL STAND STARTING LATE TONIGHT.

LONG TERM...MODELS HAVE MODERATE WEST-SOUTHWESTERLY FLOW ALOFT OVER
THE CWA SUNDAY.  AN UPPER TROUGH MOVES EASTWARD ACROSS COLORADO
SUNDAY NIGHT. NORTH-NORTHWESTERLY FLOW ALOFT IS PROGGED ON MONDAY
..BECOMING MORE NORTHWESTERLY MONDAY NIGHT. THERE IS PRETTY
DECENT QG ASCENT OVER THE FORECAST AREA SUNDAY AND SUNDAY EVENING.
THE STRONGEST ENERGY IS PROGGED TO THE SOUTHWEST OF THE CWA AT 00Z
SUNDAY AFTERNOON. DOWNWARD MOTION IS PROGGED ON MONDAY INTO MONDAY
EVENING. THE BOUNDARY LAYER HAS UPSLOPE FLOW SUNDAY AND SUNDAY
EVENING...THEN NORTHWESTERLIES LATER SUNDAY NIGHT. NORMAL DIURNAL
PATTERNS LOOK GOOD FOR MONDAY...SAME WITH MONDAY NIGHT WITH A BIT
OF DOWNSLOPING SOUTHWESTERLIES MIXED IN. MODELS STILL SHOW DEEP
MOISTURE FOR ALL THE CWA SUNDAY AND SUNDAY EVENING. THE GFS AND
NAM START DECREASING MOISTURE AFTER 06Z SUNDAY NIGHT...THE ECMWF
KEEPS IT THROUGH 12Z MONDAY MORNING. MONDAY AND MONDAY NIGHT ARE
PRETTY DRY ON ALL THE MODELS. MODELS HAVE A BIT OF CAPE OVER THE
SOUTHWESTERN CWA SUNDAY AFTERNOON. THERE IS MEASURABLE
PRECIPITATION OVER THE CWA SUNDAY AND SUNDAY NIGHT...WITH NOTHING
MONDAY AND MONDAY NIGHT. THE GFS HAS FAIRLY HIGH AMOUNTS SUNDAY
AND SUNDAY EVENING...THE NAM LESS AND THE ECMWF WAY LESS. WE WOULD
NEED NO HIGHLIGHTS IF WE WENT WITH THE ECMWF PRECIPITATION
AMOUNTS...BUT WARNINGS FOR SNOW IF THE GFS PANS OUT FOR THE
MOUNTAINS AND FOOTHILLS. NOT SURE HOW MUCH SNOW WILL BE ABLE TO
ACCUMULATE ON THE PLAINS DURING THE DAY SUNDAY. TEMPERATURES ARE
NOT VERY COLD AND THE EARTH HAS BEEN WARMING UP QUITE A BIT THE
LAST FEW DAYS. ALL THE SAME...WIDESPREAD SNOW IS EXPECTED WITH
THE SYNOPTIC SCALE SITUATION...UPSLOPE...COLD AIR AND MOISTURE IN
MIND. WILL LET THE "WATCH" HIGHLIGHTS RIDE FOR THIS FORECAST
PACKAGE AND WILL SAY THAT SOME HIGHLIGHTS LOOK LIKELY FOR THE
DIVIDE MOUNTAINS ZONES AND FOOTHILLS ZONES FOR SURE. TEMPERATURES
LOOK TO BE 12-25 C COLDER ON SUNDAY THAN TODAY. MONDAY`S HIGHS
COME UP 3-6 C FROM SUNDAY`S. FOR THE LATER DAYS...TUESDAY THROUGH
FRIDAY...THERE IS UPPER RIDGING ON TUESDAY...THEN WEST-
SOUTHWESTERLY FLOW ALOFT ON TUESDAY NIGHT INTO WEDNESDAY. BY LATE
WEDNESDAY THROUGH WEDNESDAY NIGHT...THERE IS UPPER TROUGHING. THE
GFS SHOWS THIS SIGNIFICANTLY STRONGER THAN THE ECMWF AND THE GFS
00Z RUN FROM YESTERDAY. BOTH THE GFS AND ECMWF BRING A COLD FRONT
INTO THE CWA BY MID DAY WEDNESDAY...WITH UPSLOPE BEHIND IT. THE
GFS HAS SIGNIFICANT MOISTURE WITH IT AND COLD AIR. IN FACT...THE
00Z WEDNESDAY AFTERNOON 850 MB TEMPERATURE ON THE GFS OVER DIA IS
21 C COLDER THIS 00Z MODEL RUN COMPARED TO LAST NIGHT`S VERSION.
PRETTY SKETCHY. THE GFS HAS WAY MORE MOISTURE ON IT COMPARED FOR
WEDNESDAY MIDDAY INTO THURSDAY AFTERNOON COMPARED TO THE ECMWF.
WILL GO A BIT COOLER WITH MAYBE SOME POPS. NOT READY FOR "LIKELY"
POPS JUST YET WITH THE MID WEEK FEATURE.

AVIATION...VFR CONDITIONS TODAY WITH SOME UNCERTAINTY ABOUT WIND
DIRECTION. WINDS WILL BE UNDER 10 KNOTS THROUGH MIDDAY...EXPECTING
SOUTHWEST WINDS TO PREVAIL BUT THERE COULD BE SOME VARIABILITY.
THIS AFTERNOON THERE WILL BE A BATTLE BETWEEN WESTERLIES MIXING
DOWN AND A TENDENCY TOWARD NORTHEAST WINDS ON THE PLAINS. TAFS
SHOW THE MIXING WINNING WITH WEST TO NORTHWEST WINDS IN THE MID TO
LATE AFTERNOON...THEN NORTH WINDS INCREASING AFTER 00Z...BUT THIS
CHANGE COULD COME SOONER.

ONLY ISOLATED SHOWERS THIS AFTERNOON...POSSIBLY SOME INCREASE THIS
EVENING. SNOW WILL LIKELY BEGIN BETWEEN 08Z AND 12Z. INSTRUMENT
APPROACHES TO KDEN MAY BE NEEDED AFTER 00Z...WITH WIDESPREAD IFR
CONDITIONS LIKELY AFTER 10Z. LOOKING AT STORM TOTAL SNOWFALL
SUNDAY/SUNDAY NIGHT OF 4 TO 7 INCHES AT KDEN AND 5 TO 10 INCHES AT
KAPA/KBJC. IMPACT WILL BE LESSENED BY WARM SURFACE TEMPERATURES
CAUSING MORE MELTING THAN USUAL.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...WINTER STORM WATCH FROM LATE
TONIGHT THROUGH SUNDAY EVENING FOR COZ030>041.

&&

$$

SHORT TERM...GIMMESTAD
LONG TERM....RJK
AVIATION...GIMMESTAD
UPDATE/AVIATION...ET



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