Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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274
FXUS65 KBOU 190930
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
330 AM MDT TUE MAY 19 2015

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 330 AM MDT TUE MAY 19 2015

UPPER LEVEL LOW WILL BE OVER THE GREAT BASIN TODAY. A STRONG SHORT
WAVE TROUGH EMBEDDED IN THE SOUTHWEST FLOW ALOFT WILL MOVE ACROSS
EASTERN COLORADO TODAY. A SWATH OF PRECIPITATION WILL LIFT NORTHEAST
ACROSS THE STATE THIS MORNING DUE TO STRONG LIFT AHEAD OF THE TROUGH
AND A DIFFLUENT FLOW ALOFT. MODELS CONTINUE TO SHOW AN INCH TO AN
INCH AND HALF OF PRECIPITATION WITH THIS SYSTEM. A LITTLE MORE IN
UPSLOPE AREAS AND LESS OVER DOWNSLOPE AREAS. WILL KEEP 100 POPS IN
THROUGH THE MORNING HOURS AND THEN TAPER DOWN FROM SOUTHWEST TO
NORTHEAST AS THE WAVE LIFTS ACROSS THE STATE.

AIRMASS COOLS THROUGH MID MORNING OVER NORTHERN PARTS OF THE AREA.
COULD BE COLD ENOUGH FOR SNOW TO MIX IN WITH THE RAIN ALONG THE
CHEYENNE RIDGE AND NORTHERN FOOTHILLS. WILL LOWER TO THE SNOW LEVELS
FOR TODAY. WILL MONITOR AND MAY NEED A RAIN SNOW FOR THE LOWER
FOOTHILLS AND CHEYENNE RIDGE LATER THIS MORNING AND AFTERNOON. THERE
IS A CHANCE FOR LIGHT ACCUMULATION ALONG THE CHEYENNE RIDGE AND
LOWER NORTHERN FOOTHILLS. WITH THIS COOLER AIR COMING IN LOWERED
HIGHS FOR TODAY OVER NORTHERN PARTS OF THE AREA.

AS FAR A HIGHLIGHTS GO...ISSUED A WINTER WEATHER ADVISORY FOR ZONE
37...SOUTH PARK WHERE SNOW HAS BEEN COMING DOWN HARD SINCE THE LATE
EVENING HOURS. HEAVIEST SNOW WILL BE ALONG AND NORTH OF 285 WHERE
THE WINTER STORM WARNING IS IN EFFECT. LOWER ELEVATIONS OF PARK
COUNTY MAY SEE MOSTLY RAIN. UNLESS HEAVY RAIN DEVELOPS...PLAN ON
CANCELING THE FLASH FLOOD WARNING FOR THE FOOTHILLS. CURRENT
RAINFALL RATES ARE LESS THAN A QUARTER INCH PER HOUR. JUST EXPECT A
LONG PERIOD OF LIGHT TO MODERATE RAIN. RAIN SHOULD CHANGE TO SNOW
AROUND SUNRISE IN THE HIGHER FOOTHILLS AND COULD FALL TO 7000 FEET
IN THE NORTHERN FOOTHILLS. WILL LEAVE THE FLOOD WATCH FOR THE
NORTHEAST PLAINS AS IS FOR.

RAIN AND SNOW ARE EXPECTED TO END THIS EVENING ACROSS THE AREA. LOW
CLOUDS WILL PERSIST OVERNIGHT AND ARE EXPECTED TO KEEP TEMPERATURES
JUST ABOUT FREEZING...MID TO UPPER 30S. A FEW MODELS ARE SHOWING
LIGHT QPF LATE TONIGHT WHICH WOULD INDICATE DRIZZLE. ANY BREAKS IN
THE CLOUDS MAY ALLOW FOR ENOUGH COOLING FOR FROST.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 330 AM MDT TUE MAY 19 2015

A FLAT UPPER LEVEL RIDGE WILL BUILD OVER THE AREA ON WED AS COOL SFC
HIGH PRES REMAINS OVER ERN CO.  BEST INSTABILITY ON WED WILL BE OVER
THE HIGHER TERRAIN AS A STABLE AIRMASS RESIDES OVER THE PLAINS.
WILL KEEP IN SCT POPS OVER THE HIGHER TERRAIN WITH SOME OF THE
ACTIVITY AFFECTING THE URBAN CORRIDOR BY LATE AFTN INTO THE EARLY
EVENING HOURS. OVER THE PLAINS WILL JUST MENTION A SLIGHT CHC OF
-SHRA. HIGHS ON WED WILL ONLY BE IN THE UPPER 40S TO MID 50S OVER
NERN CO ALTHOUGH ECMWF KEEPS READINGS ROUGHLY 5 DEGREES COOLER.

BY THU ANOTHER UPPER LEVEL TROUGH WILL BE OVER CALIFORNIA WITH SWLY
FLOW ALOFT ACROSS NRN COLORADO.  SFC HIGH PRES WILL BEGIN TO SLOWLY
SHIFT INTO THE CNTRL PLAINS AS LOW PRES DEVELOPS OVER WRN CO.  THIS
WILL ALLOW FOR SELY LOW LVL FLOW EAST OF THE MTNS.  ONCE AGAIN IT
APPEARS THE BEST INSTABILITY WILL STAY IN THE MTNS AND FOOTHILLS
WITH A MORE STABLE AIRMASS OVER THE PLAINS.  THUS WILL KEEP SCT POPS
OVER THE HIGHER TERRAIN WITH ONLY A SLIGHT CHC OVER NERN CO.  HIGHS
ON THU MAY BEGIN TO MODERATE SLOWLY WITH READINGS RISING INTO THE
UPPER 50S TO LOWER 60S.

FOR THU NIGHT INTO FRI APPEARS THERE WILL BE A DISTURBANCE MOVING NE
ACROSS THE AREA AS DEEPER LOW LVL MOISTURE BEGINS TO ADVECT INTO
NERN CO IN SELY LOW LVL FLOW.  BOTH THE ECMWF AND GFS CONTINUE TO
SHOW FAVORABLE MID LVL ASCENT MOVING ACROSS THE AREA SO THERE
SHOULD BE A GOOD CHC OF SHOWERS AND A FEW TSTMS. WITH INCREASING
PRECIPITABLE WATER VALUES MAY SEE SOME HEAVY RAIN OVER PORTIONS OF
NERN CO. BY FRI AFTN THE DISTURBANCE WILL MOVE OUT OF THE AREA
WITH MID LVL DESCENT DEVELOPING ACROSS THE AREA. HOWEVER IF ENOUGH
HEATING OCCURS COULD STILL SEE SOME REDEVELOPMENT OF SCT SHOWERS
AND TSTMS IN SOME AREAS ESPECIALLY OVER THE HIGHER TERRAIN AND
OVER THE URBAN CORRIDOR BY LATE AFTN INTO THE EARLY EVENING
HOURS. AS FOR HIGHS ON FRI WILL KEEP READINGS IN THE LOWER 60S FM
DENVER TOWARDS LIMON WHILE FURTHER NORTH ALONG THE WY-NE BORDER
HIGHS MAY ONLY BE IN THE LOWER TO MID 50S.

BY SAT THE UPPER LEVEL TROUGH OVER THE SWRN US WILL MOVE INTO THE
GREAT BASIN WITH SSW FLOW ALOFT OVER THE AREA.  SFC LOW PRES WILL
EXTEND FM CNTRL WY INTO ERN CO WITH SELY LOW LVL FLOW EAST OF THE
MTNS.  WITH ANOTHER SHOT OF MID LVL ASCENT FCST TO AFFECT THE AREA
WILL LIKELY SEE A GOOD CHC OF SHOWERS AND TSTMS ACROSS THE AREA
WITH SOME SNOW IN THE MTNS.

FOR SAT NIGHT INTO SUN THERE IS SOME DISAGREEMENT BETWEEN THE ECMWF
AND GFS.  THE GFS LIFTS THE MAIN TROUGH INTO WY WHILE THE ECMWF
MOVES IT ACROSS COLORADO.  IF THE TROUGH LIFTS INTO WY THEN PCPN
CHANCES ACROSS NRN CO WOULD BE LOWER WHILE THE ECMWF SOLUTION WOULD
LEAD TO MORE UNSETTLED WEATHER FOR SUN.  FOR NOW WILL JUST KEEP IN A
CHC OF PCPN AND KEEP HIGHS BLO NORMAL.  BY MON THE UPPER LEVEL
TROUGH SHOULD BE EAST OF THE AREA WITH SWLY MID LVL FLOW DEVELOPING.
THIS SHOULD LEAD TO DRIER CONDITIONS WITH WARMER TEMPS.  HOWEVER
THERE WILL STILL BE ENOUGH INSTABILITY FOR AT LEAST A SLIGHT CHC OF
TSTMS ACROSS THE AREA.

&&

.AVIATION...(FOR THE TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 330 AM MDT TUE MAY 19 2015

LOW CLOUDS WILL PREVAIL TODAY AND TONIGHT. CEILINGS WILL FALL TO 500
TO 2000 FEET THROUGH 15Z AND THEN SLOWLY RISE THROUGH THE DAY.
CEILINGS WILL THEN LOWER OVERNIGHT...LIKELY BELOW 1000 FEET BY 12Z
WEDNESDAY. COULD ALSO BE FOG WEDNESDAY MORNING. RAIN WILL PREVAIL
THROUGH ABOUT 18Z TODAY AND MAY LOWER VISIBILITY TO 2-3 MILES. A
DENVER CYCLONE HAS PRODUCE VARIABLE WINDS BUT HAS DISSIPATED.
EASTERLY WINDS UP TO 20 KNOTS ARE EXPECTED THROUGH 00Z. A DENVER
CYCLONE MAY REFORM LATER TODAY AND PRODUCE VARIABLE WINDS AGAIN.

&&

.HYDROLOGY...
ISSUED AT 330 AM MDT TUE MAY 19 2015

STILL ON TRACK FOR AN INCH TO AN INCH AND HALF OF RAINFALL ACROSS
NORTHEAST COLORADO THROUGH TODAY. THERE WILL BE A FEW POCKETS OF
HEAVIER RAINFALL. BEST CHANCE FOR THIS LOOKS TO BE IN THE NORTHERN
FOOTHILLS AND ALSO OVER SOUTHERN WASHINGTON AND LINCOLN COUNTIES.
WOULD EXPECT SOME PONDING OR MINOR FLOODING OF LOW LYING AREAS DUE
TO THE RAIN ON TOP OF SATURATED SOILS. RAINFALL RATES WILL GENERALLY
BE LESS THAN A QUARTER INCH PER HOUR SO THE THREAT FOR FLASH
FLOODING IS LOW AND WILL CANCEL THE FLASH FLOOD WATCH.

WILL LEAVE THE FLOOD WATCH FOR THE CACHE LA POUDRE AND SOUTH PLATTER
RIVER IN EFFECT. DUE TO THE RAINFALL EXPECTED...RIVERS ARE EXPECTED
TO RISE OVER THE NEXT FEW DAYS.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL NOON MDT TODAY FOR COZ037.

WINTER STORM WARNING UNTIL 6 PM MDT THIS EVENING FOR COZ033-034.

&&

$$

SHORT TERM...MEIER
LONG TERM...RPK
AVIATION...MEIER
HYDROLOGY...MEIER



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