Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 041559
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
959 AM MDT MON MAY 4 2015

.UPDATE...
ISSUED AT 1005 AM MDT MON MAY 4 2015

THE BIG PICTURE SHOWS A MOIST AND CLOUDY AIRMASS OVER NORTHEAST
COLORADO WITH A FEW LINGERING SHOWERS. THE MOUNTAINS AND SOUTHWEST
COLORADO ARE MOSTLY SUNNY TO PARTLY CLOUDY. THERE IS AN UPPER LOW
IN SOUTHWEST ARIZONA WITH QUITE A BIT OF THUNDERSTORM ACTIVITY
ACROSS ARIZONA. AS WE LOOK AHEAD TO THIS AFTERNOON THROUGH TONIGHT
WE EXPECT CONVECTION TO DEVELOP ACROSS THE MOUNTAINS AROUND MIDDAY IN
DIFFLUENT SOUTHERLY FLOW ALOFT...THEN SPREAD TO THE PALMER
DIVIDE...AND URBAN CORRIDOR THIS AFTERNOON. THIS EVENING SHOWERS
AND THUNDERSTORMS WILL CONTINUE ACROSS THE CWA WITH A GENERALLY
DECREASING TREND AFTER MIDNIGHT. THE REAL CHALLENGE IS IN THE
DETAILS...MODELS SUGGEST BEST CHANCE OF PRECIPITATION WILL BE FOR
THE PALMER DIVIDE...URBAN CORRIDOR AND FOOTHILLS. NAM SHOWS A HALF
INCH OF RAIN ALONG THAT AREA BY 06Z TONIGHT.  PW VALUES AT 0.74
INCHES THIS MORNING ARE NEAR THE CLIMATOLOGICAL MAX FOR THE
DATE...AND ARE FORECAST TO INCREASE TO 0.87 TONIGHT. WINDS ALOFT
OF 10 TO 15 KNOTS WILL HELP STORMS MOVE...SO THREAT OF FLOODING IS
LOW...BUT ANY THUNDERSTORMS WILL BE CAPABLE OF AN INCH OF RAIN IN
LESS THAN AN HOUR.

&&

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 425 AM MDT MON MAY 4 2015

AIRMASS CONTINUES TO MOISTEN AS MOISTURE IS ADVECTED NORTH AHEAD
OF AN UPPER LOW MOVING OVER CA AND AZ TODAY. HIGH SURFACE PRESSURE
OVER THE DAKOTAS WILL KEEP EASTERLY UPSLOPE FLOW INTO THE STATE
TODAY...THEREFORE BRINGING A CLOUDY COOL DAY WITH GOOD PROBABILITY
OF RAIN. THE DETAILS IN TIMING AND COVERAGE ARE QUITE
DIFFICULT...ESPECIALLY WITH HIGH RES AND MESOSCALE MODELS SHOWING
DRASTICALLY DIFFERENT SOLUTIONS RUN TO RUN.  SCATTERED SHOWERS
THIS MORNING...MAINLY AGAINST THE FOOTHILLS AND SPREADING OVER THE
METRO AREAS SHOULD DECREASE SLIGHTLY THROUGH MID MORNING BEFORE WE
START TO DESTABILIZE A BIT AND SEE AN INCREASE IN COVERAGE AND A
THUNDERSTORMS THIS AFTERNOON. CAPES ARE NOT VERY HIGH AND CURRENT
PW VALUE AROUND 0.7" IS EXPECTED TO INCREASE SLIGHTLY MORE THROUGH
THE DAY...REACHING NEAR RECORD VALUES. THIS WILL MAKE
THUNDERSTORMS MORE PRONE TO LOCALLY HEAVY RAIN. WITH COOLER AIR
OVER THE FAR NORTHEASTERN PLAINS...MORE STABILITY IS EXPECTED
HOWEVER CANNOT TOTALLY RULE OUT TSTORMS. HAVE KEPT THEM OUT OF
THIS AFTERNOON TIME FRAME BUT INCLUDED THEM TONIGHT WHEN COOLER
MIDLEVEL AIR MOVES IN. THE UPSLOPE FLOW IS EXPECTED TO INCREASE
THROUGH THE DAY AND EVENING AND BECOME MORE SOUTHEASTERLY. THIS IS
A FAVORED DIRECTION FOR SOUTH PARK AND THE SOUTHERN FRONT RANGES
AND MOSQUITO RANGE.

AN AREA OF INCREASED MOISTURE WILL MOVE UP FROM THE SOUTH TONIGHT
FOR A CONTINUED CHANCE OF RAIN...POSSIBLY HEAVY AT TIMES WITH
EMBEDDED THUNDERSTORMS....MAINLY EAST OF THE DIVIDE.  AGAIN...DETAILS
ARE HARD TO PINPOINT DOWN. EXPECT SCATTERED TO NUMEROUS SHOWERS
AND MINIMUM TEMPERATURES TO REMAIN MODERATED UNDER LOW CLOUDS.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 425 AM MDT MON MAY 4 2015

...WET AND UNSETTLED WEATHER PATTERN REMAINS IN PLACE THIS WEEK...

THE UPPER LEVEL TROUGH WILL GET KICKED NORTHEAST ACROSS THE
FORECAST AREA TUESDAY AND TUESDAY NIGHT. UNSEASONABLY HIGH
PRECIPITABLE WATER VALUES...A SLIGHTLY UNSTABLE AIRMASS...AND
SKINNY CAPE PROFILES WILL KEEP A THREAT OF LOCALLY HEAVY RAINFALL
IN THE FORECAST. PW VALUES ON TUESDAY WILL RANGE ANYWHERE FROM
0.80 NEAR THE FRONT RANGE TO AS MUCH AS 1 INCH ON THE EASTERN
PLAINS...AT OR NEAR RECORD VALUES FOR THIS TIME OF YEAR.

Q-G LIFT...ALBEIT WEAK...WILL INCREASE AS THE SHORT WAVE
APPROACHES. THIS ALONG WITH A NEUTRAL TO SLIGHTLY UNSTABLE AIRMASS
AND THETA-E/MOIST ADVECTION FROM THE SOUTH SHOULD COMBINE TO BRING
A ROUND OF WIDESPREAD SHOWERS AND A FEW THUNDERSTORMS STARTING
TUESDAY MORNING. WHILE MODELS AGREE WELL IN THE LARGE SCALE
FEATURES...ANY CONVECTIVE COMPLEXES COULD MAKE BIG DIFFERENCES ON
WHERE THE HEAVIER RAIN FALLS. GIVEN THE WIDESPREAD PRECIPITATION
AND LIMITED INSTABILITY WITH CAPES OF JUST A FEW HUNDRED
J/KG...DONT SEE MUCH THREAT OF ANY SEVERE WEATHER. HOWEVER...THERE
MAY BE A THREAT OF SHORT LIVED WEAK TORNADOES AS LOW LEVEL WIND
FIELD STRENGTHENS AND LCLS WILL BE QUITE LOW IN THE 2000-3000 FT
RANGE.

BY LATE TUESDAY NIGHT INTO WEDNESDAY...THE UPPER LEVEL TROUGH
WILL BE MOVING NORTHEAST INTO THE CENTRAL HIGH PLAINS TAKING THE
MAIN AREA OF PRECIPITATION WITH IT. HOWEVER...THERE IS ENOUGH
INSTABILITY LINGERING IN THE STILL RATHER MOIST AND SLIGHTLY
UNSTABLE ENVIRONMENT BEHIND THE TROUGH AXIS TO KEEP A DECENT
CHANCE OF SHOWERS AND A FEW THUNDERSTORMS IN THE FORECAST THROUGH
WEDNESDAY. IT SHOULD BE NOTED THE HIGHER MOUNTAINS COULD ACTUALLY
SEE HEALTHY SNOW ACCUMULATIONS IN THE BACK EDGE DEFORMATION ZONE
OF UPPER TROUGH. SNOW LEVELS EXPECTED TO LOWER A BIT TUESDAY NIGHT
WITH SOME WEAK COLD ADVECTION...SO SNOW LEVELS MAY DROP TO
9500-10000 FEET. OVERALL...THE MORE SIGNIFICANT SNOW TOTALS SHOULD
BE LIMITED TO THE HIGHER MOUNTAIN PEAKS ABOVE 11-12 THOUSAND FEET
WHERE SEVERAL INCHES TO OVER A FOOT OF SNOW WILL BE POSSIBLE
THROUGH THIS EVENT.

A DRIER PERIOD IS STILL EXPECTED LATE WEDNESDAY NIGHT INTO
THURSDAY...ALTHOUGH STILL CANT RULE OUT ISOLATED TO SCATTERED
SHOWER AND STORM DEVELOPMENT AS MOISTURE DOES NOT SCOUR OUT
COMPLETELY.

FOR FRIDAY INTO NEXT WEEKEND...THE STRONGER UPPER LEVEL CLOSED
LOW DROPPING INTO THE DESERT SOUTHWEST AND ANOTHER FRONT BACKING
ACROSS THE PLAINS WILL KEEP THE CHANCE OF SHOWERS AND STORMS IN
THE FORECAST. IT NOW APPEARS THE THREAT OF SEVERE WEATHER WOULD BE
MUCH LOWER AS LONG AS THE COLD FRONT DROPS AND HOLDS FAR ENOUGH
SOUTH KEEPING US IN THE COOLER AIRMASS. A POST FRONTAL UPSLOPE
FLOW WOULD BRING HIGHER PRECIP CHANCES...SO POPS AT OR ABOVE
CLIMATOLOGY WOULD BE WARRANTED. COULD SEE MORE SNOW ACCUMULATION
OVER THE HIGHER MOUNTAINS AGAIN...THIS STORM SYSTEM SEEMS A
LITTLE COLDER THAN TUESDAYS SO SNOW LEVELS MAY REACH VALLEY FLOORS
WHENEVER UPPER TROUGH FINALLY MOVES ACROSS THE STATE.

&&

.AVIATION...(FOR THE TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 1005 AM MDT MON MAY 4 2015

SHOWERS ARE MOSTLY NORTH OF THE METRO AREA AIRPORTS THIS
MORNING...BUT WE HAVE SOME LINGERING STRATUS UP AGAINST THE
FOOTHILLS AS SEEN AT KBJC. AS THE DAY PROGRESSES THE CHANCES OF
PRECIPITATION RETURN WITH SHOWERS AND THUNDERSTORMS LIKELY BY 21Z.
MVRF CIGS AND VSBYS CAN BE EXPECTED NEAR THUNDERSTORMS.
LATER TONIGHT STRATUS AND SHOWERS WILL KEEP WIDESPREAD MVFR CIGS
AND VSBYS AND ISOLATED IFR CONDITIONS THROUGH THE NIGHT.



&&

.HYDROLOGY...
ISSUED AT 425 AM MDT MON MAY 4 2015

INCREASING PRECIPITABLE WATER VALUES TO NEAR RECORD
VALUES...UPSLOPE FLOW THROUGH THE DAY AND WIDESPREAD LIGHT UPWARD
MOTION WILL HELP PRODUCE WIDESPREAD SHOWERS TODAY WITH SOME
EMBEDDED THUNDERSTORMS. SOME STORMS MAY PRODUCE LOCALLY HEAVY
RAINFALL THIS AFTERNOON AND EARLY EVENING...RAINFALL RATES OF
HALF AN INCH OR MORE IN 30 MINUTES ARE POSSIBLE...ESPECIALLY WITH
SLOW MOVING STORMS.

SHOWERS WILL LINGER AND SLOWLY DECREASE IN INTENSITY
TONIGHT...THEN WIDESPREAD SHOWERS AND A FEW THUNDERSTORMS WILL
OCCUR TUESDAY WITH ADDITIONAL RAINFALL AMOUNTS EXPECTED TO AVERAGE
AROUND ONE HALF INCH. HOWEVER...WITH THE HIGH THETA-E AND
PRECIPITABLE WATER VALUES IN PLACE...SOME LOCATIONS COULD EASILY
SEE RAINFALL AMOUNTS IN EXCESS OF 1 INCH DURING THE DAY. AT THIS
TIME...THIS FAVORS POINTS JUST EAST OF THE FRONT RANGE I-25
CORRIDOR WITH THE DEEP SOUTHERLY FLOW. JUST A BIT MORE TURNING
THOUGH AND A STRONGER EASTERLY COMPONENT INTO THE FRONT RANGE
COULD BRING HEAVIER PRECIPITATION THREAT TO THE I-25 CORRIDOR AND
FOOTHILLS. SOME POTENTIAL FOR FLOOD ISSUES IN BURN SCARS IF THAT
SCENARIO UNFOLDS. PRECIP RATES COULD STILL BE LIMITED BY
WIDESPREAD NATURE OF RAIN...AND ONLY ISOLATED TO SCATTERED
THUNDERSTORMS PRODUCING THE LOCALLY HEAVY RAINFALL.

THREAT OF HEAVIER RAINFALL WILL BE ENDING TUESDAY EVENING AS UPPER
TROUGH AND MAIN PRECIPITATION SHIELD PUSHES OFF TO THE NORTHEAST.

&&

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

$$

UPDATE...RTG
SHORT TERM...KRIEDERMAN
LONG TERM...BARJENBRUCH
AVIATION...RTG
HYDROLOGY...RTG/BARJENBRUCH/KRIEDERMAN


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