Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 210332
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
932 PM MDT WED MAY 20 2015

.UPDATE...
ISSUED AT 932 PM MDT WED MAY 20 2015

SHOWERS HAVE DIMINISHED...THOUGH THERE ARE STILL A FEW SPRINKLES
AND SOME SPOTTY DRIZZLE. WILL MAINTAIN SOME LOW POPS BUT AMOUNTS
WILL BE VERY LIGHT. ONLY MINOR CHANGES...MAINLY DECREASING THE
SHOWERS MORE QUICKLY.

THE BIG THOMPSON RIVER HAS CRESTED AT ITS MOUTH AND NO PROBLEMS
WERE BEING EXPERIENCED...SO THAT WARNING WAS ALLOWED TO EXPIRE.
OTHERWISE ONLY MINOR TIMING CHANGES TO THE FLOOD FORECASTS ON THE
SOUTH PLATTE FROM KERSEY DOWNSTREAM.

&&

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 304 PM MDT WED MAY 20 2015

LOW CLOUDS REMAIN ENTRENCHED OVER THE PLAINS AS HIGH SURFACE
PRESSURE OVER NEBRASKA KEEPS MOIST EASTERLY FLOW INTO THE STATE.
AS THE RIGHT ENTRANCE REGION OF A JET MOVES OVER THE
AREA...SHOWERS AND THUNDERSTORMS ARE FIRING OVER THE HIGHER
TERRAIN THIS AFTERNOON. CAPE VALUES OVER THE MOUNTAINS ARE
EXPECTED TO BE WEAK...GENERALLY 200-500 J/KG THROUGH EARLY THIS
EVENING...ALLOWING FOR ISOLATED STORMS WITH THE BIGGEST THREAT
BEING CLOUD TO GROUND LIGHTNING. AS THE FOOTHILLS AND PALMER
DIVIDE ARE CLEARING...SOME SHOWERS ARE EXPECTED TO PUSH EAST AND
AFFECT THE METRO AREAS AND EAST OF THE PALMER DIVIDE THIS EVENING.
RAINFALL AMOUNTS ARE EXPECTED TO BE LIGHT...GENERALLY A TENTH OF
AN INCH OR LESS. FORECAST SOUNDINGS NOT SHOWING A LOT IN THE WAY
OF DRIZZLE TONIGHT...PERHAPS SOME PATCHY FOG...BUT NOT AS MUCH AS
WE SAW LAST NIGHT. LOW CLOUDS ARE EXPECTED TO REMAIN OVER THE
PLAINS OVERNIGHT WHICH WILL KEEP LOW TEMPERATURES MODERATED...AND
SLIGHTLY WARMER THAN LAST NIGHT.

WESTERLY FLOW ALOFT WILL BECOME SOUTHWEST THURSDAY AS AN UPPER LOW
PUSHES INTO THE SOUTHWEST US. WITH HIGH SURFACE PRESSURE DROPPING
SOUTH INTO KANSAS...ADDITIONAL LOW AND MID LEVEL MOISTURE WILL BE
BROUGHT NORTHWARD INTO THE STATE. THIS WILL ALLOW FOR SOUTHEAST
LOW LEVEL WINDS AND LESS OF A STABLE ATMOSPHERE OVER THE PLAINS. EXPECT
SCATTERED SHOWERS TO BEGIN FORMING OVER THE HIGH TERRAIN BY NOON
AND BECOME WIDESPREAD IN THE AFTERNOON AS THEY SPREAD EAST ONTO
THE PLAINS. RAINFALL AMOUNTS WILL INCREASE THROUGH THE DAY WITH
THE ADDITIONAL MOISTURE PUMPED UP FROM THE SOUTH AND HIGHER CAPE
VALUES. SNOW LEVELS LOOK TO STAY AT 11 KFT OR HIGHER. EXPECTING
SOUTHEASTERLY LOW AND MIDLEVEL FLOW IN THE AFTERNOON WHICH IS
FAVORED FOR THE SOUTH PARK AREA...EXPECT HIGHER RAIN AND SNOWFALL
AMOUNTS THERE LATE AFTERNOON. MAX TEMPERATURES WILL BE ABOUT 5 TO
10 DEGREES WARMER THAN TODAY.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 304 PM MDT WED MAY 20 2015

THURSDAY NIGHT TO FRIDAY... LONGWAVE TROF POSITION IN THE SOUTHWEST
KEEPS CWA IN MOIST ACTIVE FLOW THROUGH WEEKEND. A STRONG SHORTWAVE
IN THE PATTERN SHOULD MOVE FROM THE DESERT SOUTHWEST TO NORTHEAST
COLORADO LATE THUR THRU EARLY FRI. ALTHOUGH LOW LEVEL UPSLOPE
ALONG EASTERN FOOTHILLS MAY BE WEAKER THAN PREVIOUS STORM... THE
SUBTROPICAL JET POSITION AND QG FIELD SUGGEST GOOD SUPPORT FOR
UPWARD MOTION LATER THURSDAY AND THURSDAY NIGHT IN NORTHEASTERN
COLORADO. BOTH ECMWF AND GFS SUGGEST A LARGE AREA OF MODERATE
RAINFALL MOVING SOUTH TO NORTH THRU THE CWA. THE MAIN DIFFERENCE
BETWEEN THE TWO MEDIUM RANGE MODELS IS THAT THE GFS IS ROUGHLY 6
HOURS FASTER. SNOW LEVELS ARE LIKELY TO REMAIN ABOVE 12000 FEET
WHERE 5-10 INCHES MAY OCCUR. SOME BREAKS IN THE OVERCAST ARE
LIKELY DURING THE DAY FRIDAY... BUT MODEL SOUNDINGS INDICATE THAT
ANY WARMING WOULD BE ABLE TO TRIGGER SOME SHOWERS OR
THUNDERSHOWERS LATE IN THE DAY.

FOR SATURDAY AND SUNDAY... ANOTHER SHORTWAVE IN THE SOUTHWESTERN
TROF SHOULD LIFT THROUGH BUT THE UNCERTAINTY IS WHETHER THE MAIN
PIECE WILL COME OUT SATURDAY AS THE ECMWF SUGGESTS... OR SUNDAY AS
THE GFS SUGGESTS. THIS NEXT SYSTEM DOES NOT HAVE A STRONG DYNAMIC
STRUCTURE LIKE THE ONE THURSDAY NIGHT DOES. EXPECT SOME BREAKS IN
THE OVERCAST AT TIMES BUT WITH PERIODS OF SHOWERS/THUNDERSHOWERS...
ESPECIALLY LATE IN THE DAY. LATER SHIFTS SHOULD WATCH FOR THE
POSSIBILITY OF A COOL & WET DAY ON SUNDAY AS SOME MODEL MEMBERS
SUGGEST.

MONDAY-WEDNESDAY... MORE ACTIVITY CONTINUES WITH THE RELATIVELY
MOIST SOUTHWEST FLOW. EXPECT SUNNY PERIODS BUT WITH LATE DAY
SHOWERS AND THUNDERSHOWERS. ENSEMBLES SUGGEST A TENDENCY TOWARD
MORE ZONAL FLOW BY MIDWEEK WHICH COULD LEAD TO A WARMER AND DRIER
TREND... BUT NOT VERY CONFIDENT ON THAT SOLUTION YET.

&&

.AVIATION...(FOR THE TAFS THROUGH 06Z THURSDAY EVENING)
ISSUED AT 932 PM MDT WED MAY 20 2015

MVFR CONDITIONS WITH AREAS OF IFR WILL CONTINUE OVERNIGHT. A WEAK
DENVER CYCLONE WILL LIKELY FORM AROUND SUNRISE...POTENTIALLY
ALLOWING AREAS EAST AND SOUTH OF THE CITY TO CLEAR BUT HOLDING LOW
CLOUDS OVER DENVER THROUGH MIDDAY. NOT SURE WHICH SIDE KDEN WILL
BE ON...BUT MORE LIKELY IT WILL BE IN THE CLOUDS AT LEAST THROUGH
16Z AND POSSIBLY AS LONG AS 18Z. CEILINGS SHOULD BE SLOWLY LIFTING
IN THE CLOUD DECK THOUGH...PROBABLY IN THE MVFR CATEGORY AT KDEN
BY 16Z. SCATTERED SHOWERS WITH AREAS OF MVFR WILL REDEVELOP IN THE
LATE AFTERNOON...BUT MORE WIDESPREAD RAIN WILL LIKELY WAIT UNTIL
EVENING.

&&

.HYDROLOGY...
ISSUED AT 304 PM MDT WED MAY 20 2015

FLOOD WARNINGS CONTINUE FOR THE SOUTH PLATTE FROM CENTRAL WELD
COUNTY INTO MORGAN AND NORTHWEST WASHINGTON COUNTIES. THE CREST
WILL BE MOVING DOWNSTREAM TOWARD KERSEY AND EASTERN WELD COUNTY
TONIGHT...AND WILL PUSH THROUGH CENTRAL MORGAN COUNTY ON
THURSDAY. AT THIS TIME...GENERALLY MINOR FLOODING IS ANTICIPATED
WITH WATER LEVELS BELOW LAST WEEKS CREST. MINOR FLOODING ALSO
ANTICIPATED ON THE CACHE LA POUDRE NEAR GREELEY. MEANWHILE...THE
BIG THOMPSON FROM MILLIKEN TO THE CONFLUENCE WITH THE SOUTH PLATTE
NEAR LASALLE APPEARS TO BE PEAKING IN FLOWS THIS AFTERNOON AND
FLOOD WARNING SHOULD BE ALLOWED TO EXPIRE LATER THIS EVENING.

ANOTHER ORGANIZED SHORTWAVE MOVING THROUGH THE REGION LATE
THURSDAY AND THURSDAY NIGHT IS LIKELY TO TRIGGER AN AREA OF RAIN
WITH SOME EMBEDDED LOCALLY MODERATE-HEAVY SHOWERS OR
THUNDERSHOWERS. TOTAL LIQUID PRECIPITATION AMOUNTS ARE LIKELY TO
EXCEED 0.50 INCHES IN MANY AREAS... WITH SOME LOCAL AMOUNTS
GREATER THAN AN INCH. ALTHOUGH THESE ARE NOT EXCEPTIONAL NUMBERS
THE SATURATED GROUND CONDITIONS SHOULD RESULT IN EFFICIENT RUNOFF.
EXPECT THE CONTINUATION OF HIGH FLOWS IN RIVERS AND STREAMS THAT
ARE ALREADY HIGH... AND POSSIBLY THE DEVELOPMENT OF BANKFULL OR
MINOR FLOODING IN OTHER STREAM AND RIVERS. LOCAL FLOODING MAY
OCCUR IN AREAS OF HEAVIER SHOWERS.

&&

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

$$

UPDATE...GIMMESTAD
SHORT TERM...KRIEDERMAN
LONG TERM...BARJENBRUCH/KELSCH
AVIATION...GIMMESTAD
HYDROLOGY...BARJENBRUCH/KELSCH



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