Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 220401
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
1001 PM MDT THU MAY 21 2015

.UPDATE...
ISSUED AT 1001 PM MDT THU MAY 21 2015

FORECAST IS LOOKING PRETTY GOOD. EASTWARD PROGRESSION OF SHOWERS
REMAINS A LITTLE SLOW...BUT WITH THE LIFT AND COOLING ALOFT
ARRIVING SHOWERS HAVE FORMED ALONG THE LOWER FOOTHILLS THE LAST
COUPLE OF HOURS...A SIGN THAT THE ENVIRONMENT IS BECOMING MORE
FAVORABLE. STILL EXPECTING THESE TO SPREAD EASTWARD OVER THE NEXT
COUPLE OF HOURS. UPSTREAM RADAR SHOWS A BIT OF A BREAK OVER SOUTH
CENTRAL COLORADO THEN SOME STRONGER CONVECTION ON THE BACK EDGE OF
THE SHORTWAVE...BUT SUSPECT THAT THIS DRIER AREA WILL ACTUALLY
FILL IN WHEN IT GETS EAST OF THE MOUNTAINS INTO THE BETTER
MOISTURE AND CONVERGENCE. SO THE FORECAST OF A BROADER RAIN BAND
FORMING AND MOVING OVER NORTHEASTERN COLORADO LATER TONIGHT AND
EARLY FRIDAY MORNING STILL LOOKS GOOD. I DID LOWER THE LOW
TEMPERATURES A COUPLE OF DEGREES BASED ON CURRENT TRENDS...SNOW
LEVEL MAY DROP AS LOW AS 9000 FEET BUT THE HEAVIEST SNOW AND
IMPACT SHOULD BE ABOVE 10 THOUSAND.

ONLY MINOR CHANGES TO THE RIVER FORECAST. CURRENT CREST MOVING
INTO MORGAN COUNTY...AND ANOTHER OF SIMILAR HEIGHT EXPECTED TO
PASS THROUGH WELD AND MORGAN COUNTIES OVER THE WEEKEND. ONLY MINOR
FLOODING AND ATTENUATING INTO HIGH FLOWS A LITTLE BELOW FLOOD
STAGE BELOW FORT MORGAN...UNLESS THERE IS HEAVIER RAIN THAN
EXPECTED AT SOME POINT.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 339 PM MDT THU MAY 21 2015

CLOUD COVER OVER THE FORECAST AREA HAS BEEN INCREASING AS AN
EJECTING UPPER LEVEL TROUGH ROTATES INTO THE STATE FROM THE SOUTH.
SCATTERED SHOWER ACTIVITY HAS DEVELOPED OVER THE MOUNTAINS BUT
CONVECTION ON THE PLAINS HAS BEEN LIMITED BY THE STABLE LAYER IN
PLACE ACROSS NORTHEAST COLORADO. LATER THIS EVENING...DYNAMIC
FORCING ALOFT SHOULD PRODUCE A WIDESPREAD SHIELD OF PRECIPITATION
THAT EXTENDS FROM THE MOUNTAINS OUT ACROSS THE PLAINS. SNOW LEVELS
IN THE MOUNTAINS SHOULD GRADUALLY COME DOWN...BUT ONLY TO ABOUT
9500 OR 10 THOUSAND FEET. HIGHER MOUNTAIN PASSES ARE EXPECTED TO
PICK UP SEVERAL INCHES OF SNOW...AND THE WINTER WEATHER ADVISORY
REMAINS IN EFFECT FOR THIS.

SHORT RANGE MODELS CONTINUE TO SHOW GENERALLY LIGHT AMOUNTS OF QPF
FROM THIS SYSTEM...WITH THE RAP RUN SHOWING ONE-HALF INCH OR LESS
ACROSS THE PLAINS. ANY RAIN THAT FALLS WILL NOT TAKE VERY LONG TO
FIND ITS WAY TO CREEKS AND STREAMS SINCE THE GROUND REMAINS SO
CLOSE TO SATURATION. LIGHTER AMOUNTS OF RAIN SHOULD REDUCE THE
STRAIN ON THE HYDROLOGIC SITUATION. RIVER LEVELS IN THE DENVER AND
BOULDER AREA HAVE PLENTY OF CAPACITY TO HANDLE TONIGHTS RAINFALL.

LINGERING LIGHT RAIN SHOWERS ARE EXPECTED FRIDAY MORNING AS THE
UPPER TROUGH SLOWLY EXITS THE STATE. THERE SHOULD BE A BREAK IN
THE RAIN BY MIDDAY...BUT AFTERNOON HEATING OF THE MOIST AIRMASS
MAY DE-STABILIZE THE ATMOSPHERE AND PRODUCE SCATTERED
THUNDERSTORMS LATE IN THE AFTERNOON. TEMPERATURES ARE FORECAST TO
BE 5-10 DEGREES WARMER THAN THIS AFTERNOON. THE THREAT OF
LOCALIZED FLOOD PROBLEMS FRIDAY AFTERNOON WILL HINGE ON HOW MUCH
RAIN FALLS TONIGHT AND WHETHER AFTERNOON STORMS TRACK OVER AREAS
THAT RECEIVE APPRECIABLE RAIN TONIGHT.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 339 PM MDT THU MAY 21 2015

SCATTERED RAIN SHOWERS AND ISOLATED THUNDERSTORMS ON FRIDAY
EVENING ARE EXPECTED TO GRADUALLY DECREASE AS THE AIRMASS
STABILIZES...WITH MOST AREAS SEEING PARTIAL CLEARING OVERNIGHT.

SATURDAY IS SHAPING UP TO BE A MORE ACTIVE WEATHER DAY. THE LATEST
MODEL RUNS INDICATE A STRONGER WAVE WITH LARGE SCALE Q-G
ASCENT...NOW LOCATED IN THE EASTERN PACIFIC...ROTATING NORTHEAST
OUT OF THE SOUTHWEST U.S. TROUGH. THE FORECAST AREA WILL LIKELY
RESIDE NEAR THE RIGHT REAR ENTRANCE REGION OF A DEPARTING JET AND
THE LEFT EXIT REGION OF AN APPROACHING SPEED MAX BY AFTERNOON. AT
THE SAME TIME...LOW/MID LEVEL WIND FIELDS WILL BE STRENGTHENING...
AND A SURFACE LOW PRESSURE IS EXPECTED TO DEEPEN OVER EASTERN
COLORADO. THIS WOULD PUT A DRYLINE INTO PLAY DEPENDING EXACTLY ON
WHERE THE SURFACE LOW DEEPENS. THINK THE GFS IS OVERDOING THE LOW
LEVEL DRYING OVER NORTHEAST COLORADO...SO AT THIS TIME FAVOR THE
ECMWF/NAM DEPICTION. CAPES ALONG AND AHEAD OF POTENTIAL DRYLINE
WOULD BE CAPABLE OF INCREASING TO 1500-2000 J/KG WITH SUFFICIENT
HEATING AND T/TD OF 68/50. WIND SHEAR WOULD SUPPORT SUPERCELLS
WITH LARGE HAIL AND TORNADO POTENTIAL...BUT ONLY IF WE GET THE
REQUIRED HEATING. WILL CONTINUE TO MONITOR THIS SEVERE POTENTIAL
THROUGH SATURDAY.

BY SUNDAY...AIRMASS IS STILL EXPECTED TO BE UNSTABLE UNDER
GENERAL TROUGHINESS. BOTH WIND SHEAR AND INSTABILITY WOULD BE A
LITTLE WEAKER THOUGH. SEVERE THREAT IS STILL THERE BUT LOWER THAN
SATURDAY. WILL CONTINUE THE FORECAST OF SCATTERED SHOWERS AND
THUNDERSTORMS.

MONDAY THROUGH MOST OF NEXT WEEK WILL FEATURE MORE AFTERNOON AND
EVENING CONVECTION EACH DAY WITH PLENTY OF RESIDUAL MOISTURE.
HOWEVER...TEMPERATURES WILL BE MODERATING AS FLOW ALOFT TURNS
MORE WESTERLY AND WE SHOULD FINALLY SEE MORE SUNSHINE AT LEAST
DURING THE MORNING HOURS. POTENTIAL FOR EMBEDDED DISTURBANCES
THROUGH THIS PERIOD BUT HARD TO TIME THESE RIGHT NOW.

&&

.AVIATION...(FOR THE TAFS THROUGH 06Z FRIDAY EVENING)
ISSUED AT 1001 PM MDT THU MAY 21 2015

MVFR CONDITIONS WILL PREVAIL OVERNIGHT AS RAIN BECOMES WIDESPREAD.
LOCALIZED IFR IS POSSIBLE. CONDITIONS WILL IMPROVE BETWEEN 15Z AND
18Z AS THE RAIN MOVES OUT...BUT INSTRUMENT APPROACHES TO KDEN WILL
LIKELY STILL BE NEEDED. SCATTERED SHOWERS WILL REDEVELOP IN THE
LATE AFTERNOON AND EVENING WITH LOCALIZED MVFR CONDITIONS AGAIN.

&&

.HYDROLOGY...
ISSUED AT 339 PM MDT THU MAY 21 2015

FLOOD WARNINGS CONTINUE FOR THE SOUTH PLATTE FROM CENTRAL WELD
COUNTY INTO WESTERN MORGAN COUNTY. AT THIS TIME...GENERALLY MINOR
FLOODING IS ANTICIPATED WITH WATER LEVELS BELOW LAST WEEKS CREST.
CONTINUED MINOR FLOODING IS STILL ANTICIPATED ON THE CACHE LA
POUDRE IN WESTERN WELD COUNTY THROUGH EARLY NEXT WEEK.

NO APPRECIABLE RAIN HAS FALLEN IN THE PAST 36-48 HOURS SO THE
RIVERS SHOULD CONTINUE A SLOW DECREASE THROUGH THIS EVENING EXCEPT
FOR THE FLOOD CREST MOVING DOWN THE SOUTH PLATTE WHICH WILL MOVE
THROUGH FORT MORGAN AFTER MIDNIGHT.

ANOTHER ORGANIZED SHORTWAVE WILL MOVE THROUGH THE REGION TONIGHT
WITH MORE LIGHT TO MODERATE RAIN AND SOME EMBEDDED
THUNDERSHOWERS. TOTAL LIQUID PRECIPITATION IS EXPECTED TO RANGE
FROM .25 TO .75 INCHES ON THE PLAINS WITH UPWARDS OF AN INCH
POSSIBLE IN THE MOUNTAINS AND HIGHER FOOTHILLS. ALTHOUGH THESE
AMOUNTS DO NOT SEEM LARGE...THE SATURATED GROUND CONDITIONS
SHOULD RESULT IN EFFICIENT RUNOFF. RIVERS AND STREAMS THAT ARE
ALREADY RUNNING HIGH WILL CONTINUE TO DO SO.

SATURDAY WILL HAVE POTENTIAL FOR STRONGER THUNDERSTORMS WITH
HEAVY RAINFALL AND A FLASH FLOOD THREAT. PRECIPITABLE WATER
VALUES NEAR 0.70 TO 0.90 INCH ON THE PLAINS AND ANY STRONGER DEEP
CONVECTION THAT DEVELOPS WOULD SUPPORT POTENTIAL FOR QUICK 1 TO
1.5 INCH RAINFALL AMOUNTS FROM THE ISOLATED STRONGER STORMS. FLASH
FLOOD GUIDANCE CONTINUES TO DROP WITH ADDITIONAL RAINFALL AND SOIL
SATURATION. SUNDAY MAY ALSO SEE SOME THREAT OF LOCALIZED FLASH
FLOODING BUT MOISTURE LEVELS AND INSTABILITY WILL BE LESS THAN
SATURDAY.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 6 AM MDT FRIDAY FOR COZ034.

&&

$$

UPDATE...GIMMESTAD
SHORT TERM...DANKERS
LONG TERM...BARJENBRUCH
AVIATION...GIMMESTAD
HYDROLOGY...BARJENBRUCH/DANKERS


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