499  
FXUS65 KBOU 291620  
AFDBOU  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DENVER/BOULDER CO  
1020 AM MDT THU JUL 29 2021  
   
UPDATE
 
 
ISSUED AT 1020 AM MDT THU JUL 29 2021  
 
SATELLITE SHOWS A SHORT WAVE LIFTING NORTHWARD THROUGH WYOMING,  
WHILE MID LEVEL DRYING AND SUBSIDENCE IS NOTED OVER MOST OF OUR  
FORECAST AREA - BUILDING IN FROM THE SOUTHEAST AROUND THE  
DOMINATING UPPER LEVEL HIGH CENTERED OVER KANSAS. THAT SAID, THERE  
WAS A LITTLE MORE MID LEVEL MOISTURE THIS MORNING AS NOTED BY  
SATELLITE TRENDS AND SCATTERED MID LEVEL CLOUDS. UNFORTUNATELY,  
THE 12Z DENVER SOUNDING WAS UNAVAILABLE. AT THE SURFACE, LOW LEVEL  
MOISTURE HAD INCREASED ACROSS THE PLAINS BEHIND A WEAK FRONTAL  
SURGE. THAT SHOULD OFFER UP A COUPLE DEGREES OF COOLING FROM  
YESTERDAY, BUT IT WILL STILL BE HOT! THE FRONT WAS ALREADY WASHING  
OUT PER LATEST OBSERVATIONS TRENDING MORE EASTERLY.  
 
REGARDING THE FORECAST, THERE COULD BE JUST ENOUGH LOW LEVEL  
CONVERGENCE AND WEAKENING OF THE CAP TO PRODUCE ISOLATED  
THUNDERSTORMS. MLCAPE IS QUITE LIMITED ALONG THE FRONT RANGE, BUT  
THE NORTHEAST CORNER HAS UP TO 2000 J/KG OF MLCAPE SO IF WE CAN  
BREAK THE CAP THERE CAN'T RULE OUT AN ISOLATED PULSE SEVERE STORM.  
WE COULD ALSO SEE A COUPLE STORMS WITH LOCALLY HEAVY RAIN TOWARD  
THE NORTHERN BORDER AREA IN THE MOUNTAINS THIS AFTERNOON WHERE MID  
LEVEL MOISTURE IS SLOWER TO SCOUR OUT - PER RECENT WATER VAPOR  
IMAGERY. IF WE DO POP A SHOWER/STORM ALONG THE I-25 CORRIDOR, IT  
WOULD MOST LIKELY BE OVER THE PALMER DIVIDE/SOUTHERN DENVER METRO  
AREA WITH A BIT OF LOW LEVEL CONVERGENCE THERE TO HELP CONVECTIVE  
INITIATION. WOULDN'T EXPECT MORE THAN A BRIEF PERIOD OF  
LIGHT/MODERATE RAIN, GUSTY WINDS, OR AN ISOLATED LIGHTNING STRIKE.  
 

 
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 331 AM MDT THU JUL 29 2021  
 
HOT, DRY AND MOSTLY CLEAR CONDITIONS WILL PERSIST TODAY WITH THE  
RIDGE FAIRLY STATIONARY OVER THE COUNTRY, CENTERED OVER KANSAS.  
THE WARMING TREND SHOULD BREAK WITH HIGHS COOLING A FEW DEGREES  
ACROSS NORTHEAST COLORADO, THOUGH STILL A BIT WARMER THAN NORMAL.  
OVERALL SMOKE CONCENTRATIONS SHOULD REMAIN RELATIVELY LOW AS  
CIRCULATION AROUND THE HIGH KEEPS SMOKE NORTH OF THE STATE BORDER  
AGAIN. SATELLITE WATER VAPOR IMAGERY SHOWS INCREASING MID LEVEL  
MOISTURE TO OUR WEST, WHICH IS GRADUALLY SHIFTING EAST TO OUR  
MOUNTAINS. INSTABILITY IS INCREASING BUT FORECAST SOUNDINGS  
SUGGEST THAT MODERATE CAPPING WILL REMAIN IN PLACE WHICH SHOULD  
CONTINUE TO LIMIT CONVECTION. STILL, ISOLATED TO SCATTERED SHOWERS  
AND WEAK THUNDERSTORMS ARE POSSIBLE, MAINLY OVER THE HIGH TERRAIN  
THOUGH THERE IS SOME POTENTIAL FOR ISOLATED STORMS ON OUR  
NORTHEAST PLAINS CLOSE TO A BAND OF STRONGER INSTABILITY NEARBY IN  
NEBRASKA. STORMS MAY BRING LIGHT PRECIPITATION AND GUSTY OUTFLOW  
WINDS BUT NO SIGNIFICANT HAZARDS ARE LIKELY. EXPECT MOSTLY CLEAR  
TO PARTLY CLOUDY SKIES OVERNIGHT WITH LOWS SIMILAR TO THIS  
MORNING, IN THE MID 60S ON THE PLAINS AND UPPER 40S AND LOWER 50S  
IN THE HIGH COUNTRY.  
   
LONG TERM
 
(FRIDAY THROUGH WEDNESDAY)  
ISSUED AT 331 AM MDT THU JUL 29 2021  
 
FRIDAY AND FRIDAY NIGHT, A BROAD UPPER LEVEL RIDGE AXIS WILL STRETCH  
FROM THE SOUTHERN PLAINS INTO THE NORTHERN ROCKIES. THE MODELS  
SHOW SUBTROPICAL MOISTURE ACROSS MEXICO ADVECTING INTO THE GREAT  
BASIN/WESTERN CO LATE IN THE DAY. THE FLOW ALOFT OVER THE FORECAST  
AREA WILL BE WEAK AND GENERALLY OUT OF THE NORTHWEST, WITH SOME  
OF THESE STORMS DRIFTING SOUTHEAST OFF THE FOOTHILLS AND INTO THE  
URBAN CORRIDOR. THE MODELS ALL INDICATE THE 700/500 LAYER MAX  
THETA-E VALUES ACROSS WESTERN AND NORTHERN CO AT 00Z SATURDAY,  
WITH MIXING RATIO OF 6-8G/KG. PWAT VALUES 0-8-0.9 INCH IN THE  
MOUNTAINS. AND UP TO 1.10 INCH ACROSS THE NORTHEAST PLAINS. HIGH  
TEMPERATURES ON FRIDAY AGAIN HOT, IN THE MID 90S ACROSS THE URBAN  
CORRIDOR AND NORTHEAST PLAINS THROUGH MID AFTERNOON, WITH A COLD  
FRONT PUSHING ACROSS LATE IN THE DAY. BEST CHANCE OF THUNDERSTORMS  
WILL BE OVER THE MOUNTAINS DURING THE AFTERNOON, WITH THE  
COVERAGE INCREASE ACROSS THE PLAINS IN THE LATE AFTERNOON AND  
EVENING, AS A FRONTAL BOUNDARY PUSHES SOUTH AND WEST INTO THE  
PLAINS. THIS WILL SET THE TABLE FOR A HIGHER LIKELIHOOD OF  
SHOWERS AND THUNDERSTORMS FOR SATURDAY.  
 
SATURDAY INTO SATURDAY NIGHT, THE AIRMASS WILL BE MOIST ACROSS THE  
MOUNTAINS AND PLAINS. ON SATURDAY, THE FLOW ALOFT SHOULD BE EVEN  
WEAKER WITH THE RIDGE AXIS EXTENDING FROM WEST TX INTO THE  
NORTHERN ROCKIES. THE MODELS ALL SHOW THE 700/500 LAYER MAX  
THETA-E ACROSS MUCH OF CO, IN AND NEAR THE FRONT RANGE  
MOUNTAINS/FOOTHILLS AND PALMER DIVIDE SATURDAY AFTERNOON AND  
EVENING. LOW LEVEL EASTERLY WINDS WILL KEEP THE BEST MOISTURE  
CONVERGENCE ANCHORED IN AND NEAR THE FRONT RANGE FOOTHILLS/PALMER  
DIVIDE, WHICH WILL ELEVATE THE FLASH FLOOD THREAT ESPECIALLY IN  
AND NEAR THESE REGIONS WITH THE GREATEST AREA OF CONCERN IN THE  
BURN SCARS. 500/700 LAYER MIXING RATIOS AROUND 6 G/KG ACROSS THE  
FORECAST AREA. WEAK STORM MOTIONS COUPLED WITH WITH PWAT VALUES  
1.0-1.3 INCHES POSSIBLE. COOLER TEMPERATURES ACROSS THE NORTHEAST  
PLAINS WILL ALLOW FOR BETTER STABILITY, ESPECIALLY OVER THE  
NORTHEAST CORNER. THE AIRMASS WILL BECOME INCREASINGLY UNSTABLE  
AS YOU GO WESTWARD INTO THE FOOTHILLS. THIS WILL RESULT IN  
POTENTIAL RAINFALL RATES UP TO 2 INCHES IN LESS THAN ONE HOUR,  
WITH SOME OF THE STORMS.  
 
SUNDAY INTO SUNDAY NIGHT, THE SYNOPTIC PATTERN DOES NOT CHANGE  
MUCH. ANOTHER COOL FRONT PUSHES INTO THE NORTHEAST PLAINS SUNDAY.  
NORTHEAST WINDS BEHIND THE FRONT WILL KEEP THE MOISTURE  
CONVERGENCE ANCHORED ALONG THE HIGHER TERRAIN. PWAT VALUES REMAIN  
HIGH RANGING FROM 1.0 INCH IN THE MOUNTAINS TO 1.4 INCH ACROSS THE  
PLAINS. MOISTURE IS NOT GOING ANYWHERE, NOR WILL THE THREAT FOR  
FLASH FLOODING. BURN SCARS WILL REMAIN THE MOST VULNERABLE BUT  
THE THREAT OF FLASH FLOODING WILL EXIST OUTSIDE THOSE AREAS AS  
WELL. STABILITY WILL BE GREATEST OVER THE FAR NORTHEAST PLAINS,  
THEN DECREASE WESTWARD INTO THE FRONT RANGE.  
 
OVERALL THE TREND FOR EARLY NEXT WEEK WILL BE FOR A GRADUAL DECREASE  
IN MOISTURE AND A GRADUAL INCREASE IN TEMPERATURES. THE THREAT FOR  
HEAVY RAIN PRODUCING THUNDERSTORMS STILL EXISTS, ALTHOUGH THE  
COVERAGE WILL DECREASE SOMEWHAT. THE RIDGE BY THAT TIME WILL BE  
OVER THE DESERT SOUTHWEST, ALLOWING FOR MORE OF NORTHWESTERLY FLOW  
ALOFT OVER THE FORECAST AREA. THIS SHOULD START TO SHIFT THE BEST  
MOISTURE MORE TO THE WEST AND SOUTH. A MID LEVEL TROUGH OVER THE  
WEST COAST FINALLY MOVES ONSHORE AND PASSES ACROSS THE NORTHERN  
ROCKIES BY MIDWEEK. THIS COULD STIR UP A BETTER CHANCE OF  
THUNDERSTORMS AS WELL AS THE TROUGH AXIS BRUSHES ACROSS WY.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)  
ISSUED AT 1020 AM MDT THU JUL 29 2021  
 
VFR CONDITIONS WILL PERSIST THROUGH 18Z FRIDAY. NORTH/NORTHEAST  
WINDS ARE EXPECTED TO SHIFT MORE EAST/SOUTHEAST THROUGH THE DAY AS  
THE WEAK FRONTAL BOUNDARY WASHES OUT. THERE IS A LOW RISK OF AN  
ISOLATED SHOWER/STORM PRODUCING GUSTY OUTFLOW WINDS TO AROUND 35  
KNOTS 22Z-01Z. MAIN CHANCE OF THAT WOULD STAY JUST SOUTH/EAST OF  
DIA. WINDS ARE EXPECTED TO TURN BACK TO SOUTH/SOUTHWEST BY 06Z  
TONIGHT AND THEN SWITCH MORE WEST/NORTHWEST AGAIN 13Z-17Z FRIDAY.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 1020 AM MDT THU JUL 29 2021  
 
FOR THIS AFTERNOON AND EVENING, THE CAMERON PEAK AND EAST  
TROUBLESOME BURN AREAS WILL BE ON THE EDGE OF THE MONSOONAL  
MOISTURE PLUME. THUS, THERE IS A LIMITED THREAT OF FLASH FLOODING.  
A STRONGER STORM WOULD BE CAPABLE OF PRODUCING A HALF INCH OF  
RAIN IN 20-30 MINUTES. THE CALWOOD AND WILLIAMS FORK BURNS ARE  
FARTHER SOUTH AND EAST IN THE DRIER AIR WITH LITTLE TO NO THREAT  
OF HYDROLOGIC ISSUES LATER TODAY.  
 
FOR FRIDAY, THE THREAT OF FLASH FLOODING WILL INCREASE A LITTLE  
MORE AS THERE IS MORE CONFIDENCE THE MOISTURE PLUME WILL SHIFT  
SOUTH AND EAST ENOUGH TO BRING STRONGER STORMS INTO THE AREA. WE  
MAY NEED TO INCREASE THE THREAT CATEGORY TO "ELEVATED" FOR MOST OF  
THE BURN AREAS FOR THE AFTERNOON AND EVENING HOURS. CALWOOD SHOULD  
REMAIN A LOWER "LIMITED" THREAT. STRONGER STORMS MAY BE CAPABLE  
OF PRODUCING AN INCH OF RAIN IN LESS THAN AN HOUR.  
 
A SUBSTANTIAL INCREASE IN THE FLASH FLOOD THREAT IS STILL  
EXPECTED SATURDAY AND SATURDAY NIGHT, POSSIBLY LASTING INTO  
SUNDAY. INGREDIENTS FOR HEAVY RAINFALL AND MORE SIGNIFICANT FLASH  
FLOODING (ESPECIALLY BURN AREAS) WILL INCLUDE A DEEP MONSOONAL  
MOISTURE PLUME, MOIST LOW LEVEL UPSLOPE FLOW INTO THE FRONT RANGE,  
SLOW AND REPEATING STORMS, AND A DEEP WARM CLOUD ENVIRONMENT  
SUPPORTING EFFICIENT RAINFALL PROCESSES. STRONGER STORMS IN THIS  
TIME FRAME MAY BE CAPABLE OF PRODUCING 2 INCHES IN LESS THAN AN  
HOUR.  
 
WHILE STORMS WILL BE LESS NUMEROUS MONDAY THROUGH WEDNESDAY, THERE  
WILL STILL BE A THREAT OF LOCALLY HEAVY RAINFALL. IN ADDITION,  
SATURATION OF THE GROUND FROM THE STORMS OVER THE WEEKEND, MAY  
HELP COMPOUND THE THREAT ESPECIALLY ON MONDAY.  
 

 
   
BOU WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
UPDATE...BARJENBRUCH  
SHORT TERM...EJD  
LONG TERM...COOPER  
AVIATION...BARJENBRUCH  
HYDROLOGY...EJD/COOPER  
 
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