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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