092  
FXUS65 KBOU 271709  
AFDBOU  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DENVER/BOULDER CO  
1109 AM MDT THU JUL 27 2017  
   
UPDATE
 
 
ISSUED AT 1105 AM MDT THU JUL 27 2017  
 
THE NORTHERN FRINGE OF THE MID-LEVEL MONSOON MOISTURE PLUME HAS  
DISPLACED JUST SOUTH OF THE CWA THIS MORNING AS PER GOES-16 VIS  
AND H2O SATELLITE IMAGERY. HOWEVER, THAT DOES NOT MEAN THAT  
MOISTURE NAMELY WITHIN THE BOUNDARY LAYER, HAS SCOURED OUT. A  
10-20KT SOUTHEAST SFC WIND CONTINUES TO ADVECT LOW-LEVEL MOISTURE  
UP ACRS NERN COLORADO THIS MORNING. THIS MOISTURE IS CLEARLY EVIDENT  
BY THE EXPANDING FIELD OF STRATOCUMULUS/CUMULUS ACROSS NORTHERN  
PORTIONS OF THE CWA, AND THE LOW TO MID 60F DEWPOINTS ON THE  
PLAINS. THE PATCHY FOG IN THE LOWER SOUTH PLATTE VALLEY HAS  
PRETTY MUCH DISSIPATED.  
 
HIGH RES MODELS INDICATE LESS STORM DEVELOPMENT TODAY THAN WAS  
OBSERVED YESTERDAY. HOWEVER THEY DO SHOW T-STORMS INITIATING OVER  
HIGHER REACHES OF THE FRONT RANGE MTNS IN THE NEXT 1-2 HOURS, THE  
PRODUCT OF STRONG LEE SLOPE SOLAR HEATING. NOT LONG AFTER THAT  
MODELS INDICATE A SECOND AREA OF ACTIVE STORM FORMATION UP ALONG  
THE WYOMING BORDER, FED BY A MOIST SELY INFLOW. MODELS INDICATE  
SFC BASED CAPES IN THE 1000-1500 J/KG RANGE UP AGAINST THE  
FOOTHILLS AND CHEYENNE RIDGE BETWEEN 18Z-21Z. COULD SEE A FEW  
STORMS IN THESE AREAS, PARTICULARLY UP ALONG THE WYOMING BORDER,  
GO SEVERE THIS AFTERNOON WITH HAIL UP TO AN INCH IN DIAMETER,  
WIND GUSTS TO 50 KTS AND BRIEF HEAVY RAINFALL. FARTHER SOUTH...  
ISOLATED TO SCATTERED STORMS DRIFTING OFF THE FRONT RANGE AND  
ACROSS THE I-25 URBAN CORRIDOR LATER THIS AFTERNOON COULD PRODUCE  
WIND GUSTS TO 40 KTS AND BRIEF HEAVY RAINFALL.  
 
THIS EVENING...HIGH RES MODELS INDICATE A FAIRLY RAPID DROP OFF IN  
STORM ACTIVITY IN THE HIGH COUNTRY AND SOUTHERN SECTIONS OF THE  
CWA DUE TO A LACK OF UPPER LEVEL SUPPORT. WHEREAS, THESE SAME  
MODELS SHOW A BOUNDARY SWINGING SEWRD OUT OF SERN WYOMING THIS  
EVENING, INITIATING A LINE OF T-STORMS ACROSS WELD, MORGAN AND  
LOGAN COUNTIES. HAVE INTRODUCED THIS POSSIBILITY OF EVENING  
T-STORMS TO THIS EVENING'S FORECAST.  
 
OTHERWISE, TODAY'S TEMPERATURE AND WIND FORECAST LOOKS TO BE ON  
TRACK.  
 

 
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 349 AM MDT THU JUL 27 2017  
 
STILL A FEW LIGHT RAIN SHOWERS LINGERING OVER THE PALMER DIVIDE  
AREA INTO LINCOLN COUNTY IN THE PRE-DAWN HOURS, BUT OVERALL THINGS  
HAVE SETTLED DOWN SIGNIFICANTLY SINCE THE LOCALIZED HEAVY  
RAINFALL AND FLOODING LAST EVENING. A FEW SPOTS FROM CASTLE ROCK  
TO NEAR PONDEROSA PARK, AND ALSO IN PARK COUNTY, RECEIVED TOTALS  
IN EXCESS OF 3 INCHES.  
 
FOR TODAY, THE ATMOSPHERE IS DRYING ALOFT IN THE SOUTHWEST FLOW,  
AND SOME OF THIS CAN BE SEEN IN THE GOES 16 LOW LEVEL WATER VAPOR  
IMAGERY, AND IN THE INTEGRATED PRECIPITABLE WATER (PW) TRENDS.  
NONETHELESS, PW WILL STILL BE WELL ABOVE NORMAL WITH VALUES  
LIKELY STEADYING OUT BETWEEN 1 AND 1.25 INCHES. CONSIDERABLE  
UNCERTAINTY IN THE EXPECTED FORECAST BY AFTERNOON STILL EXISTS,  
AS WE REALLY WORKED OVER THE AIRMASS LAST NIGHT, AND THE  
LINGERING EFFECTS OF AN MESOSCALE CONVECTIVE SYSTEM (MCS) IN  
SOUTHEAST COLORADO REMAINS. THAT COULD LEAD TO MORE STABILIZATION  
AND LESS CONVECTIVE COVERAGE ESPECIALLY ON THE PLAINS. THAT SAID,  
IF WE CAN BREAK THROUGH THE CAP, A T/TD OF 85/57 YIELDS 1500-1800  
J/KG CAPE AND A MARGINAL PULSE SEVERE THREAT WITH STRONG WINDS AND  
MARGINAL HAIL GIVEN THE DRYING ALOFT. OTHERWISE, MAIN THREAT WILL  
ONCE AGAIN BE LOCALLY HEAVY RAINFALL. SEE HYDRO SECTION BELOW.  
 
HIGHEST POPS WILL BE FOCUSED IN/NEAR THE FRONT RANGE MOUNTAINS  
WHERE CAP IS WEAKEST, AND ESPECIALLY PARK COUNTY WHERE SOUTHEAST  
LOW LEVEL FLOW IS FAVORABLE. WILL TAPER THOSE POPS OFF  
EAST/NORTHEAST ACROSS THE PLAINS WHERE AIRMASS IN MORE STABLE.  
OVERALL, THIS WAS ALREADY REFLECTED WELL IN THE EXISTING FORECAST  
SO ONLY MINOR ADJUSTMENTS.  
 
FOR TONIGHT, THERE IS ANOTHER DEPARTING UPPER LEVEL SPEED MAX TO  
OUR NORTH, SO CAN'T TOTALLY REMOVE POPS TIL THE LATE NIGHT HOURS  
WHEN THINGS SHOULD EVENTUALLY STABILIZE.  
 
FINALLY, PATCHY FOG EXPECTED THIS MORNING WITH PARTIAL CLEARING.  
FOG MAY BE DENSE IN A FEW SPOTS.  
   
LONG TERM
 
(FRIDAY THROUGH WEDNESDAY)  
ISSUED AT 349 AM MDT THU JUL 27 2017  
 
THE UPPER RIDGE WILL SLOWLY TRANSITION BACK WEST THROUGH THE  
WEEKEND BEFORE BECOMING QUASI-STATIONARY WHILE EXTENDING NORTH  
OVER THE DESERT SOUTHWEST AND INTO THE GREAT BASIN.  
 
A SHORTWAVE RIDING OVER THE TOP OF THE RIDGE ON FRIDAY, ALONG  
WITH HIGHER CAPE VALUES FROM WARMER SURFACE TEMPERATURES, WILL  
COMBINE TO BRING A CHANCE FOR STRONG THUNDERSTORMS MAINLY ACROSS  
THE PLAINS. CAPE VALUES ARE EXPECTED TO BE 1000-2000 J/KG, LARGEST  
OVER THE FAR NORTHERN PLAINS AND OVER THE PALMER DIVIDE. HIGHEST  
SHEAR VALUES WILL BE OVER THE NORTHEASTERN CORNER OF THE STATE, TO  
BRING THE BIGGEST THREAT OF POSSIBLE SEVERE STRENGTH STORMS. THE  
SHORTWAVE LOOKS TO BE SLOWING ITS TIMING, SO THE BEST TIME MAY  
WAIT UNTIL THE EARLY EVENING. MAIN IMPACTS FROM THESE STORMS WILL  
BE STRONG OUTFLOW WINDS, BRIEF HEAVY RAIN AND SOME HAIL. THE  
MOUNTAINS WEST OF THE DIVIDE WILL RECEIVE A BETTER CHANCE OF  
STORMS COMPARED TO RECENT DAYS.  
 
SATURDAY WILL BE SIMILAR AS ANOTHER QUICK MOVING UPPER SHORTWAVE  
MOVES OVER THE RIDGE TO BRING ANOTHER CHANCE OF STRONG STORMS OVER  
THE NORTHEASTERN PLAINS, ALONG WITH COOLER TEMPERATURES THROUGH  
SUNDAY.  
 
FOR MONDAY THROUGH THURSDAY, THE UPPER RIDGES POSITION NOW TO THE  
SOUTHWEST OF THE STATE AND EXTENDING NORTH WILL KEEP SCATTERED  
AFTERNOON AND EVENING THUNDERSTORMS IN THE FORECAST, BUT WILL  
FAVOR MORE OF THE HIGHER TERRAIN LEAVING A SLIGHT CHANCE FOR THE  
PLAINS. SUBTLE FEATURES MAY CHANGE THE STORM COVERAGE EXPECTED  
EACH DAY SLIGHTLY, BUT OVERALL PATTERN SHOULD BE SIMILAR WITH  
LITTLE CHANGE IN THE TEMPERATURES. TEMPERATURES WILL BE NEAR TO  
BELOW NORMAL THROUGH THE PERIOD.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)  
ISSUED AT 1105 AM MDT THU JUL 27 2017  
 
SCATTERED LOW STRATUS CLOUDS SHOULD BY MIDDAY ONLY TO BE REPLACED  
BY CONVECTIVE/CUMULUS TYPE CLOUDS THIS AFTERNOON. A MOIST  
SOUTHEAST WINDS 8-15KT WILL SUPPORT STORM DEVELOPMENT ALONG THE  
FRONT RANGE AND NEARBY PLAINS THROUGH THE AFTERNOON. SOME OF  
THESE STORMS MAY DRIFT EAST OVER THE METRO AREA POTENTIALLY  
PRODUCING WIND GUSTS TO 40 KTS, BRIEF HEAVY RAINFALL AND LIGHTNING.  
THE STRONGER STORMS COULD BRIEFLY PRODUCE IFR VISIBILITY AND MVFR  
CEILINGS. MAIN THREAT FOR THUNDERSTORMS IS BETWEEN 22Z AND 02Z.  
SHOULD THEN SEE WINDS RETURNING TO THEIR TYPICAL SOUTH/SOUTHWEST  
COMPONENT OF 7-12 KTS OVERNIGHT WITH PREVAILING VFR CONDITIONS.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 343 AM MDT THU JUL 27 2017  
 
PRECIPITABLE WATER (PW) VALUES ARE STILL WELL ABOVE NORMAL AND  
NEAR THE 90TH PERCENTILE, BUT DROPPING SLIGHTLY THIS MORNING WITH  
DRY AIR INTRUSION IN THE MID LEVELS. LCLS ARE ALSO A LITTLE  
HIGHER TODAY AND SHOULD REACH 6000 FT AGL OR SO BY LATE AFTERNOON,  
LIMITING THE WARM CLOUD DEPTH TO ABOUT 5000-6000 FEET. STORM  
MOTIONS ARE EXPECTED TO AVERAGE A BIT FASTER TOWARD 15-20 MPH.  
HOWEVER, STRONG STORMS WILL STILL PRODUCE VERY HEAVY RAINFALL WITH  
1 INCH POSSIBLE IN 20 MINUTES. SOME AREAS THAT SAW HEAVY RAIN  
LAST NIGHT, BURN SCARS, AND URBAN AREAS WILL BE MOST PRONE TO  
FLOODING FROM THE STRONGER STORMS. AT THIS TIME, GIVEN THE  
PARAMETERS MENTIONED ABOVE, AND LESS STORM COVERAGE, WE WILL NOT  
BE ISSUING A FLASH FLOOD WATCH AT THIS TIME, BUT CONTINUE TO  
MONITOR LATEST TRENDS TODAY.  
 
MOISTURE WILL DECREASE SLIGHTLY FRIDAY AND SATURDAY, HOWEVER  
LIKELY STILL ABOVE THE 90TH PERCENTILE FOR PW VALUES. THE FLOODING  
POTENTIAL FROM HEAVY RAINFALL OVER THE FOOTHILLS AND MOUNTAINS  
SHOULD DECREASE BEGINNING FRIDAY AS WE LOSE THE UPSLOPE FLOW  
COMPONENT. A COUPLE OF SHORTWAVES ON FRIDAY AND SATURDAY WILL  
INCREASE THE THREAT OF HEAVY RAINFALL FROM STRONGER STORMS, THOUGH  
THESE SHOULD BE FOCUSED FURTHER OVER THE NORTHEASTERN PLAINS.  
 
SUNDAY AND MONDAY WILL SEE MORE SIGNIFICANT DRYING, BEFORE ANOTHER  
SURGE OF MONSOONAL MOISTURE MAY PUSH INTO THE STATE FROM THE WEST.  
 

 
   
BOU WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

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