074  
FXUS65 KBOU 220300  
AFDBOU  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DENVER/BOULDER CO  
900 PM MDT THU JUN 21 2018  
   
UPDATE
 
 
ISSUED AT 900 PM MDT THU JUN 21 2018  
 
CONVECTION IS RAPIDLY DIMINISHING ACROSS OUR CWA THIS EVENING WITH  
THE LOSS OF HEATING ACROSS THE HIGHER TERRAIN AND INCREASING CIN  
ACROSS THE NE CORNER. THE WEAKENING SHOWERS NO LONGER CONTAIN ANY  
LIGHTNING AND WILL GRADUALLY DISSIPATE OVER THE NEXT SEVERAL  
HOURS ACROSS THE FAR NE CORNER OF COLORADO. FORECAST FOR TONIGHT  
LOOKS ON TRACK WITH THE ONLY POPS ACROSS LOGAN/PHILLIPS/SEDGWICK  
COUNTIES THROUGH MIDNIGHT. DRY ELSEWHERE WITH MOSTLY CLEAR SKIES.  
 
LATEST HIGH RES GUIDANCE REGARDING THE SEVERE THUNDERSTORM THREAT  
FOR FRIDAY AFTERNOON CONTINUES TO POINT TO THE DEVELOPMENT OF A  
CONVERGENCE ZONE SOMEWHERE NEAR A GREELEY TO DIA TO PARKER LINE.  
BULK WIND SHEAR LOOKS FAVORABLE FOR SUPERCELLS AND INSTABILITY IS  
SHOULD BE HIGH ACROSS THE FAR EASTERN PLAINS. AS DISCUSSED IN THE  
PREVIOUS DISCUSSION, IT STILL LOOKS POSSIBLE THAT SOME OF THE HIGH  
CAPE MAY GET PUSHED WEST ALONG THE CONVERGENCE ZONE DEPENDING ON  
THE LOCATION OF A LEE CYCLONE FRIDAY AFTERNOON. LARGE HAIL WILL  
AGAIN BE A SIGNIFICANT THREAT ALONG AND EAST OF THE CONVERGENCE  
ZONE. ENOUGH MOISTURE SHOULD EXIST TO TRIGGER CONVECTION OFF THE  
HIGH TERRAIN WEST OF THE CONVERGENCE ZONE BUT THE STRENGTH OF THE  
STORMS SHOULD BE MUCH LESS VS. THE EASTERN QUARTER OF THE STATE.  
AN ISOLATED TORNADO CAN'T BE RULED OUT WITH THE CONVERGENCE ZONE,  
ESPECIALLY IF HIGH INSTABILITY MAKES IT FAR ENOUGH WEST ALONG THE  
LINE OF CONVERGENCE, WITH THE MORE FAVORABLE CONDITIONS OCCURING (BUT  
LOW CHANCE OVERALL) ACROSS THE EASTERN HALF OF WELD COUNTY.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH FRIDAY)  
ISSUED AT 400 PM MDT THU JUN 21 2018  
 
THE UPPER LEVEL RIDGE HAS SHIFTED SOUTH AS A SHORTWAVE DROPS SE INTO  
WY AND PORTIONS OF NORTHERN CO. THERE WILL BE ENOUGH INSTABILITY  
WITH DEWPOINTS IN THE LOW 50S AND CAPE HOVERING BETWEEN 500 TO  
1000 J/KG. THE FORCING PROVIDED BY THE SPEED MAX AND QG ASCENT  
WILL HELP TO FORM STORMS ALONG THE FOOTHILLS AND PUSH EASTWARD  
ALONG AND NORTH OF A LINE FROM FT COLLINS TO AKRON THROUGH THE  
EVENING HOURS. MODEL SOUNDINGS SHOW DECENT DEEP LAYER SHEAR THAT  
COULD HELP TO PRODUCE AN ISOLATED SEVERE STORM OR TWO WITH LARGE  
HAIL AND GUSTY WINDS ALONG WITH BRIEF MODERATE RAIN SHOWERS.  
CONDITIONS WILL STABILIZE OVERNIGHT WITH INCREASED MID-LEVEL FLOW  
HELPING TO KEEP OVERNIGHT TEMPERATURES IN THE MID 50S.  
 
FOR FRIDAY AN UPPER TROUGH WILL PUSH IN FROM THE NW WITH EMBEDDED  
VORT MAX CENTERS, WHICH IS PROGGED TO MOVE OVER THE NE PORTIONS OF  
CO DURING PEAK INSTABILITY. A DEEPENING SURFACE LOW ON THE LEE  
SIDE OF THE NORTHERN MOUNTAINS WILL HELP WITH INCREASING UPSLOPE  
AND SURFACE CONVERGENCE MAINLY EAST OF I-25 BY THE LATE AFTERNOON.  
SURFACE DEWPOINTS RISING INTO THE MID TO UPPER 50S WITH DECENT  
SURFACE HEATING WILL ALLOW FOR MLCAPES OF 1000-1500 J/KG WITH  
DECENT LIFT IN THE HAIL GROWTH ZONE. IT IS FOR THIS REASON SEVERE  
CHANCES WILL INCREASE FOR THE EASTERN PLAINS TOMORROW WITH THE  
MAIN HAZARD BEING LARGE HAIL. TEMPERATURES WILL BE SIMILAR TO  
TODAY WITH HIGHS REACHING INTO THE MID 80S ON THE PLAINS AND 60S  
TO 70S IN THE MOUNTAINS. FURTHER TO THE SE, CONDITIONS WILL BE  
DRIER AS RH LEVELS DROP INTO THE LOW TEENS WITH MIXING. LOW RH FOR  
AREAS WITH ALREADY DRY FUELS WILL MIX WITH WIND GUSTS TO INCREASE  
FIRE DANGER CONCERNS FOR FRIDAY AFTERNOON. MORE INFORMATION CAN BE  
FOUND IN THE FIRE WEATHER SECTION.  
   
LONG TERM
 
(FRIDAY NIGHT THROUGH THURSDAY)  
ISSUED AT 400 PM MDT THU JUN 21 2018  
 
CONDITIONS SHOULD BE FAVORABLE FOR CONVECTIVE GROWTH OVER THE  
NORTHEAST PLAINS FRIDAY EVENING. IT SHOULD EVENTUALLY GROW INTO A  
RAINY MCS, BUT THERE WILL BE A THREAT OF SEVERE HAIL/WIND IN THE  
EARLY TO MID EVENING HOURS. WIND PROFILE WOULD FAVOR A MOVING  
SYSTEM, SO NOT TOO MUCH OF A HEAVY RAIN THREAT.  
 
SATURDAY IS AN IN-BETWEEN DAY WITH AN AREA OF MUCH DRIER AND  
SLIGHTLY WARMER AIR ALOFT. THIS SHOULD RESTRAIN CONVECTION DESPITE  
THE PRESENCE OF LOW LEVEL MOISTURE ON THE PLAINS. SOME OF THIS  
WILL MIX OUT, WHICH WILL REDUCE THE CAPES AS WELL. THERE STILL  
SHOULD BE A LOW LEVEL OF DIURNAL STORM ACTIVITY AND PERHAPS A  
SMALL SEVERE THREAT IN THE BETTER PLAINS MOISTURE IN THE EVENING,  
ESPECIALLY IF LIFT FROM THE APPROACHING TROUGH ARRIVES EARLY  
ENOUGH.  
 
MODELS ARE IN REASONABLE AGREEMENT ON THE SATURDAY NIGHT-MONDAY  
TROUGH PASSAGE. HOWEVER, THE DETAILS WILL MATTER. AN UPPER LOW  
WILL MOVE ACROSS NORTHERN COLORADO AND SOUTHERN WYOMING WITH SOME  
LIFT AHEAD OF IT, AND DEEP UPSLOPE ON THE NORTH SIDE. THIS WILL  
FAVOR THE BEST PRECIPITATION ON THE SYNOPTIC SCALE ON THE NORTH  
SIDE, WHICH SHOULD BE ACROSS WYOMING INTO THE NEBRASKA PANHANDLE,  
AND LIKELY ALSO OUR NORTHERN BORDER AREA. THE MAIN DIFFERENCE  
BETWEEN THE MODELS IS THE CONVECTIVE PART. THE OPERATIONAL ECMWF  
DEVELOPS A LARGE AREA OF RAIN OVER NORTHEASTERN COLORADO AHEAD OF  
THE TROUGH SUNDAY MORNING WITH THE BEST SYNOPTIC LIFT, THEN  
AN MCS IN THE SAME AREA SUNDAY EVENING. THE THERMODYNAMIC AND WIND  
PROFILES SUNDAY EVENING SHOULD BE MUCH BETTER FOR HEAVY RAIN THAN  
ON FRIDAY, WITH BACKBUILDING FAVORED, AN INCREASING WARM CLOUD  
DEPTH, AND 1000-1500 J OF DEEP/SKINNY CAPE. THIS LOOKS LIKE THE  
MOST LIKELY TIME FOR ANY FLOODING THREAT, WHICH IS LIKELY TO BE  
WELL NORTHEAST OF DENVER. THE GFS LACKS THE SUNDAY MORNING RAIN,  
AND HAS NOT BEEN AS CONSTANT WITH THE MCS TIMING/LOCATION.  
 
MONDAY WILL BE A TRANSITION DAY, WITH SOME DRYING ALOFT, BUT STILL  
LOW LEVEL MOISTURE AND PROBABLY WARM ENOUGH FOR DIURNAL  
CONVECTION. SOME SIGNS THE WEST PART MAY BE DRYING OUT, BUT THERE  
MAY BE SOME SEVERE THREAT IF THE MOISTURE LINGERS ENOUGH.  
 
FROM TUESDAY THROUGH THE REST OF THE WEEK, IT LOOKS HOT AND  
RELATIVELY DRY. MODEL TEMPERATURES WOULD SUPPORT MID TO UPPER 90S  
ON THE PLAINS. A WEAK COLD FRONT ABOUT WEDNESDAY COULD KEEP IT  
FROM BEING EVEN WARMER AND PROVIDE A LITTLE PLAINS MOISTURE THAT  
COULD GIVE SOME ISOLATED STORMS. WINDS SHOULD BE FAIRLY LIGHT  
MIDWEEK PROBABLY DELAYING ANY POTENTIAL RED FLAG CONDITIONS UNTIL  
LATER IN THE WEEK WHEN THE SW WINDS ALOFT COULD PICK UP A BIT.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)  
ISSUED AT 900 PM MDT THU JUN 21 2018  
 
CONVECTION WINDING DOWN ACROSS THE STATE AND WILL NOT IMPACT THE  
TERMINALS NOR THE ARRIVAL/DEPARTURE GATES FROM NOW THROUGH  
TOMORROW MORNING. VFR TONIGHT THROUGH FRIDAY. WINDS WILL GO TO  
DRAINAGE AFTER 07-08Z (SSW AT DEN AROUND 12 KTS, SSW AT APA AROUND  
8-10 KTS, W AT BJC AROUND 5 KTS). TOMORROW BY LATE MORNING  
DIURNAL NORTHEASTERLY WINDS SHOULD OCCUR AT DEN AND APA, AND A  
LEE CYCLONE NORTH OF THE TERMINALS WILL LIKELY SET UP A  
CONVERGENCE ZONE SOMEWHERE NEAR KDEN BY MID AFTERNOON. THIS  
CONVERGENCE ZONE, IN ADDITION TO CONTAINING A SHARP WIND SHIFT  
WILL BE THE FOCUS FOR THUNDERSTORMS, ESPECIALLY NEAR OR OVER KDEN.  
HANDLING WITH A PROB30 FOR NOW. DEPENDING ON WHERE THE  
CONVERGENCE ZONE SETS UP, BJC AND APA COULD ALSO SEE THUNDERSTORM  
DEVELOPMENT FRIDAY AFTERNOON, THOUGH THERE SHOULD BE ENOUGH  
MOISTURE FOR WEAK CONVECTION OFF THE FOOTHILLS AND PALMER DIVIDE  
THAT COULD IMPACT BJC AND APA. STORMS SHOULD MOVE OUT OF THE AREA  
BY EARLY EVENING.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 400 PM MDT THU JUN 21 2018  
 
RELATIVE HUMIDITY VALUES WILL DROP BELOW 15% BY FRIDAY AFTERNOON  
OVER PORTIONS OF SOUTH PARK, ZONE 214. THESE DRY CONDITIONS WILL  
COMBINE WITH WNW WINDS OF 10 TO 20 MPH WITH GUSTING UP TO 30 MPH  
TO CREATE HEIGHTENED FIRE WEATHER CONCERNS. CONFIDENCE ON THE  
LENGTH OF TIME THESE CONDITIONS WILL BE MET IS MEDIUM SO A FIRE  
WEATHER WATCH WILL BE IN EFFECT FROM FRIDAY MORNING UNTIL FRIDAY  
EVENING.  
 

 
   
BOU WATCHES/WARNINGS/ADVISORIES
 
 
FIRE WEATHER WATCH FROM FRIDAY MORNING THROUGH FRIDAY EVENING  
FOR COZ214.  
 

 
 

 
 
UPDATE...SCHLATTER  
SHORT TERM...BOWEN  
LONG TERM...GIMMESTAD  
AVIATION...SCHLATTER  
FIRE WEATHER...BOWEN  
 
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