241  
FXUS65 KBOU 230145  
AFDBOU  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DENVER/BOULDER CO  
645 PM MST THU FEB 22 2018  
   
UPDATE
 
 
ISSUED AT 640 PM MST THU FEB 22 2018  
 
MAIN CONVECTIVE SNOW BAND NOW HANGS OVER THE FOOTHILLS IN NORTHERN  
JEFFERSON AND SOUTHERN BOULDER COUNTIES, AND NORTHERN PORTIONS OF  
THE DENVER/BOULDER METRO AREA. A BIT AGO SPOTTERS UNDER THE CORE  
OF THE SNOW BAND IN THE WHEATRIDGE AND ARVADA RECORDED 2-3 INCHES  
OF SNOWFALL IN A SHORT PERIOD OF TIME. THIS CORE HAS SINCE MOVED  
VERY SLOWLY EAST AND WAS NOW OVER THE NORTHGLENN, NORTH DENVER AND  
THORNTON AREAS. THOSE AREAS COULD RECEIVE A QUICK 1-2 INCHES OF  
SNOW BEFORE THIS NARROW BAND OF LIGHT TO MODERATE SNOWFALL MOVES  
EAST OF THE AREA. HIRES MODELS SHOW THIS AND OTHER WEAK SNOW BANDS  
MOVING OFF THE FOOTHILLS WEAKENING IN THE NEXT 30-90 MINUTES AND  
EVENTUALLY DISSIPATING FARTHER OUT ON THE PLAINS BEFORE MIDNIGHT.  
GOES-16 WATER VAPOR SATELLITE IMAGERY SHOWS A WEAK MID- LEVEL  
DISTURBANCE MOVING EASTWARD OVER THE I-25 CORRIDOR AT THE MOMENT.  
THE BACK EDGE OF THIS DISTURBANCE, IE., MARKED BY A DRIER AIR, IS  
NOW PASSING OVER THE CONTINENTAL DIVIDE. BUT, THIS BREAK IN THE  
MOISTURE APPEARS SMALL, WITH YET ANOTHER BATCH OF MAINLY MID-LEVEL  
MOISTURE EXPANDING OVER WESTERN COLORADO. MODEL Q-G OMEGA FIELDS  
INDICATE A WIDENING AREA OF MOSTLY WEAK LARGE SCALE ASCENT  
ASSOCIATED WITH THIS WEST SLOPE MOISTURE. THIS REGION OF MOISTURE  
AND LIFT IS PROJECTED TO REACH THE FRONT RANGE AND ADJACENT PLAINS  
OF NORTHEAST COLORADO BY FRIDAY MORNING. WE'LL LEAVE THAT FOR  
LATER. FOR NOW, HAVE UPDATED THE FORECAST GRIDS FOR THE NEXT 6  
HOURS TO RAISE POPS ON THE PLAINS, ESPLY OVER NORTHERN PORTIONS OF  
THE METRO AREA AND TO ADD SNOW ACCUMULATIONS AS DESCRIBED ABOVE.  
AT THIS LATE HOUR, STILL ON THE FENCE AS TO WHEN AND IF FOG WILL  
BACK INTO THE I-25 CORRIDOR. TO PLAY IT SAFE ADDED AREAS OF FOG  
LATE TONIGHT FOR AREAS NORTH THROUGH EAST OF THE DENVER.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH FRIDAY)  
ISSUED AT 157 PM MST THU FEB 22 2018  
 
RADARS CONTINUE TO SHOW WIDELY SCATTERED SNOW SHOWERS MOVING  
NORTHEASTWARD ACROSS THE CWA THIS AFTERNOON. THEY WILL NOT CAUSE  
MUCH ACCUMULATION. THERE IS A BETTER LOOKING BATCH OF CLOUDINESS  
AND RADAR RETURNS JUST UPSTREAM. THIS SHOULD IMPACT THE  
NORTHWESTERN HALF OF THE CWA THIS EVENING. STRONG SOUTHWESTERLY  
FLOW ALOFT IS EXPECTED TO CONTINUE TONIGHT OVER THE CWA. AN UPPER  
TROUGH OVER THE GREAT BASIN WILL MOVE SLOWLY EASTWARD TONIGHT AND  
FRIDAY. THE TROUGH AXIS WILL BE OVER CENTRAL UTAH BY 00Z LATE  
FRIDAY. THERE IS DECENT SYNOPTIC SCALE ENERGY ON FRIDAY AFTERNOON  
FOR ALL OF THE CWA. THE BOUNDARY LAYER FLOW CONTINUES TO BE PRETTY  
WEAK OVERNIGHT. ON FRIDAY, DECENT SOUTHEASTERLY FLOW IS EXPECTED  
LATE MORNING THROUGH AFTERNOON. LOOKING AT MOISTURE, THERE IS  
QUITE A BIT THIS EVENING, THEN IT DECREASES AFTER 06Z TONIGHT  
THROUGH 18Z ON FRIDAY. MOISTURE INCREASES SIGNIFICANTLY FRIDAY  
AFTERNOON. CROSS SECTIONS KEEP MOISTURE AROUND MOST OF TONIGHT IN  
THE LOWEST LEVEL OVER THE PLAINS SO WILL KEEP SOME MENTION OF FOG  
AS THE CURRENT GRIDS HAVE. FOR POPS TONIGHT, WILL GO WITH  
"LIKELY"S IN THE HIGH MOUNTAINS, THEN DECREASING AFTER MIDNIGHT  
THROUGH NOON FRIDAY. WILL GO WITH "CHANCE"S FOR THE WESTERN HALF  
OF THE PLAINS THIS EVENING, THEN NOTHING OVERNIGHT INTO MID FRIDAY  
AFTERNOON FOR ALL THE PLAINS. ON SATURDAY AFTERNOON, WILL  
INCREASE POPS AGAIN FOR MUCH OF THE CWA. FOR TEMPERATURES,  
FRIDAY'S HIGHS WILL BE 1-4 C WARMER THAN THIS AFTERNOON'S HIGHS.  
   
LONG TERM
 
(FRIDAY NIGHT THROUGH THURSDAY)  
ISSUED AT 157 PM MST THU FEB 22 2018  
 
THE UPPER TROUGH OVER UTAH FRIDAY EVENING WILL SWING EAST THROUGH  
THE NIGHT, INCREASING QG LIFT OVER NORTHEASTERN COLORADO.  
EXPECTING SOME CONVECTIVE SNOW LINING UP IN SOUTHWEST TO NORTHEAST  
BANDS ACROSS THE MOUNTAINS, LIKELY HEAVIEST DURING THE EVENING  
HOURS. ACROSS THE NORTHEASTERN PLAINS, MODELS HAVE BEEN HANDLING  
THE SYSTEM DIFFERENTLY. GFS SHOWS SLIGHTLY MORE DIGGING BY THE  
UPPER TROUGH ALONG WITH MUCH DEEPER MOISTURE RESULTING IN HIGHER  
UPWARD QG VALUES AND HIGHER QPF VALUES, ESPECIALLY OVER THE FAR  
NORTHEASTERN PLAINS WHERE UP TO 10 INCHES OF SNOW MAY OCCUR. NAM,  
GEM AND TO A LESSER EXTENT THE ECMWF SHOW A MUCH SHALLOWER  
MOISTURE LAYER, SHALLOW ENOUGH TO PRESENT THE THREAT OF FREEZING  
DRIZZLE ALONG WITH SOME SNOW. HOWEVER, SO MUCH QG LIFT MAY INHIBIT  
MUCH OF THE FREEZING DRIZZLE POTENTIAL, HOWEVER HARD TO GO AGAINST  
THE STEADY MENTION OF FREEZING DRIZZLE IN THE MODELS. SREF PLUMES  
HAVE BEEN STEADILY INCREASING THEIR SNOW AMOUNTS FOR THE PAST 4  
RUNS, INCREASING MY CONFIDENCE OF AN IMPACTFUL WEATHER EVENT. WILL  
KEEP THE MENTION OF FREEZING DRIZZLE ALONG WITH A CHANGE OVER TO  
SNOW WITH A POSSIBLE 2 TO 6 INCHES OF SNOW FRIDAY NIGHT, MAINLY  
OVER LOGAN, PHILLIPS, SEDGWICK AND WASHINGTON COUNTIES. WILL ISSUE  
A WINTER STORM WATCH FOR THE WINTRY MIX OF FREEZING DRIZZLE AND  
ACCUMULATING SNOW. FOR THE MOUNTAINS, ANOTHER 2 TO 4 INCHES TO  
FALL FRIDAY NIGHT BEFORE DIMINISHING SATURDAY MORNING. WESTERLY  
FLOW WILL TEND TO DOWNSLOPE THE URBAN CORRIDOR, THOUGH THE  
CONVECTIVE NATURE AND POSSIBLE BANDING MAY STILL ALLOW 1 TO 2  
INCHES TO FALL. THERE MAY BE SOME FREEZING DRIZZLE PUSHING BACK  
WEST INTO WELD COUNTY AT LEAST FROM THE NORTHEASTERN PLAINS AS  
MOISTURE DEPTH DECREASES THROUGH THE NIGHT.  
 
AS THE TROUGH PASSES OVERHEAD EARLY SATURDAY MORNING, STRONG  
SUBSIDENCE WILL DECREASE SNOW WEST TO EAST AS WELL AS INCREASE  
NORTHWESTERLY WINDS. THIS MAY CAUSE BLOWING SNOW OVER THE HIGH  
COUNTRY, AND POSSIBLY OVER THE FAR NORTHEASTERN PLAINS, DEPENDING  
ON HOW MUCH FALLS. GUSTS OF 30 TO 40 MPH WILL BE POSSIBLE. ANOTHER  
WEAK SHORTWAVE WILL PUSH MORE SNOW INTO THE MOUNTAINS SATURDAY  
EVENING INTO SUNDAY MORNING, WITH ANOTHER 2 TO 4 INCHES EXPECTED.  
THE PLAINS SHOULD REMAIN DRY WITH SLIGHTLY WARMER TEMPERATURES  
SUNDAY AND AGAIN ON MONDAY AS SHORTWAVE RIDGING MOVES OVERHEAD.  
 
ON TUESDAY, SOME MOISTURE BEGINS TO PUSH IN AS ANOTHER UPPER  
TROUGH DROPS INTO THE GREAT BASIN AND DESERT SOUTHWEST. ALSO, A  
BACKDOOR COLD FRONT MAY EITHER KEEP TEMPERATURES THE SAME OR LOWER  
THEM TUESDAY EVEN THOUGH SOUTHWEST FLOW ALOFT CONTINUES. SNOW  
SHOULD PUSH INTO THE HIGH COUNTRY THAT EVENING SHOULD STICK TO  
THE HIGHER TERRAIN WEDNESDAY AS THE PLAINS ARE MAINLY DOWNSLOPED,  
HOWEVER THE NORTHERN PLAINS MAY SEE SOME LIGHT ACCUMULATIONS DUE  
TO A STRONGER COLD PUSH UP THERE. GFS IS MUCH WEAKER THAN THE EC  
OR GEM WITH THIS TROUGH, SO MAY NEED TO HOLD ON TO POPS LONGER  
DEPENDING ON MODEL CONSISTENCY. OTHERWISE THURSDAY SHOULD BE DRY  
AND SLIGHTLY WARMER AS THE TROUGH PUSHES EAST AND UPPER RIDGING  
REPLACES IT.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)  
ISSUED AT 640 PM MST THU FEB 22 2018  
 
LIGHT TO MODERATE SNOW SHOWERS SLOWLY TRACKING NORTHEAST OVER  
PORTIONS OF THE DENVER METRO AREA AT THIS HOUR NOW IMPACTING  
MAINLY KBJC AND KDEN. VSBY AT KBJC PRESENTLY DOWN TO A MILE, AND  
2.5 MILES AT KDEN. COULD STILL SEE LOWER VSBYS AND BOTH NORTH  
METRO AIRPORTS DURING THE NEXT 30-60 MINUTES (E.G. ABOUT 03Z),  
WITH UPWARDS OF AN INCH OF SNOW ACCUMULATION POSSIBLE. OTHERWISE,  
MVFR CIGS WILL PREVAIL THIS EVENING, WITH LOCAL CIGS DOWN TO  
500-800 FEET AGL WITH PASSING SNOW SHOWERS. BY LATE THIS EVENING,  
AFTER 04Z, MUCH OF THIS SHOWER ACTIVITY SHOULD EAST OF THE METRO  
AREA, ALTHOUGH AREAS OF VERY LIGHT SNOWFALL OR SNOW FLURRIES MAY  
LINGER UNTIL MIDNIGHT LST. AFTER MIDNIGHT, AIRPORTS COULD SEE  
PARTIAL CLEARING WHICH COULD RESULT IN THE FORMATION OF FOG. TO  
WHAT EXTENT, REMAINS UNCERTAIN. WILL CONTINUE TO CLOSELY MONITOR  
AND WILL ADD TO TERMINAL FORECASTS AS SOON AS POSSIBLE IF  
NECESSARY.  
 

 
   
BOU WATCHES/WARNINGS/ADVISORIES
 
 
WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH SATURDAY  
MORNING FOR COZ048>051.  
 

 
 

 
 
UPDATE...BAKER  
SHORT TERM...RJK  
LONG TERM...KRIEDERMAN  
AVIATION...BAKER  
 
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