651
FXUS65 KBOU 301139
AFDBOU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
439 AM MST THU JAN 30 2025
KEY MESSAGES
- SNOW, HEAVY AT TIMES, EXPECTED TO DEVELOP AND PERSIST THROUGH
THE EARLY AFTERNOON HOURS... MAINLY SOUTH AND EAST OF THE DENVER
METRO. AS MUCH AS 5-10 INCHES OF SNOW POSSIBLE IN BANDED SNOW.
- SNOW WILL LEAD TO A SLICK MORNING COMMUTE FOR AREAS SOUTH AND
EAST OF DENVER. WINTER WEATHER ADVISORIES REMAIN IN EFFECT.
- WARMER BUT BREEZY FRIDAY THROUGH THE WEEKEND. LOTS OF
UNCERTAINTY REMAINS WITH THE MAGNITUDE OF A BACKDOOR COLD FRONT
SUNDAY NIGHT INTO EARLY NEXT WEEK.
SHORT TERM /THROUGH TONIGHT/
ISSUED AT 333 AM MST THU JAN 30 2025
YESTERDAY'S DAY SHIFT MENTIONED THAT THERE WERE "STILL A FEW
QUESTIONS LEFT UNANSWERED" REGARDING THIS STORM SYSTEM, AND IF
IT'S POSSIBLE, I MAY HAVE EVEN MORE QUESTIONS NOW. THE SUMMARY?
WE WON'T HAVE A GREAT HANDLE ON THE AXIS OF HEAVIER SNOW TOTALS
UNTIL BANDED SNOWFALL DEVELOPS OVER THE NEXT FEW HOURS. WANT MORE
DETAILS? LET'S DIVE IN.
THE CENTER OF THE UPPER LOW IS WELL DEFINED ON WATER VAPOR
SATELLITE, WITH THE LATEST RAP ANALYSIS DATA SHOWING A 546 DAM
CLOSED LOW NEAR SPRINGFIELD IN FAR SOUTHEAST COLORADO. GUIDANCE
CONTINUES TO SUGGEST THAT THIS LOW WILL DRIFT A LITTLE FURTHER
NORTHEAST THIS MORNING, BEFORE WEAKENING AND SHIFTING BACK TO THE
SOUTHEAST BY THIS EVENING. THE FIRST ROUND OF MOISTURE THAT
ROTATED INTO OUR CWA HAS PRODUCED SOME LIGHT SNOW, BUT HAS LARGELY
BEEN DISORGANIZED. MOST OF THE METRO HAS STAYED DRY THANKS TO DEW
POINT DEPRESSIONS AROUND 10F. THE SECOND, MORE IMPRESSIVE WAVE IS
DEVELOPING OVER EASTERN COLORADO (YUMA/KIT CARSON COUNTIES) AND IS
PUSHING EASTWARD.
CONFIDENCE CONTINUES TO INCREASE THAT THE HEAVIEST SNOW WILL
REMAIN JUST EAST OF THE DENVER METRO, WITH MOST OF THE IMPACTS
STRETCHING FROM THE PALMER DIVIDE INTO TOWARDS LIMON/AKRON.
THERE'S AT LEAST A LITTLE BETTER AGREEMENT THAT THE BEST
FRONTOGENESIS SETS UP THERE, AND THE OVERALL MODEL CONSENSUS STILL
SHOWS THE POTENTIAL FOR AROUND SEVERAL INCHES OF SNOW THROUGH THE
REST OF THE MORNING HOURS UNDER A NARROW BUT INTENSE BAND. THE
WINTER WEATHER ADVISORIES LOOK TO BE GOOD ENOUGH, THOUGH THERE
WILL CERTAINLY BE QUITE A BIT OF VARIATION IN SNOW TOTALS ACROSS
THE ADVISORY AREA.
FOR THE DENVER METRO, THE FORECAST IS STILL SOMEWHAT CONVOLUTED.
BOTH THE HRRR AND FV3 REMAIN ON THE WESTERN FLANK OF GUIDANCE, AND
BOTH MAINTAIN SOME SORT OF NNE COMPONENT TO THE SURFACE/BOUNDARY
LAYER WINDS. EVEN THEN, THESE MODELS DEPICT A VERY SHARP GRADIENT
OF SNOW ACROSS THE METRO, WITH A PRONOUNCED DRY LAYER BELOW 700MB
(PREVIOUSLY NOTED BY ACARS SOUNDINGS). THOUGH CURRENT VAD PROFILE
DATA FROM KFTG SHOWS PLENTY OF NE WINDS JUST OFF THE DECK, NEAR-
SURFACE WINDS ARE STILL WNWERLY AND SHOULD MAINTAIN A DIRECTION
JUST NORTH OF WEST THIS MORNING. GIVEN THE LATEST OBS AND MODEL
TRENDS OVERNIGHT, I HAVE A FEELING THE SNOW FORECAST IS A LITTLE
TOO OPTIMISTIC FOR DENVER (ALTHOUGH IT'S GENERALLY <0.5").
ACROSS THE REST OF THE AREA, THE INCREASING NORTH-NORTHWESTERLY
WINDS WILL LEAD TO SOME DOWNSLOPING, LEADING TO MILD TEMPERATURES
OVER THE NORTHERN I-25 CORRIDOR. COULD SEE SOME UPPER 40S TO
PERHAPS LOW 50S FROM BOULDER TO FORT COLLINS THIS AFTERNOON.
THE WEATHER SHOULD TURN MUCH QUIETER TONIGHT AS THE UPPER LOW
DEPARTS AND DRIER AIR RETURNS.
LONG TERM /FRIDAY THROUGH WEDNESDAY/
ISSUED AT 225 AM MST THU JAN 30 2025
WESTERLY FLOW ALOFT WILL GRADUALLY DEVELOP ON FRI AND CONTINUE THRU
THE WEEKEND. AT THE SFC, A LEE TROUGH WILL BE IN PLACE ALONG THE
FRONT RANGE WITH DOWNSLOPE FLOW IN PLACE. CROSS-SECTIONS SHOW
VARYING AMOUNTS OF MID LEVEL MOISTURE EMBEDDED IN THE FLOW. THIS
MOISTURE COMBINED WITH FAVORABLE OROGRAPHIC COMPONENT MAY LEAD TO A
CHC OF SNOW SAT AND SUN IN THE NRN MTNS. HOWEVER, LAPSE RATES ARE
RATHER POOR, SO ANY SNOW THAT DOES FALL WILL BE ON THE LIGHT SIDE.
WINDS WILL BE GUSTY AT TIMES THRU THE WEEKEND WITH SOME POTENTIAL
FOR STRONGER WINDS SAT NIGHT INTO SUN MORNING OVER THE HIGHER
TERRAIN.
ACROSS THE PLAINS, IT WILL BE DRY WITH ABOVE NORMAL TEMPS EACH DAY.
ON AVERAGE, ECMWF HAS READINGS 3-5 DEGREES WARMER VS THE GFS
ACROSS THE PLAINS. AS A RESULT, ECMWF HAS HIGHS IN THE MID 50S TO
LOWER 60'S FRI AND SAT WITH UPPER 50'S TO MID 60'S BY SUN. GFS HAS
READINGS MOSTLY IN THE 55 TO 60 DEGREE RANGE EACH DAY. RECENT
SNOW COVER MAY ALTER READINGS SOMEWHAT OVER PORTIONS OF THE PLAINS
FRI AND SAT.
FOR EARLY NEXT WEEK, STILL HAVE TO CONTEND WITH A BACKDOOR COLD
FRONT AND SHALLOW COLD AIRMASS ACROSS THE PLAINS. ONCE AGAIN THE
GFS HAS THIS FRONT BACKING INTO THE I-25 CORRIDOR ON MON WHILE THE
ECMWF HAS IT REMAINING TO THE NORTHEAST OF THE AREA. THUS THIS MAY
LEAD TO SUBSTANTIAL TEMP DIFFERENCES ACROSS NERN CO DEPENDING ON
WHERE THE FRONT IS LOCATED. NATURALLY IF IT STAYS NORTHEAST OF THE
AREA, HIGHS ACROSS THE PLAINS WILL BE WELL ABOVE NORMAL DUE TO
DOWNSLOPE FLOW. HOWEVER, IF THE SHALLOW COLD AIRMASS DOES MAKE IT
IN IT MAY BE HARD TO ERODE WHICH WOULD LEAD TO HIGHS IN THE 30'S
BOTH MON AND TUE. CONFIDENCE REMAINS ON THE LOW SIDE AS TO WHICH
SOLUTION IS THE BEST. IN THE MTNS, CROSS-SECTIONS SHOW LIMITED
MOISTURE BOTH DAYS IN WSW FLOW ALOFT. OVERALL, NOT REAL SURE WHY
BLENDED DATA IS SHOWING QPF BOTH DAYS AS CROSS-SECTIONS DON'T
SUPPORT IT. THUS HAVE LOWERED POPS AND QPF FROM GUIDANCE.
BY WED, THE FLOW ALOFT WILL REMAIN WSW. THE BATTLE BETWEEN THE
ECMWF AND GFS CONTINUES AS TO WHETHER THE SHALLOW COLD AIRMASS
WILL LINGER OVER THE PLAINS OR NOT. THE GFS STILL HAS IT AFFECTING
THE PLAINS WHILE THE ECMWF DOESN'T. IN THE MTNS, CROSS-SECTIONS
HAVE VARYING AMOUNTS OF MOISTURE EMBEDDED IN THE FLOW SO WILL JUST
KEEP IN A CHC OF SNOW.
AVIATION /12Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 434 AM MST THU JAN 30 2025
VERY DIFFICULT FORECAST THROUGH ROUGHLY 21Z TODAY. EDGE OF THE
PRECIP SHIELD IS JUST EAST OF A DEN/BKF/APA LINE THIS MORNING, AND
THIS WILL LIKELY BE THE CASE OVER THE NEXT SEVERAL HOURS AS SNOW
EVENTUALLY ORGANIZES INTO A STRONGER BAND. CURRENT THOUGHT IS THAT
BOTH DEN/APA WILL STAY WITH ILS CIGS, PERHAPS DROPPING TO MVFR
CIGS, WITH VISIBILITY REMAINING NEAR OR ABOVE 5 MILES. HOWEVER, IF
THAT BAND DOES SHIFT A LITTLE WEST, THERE WOULD LIKELY BE A DROP
TOWARDS LIFR VISBY. BEST CHANCE OF THAT HAPPENING IS SOMETIME
AROUND 13-17Z, BUT AGAIN LOW CONFIDENCE. MADE SOME TWEAKS TO THE
PREVAILING/PROB30 GROUPS TO TRY TO CAPTURE THE UNCERTAINTY.
THE STORM SYSTEM SHOULD WEAKEN AND SHIFT OFF TO THE EAST FOR THE
LATTER HALF OF THE DAY, WITH CEILINGS RISING AND EVENTUALLY
SCATTERING OUT. BY THIS EVENING VFR CONDITIONS ARE LIKELY AT ALL
OF THE TERMINALS, WITH NORTHERLY WINDS EVENTUALLY WEAKENING AND
SHIFTING TO TYPICAL DRAINAGE PATTERNS OVERNIGHT.
BOU WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY UNTIL 2 PM MST THIS AFTERNOON FOR COZ041-
044-045-049.
WINTER WEATHER ADVISORY UNTIL NOON MST TODAY FOR COZ046-047.
SHORT TERM...HIRIS
LONG TERM...RPK
AVIATION...HIRIS
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