330
FXUS65 KBOU 290603
AFDBOU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
1103 PM MST TUE JAN 28 2025
KEY MESSAGES
- WATCHING NEXT SYSTEM CLOSELY, BUT GROWING CONFIDENCE THIS IS
MAINLY A LIGHT SNOW EVENT WEDNESDAY NIGHT - THURSDAY NOON, WITH
A FOCUS TOWARD THE PALMER DIVIDE AND ADJACENT PLAINS THROUGH
EAST CENTRAL COLORADO.
- WARMER BUT BREEZY FRIDAY INTO THE WEEKEND. LOTS OF UNCERTAINTY
WITH MAGNITUDE OF WARMUP WITH POTENTIAL FOR BACKDOOR COLD
FRONT(S) SUNDAY INTO EARLY NEXT WEEK.
UPDATE
ISSUED AT 753 PM MST TUE JAN 28 2025
CLEAR SKIES AND LIGHT WINDS WILL PREVAIL THROUGH THE REST OF THE
NIGHT. THIS WILL LEAD TO ANOTHER COLD NIGHT IN THE TYPICAL
MOUNTAIN VALLEY LOCATIONS WHERE LOWS OF -10 TO -20F ARE EXPECTED.
ALSO NUDGED TEMPERATURES LOWER IN THE LOW LYING AREAS NORTH OF
DENVER INTO THE LOWER TO MID TEENS.
REGARDING THE WEDNESDAY NIGHT AND THURSDAY SYSTEM, THE 18Z MODELS
AND THE FEW 00Z MODELS IN SO FAR HAVEN'T CLEARED THE PICTURE AT
ALL. THE 00Z NAM AND HRRR SHOW 0.50 TO 0.75 (IN) OF PRECIPITATION
FOR SOUTHERN AND EASTERN PARTS OF THE DENVER AREA. THIS WOULD
YIELD 5 TO 10 INCHES OF SNOWFALL. THE 18Z GFS DID TAKE A STEP
DRIER, WHILE THE 18Z ECMWF HELD STEADY WITH THE HEAVIER BAND OF
SNOW STAYING OVER THE EASTERN PLAINS WITH THE DENVER AREA DRY. NO
CHANGES TO THIS PART OF THE FORECAST AT THIS TIME. WE WILL NEED
TO TAKE A GOOD LOOK AT ALL THE 00Z MODEL GUIDANCE BEFORE MAKING
CHANGES.
SHORT TERM /THROUGH WEDNESDAY/
ISSUED AT 124 PM MST TUE JAN 28 2025
ONLY MINOR CHANGES TO THE FORECAST WITH AN ALMOST CLEAR NIGHT
AHEAD. SOUTH PARK WARMED UP TODAY, SO WE'VE BACKED OFF A LITTLE ON
THE COLD OVERNIGHT LOWS THERE. NOT SO MUCH IN GRAND AND JACKSON
COUNTIES WHERE THERE ARE STILL SUBSTANTIAL INVERSIONS. IT SHOULD
BE AT LEAST 10-20 DEGREES WARMER THAN LAST NIGHT, BUT THAT STILL
MEANS LOWS OF ZERO TO 15 BELOW IN THE VALLEYS.
DURING THE DAY WEDNESDAY, THE CENTRAL MOUNTAINS WILL BE ON THE
EDGE OF THE LIFT AS THE NEXT SYSTEM APPROACHES. CLOUDS WILL BE
SPREADING IN, BUT IT DOESN'T LOOK LIKE THERE'S MUCH CHANGE OF
APPRECIABLE SNOW UNTIL LATE IN THE DAY OR MORE LIKELY THE EVENING.
WE SLOWED THE ADVENT OF THE CLOUDS, AND FOCUSED THE POPS MORE IN
THIS AREA AND LESS FURTHER NORTH IN THE AFTERNOON.
LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/
ISSUED AT 245 PM MST TUE JAN 28 2025
THE MAIN CONCERN CONTINUES TO REVOLVE AROUND THE UPPER LEVEL LOW
THAT MOVES SLOWLY EAST/NORTHEAST ACROSS NORTHERN NEW MEXICO
WEDNESDAY NIGHT, AND THEN INTO SOUTHWEST KANSAS THURSDAY. THERE
ARE SMALL DIFFERENCES IN EACH OF THE ENSEMBLE DATASETS WITH REGARD
TO THE TRACK, WITH THE GEFS/SREF/NAM BEING FARTHER NORTH
(SOUTHEAST COLORADO), THE EPS MIDDLE OF THE ROAD (CO/KS/OK TRI
STATE AREA), AND THE CMCE JUST A TOUCH FARTHER SOUTH BUT TRENDING
TOWARD THE EPS SOLUTION.
WHILE THIS TRACK IS FAVORABLE FOR SNOW ACROSS THE FORECAST AREA,
THIS PARTICULAR STORM HAS LIMITING FACTORS SUCH AS; 1) LACK OF
LEE SIDE CYCLOGENESIS AND THUS LIMITED UPSLOPE FORCING, 2) A VERY
DRY AIRMASS TO START, 3) SOME DRY SLOTS ALOFT DURING THE EVENT,
AND 4) LACK OF A DEEP DGZ. MEANWHILE, FAVORABLE ATTRIBUTES
INCLUDE 1) THE TRACK RESULTING IN PERSISTENT QG LIFT, 2) SOME
INFLUX OF GULF MOISTURE, AND 3) MODEST MID LEVEL LAPSE RATES
OF 6-7 C/KM.
DUE TO THE CONTINUED UNCERTAINTY, WE'LL STILL RELY ON THE VAST
ARRAY OF ENSEMBLE DATA AND AVERAGE CLOSE TO THE MEAN OF ALL
SYSTEMS. THIS PUTS LOCATIONS SUCH AS THE PALMER DIVIDE AND EAST
CENTRAL PLAINS OF COLORADO THROUGH LIMON AND LINCOLN COUNTY IN THE
MOST FAVORED LOCATIONS FOR ACCUMULATING SNOWFALL, WITH A MUCH
LOWER THREAT OF ACCUMULATING SNOW FROM BOULDER AND THE NORTHWEST
DENVER SUBURBS TOWARD FORT COLLINS AND GREELEY. THOSE LATEST
LOCATIONS LISTED WOULD ALSO BE MORE PRONE TO DOWNSLOPE FROM
SHALLOW NORTHWEST WINDS OFF THE FOOTHILLS AND CHEYENNE RIDGE, A
RESULT OF THE LACK OF SIGNIFICANT CYCLOGENESIS. THUS, WE FEEL
PRETTY CONFIDENT THAT THOSE AREA WOULD SEE LITTLE IF ANY
ACCUMULATION, AND THE ONLY WAY THAT WOULD CHANGE IS IF THIS STORM
SUDDENLY TRENDS TO, OR NORTH OF, THE GEFS/HREF TRACKS. IF IT DID,
THEN MORE UPSLOPE WOULD OCCUR INTO THE NORTHERN FOOTHILLS, BUT
ONLY ABOUT A 20% CHANCE OF THAT. THE OPPOSITE COULD HOLD TRUE OVER
THE SOUTHERN/EASTERN SECTIONS OF METRO DENVER INTO THE PALMER
DIVIDE, WHERE DEEP NNW FLOW SUPPORTS UPSLOPE FLOW ON THE BACK END
OF THIS CYCLONE. WE SAW A SIMILAR FLOW PATTERN ON JANUARY 9TH
WHICH BROUGHT MORE ACCUMULATION THAN ANTICIPATED OVER THE FAR
SOUTHEASTERN SUBURBS INTO PARKER AND ELIZABETH, SO IF THE STORM
DID GET SUFFICIENT MOISTURE WRAPPED INTO IT WITHOUT DRY SLOTS THEN
MORE SNOW WOULD BE POSSIBLE. THIS APPEARS TO BE A PRETTY LOW
CONFIDENCE THOUGH SINCE THE SYSTEM IS RELATIVELY MOISTURE STARVED
EARLY ON, AND THERE'S ONLY ABOUT A 6 HOUR PERIOD LATE WEDNESDAY
NIGHT - THURSDAY MORNING WHEN HEAVIER SNOW WOULD BE POSSIBLE. ONLY
A FEW OF THE ENSEMBLE MEMBERS (10-20%) SHOWED POSSIBILITY OF A
4-6" SNOW ON THE PALMER DIVIDE. HOWEVER, THERE'S SMOOTHING IN THE
COURSER ENSEMBLE RUNS SO OUR DETERMINISTIC FORECAST WILL BE CLOSER
TO (NOT AT) THAT HIGHER END FOR NOW. AGAIN, THE OPPOSITE HOLDS
TRUE FROM ABOUT DOWNTOWN DENVER NORTHWARD WHERE WE'VE LOWERED
ENSEMBLE OUTPUT IN THE DETERMINISTIC FORECAST (0-1").
FOR THURSDAY AFTERNOON, WE'LL SEE THE SNOW TAPER OFF AND END FROM
NORTHWEST TO SOUTHEAST, WITH SOME SUNSHINE RETURNING BY LATE IN
THE DAY. TEMPERATURES WILL BE A LITTLE CHILLY TO START, BUT
THERE'S ESSENTIALLY NO COLD AIR ADVECTION WITH THIS CUTOFF LOW SO
DON'T LOOK FOR MUCH COOLING OVERALL.
THE QUICK DEPARTURE AND LACK OF COLD ADVECTION IN THIS SYSTEM'S
WAKE WILL SUPPORT A FURTHER WARMUP FOR FRIDAY, AND THIS WARMING
TREND WILL LIKELY (70% CONFIDENCE) CONTINUE THROUGH THE WEEKEND.
HOWEVER, THERE IS A REAL THREAT OF A BACKDOOR COLD FRONT SNEAKING
ACROSS THE PLAINS BY SUNDAY AND ESPECIALLY BY MONDAY. THE FORECAST
AREAS WILL BE A REAL BATTLEGROUND BETWEEN SPRINGLIKE WARMTH AND
WINTER'S COLD. THIS CAN BE SEEN IN THE 25TH-75TH PERCENTILES OF
THE EPS OUTPUT RANGING ANYWHERE FROM 38-65 FOR MONDAY, WHILE THE
FAR EXTREMES SHOW POTENTIAL ANYWHERE FROM HIGHS IN THE MID TEENS
TO MID 70S! GEFS PROBABILITIES ARE NOT QUITE AS SCARY AND SHOOT
CLOSER TO THE MIDDLE OF THAT RANGE. WHERE THE COOL AIR DOES NOT
SURGE IN, WE'LL SEE BREEZY TO POTENTIALLY WINDY CONDITIONS AT
TIMES. THOSE WINDY CONDITIONS FAVOR LOCATIONS IN AND IMMEDIATELY
NEXT TO THE FRONT RANGE MOUNTAINS AND FOOTHILLS. MOSTLY DRY
WEATHER SHOULD PREVAIL THROUGH THIS PERIOD, ALTHOUGH THE NORTHERN
MOUNTAINS MAY RESIDE ON THE FAR SOUTHERN EXTENT OF A PACIFIC
MOISTURE PLUME, JUST ENOUGH TO KEEP SOME CHANCE OF LIGHT SNOW
SHOWERS IN THE FORECAST THERE.
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 1044 PM MST TUE JAN 28 2025
VFR THROUGH AT LEAST WEDNESDAY AFTERNOON, WITH DECREASING CEILINGS
LIKELY WEDNESDAY NIGHT INTO THURSDAY. WINDS ARE A LITTLE VARIABLE
OUT THERE BUT SHOULD SETTLE ON DRAINAGE WINDS SOON. EXPECT ANOTHER
TURN TO THE NORTH OR NORTHEAST BY THE AFTERNOON.
THERE SHOULD BE A GRADUAL INCREASE IN CLOUD COVER BY LATE
AFTERNOON OR EVENING, WITH SOME ILS/MVFR CIGS POSSIBLE BY THE END
OF THE TAF PERIOD. SOME SNOW WOULD ALSO BE POSSIBLE AFTER 06Z,
MAINLY OR APA/DEN.
BOU WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...MEIER
SHORT TERM...GIMMESTAD
LONG TERM...BARJENBRUCH
AVIATION...HIRIS
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