860
FXUS65 KBOU 240341
AFDBOU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
841 PM MST THU JAN 23 2025
KEY MESSAGES
- WINDY TONIGHT FOR MOUNTAINS, FOOTHILLS AND ADJACENT AREAS WITH
AREAS OF BLOWING SNOW LATE TONIGHT INTO FRIDAY MORNING.
- ANOTHER ROUND OF SNOW WITH TRAVEL IMPACTS AND COLDER
TEMPERATURES ARRIVES FRIDAY EVENING INTO SATURDAY. >80%
CONFIDENCE OF ACCUMULATING SNOW FOR THE MOUNTAINS, FOOTHILLS,
AND I-25 CORRIDOR, BUT ONLY 30-40% CONFIDENCE FARTHER EAST ON
THE PLAINS OF ANY IMPACTFUL SNOW.
- DRY WEATHER EXPECTED EARLY NEXT WEEK WITH MODERATING
TEMPERATURES.
- EYEING POTENTIAL RETURN OF SNOW (20-30% CHANCE) TOWARD THE
MIDDLE OF NEXT WEEK, CONFIDENCE IS LOW.
UPDATE
ISSUED AT 839 PM MST THU JAN 23 2025
CROSS-SECTIONS SHOW POTENTIAL FOR A MTN WAVE OVERNIGHT INTO FRI
MORNING WITH CROSS BARRIER FLOW FROM 35-45 KTS. THUS WILL SEE GUSTY
WINDS DEVELOP OVER THE HIGHER TERRAIN AFTER MIDNIGHT WHICH WILL
LINGER THRU FRI MORNING. THE WINDS MAY MIX DOWN TO THE BASE OF THE
FOOTHILLS AS WELL, SO HAVE ADDED AREAS OF BLOWING SNOW IN THE
NORMAL WINDY SPOTS, WHICH MAY AFFECT HWY 93 LATE TONIGHT THRU MID
MORNING ON FRI. GUSTS FROM 55 TO 65 MPH WILL BE POSSIBLE, AT
TIMES, IF THE WINDS DO MIX DOWN TO THE BASE OF THE FOOTHILLS.
SHORT TERM /THROUGH FRIDAY/
ISSUED AT 200 PM MST THU JAN 23 2025
IT'S A PRETTY ALBEIT CHILLY AFTERNOON AS TEMPERATURES HOVER WITHIN A
FEW DEGREES OF THE FREEZING MARK ACROSS OUR LOWER ELEVATIONS. IN THE
EASTERN PLAINS, THERE'S ENOUGH ELEVATED MOISTURE AND MARGINAL
INSTABILITY FOR A FEW CONVECTIVE HIGH-BASED SNOW SHOWERS, AS
EVIDENCED BY THE PHOTOGENIC CUMULUS STRIATIONS ON SATELLITE.
HOWEVER, WITH DEWPOINTS HOLDING IN SINGLE DIGITS TO LOW TEENS,
CONDITIONS REMAIN TOO DRY TO SUPPORT MORE THAN 15% POPS FOR A FEW
HOURS THIS AFTERNOON.
AS WE TRANSITION INTO THE EVENING AND OVERNIGHT HOURS, WINDS ALOFT
WILL BEGIN THEIR SHIFT TO A NORTHWESTERLY COMPONENT AHEAD OF A
DEVELOPING TROUGH OVER THE NORTHERN ROCKIES. MEANWHILE, SURFACE
PRESSURE GRADIENTS WILL TIGHTEN CONSIDERABLY, HELPING DRIVE ENHANCED
CROSS-BARRIER FLOW OF AROUND 40 KTS OVER THE FRONT RANGE MOUNTAINS.
A MOUNTAINTOP CRITICAL LAYER AND FAVORABLE SHEAR PROFILE SHOULD
SUPPORT MODEST MOUNTAIN WAVE DEVELOPMENT, STRONGEST BETWEEN MIDNIGHT
TONIGHT AND MID-MORNING FRIDAY, ALTHOUGH THE PREVAILING NW/WNW FLOW
ISN'T OPTIMAL FOR SIGNIFICANT AMPLIFICATION. PEAK GUSTS OF 60-70 MPH
LOOK QUITE ACHIEVABLE FROM OUR CENTRAL FOOTHILLS, ALTHOUGH ISOLATED
HIGHER GUSTS WILL BE POSSIBLE, PARTICULARLY IN THE MOST WIND-PRONE
LOCATIONS OF BOULDER COUNTY. THE WINDS WILL HELP TAPER OVERNIGHT
LOWS IN THE LOWER FOOTHILLS AND ADJACENT AREAS, BUT OVERALL IT'LL BE
ANOTHER COLD NIGHT WITH LOWS MOSTLY IN THE SINGLE DIGITS AND TEENS
FOR THE PLAINS, AND INTO THE NEGATIVES FOR THE MOUNTAIN VALLEYS AND
SKY COVER CLEARS OUT.
DAYTIME CONDITIONS ON FRIDAY WILL BE MILDER, WITH 700MB TEMPERATURES
RISING SOME 10 DEGREES C AND COMPRESSIONAL WARMING FURTHER BOOSTING
TEMPERATURES IN THE LEE OF THE FRONT RANGE, SO HIGHS SHOULD MAKE IT
INTO THE LOW TO MID 40'S FOR AREAS NEAR THE BASE OF THE FOOTHILLS
AND ROUGHLY SOUTH OF I-76. IN THE HIGH COUNTRY, MID-LEVEL MOISTURE
WILL INCREASE THROUGH THE AFTERNOON, WITH FAVORABLE OROGRAPHICS
SUPPORTING DEVELOPMENT OF SNOW SHOWERS AROUND MID-AFTERNOON IN THE
NORTHERN MOUNTAINS. A WINTER WEATHER ADVISORY WILL GO INTO EFFECT AT
5PM FOR OUR MOUNTAIN ZONES - SEE THE DISCUSSION BELOW FOR MORE
DETAILS ON THE INCOMING SNOW. FOR THE LOWLANDS, DESPITE A COLD FRONT
SWEEPING SOUTH THROUGH THE AFTERNOON, LOW-LEVEL MOISTURE WILL BE
LAGGING BEHIND, SO NO PRECIPITATION IS EXPECTED UNTIL LATER IN THE
EVENING OR OVERNIGHT.
LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/
ISSUED AT 230 PM MST THU JAN 23 2025
MAIN CONCERN FOR THIS FORECAST PERIOD WILL BE THE SNOW AND RENEWED
COLD STARTING FRIDAY NIGHT AND CONTINUING THROUGH SATURDAY, AND
STAYING AS LATE AS LATE SATURDAY NIGHT/EARLY SUNDAY MORNING IN
THE MOUNTAINS.
THE NORTHERN MOUNTAINS AND FOOTHILLS ARE GETTING THEMSELVES INTO A
MORE FAVORABLE PATTERN FOR MODERATE SNOW ACCUMULATIONS. A COUPLE
THINGS GOING FOR THIS WILL BE PERSISTENT FRONTOGENESIS STRADDLING
THE WYOMING/COLORADO BORDER, WEAK Q-G LIFT, AND FAVORABLE RESIDENCE
IN THE RIGHT REAR ENTRANCE REGION OF THE UPPER LEVEL JET. THIS
WILL ALSO BE A PROLONGED EVENT DUE TO THESE FORCING MECHANISMS
STAYING LINKED UP FOR A GOOD 18-24 HOURS, SO WHILE OVERALL
MOISTURE AMOUNTS ARE RATHER LIMITED (700-500 MB SPECIFIC HUMIDITY
<1.5 G/KG), ACCUMULATIONS SHOULD MOUNT UP OVER AN EXTENDED PERIOD.
FURTHERMORE, WE'LL HAVE A WEAK UPSLOPE COMPONENT ON THIS SIDE OF
THE DIVIDE, SO NORTHERN FOOTHILLS AND AT LEAST THE WESTERN-MOST
COMMUNITIES OF THE I-25 CORRIDOR NEAR THE FOOTHILLS SHOULD DO
REASONABLY WELL. A DEEP DGZ (DENDRITIC GROWTH ZONE) OF UP TO 7,000
FEET IS EXPECTED INITIALLY, WHICH SHOULD BRING 20:1 SNOW TO
LIQUID RATIOS (SLR). HOWEVER, THOSE WILL LIKELY DROP OFF LATER IN
THE EVENT TOWARD LATE MORNING/MID DAY SATURDAY AS WE LOSE THE DGZ
IN THE SHALLOW UPSLOPE LAYER, AND THE DGZ TOTAL DEPTH DROPS CLOSER
TO 2,000 FEET.
WITH ALL THINGS CONSIDERED, INITIAL INDICATIONS WOULD BE FOR
6-12" OF SNOW IN THE NORTHERN MOUNTAINS, 4-9" AMOUNTS IN THE
FOOTHILLS OF BOULDER AND LARIMER COUNTIES, AND 2-5" FOR THE
SOUTHERN FRONT RANGE FOOTHILLS AND WESTERN DENVER SUBURBS TO THE
WEST SIDE OF FORT COLLINS. WE'VE OPTED TO ISSUE WINTER WEATHER
ADVISORIES FOR THE LOCATIONS OF HEAVIER SNOWFALL, WHILE THE
LIGHTER AMOUNTS FOR THE I-25 CORRIDOR AND SOUTHERN FOOTHILLS WOULD
BE SHY OF CRITERIA AND OUTSIDE OF PEAK COMMUTE TIMES. AMOUNTS
WILL LIKELY TAPER OFF PRETTY FAST TO THE EAST, WITH SOME LOW LEVEL
DRY AIR INTRUSION. ONE THING THAT COULD OFFSET THAT HOWEVER, IS
THE PROXIMITY OF THE MID LEVEL F-GEN. WE'LL ALSO HAVE TO WATCH THE
I-70 MOUNTAIN CORRIDOR FOR POTENTIAL IMPACTS ON THE SKI WEEKEND,
BUT SO FAR SNOWFALL RATES THERE LOOK PRETTY LIMITED AND THERE HAS
BEEN JUST A SLIGHT TREND NORTHWARD WITH THE LATEST QPF FORECASTS.
SNOW SHOULD ESSENTIALLY TAPER OFF ACROSS THE LOWER ELEVATIONS
SATURDAY AFTERNOON AND EVENING, AND THEN ACROSS THE MOUNTAINS
SATURDAY NIGHT AS WE LOSE THE FORCING MECHANISMS.
MAINLY DRY WEATHER WILL SETTLE INTO THE AREA UNDER A COL FOR LATER
SUNDAY THROUGH MOST OF TUESDAY. THERE IS A LITTLE MORE CONCERN
TOWARD TUESDAY NIGHT OR WEDNESDAY THAT THE UPPER LOW COULD KICK
OUT FAR ENOUGH NORTH TO BRING A RETURN OF SNOW TO THE FORECAST
AREA. THAT'S STILL A RELATIVELY LOW PROBABILITY (20-30%), BUT
LATEST ENSEMBLES ARE TRENDING TOWARD POTENTIAL FOR ADDITIONAL
ACCUMULATING SNOW. ONE CYCLE DOESN'T MAKE A STRONG TREND, BUT THIS
IS SOMETHING TO WATCH OVER THE NEXT FEW DAYS. WE PROBABLY WON'T
KNOW A LOT MORE UNTIL THE UPPER LOW FINALLY SETTLES OFF/NEAR THE
CALIFORNIA COAST SUNDAY.
AVIATION /00Z TAFS THROUGH 00Z SATURDAY/
ISSUED AT 427 PM MST THU JAN 23 2025
VFR CONDITIONS THRU THE PERIOD. DRAINAGE WINDS TONIGHT WILL
CONTINUE THRU FRIDAY MORNING. UNCERTAIN ABOUT WINDS IN THE AFTN
AS GUIDANCE IS ALL OVER THE PLACE. FOR NOW HAVE MAINTAINED A NE
WIND BY 20Z FROM THE PREVIOUS TAF AT DIA. BJC MAY SEE GUSTY WNW
WINDS LATER THIS EVENING BUT SHOULD SUBSIDE BY 12Z.
BOU WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY FROM 5 PM FRIDAY TO 5 AM MST SUNDAY FOR
COZ031-033.
WINTER WEATHER ADVISORY FROM 9 PM FRIDAY TO 5 AM MST SUNDAY FOR
COZ035.
UPDATE...RPK
SHORT TERM...RODRIGUEZ
LONG TERM...BARJENBRUCH
AVIATION...RPK
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