438
FXUS65 KBOU 292338
AFDBOU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
438 PM MST WED JAN 29 2025
KEY MESSAGES
- SNOW DEVELOPS IN PLAINS TONIGHT, SPREADS INTO I-70 CORRIDOR AND
PALMER DIVIDE EARLY MORNING.
- SNOW WILL LEAD TO SLICK COMMUTE THU AM FOR AREAS SOUTH AND EAST
OF DOWNTOWN DENVER.
- WARMER BUT BREEZY FRIDAY THROUGH THE WEEKEND. LOTS OF
UNCERTAINTY WITH THE MAGNITUDE OF A BACKDOOR COLD FRONT SUNDAY
NIGHT INTO EARLY NEXT WEEK.
SHORT TERM /THROUGH THURSDAY/
ISSUED AT 231 PM MST WED JAN 29 2025
THERE ARE STILL A FEW QUESTIONS LEFT UNANSWERED AS THEY RELATE TO
OUR UPCOMING STORM SYSTEM, BUT THERE'S ONE ASPECT WHERE CONFIDENCE
IS HIGH: WHETHER IN THE SNOW-LOVER CAMP OR NOT, MANY FOLKS WILL BE
SORELY DISAPPOINTED, AND MANY WILL BE QUITE PLEASED ONCE THE SNOW
WRAPS UP. SUCH IS THE BEAUTY OF A BANDED SNOW EVENT!
LET'S FIRST TAKE A FEW STEPS BACK THOUGH. SUN ABOUNDS THIS AFTERNOON
AS WE AWAIT THE APPROACHING SYSTEM, WITH MILD SOUTHERLY FLOW IN
PLACE ALONG THE LEADING EDGE OF THE CLOSED LOW, WHICH IS CURRENTLY
SITTING OVER NORTH-CENTRAL ARIZONA. IN OUR SOUTHEAST PLAINS, CLEAR
SKIES ARE RAPIDLY GIVING WAY TO AN EXPANDING STRATUS DECK AS THIS
SOUTHERLY FLOW ADVECTS A TONGUE OF HEALTHY GULF MOISTURE INTO THE
REGION. BY THIS EVENING, CROSS-SECTIONS INDICATE DEEPENING MID-LEVEL
MOISTURE THAT WOULD SUPPORT GRADUAL DEVELOPMENT OF SHOWERS IN THE
EASTERN PLAINS, ESPECIALLY LINCOLN/WASHINGTON COUNTIES. MARGINAL
SURFACE TEMPERATURES COULD SUPPORT A BRIEF RAIN SHOWER OR WINTRY MIX
DURING THE ONSET OF PRECIPITATION, BUT A CHANGEOVER TO SNOW
SHOULDN'T BE FAR BEHIND FOR *MOST* AREAS (CAVEAT TO COME SHORTLY).
AS THE FRONT OCCLUDES OVERNIGHT, A PRONOUNCED NE-SW TROWAL WILL
DEVELOP THROUGH THE EARLY MORNING HOURS FROM THE NORTHERN PLAINS
INTO THE PALMER DIVIDE. ONE EFFECT OF THE WARMER AIR ALOFT WILL BE
TO SUSTAIN A WARM NOSE NEAR 800MB ACROSS THE NORTHEAST PLAINS, WHICH
OPENS THE DOOR TO A PERIOD OF FREEZING RAIN OR A WINTRY MIX FOR
THOSE AREAS AS SURFACE TEMPERATURES DROP BELOW FREEZING. HAVE THUS
INTRODUCED THIS INTO THE FORECAST.
THE TROWAL WILL ALSO ENHANCE LOW-LEVEL FRONTOGENESIS, PROMOTING A
TRANSITION TO MORE OF A BANDED SNOW EVENT BY THURSDAY MORNING, WHICH
WILL CARRY POTENTIAL FOR A PERIOD OF MODERATE TO HEAVY SNOW WITH
RATES NEAR 1"/HR FOR SEVERAL HOURS TO THE SOUTHEAST OF DENVER.
MODELS HAVE A LOOSE IDEA - RATHER THAN A FIRM HOLD - ON THE
PLACEMENT OF THIS BAND OF HEAVIER SNOW, BUT THE AREA OF GREATEST
CONFIDENCE IN HEAVIER SNOW THURSDAY MORNING EXTENDS FROM THE PALMER
DIVIDE NORTHEASTWARD (WHERE NORTHERLY UPSLOPE FLOW WILL BE
MAXIMIZED), AND ACROSS THE I-70 CORRIDOR BETWEEN BENNETT AND LIMON.
WITH HIGH CONFIDENCE IN IMPACTS FOR THE MORNING COMMUTE, A WINTER
WEATHER ADVISORY WAS ISSUED FOR THESE AREAS. ADJACENT PLAINS ZONES
(E.G. MORGAN, WASHINGTON, SOUTHERN LINCOLN COUNTIES) WERE INCLUDED
TO CAPTURE SPATIAL UNCERTAINTY IN THE BANDING. ADDITIONALLY, HI-
RESOLUTION GUIDANCE REMAINS RATHER STEADFAST IN AMPLIFYING QPF
ACROSS OUR SOUTHERN FOOTHILLS. HOWEVER, STILL BELIEVE THIS IS
OVERDONE IN SOME OF THE RECENT RUNS, CONSIDERING LESS-THAN-FAVORABLE
NORTH/NORTHWEST WINDS. THIS WILL ALSO KEEP AREAS TO THE NORTH OF
DENVER LARGELY DRY.
SO WITH ALL OF THAT SAID, THERE'S REASONABLE CONFIDENCE IN LITTLE TO
NO IMPACTS FOR THE MOUNTAINS, NORTHERN FOOTHILLS, AND NORTHERN I-25
CORRIDOR EXTENDING FROM THE NW DENVER SUBURBS TO THE WY BORDER. THE
AXIS OF GREATEST UNCERTAINTY WILL BE FOCUSED ACROSS THE SW DENVER
SUBURBS TOWARDS DIA AND THE NORTHEAST PLAINS, WHERE A STEEP SNOWFALL
GRADIENT CAN BE EXPECTED. THE MOST FAVORED LOCATIONS UNDER THE
HEAVIER SNOW BAND MAY WELL RECEIVE 5-10" WHEN ALL IS SAID AND DONE
IN/NEAR THE PALMER DIVIDE, BUT SUCH AMOUNTS WON'T BE OVERLY
WIDESPREAD. SNOW WILL RAMP DOWN QUICKLY BY MIDDAY AS BREEZY
NORTHERLY WINDS DEVELOP ACROSS THE LOWER ELEVATIONS, WITH
TEMPERATURES LIKELY CLIMBING INTO THE 40'S FOR SNOW-FREE AREAS OF
THE PLAINS AND URBAN CORRIDOR.
LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/
ISSUED AT 231 PM MST WED JAN 29 2025
DRY CONDITIONS ARE EXPECTED ACROSS THE FORECAST AREA THURSDAY NIGHT
AS THE 500MB UPPER LOW MOVES BE OVER THE CENTRAL PLAINS STATES AND A
DRY NORTHERLY FLOW SETS UP OVER COLORADO. ON FRIDAY, DRY AND WARMER
CONDITIONS ARE EXPECTED OVER THE CWA AS AN UPPER LEVEL RIDGE OF HIGH
PRESSURE BUILDS OVER THE STATE. COLORADO WILL BE UNDER THE INFLUENCE
OF A ZONAL FLOW ALOFT THIS WEEKEND WITH SOME DOWNSLOPING FLOW EAST
OF THE MOUNTAINS. THIS PATTERN WILL RESULT IN MILD AND DRY
CONDITIONS ACROSS THE PLAINS WITH HIGH TEMPERATURES RANGING FROM THE
MID 50S TO LOWER 60S. THERE MAY BE ENOUGH MID LEVEL MOISTURE CAUGHT
UP IN THE FLOW TO PRODUCE A 20-50% CHANCE OF LIGHT SNOW ACROSS THE
HIGH COUNTRY OVER THE WEEKEND. IN ADDITION, THE PATTERN WILL PRODUCE
BREEZY TO WINDY CONDITIONS ACROSS THE HIGH COUNTRY FRIDAY NIGHT
THROUGH THE WEEKEND WITH WIND GUSTS TO 65 MPH POSSIBLE ACROSS THE
FRONT RANGE MOUNTAINS AND FOOTHILLS.
FOR THE MONDAY THROUGH WEDNESDAY PERIOD, THE ZONAL FLOW ALOFT
CONTINUES WITH SOME WEAK UPPER LEVEL RIDGING OVER THE REGION. THE
HIGH COUNTRY SHOULD SEE A CONTINUED 20-50% CHANCE FOR LIGHT SNOW DUE
TO SOME MID LEVEL MOISTURE COMBINED WITH OROGRAPHIC LIFT. THERE IS
QUITE A BIT OF FORECAST UNCERTAINTY EAST OF THE MOUNTAINS DUE TO
MODEL DIFFERENCES. THE GFS DETERMINISTIC AND GEFS ENSEMBLES ARE
SUGGESTING A COLD FRONT MOVING ACROSS THE EASTERN PLAINS MONDAY
MORNING WITH A SHALLOW COLD AIR MASS SETTLING IN BEHIND IT. THIS
SCENARIO WOULD RESULT IN MUCH COLDER TEMPERATURES ON THE PLAINS WITH
DAYTIME READINGS ONLY CLIMBING INTO THE 30S ALONG WITH THE
POSSIBILITY FOR SOME VERY LIGHT SNOWFALL. ON THE OTHER HAND, MOST OF
THE OTHER MODELS KEEP THE FRONT NORTH OF OUR CWA WITH WARM AND DRY
WEATHER CONTINUING. AN EXAMPLE OF THIS WOULD BE THE ECMWF AND GEM
DETERMINISTIC SOLUTIONS WHICH ARE SHOWING DENVER'S MAX TEMPERATURES
CLIMBING INTO THE LOWER 70S BOTH MONDAY AND TUESDAY AFTERNOON.
HOWEVER, IT WOULD MOST LIKELY BE COOLER THAN THIS SINCE THESE
SOLUTIONS ARE OUTLIERS. FOR NOW HAVE DECIDED TO GO WITH THE
FORECAST MODEL BLEND WHICH HAS HIGH TEMPERATURES IN THE MID 40S TO
MID 50S ON THE PLAINS.
AVIATION /00Z TAFS THROUGH 00Z FRIDAY/
ISSUED AT 438 PM MST WED JAN 29 2025
CLOUDS WILL CONTINUE TO CREEP NORTH BRINGING CEILINGS OF 6000 TO
8000 FEET AFTER 00Z. CEILINGS ARE EXPECTED TO FALL BELOW 6000 FEET
03Z TO 06Z AND CONTINUE TO LOWER, FALLING BELOW 3000 FEET TOWARDS
12Z THURSDAY. GROWING CONFIDENCE THE HEAVIER SNOW STAYS JUST EAST
AND SOUTHEAST OF DEN. THOUGH LIGHT SNOW IS STILL EXPECTED, MAINLY
IN THE 10-17Z WINDOW. WINDS TO STAY LIGHT THE REST OF THE
EVENING, AND THEN PICK UP OUT OF THE NORTH AROUND 12Z WITH GUSTS
TO 25 KNOTS POSSIBLE MUCH OF THE DAY THURSDAY. THE SNOW AND
CLOUDS SHIFT EAST OF THE AREA AFTER 18Z WITH VFR CONDITIONS
EXPECTED BY 21Z.
BOU WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY FROM 5 AM TO 2 PM MST THURSDAY FOR
COZ041-044-045-049.
WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO NOON MST
THURSDAY FOR COZ046-047.
SHORT TERM...RODRIGUEZ
LONG TERM...JK
AVIATION...MEIER
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