159
FXUS65 KBOU 060117
AFDBOU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
617 PM MST WED MAR 5 2025
KEY MESSAGES
- FIRST ROUND OF SNOW MOVES INTO THE MOUNTAINS THIS EVENING. MAIN
IMPACT WILL BE IN THE NORTHERN TIER OF MOUNTAINS WITH SLICK
TRAVEL. SCATTERED LIGHT RAIN/SNOW SHOWERS SPILLING ONTO FAR
NORTHERN PLAINS.
- SECOND ROUND OF SNOW FOR THE MOUNTAINS STARTS THURSDAY
AFTERNOON, WITH A HEAVIER ROUND OF SNOW FRIDAY PM. SEVERAL
INCHES OF SNOW AND POOR TRAVEL CONDITIONS ACROSS SOME OF THE
MOUNTAIN PASSES.
- FRIDAY AFTERNOON/EVENING WILL BRING OPPORTUNITY FOR A FEW INCHES
OF SNOW TO THE FOOTHILLS AND ADJACENT LOWER ELEVATIONS.
- MUCH MILDER WITH DRY WEATHER STARTING SATURDAY AND PEAKING
MONDAY, WHEN HIGHS MAY BREAK 70 DEGREES IN SPOTS.
SHORT TERM /THROUGH THURSDAY/
ISSUED AT 245 PM MST WED MAR 5 2025
MAIN FOCUSES WILL BE THE INCOMING MOISTURE PLUME TONIGHT, A BREAK
THURSDAY, AND THEN THE NEXT DISTURBANCE ARRIVING THURSDAY AFTERNOON.
THE FIRST MOISTURE PLUME COMING OFF THE PACIFIC IS ALREADY
PUSHING INTO THE DESERT SOUTHWEST THIS AFTERNOON. WHILE THIS
PLUME IS QUITE IMPRESSIVE (700-500 MB SPECIFIC HUMIDITY NEAR 3
G/KG), THE LAPSE RATES ARE WEAK AND ONLY IN THE 3-5C/KM RANGE.
THUS, WHILE SNOW WILL BE DEVELOPING IN THE MOUNTAINS, THE RATES
AND SLRS WILL BE LIMITED BY THE WEAK LAPSE RATES AND RATHER
SHALLOW DENDRITIC GROWTH ZONE (DGZ). THE BEST SNOW THAT STARTS
LATER THIS EVENING WILL DEFINITELY FOCUS NORTH - TOWARD THE
NORTHERN TIER OF MOUNTAINS ALONG/NORTH OF RABBIT EARS PASS TO
ROCKY MOUNTAIN NATIONAL PARK. 2-5" OF SNOW CAN BE EXPECTED
THERE THROUGH EARLY THURSDAY MORNING, WHILE THE I-70 MOUNTAIN
CORRIDOR WILL LIKELY SEE AMOUNTS LESS THAN 2". THUS, WE'LL START
THE WINTER WEATHER ADVISORY FOR THE NORTHERN TIER THIS EVENING,
WHILE HOLDING OFF ON THE I-70 CORRIDOR TIL LATE THURSDAY
AFTERNOON. MORE ON THAT IN A BIT.
IN THE MEANTIME, WE'LL SEE MOSTLY CLOUDY SKIES ACROSS THE PLAINS
AS THE MOISTURE PLUME ARRIVES, BUT IN THIS WARM AIR ADVECTION
PATTERN IT'S ALWAYS HARD TO SATURATE THE LOW LEVELS - DUE TO
DOWNSLOPE. THE NORTHERN BORDER WILL STILL SEE AN OPPORTUNITY OF
LIGHT RAIN/SNOW OVERNIGHT INTO EARLY THURSDAY MORNING, SUPPORTED
BY STRONGER FRONTOGENESIS THERE, BUT LITTLE IF ANY SNOW
ACCUMULATION DUE TO MARGINAL TEMPS AND ONLY LIGHT PRECIPITATION.
POSSIBLY JUST A BRIEF SPRINKLE OR FLURRY CLOSER TO DENVER.
NOW, SHIFTING GEARS TO THURSDAY. THERE WILL LIKELY BE A BREAK IN
BETWEEN TONIGHT'S WARM/MOIST ADVECTION AND TOMORROW'S DISTURBANCE.
QG LIFT INCREASES LATE IN THE DAY AS THE NEXT SHORTWAVE
APPROACHES. IN ADDITION, LAPSE RATES IMPROVE RATHER DRAMATICALLY
FROM TONIGHT'S, WITH NEAR NEUTRAL LAPSES RATES OF 6-7 C/KM
BY TOMORROW AFTERNOON. THEREFORE, WE EXPECT SHOWERS TO GENERATE
RATHER EFFICIENTLY LATER IN THE DAY, WHILE ALSO SPREADING INTO THE
ADJACENT PLAINS LATE AFTERNOON AND EVENING. GIVEN THE INCREASED
SYNOPTIC SUPPORT AND MOUNTAIN SNOW CONTINUING OFF/ON THROUGH
FRIDAY EVENING, WE'LL START THE WINTER WEATHER ADVISORY FOR THE
I-70 MOUNTAIN CORRIDOR/SUMMIT COUNTY AT 3 PM TOMORROW.
FINALLY, WE NUDGED TEMPERATURES DOWN SEVERAL DEGREES TOMORROW
ALONG/NORTH OF AN EXPECTED DENVER CYCLONE. THESE ARE ALWAYS TRICKY
EVENTS DEPENDING ON HOW/IF STRATUS DEVELOPS LATE TONIGHT/EARLY
THURSDAY MORNING. BOTTOM LINE IS WE TRENDED COOLER, BUT POTENTIAL
FOR A "BUST" IS THERE REGARDING TEMPERATURES. ELEVATED FIRE
WEATHER CONDITIONS ARE ALSO EXPECTED IN SOUTHERN LINCOLN COUNTY
AND PARK COUNTIES WHICH HAVE HIGHER CONFIDENCE OF GUSTY WINDS TO
35 MPH AND NO INFLUENCE FROM DENVER CYCLONE. PALMER DIVIDE ALSO
HAS SOME LINGERING SNOW COVER TO REDUCE THREAT THERE.
LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/
ISSUED AT 156 PM MST WED MAR 5 2025
WITH A WEAK SHORTWAVE CLIPPING NORTHERN COLORADO THURSDAY EVENING
AND NIGHT, THE BULK OF THE PRECIPITATION POTENTIAL WILL BE FOCUSED
ACROSS THE NORTHERN HALF OF OUR FORECAST AREA, WITH INCREASING NORTH
WINDS CIRCULATING ALONG THE BACKSIDE OF AN AREA OF LEE CYCLOGENESIS
THAT WILL BE PUSHING DEEPER INTO THE PLAINS. ASSOCIATED COLD
ADVECTION WILL HELP PROMOTE A TRANSITION TO SNOW IN THE EVENING WITH
ANY LINGERING CONVECTIVE SHOWERS, AND AN AXIS OF MODERATE
FRONTOGENESIS IN THE NORTHEAST PLAINS COULD SUPPORT LOCALLY HIGHER
AMOUNTS. THAT BEING SAID, THERE'S SOME UNCERTAINTY IN THE SOUTHERN
EXTENT OF THE EVENING AND OVERNIGHT PRECIPITATION, WITH THE HEAVIEST
AMOUNTS EXPECTED TO REMAIN NORTH OF THE WY/NE STATE LINE.
SLIGHTLY DRIER AIR FILLS IN BY EARLY FRIDAY MORNING AND WITH LIGHT
DOWNSLOPE TO NORTH FLOW IN PLACE ALONG AND NEAR THE FOOTHILLS,
PRECIPITATION POTENTIAL SHOULD BE REDUCED FOR MOST AREAS, THOUGH NOT
ENTIRELY GONE. HOWEVER, COME FRIDAY AFTERNOON AND EVENING,
DEVELOPMENT OF A CLOSED LOW OVER AZ/NM SHOULD BE SUFFICIENT FOR A
BRIEF WINDOW OF FAIRLY LIGHT NORTHEAST SURFACE FLOW THROUGH THE
EVENING HOURS, AND THUS SHALLOW UPSLOPE ENHANCEMENT OVER THE
FOOTHILLS AND ADJACENT LOWER ELEVATIONS. IT'S THIS PERIOD THAT
CARRIES THE GREATER POTENTIAL FOR A FEW INCHES OF SNOW ACCUMULATIONS
(1-3" FOR AREAS WEST OF I-25, AND 2-6" FOR THE FOOTHILLS). THESE
AREAS MAY ULTIMATELY NEED ADVISORIES BUT THERE'S STILL TOO MUCH
MODEL INCONSISTENCY TO PULL THE TRIGGER. UNDER PLENTY OF CLOUD
COVER AND CONTINUED COOL MOSTLY NORTHEAST FLOW FRIDAY, OPTED FOR
THE COOLER END OF THE MODEL GUIDANCE WITH HIGHS IN THE LOW TO MID
30'S ACROSS THE PLAINS AND URBAN CORRIDOR.
AFTER ONE MORE SEASONABLY CHILLY NIGHT FRIDAY NIGHT, WE'LL LEAVE OUR
LITTLE TASTE OF WINTER BEHIND WITH NOTABLY MILDER TEMPERATURES
RETURNING FOR SATURDAY AS SUBSIDENT FLOW TAKES HOLD AND CLEAR SKIES
DOMINATE. THIS WARMING WILL ACCELERATE SUNDAY AS UPPER-LEVEL RIDGING
EXPANDS INTO THE REGION, PUSHING TEMPERATURES TO BETWEEN 5 AND 10
DEGREES ABOVE AVERAGE, WITH THE TREND EXPECTED TO CONTINUE INTO
MONDAY WHEN THE NBM INDICATES AN 85% PROBABILITY OF DENVER REACHING
70F OR HIGHER.
ENSEMBLE GUIDANCE POINTS TO AMPLIFYING LOW PRESSURE OVER SOCAL FOR
TUESDAY, WITH INCREASING SOUTHWEST FLOW LEADING TO BREEZIER
CONDITIONS REGION-WIDE. FOR NOW, IT SEEMS AS THOUGH ENOUGH DRY AIR
COULD LINGER AHEAD OF THIS SYSTEM TO RESULT IN FIRE WEATHER CONCERNS
ACROSS PORTIONS OF THE LOWER ELEVATIONS, WHILE THE MOUNTAINS SEE THE
POTENTIAL FOR SOME SNOW TO RETURN BY THE OVERNIGHT PERIOD AS
MOISTURE IS ADVECTED INTO COLORADO WITHIN THE SOUTHWEST FLOW ALOFT.
HOW THE TROUGH PROGRESSES ISN'T CLEAR WITH A FAIR AMOUNT OF
DISTRIBUTION AMONG CLUSTERS FOR THE TUE-WED TIMEFRAME, BUT THEY
GENERALLY DON'T PROVIDE MORE THAN A WEAK SIGNAL FOR ANY
PRECIPITATION OUTSIDE OF THE HIGH COUNTRY.
AVIATION /00Z TAFS THROUGH 00Z FRIDAY/
ISSUED AT 607 PM MST WED MAR 5 2025
MOST OF THE MODELS KEEP THE WINDS A BIT EAST OF TRUE DRAINAGE
PATTERNS AT DIA FOR MOST OF TONIGHT. THEY SHOW WEAKER WEST AND
NORTHWESTERLY WINDS JUST BEFORE 12Z THURSDAY MORNING. WEAK NORMAL
DIURNAL PATTERNS ARE PROGGED THROUGH THE DAY THURSDAY. THERE IS A
SIGNIFICANT AREA OF CLOUDINESS OVER MUCH OF THE WESTERN QUARTER
OF U.S. AT THIS TIME. THIS AREA IS MOVING EASTWARD AND GETTING
INTO EASTERN COLORADO PRESENTLY. CROSS SECTIONS ON SOME OF THE
MODELS SHOW A FEW-SCT040-050 CLOUD DECK AFTER 10Z. I ALSO PUT A
TEMPO IN FOR BKN010 2SM BR FOR A FEW HOURS IN AND AROUND SUNRISE,
AS SOME MODELS SHOW THIS POTENTIAL. WE WILL SEE!
BOU WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY UNTIL 11 PM MST FRIDAY FOR COZ031-033.
WINTER WEATHER ADVISORY FROM 3 PM THURSDAY TO 11 PM MST FRIDAY
FOR COZ034.
SHORT TERM...BARJENBRUCH
LONG TERM....RODRIGUEZ
AVIATION.....RJK
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