Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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508
FXUS65 KBOU 272200
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
400 PM MDT WED APR 27 2016

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 355 PM MDT WED APR 27 2016

LOWER SPECIFIC HUMIDITY/PRECIPITABLE WATER AND A MID-LEVEL CAP
BENEATH A PASSING SHORTWAVE RIDGE PRETTY MUCH SQUELCHED SHOWER
FORMATION AND SUPPRESSED UPDRAFTS TODAY. THE ISOLATED SHOWERS
IN THE FCST WORKED OUT. THE GUSTY N-NWLY WINDS ALSO MATERIALIZED
ON THE PLAINS AND ON THE HIGH MTN RIDGES ON THE BACKSIDE OF THE
DEPARTING UPPER TROUGH.

OVERNIGHT...ATTENTION SHIFTS TO THE LARGE UPPER TROUGH WINDING UP
OVER THE DESERT SOUTHWEST/LOWER GREAT BASIN. IN ADVANCE OF THIS
SYSTEM...MODELS SHOW A DEEPENING SOUTHWESTERLY TRANSPORTING
HIGHER THETA-E AIR NORTHWARD UP INTO COLORADO AND BY LATE TONIGHT
COULD SEE SNOWFALL ON THE INCREASE OVER HIGHER ELEVATIONS ACRS
SWRN PORTIONS OF THE CWA. MEANWHILE...MODELS SHOW EAST-
SOUTHEASTERLY LOW-LEVEL FLOW ON THE PLAINS MOVING MOISTURE
WESTWARD UP ALONG THE PALMER DIVIDE AND BY LATE TONIGHT RESULTING
IN PATCHY TO AREAS OF FOG AS FAR NORTH AS ERN PORTIONS OF THE
DENVER METRO AREA. VSBYS GENERALLY IN THE 3-5 MILE RANGE.
HOWEVER...THIS SAME ELY FLOW IS PROJECTED TO PRODUCE NEAR
SATURATED CONDITIONS IN THE FRONT RANGE FOOTHILLS LATE TONIGHT
THRU MID-MORNING ON THURSDAY. SO ADDED AREAS OF FOG HERE WHERE
SOME VSBYS IN SOME AREAS COULD DROP TO BELOW A MILE AROUND
SUNRISE. LOWS TONIGHT ONLY SLIGHTLY WARMER THAN LAST NIGHT

ON THURSDAY...WITH THE UPPER TROUGH CLOSING IN...SHOW SEE SNOWFALL
COVERAGE EXPANDING NORTHWARD ACROSS THE HIGH COUNTRY AND OVER THE
FRONT RANGE FOOTHILLS. PRECIP MAY START OUT AS A RAIN/SNOW MIX IN
THE FOOTHILLS AND LOWER MTN VALLEYS BUT WITH TIME CHANGE OVER TO
ALL SNOW IN THE AFTERNOON WITH PRECIP BECOMING MORE CONVECTIVE IN
CHARACTER. ON THE PLAINS...NO PRECIP TO START OUT THE DAY AND BY
MID-MORNING THE FOG SHOULD DISSIPATE. BY AFTERNOON SHOWERS FORMING
OVER THE FRONT RANGE FOOTHILLS WITH ENHANCED UPSLOPE FLOW ARE
EXPECTED TO BEGIN SPREADING OUT ONTO THE PLAINS WITH SWLY
TRANSPORT WINDS. WILL SLOWLY FALLING TEMPERATURES...COULD SEE
PRECIP IN AREAS NEAR THE FOOTHILLS AND ON THE PALMER DIVIDE
CHANGING TO A MIX OF RAIN/SNOW. MAY EVEN SEE A STRAY T-STORM OR
TWO ON THE PALMER DIVIDE LATE. HIGH TEMPS TOMORROW PROGGED TO BE
GENERALLY 3-5 DEG F LOWER THAN THOSE OBSERVED TODAY.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 355 PM MDT WED APR 27 2016

PRETTY REMARKABLE AGREEMENT BETWEEN THE MODELS REGARDING THE
SYNOPTIC SCALE EVOLUTION/MOVEMENT OF THE UPPER LOW AND ATTENDANT
QG VERTICAL VELOCITY FIELDS THROUGHOUT THE DURATION OF THE
UPCOMING STORM. THE TRACK IS NOT NECESSARILY PERFECT FOR A MAJOR
STORM...A BIT TOO FAR NORTH...BUT ENOUGH ASCENT FOR A LONG ENOUGH
TIME TO GENERATE DECENT PRECIPITATION AMOUNTS ACROSS MUCH OF THE
CWA. SURFACE EVOLUTION IS ALSO DECENT...PERHAPS NOT PERFECT...WITH
THE LATEST ECMWF SUGGESTING A BIT LESS UPSLOPE THAN THE OTHER
MODELS DURING THE DAY FRIDAY. THE OTHER BIG CONCERN...LIKELY THE
MOST IMPORTANT...IS THE THERMODYNAMIC STRUCTURE OF THE AIRMASS.
LOTS OF DISCREPANCIES BETWIXT THE MODELS WITH THE ECMWF AND NAM
SUGGESTING MORE SNOW AT LOWER ELEVATIONS WHILST THE GFS IS QUITE
A BIT WARMER. LASTLY...THE GFS HAS ABOUT 3-4 TIMES THE QPF ACROSS
PARTS OF THE CWA COMPARED TO THE OTHER SIMULATIONS SO PLENTY OF
UNCERTAINTY STILL LINGERS IN THE DETAILS. FORECAST PRECIPITABLE
WATER NUMBERS ARE SUBSTANTIAL ENOUGH TO SUGGEST THAT 0.5 TO 1.0
INCH OF WATER IS NOT OUT OF THE QUESTION IN MOST AREAS BEFORE ALL
IS SAID AND DONE. WINTER STORM WATCH HAS ALREADY BEEN POSTED FOR
THE FOOTHILLS...SOUTH PARK AND MOST OF THE MOUNTAINS.

LATER ON DOWN THE LINE GENERAL TROUGHINESS REMAINS OVER THE
CENTRAL ROCKIES WITH BELOW NORMAL TEMPERATURES THROUGH THE EARLY
PART OF NEXT WEEK. WARMER DRIER CONDITIONS MAY RETURN BY MIDWEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 355 PM MDT WED APR 27 2016

VFR CIGS AND VSBYS ANTICIPATED THROUGH 05Z TONIGHT...THEN MOST
AREAS SHOULD SEE CIGS LOWERING WITH A MOIST EAST-SOUTHEAST
UPSLOPE FLOW. SOUTHERN AND EASTERN SECTIONS OF THE DENVER METRO
AREA...INCLUDING KDEN AND KAPA MAY SEE PATCHY FOG FORMING AFTER
09Z TONIGHT...WITH VSBYS GENERALLY IN THE 3-5 MILE RANGE THROUGH
ABOUT 15Z. THEN DISSIPATING WITH LIGHT RAIN SHOWERS BEGINNING TO
MOVE OFF THE FOOTHILLS. DURING THE AFTERNOON THERE IS A CHANCE OF
RAIN SHOWERS AT ALL DENVER AREA AIRPORT AND A CHANCE THAT THESE
SHOWERS MAY CHANGE TO A RAIN/SNOW MIX AT KAPA AND KBJC AFTER 21Z
WITH MVFR CIGS.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM THURSDAY EVENING THROUGH FRIDAY EVENING
FOR COZ033>037.

&&

$$

SHORT TERM...BAKER
LONG TERM...ET
AVIATION...BAKER



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