Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 041751
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
1151 AM MDT SAT JUL 4 2015

.UPDATE...
ISSUED AT 1151 AM MDT SAT JUL 4 2015

ONLY MINOR CHANGES FOR A BIT SLOWER EVOLUTION OF CONVECTION TODAY.
IN GENERAL THE AIRMASS OVER THE PLAINS WILL BE A FEW DEGREES SHY
OF THE CONVECTIVE TEMPERATURE. HOWEVER EVENTUAL OUTFLOW BOUNDARIES
FROM THE MOUNTAINS AND WEAK LIFT FROM AN ALMOST IMPERCEPIBLE
SHORTWAVE STRETCHED ACROSS SOUTHERN WYOMING NOW WILL ALLOW FOR A
FEW STORMS TO FORM. SHOULD BE SOME MIXING OUT OF THE MOISTURE NEAR
THE MOUNTAINS WITH CAPES BELOW 1000 J/KG...FURTHER EAST ON THE
PLAINS A BIT MORE CAPPED BUT CAPES WILL WIND UP IN THE 1000-1500
J/KG RANGE. SHEAR DECREASING...BUT 0-6 KM SHEAR STILL AROUND 30
KNOTS ON THE EASTERN BORDER THIS AFTERNOON SO THE COMBINATION IS
ENOUGH FOR MARGINAL SEVERE POTENTIAL...AND POSSIBLY EVEN LARGER
HAIL IN THE INITIAL PULSES. STORMS OUT THERE WOULD ALSO BE SLOW
MOVING DUE TO THE LIGHTER WINDS ALOFT AND INCREASING SOUTHERLY
INFLOW...POTENTIAL HEAVY RAIN/MINOR FLOODING POTENTIAL...BUT THIS
IS MAINLY A THREAT FOR AREAS FURTHER EAST. GIVEN THE MARGINAL
ENVIRONMENT STORMS SHOULD FADE QUICKLY THIS EVENING EXCEPT FOR
INFLOW DRIVEN STORMS NEAR THE EASTERN BORDER. CLOUD COVER FROM
TODAYS WEAK CONVECTION AND MOISTURE TRAPPED IN THE RIDGE WILL
LINGER HOWEVER.

&&

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 327 AM MDT SAT JUL 4 2015

THE UPPER LEVEL RIDGE AXIS OVER THE GREAT BASIN WILL BEGIN TO
SHIFT EASTWARD TODAY AND TONIGHT. AS A RESULT...WE WILL SEE
SEVERAL DEGREES OF WARMING BOTH AT THE SURFACE AND ALOFT. THE
WARMING ALOFT WOULD TEND TO SUPPRESS CONVECTION...BUT AT THE SAME
TIME THERE IS STILL SOME MOISTURE WITH MODEST PRECIPITABLE WATER
VALUES UNDER THE RIDGE. STRONGER SURFACE HEATING WILL STILL ALLOW
SURFACE BASED CONVECTION TO FIRE OVER THE MOUNTAINS AND FOOTHILLS
BY NOON AND THEN SHIFT EASTWARD ACROSS THE PLAINS DURING THE
AFTERNOON AND EVENING. WITH THE WARMING...BASES WILL BE HIGHER SO
EXPECT MAINLY GUSTY WINDS...LIGHTNING...AND BRIEF MODERATE RAIN
WITH THE STORMS. FARTHER EAST ON THE PLAINS...THE LOW LEVEL
MOISTURE IS EXPECTED TO HOLD IN PLACE AHEAD OF A DEVELOPING LEE
TROUGH...SO SOME SEVERE THREAT ROUGHLY ALONG AND EAST OF A
STERLING TO AKRON LINE WHERE CAPES OF 2000 J/KG EXPECTED. SPC HAS
THIS AREA UNDER A SLIGHT RISK AND SEEMS REASONABLE IF CAP IS ABLE
TO BREAK THAT FAR EAST.

CONVECTION WILL DECREASE RATHER QUICKLY THIS EVENING WITH THE
WARMER AIRMASS ALOFT...SO BY DARK/FIREWORKS TIME THE STORMS
SHOULD BE PRETTY MUCH OVER. NEXT ROUND AHEAD OF SHOWERS/STORMS
HEADED FOR THE MOUNTAINS AHEAD OF NEXT SHORT WAVE SHOULD MOSTLY
HOLD OFF UNTIL SUNDAY MORNING...BUT WILL MENTION SOME THREAT FOR
CONSISTENCY.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 327 AM MDT SAT JUL 4 2015

ON SUNDAY...THE RIDGE AXIS WILL SHIFT EAST AS AN UPPER LEVEL
DISTURBANCE MOVES INTO WESTERN COLORADO AND A STRONGER TROUGH
PASSES THROUGH THE NORTHERN ROCKIES. WILL BUMP THE POPS UP TO
LIKELY IN THE HIGH COUNTRY...WITH ISOLATED TO SCATTERED POPS
ALONG THE FRONT RANGE AND NORTHEAST PLAINS. FORECAST SOUNDINGS IN
THE AFTN SHOW MAINLY MID AND UPPER LEVEL MOISTURE WITH DRIER AIR
IN THE LOWER LEVELS AT DENVER WITH CAPES OF 150-300 J/KG. PW
VALUES WILL BE OVER AN INCH AS SUBTROPICAL MOISTURE FM THE SOUTH
ADVECTS INTO WESTERN COLORADO. AS A RESULT BRIEF HEAVY RAIN AND
STRONG WIND GUSTS WILL BE THE MAIN THREATS. SUNDAY NIGHT INTO
MONDAY...A COLD FRONT WILL PUSH INTO THE AREA FROM THE NORTH. BEST
SHOWERS/TSTM COVERAGE WILL BE ALONG THE FRONTAL BOUNDARY AS IT
PUSHES THROUGH THE CWA...ALONG WITH SOME WEAK MID LEVEL QG
ASCENT. THE POST FRONTAL AIRMASS WILL BECOME INCREASINGLY STABLE
OVER THE NORTHEAST PLAINS BY MONDAY MORNING. THE BEST INSTABILITY
WILL BE OVER THE HIGH COUNTRY MONDAY AFTERNOON. FORECAST SOUNDINGS
FOR DENVER ARE FAIRLY MINIMAL REGARDING THE CAPE. THE BEST LOW
LEVEL UPSLOPE IS PROGGED IN THE MORNING. BY LATE MONDAY AFTERNOON
AND EVENING...NOT MUCH UPSLOPE PRESENT IN SPITE OF THE SATURATED
AIRMASS. THE PW VALUES ARE CLOSE TO 1.2 INCHES OFF THE GFS/NAM
SOUNDINGS BY 00Z TUESDAY...BUT MINIMAL UPSLOPE/CAPE AT THAT TIME
AS HIGHS WILL BE 15-20 DEGREES COOLER THAN THOSE ON SUNDAY. WILL
NOT RULE OUT HEAVY RAIN ESPECIALLY IN THE HIGH COUNTRY...BUT SOME
QUESTIONS REGARDING HOW ELEVATED THE THREAT WILL BE ALONG THE
FRONT RANGE IF THE UPSLOPE DOES NOT PAN OUT. FOR TUESDAY...THE
FLOW ALOFT WILL BE WEAKER AND FM THE NORTHWEST WITH THE RIDGE AXIS
SHIFTING BACK TO THE WEST A BIT. THE BEST MOISTURE/CONVERGENCE
WILL BE OVER THE FRONT RANGE MOUNTAINS/FOOTHILLS. THE AMS OVER THE
NORTHEAST PLAINS WILL STILL BE FAIRLY COOL STILL WHICH WILL LIMIT
THE THUNDERSTORM COVERAGE IN THE AFTN/EVNG. WEDNESDAY THROUGH
FRIDAY...THE RIDGE WILL STAY TO THE SOUTH WITH A WEST/NORTHWEST
FLOW ALOFT OVER COLORADO. THE SURFACE HIGH OVER THE NORTHEAST
PLAINS WILL MOVE EASTWARD. AS A RESULT...TEMPERATURES WILL CLIMB
BACK INTO THE 80S. MID LEVELS WILL REMAIN RELATIVELY MOIST AND
SUBTROPICAL MOISTURE CONTINUES MOVE INTO THE STATE FM THE
SOUTH/SOUTHWEST. AS A RESULT...WL KEEP SLGT CHC OF TSTMS IN THE
GRIDS EACH AFTN/EVNG.

&&

.AVIATION...(FOR THE TAFS THROUGH 18Z SUNDAY MORNING)
ISSUED AT 1151 AM MDT SAT JUL 4 2015

VFR THROUGH TONIGHT. ISOLATED STORMS ARE EXPECTED IN THE DENVER
AREA AFTER 21Z WITH A SHORT PERIOD OF VARIABLE WINDS TO AROUND 30
KNOTS LIKELY SOMETIME DURING THE LATE AFTERNOON.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...GIMMESTAD
SHORT TERM...BARJENBRUCH
LONG TERM...COOPER
AVIATION...GIMMESTAD



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