000
FXUS63 KFSD 210506
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1206 AM CDT MON JUL 21 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 310 PM CDT SUN JUL 20 2014

EXTENSIVE AREA OF STRATOCU OUT THERE AGAIN THIS AFTERNOON EAST OF
THE JAMES RIVER. MODELS HAVE REALLY STRUGGLED WITH THIS MOISTURE
TRAPPED BELOW THE INVERSION THE PAST COUPLE DAYS. THINK WE WILL SEE
MOST OF THE CLOUD COVER DISSIPATE AFTER SUNSET. HOWEVER THERE IS
A SIGNAL WITHIN THE MODELS...AND ESPECIALLY THE GFS AND SOME OF THE
SREF MEMBERS...THAT STRATUS WILL ONCE AGAIN FORM LATE TONIGHT. THIS
TIME IT MAY VERY WELL FORM RIGHT OVERHEAD...AS MOISTURE CONTINUES TO
ADVECT INTO THE AREA. THUS WENT AHEAD AND SIGNIFICANTLY INCREASED
CLOUD COVER LATER TONIGHT INTO TOMORROW ACROSS THE AREA. THINK THE
CLOUDS WILL AGAIN BE SLOW TO CLEAR TOMORROW...ESPECIALLY EAST OF THE
JAMES RIVER...WHERE IT MAY VERY WELL BE PARTLY OR MOSTLY CLOUDY
THROUGH THE DAY. INCREASING LOW LEVEL MOISTURE THROUGH THE DAY UNDER
A STRONG INVERSION JUST DOES NOT SEEM CONDUCIVE TO RAPID CLEARING.
AGAIN THIS STRATUS AND STRATOCU DEVELOPMENT IS NOT A SURE BET...BUT
LOOKS PRETTY LIKELY BASED ON WHATS HAPPENED THE PAST COUPLE DAYS AND
WHAT MODEL SOUNDINGS LOOK LIKE TOMORROW.

THIS ALL MEANS THAT HIGHS TOMORROW WILL PROBABLY BE COOLER THAN WHAT
WE HAVE BEEN GOING WITH EAST OF THE JAMES RIVER. THUS COOLED THINGS
OFF BY A FEW DEGREES...WITH UPPER 80S TO LOW 90S. EVEN IF IT BECOMES
MOSTLY SUNNY...WE JUST HAVE NOT BEEN MIXING WELL IN THIS
PATTERN...AND THUS THINK THE LOWER HIGHS ARE THE WAY TO GO. MIGHT
EVEN END UP A BIT COOLER THAN THIS CURRENT FORECAST. STILL SHOULD
SEE MID 90S TO AROUND 100 ALONG AND WEST OF THE JAMES RIVER WHERE
SLIGHTLY BETTER MIXING IS EXPECTED. HOWEVER...DEWPOINTS ARE STILL
EXPECTED TO BE IN THE MID 70S OVER A MAJORITY OF THE AREA...ONLY
DROPPING INTO THE 60S ACROSS OUR FAR WESTERN AREAS. AS MENTIONED
ABOVE...THE STRONG INVERSION AND LIMITED MIXING MAY EVEN ALLOW
DEWPOINTS TO GET A BIT HIGHER THAN FORECAST IN SOME LOCATIONS. SO
DESPITE THE COOLER HIGHS...HEAT INDEX VALUES BETWEEN 100 AND 105
LOOK LIKELY OVER A MAJORITY OF THE AREA TOMORROW AFTERNOON AND
EARLY EVENING. WOULD NOT BE SURPRISED TO SEE AREAS ALONG THE
MISSOURI RIVER FROM SIOUX CITY TO YANKTON...THEN UP THE JAMES
RIVER TO MITCHELL...SEE A PERIOD OF HEAT INDICES BETWEEN 105 AND
110. BUT WITH UNCERTAINTY AND EXPECTED LIMITED AREAL COVERAGE OF
THESE HIGHER VALUES...WILL NOT BE ISSUING ANY HEAT WARNINGS...AND
WILL KEEP THE ADVISORY AS IS FOR THE ENTIRE CWA. WILL BE DRY
THROUGH 00Z...AS EVEN THOUGH CAPE WILL BE AROUND 5000 J/KG...OUR
CWA WILL BE UNDER A STRONG CAP.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 310 PM CDT SUN JUL 20 2014

THE MAIN FEATURE FOR MONDAY NIGHT IS THE POTENTIAL FOR A MAJOR
CONVECTIVE SYSTEM BRUSHING THE NORTHERN AND EAST CENTRAL PARTS OF
OUR FORECAST AREA. THERE SEEMS TO BE A DECENT CONSENSUS ON THIS WITH
UPPER SUPPORT...THERMAL SUPPORT...AND INSTABILITY COMING TOGETHER ON
THE MODELS. SPC OUTLOOK LOOKS PRETTY REASONABLE THOUGH MODELS SEEM
TO SHOW THE MAIN SEVERE RISK JUST NORTH OF OUR AREA...THAT IS NOT
MUCH DIFFERENCE FROM THE MODERATE RISK CONTAINING OUR TWO
NORTHERNMOST SOUTHWEST MN COUNTIES. IN ANY EVENT THE BEST CHANCE OF
STORMS MONDAY NIGHT WILL BE NORTHEAST...WITH PRETTY LITTLE THREAT
SOUTHWEST IN THE CAPPED AIR. ALSO...BY THE TIME THE COLD FRONT MOVES
ACROSS THE SOUTHERN EDGE OF OUR AREA EARLY TUESDAY...THE MAIN UPPER
SUPPORT WILL BE OFF TO THE EAST AND WIND FIELDS WILL BE MORE
ANEMIC.

COOLER LOW LEVEL AIR WILL BEGIN TO SEEP INTO THE AREA FROM THE NORTH
BEHIND THE FRONT TUESDAY THOUGH IT MAY STILL BE WARM AND MUGGY
SOUTH. THIS FLOW WILL STIFFEN A LITTLE AS THE UPPER FLOW TURNS MORE
NORTHWESTERLY IN RESPONSE TO THE UPPER RIDGE REBUILDING TEMPORARILY
OVER THE FAR WESTERN USA. THIS COOLER REGION AND DRY WEATHER SHOULD
HOLD TUESDAY NIGHT THROUGH WEDNESDAY DROPS SOUTHEAST TO OUR EAST.

A WARMING PATTERN WILL AGAIN DEVELOP ESPECIALLY ALOFT LATE IN THE
WEEK AS THE UPPER RIDGE IS FORCED EASTWARD BY A STRONG PACIFIC
TROUGH. THIS WILL RESULT IN THE SLOW REDEVELOPMENT OF A STORM THREAT
THURSDAY AND THURSDAY NIGHT AHEAD OF THE MAIN WAVE AND COLD FRONT.
THIS SYSTEM IS LIKELY TO PASS FRIDAY AND NIGHT AND THAT IS WHEN THIS
NEXT STORM THREAT SHOULD PEAK. MODEST WARMING LATE IN THE WEEK WILL
THEN GIVE WAY TO SOME COOLING BEHIND THE SYSTEM OVER THE WEEKEND.
SATURDAY LOOKS DRY FOR NOW...BUT MODELS SHOW A SECONDARY CANADIAN
WAVE PASSING FOR SUNDAY AND HAVE GONE WITH EXTENDED GUIDANCE CHANCE
OF STORMS FOR THAT DAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1205 AM CDT MON JUL 21 2014

LARGEST AVIATION CONCERN DEALS WITH POTENTIAL FOR REDEVELOPMENT OF
MVFR CEILINGS...OR LOWER...IN THE IMMEDIATE TERM. EVEN SOUNDINGS
SHOW THE HIGH MOISTURE CONTENT OF BOUNDARY LAYER AIRMASS...CAPPED
BY DECENT INVERSION. GRADIENT NOT AS STRONG...AND EXPECT TO SEE A
LATER NIGHT DEVELOPMENT OF LOWER CLOUDS AND FOG. IFR CEILINGS AND
MVFR VISIBILITIES APPEAR POSSIBLE WITH DEVELOPMENT OF LOWER
CLOUDS/FOG...WITH KHON ON THE EDGE OF ANY DEVELOPMENT. THIS WILL
AGAIN UNDERGO A DIURNAL INTENSIFICATION EARLY IN THE DAY...WITH
EVENTUAL MIXING AND ADVECTION OF CLOUD MASS ERODING OUT OF THE
AREA. REMAIN A BIT OPTIMISTIC ABOUT BREAKING CLOUDS BY
MIDDAY...BUT GIVEN THE STRENGTH OF INVERSION ALOFT WOULD NOT BE
SURPRISED TO END UP WITH A DELAY UNTIL 20-22Z FOR KFSD AREA...A
BIT EARLIER DEPARTURE FOR KSUX.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...HEAT ADVISORY FROM 11 AM THIS MORNING TO 9 PM CDT THIS EVENING
     FOR SDZ038>040-050-052>071.

MN...HEAT ADVISORY FROM 11 AM THIS MORNING TO 9 PM CDT THIS EVENING
     FOR MNZ071-072-080-081-089-090-097-098.

IA...HEAT ADVISORY FROM 11 AM THIS MORNING TO 9 PM CDT THIS EVENING
     FOR IAZ001>003-012>014-020>022-031-032.

NE...HEAT ADVISORY FROM 11 AM THIS MORNING TO 9 PM CDT THIS EVENING
     FOR NEZ013-014.

&&

$$

SHORT TERM...CHENARD
LONG TERM...
AVIATION...CHAPMAN