National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KFSD 202348
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
648 PM CDT SUN JUL 20 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 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 648 PM CDT SUN JUL 20 2014

A PATCH OF MVFR STRATOCUMULUS IN EXTREME SE SD...SW MN...
AND NW IA WILL DISSIPATE FAIRLY QUICKLY THIS EVENING. HOWEVER...
CONDITIONS WITH EXISTING INVERSION AND HIGH MOISTURE CONTENT OF
BOUNDARY LAYER AIRMASS WILL REDEVELOP LOWER CLOUDS AND FOG AS WE
HEAD THROUGH THE NIGHT. 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 NEED TO
DELAY UNTIL 20-22Z FOR KFSD AREA...A BIT EARLIER DEPARTURE FOR
KSUX.

&&

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

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

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

NE...HEAT ADVISORY FROM 11 AM TO 9 PM CDT MONDAY FOR NEZ013-014.

&&

$$

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