Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 210852
AFDFSD

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

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 352 AM CDT MON JUL 21 2014

EXPECTING A HOT AND HUMID DAY ACROSS THE REGION AS OPPRESSIVE
HUMIDITY LEVELS CONTINUE.  EARLY THIS MORNING...STILL MONITORING FOR
THE DEVELOPMENT OF STRATUS ALONG THE MISSOURI RIVER WHICH COULD
SPREAD NORTHEAST IN THE MORNING HOURS.  AS NOTED IN PREVIOUS
DISCUSSION...MODELS HAVING A POOR TIME RESOLVING LOW-LEVEL MOISTURE
AND CONTINUE TO DO SO THIS MORNING.  SREF CONTINUES TO SUGGEST
RELATIVELY HIGH PROBABILITIES AOA 60 PERCENT OF A SUB 3K FT AGL DECK
FORMING BETWEEN 09-12Z.  SOUNDINGS INDICATE THIS DECK SHOULD
GRADUALLY LIFT THROUGH THE MORNING HOURS...BUT MAY HANG AROUND FOR A
GOOD PORTION OF THE DAY...ESPECIALLY ALONG AND EAST OF THE I-29
CORRIDOR.

TEMPERATURES THIS AFTERNOON COULD BE IMPACTED BY A FEW FORECAST
CONCERNS.  PRIMARILY THE INCREASE IN MID-LEVEL CLOUDS AHEAD OF AN
APPROACHING SHORTWAVE WITHIN MOISTURE PLUME VISIBLE IN WV IMAGERY...
SECONDLY THE EXCESSIVE BOUNDARY LAYER MOISTURE...AND FINALLY THE
LACK OF DEEP MIXING THIS AFTERNOON ESPECIALLY OVER THE EASTERN CWA.
TEMPERATURES MAY END UP BEING STUCK NEAR OR EVEN SLIGHTLY BELOW THE
90 DEGREE MARK EAST OF I-29.  FURTHER WEST...NOT AS MANY
COMPLICATIONS...WHICH SHOULD RESULT IN TEMPERATURES AT THE TRIPLE
DIGIT MARK.   DEW POINTS SUNDAY CLIMBED INTO THE LOW 70S...AND TODAY
SHOULD REACH THE MIDDLE 70S.  THE RESULTANT HEAT INDEX VALUES WILL
AVERAGE BETWEEN 100-105 DEGREES.

00Z MODEL GUIDANCE SEEMED TO CAPTURE THE LOW-LEVEL THERMAL FIELDS
WELL...SUGGESTIVE OF A SUBSTANTIAL CAP ACROSS THE ENTIRE CWA TODAY
WHICH SHOULD KEEP THE CWA DRY. WITH THE UPPER SHORT WAVE TRACKING A
BIT FURTHER NORTH...AND +14 TO +16 700 MB TEMPS EXTENDING ALL THE
WAY TO THE ND BORDER...FEEL BEST CHANCES FOR THUNDERSTORMS INTO THE
OVERNIGHT HOURS WILL REMAIN WELL NORTH AND NORTHEAST OF THE FORECAST
AREA. THIS IDEA IS ALSO BACKED UP BY THE SUITE OF HIGH-RES MODEL
SOLUTIONS THIS MORNING.  THUS...HAVE TRIMMED POPS SUBSTANTIALLY AS A
FRONT SWINGS THROUGH THE CWA AFTER MIDNIGHT.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 352 AM CDT MON JUL 21 2014

WITH MCS TO OUR NORTH/NORTHEAST QUICKLY EXITING INTO THE GREAT LAKES
ON TUESDAY...WILL BE LEFT WITH LITTLE SUPPORT FOR PRECIPITATION OVER
OUR FORECAST AREA DURING THE DAY TUESDAY. SURFACE FRONT EXPECTED TO
BE NEAR SOUTHEAST CORNER OF THE AREA BY 12Z TUESDAY...BUT THERMAL
RIDGE LAGS A BIT BEHIND...WITH STRONGER COLD ADVECTION PUSH NOT
ARRIVING UNTIL MIDDAY/EARLY AFTERNOON. WITH FAIR POST-FRONTAL MIXING
POTENTIAL...SHOULD SEE A QUICK RISE INTO THE 80S THROUGH MIDDAY. BUT
THEN READINGS SHOULD LEVEL OFF...OR EVEN DROP OFF A BIT SOONER THAN
TYPICAL DIURNAL TREND...AS COOLER AIR MOVES IN ALOFT. LOW LEVEL
MOISTURE WILL LIKEWISE BE SLUGGISH TO DEPART THE SOUTHEAST PORTIONS
OF THE AREA WITH DEW POINTS IN THE LOWER 70S LIKELY HANGING ON OVER
NORTHWEST IOWA INTO THE EARLY EVENING. FORTUNATELY TEMPERATURES ARE
EXPECTED TO BE COOLER THAN TODAY...SO HEAT INDICES SHOULD REMAIN
BELOW ADVISORY LEVELS.

WILL THEN SEE A RETURN OF SLIGHTLY BELOW NORMAL TEMPERATURES THROUGH
THE MIDDLE PART OF THE WEEK...AS SURFACE RIDGE MOVES THROUGH THE
REGION. RETURN FLOW/WARM ADVECTION FAIRLY QUICK TO RETURN TO WESTERN
PORTIONS OF THE FORECAST AREA BY LATER WEDNESDAY NIGHT THOUGH...AND
WILL BRING SOME LOW POPS INTO OUR WEST AFTER 06Z...WITH THE CHANCE
SPREADING EAST THROUGH THE DAY THURSDAY. STRONGER SIGNAL FOR PRECIP
CHANCES THURSDAY NIGHT INTO FRIDAY...MAINLY EAST OF THE JAMES RIVER
WITH BROAD WARM ADVECTION AND WEAK WAVES SLIDING OVER THE TOP OF
COLLAPSING SOUTHERN/CENTRAL PLAINS RIDGE. MODELS IN FAIR AGREEMENT
IN TIMING OF THE LATE WEEK WAVE...WITH DISCREPANCIES REGARDING MORE
FAVORED LOCATION AT THIS RANGE. THUS WILL KEEP BROAD CHANCE POPS AS
GIVEN BY CONSENSUS GRIDS THURSDAY NIGHT/FRIDAY...WITH CHANCES THEN
TAPERING ACROSS OUR WEST FRIDAY NIGHT AS CONSENSUS SHOWS MAIN WAVE
EXITING INTO THE UPPER MISSISSIPPI VALLEY. LATE WEEK TEMPERATURES
REMAIN SEASONABLE FOR LATE JULY...WITH HIGHS MAINLY IN THE UPPER 70S
AND 80S. HUMIDITY LEVELS SHOULD BE FAIRLY COMFORTABLE THROUGH THE
MIDDLE PORTION OF THE WEEK...BUT CREEP UP AGAIN FRIDAY AS MOISTURE
POOLS ALONG/AHEAD OF SLOW MOVING BOUNDARY. OVERALL NEXT WEEKEND
LOOKS TO BE ON THE DRY SIDE...THOUGH WILL HANG ONTO A CHANCE OF
PRECIP IN OUR EAST ON SUNDAY AS GFS SHOWS UPPER TROUGH DROPPING
SOUTHEAST INTO THE UPPER MIDWEST.

&&

.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...DUX
LONG TERM...JH
AVIATION...CHAPMAN







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