Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 200855
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
355 AM CDT SUN JUL 20 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 351 AM CDT SUN JUL 20 2014

DEVELOPMENT OF STRATOCU IN EASTERN PORTIONS OF THE AREA YESTERDAY
PUT A DAMPER ON EXPECTED WARMING. MODELS SHOWING THAT LOW LEVEL
MOISTURE STILL HANGING AROUND ACROSS THE EAST TODAY BENEATH THE
INVERSION...THOUGH NOT VERY DEEP ON FORECAST SOUNDINGS. EXPECT WE
WILL SEE SOME DEVELOPMENT AGAIN TODAY...THOUGH AT THIS POINT DO NOT
ANTICIPATE COVERAGE TO BE AS EXTENSIVE AS YESTERDAY AND THUS LOWER
TO MID 80S SHOULD BE ATTAINABLE FOR HIGHS NEAR/EAST OF I-29. AREAS
ALONG/WEST OF THE JAMES SEE MORE NOTABLE LOW LEVEL WARMING AND WILL
STICK WITH IDEA OF LOWER-MID 90S FOR HIGHS IN THIS AREA. THIS NEAR
THE WARMEST GUIDANCE SOLUTIONS...WITH SOME OF THE GLOBAL MODELS AND
NUMERICAL GUIDANCE A FEW DEGREES LOWER. WITH FORECAST DEW POINTS IN
THE UPPER 60S TO AROUND 70...LOCATIONS IN OUR WEST DO BRUSH TRIPLE
DIGIT HEAT INDICES FOR 2-3 HOURS THIS AFTERNOON. HOWEVER WITH SMOKE
LAYER ALOFT STILL EXPECTED TO BE FAIRLY WIDESPREAD...THIS COULD HOLD
TEMPS DOWN A BIT FROM FULL MIXING POTENTIAL...AND THUS HAVE OPTED TO
HOLD OFF ON ISSUING HEAT ADVISORY IN OUR WEST AT THIS TIME. WILL BE
SOMETHING FOR DAY SHIFT TO MONITOR THOUGH.

OTHER QUESTION FOR THE LATE AFTERNOON/EVENING IS WHETHER BOUNDARY
WILL SAG FAR ENOUGH SOUTHEAST TO ALLOW ISOLATED STORMS TO BRUSH OUR
NORTHWEST CWA. MOST GUIDANCE HOLDS THE BOUNDARY WELL NORTH OF THE
AREA...WITH STRONG CAP KEEPING OUR AREA DRY THROUGH TONIGHT. HOWEVER
HI-RES ARW AND RAP/HRRR MORE AGGRESSIVE IN DROPPING THE BOUNDARY
FARTHER SOUTH AND DEVELOPING CONVECTION INTO OUR NORTHWEST CORNER BY
EVENING. SIDING WITH THE NORTHERN/DRY SOLUTION FOR NOW...BUT AGAIN
WILL BE SOMETHING TO WATCH THROUGH THE DAY.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 351 AM CDT SUN JUL 20 2014

PRIMARY FOCUS IN THE MEDIUM RANGE AND EXTENDED PORTIONS OF THE
FORECAST REMAINS ON HOT AND HUMID CONDITIONS OF MONDAY...ALONG WITH
SEVERE WEATHER POTENTIAL MONDAY NIGHT.

ON MONDAY...INCREASING MID-LEVEL HEIGHTS AND SIGNIFICANT NORTHWARD
ADVECTION OF BOUNDARY LAYER MOISTURE WILL WORK IN TANDEM TO PRODUCE A
RAPID SHIFT FROM SEASONALLY COOL CONDITIONS OF THE PAST WEEK TO A
BRIEF STINT OF DANGEROUS HEAT. AS A MID-LEVEL SHORTWAVE ROTATES AROUND
THE WESTERN FLANK OF THE MID-LEVEL RIDGE...SURFACE CYCLOGENESIS WILL
OCCUR OVER WEST CENTRAL SOUTH DAKOTA EARLY MONDAY MORNING. A WARM
FRONT IS EXPECTED TO FORM NORTH OF THE CWA WITH THE INCREASED
MERIDIONAL FLOW ALLOWING MOISTURE TO POOL SOUTH OF THE BOUNDARY
MONDAY AFTERNOON. ADJUSTING RAW MODEL DEW POINTS NEAR 80F...BY TAKING
ACCOUNT OF SLIGHT DOWNWARD MIXING OF DRIER AIR ALOFT...SHOULD STILL
RESULT IN DEW POINT VALUES 74-78 OVER MUCH OF THE CWA. ALOFT...H850
TEMPERATURES APPROACHING +30C SHOULD MOVE OVERHEAD...EFFECTIVELY
CAPPING THE CWA THROUGH THE AFTERNOON. TEMPERATURES WILL RISE AROUND
THE 90 DEGREE MARK IN AREAS ALONG AND EAST OF I-29...WITH READINGS
PUSHING 100 DEGREES WEST OF THE JAMES RIVER.

GIVEN THE RECENT COOL SPELL...THE ABSENCE OF ANY SIGNIFICANT HEAT
THIS SUMMER SEASON...AND THE DEGREE OF HUMIDITY THAT WILL BE PRESENT
MONDAY AFTERNOON...THE POTENTIAL IMPACTS FROM A SHORT DURATION SPELL
OF HEAT COULD BE AMPLIFIED. THUS...WILL GO AHEAD AND ISSUE A HEAT
ADVISORY A BIT EARLY AND AHEAD OF THE NEW WORK WEEK.

REGARDING CONVECTION CHANCES MONDAY NIGHT...STRONG SIGNALS CONTINUE
TO PERSIST THAT SEVERE CONVECTION WILL FORM EARLY MONDAY AFTERNOON
ACROSS NERN SD AND SOUTHERN ND AS LARGE SCALE LIFT FROM AN
APPROACHING SHORTWAVE REACHES THE REGION.  THE MAJORITY OF THIS
ACTIVITY SHOULD STAY NORTH OF THE CWA THROUGH THE AFTERNOON.  THE
CONCERNS HOWEVER WOULD BE THE POTENTIAL THAT ONCE A WELL DEFINED
COLD POOL FORMS...SEVERAL OF THESE CLUSTERS COULD BEGIN TO TAKE A
TURN TO THE SOUTH AND SOUTHEAST MONDAY EVENING.  CORFIDI VECTORS BY
03Z SHOW INCREASED POTENTIAL FOR A SHIFT SOUTHEAST WHICH COULD BRING
THE TAIL-END OF THIS ACTIVITY ACROSS THE NORTHEASTERN THIRD OF THE
CWA.  THE PRIMARY RISKS WOULD BE DAMAGING WINDS.

A COLD FRONT WILL PASS THROUGH THE CWA EARLY TUESDAY MORNING...AND
THIS WILL LEAD TO SLIGHTLY COOLER TEMPERATURES.

TEMPERATURES WILL RUN NEAR THE SEASONAL NORMAL WEDNESDAY AND
THURSDAY...BEFORE A STRONG UPPER LOW EJECTS EASTWARD FROM BRITISH
COLUMBIA.  THE GFS REMAINS A STRONG AND FURTHER SOUTH OUTLIER THAN
THE EC/GEM...AND THUS WILL NOT GO QUITE AS BULLISH WITH POPS ON
THUR/FRI...BUT CONTINUE TO ADVERTISE LOW CHC POPS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1104 PM CDT SAT JUL 19 2014

A BULK...IF NOT ALL...OF THE TAF PERIOD IS EXPECTED TO REMAIN VFR.
AGAIN WILL HAVE THE VERY REMOTE POSSIBILITY OF AN ISOLATED
THUNDERSTORM LATE NIGHT AND EARLY MORNING FOR KHON...BUT FAR BELOW
MENTIONABLE CERTAINTY. ANY ISOLATED STORMS WOULD BE CAPABLE OF A
BRIEF MVFR VISIBILITY OR CEILING. LIKELY THAT SOUTHERLY WINDS WILL
INCREASE SOMEWHAT AGAIN ON SUNDAY... WITH GUSTS NEAR OR ABOVE 25
KNOTS AT TIMES NEAR AND EAST OF INTERSTATE 29. SOME DIURNALLY
FAVORED STRATOCUMULUS DEVELOPMENT IS AGAIN LIKELY WITH MOISTURE
TRAPPED BELOW INVERSION...BUT COVERAGE SHOULD BE LESS THAN
SATURDAY. IF CEILINGS DO FORM...WOULD LIKELY BE VERY LOW END VFR.


&&

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





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