Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 210407
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1107 PM CDT MON OCT 20 2014

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 405 PM CDT MON OCT 20 2014

QUIET WEATHER AHEAD FOR TONIGHT AND TUESDAY WITH THE ONLY REAL
ISSUES FIRE WEATHER TUESDAY AFTERNOON. A RIDGE OF HIGH PRESSURE WILL
MOVE ACROSS THE AREA WITH SOUTHEAST WINDS DEVELOPING IN ITS WAKE.
THESE SOUTHEAST WINDS WILL BECOME A BIT BREEZY ON
TUESDAY...ESPECIALLY WEST OF INTERSTATE 29. COUPLE THIS WITH FAIRLY
LOW DEW POINTS AND A VERY HIGHS FIRE DANGER WILL EXIST AS RELATIVE
HUMIDITIES FALL INTO THE LOWER 30S. LOWS TONIGHT WILL RANGE FROM THE
UPPER 30S IN THE FAR EASTERN CWA TO THE MID 40S IN CENTRAL SD. HIGHS
ON TUESDAY WILL RANGE FROM THE MID 60S IN FAR EASTERN CWA TO THE MID
70S IN CENTRAL SD AS WARM AIR SURGES NORTHWARD BEHIND THE EXITING
HIGH PRESSURE.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 405 PM CDT MON OCT 20 2014

STRONG SOUTHERLY FLOW WILL CONTINUE TUESDAY NIGHT...BUT A SMALL
WINDOW FOR A MORE IMPACTFUL DECOUPLING WILL OCCUR FOR PARTS OF NW
IA WHERE DRIER AIR MASS IN PLACE. OVERALL...TEMPS WILL BE
MILDER...BUT MAY SEE LARGELY LEVEL TO SLOWLY FALLING READINGS
AFTER QUICKER INITIAL FALL...WITH CLOUDS INCREASING WEST AND
GRADIENT INCREASING EAST. STRONG UPPER LEVEL WAVE WILL BEGIN TO
PUSH THROUGH THE NORTHERN ROCKIES TUESDAY NIGHT...WITH QG FORCING
AND INCREASE IN MID LEVEL THETA E ADVECTION PUSHING INTO THE CWA
LATE NIGHT. INITIAL ATMOSPHERE IS QUITE DRY AS FIRST PULSE OF MID
LEVEL INSTABILITY MOVES IN LATER TUESDAY NIGHT AND EARLY THURSDAY.
LIKELY THAT START OF THE DAY WILL NOT BRING MORE THAN THICKENING
MID CLOUDS...BUT ENOUGH ELEVATED INSTABILITY THAT ISOLATED LIGHT
SHOWERS WOULD NOT BE OUT OF THE QUESTION...AND PERHAPS EVEN A
RUMBLE OR TWO OF THUNDER.

BETTER THREAT FOR PRECIPITATION WILL COME AS MAIN BELT OF DEEPER
DYNAMIC FORCING NEAR TROUGH AXIS SWINGS OUT INTO THE CWA DURING
THE AFTERNOON AND EVENING. TREND HAS BEEN FOR A LITTLE QUICKER
PROGRESSION ON ALMOST ALL SOLUTIONS. DEEPER CONVERGENCE AND
MARGINAL INSTABILITY SUGGESTS POTENTIAL FOR A DECENT COVERAGE
OF PRECIP...PERHAPS A QUARTER TO THIRD INCH IN PLACES MAINLY NEAR
AND EAST OF I 29...AS WELL AS AT LEAST AN ISOLATED THUNDER THREAT.
WITH INCREASED CLOUDS AND PRECIPITATION...TEMPS WILL BE SOMEWHAT
COOLER ON WEDNESDAY...MAINLY LOWER TO MID 60S IN THE CENTRAL
CWA...TO NEAR 70 IN THE FAR WEST.

QUICKER EXIT MEANS PRACTICALLY NO THREAT FOR RAINFALL BY
THURSDAY...AND ONLY CARRIED A 20 POP EARLY FOR THE EXTREME EAST.
SOME SIGNIFICANT DIFFERENCE IN DEALING WITH LOWER LEVEL
WIND/MOISTURE FIELDS BETWEEN MODELS...WITH NAM FAILING TO SHIFT
LOW LEVEL WINDS AT ALL TO A WESTERLY DIRECTION WITH TROUGH
PASSAGE...WHILE GFS/ECMWF/CANADIAN GIVE A DECENT PERIOD OF
WESTERLY COMPONENT AND A MUCH DRIER AIRMASS. RAW MIXED LAYER DEW
POINT TEMPS ARE AS MUCH AS 15 TO 20 DEGREES LOWER...AND WOULD SEEM
TO BE A BIT PREFERRED IN THIS CASE...ESPECIALLY WEST OF I 29.
A BIT WARMER AGAIN AS A RESULT WITH MORE SUNSHINE...MID 60S EAST TO
LOWER 70S WEST.

FOR THE EXTENDED RANGE...LARGELY A QUIET TIME...WITH A WEAK COLD
FRONT EXPECTED TO PASS IN THE FRIDAY NIGHT WINDOW. FRIDAY BECOMES
A PRE FRONTAL DAY WITH A DECENT POTENTIAL FOR WESTERLY MIXED
COMPONENT TO WIND. HAVE PUSHED TEMPS SEVERAL DEGREES UPWARD ON
FRIDAY...WITH LOWER TO MID 70S SHARED BY ALL. WHILE SATURDAY WILL
CONTINUE DRY...HIGH PRESSURE RIDGE SETTLING IN FROM THE NORTH WILL
COOL THINGS OFF JUST A TOUCH. LIGHT WINDS AND DRY AIR TO
START...ESPECIALLY FOR EASTERN CWA...WILL FAVOR QUITE LARGE
DIURNAL RANGES...AND HAVE STRETCHED OUT A BIT OVER INITIALIZATION
VALUES. POTENTIAL BY THE END OF THE PERIOD THAT SOME IMPACT OF THE
HAWAIIAN TROPICAL SYSTEM WILL QUICKLY MOVE IN WESTERN FLOW INTO
THE VICINITY. STRUCTURE OF TROUGHING IS UP IN THE AIR AS IT MOVES
THROUGH THE REGION AROUND SUNDAY NIGHT/MONDAY...SO IDEA OF LOWER
PRECIPITATION CHANCES FITS AT THIS TIME. TEMPS COOLING BACK BELOW
NORMAL A BIT ON MONDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1106 PM CDT MON OCT 20 2014

VFR WILL PREVAIL THROUGH TUESDAY AND TUESDAY EVENING WITH A COUPLE
OF CONCERNS. FIRST OF ALL...SOUTHERLY WINDS WILL LIKELY BE GUSTING
TO 25 KNOTS OR A LITTLE STRONG ALONG AND WEST OF THE JAMES RIVER
VALLEY TUESDAY AFTERNOON. CATEGORY WISE...KSUX IS ALREADY
EXHIBITING A VERY SMALL SURFACE DEW POINT DEPRESSION. THEREFORE
WOULD NOT BE SURPRISED IF SHALLOW FOG DEVELOPS FOR THAT TAF SITE.
DID NOT WANT TO INCLUDE TOO MUCH OF THIS POSSIBILITY YET...AND
ONLY MENTIONED A TEMPO MVFR AS A HEADS UP THAT SHALLOW RIVER FOG
COULD DEVELOP. MUCH LATER...THE NAM CONTINUES TO SHOW SOME SHALLOW
MOISTURE STREAMING UP LATE TUESDAY EVENING JUST BEFORE THE END OF
THE TAF PERIOD. IT APPEARS TO BE BASED BELOW THE BOUNDARY LAYER
AND WILL LIKELY NOT TRANSLATE INTO CLOUDS.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&

$$

SHORT TERM...08
LONG TERM...CHAPMAN
AVIATION...MJ



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