Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 161716
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1216 PM CDT SAT AUG 16 2014

.UPDATE...
ISSUED AT 1101 AM CDT SAT AUG 16 2014

VISIBILITIES CONTINUE TO IMPROVE ACROSS THE AREA AND LET THE DENSE
FOG ADVISORY EXPIRE AS SCHEDULED.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 342 AM CDT SAT AUG 16 2014

WIDESPREAD LOW STRATUS OUT THERE THIS MORNING EAST OF THE JAMES
RIVER...WITH PATCHY DENSE FOG AS WELL. AT THIS POINT COVERAGE OF
DENSE FOG SEEMS TOO LOW TO WARRANT AN ADVISORY...BUT WILL CONTINUE
TO MONITOR TRENDS. EXPECT THIS FOG AND LOW STRATUS TO SLOWLY LIFT
AFTER SUNRISE...ALTHOUGH A SCATTERED TO BROKEN STRATOCU DECK WILL
LIKELY LINGER THROUGH THE DAY OVER MOST OF THE AREA GIVEN THE
ABUNDANT LOW LEVEL MOISTURE AND WEAK FLOW. DO THINK WE WILL SEE SOME
BREAKS OF SUN BY AFTERNOON THOUGH...AND NUDGED HIGHS UP A LITTLE TO
ACCOUNT FOR THIS.

OTHER CONCERN IS CONVECTION THREAT TODAY INTO TONIGHT. THE MAIN
PRECIPITATION THREAT SHOULD BE TIED TO THE VORTICITY MAXIMUMS...AS
LITTLE IN THE WAY OF OTHER FORCING TO GET THINGS GOING. FOR MUCH OF
TODAY OUR AREA WILL BE IN BETWEEN THE TWO VORTICITY AREAS WITH ONE
NEAR THE NORTH AND SOUTH DAKOTA BORDER AND THE OTHER OVER SOUTHERN
IOWA AND NORTHERN MISSOURI. THIS MAY EVEN RESULT IN SOME MID LEVEL
SUBSIDENCE OVER THE CWA. HOWEVER AS THE NORTHERN WAVE SLOWLY PUSHES
EAST...THE SURFACE CONVERGENCE TROUGH WILL PUSH CLOSE TO THE JAMES
RIVER. THINKING WE SHOULD BE ABLE TO GET SCATTERED THUNDERSTORM
ACTIVITY ALONG THIS BOUNDARY ANYTIME FROM THIS MORNING INTO THE
AFTERNOON. PRECIPITATION CHANCES SHOULD BE PRETTY LOW EAST OF THE
JAMES RIVER GIVEN THE LACK OF FORCING MENTIONED ABOVE...AND THUS
LOWERED POPS THERE.

AS WE HEAD INTO TONIGHT...THE VORTICITY AREA PUSHES EAST CLOSER TO
OUR AREA...WITH THE SURFACE TROUGH PUSHING SLOWLY EAST AS WELL.
THUS THE BEST CHANCE OF PRECIPITATION EAST OF THE JAMES RIVER WILL
PROBABLY BE TONIGHT. STILL THINK THE BEST COVERAGE WILL STAY NORTH
OF THE CWA COINCIDENT WITH THE UPPER VORT MAX...AND THUS WILL KEEP
THE HIGHEST POPS ALONG THE HIGHWAY 14 CORRIDOR. HOWEVER MAKES SENSE
THAT WE SHOULD BE ABLE TO GET SCATTERED ACTIVITY FURTHER SOUTH ALONG
THE TROUGH AXIS...SUCH AS SHOWN BY THE HI RES ARW AND NMM. GIVEN
THE MOIST LOW LEVELS AND WEAK FLOW...WOULD SEEM LIKE FOG AND LOW
STRATUS MAY VERY WELL FORM AGAIN TONIGHT...THUS ADDED THIS INTO THE
GRIDS. WITH WEAK FLOW...STORM MOTIONS BOTH TODAY AND TONIGHT WILL BE
SLOW...WHICH WHEN COMBINED WITH A MOIST ENVIRONMENT FEATURING PWATS
UP TO 2 STANDARD DEVIATIONS ABOVE NORMAL...WILL RESULT IN A
LOCALIZED HEAVY RAIN THREAT WITH ANY STORMS. WITH RELATIVELY THIN
CAPE AND WEAK SHEAR...SEVERE WEATHER SEEMS UNLIKELY TODAY AND
TONIGHT THOUGH.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 342 AM CDT SAT AUG 16 2014

A CONTINUATION OF A RELATIVELY ACTIVE WEATHER PATTERN ALONG WITH
CLIMBING TEMPERATURES WILL BE THE PRIMARY FORECAST THEME IN THE
MEDIUM AND EXTENDED FORECAST PERIODS. BY SUNDAY...WEAK SHORTWAVE
ENERGY WILL CONTINUE TO DRIFT FROM NORTHERN SOUTH DAKOTA SOUTHEAST
INTO WESTERN MINNESOTA BY SUNDAY AFTERNOON. A FEW LIGHT SHOWERS MAY
LINGER SUNDAY MORNING...WITH AN OUTSIDE POTENTIAL FOR SCATTERED STORM
REDEVELOPMENT EAST OF INTERSTATE 29 SUNDAY AFTERNOON. SOUNDINGS SHOW
A FAIRLY UNSTABLE/UNCAPPED ENVIRONMENT SUNDAY AFTERNOON AFTER MORNING
STRATUS/FOG DISSIPATES. SO WHILE THE MAJORITY OF THE ACTIVITY SHOULD BE
EAST OF THE CWA WHERE SLIGHTLY BETTER FORCING RESIDES...WOULD NOT RULE
OUT A STRONG STORM IN THE EASTERN ZONES.

FURTHER WEST...A STRONGER SYNOPTIC WAVE WILL BEGIN TO PUSH INTO THE
NORTHERN PLAINS. SCATTERED CONVECTION WILL FORM ALONG AN EASTWARD
ADVANCING COLD FRONT AND UNDER WEAKLY SHEARED ENVIRONMENT OVER THE
WESTERN DAKOTAS LATE SUNDAY AFTERNOON. THIS ACTIVITY SHOULD CONTINUE
EASTWARD INTO THE OVERNIGHT HOURS...WITH A LOWER...BUT NOT ZERO
SEVERE WEATHER RISK POSSIBLE AS 1000-1500 J/KG MUCAPE WILL STILL
RESIDE WEST OF THE JAMES RIVER.

THIS ACTIVITY WILL LINGER INTO MONDAY OVER THE WESTERN HALF OF THE
CWA...BEFORE SLIGHTLY DRIER AIR FILTERS INTO THE REGION MONDAY NIGHT
AND TUESDAY. TEMPERATURES BOTH DAYS WILL STILL AVERAGE NEAR SEASONAL
NORMALS.

BY MID-WEEK THE LONGWAVE PATTERN WILL SLOWLY TRANSITION...AS LONGWAVE
TROUGHING DIGS INTO THE WESTERN CONUS AND RIDGING BUILDS OVER THE
EAST. GFS REMAINS MUCH MORE AMPLIFIED WITH THESE FEATURES THAN THE
ECMWF/GEM WHICH ARE MORE SUPPRESSED.  NEVERTHELESS...SEVERAL RIPPLES
OF ENERGY WILL PASS THROUGH THE REGION AS THIS PATTERN UNFOLDS
LIKELY ON WEDNESDAY AND AGAIN THURSDAY. FAR TOO MUCH UNCERTAINTY TO
MAKE WHOLESALE CHANGES TO THE ONGOING FORECAST...BUT ATTM THE
HIGHEST PRECIPITATION CHANCES ARE FOCUSED AROUND WEDNESDAY NIGHT THROUGH
THURSDAY AS A WARM FRONT LIFTS INTO THE AREA AND PROGRESSIVE
SHORTWAVE LIFTS THROUGH THE SWRN MID-LVL FLOW.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1206 PM CDT SAT AUG 16 2014

EXPECT ANY LINGERING MVFR/IFR CEILINGS TO LIFT THROUGH THE
AFTERNOON. OTHERWISE...MAY SEE SCATTERED CONVECTION DEVELOP LATER
THIS AFTERNOON AND EVENING OVER PORTIONS OF THE AREA...THOUGH WITH
LOW CONFIDENCE ON TIMING AND EXPECTED SCATTERED TO ISOLATED NATURE
OF THE CONVECTION DID NOT INCLUDE IN TAFS. WITH LIGHT WINDS AND
LOW LEVEL MOISTURE IN PLACE ACROSS THE AREA...THINK THAT AREAS OF
FOG AND LOW STRATUS WILL DEVELOP AGAIN AFTER 07Z TONIGHT.

&&

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

$$

UPDATE...JM
SHORT TERM...DUX
LONG TERM...CHENARD
AVIATION...JM





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