Area Forecast Discussion
Issued by NWS Sioux Falls, SD

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
000
FXUS63 KFSD 222125
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
425 PM CDT FRI APR 22 2016

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 425 PM CDT FRI APR 22 2016

SURFACE RIDGE AXIS OVER SOUTHWEST MN/NORTHWEST IOWA AT MID AFTERNOON
WILL CONTINUE TO NUDGE EAST TONIGHT...ALLOWING FOR AN INCREASE IN
SOUTHEAST TO SOUTH WINDS ACROSS THE AREA OVERNIGHT AND THROUGH THE
DAY ON SATURDAY. THIS WILL BE THE PRIMARY WEATHER FEATURE FOR THE
NEXT 24 HOURS...AS PATTERN ALOFT TRANSITIONS FROM DECENT MID LEVEL
RIDGE TO SOUTHWEST FLOW AS THE RIDGE SHIFTS EAST AND ANOTHER TROUGH
STRENGTHENS OVER THE NORTHERN/CENTRAL ROCKIES.

WITH SURFACE RIDGE STILL NEAR THE EASTERN EDGE OF THE FORECAST AREA
THIS EVENING...WILL LIKELY SEE TEMPERATURES DROP BACK INTO THE 40S
FAIRLY QUICKLY...BUT THEN LEVEL OFF AS THE RIDGE SHIFTS FARTHER EAST
AND SOUTHERLY FLOW BEGINS TO PICK UP. OVERALL LOOKING FOR LOWS FROM
THE MID 40S ALONG/EAST OF I-29 TO NEAR 50 IN SOUTH CENTRAL SD.

WILL SEE AN INCREASE IN LOW LEVEL MOISTURE SATURDAY...BUT REMAINS
FAIRLY SHALLOW THROUGH THE DAY SO EXPECT MIXING TO TREND DEW POINTS
TOWARD THE LOWER END OF AVAILABLE GUIDANCE DURING THE AFTERNOON. GFS
TRYING TO PRODUCE SOME LIGHT QPF ACROSS OUR MN/IA COUNTIES SATURDAY
AFTERNOON AS A SUBTLE WAVE SLIDES NORTHEAST...BUT FORECAST SOUNDINGS
ARE NOT VERY SUPPORTIVE OF PRECIP THREAT WITH LIMITED MOISTURE AND
LITTLE IF ANY INSTABILITY...SO WILL LEAVE FORECAST DRY. DESPITE THE
RECENT RAINS...SHOULD BE ABLE TO MIX WELL IN THE STRONG SOUTHERLY
FLOW...SO CONTINUE TO FAVOR WARMER END OF GUIDANCE TEMPERATURES WITH
HIGHS SATURDAY FROM THE MID 70S IN SOUTHWEST MN/IOWA GREAT LAKES TO
LOWER 80S WEST OF THE JAMES VALLEY.


.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 425 PM CDT FRI APR 22 2016

A PERIODICALLY ACTIVE AND CHALLENGING PATTERN ON THE WAY THROUGH
NEXT WEEK...WITH A PAIR OF DEEP CLOSED UPPER WAVES IMPACTING WEATHER
AROUND SUNDAY AND WEDNESDAY.

THE INITIAL UPPER WAVE WILL PUSH INTO THE WESTERN PLAINS ON SATURDAY
NIGHT...MOVING A BIT MORE SLOWLY AND COHERENTLY ACROSS WYOMING AND
TOWARD WESTERN SOUTH DAKOTA BY DAYBREAK SUNDAY THAN PREVIOUS MODEL
RUNS. LIKELY THAT DRYLINE/TROUGH IN FAR WESTERN PLAINS WILL FOCUS
MUCH OF THE INITIAL DEVELOPMENT OF STORMS SATURDAY EVENING...BUT
THIS DEVELOPMENT WILL BE INDUCED NORTH/EAST TOWARD SOUTH CENTRAL
SOUTH DAKOTA AFTER MIDNIGHT BY APPROACH OF A FIRST LOBE WRAPPING
NORTHWARD THROUGH THE WESTERN PLAINS. FURTHER EAST... MOISTURE
PROFILES ARE GENERALLY PRETTY SPARSE...WITH RANDOM MODEL SOLUTIONS
INDICATING A BIT MORE MOISTURE IN 800-650 HPA LAYER AND SOME
TENDENCY FOR REDUCING ELEVATED CAP LATER IN THE NIGHT. MID-LEVEL
LAPSE RATES OF 8-9C/KM ARE IN PLACE...AND ONLY IN RARE OCCURRENCES
WOULD YOU NOT EXPECT TO SEE SOME DEGREE OF ELEVATED CONVECTION...
EVEN IN CASES SUCH AS THIS WITH FAIRLY MARGINAL MOISTURE. BEST
THREAT FOR ISOLATED TYPE SHOWERS/THUNDER SHOULD SPREAD TOWARD THE
MISSOURI VALLEY AFTER 06Z...AND GRADUALLY NORTH/EAST THROUGH 12Z
WITH LEADING MID LEVEL VORT LOBE APPROACHING RETREATING RIDGE AXIS.

CLOUDS AND A FEW LINGERING SHOWERS WILL BE RETREATING NORTHEAST...
BUT SOUTHWESTERLY TRAJECTORY OF A BIT MORE MOISTURE ALOFT WILL
LINGER ACROSS NORTHWEST IOWA INTO AT LEAST MIDDAY. AS UPPER LOW AND
SURFACE WAVE PULL EASTWARD...FAIRLY SHARP DRY LINE LIKELY TO DEVELOP
ACROSS CENTRAL AND INTO EASTERN NEBRASKA DURING SUNDAY...AND HOW FAR
EAST THE DISCONTINUITY PROGRESSES AND HOW MUCH THE TRAJECTORY OF MID
LEVEL MOISTURE/INSTABILITY WILL IMPACT THE POTENTIAL DEVELOPMENT.
TEMPS WILL MIX OUT NICELY NEAR AND WEST OF THE DRYLINE...WITH SOME
NEAR 80 READINGS POSSIBLE IN THE LOWER JAMES TO MID MISSOURI VALLEY.
MODELS VARY WITH PROGRESSION OF UPPER WAVE...AND THUS HOW QUICKLY
EASTWARD FEATURES SPREAD. WITH SURFACE DEWPOINT LIKELY ONLY IN THE
MID 50S...SURFACE REMAINS QUITE CAPPED WELL INTO THE AFTERNOON...
WITH POTENTIAL INSTABILITY REACHING PERHAPS 1500 J/KG IN THE LOWER
MISSOURI VALLEY EASTWARD THROUGH NORTHWEST IOWA. SHEAR IS FAIRLY
UNIDIRECTIONAL IN THIS AREA...BUT STRONG ENOUGH WITH GOOD INCREASE
IN MID AND UPPER WINDS SOUTHEAST OF UPPER LOW. PARAMETERS SUGGEST A
MENTIONABLE SEVERE THREAT...WITH MAINLY HAIL/WIND THREAT WITH
SOMEWHAT A MINIMAL SHEAR IN LOWEST KM...AND LACK OF DEEPER
CONVERGENCE ALONG THE DRY LINE FEATURE. DIRECTIONAL SHEAR ACTUALLY
IS STRONGER ACROSS THE NORTHERN CWA CLOSER TO WARM FRONT...BUT MIXED
LAYER INSTABILITY IS SLIGHTLY LOWER AS WELL TOWARD THE HIGHWAY 14
CORRIDOR COMPARED TO THAT ACROSS NORTHWEST IOWA. AT THIS TIME...MOST
CONCERN FOR A FEW SEVERE STORMS IS WITH THE BOUNDARY ACROSS PARTS OF
NORTHEAST NEBRASKA/NORTHWEST IOWA...BUT STILL MUST KEEP A WATCHFUL
EYE OVER THE NORTHERN CWA BACK TOWARD SURFACE LOW IN CENTRAL SD TO
MID JAMES VALLEY.

INITIAL CONVECTION SHIFTS EASTWARD IN THE EVENING...AND AREAS TO THE
WEST BACK TOWARD I 29 COULD SEE A FAIRLY QUIET PERIOD...UNTIL
PRECIPITATION WRAPS SOUTHWARD AS WAVE PULLS EASTWARD. SEVERE THREAT
WOULD CONTINUE THROUGH THE EARLY EVENING...THEN TRANSITION TO MAINLY
SHOWERS WITH ISOLATED THUNDER AHEAD OF FEATURE SW MN/NW IA. IN THE
WAKE OF SYSTEM...LIKELY TO FIND A CONSIDERABLE STRATUS FIELD...AND
IMPACT WOULD BE FOR TEMPS TO STRUGGLE WITH A NORTH/NORTHEAST LOW
LEVEL FLOW. PRECIPITATION WOULD WIND DOWN FAIRLY QUICKLY AND FAVOR
MAINLY NORTH OF I 90 EARLY IN THE DAY...AS DEEPER DYNAMICS FADE WITH
EASTWARD SHEARING WAVE. STACKED TOWARD LOWER LEVEL BAROCLINICITY AND
DRYING OUT THE MID LEVELS SUGGEST PERHAPS A BIT OF DRIZZLE THREAT
LINGERING THROUGH THE DAY. WITH CLOUDS AND NORTHERLY FLOW...HIGHS
WILL BE 15 TO 20 DEGREES COOLER FOR MOST AND WEIGHTED MAINLY EARLIER
IN THE DAY...LOWER 50S ALONG HIGHWAY 14...PERHAPS ABLE TO SQUEEZE
OUT LOWER 60S IN NORTHWEST IOWA.

SHORT WAVE RIDGING MONDAY NIGHT IN UPPER LEVELS...WHILE A SHALLOW
COOL NORTHERLY TO EASTERLY FLOW REGIME TAKES HOLD AT LOWER LEVELS.
GRADUALLY...THE NEXT DEEP UPPER LOW IN THIS ACTIVE PATTERN WILL
START TO TREK OUT OF THE SOUTHWEST AND INTO THE ROCKIES. STRONG WARM
ADVECTION ALOFT WILL AGAIN DEVELOP THROUGH THE DAY...WITH ELEVATED
INSTABILITY BRINGING A SCATTERED SHOWERS AND PERHAPS SOME THUNDER
WITH ELEVATED INSTABILITY TOWARD THE MISSOURI VALLEY BY LATE TUESDAY.

FOR THIS SYSTEM MIDWEEK...QUITE A BIT OF DIVERSITY IN TRACK OF UPPER
WAVE AT THIS POINT...WHICH WOULD GO FROM KEEPING THE WARMER LOW
LEVEL AIR FULLY BOTTLED UP ALONG I 80...TO AN ECMWF-LIKE SOLUTION
WHICH TAKES A MUCH MORE WRAPPED LOW FURTHER NORTH BY WEDNESDAY
EVENING. HARD TO GET HUNG UP ON DETAILS AT THIS POINT...BUT
GENERALLY WILL ADVERTISE STRONGLY INCREASING SHOWER/THUNDERSTORM
ACTIVITY FOR TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. COULD GET SOME
FAIRLY DECENT RAINS AND EVEN SOME SEVERE WEATHER OUT OF THE SYSTEM
AS WELL...BUT LOCATION IS YET TO BE DETERMINED.

NOT MANY CHANGES MADE TO FORECAST BEYOND SYSTEM ON THURSDAY AND
FRIDAY...BUT MAY SEE IMPACT OF NEXT UPPER WAVE BY LATE FRIDAY IN THE
FORM OF A FEW SHOWERS OR ELEVATED STORMS MAINLY JAMES/MISSOURI
VALLEY LOCATIONS. TEMPS REMAINING SEASONABLY COOL LATE WEEK...MAINLY
HIGHS 50S AND LOWS UPPER 30S TO AROUND 40.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1212 PM CDT FRI APR 22 2016

MVFR CEILINGS LINGERING ACROSS PARTS OF NORTHWEST IOWA AND SOUTHWEST
MINNESOTA HAVE BEEN DECREASING WITH APPROACHING SURFACE RIDGE...WITH
VFR CONDITIONS EXPECTED TO DOMINATE ALONG/WEST OF HIGHWAY 71 BY 20Z.

LIGHT VARIABLE WINDS GRADUALLY BECOMING SOUTHEAST TO SOUTH AS THE
RIDGE AXIS SHIFTS EAST. INCREASING WINDS ALOFT OVER CENTRAL SD COULD
PRODUCE A PERIOD OF LOW LEVEL WIND SHEAR LATE TONIGHT/EARLY SATURDAY
IN AREAS ALONG/WEST OF THE JAMES RIVER VALLEY...THEN SOUTHERLY GUSTS
EXPECTED TO INCREASE TO NEAR 25KT AS STRONGER WINDS BEGIN TO MIX
DOWN AFTER 14Z SATURDAY.

&&

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

$$

SHORT TERM...JH
LONG TERM...CHAPMAN
AVIATION...JH



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.