Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 021118
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
618 AM CDT SAT MAY 2 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 404 AM CDT SAT MAY 2 2015

SHORT TERM CONCERNS ARE FOCUSED ON CHANCES OF CONVECTION TODAY AND
TONIGHT...ALONG WITH VERY WARM TEMPERATURES AND FIRE WEATHER
CONCERNS. EARLY THIS MORNING...WATCHING WEAK SHORTWAVE ENERGY CROSS
SOUTH CENTRAL SOUTH DAKOTA. THIS SHORTWAVE IS DRAWING ENOUGH
MOISTURE NORTHWARD TO RESULT IN SCATTERED CONVECTION OVER NEBRASKA
ALONG THE EDGE OF NORTHEASTWARD ADVECTING THETA-E GRADIENT. SHORT
TERM MESOSCALE MODELS HAVE CAPTURED THIS TREND WELL...SHOWING THE
STRONGEST THETA-E ADVECTION LIFTING FROM YANKTON TO SIOUX CITY TO
OMAHA AFTER DAYBREAK. AS THIS WAVE CONTINUES TO MOVE TOWARD
NORTHWEST IOWA THIS AFTERNOON...A MODESTLY UNSTABLE AIRMASS WILL
DEVELOP OVER NW IOWA. WOULD NOT BE SURPRISED TO SEE A BIT OF
ADDITIONAL CONVECTION FORM...BUT THE TIMING OF THE WAVE IS NOT
CONDUCIVE TO MORE SUBSTANTIAL DEVELOPMENT IN THE LOCAL AREA...BUT
INSTEAD FURTHER SOUTHEAST INTO IOWA.

TEMPERATURES TODAY WILL SOAR WELL ABOVE NORMAL...WITH MIXING TO
800MB SUGGESTING FAIRLY WIDESPREAD 80S ARE LIKELY TODAY.  IN
FACT...AREAS WEST OF THE JAMES RIVER...AND ESPECIALLY WEST OF THE
MISSOURI RIVER COULD SPIKE NEAR OR AT 90.

TO THE WEST OF THE MISSOURI RIVER...WILL KEEP AN EYE ON A WEAK
SURFACE TROUGH EXPECTED TO FORM OVER WEST CENTRAL SOUTH DAKOTA LATER
THIS AFTERNOON.  GUIDANCE TRIES TO BUILD POCKETS OF UPWARDS OF 1000
J/KG MLCAPE...HOWEVER A SUBSTANTIAL CAP WILL PERSIST AS 700 MB
TEMPERATURE WARM BEHIND THE DEPARTING SHORTWAVE TROUGH. IT IS
POSSIBLE THE CAP COULD BE BROKEN THROUGH LATE IN THE AFTERNOON WELL
WEST OF THE AREA...OWING TO AN ISOLATED STORM OR TWO...BUT GIVEN THE
ANTICIPATED DIURNAL NATURE TO THIS ACTIVITY AND SHALLOW NATURE OF
THE MOISTURE ASSOCIATED WITH IT...FEEL IT WOULD STRUGGLE TO MOVE
INTO THE WESTERN ZONES. THE MAIN THREAT IN THIS ACTIVITY WOULD BE
WINDS.  THERE COULD BE A FEW DECAYING SHOWERS MOVE ACROSS THE CWA
OVERNIGHT...BUT FOR NOW WILL CONTINUE WITH ONLY SLIGHT CHANCE WORDING.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 404 AM CDT SAT MAY 2 2015

START OF THE DAY SUNDAY SHOULD BE GREETED WITH MINIMAL FANFARE. MAY
BE PROGRESSION OF A FEW HIGHER BASED SHOWERS/THUNDERSTORMS RIDING
ALONG THE NORTHEASTERN BORDER OF THE CWA ALONG THE EDGE OF THE
WARMER PLUME ALOFT...BUT LOW ENOUGH THREAT TO KEEP AT MINIMAL CHANCE
WITH THE LOW LEVEL JET WELL VEERED ALREADY BY THIS TIME AND
CONVERGENCE MEAGER ACROSS THE AREA.  MORE LIKELY WITH THE DRIER AIR
INTERVENING BETWEEN LIMITED NEAR SURFACE INCREASE AND MID LEVELS TO
MAKE FOR SOME FAIRLY EXTENSIVE VIRGA.  SURFACE FRONTAL BOUNDARY
SHOULD BE JUST ENTERING THE FAR NORTHWEST CWA BY EARLY MORNING...
AND THIS BOUNDARY WILL MAKE A STEADY SOUTHEASTWARD PUSH THROUGH THE
DAY...MOVING TO A TRACY...SIOUX FALLS...YANKTON LINE BY VERY EARLY
AFTERNOON. ENOUGH OF A WARM LAYER ALOFT TO LIMIT ANY SURFACE OR NEAR
SURFACE BASED INSTABILITY FROM BEING TAPPED UNTIL AT LEAST MID TO
LATE AFTERNOON...AT WHICH POINT WILL BEGIN TO FEEL THE TAIL OF
FORCING FROM WAVE MOVING ALONG THE INTERNATIONAL BORDER AND START TO
GET SCATTERED DEVELOPMENT IN CONVERGENCE ZONE ALONG BOUNDARY.  FOR
THE TIME...SHEAR AND INSTABILITY PARAMETERS ARE INDICATIVE OF A
MARGINAL SET UP FOR SEVERE STORMS...WITH MLCAPE AROUND 1500 J/KG AT
MOST... AND A DEEP LAYER BULK SHEAR OF 25 TO 35 KNOTS. PRESENCE OF
DRY LAYER WOULD SUGGEST SOME THREAT FOR DAMAGING WIND GUSTS...AND
HIGHER WEIGHTED INSTABILITY PROFILE FOR LARGE HAIL THREAT AS WELL.
POTENTIAL THAT SOME LOCALLY ENHANCED SHEAR NEAR BOUNDARY COULD
SUPPORT A BRIEF PERIOD FOR SUPERCELLULAR BEHAVIOR...BUT MUCH MORE
LIKELY TO SEE MULTICELL ORGANIZATION...AGAIN SUPPORTIVE OF A
MARGINAL TYPE SEVERE WEATHER EVENT...AS PER AREA HIGHLIGHTED IN SPC
DAY 2 OUTLOOK...SOUTHEAST OF A LINE FROM WINDOM TO VERMILLION FROM
MID AFTERNOON THROUGH EARLY EVENING. CONVECTIVE LINE SHOULD SHIFT
SOUTHWARD WITH FAIRLY GOOD EFFICIENCY WITH PROGRESSION OF LOW LEVEL
CONVERGENCE AND SUPPORT FROM EXTENSIVE COLD POOL DEVELOPMENT. MOST
LINGERING SHOWERS AND STORMS SHOULD BE OUT OF THE CWA BY MID TO LATE
EVENING.

AS FAR AS TEMPERATURES GO...WILL AGAIN BE A TASTE OF LATE
SPRING/EARLY SUMMER READINGS ON SUNDAY...AS WARM OFF SURFACE TEMPS
AHEAD OF THE FRONT SHOULD BE ABLE TO MIX OUT...WITH PREFRONTAL
WARMING AND SOME SUNSHINE LEADING TO WIDESPREAD LOWER TO MID
80S...WHILE EVEN BEHIND THE BOUNDARY...MID TO UPPER 70S SHOULD
PREVAIL.

ON MONDAY...WILL SEE JET ENTRANCE REGION SLIDING ACROSS THE AREA...
AND COHERENT AREA OF DIV Q. DISAGREEMENT BETWEEN MODELS ON IMPACT OF
SYSTEM...WITH ECMWF VERY FORCEFUL WITH LOW LEVEL DRYING TO THE POINT
WHERE BOUNDARY FAR ENOUGH SOUTH TO SHOW MINIMAL REACTION TO PASSAGE
OF WEAK DIV Q. GFS HOLDS BOUNDARY IN A MORE NORTHWARD LOCATION...AND
WOULD SEEM TO BE LESS IN FAVOR GIVEN NATURE OF BOUNDARY AND PASSAGE
OF JET ENTRANCE REGION. CANNOT FULLY DISCOUNT THAT MORE ORGANIZED
CONVECTION TO THE SOUTH WILL BULGE A BIT NORTHWARD DURING THE
AFTERNOON AND EVENING...BUT OVERALL EXPECT THAT MORE ORGANIZED
NORTHWARD PUSH TO PRECIPITATION WILL START BY LATER MONDAY NIGHT AND
TUESDAY WITH HEIGHTS BUILDING BACK AND DEEPER SOUTHERLY FLOW
BECOMING ESTABLISHED AHEAD OF WAVE PUSHING INTO THE SOUTHERN TO
CENTRAL HIGH PLAINS. PROBABLY NOT A GREAT DEAL OF THUNDER WITH
MAINLY NEUTRAL THERMAL PROFILES INTO MONDAY NIGHT...BUT DID KEEP A
BIT HIGHER MENTION OF THUNDER AROUND NORTHEASTERN NEBRASKA IN THE
AFTERNOON AND EVENING.

TUESDAY APPEARS TO BE DAY WHEN INITIAL ISENTROPIC LIFT WORKS
NORTHWARD ACROSS THE AREA...AND SHOULD BE ACCOMPANIED BY A BAND OF
SHOWERS AND THUNDERSTORMS. SIGNS POINT TOWARD A GENERAL DECREASE IN
PRECIP POTENTIAL TUESDAY NIGHT WITH MAIN LIFT/CONVERGENCE PUSHING
NORTH OF THE CWA...BUT PERHAPS WRAPPING BACK INTO THE WESTERN CWA BY
LATER IN THE NIGHT AS HIGH PLAINS SYSTEM LIFTS NORTH AND NORTHEAST.
OVERALL...SHEAR AND INSTABILITY IS FAIRLY WEAK WITH THE
UNIDIRECTIONAL WIND PROFILE AND INCREASED DEEPER MOISTURE. LIKELY TO
FIND A FEW BANDS OF SHOWERS AND THUNDER WRAPPING NORTHWARD WEDNESDAY
AND WEDNESDAY NIGHT. IF TIMING OF BANDS CAN GET IN PHASE A BIT MORE
WITH DIURNAL DESTABILIZATION...MAY HAVE A LITTLE BETTER THREAT FOR
SEVERE WEATHER. AS OF THE CURRENT MODEL SET...MAIN DYNAMIC LIFT IS A
BIT MORE CENTERED ON THE OVERNIGHT PERIOD.

THURSDAY PERHAPS A BIT MORE INTERESTING WITH LOW LEVEL BOUNDARY
LALLYGAGGING EASTWARD THROUGH THE CWA...CONDITIONS ALOFT DRYING OUT
A BIT MORE WITH AN INCREASE IN DEEPER SHEAR AND POTENTIAL
INSTABILITY...AND COULD HAVE TO WATCH FOR A SLIGHTLY BETTER SEVERE
POTENTIAL.

BY THE END OF THE WEEK...VERY LITTLE AGREEMENT IN THE DETAILS OF
LARGER SCALE...AND WITH A 10 TO 15 DEGREE C RANGE IN LOWER LEVEL
TEMPS...HAVE ELECTED TO STICK FAIRLY CLOSE TO THE INITIALIZATION
BLEND VALUES...RATHER THAN OUTGUESS THE DIVISIVE MODEL SOLUTIONS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 615 AM CDT SAT MAY 2 2015

A WEAK WAVE MOVING THROUGH THE REGION WILL BRING A FEW SHOWERS TO
THE KSUX TERMINAL THIS MORNING...OTHERWISE VFR CONDITIONS ARE
ANTICIPATED. WINDS WILL REMAIN SOUTHERLY THROUGH THE DAY...WITH A
FEW SCATTERED CU FORMING THIS AFTERNOON.

TONIGHT...VFR CONDITIONS AGAIN LIKELY. WINDS WILL REMAIN SOUTHERLY
AHEAD OF A FRONT THAT WILL APPROACH THE AREA TOWARDS DAYBREAK
SUNDAY.

&&

.FIRE WEATHER...
ISSUED AT 404 AM CDT SAT MAY 2 2015

A VERY WARM DAY IS EXPECTED WITH SOUTHERLY WINDS PREVAILING.
RELATIVE HUMIDITY VALUES MAY DROP AS LOW AS 20
PERCENT...ESPECIALLY IN AREAS NORTH OF INTERSTATE 90.
HOWEVER...WINDS REMAIN THE BIGGEST CHALLENGE TODAY. CURRENT MIXING
SUGGESTS THAT WE WOULD STRUGGLE TO SEE SUSTAINED 10 TO 15 KNOT
WINDS...WITH ONLY THE OCCASIONAL GUST TO 20 KNOTS. THE FIRE DANGER
RISK WILL BE HIGH TO VERY HIGH...BUT MAY STAY JUST BELOW CRITICAL
LEVELS NEEDED FOR A RFW. CONDITIONS WILL NEED TO BE MONITORED
TODAY.

ON SUNDAY...AREAS POSTFRONTAL IN SOUTHEAST SOUTH DAKOTA WILL FIND
AFTERNOON RELATIVE HUMIDITY DROPPING TO 25 TO 35 PERCENT...BUT
MORE IMPACTFULLY A WIND INCREASE TO A GUSTY NORTHERLY 20 TO 30
MPH. THIS WILL AGAIN DRIVE FIRE DANGER INTO THE VERY HIGH RANGE
WEST OF A BROOKINGS TO TYNDALL LINE.

&&

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

$$

SHORT TERM...DUX
LONG TERM...CHAPMAN
AVIATION...DUX
FIRE WEATHER...CHAPMAN/DUX


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