Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 190356
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1056 PM CDT SAT APR 18 2015

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 253 PM CDT SAT APR 18 2015

CORRIDOR OF MODERATE ISENTROPIC LIFT CONTINUES TO LIFT NORTHWARD
THROUGH THE AREA...PRODUCING A NARROW CORRIDOR OF SLOW
MOVING...RAINFALL. SEVERAL WEAK CONVECTIVE DRIVEN SHORTWAVES ALSO
APPEAR TO BE TIED TO THIS CONVECTION...WITH THE STRONGEST WAVE NOW
BEGINNING TO LIFT NORTHEAST FROM NW MISSOURI. THIS SOUTHERN WAVE
SEEMS TO BE DRIVING A BIT MORE CONVECTION OVER IA/MO THAT IN
RETURN COULD LEAD TO LOWER QPF IN THE LOCAL AREA. AT THE
SURFACE...BROAD WARM SECTOR BEGINNING ACROSS WESTERN NEBRASKA AND
EXTREME SW SOUTH DAKOTA. FAIRLY COOL AND STABLE AIR REMAINS
SETTLED OVER THE EASTERN HALF OF SD/NE.

INTO THE AFTERNOON/EVENING...HIGH-RES MODELS DOING A GOOD JOB
HANDLING THIS EVENT SO FAR SUGGESTING THAT THE LINEAR BAND OF RAIN
CONTINUES TO LIFT NORTHEAST AND TOWARDS THE NERN EDGE OF THE CWA BY
00Z. SHORTWAVE ENERGY OVER NW MO SHOULD FORCE ANY PRECIP ASSOCIATED
WITH IT TO THE EAST OF THE AREA. HOWEVER...RAINFALL INTENSITIES
CONTINUE TO DROP OFF...SO HAVE LOWERED QPF FOR THE EVENT.
IN GENERAL THE HIGHEST POTENTIAL FOR ANY REDEVELOPMENT WOULD BE
FOUND IN THE WARM SECTOR SOUTHWEST OF THE CWA. THUS...WILL
CONTINUE TO LOWER POPS FOR THIS EVENING.

OVERNIGHT...LOWER POPS DURING THE EARLY OVERNIGHT HOURS BEGIN TO
INCREASE SLIGHTLY LATE THIS EVENING AND TOWARDS MIDNIGHT AHEAD OF
850MB TROUGH AXIS. MODELS INDICATING MUCAPE UPWARDS OF 500-800
J/KG ADVECTING INTO THE AREAS SOUTH OF I-90 LATE TONIGHT. THIN
NATURE OF CAPE AND WEAK SHEAR WOULD NOT SUPPORT SEVERE
WEATHER...BUT A FEW SCATTERED STORMS OR SHOWERS COULD BE
POSSIBLE. WITH THE PASSAGE OF THE SFC TROUGH...WOULD NOT RULE OUT
A BIT OF DRIZZLE.

SUNDAY...LOW-LVL AND SURFACE TROUGHS WILL SWING QUICKLY THROUGH THE
AREA ON SUNDAY...WITH STRONG ISENTROPIC DOWNGLIDE ENDING ANY
PRECIPITATION CHANCES QUICKLY.  CONSIDERABLE CLOUD COVER WILL HANG
AROUND THROUGH THE DAY. IT WILL ALSO BE QUITE WINDY WITH DOWNWARD
MIXING PULLING WIND GUSTS AOA 30 KNOTS IN THE LATE MORNING AND
AFTERNOON.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 253 PM CDT SAT APR 18 2015

COOL PATTERN FOR THE UPCOMING WEEK AS NORTHWEST FLOW REMAINS MUCH OF
THE WEEK AS HUDSON BAY LOW REMAINS THROUGH MUCH OF THE WEEK. BREEZY
NORTHWEST FLOW OVERNIGHT SUNDAY NIGHT WILL KEEP TEMPERATURES FROM
RADIATING TOO MUCH SUNDAY NIGHT.  WINDS WILL INCREASE DURING THE DAY
MONDAY AS MOMENTUM FROM ALOFT IS BROUGHT DOWN TO THE SURFACE.  WITH
DRY AIR MIXING DOWN FROM ALOFT...NEAR RED FLAG CONDITIONS RETURN TO
THE REGION ESPECIALLY ACROSS THE WEST.  WILL LIKELY NEED TO CONSIDER
FIRE WEATHER WATCH FOR MONDAY AND TUESDAY FOR PORTIONS OF THE
REGION.  ACROSS THE EAST ON MONDAY...COULD SEE SOME DIURNALLY DRIVEN
INSTABILITY SHOWERS...THOUGH MODELS HAVE REDUCED INSTABILITY ALOFT
SLIGHTLY.

MONDAY NIGHT AND TUESDAY NIGHT...TEMPERATURES GET COOL ENOUGH BOTH
NIGHTS COULD SEE SOME FRONT/FREEZE CONCERNS ACROSS THE AREA. WITH
DRY DEW POINTS...AM NOT SURE HOW MUCH FROST THERE WILL BE...SO LEFT
MENTION OUT OF THE FORECAST FOR NOW.

WINDS ARE LIGHTER ON WEDNESDAY...THOUGH THE GFS CONTINUES TO SUGGEST
A SECONDARY DROPPING SOUTH ACROSS THE AREA DURING THE AFTERNOON
HOURS.  HARD TO SE...BUT THE ECMWF HINTS AT SOMETHING SIMILAR THOUGH
THE COLD AIR IS MUCH WEAKER BEHIND THE FRONT.  AS SUCH....KEPT
INCREASING WINDS IN THE CONS ALL FOR THE LATER HALF OF WEDNESDAY.
CERTAINLY DOESN/T LOOK LIKE ENOUGH MOISTURE IS AVAILABLE FOR
SHOWERS.

DRY CONDITIONS CONTINUE INTO LATE IN THE WEEK.  THOUGH THE WINDS ARE
ARE EXPECTED TO FALL INTO THE 10-20 RANGE...RHS WILL STILL BE QUITE
LOW KEEPING THE FIRE DANGER ELEVATED THROUGH MUCH OF THE WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1048 PM CDT SAT APR 18 2015

CONFIDENCE IS FAIRLY LOW FOR THE 06Z TAFS IN THE NEAR TERM WITH A
TROUBLESOME SCENARIO PRIMARILY WITH THE CEILINGS. IFR CONDITIONS
COULD BE PRESENT IN OUR FAR WEST AND NORTHWEST ZONES FOR THE NEXT
FEW HOURS AS LIGHT RAIN OR DRIZZLE LOWERS VISIBILITIES. THIS WAS
ACCOUNTED FOR IN THE KHON TAF SITE...HOWEVER IT NEEDS TO BE NOTED
THAT THESE CONDITIONS MAY NOT PREVAIL ALL THE TIME...THUS THE
TEMPO GROUP. THE WIND SHIFT TO THE NORTHWEST WILL THEN MAKE IT TO
KHON AROUND 08Z WHICH SHOULD BEGIN TO IMPROVE THEIR VISIBILITY AND
ALSO GIVE A SLOW RISE TO THE CEILINGS...LEADING INTO A WINDY DAY
ON SUNDAY WITH VFR CONDITIONS BY LATE MORNING.

SPOTTY IFR CEILINGS ALSO CURRENTLY EXIST AROUND KFSD BUT UPSTREAM
OBSERVATIONS IN NORTHWEST IA ARE PRIMARILY MVFR TO VFR. SO THIS IS
QUITE A CHALLENGE. DECIDED TO RAISE THE IFR CEILINGS TO MVFR BY
LATE TONIGHT JUST AHEAD OF THE WIND SHIFT AS LOW LEVEL WINDS VEER
MORE TO A SOUTH TO SOUTHWEST DIRECTION WHERE CEILINGS ARE HIGHER.
SIMILAR TO KHON...AFTER THE WIND SHIFT HITS KFSD THE CEILINGS
SHOULD BEGIN A SLOW RISE TOWARD VFR. KSUX IS CURRENTLY VFR AS A
DRY SLOT HAS IMPACTED THEM OOZING UP FROM EASTERN NEBRASKA. IT
COULD BE POSSIBLE THAT SOME LOWERED CEILINGS IN THE MVFR RANGE
COULD AFFECT KSUX JUST BEHIND THE WIND SHIFT.

&&

.FIRE WEATHER...
ISSUED AT 355 AM CDT SAT APR 18 2015

RATHER LIGHT PRECIPITATION AMOUNTS WEST OF THE JAMES RIVER WILL NOT
HELP ONGOING FIRE CONCERNS ON SUNDAY.  STRONG WINDS 20 TO 30 MPH
WILL REACH THE AREA THROUGH THE DAY...WITH RH VALUES FALLING NEAR 30
PERCENT.  WILL MAINTAIN A VERY HIGH FIRE DANGER RISK OVER WESTERN
FIRE WEATHER ZONES.  FURTHER EAST...SLIGHTLY MORE RAIN WILL
FALL...AND WILL LESSEN FIRE DANGER A BIT.

NEAR RED FLAG CONDITIONS EXPECTED ACROSS CENTRAL SOUTH DAKOTA MONDAY
AND ALONG AND EAST OF I-29 TUESDAY.  STRONG NORTHWEST WINDS OF 20-30
MPH EXPECTED BOTH DAYS.  WITH DRY AIR MIXING DOWN FROM
ALOFT...RELATIVE HUMIDITY VALUES ARE EXPECTED TO FALL INTO THE 15 TO
25 PERCENT RANGE BOTH DAYS.

ELEVATED FIRE WEATHER CONCERNS CONTINUE LATE INTO THE WEEK.  WHILE
WINDS ARE EXPECTED TO BE SLIGHTLY LESS...A DRY AIRMASS ACROSS THE
AREA WILL LEAD TO MINIMUM RELATIVE HUMIDITY VALUES OF 20 TO 30
PERCENT.

&&

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

$$

SHORT TERM...DUX
LONG TERM...
AVIATION...MJ
FIRE WEATHER...


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