Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 241654
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1154 AM CDT SUN MAY 24 2015

.UPDATE...
ISSUED AT 1154 AM CDT SUN MAY 24 2015

GENERALLY MOIST NEUTRAL LOWER TO MID ATMOSPHERE PROVIDING NO
RESISTANCE TO CONTINUED BROAD AND WEAK ISENTROPIC LIFT ACROSS THE
AREA...ALLOWING LIGHT RAIN AND DRIZZLE TO BLOSSOM ACROSS MUCH OF
THE AREA. STUBBORN WIDESPREAD LOW CLOUDS VIRTUALLY LEAVING NO
CHANCE FOR THUNDER INTO THE EVENING WITH EVEN ELEVATED INSTABILITY
NEARLY NON EXISTENT...WITH THE ONLY LOCATION BY LATER AFTERNOON
TOWARD SOUTH CENTRAL SD THAT EVEN GETS CLOSE TO EXHIBITING ANY
ELEVATED INSTABILITY. MODELS TRENDING AWAY FROM BREAKING OUT
CLOUDS TO ANY GREAT DEGREE...SO HAVE REMOVED THUNDER FOR ALMOST
THE WHOLE CWA EVEN THROUGH THE OVERNIGHT...WITH EXCEPTION OF THE
FAR SOUTH WHERE DRYING ALOFT COULD LEAD TO SOME MEAGER AMOUNTS OF
ELEVATED INSTABILITY.

OTHER CHANGES MADE TO THE OVERNIGHT PRECIP...MAINLY TO REDUCE
BY QUITE A BIT...BOTH IN COVERAGE AND QUANTITY. DRY SLOT ALOFT
WILL CONTINUE TO PUSH NORTH INTO THE AREA AHEAD OF ORIGINAL UPPER
WAVE WANDERING AND WEAKENING OVER WYOMING...WHILE SECONDARY
WAVE/MCV FROM SOUTHERN PLAINS CONVECTION LIKELY TO SPREAD
NORTHWARD TO THE EAST ACROSS IOWA OVERNIGHT. LOW LEVEL JET AGAIN
DIVERTED EASTWARD...AND ACTUALLY SEE DIMINISHMENT IN THE
ISENTROPIC SUPPORT THROUGH THE NIGHT. ENDING UP BETWEEN THESE
WAVES...OVERALL FLOW THROUGH MID LEVELS IS QUITE WEAK THOUGH DEEP
LAYER. HEAVY PRECIPITATION NOW LOOKS UNLIKELY WITH LACK OF ANY
PERSISTENT FORCING...BUT GIVEN LIKELY SLOW MOVEMENT OF ANY PRECIP
AREAS WHICH DO DEVELOP...IT WOULD BE PARTICULARLY LOCALIZED IF
DOES OCCUR TOWARD THE SOUTHERN/EASTERN CWA.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 419 AM CDT SUN MAY 24 2015

STRONG MOISTURE TRANSPORT COMBINED WITH ISENTROPIC LIFT ABOVE 850 MB
LEADING TO SHOWERS ACROSS THE REGION THIS MORNING. MID LEVEL LIFT
WEAKENS SOME THROUGHOUT THE DAY AS SHORT WAVES CURRENTLY ACROSS THE
AREA LIFT NORTH.  THE NET RESULT WILL BE DECREASING PRECIP CHANCES
WEST OF I-29.  FURTHER TO THE EAST...WARM CONVEYOR ACROSS THE
CENTRAL PLAINS CONTINUES TO FEED MOISTURE INTO THE REGION RESULTING
IN SCATTERED SHOWERS AS WARM FRONT LIFTS NORTH ACROSS THE AREA.
BELIEVE THERE WILL BE A BREAK IN THE ACTIVITY ACROSS THE WEST IN THE
LATE MORNING AND EARLY AFTERNOON HOURS...LEADING TO A SMALL AMOUNT
OF INSTABILITY DEVELOPING BEFORE ADDITIONAL THUNDERSTORMS DEVELOP
IN THE MID TO LAT AFTERNOON HOURS. UNLESS THERE IS PRETTY GOOD
CLEARING...DO NOT EXPECT SEVERE WEATHER TODAY. HAVE LOWERED
FORECAST HIGHS IN THE EAST WITH THE EXPECTATION OF SHOWERS THROUGH
MUCH OF THE TODAY.

MESSY PATTERN TONIGHT WITH UPPER LEVEL LOW WEAKENING TO THE WEST AND
SECONDARY LOW DEVELOPING AND LIFTING NORTHEAST ACROSS THE AREA. PWAT
VALUES BY THIS EVENING CLIMB TO NEARLY 1.3 INCHES...GREATER THAN TWO
STANDARD DEVIATION`S FROM THE NORM. THIS LEADS TO AN EFFICIENT
ATMOSPHERE TO PRODUCE MODERATE TO HEAVY RAIN ACROSS THE AREA.
RAISED POP AND QPF VALUES THROUGH THE NIGHT...AND HAVE ALSO RAISED
LOWS SLIGHTLY WITH RELATIVELY SOUPY ATMOSPHERE.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 419 AM CDT SUN MAY 24 2015

THE OVERALL UPPER AIR PATTERN FOR THE UPCOMING WEEK IS VERY
CHAOTIC...AND THUS VERY DIFFICULT TO LATCH ONTO ANY ONE STRONG
FEATURE. THEREFORE WITH THIS TYPE OF SCENARIO HAD A TENDENCY TO
BLEND MANY MODEL SOLUTIONS TOGETHER. ON MEMORIAL DAY...LARGE UPPER
LOW CONTINUES IT VERY SLOW TRACK INTO THE CENTRAL AND NORTHERN
PLAINS AND BEGINS TO WEAKEN. IN RESPONSE...A RATHER STRONG SURFACE
LOW GENERATES THEN LIFTS NORTHEASTWARD ALONG A TRACK WHICH IS MAINLY
SOUTHEAST OF OUR FORECAST AREA. IT STILL LOOKS LIKE THE LAST
REMNANTS OF THE UPPER LOW IS ON TARGET TO MOVE ACROSS OUR AREA ON
TUESDAY. SO NEEDLESS THE WEATHER REMAINS UNSETTLED BUT RAINFALL
CHANCES GENERALLY WANE THROUGH THE EARLY WEEK.

ON MONDAY...IT APPEARS THE HIGHEST POPS ARE WARRANTED IN OUR EASTERN
ZONES EARLY IN THE MORNING AS ONE SHORT WAVE EXITS. AFTER THAT...
RAIN CHANCES GET PRETTY SPOTTY. DRIER AIR BEGINS TO ENTRAIN INTO OUR
NORTHERN ZONES MONDAY NIGHT...CONTINUING TO NUDGE SOUTHWARD THROUGH
THE DAY ON TUESDAY. THEREFORE MOST OF THE CHANCES FOR SHOWERS WILL
BE BOTTLED UP ACROSS OUR SOUTHERN ZONES MONDAY NIGHT AND TUESDAY
BEFORE GOING DRY OVER THE ENTIRE FORECAST AREA TUESDAY NIGHT. THINGS
COULD CHANGE AS CONFIDENCE IN THE PRECIPITATION PATTERN IS NOT AT
ALL HIGH DUE TO THE RUN TO RUN VARIANCE IN THE MODEL SOLUTIONS FROM
DAY TO DAY. A LITTLE MORE CONFIDENT ON THE TEMPERATURE REGIME...WITH
RATHER SEASONABLE HIGHS IN THE UPPER 60S AND 70S MEMORIAL DAY AND
TUESDAY...WITH LOWS MONDAY NIGHT AND TUESDAY NIGHT IN THE 50S.

A QUASI ZONAL AND WAVY PATTERN RETURNS BY MID WEEK...WITH ANOTHER
UPPER LOW FORMING BY THURSDAY THROUGHOUT THE INTERMOUNTAIN WEST. ONE
LARGE DISCREPANCY BETWEEN THE GFS AND ECMWF IS THAT THE GFS IS
QUICKER WITH A NORTHERN STREAM TROUGH MOVING ACROSS SOUTHERN CANADA
AND NORTHERN MN BY EARLY FRIDAY. IF THIS VERIFIES...ARE MOISTURE
SUPPLY WILL BE CUTOFF MORE QUICKLY THAN WHAT THE ECMWF IS SHOWING.
AT ANY RATE...A DECENT SHORT WAVE MOVES THROUGH WEDNESDAY NIGHT AND
THURSDAY WHICH WILL GIVE ANOTHER CHANCE FOR SHOWERS AND
THUNDERSTORMS. BEGINNING FRIDAY...PREDICTING RAINFALL CHANCES GETS
TRICKIER DUE TO THE DISCREPANCIES MENTIONED ABOVE. FOR NOW AM SIDING
WITH THE SLOWER ECMWF SO KEPT CHANCE POPS IN FRIDAY AND FRIDAY
NIGHT...THEN PUSHING ACROSS OUR SOUTHERN ZONES ON SATURDAY. IF THE
CURRENT TRENDS CONTINUE...WOULD NOT BE SURPRISED IF ALL OF THE
VARIOUS MEDIUM RANGE MODELS DRY THINGS OUT ACROSS OUR ENTIRE
FORECAST AREA BY SATURDAY SO WE MAY HAVE TO ELIMINATE THOSE POPS IN
FUTURE FORECASTS. HIGHS REMAIN BENIGN...IN THE UPPER 60S AND 70S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1153 AM CDT SUN MAY 24 2015

ABUNDANT LOW LEVEL MOISTURE LEADING TO FAIRLY WIDESPREAD IFR
CONDITIONS THIS MORNING...WHICH WILL SLOWLY CLIMB INTO THE MVFR
RANGE DURING THE AFTERNOON. DEGRADED CEILINGS AND AREAS OF LOWER
VISIBILITIES IN FOG AND LIGHT PRECIPITATION WILL CONTINUE TO BE A
FEATURE THROUGH 18Z MON.

&&

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

$$

UPDATE...CHAPMAN
SHORT TERM...
LONG TERM...MJ
AVIATION...CHAPMAN


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