Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 051153
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
653 AM CDT TUE MAY 5 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 402 AM CDT TUE MAY 5 2015

BATTLE LINES CONTINUE TO BE DRAWN BETWEEN THE DRY EASTERLY LOWER
LEVEL TRAJECTORY INTO AREAS NEAR AND NORTH OF INTERSTATE 90...WITH
TRANSITION TO MORE MOIST SOUTH TO SOUTHEAST INITIATING ACROSS PARTS
OF EASTERN NEBRASKA. THIS TIME...MOST IF NOT ALL MODELS ARE
ACKNOWLEDGING THE DIFFICULTY THAT PRECIPITATION WILL HAVE SPREADING
NORTHWARD TODAY...EVEN WITH SHORTCOMINGS ON TOO RAPID INCREASE OF
NEAR SURFACE DEWPOINTS THROUGH AT LEAST MIDDAY FROM I-90 NORTHWARD.
CURRENT EAST TO WEST BAND OF SHOWERS ALONG THE LEADING EDGE OF LOW
TO MID LEVEL MOISTURE CONVERGENCE LIFTING NORTHWARD TOWARD THE LOWER
MISSOURI VALLEY AND NORTHWEST IOWA EXPECTED TO DISSIPATE WORKING
NORTHWARD...LIKELY BEFORE REACHING I-90 BY LATE MORNING.  WILL AGAIN
TODAY WATCH FOR A WEAK IMPULSE LIFTING NORTHEASTWARD FROM KANSAS
INTO THE TRI STATE AREA BY LATE DAY...AND BY THIS TIME WILL SEE
INCREASING SOUTHERLY TRANSPORT OF MOISTURE. SHOULD WORK ON A LEAST A
SCATTERED COVERAGE OF PRECIPITATION AS FORCING FOR LIFT INCREASES
DURING THE MID TO LATER AFTERNOON HOURS...LAST TO REACH NORTHERN
AREAS. OVERALL...NOT IMPRESSED BY THE INSTABILITY AND PREFER A
MINIMIZATION OF THUNDER MENTION FOR MUCH OF THE DAY...LIKELY
REMAINING ISOLATED IN COVERAGE AT BEST. ANY INSTABILITY IS LARGELY
DUE TO SURFACE HEATING...WITH MAINLY A GLORIFIED MOIST NEUTRAL
PROFILE.  ROOM AGAIN FOR TEMPS TO RISE TO MILD READINGS IN THE UPPER
60S TO MID 70S...ESPECIALLY DRIEST TRAJECTORY ACROSS THE
NORTH/NORTHEAST. WILL HAVE MORE CLOUDS TODAY...SO HAVE KEPT A BIT
CLOSER TO MEAN SOLUTION...ESPECIALLY IN THE MORE CLOUDY SOUTHEAST.

BEHIND THE WEAK IMPULSE TONIGHT...WILL SEE A PERIOD OF DRYING ALOFT
PUSH THROUGH THE EASTERN CWA...WHILE MAX MOISTURE TRANSPORT ON LOW
LEVEL JET OF 30 TO 40 KNOTS BECOMES FOCUSED INTO THE WESTERN CWA
INITIALLY...DIVERTING GRADUALLY EASTWARD OVERNIGHT. CONVECTION
DEVELOPING ON EDGE OF AREA ACROSS WESTERN NEBRASKA AND KANSAS WILL
BE ROTATING NORTH AND NORTHEAST ON UNIDIRECTIONAL FLOW AHEAD OF
CLOSED UPPER WAVE THROUGH THE NIGHT...PERHAPS AS FAR EAST AS I-29 BY
LATE NIGHT. BREEZY SOUTH TO SOUTHEAST WINDS WILL MAKE FOR A MILD
NIGHT...LOWS MAINLY UPPER 50S TO LOWER 60S...AND NOTICEABLY MORE
MOIST THAN RECENT NIGHTS.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 402 AM CDT TUE MAY 5 2015

STRONG NORTHWARD MOISTURE TRANSPORT CONTINUES AS WE HEAD INTO
WEDNESDAY...AHEAD OF A UPPER TROUGH ROTATING INTO THE REGION THROUGH
THE DAY.  BROAD SYNOPTIC LIFT SUGGESTS THAT SCATTERED SHOWER
ACTIVITY SHOULD OVERSPREAD THE AREA THROUGH THE FIRST HALF
WEDNESDAY. SOUNDINGS ARE VERY MOIST NEUTRAL...AND WOULD SUGGEST A
LOW END CHANCE OF THUNDER IN THE MORNING...WITH LIGHT QPF. PERIODIC
RAIN CHANCES WILL CONTINUE THROUGH THE AFTERNOON AS LIFT REMAINS
STRONG.  A BIT MORE INSTABILITY IN THE SOUNDINGS IN THE
AFTERNOON...SO WILL MENTION PREVAILING THUNDER.  THERE MAY BE A
BRIEF BREAK IN PRECIPITATION THE EVENING AS CONVECTION RELOADS ALONG
THE WESTERN PLAINS.  MODEL GUIDANCE CONTINUES TO BRING UPWARDS OF
500 TO 800 J/KG CAPE INTO THE SOUTHERN HALF OF THE CWA BY WEDNESDAY
EVENING AS MID-LVL LAPSE RATES SHARPEN. CANNOT RULE OUT A STRONGER
STORM. THE HIGHEST RAINFALL AMOUNTS WILL FALL OVERNIGHT INTO
THURSDAY MORNING AS THE SHORTWAVE MOVES THROUGH AND CONVECTION FROM
THE WESTERN PLAINS LIFTS NORTHEAST. WOULD ANTICIPATE CONSIDERABLY
HIGHER AMOUNTS OF THUNDER AND QPF. THE BOUNDARY WILL LINGER INTO
THURSDAY...AND WITH A SECONDARY SHORTWAVE ZIPPING NORTHEASTWARD...A
BIT OF AFTERNOON REDEVELOPMENT COULD BE POSSIBLE.

THE STORY HEADING INTO THE WEEKEND WILL BE LARGE UPPER TROUGH
DIGGING INTO THE SOUTHWESTERN UNITED STATES...AND THE IMPACT IT HAS
ON THE WEATHER INTO NEXT WEEKEND. FRIDAY REMAINS THE DAY WITH THE
HIGHEST POTENTIAL TO REMAIN DRY...HOWEVER SOUTHWESTERLY FLOW
ALOFT WILL PREVAIL AHEAD OF THE MAIN TROUGH AND ANY SHORTWAVE THAT
LIFTS NORTHWARD COULD PUSH SHOWERS BACK INTO THE AREA EARLY IN THE
WEEKEND.

GUIDANCE CONTINUES TO BRING THIS UPPER TROUGH INTO THE NORTHERN
PLAINS AS WE FINISH NEXT WEEKEND...WITH A GOOD PROBABILITY OF
UNSETTLED WEATHER INTO EARLY NEXT WEEK.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 653 AM CDT TUE MAY 5 2015

MESSY AVIATION FORECAST RESULT OF INCREASING LOW LEVEL MOISTURE
STARTING TO STREAM NORTHWARD INTO THE AREA. BAND OF SHOWERS
LIFTING NORTHWARD THROUGH KSUX AREA EARLY THIS MORNING WITH
BRIEF MVFR VISIBILITY AND CEILING...BUT MAY DEGRADE FOR SEVERAL
HOURS THIS MORNING FOLLOWING TO PERSISTENT IFR CONDITIONS...MAINLY
CEILINGS. FURTHER NORTH...A QUESTION AS TO WHETHER DRY AIR
TRAJECTORY INITIALLY AND DIURNAL HEATING WILL HOLD OFF ADVANCE OF
MVFR CEILINGS AND DRY UP PRECIPITATION BAND BEFORE REACHING KFSD
LATE MORNING. GRADUALLY SHOULD SEE TENDENCY FOR SCATTERED SHOWERS
TO DEVELOP THIS AFTERNOON AND EVENING...AND A MORE WIDESPREAD
THREAT FOR RAINFALL SPREADING FROM THE SOUTH AND WEST DURING THE
NIGHT. THIS AREA OF RAINFALL WILL BE ASSOCIATED WITH PREVAILING
MVFR CONDITIONS...AND LIKELY SOME BRIEF TRANSITS TO IFR
CONDITIONS.

&&

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

$$

SHORT TERM...CHAPMAN
LONG TERM...DUX
AVIATION...CHAPMAN


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