Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 010855
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
355 AM CDT SUN MAY 1 2016

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 355 AM CDT SUN MAY 1 2016

VERY LIGHT RAIN CONTINUES ACROSS AREAS BASICALLY INCLUDING THE
SOUTHEAST HALF OF OUR FORECAST AREA. LOW LEVEL FRONTOGENESIS IS
MAXIMIZED IN THE 850-800MB LAYER WHERE PLENTY OF MOISTURE RESIDES IN
THESE LOCATIONS. IN ADDITION TO THIS...A STRIPE OF THETAE
RIDGING...ALMOST A TROWAL LIKE FEATURE...CONTINUES TO WRAP BACK INTO
THE FORECAST AREA FROM THE EAST...AND IS VERY SLOW TO MOVE SOUTHEAST
THROUGH THE DAY. ADD SOME UPPER CYCLONIC FLOW AND COLD TEMPERATURES
ALOFT...HAVE HIGH POPS LINGERING ACROSS OUR SOUTH CENTRAL AND
SOUTHEAST ZONES THROUGH THE MORNING HOURS...BUT THE RAINFALL
POTENTIAL WILL BE LIGHT. THIS AFTERNOON...THE FOCUS TURNS MORE TO A
SHOWERY EVENT. UPPER CYCLONIC FLOW CONTINUES...AND SOUNDINGS BECOME
QUITE UNSTABLE FROM THE SURFACE TO 850MB. THEREFORE HAVE SCATTERED
SHOWERS ACROSS EXTREME SOUTHEAST SD...EXTREME NORTHEAST NEB...AND
MUCH OF NORTHWEST IA WHERE 4KM DEEP MOISTURE STILL RESIDES. AT THE
TOP OF THE CLOUD LAYER...TEMPERATURES ARE CLOSE TO -10C. THIS IS
BORDERLINE WHETHER ANY ICE CAN GET INTRODUCED IN THE CLOUD
LAYER...SO LEFT THE MENTION OF ISOLATED THUNDER OUT FOR NOW. HIGHS
TODAY SHOULD VARY QUITE A BIT FROM NORTHWEST TO SOUTHEAST. ACTUALLY
THE MAV GUIDANCE LOOKED PRETTY GOOD TODAY...GIVING HURON THE WARMEST
READING AT 62. CONVERSELY WHERE THE CLOUD COVER REMAINS DEEP THROUGH
THE DAY...STORM LAKE MAY STRUGGLE TO GET MUCH ABOVE 50 DEGREES.
WHERE THE AIR IS DRIER ACROSS OUR NORTHERN AND WESTERN ZONES...THE
SOUNDINGS DO SUGGEST A DECENT AMOUNT OF CUMULUS DEVELOPMENT IN THE
MIDDAY AND AFTERNOON HOURS. THIS STANDS TO REASON OVER WET GROUND...
AND IT COULD BE ENOUGH TO HOLD TEMPERATURES DOWN A BIT IN THOSE
LOCATIONS. THUS EXCEPT FOR HURON...WANTED TO KEEP EVERYONE ELSE IN
THE UPPER 50S THROUGH OUR NORTH AND WEST.

TONIGHT...WE STILL HAVE A SECONDARY WEAK UPPER LOW MOVING ACROSS
NORTHWEST IA...WITH ANOTHER ONE DIVING DOWN INTO ND FROM SOUTH
CENTRAL CANADA. BUT AT THE SURFACE...HIGH PRESSURE WILL DOMINATE...
GIVING LIGHT WINDS. SKIES SHOULD BE PRETTY CLEAR...EXCEPT IN
NORTHWEST IA WHERE SOME CLOUD COVER COULD LINGER FOR A WHILE BEFORE
CLEARING OUT LATER. BECAUSE OF THIS...LEFT THE POSSIBILITY OF SOME
FOG FORMATION FOR OUR SOUTHEAST ZONES NOTING THE WET GROUND AND LATER
CLEARING. ALSO THREW IN SOME PATCHY FROST FOR A GOOD PORTION OF
OUR NORTHERN AND WESTERN ZONES WHO SHOULD DIP DOWN INTO THE 34 TO 35
DEGREE RANGE. ONCE AGAIN...THE MAV GUIDANCE CAPTURED THE LOWS
PRETTY GOOD AS WELL AS CONSENSUS RAW MODEL VALUES. AT THIS TIME...
DO NOT BELIEVE THE FROST POTENTIAL IS WIDESPREAD ENOUGH TO WARRANT A
HEADLINE.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 355 AM CDT SUN MAY 1 2016

A COOL START TO MONDAY WITH SOME PATCHES OF FROST TO GREET THE DAY
NORTH OF I-90...BUT SOME EARLY DAY SUNSHINE WILL HELP TO QUICKLY
BRING TEMPS UP. SUNSHINE WILL FADE...HOWEVER...BETWEEN DEVELOPING OF
SOME DAYTIME HEATING CUMULUS BY MIDDAY...AND ALSO FROM UPPER LEVEL
WAVE DROPPING SOUTH INTO THE REGION. THIS FEATURE...CURRENTLY OVER
FAR NORTHERN REACHES OF SASKATCHEWAN...IS EXPECTED TO DIG SOUTHWARD
ACROSS THE DAKOTAS DURING THE AFTERNOON AND EARLY EVENING.  FAIRLY
COLD TEMPERATURES ALOFT ACCOMPANY THE WAVE...AND SEEMS TO BE
POTENTIAL FOR MUCH MORE OF A WEAK CONVERGENCE BOUNDARY THAN ANY
MODEL SOLUTION OTHER THAN THE CANADIAN REGIONAL WOULD INDICATE.
AS A RESULT...DIURNAL CYCLE AIDS IN SURFACE BASED DESTABILIZATION...
AND AREAS WEST OF THE JAMES VALLEY LOOK TO GENERATE UP TO 50-100
J/KG MLCAPE. HAVE ADDED IN ISOLATED OR SCATTERED SHOWERS WEST OF I-
29 DEVELOPING BY EARLY AFTERNOON...AND LINGERING UNTIL THE EARLY
EVENING EXIT OF THE UPPER LEVEL LOW. WITH INSTABILITY AND LIKELIHOOD
OF CLOUD BEARING TEMPS SUPPORTING ICE GROWTH...HAVE ALSO MENTIONED A
SLIGHT THREAT FOR THUNDER IN SOME AREAS.

WEAK FLOW MONDAY NIGHT AS SKIES GRADUALLY CLEAR...BUT SOUTHWARD
SINKING RIDGE AXIS SHOULD ALLOW DEVELOPMENT OF SLIGHTLY INCREASED
WESTERLY FLOW...ESPECIALLY AT ELEVATION IN SW MN. AT LAST...TUESDAY
SHOULD MARK OUR FIRST SIGNIFICANTLY WARMER DAY... WITH TEMPS IN A
DEEPER WESTERLY FLOW ENVIRONMENT FAVORING FULLY MIXED READINGS INTO
THE 70S.

STRONGER UPPER WAVE WILL PUSH INTO THE GREAT LAKES TUESDAY NIGHT...
DRIVING A BACKDOOR FRONT SOUTHWARD THROUGH THE CWA. TAIL OF STRONGER
DIV Q WILL REMAIN EAST OF THE CWA ALONG WITH FAIRLY LIMITED
MOISTURE...SO HAVE KEPT FRONTAL PASSAGE DRY. THERE IS 20-25 KNOTS OF
WIND NOT FAR OFF SURFACE IN ONLY A WEAKLY STABILIZED ENVIRONMENT...
SO SOME CONCERN OF A BIT STRONGER NORTHERLY POST FRONTAL WIND AT 15
TO 25 MPH FOR A TIME ON TUESDAY NIGHT.

LATER ON THROUGH THE FORECAST...DEEPENING WAVES TOWARD THE EASTERN
U.S. AND WESTERN U.S. SET UP A STRONG OMEGA BLOCK PATTERN.
TRANSITIONING INTO THIS PATTERN ON WEDNESDAY...TEMPERATURES WILL
COOL BACK BELOW NORMAL AS SURFACE RIDGE SINKS SOUTHWARD INTO THE
AREA FOR WEDNESDAY NIGHT. HAVE SHADED COOLER THAN INITIALIZATION
BLEND WED NIGHT...TAKING SOME TEMPS ALONG AND EAST OF I-29 INTO THE
MID TO UPPER 30S. NOT OUT OF THE QUESTION THAT MAY HAVE TO WATCH FOR
A BIT OF PATCHY FROST IF TEMPS TAKE TREND DOWN A BIT MORE WITH A
FAIRLY DRY AIR MASS LIKELY.

THURSDAY AND FRIDAY WILL FIND TEMPERATURES RETURNING TO ABOVE NORMAL
LEVELS...WITH PLENTY OF SUNSHINE THURSDAY...WITH A FEW MORE CLOUDS
ON FRIDAY. SHOULD SEE ALL 70S BY FRIDAY...WITH SOME UPPER 60S
NEAR/EAST OF I-29 ON THURSDAY. SOME DIFFERENCES ON HOW MODELS TREAT
A WAVE CROSSING THE RIDGE SATURDAY...WITH ECMWF MUCH MORE
FLATTENING...AND DRIVING A FRONTAL BOUNDARY SOUTH ALL THE WAY TO
NEAR I-80 BY LATE SATURDAY...WHILE GFS AND MAJORITY OF ITS ENSEMBLE
MEMBERS MUCH WEAKER AND KEEPING ORPHANED FRONTAL BOUNDARY WELL NORTH.
ALL IN ALL...SHOULD ONLY BE A SMALL CHANCE FOR THUNDERSTORMS AT BEST
THROUGH SATURDAY AS BLOCK PERHAPS SHIFTS JUST A BIT EASTWARD...AND
DAYS OF SOUTHERLY FLOW WORK TO SLIGHTLY INCREASE LOWER LEVEL
MOISTURE. HARD TO PICTURE MUCH HAPPENING GIVEN THE WARMER PLUME OF
TEMPS ALOFT.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1052 PM CDT SAT APR 30 2016

BAND OF RAIN CONTINUES TO WEAKEN AND WILL VERY SLOWLY SHIFT
SOUTHEAST THROUGH THE OVERNIGHT HOURS...LINGERING INTO MID MORNING
IN PORTIONS OF NORTHWEST IOWA. MVFR TO IFR CEILINGS WILL PERSIST
WITH THIS RAIN BAND...BUT WILL ALSO SEE IMPROVEMENT AS THE SYSTEM
EXITS. CLEARING WILL ALSO ARRIVE FROM NORTHWEST TO SOUTHEAST ON
SUNDAY.


&&

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

$$

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


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