Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 291731
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1231 PM CDT WED APR 29 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 343 AM CDT WED APR 29 2015

NEARLY PERFECT SPRING DAY ACROSS THE REGION TODAY AS DRY HIGH
PRESSURE BUILDS INTO THE REGION LEADING TO CLEAR SKIES AND LIGHT
WINDS THROUGHOUT THE DAY.  WITH DRY AIR MIXING DOWN FROM
ALOFT...HAVE SIDED TOWARDS LOWER GUIDANCE VALUES FOR DEW POINTS.
THIS WILL YIELD RH VALUES 15-20 PERCENT THIS AFTERNOON...BUT THE
LIGHT WINDS WILL KEEP THE FIRE DANGER IN CHECK. HAVE SIDED WITH
WARMEST GUIDANCE VALUES GIVEN THE DRY MIXY ENVIRONMENT.

TONIGHT...RETURN FLOW INCREASES FROM WEST TO EAST OVERNIGHT.  NEARLY
IDEAL RADIATIONAL CONDITIONS EXIST EAST OF I-29...SO HAVE UNDERCUT
GUIDANCE VALUES ESPECIALLY IN THE RADIATIVE PITS.  COULD BE A FEW
HIGH CLOUDS SNEAKING INTO SOUTHWEST MINNESOTA LATE...SO DID NOT GO
AS COOL IN THE NORTH AS THE SOUTH.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 343 AM CDT WED APR 29 2015

SURFACE HIGH PRESSURE WILL MOVE EASTWARD INTO WISCONSIN AND ILLINOIS
BY LATE THURSDAY...WHICH WILL STRENGTHEN THE RETURN SOUTH TO
SOUTHEAST FLOW OF AIR WEST OF INTERSTATE 29. A WARM AIR MASS IS
CERTAINLY IN PLACE...WITH HIGHS MAINLY 75 TO 80 DEGREES ALLOWING FOR
MIXING UP TO ABOUT 800MB WHICH IS WHAT THE NAM AND GFS ARE SHOWING.

ON THURSDAY NIGHT...MODELS ARE STILL SHOWING SOME RAINFALL
ASSOCIATED WITH A WEAK COLD FRONT...REALLY LITTLE MORE THAN A WIND
SHIFT LINE...AND ACCOMPANYING SHORT WAVE. PRE CONVECTIVE LAPSE RATES
ARE CONDITIONALLY UNSTABLE...PRIMARILY PSEUDO ADIABATIC. THEREFORE
ONLY ISOLATED THUNDER WITH THE SHOWERS IS WARRANTED AT THIS TIME.
DUE TO THE WINDS...DID NOT TANK ANY LOWS IN LOW LYING LOCATIONS.
WEAK HIGH PRESSURE WILL BE IN CONTROL ON FRIDAY...THEREFORE AM
EXPECTING DECREASING WINDS IN THE AFTERNOON HOURS HELPING TO KEEP
FIRE DANGER DOWN SOMEWHAT. ONCE AGAIN THE LOWER ATMOSPHERE MIXES TO
AROUND 800MB...GIVING HIGHS IN THE 70S.

MEDIUM RANGE MODELS ARE STILL SHOWING A RATHER WAVY PATTERN
BEGINNING THIS WEEKEND. NOT REAL EXCITED ABOUT RAINFALL CHANCES
ANYMORE ON SATURDAY AND SATURDAY NIGHT WITH NOTHING REALLY IN THE
WAY OF A FOCUSING MECHANISM AND A NONDESCRIPT WARM AIR ADVECTION
REGIME. THEREFORE THIS BEGINS TO CHANGE ON SUNDAY WHEN A COLD
FRONT OOZES SOUTHWARD PROVIDING A FOCUS. CHANCES FOR THUNDERSTORMS
ARE PRETTY DECENT LATER SUNDAY AND SUNDAY NIGHT WITH WARM
TEMPERATURES HELPING TO PROVIDE LITTLE IN THE WAY OF INHIBITION.
ON MONDAY AND TUESDAY THERE IS SOME DISCREPANCY BETWEEN THE
DETERMINISTIC GFS AND ECMWF. THEY BOTH HAVE HIGH PRESSURE MOVING
FROM WEST TO EAST NEAR THE CANADIAN BORDER. HOWEVER THE ECMWF IS
FURTHER NORTH WITH SURFACE LOW PRESSURE WHICH WOULD GIVE OUR
NORTHWEST IA ZONES A BETTER CHANCE FOR RAINFALL MONDAY AND
TUESDAY. IN FACT THE 850MB WARM FRONTAL ZONE IS SQUARELY ACROSS
NORTHWEST IA ON MONDAY AND TUESDAY WHICH IS WHY THE ECMWF IS QUITE
WET IN OUR SOUTHEAST ZONES FOR THESE PERIODS. BOTH MODELS ARE
SIMILAR WITH THE UPPER AIR PATTERN IN SHOWING TROUGHING TO THE
SOUTHWEST IN THE SOUTHERN ROCKIES. BUT THE GFS IS SLIGHTLY
STRONGER WITH AN UPPER LOW WELL NORTHWARD IN SOUTHEAST CANADA
ALLOWING A STRONGER PUSH OF EAST TO NORTHEAST BOUNDARY LAYER AIR
TO MOVE SOUTHWARD. SO IT IS DIFFICULT TO TELL WHICH LOW LEVEL AIR
PATTERN IS CLOSER BETWEEN THE TWO MODELS. AT ANY RATE...IT IS
CERTAINLY ENOUGH TO KEEP THE MENTION OF SOME POPS GOING IN OUR
SOUTHEAST ZONES UNTIL WE CAN GET A BETTER HANDLE ON THIS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1231 PM CDT WED APR 29 2015

VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD.

&&

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

$$

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


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