Area Forecast Discussion
Issued by NWS Rapid City, SD

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

000
FXUS63 KUNR 222315
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
515 PM MDT FRI APR 22 2016

.SHORT TERM...THIS EVENING THROUGH SATURDAY NIGHT
ISSUED AT 223 PM MDT FRI APR 22 2016

CURRENT UPPER AIR ANALYSIS DEPICTS A STRONG ULL MOVING INTO THE
WESTERN CONUS WHILE THE CENTRAL CONUS IS UNDER THE INFLUENCE OF A
RIDGE. SATELLITE REVEALS SOME THIN CIRRUS CLOUDS MAKING THEIR WAY
INTO THE REGION AHEAD OF THE NEXT SYSTEM. AT THE SURFACE...1003MB
SURFACE LOW OVER CENTRAL MONTANA IS INFLUENCING THE
SOUTHERLY/SOUTHEASTERLY RETURN FLOW ACROSS OUR CWA.

TONIGHT...A 40 TO 50 KNOT LLJ DEVELOPS ACROSS THE SOUTH DAKOTA
PLAINS IN RESPONSE TO TIGHTENING TEMPERATURE/PRESSURE GRADIENT AHEAD
OF THE ULL. THIS IN TURN WILL HELP BRING LOW LEVEL MOISTURE UP TO
THE REGION AND KEEP OVERNIGHT TEMPERATURES RELATIVELY MILD.

BY SATURDAY...THE RIDGE AXIS SLIDES EAST OF AREA...BUT CORE OF VERY
WARM AIR WILL REMAIN OVER THE REGION DURING THE DAY. MOST MODELS ARE
SHOWING 850MB TEMPERATURES BETWEEN 20 TO 24 DEGREES CELSIUS DURING
THE AFTERNOON SATURDAY...WITH WARMEST AIR ALOFT GENERALLY OVER
SOUTHWESTERN SOUTH DAKOTA. SHOULD SEE LOTS OF MID 80S FOR HIGHS
ACROSS THE SOUTH DAKOTA PLAINS.

REGARDING THE SEVERE WEATHER POTENTIAL...NWP GUIDANCE HAVE SHOWN A
PLUME OF MOISTURE/INSTABILITY DEVELOPING ACROSS CENTRAL AND
NORTHWESTERN SOUTH DAKOTA DURING THE DAY SATURDAY...BUT VARY ON THE
AMOUNTS. THE GFS REMAINS THE MOST CONSERVATIVE WITH SBCAPE REMAINING
UNDER 1500J/KG AND MIXING OUT MOST BOUNDARY-LAYER MOISTURE IN THE
CWA WITH ALMOST UNIDIRECTIONAL SOUTHWEST FLOW...WHILE THE NAM AND
ECMWF HAVE AS MUCH AS 2000J/KG TO 3000J/KG ACROSS EASTERN/NORTHERN
PORTIONS OF THE CWA WITH MORE SOUTHERLY/SOUTHEASTERLY FLOW AND A
NORTHWEST TO SOUTHEAST ORIENTED BOUNDARY/DRYLINE DRAPED ACROSS THE
SOUTH DAKOTA PLAINS.

SHOULD THE NAM/ECMWF SOLUTION VERIFY...THERE IS A SMALL WINDOW OF
OPPORTUNITY FOR ISOLATED...POTENTIALLY SEVERE...SURFACE-BASED
CONVECTION TO FIRE OFF BETWEEN 21Z AND 00Z. FORECAST CIN WILL DROP
BETWEEN 10J/KG TO 20J/KG AHEAD OF THE DRYLINE...AND SEVERAL HIGH-RES
CAM`S ALONG WITH THE 12KM NAM DEVELOP ISOLATED CONVECTION IN
NORTHWESTERN SOUTH DAKOTA. THE 0-6KM SHEAR SHOULD SUPPORT ORGANIZED
CONVECTION AS VALUES RANGE FROM 25KT TO 35KT. THE LIMITING FACTORS
TO SURFACE-BASED CONVECTION WILL BE DRY AIR ENTRAINMENT AND CIN.
LCL`S ALONG THE DRYLINE WILL BE CLOSE TO 10KFT...AND WITH THE VERY
DRY AIR NEAR THE SURFACE WOULD EXPECT IT TO BE DIFFICULT TO ACHIEVE
CONVECTIVE INITIATION. ADDITIONALLY...CIN INCREASES DRAMATICALLY
AHEAD OF THE DRYLINE WHERE THE DEEPER MOISTURE RESIDES...AND STORMS
COULD STRUGGLE TO PERSIST IN THAT ENVIRONMENT.

THE SURFACE LOW MOVES INTO THE REGION SATURDAY EVENING...AND
ELEVATED CONVECTION STARTS DEVELOPING AFTER 03Z SUNDAY IN THE CWA.
AS THE ULL SWINGS INTO THE REGION...STRONG ISENTROPIC LIFT ON THE
BACKSIDE OF THE ULL WILL CREATE WIDESPREAD PRECIPITATION ACROSS
NORTHEASTERN WYOMING AND NORTHWESTERN SOUTH DAKOTA BY SUNDAY MORNING.

.LONG TERM...SUNDAY THROUGH FRIDAY
ISSUED AT 223 PM MDT FRI APR 22 2016

A SERIES OF UPPER LOWS ARE EXPECTED TO CROSS THE REGION
THROUGH THE LONG TERM BRINGING WET WEATHER TO THE AREA. THE FIRST
UPPER LOW WILL MOVE SLOWLY E-W ACROSS SOUTH DAKOTA FROM SUNDAY
MORNING THROUGH SUNDAY EVENING BRINGING CLOUDS...WIDESPREAD SHOWERS
AND THUNDERSTORMS AND COOLING TEMPERATURES. PROFILES IN MODEL
SOUNDINGS INDICATE CONDITIONS MAY BE COOL ENOUGH FOR A LITTLE SNOW
OVER THE HIGHER ELEVATIONS OF THE BLACK HILLS LATE SUNDAY
NIGHT/EARLY MONDAY MORNING WITH A RAIN/SNOW MIX POSSIBLE OVER PARTS
OF FAR NORTHWESTERN SOUTH DAKOTA AND NORTHEASTERN WYOMING. GENERALLY
DRIER WEATHER IS EXPECTED MONDAY AHEAD OF THE NEXT LOW...BUT PRECIP
WILL RETURN MON NIGHT AS THE LOW PUSHES INTO THE GREAT BASIN. THE
RELATIVELY SLOW MOVEMENT OF THIS SECOND UPPER LOW WILL KEEP CHANCES
OF SHOWERS AND THUNDERSTORMS...ALONG WITH COOLER TEMPERATURES...IN
THE FORECAST FROM MONDAY NIGHT THROUGH WEDNESDAY NIGHT. TEMPERATURES
ALOFT AND AT THE SFC MAY AGAIN BE COOL ENOUGH FOR SOME LIGHT SNOW
OVER THE HIGHER BLACK HILLS EARLY EACH MORNING...ESPECIALLY WED
MORNING. DRY WEATHER IS EXPECTED THURSDAY BEFORE THE THIRD UPPER LOW
BRINGS ANOTHER CHANCE OF PRECIPITATION ON FRIDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 515 PM MDT FRI APR 22 2016

VFR CONDITIONS WILL CONTINUE THROUGH THE FORECAST PERIOD.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&

$$

SHORT TERM...MCKEMY
LONG TERM...13
AVIATION...7



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.