Severe Thunderstorm Warning 183, NWS Aberdeen, SD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ABERDEEN SD
349 AM CDT FRI AUG 17 2007

.SHORT TERM...TODAY THROUGH SUNDAY AFTERNOON
FOCUS IN THE SHORT TERM REMAINS ON POTENTIAL FOR RAIN AND
THUNDERSTORMS TODAY THROUGH SUNDAY MORNING. SEVERAL IMPULSES
PROGRESSING THROUGH THE UPPER RIDGE JUST TO THE WEST WILL MOVE
THROUGH THE AREA...WITH POTENTIAL FOR THUNDERSTORM DEVELOPMENT
WITH EACH ONE.

EARLY THIS MORNING...AN ACCAS FIELD DEVELOPED RELATIVELY QUICKLY
OVER PORTIONS OF CENTRAL AND NORTHEAST SOUTH DAKOTA ASSOCIATED
WITH WARM ADVECTION...AN INCREASING LOW LEVEL JET...AND A WARM
FRONT BEGINNING TO LIFT NORTHEASTWARD THROUGH THE REGION. A FEW
SHOWERS AND THUNDERSTORMS HAVE DEVELOPED OVER THIS AREA AND ARE
INCREASING SOMEWHAT IN COVERAGE AS OF 08Z. HAVE EXPANDED POPS
BEFORE 12Z TO ACCOUNT FOR THE DEVELOPING SHOWERS AND ACCAS FIELD.
AS THE MORNING PASSES...EXPECT THAT THE LLJ WILL DECREASE AND
COVERAGE OF STORMS WILL BE MOSTLY REGULATED TO THE AREA NEAR
WHERE AN INITIAL IMPULSE IS PASSING THROUGH NEAR THE NORTH/SOUTH
DAKOTA BORDER THROUGH THE REMAINDER OF THE MORNING HOURS...THOUGH
A 700 HPA THETA E RIDGE CONTINUES PASSING TO THE EAST THROUGHOUT
THE MORNING SO HAVE KEPT SLIGHT CHANCE POPS IN FOR THE SOUTHEAST
THROUGH THE MORNING.

THIS AFTERNOON THROUGH TONIGHT...MODELS HAVE PROGRESSIVELY SLOWED
DOWN A BIT THE MIGRATION OF THE IMPULSES THROUGH THE RIDGE...WHICH
MAKES SENSE CONSIDERING THE STRENGTH OF THE RIDGE. THUS...HAVE
SLOWED DOWN POPS/WEATHER ABOUT SIX HOURS DURING THIS TIME
PERIOD...WITH THE GREATEST COVERAGE OF THUNDERSTORMS NOW EXPECTED
TO BE BETWEEN 03Z AND 15Z SATURDAY. HAVE GENERALLY WENT ALONG WITH
HPC IN PREFERRING THE GFS PLACEMENT OF POPS FOR THIS
EVENT...RATHER THAN THE NAM...WHICH IS FURTHER NORTH. THIS PLACES
THE AXIS OF GREATEST POPS GENERALLY STRAIGHT THROUGH OUR
CWA...WITH VERY STRONG 850 MOISTURE ADVECTION NOTED ON THE GFS
FROM 06Z-12Z SATURDAY IN NORTHEAST SOUTH DAKOTA DUE PRIMARILY TO
THE LOW LEVEL JET CRANKING UP TO 40 TO 45 KNOTS...BRINGING MUCH
HIGHER THETA E AIR INTO THE AREA. SPC HAS MOVED THE SLIGHT RISK
FOR SEVERE WEATHER FURTHER WEST..IN OUR WESTERN CWA...WHICH MAKES
SENSE CONSIDERING THE SLOWER TIMING OF THE SYSTEM...AND DO BELIEVE
THAT SOME SEVERE WEATHER IS POSSIBLE IN THE WESTERN CWA WITH SOME
MIXED LEVEL CAPE. HOWEVER...HIGHEST INSTABILITY IS IN THE
SOUTHWEST CWA JUST SOUTH OF THE WARM FRONT WHERE TEMPERATURES WILL
BE ABLE TO RISE QUITE A BIT MORE WITH HIGHER DEWPOINTS THAN THE
REMAINDER OF THE CWA. SEEING AS THOUGH THE BEST SUPPORT OTHERWISE
FOR THUNDERSTORMS WILL BE TO THE NORTH...IT MAY WELL BE THAT
SEVERE PARAMETERS WILL NOT MATCH UP IN SPACE. THUS...THIS MAY BE
MORE OF A LOCALLY HEAVY RAIN EVENT AS THUNDERSTORMS CONSOLIDATE
INTO AN MCS AND APPEAR TO MOVE ACROSS THE CWA TONIGHT. WILL
MENTION THE POSSIBILITY OF HEAVY RAINFALL IN THE FORECAST THIS
MORNING AS WELL...AS PWATS QUICKLY RISE TO AROUND 2 INCHES
TONIGHT...THOUGH THE STORMS THEMSELVES ARE NOT EXPECTED TO BE
PARTICULARLY SLOW MOVERS. THIS MCS IS EXPECTED TO CONTINUE OVER
PARTS OF THE AREA THROUGH THE MORNING ON SATURDAY.

ON SATURDAY...THE MCS MOVES TO THE EAST THROUGH MINNESOTA AS
FRIDAYS WARM FRONT...WHICH BECOMES A STATIONARY FRONT OVERNIGHT
TONIGHT...REMAINS AS A STATIONARY FRONT ACROSS THE AREA. EASTERLY
WINDS AS WELL AS REMAINING CONVECTION FROM TONIGHTS MCS...MOSTLY
IN THE MORNING HOURS...COULD KEEP HIGH TEMPERATURES RELATIVELY LOW
IN THE NORTHEAST CWA AND LOWERED FORECAST HIGHS ACCORDINGLY. SUBSIDENCE
BEHIND THE MCS AND SOMEWHAT OF A CAP DEVELOPING OVER THE AREA
SHOULD KEEP DRY CONDITIONS AFTER THE FIRST MCS PASSES...BUT SOME
REDEVELOPMENT COULD OCCUR SATURDAY NIGHT AS THE LOW LEVEL JET
INCREASES AGAIN OVER THE AREA. ON SUNDAY...THE FRONT BEGINS
PROGRESSING NORTH AGAIN AS A WARM FRONT...AND WARMER 700MB
TEMPERATURES SHOULD HELP LIMIT CONVECTIVE POTENTIAL THROUGH THE
AFTERNOON HOURS.

.LONG TERM...SUNDAY NIGHT THROUGH THURSDAY
PCPN REMAINS THE MAIN FORECAST CHALLENGE THROUGH THE MEDIUM RANGE.
MEANWHILE THE 00Z MODELS ARE GENERALLY SIMILAR WITH THE LONG WAVE
PATTERN OVER THE CONUS DURING THE FORECAST PERIOD. DURING THAT
TIME PERIOD A WEALTH OF ENERGY COMES ACROSS THE ROCKIES AND HELPS
SHOVE THIS SUMMERS SEMI PERMANENT MID LEVEL RIDGE TOWARD THE
EASTERN CONUS. BEING MORE SPECIFIC...FOR SUNDAY NIGHT AND MONDAY...AN
ELEVATED WARM THERMAL LAYER ADVECTS OFF THE HIGH PLAINS AND INTO
THE FORECAST AREA. THIS WARM LAYER ALOFT MAY WELL SERVE TO CAP OFF
THE REGION. HAVE THEREFORE PULLED POPS BACK A BIT...BUT BECAUSE OF
AN ADVANCING SFC BOUNDARY...DID NOT ENTIRELY ELIMINATE THEM. FOR
MONDAY NIGHT AND TUESDAY...MORE ENERGY IS PROGGED TO CROSS THE
NORTHERN PLAINS WITHIN QUICKENING FLOW ALOFT. THIS ENERGY...ALONG
WITH COLLAPSING HEIGHTS SUGGESTS THERE IS STILL SOME CHANCE FOR
RAIN THOSE FORECAST PERIOD UNTIL DRIER AIR ADVECTS IN FROM THE
NORTH ON TUESDAY NIGHT OR WEDNESDAY. CONCERNING
TEMPERATURES...ONLY SLIGHT MODIFICATIONS WERE MADE TO THE INHERITED
GRIDS. THE OVERALL TREND FOR THE NEXT WORK WEEK WILL BE GRADUALLY
COOLING TEMPERATURES AS WE TREND ALOFT FROM A RIDGE TO A TROF.

&&

.AVIATION...
MOSTLY VFR CONDITIONS EXPECTED TODAY FOR KMBG/KPIR/KATY AND KABR.
HOWEVER...ISOLATED TO SCATTERED MORNING SHOWERS AND STORMS WILL BE
POSSIBLE FOR KPIR AND KMBG. SOME OF THAT ACTIVITY COULD SPREAD
INTO THE KATY/KABR AREAS BY AFTERNOON. A LARGER COVERAGE OF
SHOWERS AND STORMS IS EXPECTED ACROSS THE REGION TONIGHT INTO
SATURDAY MORNING.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
&&

SHORT TERM...ECKSTEIN
LONG TERM...TDK
AVIATION...TDK

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