Severe Thunderstorm Warning 4, NWS Aberdeen, SD

AREA FORECAST DISCUSSION FOR CENTRAL/NORTHCENTRAL AND NORTHEAST
SOUTH DAKOTA AND WEST CENTRAL MINNESOTA
NATIONAL WEATHER SERVICE ABERDEEN SD
320 PM CDT FRI MAY 18 2001

PLENTY OF HEADACHES WITH THIS PACKAGE. FIRST IS TNGHT AND TSRA
CHANCES WEST CWA AND IF/HOW LONG THEY WOULD HOLD. DIURNAL CU FIELD
DVLPING WITH BASES AOA 8KFT...WITH >30 DEGREE T/TD SPREAD. NICE
CLOUD STREETS SHOWING INCREASING SOUTHERLY/WAA FLOW ACROSS CWA.
KBIS/KBLX 88DS SHOWING -SHRA ON THE SLOW INCREASE. KBIS NOW SHOWING
TSRA DVLPMENT AND NOT TOO SURPRISED GIVEN TROF LOCATION AND MOST
UNSTABLE THIS AREA PER LAPS/MSAS SFC ANALYSIS. RUC FCST SNDGS SHOW
THAT ISOLATED STORMS COULD BRING GUSTY WINDS WITH NICE INVERTED V
SOUNDINGS. BUT SVR THREAT MINIMAL GIVEN DEGREE OF INSTABILITY AND
STRENGTH OF TROF. FEEL ALL MDLS WAY OVERDONE ON QPF GIVEN SCANT
MOISTURE/INSTABILITY/VORT ENERGY. ONLY PLUSES TO ORAGANIZED SHRA
WOULD BE JET ENERGY AND WEAK UPPER DIVERGENCE SHOWN ON ETA/AVN. BUT
ONCE DARKNESS SETS IN...LITTLE/NO MOISTURE OR TEMP ADVECTION TO
SUSTAIN CONVECTION. SHOULD DECREASE SUBSTANTIALLY AFTER SUNSET.

BNDRY GLIDES EAST OVRNIGHT INTO SATURDAY...BUT ESSENTIALLY WASHES
OUT AS H5 VORT DAMPENS OUT. THIS CAUSES CONCERN AS ALL GUIDANCE
KEEPS CONVERGENCE LINE IN EAST CWA...WITH MOISTURE/INSTABILITY
POOLING ALONG IT.  VERY WEAK SFC-H7 WIND FIELDS CONTINUE...SO
NOTHING SUBSTANTIAL SHOULD HAPPEN. MENTIONED A SLIGHT POP FOR PM
SHOWER. MAYBE A PULSE T-STORM IN EAST SAT PM BUT WILL NOT MENTION
THUNDER. OTHR AREAS MILD AND P/C.

MAJOR CHANGE IN WX COMING SUN/MON. MARCH-LIKE SYSTEM WITH VERY
STRONG JET ENERGY DIGGING INTO TROF...CARVING OUT AND CLOSING UPPER
LOW ON SUNDAY. LIKE THE ETA TIMING...BUT THE AVN STRENGTH. BOTH MDLS
UNDERESTIMATING 150+KT JET SEEN IN ACARS DATA THIS MORNING IN PAC
OCEAN.  ETA SLOWER BY A BIT WHICH SEEMS BETTER WITH THE STRENGTH OF
SYSTEM...BUT I DO NORMALLY PREFER AVN EVOLUTION OF STRONG PAC JETS
CARVING CONUS TROFS.  EITHER WAY...WINDY AND COOLER ON SUNDAY WITH
FIRST COLD FRONT. IF IT SLOWS ENOUGH...COULD GET STRONG STORMS ON
COLD FRONT SUN AFTERNOON IN EAST CWA...AS HIGH THETA-E AIR ADVECTS
NORTHWARD ALONG/AHEAD OF FRONT. WEST CWA GETS VERY COOL AND
WINDY...WITH STEADY/FALLING TEMPS. 850 TEMPS/1000-850 THICKNESS
CRASH SUNDAY NIGHT...AS SECOND SURGE/VORT LOBE ROTATES THRU AREA.
TEMPS MONDAY LOOK SCARY. (850 TEMPS -3 TO -4).

MANY THANKS TO WFO BIS/FGF FOR COORDINATION.

BINAU

.EXTENDED DISCUSSION...
THERE ARE FEW DISAGREEMENTS IN THE EXTENDED MODELS THIS AFTERNOON
BUT OVERALL THEY DO HAVE SOME CONTINUITY. AFTER ANALYZING THE MODELS
AND THE ENSEMBLES A LITTLE MORE I DECIDED TO GO WITH THE AVN/MRF FOR
THE FORECAST PACKAGE. THE UPPER TROF AND ASSOCIATED SURFACE FRONT
WILL BE EXITING THE CWA ON MONDAY WITH AN UPPER RIDGE AND SURFACE
HIGH BUILDING OVER THE AREA TUESDAY THROUGH FRIDAY. THERE WILL BE
PLENTY OF MOISTURE AND LIFT TO CONTINUE THE CHANCE OF SHOWERS FOR
MONDAY. A FEW THUNDERSTORMS ARE ALSO POSSIBLE. BUT THE MAIN THREAT
OF SHOWERS WILL BE IN THE EAST. THE REST OF THE FORECAST PERIOD
SHOULD BE MOSTLY DRY. STRONG CAA ON MONDAY AND PARTIAL CLEARING
MONDAY NIGHT WILL BRING SOME VERY COLD TEMPERATURES FOR TUESDAY
MORNING. A SLOW WARMING TREND IS IN STORE FOR THE REST OF THE WEEK.
FOR THE TEMPS I TOOK A BLEND OF THE FMR AND MEX GUIDANCE.

SALMONS

.ABR...NONE.