Severe Thunderstorm Warning 196, NWS Hastings, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HASTINGS NE
609 PM CDT TUE JUN 10 2008

.AVIATION...MAIN ISSUES FOR THE 00Z TAF ARE THE CHANCE OF
THUNDERSTORMS AND STRATUS. APPEARS MVFR CELINGS WILL TRY TO
DEVELOP LATE TONIGHT AS MOISTURE INCREASES ACROSS THE REGION ON
SOUTHEASTERLY WINDS. THERE IS SOME CHANCE THAT EVEN LOWER CELINGS
COULD TRY TO DEVELOP...BUT FOR NOW DECIDED TO WAIT AND SEE HOW
THINGS PROGRESS BEFORE GOING INTO THE IFR CATEGORY. ISOLATED
THUNDERSTORMS ARE ALSO POSSIBLE TONIGHT...BUT AGAIN THE ODDS OF
ONE REACHING THE KGRI TERMINAL LOCATION APPEAR LOW ENOUGH TO LEAVE
IT OUT AT THE MOMENT. THE NEXT BETTER CHANCE OF THUNDERSTORMS
SHOULD ARRIVE JUST AFTER THIS TAF VALID PERIOD.

&&

.PREV DISCUSSION... /ISSUED 313 PM CDT TUE JUN 10 2008/

SHORT TERM...LATEST WATER VAPOR IMAGERY SHOWS A POTENT UPPER WAVE
DIGGING EAST TO SOUTHEAST ACROSS THE PACIFIC NORTHWEST WHILE
DOWNSTREAM A WEAK RIDGE IS IN PLACE ACROSS THE CENTRAL TO NORTHERN
HIGH PLAINS.  ROUNDING THE BASE OF THE TROUGH IS A 120 TO 130 KT
UPPER JET STREAK WHICH WILL BEGIN TO ACT AS A CATALYST FOR
THUNDERSTORM DEVELOPMENT LATER TONIGHT AND AGAIN ON WEDNESDAY.
RECENT OBJECTIVE SURFACE ANALYSIS SHOWS A DEEPENING AREA OF LOW
PRESSURE ACROSS SOUTHEAST WYOMING WITH A WARM FRONT SEEN EXTENDING
EAST ALONG THE NEBRASKA...SOUTH DAKOTA BORDER WHILE A DRYLINE IS
SHOWN STRETCHING FROM NEAR THE BLACK HILLS REGION SOUTHWARD ACROSS
WESTERN NEBRASKA AND KANSAS. EAST OF THIS DRYLINE...ML CAPES OF
1500 TO 2500 J/KG ARE ALREADY SEEN ACROSS WESTERN KANSAS AND
NEBRASKA ALTHOUGH STRONG INHIBITION IS KEEPING THE ATMOSPHERE
CAPPED THIS MID AFTERNOON.

MAIN QUESTION AS THE AREA HEADS INTO THE EVENING HOURS IS IF ANY
CONVECTION CAN DEVELOP ALONG THE DRYLINE DESPITE THE MAIN MID TO
UPPER FORCING FROM THIS WAVE REMAINING WELL TO THE NORTHWEST OF THE
REGION.  WITH THE DRYLINE SHOWN TO RETREAT TO THE WEST BY MID
EVENING...THE WINDOW FOR CONVECTION TO FIRE WILL BE SMALL.  STILL
NOT REAL CONFIDENT ANY CONVECTION WILL DEVELOP NEAR OR IN THE GID
CWA...BUT WITH STEEP LOW LEVEL LAPSE RATES ALREADY IN PLACE AND
INHIBITION SHOWN TO WEAKEN...CAN/T RULE OUT ONE OR TWO ISOLATED
THUNDERSTORMS MOVING INTO/ACROSS THE CWA THIS EVENING.  ANY
CONVECTION THAT WOULD MOVE ACROSS THE CWA WOULD HAVE THE POTENTIAL
TO BE STRONG TO SEVERE GIVEN EFFECTIVE BULK SHEAR VALUES IN EXCESS
OF 40 KNOTS ALLOWING FOR SOME CELL ROTATION.  THE FOCUS FOR
ADDITIONAL CONVECTION FOR THE REMAINDER OF TONIGHT THEN SHIFTS INTO
AN ELEVATED MODE AS A 60 TO 70 KT LLJ IS SHOWN TO DEVELOP ACROSS THE
REGION.  WHILE THE BEST CHANCE FOR ELEVATED NOCTURNAL CONVECTION
SHOULD BE CLOSER TO THE NOSE OF THE JET ACROSS SOUTHERN SOUTH DAKOTA
INTO NORTHEAST NEBRASKA...CAN/T RULE OUT A STRAY THUNDERSTORM OR TWO
DEVELOPING WITHIN THE JET AXIS DURING THE OVERNIGHT HOURS BEFORE THE
JET AXIS SLIPS EAST INTO THE MISSOURI VALLEY REGION BY 12Z.  THE
FINAL ISSUE TO RESOLVE FOR TONIGHT REVOLVES AROUND THE TIGHT
PRESSURE GRADIENT AHEAD OF THE AREA OF LOW PRESSURE AND IF WINDS MAY
FLIRT WITH WIND ADVISORY CRITERIA. BUFKIT MOMENTUM TRANSFER DOES
SHOW MIXING POTENTIAL AT THE 10 M LEVEL RESULTING IN MEAN LAYER
WINDS OVER 30 KNOTS. HOWEVER...FEEL BOUNDARY LAYER WILL DECOUPLE
ENOUGH TO KEEP SPEEDS BELOW 30 MPH AND WILL NOT PUT OUT A WIND
ADVISORY.

WEDNESDAY INTO WEDNESDAY NIGHT ARE SHAPING UP TO A BE ANOTHER ACTIVE
CONVECTIVE PERIOD ACROSS PORTIONS OF THE CWA AS THE PAC NW UPPER
WAVE PLOWS EASTWARD INTO THE NORTHERN PLAINS.  IN RESPONSE TO THIS
WAVE...A COLD FRONT WILL PUSH SOUTHEAST ACROSS THE CWA DURING THE
MORNING HOURS BEFORE NEARLY STALLING ALONG A YORK TO RED CLOUD TO
OSBORNE LINE.  AHEAD OF THIS FRONT...DEEP BOUNDARY LAYER MOISTURE
WILL RESULT IN HIGH TO EXTREME ML CAPES OF 3000 TO 4000 J/KG. THIS
ALONG WITH WEAK INHIBITION AND LARGE SCALE ASCENT SHOULD ALLOW
CONVECTION TO DEVELOP ALONG AND SOUTH OF THE FRONT DURING THE MID
AFTERNOON TO MID EVENING.  WITH EFFECTIVE BULK SHEAR IN EXCESS OF 40
KNOTS...ANY STORMS THAT DO DEVELOP SHOULD RAPIDLY BECOME SEVERE WITH
LARGE HAIL AND DAMAGING WINDS THE MAIN HAZARDS.  ALTHOUGH THE BEST
ENVIRONMENT FOR TORNADOES SHOULD EXIST OVER IOWA INTO EASTERN
NEBRASKA...SIG TOR VALUES DO INCREASE TO ABOVE 3 DURING THE MID
EVENING HOURS IN RESPONSE TO THE DEVELOPMENT OF A LLJ. BASED ON
THIS...CAN/T RULE OUT ONE OR TWO ISOLATED TORNADOES AS WELL.  THE
BIGGER ISSUE AS THE EVENING PROGRESSES WILL BE THE POTENTIAL FOR
FLASH FLOODING AS THE CONVECTION EVOLVES INTO ONE OR TWO LARGE
CONVECTIVE SYSTEMS.  WITH HIGH PW VALUES AND DIFFLUENT 850-300MB
THICKNESS SHOWN...THE ENVIRONMENT WILL BE PRIMED FOR BACK BUILDING
CONVECTION PRODUCING VERY HIGH RAINFALL RATES.  WILL HOLD OFF ON
ISSUING A THIRD PERIOD FLOOD WATCH...BUT THIS WILL HAVE TO BE
WATCHED VERY CLOSELY OVER THE NEXT 24 HOURS.

LONG TERM...12Z THURSDAY THROUGH TUESDAY. THURSDAY WILL BE
BEGIN WITH THE CWFA IN THE WAKE OF A RAIN PRODUCING FRONT FROM
THE EVENING BEFORE. TRENDS SUGGEST THE FRONT WILL BE SOUTHEAST
OF THE CWFA BY DAWN...BUT SOME LINGERING SHOWERS COULD BE FOUND
IN THE SOUTHEAST CWFA. SOME ADDITIONAL LIFT AROUND THE UPPER LEVEL
LOW TO THE NORTH...MAY MOVE IN LATE IN THE DAY THURSDAY AND BRING
SOME SPRINKLES. WILL SEE WHAT TRENDS DEVELOP WITH THIS BEFORE
ADDING ANY SMALL POPS IN THE LATE AFTERNOON/EVENING.

BOTH FRIDAY AND SATURDAY LOOK DRY AND PRETTY NICE WITH SOMEWHAT
DRIER AIR AND THE CWFA IN BETWEEN SYSTEMS. MOISTURE WILL BE FLOWING
NORTH AHEAD OF THAT NEXT SYSTEM...WHICH SEEMS TO BE TIMED OUT AROUND
SUNDAY EVENING. UPPER SUPPORT IS MORE OF A GLANCING NORTHWEST FLOW
WAVE...SO THAT WARRANTS SMALLISH PRECIPITATION CHANCES AT THIS
TIME. SURFACE HIGH PRESSURE BUILDS INTO THE AREA MONDAY/TUESDAY
WITH TEMPERATURES NEAR OR JUST SLIGHTLY BELOW NORMAL. FORECAST HIGH
POSITION WOULD GENERALLY KEEP PRECIPITATION CLOSER TO THE FRONT
RANGE. REMOP ALONG WITH OPERATIONAL MODELS SUGGEST UPPER RIDGING
WILL MOVE OVERHEAD SUGGESTING MORE DRY WEATHER THROUGH MID NEXT
WEEK.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&

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