Severe Thunderstorm Warning 221, NWS Hastings, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HASTINGS NE
638 AM CDT SUN JUN 15 2008

.AVIATION...12Z TAF. PERIODIC MVFR CONDITIONS POSSIBLE AT THE KGRI
TERMINAL THIS MORNING...WITH VFR CONDITIONS EXPECTED LATER TODAY
THROUGH EARLY MONDAY. CONVECTION CURRENTLY FIRING NORTHEAST OF KGRI
IS SHOWING SIGNS OF SPREADING SOUTHWESTWARD. THUNDERSTORMS WILL BE
POSSIBLE WITH CLOUD BASES NEAR 2000 FT AGL THROUGH MID TO LATE
MORNING. CONVECTION WILL PUSH EASTWARD LATER IN THE DAY...LEAVING
BEHIND CEILINGS NEAR 6000 FT AGL. SURFACE WINDS WILL BE VARIABLE
EARLY...PREVAILING FROM THE NORTHEAST MIDDAY THROUGH EARLY MONDAY.

&

.PREV DISCUSSION... /ISSUED 316 AM CDT SUN JUN 15 2008/

DISCUSSION...MAIN CONCERN FOR THIS FORECAST WILL BE THE CHANCE OF
THUNDERSTORMS TODAY.  EARLY MORNING RADAR MOSAIC SHOWS A FEW LIGHT
RETURNS ACROSS NORTHERN NEBRASKA...BUT MUCH OF THOSE RETURNS ARE MID
LEVEL CLOUDS WITH LITTLE PRECIPITATION ACTUALLY REACHING THE GROUND.
EARLY MORNING SURFACE ANALYSIS PLACED A FRONTAL BOUNDARY FROM
NORTHWEST IOWA INTO SOUTHWEST NEBRASKA.  THIS FEATURE WILL BE THE
PRIMARY FOCUS FOR THUNDERSTORMS TODAY AS IT SHIFTS SOUTH THROUGH THE
DAY.  THE 00Z NAM/WRF AND GFS ARE RELATIVELY SIMILAR IN THAT THEY
FOCUS THE BEST THUNDERSTORM CHANCES ACROSS THE EAST AND SOUTH
PORTIONS OF THE FORECAST AREA.  IT APPEARS THAT THE THUNDERSTORMS
WILL FIRE RELATIVELY EARLY TODAY AS A SHORTWAVE CURRENTLY OVER THE
HIGH PLAINS SHIFTS EAST ALONG WITH THE LEFT FRONT QUADRANT OF THE
UPPER JET.  INSTABILITY INCREASES RAPIDLY THIS MORNING WITH SBCAPES
OF 2000-3000 J/KG BY MID MORNING.  DEEP LAYER SHEAR (0-6KM) IS
EXPECTED TO BE 30-35 KTS WHICH SHOULD BE SUFFICIENT FOR THE STORMS
TO ORGANIZE AND BECOME LARGE HAIL PRODUCERS.  0-1KM HELICITY REMAINS
LOW WHICH SHOULD MINIMIZE THE TORNADO THREAT...THOUGH ANY TIME
STORMS DEVELOP NEAR/ALONG A BOUNDARY THEY CAN SOMETIMES FIND
SUFFICIENT LOCALIZED LOW LEVEL SHEAR.

AS THE CONVECTION CONTINUES THIS AFTERNOON INTO THE EVENING...IT
APPEARS IT WILL ORGANIZE INTO A SEVERE MCS WITH THE THE THREAT OF
DAMAGING WINDS INCREASING.  THE SOUTHERN PORTION OF THE CWA MAY NOT
BE COMPLETELY CLEARED OF CONVECTION AS THIS HAPPENS...BUT GENERALLY
EXPECT THE MORE WIDESPREAD DAMAGING WIND THREAT WILL EXIST SOUTHEAST
OF THE FORECAST AREA AS THE MCS TRAVELS SOUTH THIS EVENING.

THE BOUNDARY SHIFTS SOUTH OF THE FORECAST AREA BY THIS EVENING...AND
OUTSIDE OF A SLIGHT CHANCE POP IN THE FAR SOUTH...WILL GO DRY. STILL
HAVE SOME CONCERN ABOUT MID-LEVEL FRONTOGENESIS DURING THE
NIGHT...BUT IT APPEARS TO REMAIN WEST OF THE FORECAST AREA TONIGHT.
THE MID-LEVEL FRONTOGENESIS SHIFTS EAST ON MONDAY...BUT LOW LEVEL
MOISTURE IS LIMITED SO HAVE LEFT IT DRY. IF ANYTHING DOES DEVELOP
IT SHOULD BE FAIRLY ISOLATED...AND THINK IT WILL PROBABLY BE
PRIMARILY A VIRGA EVENT. LATER MONDAY NIGHT CONVECTION OVER THE
HIGH PLAINS SHOULD EVENTUALLY SHIFT EAST INTO THE LOW LEVEL JET
AXIS. THIS ACTIVITY MAY GRADUALLY SHIFT INTO WESTERN PORTIONS OF
THE FORECAST AREA TOWARDS TUESDAY MORNING...THOUGH CONFIDENCE IN
HOW FAR EAST IT WILL GET IS NOT VERY HIGH.

AVIATION...06Z KGRI TAF. VFR CONDITIONS EXPECTED. MODELS ARE
INDICATING ISOLATED -TSRA IN THE AREA TOWARD DAWN AS A COLD FRONT
MOVES INTO THE AREA...BUT CHANCES SEEM QUITE LOW AND HAVE NOT
INCLUDED IN THE FORECAST. CEILING COULD DROP POSSIBLY DOWN TO
MVFR...KEPT CEILINGS ABOVE THIS AS MOISTURE IS A BIT LIMITED. ALSO
COULD BE SOME TSRA DEVELOPMENT SUNDAY AFTERNOON/EARLY EVENING...BUT
THIS APPEARS TO BE WELL SOUTHEAST OF KGRI AND HAVE KEPT THIS OUT
OF THE FORECAST AS WELL.

&&

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

&&

AVIATION...BRYANT

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