Severe Thunderstorm Warning 229, NWS Hastings, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HASTINGS NE
702 PM CDT TUE JUN 17 2008

.AVIATION...00Z KGRI TAF. PRIMARY FORECAST CONCERN WILL CENTER
AROUND ONGOING THUNDERSTORMS OVER NORTH CENTRAL NEBRASKA AND THE
POTENTIAL OF THESE STORMS IMPACTING THE GRAND ISLAND AREA.
CURRENT STORM MOTION WOULD BRING THE HOLT COUNTY STORMS INTO THE
GRAND ISLAND VICINITY JUST AFTER 930 PM. HOWEVER...THERE IS A GOOD
DEAL OF UNCERTAINTY AS TO WHETHER OR NOT THESE STORMS CAN HOLD
TOGETHER THAT LONG. THE TREND HAS BEEN FOR NEW STORMS TO FORM OFF
TO THE WEST OF OLD DECAYING STORMS WHICH WOULD PUSH THE
THUNDERSTORM THREAT JUST TO THE NORTHWEST OF GRAND ISLAND. GIVEN
THE UNCERTAINTY...HAVE ADDED A TEMPO GROUP FOR THUNDERSTORMS AT
KGRI PRIMARILY BETWEEN 930 PM AND 1130 PM. WINDS SHOULD REMAIN OUT
OF THE SOUTH TO PERHAPS SOUTH SOUTHEAST THROUGHOUT THE TAF VALID
PERIOD.

&&

.PREV DISCUSSION... /ISSUED 325 PM CDT TUE JUN 17 2008/

SHORT TERM...TONIGHT THROUGH 12Z THURSDAY. OVERALL CONFIDENCE
DURING THE FORECAST PERIOD IS NOT VERY HIGH AS ANY SUBTLE
PERTURBATIONS IN THE NORTHWEST FLOW ALOFT COULD BE ENOUGH TO
TRIGGER A FEW SHOWERS AND THUNDERSTORMS. KUEX WSR-88D THIS
AFTERNOON HAS SHOWN THIS TO BE THE CASE TODAY AS PERIODIC ISOLATED
SHOWERS CONTINUE TO MOVE ACROSS THE FORECAST AREA. THESE APPEAR TO
BE ASSOCIATED WITH A COUPLE OF WEAK WAVES MOVING ACROSS THE REGION
THIS AFTERNOON. IN GENERAL...IT APPEARS THAT THESE SHOULD REMAIN
RATHER ISOLATED WITH THE FOCUS SHIFTING TO CONVECTION WHICH IS
EXPECTED TO DEVELOP ACROSS THE HIGH PLAINS. STORMS THAT DEVELOP
ACROSS THE HIGH PLAINS SHOULD TRAVEL SOUTH/SOUTHEAST FOLLOWING THE
CORFIDI VECTORS WHICH SHOW A MORE SOUTHERLY TRAJECTORY LATER
TONIGHT AS THE LOW LEVEL JET INCREASES ACROSS WESTERN KANSAS INTO
SOUTHWEST NEBRASKA. THE 18Z NAM SUGGESTS THAT THE WESTERN PORTION
OF THE FORECAST AREA COULD GET CLIPPED BY CONVECTION CURRENTLY
DEVELOPING OVER SOUTHWEST SOUTH DAKOTA WHICH SEEMS REASONABLE...SO
WILL GO WITH 30 POPS IN THE WEST...AND TAPER THEM TO 20S IN THE
EAST.

THINGS REMAIN DIFFICULT TO PIN DOWN ON WEDNESDAY...BUT THERE IS SOME
AGREEMENT AMONG THE 12Z GFS AND NAM IN THAT A H7 WAVE WILL MOVE
ACROSS THE AREA.  IT GENERALLY APPEARS THE AFTERNOON AND EVENING
WOULD BE THE FAVORED TIME FOR THE MORE WIDESPREAD ACTIVITY AND HAVE
TRENDED TOWARDS 40-50 POPS FOR WEDNESDAY NIGHT.  INSTABILITY
INCREASES DURING THE AFTERNOON WITH SBCAPES RISING TO 1500-2500 J/KG
WHILE 0-6KM SHEAR VALUES ARE FORECAST TO BE 35-45 KTS.  THIS SHOULD
BE SUFFICIENT FOR SOME SEVERE STORMS WITH THE MAIN HAZARDS EXPECTED
TO BE LARGE HAIL AND DAMAGING WINDS.

LONG TERM...12Z THURSDAY THROUGH TUESDAY. PRECIPITATION CHANCES
AND TEMPERATURES THROUGH THE PERIOD ARE THE MAIN FORECAST CONCERN.

EXPECTING PRECIPITATION TO BE ONGOING AT THE START OF THE
PERIOD...AS LATEST SHORTWAVE TROUGH PASSES OVER THE REGION.  MAIN
UPPER LEVEL JET CONTINUES TO BE RIGHT OVERHEAD...AND A 25-35KT LLJ
WORKING ALONG WITH A WEAK SURFACE BOUNDARY WILL HELP IN KEEPING
PRECIPITATION GOING DURING THE MORNING HOURS. CONFIDENCE IN TIMING
THE END OF THE PRECIPITATION NOT REAL HIGH...AS THERE CONTINUE TO
BE SLIGHT DIFFERENCES BETWEEN MODELS WITH FEATURE DETAILS. THE
NAM/GFS IS A BIT QUICKER/FURTHER SOUTH WITH FEATURES/PRECIP BY 12Z
THURSDAY...THUS HAS PRECIPITATION ENDING SOONER...WITH THE ECMWF A
BIT SLOWER PUSHING THE SYSTEM TO THE SOUTHEAST. FORECAST IS A
BLEND...KEPT HIGHEST POPS DURING THE 12-18Z TIMEFRAME WITH A
GRADUAL TAPERING OFF OF PRECIPITATION INTO THE NIGHTTIME HOURS. AM
CONCERNED ABOUT HIGHS FOR THURSDAY...IF EVENT ENDS UP LIKE THE
ECMWF SOLUTION WITH LINGERING CLOUDS/PRECIP...TEMPERATURES WOULD
LIKELY BE A BIT COOLER THAN THE CURRENT FORECAST OF UPPER
70S/LOWER 80S. BUT WAS HESITANT TO DROP TOO MUCH...AS A QUICKER
EXIT WOULD GIVE MORE TIME FOR TEMPERATURES TO WARM BACK UP.

LOOKING TO FRIDAY THROUGH SATURDAY NIGHT...NO SIGNIFICANT CHANGES IN
OVERALL PATTERN EXPECTED...AND MODELS IN GOOD AGREEMENT.  UPPER
LEVEL TROUGH REMAINS OVER THE MIDWEST/EAST COAST REGION WITH RIDGING
OVER THE ROCKIES...LEAVING THE CENTRAL PLAINS UNDER NORTHWESTERLY
FLOW.  WEAK DISTURBANCES LOOK TO CONTINUE PASSING THROUGH THE
FLOW...AND THE MAIN UPPER LEVEL JET/ASSOCIATED STREAKS REMAIN
OVERHEAD.  WORKING ALONG WITH WEAK UPSLOPE FLOW OVER THE HIGH
PLAINS...LATE AFTERNOON/NIGHT TIME SHOWERS AND THUNDERSTORMS AGAIN A
POSSIBILITY.  CONFIDENCE IS NOT HIGH...AND SO KEPT POPS LOW...AS IT
IS VERY DIFFICULT TO PIN DOWN SPECIFICS WITH TIMING AND LOCATION OF
THESE MID/UPPER LEVEL WAVES AND WHERE ASSOCIATED PRECIPITATION WILL
DEVELOP. DO EXPECT MOST OF THE DAYTIME HOURS TO BE DRY...ALLOWING
FOR HIGHS BY SATURDAY TO REACH INTO THE MID/UPPER 80S.

FOR THE END OF THE WEEKEND AND INTO EARLY NEXT WEEK...KEPT DRY
CONDITIONS GOING.  AGAIN NO BIG CHANGES IN THE OVERALL
PATTERN...KEEPING THE REGION UNDER THE INFLUENCE OF THE WESTERN
RIDGE.  ENERGY FROM A LARGE UPPER LEVEL LOW PRESSURE SYSTEM OVER THE
GULF OF ALASKA WILL MOVE CLOSER TO THE PAC NW REGION...SHIFTING THE
RIDGE AXIS EAST OVER THE CENTRAL PLAINS.  MODELS HINT AT MORE
CHANCES OF PRECIP FROM MORE MID/UPPER LEVEL WAVES AND UPSLOPE
FLOW...BUT FEEL BEST CHANCES WILL BE TO OUR NORTH.  AS THE RIDGE
AXIS SHIFTS EAST...SO WILL WARMER AIR...WITH HIGH TEMPERATURES BY
TUESDAY EXPECTED TO REACH NEAR 90 DEGREES ACROSS THE ENTIRE CWA.

&&

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

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