Severe Thunderstorm Warning 87, NWS Omaha, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
631 AM CDT WED MAY 29 2013

.AVIATION...12Z TAFS FOR KOMA...KLNK AND KOFK.

CONVECTIVE CHANCES AND TIMING ARE THE MAIN CONCERNS TODAY. A WARM
FRONT HAS LIFTED NORTH OF THE TAF SITES WITH SOUTHEAST BREEZY
CONDITIONS EXPECTED THROUGH THE PERIOD. UPPER LEVEL DIFFLUENCE
ALONG WITH A MOIST ATMOSPHERE HAS ALLOWED SCATTERED SHOWERS TO
DEVELOP EARLY THIS MORNING...WITH POTENTIAL FOR THUNDER AT KLNK
THROUGH ABOUT 14Z. OPTED TO FORECAST VCSH AT KOMA THIS MORNING. AS
WE HEAD INTO THE AFTERNOON...CONVECTION POTENTIAL INCREASES WITH
40 TO 60 PERCENT CHANCE OF STORMS AT ALL 3 TAF SITES. COULD SEE
ADDITIONAL THUNDERSTORMS LATER IN THE PERIOD AS WELL AS ACTIVITY
FROM THE WESTERN HIGH PLAINS REACHES THE REGION. REGARDING
WINDS...SHOULD SEE WINDS INCREASE TO 15 TO 21 KNOTS SUSTAINED
FROM ABOUT 150-170 DEGREES...WITH GUSTS UP TO 25 TO 31 KNOTS
THROUGH THE AFTERNOON.

&&

.HYDROLOGY...

RIVER FLOOD WARNINGS CONTINUE FOR THE MISSOURI RIVER FROM PLATTSMOUTH
DOWNSTREAM TO RULO...WITH LEVELS CONTINUING TO SLOWLY RISE. ON THE
LITTLE SIOUX RIVER AT TURIN...A TEMPORARY CREST WAS NOTED YESTERDAY
EVENING AND IT HAS FALLEN BELOW FLOOD STAGE. WILL LEAVE THE
WARNING IN PLACE AND WILL WAIT FOR THE NEW RFC FORECAST LATER THIS
MORNING BEFORE MAKING ADJUSTMENTS.

&&

.PREV DISCUSSION... /ISSUED 416 AM CDT WED MAY 29 2013/

DISCUSSION...
SHORT TERM FORECAST CONCERNS WILL BE THUNDERSTORM CHANCES THROUGH
ESPECIALLY THURSDAY AFTERNOON AND POTENTIAL FOR SEVERE WEATHER
ALONG WITH HEAVY RAIN/FLASH FLOOD WATCH.

AT 06Z...THE FORECAST AREA WAS IN-BETWEEN CONVECTIVE
COMPLEXES...WITH ONE TRACKING ACROSS SOUTHERN IOWA/NORTHERN MISSOURI
AND ANOTHER ACROSS WESTERN NEBRASKA.  THE 00Z SOUNDING SHOWED A
MARKED DECREASE IN PRECIPITABLE WATER COMPARED TO THE LAST SEVERAL
DAYS WITH ONLY 0.68 INCHES.  THERE WAS SOME CAPE OF 1132J/KG...BUT
ALSO DECENT CIN OF -162J/KG.  LOW LEVEL SHEAR WAS NIL...AND THE SFC-
6KM MEAN WIND WAS ONLY 4KTS. THIS WAS IN SHARP CONTRAST TO KTOP/S
SOUNDING WHICH HAD PW OF 1.46 AND CAPE OF NEARLY 4300J/KG...NO CIN
AND DECENT 0-1KM SRH OF 157M2/S2.

THE 00Z UPPER AIR MAPS HAVE SOME SHORTWAVE TROF ENERGY PASSING
THROUGH...WITH THE MAIN H5 LONGWAVE TROF FROM IDAHO THROUGH
UTAH...AND ARIZONA. ONE H3 JET STREAK WAS OVER IOWA AND SOUTHERN
WI...WITH A SEASONABLY STRONG JET NOSING ACROSS NORTHERN CALIFORNIA
INTO NEVADA.

THIS MORNING...THE SURFACE WARM FRONT HAD LIFTED NORTH OF COLUMBUS
AND TEKAMAH. TODAY...SURFACE LOW PRESSURE OVER EASTERN COLORADO
WILL CONTINUE TO DEEPEN. THROUGH THURSDAY AFTERNOON...THE
FORECAST AREA WILL BE IN A FAVORABLE LOCATION FOR THUNDERSTORM
DEVELOPMENT. HEIGHT FALLS ASSOCIATED WITH THE H5 TROF OVER THE
ROCKIES WILL SHIFT INTO THE PLAINS THIS AFTERNOON. DEEP MOISTURE
IS OCCURRING THIS MORNING. BUFKIT FORECAST SOUNDINGS HAVE SOME
ELEVATED INSTABILITY THIS MORNING AND THE MODELS REDUCE THE
INHIBITION BY LUNCHTIME TO BECOME MORE SURFACE BASED. BROAD AREA
OF MID LEVEL WARM AIR ADVECTION AND LARGE SCALE LIFT IS OCCURRING
..LEADING TO STRONGLY FORCED ASCENT THIS AFTERNOON AND TONIGHT.
SHOULD SEE SOME SCATTERED THUNDERSTORM ACTIVITY THROUGH THE
AFTERNOON...HOWEVER THE TREND WILL BE FOR THE MORE ORGANIZED
CONVECTION DURING THE 00Z-18Z TIME PERIOD THEN GRADUALLY SHIFTING
EAST THURSDAY.

THE MODERATE RISK HAS BEEN SHIFTED WESTWARD...MAINLY FROM PARTS
OF OKLAHOMA INTO WESTERN KANSAS. THIS IS CLOSER TO THE
DRYLINE...WHERE THE BETTER DESTABILIZATION IS FORECAST AND AND
WHERE THE LOW LEVEL AND DEEP LAYER SHEAR WILL BE STRONGER. IN
ADDITION TO THE POTENTIAL FOR SEVERE STORMS DURING THIS PERIOD.
LOCALLY HEAVY RAIN IS POSSIBLE WITH ANY OF THE STORMS AND THE
STORM MOTIONS WILL BECOME PARALLEL TO THE UPPER LEVEL FLOW AND
STORMS MAY TRAIN OVER THE SAME AREA.  THE HIGHER CONFIDENCE IS
AFTER 00Z...THUS WILL HOLD OFF ON A FLASH FLOOD WATCH AND WILL
PASS ON TO THE DAY SHIFT AND INCLUDE IN THE HWO.

THE TROF BECOMES MORE NEGATIVELY TILTED...MOVES INTO WYOMING AND
COLORADO...TOWARD MT AND THE DAKOTAS AND WESTERN PLAINS BY 12Z
THURSDAY...CLOSING OFF OVER THE WESTERN DAKOTAS THURSDAY AND
THURSDAY NIGHT. DEEP MOISTURE WILL REMAIN IN PLACE 18Z
THURSDAY...HOWEVER DRYING WILL TAKE PLACE FROM WEST TO EAST DURING
THURSDAY AFTERNOON...THUS WILL TREND POPS LOWER FROM WEST TO EAST.
THE STORM SYSTEM SITS OVER THE NORTHERN PLAINS THROUGH FRIDAY
NIGHT...AND THEN OPENS UP AND MOVES THROUGH THE OUTLOOK AREA
SATURDAY. WITH COLD AIR ALOFT AND SOME LINGERING MOISTURE CONTINUE
THE SHOWER AND THUNDERSTORM CHANCES INTO FRIDAY...THEN DECREASING
FURTHER FOR SATURDAY.

ZAPOTOCNY

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&

DEWALD

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