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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KOAX 180425
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
1125 PM CDT FRI MAY 17 2013

.AVIATION...
-- Changed Discussion --
06Z TAFS FOR KOFK...KOMA AND KLNK.

ALTHOUGH THE BULK OF LOW LEVEL MOISTURE SPREADING FROM SOUTHERN
INTO NWRN KS SHOULD REMAIN TO THE WSW OF TAF SITES BY SATURDAY
MORNING...THERE STILL APPEARED A CHANCE LOWER CIGS COULD MOVE
TOWARD KOFK SATURDAY MORNING. THUS A TEMPO GROUP WAS MAINTAINED
FOR THAT SITE. THUNDERSTORMS WILL LIKELY INCREASE ACROSS CENTRAL
NEBR LATE SATURDAY AFTERNOON AND SPREAD TOWARD KOFK DURING THE
EVENING. ACTIVITY COULD MAKE IT TO KOMA AND KLNK SAT NIGHT...BUT
CHCS APPEARED TOO LOW TO INCLUDE MENTION BEFORE 19/06Z.

CHERMOK
-- End Changed Discussion --

&&

.PREV DISCUSSION... 
-- Changed Discussion --
/ISSUED 906 PM CDT FRI MAY 17 2013/

UPDATE...
UPDATED FORECAST TO INCLUDE SMALL TSTM POPS FAR NWRN ZONES.

DISCUSSION...

ALTHOUGH STRENGTH OF THE LEADING EDGE OF THE THUNDERSTORM COMPLEX
IN FAR NRN NEBRASKA APPEARED TO BE WEAKENING...OUTFLOW CONTINUES
MARCHING EWD. THUS ADDED SMALL POPS FAR NRN ZONES LATE THIS
EVENING/EARLY TONIGHT AND TRENDS WILL CONTINUE TO BE MONITORED.
STILL SOMEWHAT QUESTIONABLE ON HOW MUCH HOLDS TOGETHER IN OUR
FORECAST AREA AS BLYR STABILIZES SOMEWHAT WITH LOSS OF HEATING.
SHORT RANGE MODELS MIXED ON WHETHER OR NOT IT WILL...WITH LATEST
RAP/HRRR SAYING NO.
CHERMOK

PREV DISCUSSION... /ISSUED 351 PM CDT FRI MAY 17 2013/

DISCUSSION...
THE CHANCE FOR THUNDERSTORMS OVER THE WEEKEND IS THE PRIMARY
FORECAST CONCERN.

UPPER TROUGH IN THE WESTERN STATES WILL GRADUALLY MOVE INTO THE
ROCKIES ON SATURDAY...THEN EASE INTO THE PLAINS SUNDAY WHEN UPPER
LOW FORMS OVER NEBRASKA AND SOUTH DAKOTA. STRONG SOUTHWEST FLOW
AHEAD OF THIS SYSTEM WILL BRING INCREASING SHEAR PROFILES TO THE
PLAINS ON SATURDAY...THEN COLD POOL ALOFT WILL INCREASE LAPSE
RATES/INSTABILITY ON SUNDAY. AT THE SURFACE...LOWERING PRESSURE IN
THE LEE OF THE ROCKIES UNDER FAST FLOW ALOFT WILL INDUCE MOIST
SOUTHERLY FLOW FROM THE GULF INTO THE PLAINS SATURDAY...WITH THAT
SURFACE LOW MOVING INTO THE PLAINS AND OUR AREA ON SUNDAY.

BEST CHANCES FOR THUNDERSTORMS SATURDAY WILL RESIDE WEST OF OUR AREA
WHERE MOST ROBUST MOISTURE PROFILES WILL COINCIDE WITH STEEPENING
MID LEVEL LAPSE RATES AND INCREASING LOW LEVEL CONVERGENCE NORTHEAST
OF DEEPENING SURFACE LOW. WOULD EXPECT SEVERE STORMS WILL MOST
LIKELY BREAK OUT IN SOUTHWEST NEBRASKA AND NORTHWEST KANSAS
INITIALLY...BUT BROAD AREA OF INSTABILITY WILL OVERSPREAD CENTRAL
NEBRASKA DURING THE AFTERNOON AS WELL. SOME STORMS COULD FIRE IN
THIS ZONE AND WORK INTO OUR NORTHWEST CWA BEFORE 00Z. THEN AS
SURFACE LOW BEGINS TO SHIFT INTO THE PLAINS...LOW LEVEL JET AND
THETA-E CONVERGENCE SUGGESTS NORTHEAST NEBRASKA WILL LIKELY SEE
THUNDERSTORMS DURING THE EVENING...WITH AREA SPREADING EAST
OVERNIGHT ACROSS THE REST OF EASTERN NEBRASKA AND WESTERN IOWA.
ELEVATED INSTABILITY PROGS SUGGEST THE POTENTIAL FOR HAIL BUT SHEAR
PROFILES ARE MODEST AT BEST.

LINGERING SHOWERS/STORMS SUNDAY MORNING SHOULD MOVE EAST OF OUR
AREA...BUT REGENERATION OF STORMS IS LIKELY FROM LATE MORNING ON.
MODELS ARE HAVING A HARD TIME DEFINING EXACTLY WHERE SURFACE LOW
CENTER WILL SET UP...BUT GIVEN TRACK OF UPPER TROUGH/LOW THROUGH
WESTERN NEBRASKA...EXPECT SOME LOW LEVEL CIRCULATION TO SET UP
ACROSS CENTRAL OR NORTHEAST NEBRASKA. LAYER MOISTURE WILL STILL BE
ROBUST AS SURFACE DEW POINTS REMAIN IN THE 60S AND 850 DEW POINTS
HOVER IN THE 12-14C RANGE. ANY WARM AIR CAPPING STORM INITIATION
SHOULD BE QUICKLY ERODED WITH COLD AIR ALOFT SPREADING EAST. THIS
WILL LEAD TO MOST UNSTABLE CAPE VALUES WELL OVER 2000 J/KG WITH NEAR
ZERO CONVECTIVE INHIBITION. CAVEAT WILL BE REMNANT CLOUD COVER OR
SCATTERED SHOWERS/STORMS KEEPING TEMPERATURES FROM REACHING FORECAST
LEVELS IN THE LOW TO MID 80S. STILL EXPECT STRONG STORMS IN THE
AFTERNOON AND EVENING...ANY OF WHICH COULD PRODUCE HAIL OR STRONG
WINDS...BUT MOST LIKELY IN OUR SOUTHEAST HALF WHERE INSTABILITY IS
HIGHEST. WARM FRONT WILL ALSO ROTATE NORTH THROUGH THE CWA DURING
THE AFTERNOON...AND LOW LEVEL WIND SHEAR NEAR THIS BOUNDARY SUGGESTS
TORNADO THREAT IS POSSIBLE. WILL HAVE TO FINE TUNE THESE FACTORS
BEFORE PUTTING A MORE PRECISE TIME/LOCATION TO GREATEST SEVERE
RISK.

THUNDERSTORMS SHOULD ROTATE EAST AND NORTHEAST OUT OF THE CWA LATER
SUNDAY NIGHT...TAKING SEVERE THREAT WITH THEM. HOWEVER UPPER LOW
HANGING OUT JUST NORTH OF OUR AREA WILL KEEP SHOWER OR ISOLATED
THUNDER CHANCE IN THE FORECAST THROUGH THE MIDDLE OF THE WEEK BEFORE
PUSHING OFF TO THE NORTHEAST. COOLER TEMPERATURES WILL PREVAIL THEN
AS WELL...WITH HIGHS MAINLY IN THE 60S NORTH TO 70S SOUTH.

DERGAN
-- End Changed Discussion --

&&

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

$$

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