000
FXUS63 KOAX 172051
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
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

&&

.AVIATION...18Z TAFS FOR KOMA...KLNK...AND KOFK.

MAY SEE ELEVATED SHOWERS OR AN ISOLATED TSRA EAST OF THE TAF SITES
THROUGH EARLY THIS EVENING WITH HEATING DURING THE DAY...LINGERING
MOISTURE...AND A WEAK UPPER LEVEL WAVE.  THE FOCUS FOR CONVECTION
TONIGHT SHOULD BE ACROSS SOUTH DAKOTA IN THE VICINITY OF THE FRONT
AND THE AREA OF LOW PRESSURE. THERE IS A SECONDARY AREA OVER
PARTS OF KANSAS INTO CENTRAL NEBRASKA WITH THE RETURN OF DEEPER
MOISTURE. CONVECTIVE DEBRIS WILL LIKELY SPREAD INTO THE AREA
OVERNIGHT WITH VFR CIGS DEVELOPING. SOUTH WINDS 10 TO 14KTS
TODAY...SHOULD DECREASE TO UNDER 10KTS TONIGHT AND THEN INCREASE
AGAIN ABOVE 12KTS AFTER 15Z SATURDAY. THE LOW LEVEL JET WILL
INCREASE AT KOFK AND MAY NEED TO ADD TO THE TAF FORECAST. WILL
NEED TO WATCH LOW LEVEL MOISTURE RETURN FOR SATURDAY MORNING. DO
HAVE SOME MVFR VSBYS DESPITE THE CLOUD COVER AND COULD SEE SOME
MVFR CIGS TRY TO DEVELOP.

ZAPOTOCNY

&&

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

$$