Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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792
FXUS63 KOAX 152333
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
633 PM CDT FRI MAY 15 2015

.SHORT TERM...(TONIGHT THROUGH MONDAY)
ISSUED AT 322 PM CDT FRI MAY 15 2015

POTENTIAL FOR SEVERE STORMS THROUGH SATURDAY IS THE PRIMARY FORECAST
CONCERN.

A FEW STORMS THIS MORNING GOT BRIEFLY STRONG AS LAST GASP EFFORT OF
DYING LOW LEVEL JET RODE OVER WARM FRONT TO OUR SOUTH. NOW A NEW ARC
OF STORMS WAS TRACKING NORTHEAST THROUGH THE AREA AIDED BY SHORTWAVE
IN MID LEVEL FLOW. THESE STORMS WERE RELATIVELY WEAK...BUT SEEM TO
BE EFFICIENT RAIN-PRODUCERS. HOWEVER THEY WERE PROGRESSIVE SO NO
MAJOR FLOODING CONCERNS AS OF NOW. MORNING AND EARLY AFTERNOON
CONVECTION HAS KEPT INSTABILITY IN CHECK ACROSS MOST OF EASTERN
NEBRASKA AND WESTERN IOWA. BUT JUST TO OUR WEST WHERE CLOUDS HAVE
CLEARED SURFACE-BASED CAPES WERE TOPPING 2000 J/KG. THIS COUPLED
WITH STEEP MID LEVEL LAPSE RATES OVERSPREADING WESTERN
NEBRASKA...EXPECT SEVERE STORMS TO GET GOING THERE THIS AFTERNOON.
SOME CONCERN STORMS MAY FIRE AS FAR EAST AS CENTRAL NEBRASKA WHERE
CONVERGENCE ALONG WARM FRONT IS MAXIMIZED AND PLENTY OF INSOLATION
HAS OCCURRED. A SMATTERING OF CONVECTION-ALLOWING MODEL OUTPUT
SUGGESTS THIS SCENARIO MAY OCCUR...AND IF IT DOES WILL TRACK
NORTHEAST WITH WARM FRONT THROUGH THE CWA. THUS WILL MAINTAIN A
CHANCE FOR STORMS INTO THE EVENING BEFORE WARM FRONT LIFTS NORTH OF
OUR CWA LATE TONIGHT. SEVERE RISK SHOULD BE MINIMAL AFTER DARK...BUT
STRENGTHENING LOW LEVEL JET MAY POSE A RISK OF STRONG STORMS.

DURING THE DAY SATURDAY...MORNING CONVECTION SHOULD BE LIFTING OUT
OF OUR AREA. WHAT IS LEFT BEHIND IS STILL IN QUESTION AS A MAJORITY
OF MODEL OUTPUT SUGGESTS CLOUDS/SHOWERS MAY LINGER FOR MUCH OF THE
MORNING OR INTO THE AFTERNOON. THUS INSTABILITY WILL BE TOUGH TO
JUDGE AT ANY GIVEN TIME. HOWEVER...WHILE RISK OF STORMS IS MINIMAL
THROUGH THE DAY...FEEL BREAKS IN CLOUDS AND PERSISTENT MOISTENING OF
LOW LEVELS WILL LEAD TO POCKETS OF HIGH INSTABILITY LATE IN THE
AFTERNOON AND EVENING. DIFFLUENT FLOW ALOFT AHEAD OF EJECTING UPPER
LOW AND STRONG MID LEVEL FLOW WILL RESULT IN STRONG BULK SHEAR NEAR
40KT OVERSPREADING INSTABILITY. FOCUS FOR INITIATION SHOULD COME WITH
COLD FRONT/DRYLINE...WITH A CONSENSUS FORECAST SUGGESTING CENTRAL
NEBRASKA INTO KANSAS WILL SEE THE FIRST ECHOES IN THE MID TO LATE
AFTERNOON. STORMS SHOULD PROGRESS EAST THROUGH THE EVENING AND SWING
EAST OF OUR CWA LATER SATURDAY NIGHT. GIVEN INSTABILITY AND SHEAR
PARAMETERS...ANY STORMS WILL HAVE THE POTENTIAL FOR HAIL AND
DAMAGING WINDS WELL INTO THE EVENING AS STRENGTHENING LOW LEVEL JET
MAINTAINS STORMS. TORNADO RISK WILL ALSO HAVE TO BE WATCHED AS
REMNANT BOUNDARIES FROM MORNING CONVECTION OR DIFFERENTIAL HEATING
WILL ENHANCE LOW LEVEL HELICITY IN A BACKDROP OF ALREADY-SOMEWHAT-
FAVORABLE SHEAR ENVIRONMENT.

BY SUNDAY...MAIN UPPER LOW SHOULD BE EJECTING NORTHEAST INTO THE
NORTHERN PLAINS WITH ANOTHER SHORTWAVE ROTATING ALONG IS SOUTHERN
FLANK. COULD SEE SOME MORNING CONVECTION IN OUR EAST BEFORE MOVING
OUT BY NOON...THEN A FEW INSTABILITY SHOWERS ARE POSSIBLE NEAR THIS
SHORTWAVE IN THE AFTERNOON. SOUTHWEST SURFACE FLOW AND SUNSHINE WILL
HELP TEMPERATURES RECOVER INTO THE 70S IF NOT LOWER 80S OVER MUCH OF
THE SOUTHERN TWO-THIRDS OF THE CWA.

MUCH COOLER WEATHER IS ON TAP FOR THE BEGINNING OF THE WORK WEEK AS
STRONG COLD ADVECTION KICKS IN SUNDAY EVENING. IN FACT NEGATIVE 850
TEMPERATURES ARE FORECAST IN OUR NORTHERN CWA BY NOON MONDAY. LOOKS
LIKE A BREEZY...MOSTLY CLOUDY AND COOL DAY. HIGHS MAY NOT CLIMB OUT
OF THE 50S MANY AREAS.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 322 PM CDT FRI MAY 15 2015

A RELATIVELY COOL PERIOD WILL CONTINUE INTO THE WORK WEEK BEFORE THE
ATMOSPHERE RELOADS FOR POTENTIAL THUNDERSTORMS LATER IN THE WEEK.
COOL ADVECTION ON BACK SIDE OF EXITING MID LEVEL LOW PRESSURE AREA
WILL KEEP TEMPERATURES BELOW NORMAL INTO WEDNESDAY. COOL HIGH
PRESSURE WILL PUSH LOWS TO NEAR 40 TUESDAY MORNING...THEN ONLY
REBOUNDING INTO THE LOWER 60S TUESDAY AFTERNOON. AS ANOTHER LOW MID
LEVEL LOW SETTLES INTO THE SOUTHWESTERN STATES...RIPPLES OF ENERGY
RIDING INTO THE PLAINS ON SOUTHWEST FLOW ALOFT WILL BRING SPORADIC
RAIN CHANCES TO THE PLAINS. THE FIRST WILL BE WEDNESDAY WHEN GFS AND
ECMWF SUGGEST A GOOD CHANCE FOR RAIN AND ISOLATED THUNDERSTORMS.
THIS WILL PREVENT TEMPERATURES FROM RISING OUT OF THE 50S FOR THE
MOST PART. A LITTLE WARMER BEHIND THIS WAVE FOR THURSDAY AND
FRIDAY...BUT PERSISTENT EASTERLY LOW LEVEL WIND COMPONENT SHOULD
KEEP HIGHS IN THE 60S OR LOWER 70S.

&&

.AVIATION...(00Z TAFS FOR KOFK...KLNK AND KOMA.)
ISSUED AT 625 PM CDT FRI MAY 15 2015

LOW END VFR CIGS ARE QUICKLY DISSIPATING OVER ERN NEB.
HOWEVER...EXPECT DETERIORATING CONDITIONS RETURNING WITH REDEVELOPMENT
OF SCT TSRA JUST SHORTLY AFTER MIDNIGHT BTWN 07Z-09Z IN RESPONSE
TO STRENGTHENING LLVL JET. AFT 09Z...MVFR CONDITIONS EXPECTED AT
ALL TAF SITE THRU ABOUT 15Z SAT MORNING...THEN VFR REMAINDER OF
FCST PD.

&&

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

$$

SHORT TERM...DERGAN
LONG TERM...DERGAN
AVIATION...DEE



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