Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 240433
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
1133 PM CDT SAT APR 23 2016

.UPDATE...
ISSUED AT 954 PM CDT SAT APR 23 2016

THUNDERSTORMS HAVE BEGUN TO FIRE IN EASTERN COLORADO WITH THE
UPPER LEVEL JET ROUNDING THE BASE OF THE TROUGH AND SHORT WAVE
TROUGH ENERGY SWING INTO WESTERN NEBRASKA. THE 00Z OAX SOUNDING
HAD A PWAT OF 0.85 INCHES WITH H92 WINDS AROUND 30KTS. THE LOW
LEVEL JET IS FORECAST TO INCREASE TO 50KTS BY MORNING WITH
INCREASING OMEGA/H85 THETA-E ADVECTION...UPPER LEVEL SUPPORT AS
WELL AS DEEPENING MOISTURE AND A PWAT AROUND 1.25 INCHES. WILL
CONTINUE THE TREND OF SCATTERED SHOWERS AND THUNDERSTORMS
SPREADING EASTWARD OVERNIGHT INTO THE FORECAST AREA THROUGH THE
MORNING HOURS.

&&

.SHORT TERM...(TONIGHT THROUGH TUESDAY)
ISSUED AT 307 PM CDT SAT APR 23 2016

SEVERE THUNDERSTORM POTENTIAL SUNDAY AFTERNOON AND EVENING REMAINS
THE PRIMARY FORECAST CONCERN.

GUSTY SOUTH WINDS AND FILTERED SUNSHINE WERE HELPING TO PUSH
TEMPERATURES WELL INTO THE 70S WITH SOME LOWER 80S THIS AFTERNOON.
THE SOUTH WINDS WERE ALSO MAINTAINING LOW TO MID 50S DEW POINTS IN
THE AREA AS WELL...AN IMPORTANT INGREDIENT FOR STORM POTENTIAL ON
SUNDAY. MOISTURE SOURCE REGION IN THE SOUTHERN PLAINS OFFERS LITTLE
IN REGARDS TO MOISTURE SURGE FOR TOMORROW AS GULF HAS BEEN CUT OFF
BY OFFSHORE FLOW INTO THE EARLY AFTERNOON. MODELS ARE STILL
INDICATING A SMALL INCREASE IN DEW POINTS INTO THE UPPER 50S...WHICH
SEEMS DOABLE JUST AHEAD OF DRYLINE SUNDAY AFTERNOON. THAT DRYLINE IS
EXPECTED TO ENTER EASTERN NEBRASKA BY PEAK HEATING SUNDAY AS UPPER
LOW SPINS INTO SOUTH CENTRAL SOUTH DAKOTA. AGAIN TODAY MODELS HAVE
SLOWED THIS PROGRESSION SLIGHTLY FROM 24 HOURS AGO...WHICH MEANS ALL
BUT A FEW FAR WESTERN COUNTIES OF OUR WARNING AREA WILL LIE IN
BETTER MOISTURE ENVIRONMENT EAST OF DRYLINE.

AS MID LEVEL WARM ADVECTION REGIME UNDER DIFFLUENT FLOW AHEAD OF
LOW/TROUGH SPREADS ACROSS THE PLAINS TONIGHT...A PLUME OF MID LEVEL
INSTABILITY SHOULD ROLL ACROSS EASTERN NEBRASKA AFTER MIDNIGHT. THIS
COULD TOUCH OFF A FEW THUNDERSTORMS WHICH SHOULD BE EXITING TO OUR
EAST DURING THE MORNING. ATTENTION THEN TURNS TO ACTIVITY FIRING
ALONG AND EAST OF DRYLINE IN THE AFTERNOON. MODEST SURFACE-BASED
INSTABILITY IS EXPECTED WHERE DEW POINTS CAN REACH THE MID AND UPPER
50S...APPROACHING 2000 J/KG OF CAPE. STEEPENING MID LEVEL LAPSE
RATES ARE FORECAST AS COOLER AIR ATTENDANT TO MID LEVEL TROUGH
OVERSPREADS THE REGION...SO IF/WHEN WE GET STORMS TO FIRE...EXPECT
RAPID DEVELOPMENT. LOW LEVEL CONVERGENCE IS STILL AN ISSUE GIVEN
SMALL WIND DIRECTION DIFFERENCE ALONG DRYLINE. AND LOW LEVEL LAPSE
RATES ARE IN QUESTION AS LINGERING CLOUD COVER MAY LIMIT WARMING
SOMEWHAT. BUT GIVEN AVAILABLE INSTABILITY...WHEN STORMS
FIRE...STRONG 0-6KM BULK SHEAR VECTORS NEAR 40KT WILL BECOME MORE
AND MORE PERPENDICULAR TO EXPECTED CONVECTION ORIENTATION. THUS
SUPERCELLULAR STORMS ARE LIKELY WITH ASSOCIATED WIND AND HAIL THREAT.
WHILE TORNADIC POTENTIAL IS NOT ZERO GIVEN STRONG SHEAR...LACK OF
OBVIOUS BOUNDARY-INDUCED LOW LEVEL DIRECTIONAL SHEAR LIMITS THREAT
RISK AT THE MOMENT.

SYSTEM WILL BE EDGING EAST WITH TIME SUNDAY EVENING WITH SEVERE
POTENTIAL CONTINUING UNTIL AFTER SUNSET IN SOUTHWEST IOWA. MOST
ACTIVITY SHOULD BE MOVING OFF THE THE EAST AFTER MIDNIGHT WITH LOW
LEVEL WINDS BECOMING WEST LATE SUNDAY NIGHT...THEN TURNING NORTHERLY
DURING THE DAY ON MONDAY. SOME WRAP-AROUND SHOWERS COULD SKIRT FAR
NORTHEAST NEBRASKA ON MONDAY...ALONG WITH COLD AIR STRATO-CU. HIGHS
MONDAY WILL BE A GOOD 10F COOLER THAN SUNDAY.

OUR NEXT WEATHER-MAKER IN THE FORM OF ANOTHER UPPER LOW IS SLATED TO
BEGIN ITS TREK TOWARD THE PLAINS ON TUESDAY. MODELS HAVE SLOWED THIS
SYSTEM DOWN AS WELL...SO MUCH OF THE ASSOCIATED PRECIPITATION WILL
LIKELY HOLD OFF UNTIL LATER IN THE DAY TUESDAY OR TUESDAY NIGHT. 12Z
ECMWF IS STILL THE MOST AGGRESSIVE AND BRINGS ELEVATED CONVECTION
INTO THE AREA EARLY TUESDAY...SO WILL MAINTAIN AT LEAST SOME CHANCE
FOR STORMS THROUGH MUCH OF THE DAY. AND IF ECMWF IS RIGHT...COULD
SEE STRONGER STORMS IN SOUTHEAST NEBRASKA BEFORE THE END OF THE
DAY.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 307 PM CDT SAT APR 23 2016

WE WILL CONTINUE WITH FAIRLY HIGH THUNDERSTORM CHANCES INTO
WEDNESDAY BEFORE MID LEVEL SYSTEM MOVES EAST ON THURSDAY. THEN YET
ANOTHER SYSTEM IS SET TO MOVE INTO THE PLAINS ON SATURDAY.

MAJORITY OF LONGER TERM MODELS CONCUR WITH THE OVERALL MID LEVEL
FLOW PATTERN THROUGH THE WEEK. HOWEVER THEY DIFFER ON FINER SURFACE
DETAILS...ESPECIALLY WITH MID WEEK SYSTEM...THOUGH THOSE DIFFERENCES
TODAY DO NOT TRANSLATE TO AN APPRECIABLE DIFFERENCE IN SEVERE RISK.
BOTH GFS AND ECMWF SHOW SURFACE REFLECTION OF MID LEVEL LOW MOVING
THROUGH EASTERN NEBRASKA LATE TUESDAY NIGHT AND WEDNESDAY MORNING.
DIFFERENCES IN LATITUDE ARE NOTED WITH GFS FARTHER NORTHWEST...
MOVING LOW THROUGH NORTHEAST NEBRASKA...WHILE ECMWF MOVES LOW
THROUGH SOUTHEAST NEBRASKA. THE GFS SOLUTION WOULD OFFER MORE WARM
SECTOR INSTABILITY TO INVADE OUR AREA...HOWEVER OVERNIGHT TIMING
SUGGESTS SURFACE-BASED INSTABILITY WILL BE LACKING ANYWAY. SO MOST
LIKELY SCENARIO WILL BE FOR ELEVATED SHOWERS AND THUNDERSTORMS
INCREASING IN COVERAGE AND INTENSITY TUESDAY NIGHT WITH RISK OF HAIL
AS STEEP MID LEVEL LAPSE RATES AND POTENT SOUTHWEST ORIENTED BULK
SHEAR SUGGESTS SUPERCELL STRUCTURES ARE LIKELY.

OTHERWISE EXPECT PRECIPITATION TO BE WINDING DOWN THROUGH THE DAY
WEDNESDAY WITH LINGERING SHOWERS OR STORMS POSSIBLE INTO WEDNESDAY
NIGHT. A RESPITE IN ACTIVITY SHOULD ENSUE FOR THURSDAY BEFORE NEXT
MID LEVEL LOW/TROUGH MAKES ITS WAY INTO AND THROUGH THE ROCKIES
FRIDAY INTO SATURDAY. A SIMILAR PATTERN IS EXPECTED WITH AREA OF
WARM ADVECTION CONVECTION POSSIBLE IN DIFFLUENT FLOW REGIME AHEAD OF
MAIN TROUGH FOR LATE FRIDAY...WITH GOOD POTENTIAL FOR RAIN/STORMS
FRIDAY NIGHT AND SATURDAY. CURRENT SOLUTIONS KEEP SURFACE LOW SOUTH
OF OUR AREA FOR THE MOST PART...PLACING GREATEST SEVERE RISK IN
KANSAS AND OKLAHOMA.

&&

.AVIATION...(06Z TAFS FOR KOMA...KLNK...KOFK THROUGH 06Z MONDAY)
ISSUED AT 1133 PM CDT SAT APR 23 2016

PRIMARY AVIATION CONCERN REVOLVES AROUND 2 ROUNDS OF THUNDERSTORMS
THAT WILL AFFECT TAF SITES. THE FIRST WILL BE EARLY THIS MORNING
09-14Z. SECOND ROUND OF STORMS EXPECTED 21-02Z...WHICH WOULD BE
STRONGER WITH A SLIGHT RISK OF HAIL AND DAMAGING WINDS.  SECONDARY
CONCERN IS NON CONVECTIVE LOW LEVEL WIND SHEAR...WITH WINDS AT
FLIGHT LEVEL 020 AROUND 45-50 KNOTS FROM NOW THROUGH ABOUT 11-14Z.
OTHERWISE VFR CONDITIONS PREVAIL WITH SOUTHEASTERLY WINDS AT 15
TO 30 KNOTS.

&&

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

$$

UPDATE...ZAPOTOCNY
SHORT TERM...DERGAN
LONG TERM...DERGAN
AVIATION...DEWALD



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