Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 202324
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
624 PM CDT WED AUG 20 2014

.SHORT TERM...(TONIGHT THROUGH SATURDAY)
ISSUED AT 334 PM CDT WED AUG 20 2014

UNSETTLED WEATHER PATTERN WILL REMAIN IN PLACE OVER THE NEXT WEEK
WITH SEVERAL OPPORTUNITIES FOR THUNDERSTORMS. TIMING THESE CHANCES
ALONG WITH INCREASE IN HEAT AND HUMIDITY ARE THE PRIMARY FORECAST
CONCERNS.

MORNING UPPER AIR CHARTS SHOWED MID LEVEL TROUGH EXTENDING FROM THE
CANADIAN ROCKIES INTO SOUTHERN CALIFORNIA...WITH SOUTHWEST FLOW
AHEAD OF THE TROUGH RIDING INTO THE NORTHERN PLAINS. UPPER RIDGE
AXIS WAS CURRENTLY OVER THE MISSOURI RIVER VALLEY...BUT IS FORECAST
TO SHIFT EAST AND FLATTEN A BIT ON THURSDAY. THIS WILL LEAVE OUR
AREA UNDER SOUTHWEST FLOW ALOFT...WITH PATH FOR EJECTING SHORTWAVES
OVER NEBRASKA AND THE DAKOTAS. ALSO OF NOTE WAS PLUME OF MID LEVEL
MOISTURE EXTENDING FROM THE SOUTHERN BAJA INTO WESTERN KANSAS AND
SOUTHWEST NEBRASKA. WITH ONLY A SLOW DRIFT TO WESTERN
TROUGH...EXPECT THIS MOISTURE PLUME TO EXPAND OVER EASTERN NEBRASKA
AND WESTERN IOWA AND REMAIN IN PLACE AT LEAST INTO THE WEEKEND.
USING 700MB DEW POINT TEMPERATURES AS A PROXY...MODELS CONCUR WITH
THIS EXPECTATION. THE RESULT OF THESE PARAMETERS WILL BE AN
ATMOSPHERE PRIMED FOR SCATTERED CONVECTION AS SHORTWAVES ROLL INTO
THE PLAINS.

TIMING OF THOSE SHORTWAVES WILL PROVE DIFFICULT MORE THAN A DAY TO
TWO OUT. HOWEVER MODELS AGREE ON A SIGNIFICANT SHORTWAVE MOVING INTO
THE PLAINS FRIDAY NIGHT...OUR MOST LIKELY TIME FOR WIDESPREAD HEAVY
RAINS.

FOR TONIGHT...WATER VAPOR LOOPS IMPLY A SHORTWAVE IN WESTERN KANSAS
THIS AFTERNOON...EXPECTED TO LIFT NORTHEAST ACROSS OUR CWA LATER
THIS EVENING AND OVERNIGHT. GREATER THAN 7 C/KM MID LEVEL LAPSE
RATES WILL BE IN PLACE ALONG WITH ABUNDANT MID LEVEL MOISTURE.
EXPECT SCATTERED THUNDERSTORMS TO FIRE AFTER MIDNIGHT WHEN LOW LEVEL
JET KICKS UP TO 35KT WITH APPROACH OF SHORTWAVE. MAIN AREA OF
CONCERN WILL BE OVER OUR NORTHERN CWA THEN. HOWEVER THIS
EVENING...CONVECTION FROM EARLIER THIS MORNING MOVING ACROSS IOWA
LAID DOWN AN OUTFLOW BOUNDARY WHICH MOVED INTO SOUTHWEST IOWA AND
NORTHERN MISSOURI. VISIBLE SATELLITE PICS SHOW A LINE OF CUMULUS
ALONG THIS BOUNDARY...AND RAP MODEL SUGGESTS MLCAPE IS APPROACHING
3500 J/KG IN NORTHWEST MISSOURI ALONG WITH DIMINISHING CAP. LATEST
RAP AND HRRR FORECASTS KEEP CONVECTION IN CHECK THERE...BUT HAVE
ADDED SMALL POPS FOR SEVERAL HOURS THIS EVENING.

OVERNIGHT CONVECTION SHOULD BE EXITING THE CWA OR DIMINISHING BY MID
MORNING. EXPECT CLOUDS TO CLEAR ALLOWING FOR PLENTY OF INSOLATION IN
THE AFTERNOON WITH TEMPERATURES WELL INTO THE 90S AND DEW POINTS
CLOSE TO 70. A WEAK FRONTAL BOUNDARY IS FORECAST TO SETTLE INTO
NORTHEAST NEBRASKA THURSDAY AFTERNOON BEHIND WEDNESDAY NIGHT
SHORTWAVE...AND COULD FOCUS THUNDERSTORM CHANCES THERE. RELATIVELY
WARM TEMPERATURES ALOFT WILL LIKELY SUPPRESS CONVECTION IN THE
AFTERNOON...WITH BETTER CHANCES COMING LATER IN THE EVENING AS THE
FRONT SETTLES SOUTH INTO SOUTHEAST NEBRASKA AND SOUTHWEST IOWA AND
MID LEVEL TEMPERATURES COOL A BIT. CONTINUED ISENTROPIC UPGLIDE OVER
FRONTAL BOUNDARY IN MOIST ATMOSPHERE SUGGESTS AT LEAST SCATTERED
CONVECTION IS POSSIBLE THROUGH THE NIGHT.

MOST OF DAY FRIDAY SHOULD BE DRY AFTER MORNING STORMS IN THE SOUTH
MOVE OFF TO THE EAST. FRONTAL BOUNDARY WILL BEGIN LIFTING TO THE
NORTH DURING THE DAY WITH APPROACH OF STRONG SHORTWAVE FRIDAY NIGHT.
INSTABILITY FORECASTS SHOW 2000-3000 J/KG OF SURFACE-BASED CAPE
FRIDAY AFTERNOON...BUT SOUNDINGS SUGGEST A MODEST CAP WILL HOLD OFF
STORMS UNTIL NEAR 00Z OR PROBABLY AFTER. CHANCES INCREASE MARKEDLY
FRIDAY NIGHT AS SHORTWAVE AND SURFACE LOW MOVE NORTHEAST THROUGH THE
CWA. CURRENT TRACK PLACES NORTHEAST NEBRASKA IN THE CORRIDOR OF
HEAVIEST POTENTIAL RAINFALL WHERE PRECIPITABLE WATER WILL LIKELY
EXCEED 2 INCHES. CURRENT HPC QPF PROGS PAINT ABOUT THREE-QUARTERS OF
AN INCH OF RAIN IN NORTHEAST NEBRASKA...BUT WILL LIKELY SEE MUCH
MORE THAN THAT IN LOCAL AREAS GIVEN MOISTURE AVAILABLE AND POTENTIAL
FOR TRAINING OF STORMS. EXPECT ACTIVITY TO BE EXITING TO OUR
NORTHEAST SATURDAY MORNING...BUT LEFTOVER BAROCLINIC ZONE AND WIND
SHIFT WILL REMAIN IN PLACE FOR THE POTENTIAL FOR MORE STORMS LATER
IN THE DAY SATURDAY. WILL MAINTAIN A SMALL CHANCE FOR ADDITIONAL
AFTERNOON STORMS...EXPECTING SUBSIDENCE BEHIND EXITING SHORTWAVE TO
SUPPRESS CONVECTION MOST OF THE AFTERNOON.

.LONG TERM...(SATURDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 334 PM CDT WED AUG 20 2014

CONTINUED CHANCES OF THUNDERSTORMS WILL REMAIN JUST ABOUT EACH
PERIOD IN THE LONGER TERM FORECAST THROUGH WEDNESDAY. WESTERN UPPER
TROUGH WILL SLOWLY DRIFT FROM THE ROCKIES SATURDAY NIGHT INTO THE
PLAINS BY WEDNESDAY. ECMWF IS A LITTLE MORE PROGRESSIVE THAN THE GFS
WITH THIS MOVEMENT...BUT EVEN THE ECMWF LEAVES SOME SEMBLANCE OF A
TROUGH/LOW IN THE PLAINS THEN.

USING A BLEND OF ECMWF AND GFS...AND WHERE SOME CONSISTENCY IS
SHOWN...BEST CHANCES FOR MORE WIDESPREAD CONVECTION IS EXPECTED
MONDAY NIGHT INTO TUESDAY...THEN AGAIN TUESDAY NIGHT INTO WEDNESDAY.
BEFORE THEN...IMPULSES RIDING THROUGH MID LEVEL FLOW COULD SPARK
AREAS OF STORMS AT JUST ABOUT ANY TIME AS FRONTAL BOUNDARY MEANDERS
NORTH AND SOUTH THROUGH THE CWA AHEAD OF AND BEHIND EACH WAVE.
TEMPERATURES SHOULD MODERATE SOME THROUGH THE PERIOD...BEGINNING
WITH SUNDAY IN THE 80S TO NEAR 90...THEN RANGING FROM THE UPPER 70S
TO MIDDLE 80S MONDAY THROUGH WEDNESDAY.

&&

.AVIATION...(00Z TAFS FOR KOFK...KLNK AND KOMA.)
ISSUED AT 619 PM CDT WED AUG 20 2014

VFR CONDITIONS ARE EXPECTED AT THE TAFS SITES THROUGH MUCH OF THE
PERIOD. A FEW SPOTTY THUNDERSTORMS ARE POSSIBLE IN AND AROUND THE
TAF SITES...BUT CONFIDENCE IS TOO LOW TO INCLUDE THEM IN THE TAF
AT THIS POINT.

&&

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

$$

SHORT TERM...DERGAN
LONG TERM...DERGAN
AVIATION...KERN



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