Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 270437
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
1137 PM CDT TUE AUG 26 2014

.UPDATE...
ISSUED AT 925 PM CDT TUE AUG 26 2014

MAIN CONCERN OVER THE NEXT 24 HOURS OF COURSE IS CONVECTIVE
POTENTIAL AND IF/WHERE HEAVY RAINFALL WILL OCCUR. EVENING UPPER
AIR ANALYSIS INDICATED BROAD SOUTHWEST FLOW ACROSS THE CNTRL
PLAINS WITH A WELL-DEFINED SHORTWAVE TROUGH OVER ND...AND THE
NEXT UPSTREAM ONE OVER THE 4-CORNERS AREA. BETWEEN THESE TWO
SYSTEMS...THE LARGE-SCALE FORCING FOR ASCENT WAS NEGLIGIBLE. THE
H85 ANALYSIS COMPARED WITH 24 HOURS AGO INDCS LESS ON A WELL-
DEFINED FRONTAL BOUNDARY ACROSS NEB/IA...BUT THE PRESENCE OF GOOD
MOISTURE ACRS THE KS/MO WITH H85 DEW POINTS >15 C. WE UPDATED
EARLIER TO DELAY THE ONSET OF ANY PRECIP...AND GIVEN SHORT TERM
TRENDS IT MAY BE WELL AFTER MIDNIGHT BEFORE CONVECTION INCREASES
ACRS THE AREA. MODEL GUIDANCE INDCS THAT THERE WILL BE SOME
INCREASE IN THE LOW-LEVEL JET AFTER 06Z LEADING TO BROAD ASCENT ON
THE 305-310 SFC. THIS MAY LEAD TO SOME INCREASE IN
CONVECTION AFTER 06Z...BUT WITHOUT A WELL-DEFINED BOUNDARY TO
FOCUS MASS CONVERGENCE ON...IF AND WHERE A FOCUS HEAVY RAINFALL
EVENT WOULD OCCUR IS UNCERTAIN. IT APPEARS THAT THE PROSPECTS OF
HEAVY RAINFALL MAY ACTUALLY IMPROVE AS WE GET INTO WED MRNG AS THE
AZ SHRTWV TROUGH EMERGES ONTO THE HIGH PLAINS AND CREATES A
DYNAMICALLY INDUCED LOW-LEVEL JET THROUGH THE DAY ON WED ACTING ON
THE 1.80 PWATS ACRS THE AREA. A BAND OF HEAVY THUNDERSTORMS
APPEARS POSSIBLE TO MOVE FROM CNTRL INTO NE NEB THROUGH THE DAY ON
WED AND HAVE INCREASED POPS IN THIS AREA FOR THIS TIME PERIOD.

WE WILL KEEP THE FLASH FLOOD WATCH INTACT ATTM GIVEN THE
UNCERTAINTY...BUT MAY CONCENTRATE ON THE RAINFALL POTENTIAL WED
MRNG IN THE PRODUCT. OTHERWISE WILL UPDATE AGAIN A BIT LATER THIS
EVENING TO DELAY THE ONSET OF POPS A BIT FARTHER INTO THE NIGHT
AND FOR THE HIGHER POPS ON WED. OTHER ELEMENTS OF THE FORECAST
APPEAR ON TRACK ATTM.

&&

.SHORT TERM...(TONIGHT THROUGH FRIDAY)
ISSUED AT 300 PM CDT TUE AUG 26 2014

DID NOT MAKE MANY CHANGES TO THE PREVIOUS FORECAST AND OVERALL
THINKING HAS NOT CHANGED MUCH THE PAST FEW DAYS...WITH DECENT
MODEL CONSISTENCY. TIMING OF TSTMS...RAIN AMOUNTS AND AXIS OF
HEAVIEST RAIN LOCATION WILL CONTINUE TO PROVIDE THE MAIN FORECAST
CHALLENGES. THE CONVECTION FORMED ABOUT AS EXPECTED LAST NIGHT...
IN A GENERAL SENSE...BUT I DID NOT THINK WE WOULD SEE A MAX AMOUNT
OF OVER 7 INCHES. THE AMOUNTS OVER 2.5 INCHES WERE IN A FAIRLY
NARROW BAND.

LARGE SCALE FEATURES FROM THE 12Z UPPER AIR PLOTS INCLUDED THE
FOLLOWING. AT 300 MB...TWO MAIN JET SEGMENTS WERE NOTED. THE FIRST
WAS DIGGING S/SW FROM WRN NV (80 KNOTS) AND THE OTHER WAS PUNCHING
EWD ACROSS CNTRL MN (100 KNOTS). ONLY WEAK 12 HOUR HEIGHT FALLS WERE
SEEN AT 500 MB...OVER CA AND OVER SWRN CO/NWRN NM. THE CLOSED LOW
WHICH HAS BEEN OVER THE WRN UNITED STATES BECAME MORE ELONGATED AND
SHIFTED A BIT S. WATER VAPOR SHOWED THE MAIN CHUNK OF ENERGY OVER
SRN NV EARLY THIS AFTN. AT 700 MB...THE MOIST AXIS SEEMED TO HAVE
THINNED A BIT OVER THE CNTRL PLAINS AND MOST OF THE HIGHER MOISTURE
AT THIS LEVEL WAS LOCATED IN CO/AZ/NM. THE NEARLY STATIONARY LOW
LEVEL FRONT WAS STILL DOWN ACROSS KS AND MO. COOL HIGH PRESSURE
WAS OVER THE DKTS AND MN.

TONIGHT...IT SEEMS THAT CONVECTION MAY GET GOING MAINLY AFTER 05Z.
WILL KEEP SOME LOW POPS GOING THIS EVENING...THEN RAMP THEM UP VERY
QUICKLY. LOW LEVEL JET TONIGHT SEEMS A BIT WEAKER...BUT MODEL POINT
FORECAST SOUNDINGS AND PLAN VIEWS SHOW PRECIPITABLE WATER (PW)
VALUES INCREASING TO OVER 2 INCHES TONIGHT. STRONGEST FORCING AND
SUPPORT ARE IN THE SAME GENERAL AREA AS LAST NIGHT. WITH MORE SOIL
MOISTURE NOW AND A SIMILAR QPF POTENTIAL POSSIBLE TONIGHT...
DECIDED A FLASH FLOOD WATCH WAS APPROPRIATE. NOT ALL AREAS WILL
SEE FLOODING...BUT THREAT IS HIGH ENOUGH TO INCLUDE HEADLINES.
SOME PCPN SHOULD LINGER INTO MID MORNING WEDNESDAY...SO DECIDED
TO RUN THE WATCH FROM 03Z WED TO 15Z WED. LOOK FOR LOWS TONIGHT IN
THE 60S...COOLEST NRN ZONES AND WARMEST SRN ZONES.

WEDNESDAY...STORMS SHOULD TEND TO WEAKEN THROUGH THE MORNING BUT
MAY FIRE AGAIN BY LATE AFTERNOON. MODELS SUGGEST LOW PRESSURE
WILL STRENGTHEN OVER ERN CO DURING THE DAY...THEN ATTEMPT TO LIFT
NEWD WEDNESDAY NIGHT. THIS MAY SHIFT AXIS OF HEAVIEST RAIN FARTHER
N ACROSS NERN NE IN THE EVENING AND THEN TO NRN IA/SRN MN FOR THE
EARLY MORNING HOURS OF THU. UNSETTLED CONDS ARE LIKELY TO CONTINUE
THU INTO THU NGT AS THE FRONTAL BOUNDARY LINGERS IN THE AREA WITH
MID TROPOSPHERIC TROUGH NOT MOVING EAST OF OUR AREA UNTIL SAT.

.LONG TERM...(FRIDAY NIGHT THROUGH TUESDAY)
ISSUED AT 300 PM CDT TUE AUG 26 2014

THIS PERIOD GENERALLY LOOKS LESS ACTIVE...ESPECIALLY BY SAT...AND
THE 12Z MODELS WERE IN PRETTY GOOD AGREEMENT WITH THE LARGE SCALE
PATTERN ALOFT. WEAK RIDGING SHOULD BUILD INTO THE AREA FROM THE
W ON SATURDAY...BUT THIS IS SHORT-LIVED. A STRONG TROUGH WILL BE
DIGGING ACROSS THE ROCKIES OVER THE WEEKEND. IT APPEARS THIS
SHOULD BECOME MORE BROAD AND MOVE A BIT FARTHER EAST TOWARD THE
MIDLANDS BY TUESDAY. THE ECMWF...CANADIAN GEM AND THE 12Z GFS
HAVE SOME DIFFERENCES WITH THE LOW LEVEL FEATURES AND ALSO WITH
PCPN POTENTIAL. FOR NOW... GENERALLY USED A BLEND OF SOLUTIONS...
WITH A BIT MORE WEIGHT GIVEN TO THE 12Z ECMWF.

&&

.AVIATION...(06Z TAFS FOR KOFK...KLNK AND KOMA.)
ISSUED AT 1129 PM CDT TUE AUG 26 2014

MAIN CHANGE FROM EARLIER DISCUSSION IS SOMEWHAT OF A DELAY IN
CONVECTIVE INITIATION AND POSSIBLY A MORE PROLONGED TIME
POTENTIAL OF OCCURRENCE. OTHERWISE FLIGHT CONDITIONS LOOK TO BE
QUITE VARIABLE THROUGH ABOUT 18Z BEFORE BECOMING PREDOMINATLY
VFR. SOME LIKELIHOOD OF MORE CONVECTION ACROSS THE AREA AGAIN
AFTER 00Z AS SHORT WAVE ENERGY MOVES ACROSS THE REGION AHEAD OF
UPPER LOW OVER THE SOUTHWEST CONUS.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...FLASH FLOOD WATCH UNTIL 10 AM CDT WEDNESDAY FOR NEZ042>045-
     050>053-065.

IA...FLASH FLOOD WATCH UNTIL 10 AM CDT WEDNESDAY FOR IAZ055-056-069.

&&

$$

UPDATE...
SHORT TERM...MILLER
LONG TERM...MILLER
AVIATION...FOBERT


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