FXUS63 KOAX 200214
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
914 PM CDT FRI AUG 19 2011
.UPDATE...
...SHORT TERM UPDATE AND MESOSCALE CONVECTIVE DISCUSSION...
MADE MINOR CHANGES TO GOING FORECAST THIS EVENING TO ACCOUNT FOR
LATEST RADAR AND SHORT TERM MESOSCALE TRENDS. EVENING SURFACE
ANALYSIS INDICATES THAT WEAK SURFACE FRONT HAS SETTLED INTO THE
FAR SOUTHERN REACHES OF THE CWA INTO FAR NORTHERN PORTIONS OF
KANSAS. CONVECTION THAT HAS BEEN OCCURRING ALONG/SOUTH OF THIS
BOUNDARY WILL LIKELY CONTINUE TO LIFT/DEVELOP TO THE NORTH THIS
EVENING AS A 30-35 KT LOW LEVEL JET INCREASES...BEFORE EVENTUALLY
VEERING EAST WITH TIME. BEST AREA FOR ISENTROPIC
ASCENT/850 MB THETA-E ADVECTION WILL BE ALONG AND SOUTH OF
I-80...AND HAVE INCREASED POPS SOMEWHAT ACROSS THIS AREA. FURTHER
NORTH...INCREASING AMOUNTS OF DRY LOW LEVEL AIR...EVIDENCED ON
BOTH 00Z OAX SOUNDING AND RECENT SURFACE OBS...WILL LIKELY RESULT
IN A FAIRLY SHARP CUTOFF TO ACTIVITY NORTH OF THE OMAHA AREA.
AS ALLUDED TO IN PREVIOUS DISCUSSION...WIDESPREAD SEVERE WEATHER
NOT APPEARING LIKELY WITH THIS ACTIVITY THIS EVENING. THAT BEING
SAID...00Z OAX ROAB DOES INDICATE LAYER OF RATHER STEEP MID LEVEL
LAPSE RATES ACROSS THE AREA...SO A FEW ISOLATED LARGE HAILERS WILL
BE POSSIBLE. BIGGER CONCERN OVERNIGHT WILL BE WITH HEAVY RAIN AND
FLASH FLOOD POTENTIAL. HIGH FREEZING LEVELS AND PWATS IN EXCESS OF
1.5 INCHES SUGGEST THAT HEAVY RAIN WILL BE POSSIBLE WITH
CONVECTION THIS EVENING/OVERNIGHT. DON'T BELIEVE THAT POTENTIAL
WILL BE WIDESPREAD ENOUGH TO JUSTIFY A FLASH FLOOD WATCH...BUT A
FEW INSTANCES OF LOCALIZED FLASH FLOODING CAN'T BE RULED OUT
THROUGH THE NIGHT.
BOXELL
&&
.PREV DISCUSSION... /ISSUED 345 PM CDT FRI AUG 19 2011/
SHORT TERM...TONIGHT
WEAK FRONT CURRENTLY MOVING INTO THE AREA...STRETCHING FROM SIOUX
CITY THROUGH NORFOLK INTO CENTRAL NEBRASKA. CONVECTION HAS FORMED
ALONG THIS BOUNDARY IN THE LAST HOUR...AND WILL BE SCATTERED IN
NATURE THIS EVENING AS THE BOUNDARY SLOWLY SAGS SOUTH. HOWEVER...AS
LOW LEVEL JET SETS UP THIS EVENING ACROSS KANSAS...STORMS WILL
DEVELOP JUST NORTH OF THE BOUNDARY...AND SET UP A CONVECTIVE COMPLEX
OVER SOUTHEAST NEBRASKA. WITH DEWPOINTS IN THE UPPER 60S/LOWER
70S...HEAVY RAINFALL SCENARIO IS SETTING UP. SEVERE WEATHER
PARAMETERS NOT ALL THAT EXCITING...BUT LOCALLY HEAVY RAINFALL IS A
POSSIBILITY...WITH A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS THE
SOUTHERN THIRD OF THE AREA.
QUESTIONS STILL REMAIN TONIGHT WITH WHERE THE AXIS OF HEAVIEST
RAINFALL WILL SET UP...BUT THINK THAT THE FAR SOUTHERN NEBRASKA
COUNTIES HAVE THE BEST CHANCE TONIGHT...WITH THE SMALLER CHANCES
ACROSS THE NORTH. RAINFALL AMOUNTS WILL RANGE FROM A QUARTER OF AN
INCH NORTH TO OVER AN INCH ACROSS THE SOUTH...WITH LOCALLY OVER 2
INCHES.
LONG TERM...SATURDAY THROUGH FRIDAY
THE CONVECTIVE COMPLEX WILL BE MOVING DOWNSTREAM ON SATURDAY. RAIN MAY
STILL BE WIDESPREAD ACROSS SERN NEBRASKA SATURDAY MORNING...BUT
THE OVERALL TREND WILL BE FOR DECREASING RAINFALL RATES FROM THE
NORTHWEST. RAIN SHOULD BE ENDING SATURDAY AFTERNOON...A FEW HOURS
SOONER ACROSS NWRN NEBRASKA.
SATURDAY NIGHT INTO SUNDAY...EXPECT A BREAK FROM THE RAIN DURING
THIS PERIOD WITH SURFACE HIGH PRESSURE MOVING ACROSS THE NRN
PLAINS. MOISTURE WITH INCREASING INSTABILITY AS SOUTHERLY WINDS
RETURN AND THE SURFACE HIGH MOVES DOWNSTREAM. POTENTIAL FOR A FEW
SUPERCELLS COULD DEVELOP UPSTREAM FROM THE DAKOTAS AND WRN
NEBRASKA...BUT SUNDAY EVENING THESE STORMS WILL BE MOVING ACROSS THE
FORECAST AREA WITH HIGHER CHANCES ACROSS THE NRN ZONES.
MONDAY AND TUESDAY...A SHORT WAVE EJECTING FROM A PACIFIC TROUGH IS
PROGGED TO MOVE ACROSS THE NRN PLAINS DURING THIS TIME FRAME.
TIMING OF THIS SHORT WAVE MAY BECOME A FORECAST CONCERN...BUT RIGHT
NOW THE GFS INDICATES THIS WAVE IMPACTING THE REGION MONDAY
NIGHT/TUESDAY MORNING. IF THIS HOLDS...THEN IMPROVING CONDITIONS
SHOULD OCCUR BY AFTERNOON BEHIND THE SHORT WAVE.
WEDNESDAY THROUGH FRIDAY...APPEARS DRY THROUGH THE PERIOD AS HIGH
PRESSURE AT THE SURFACE AND ALOFT KEEPS THE AIR MASS MOSTLY QUIET.
THE CONSENSUS POPS DID INDICATE A SLIGHT CHANCE NEAR THE MISSOURI
RIVER ON FRIDAY AS PACIFIC ENERGY SNEAKS BENEATH THE WESTERN HIGH.
.AVIATION...
FOR TAF SITES KOFK/KOMA/KLNK
18Z TAFS...
THUNDERSTORMS FORMING ALONG A WEAK BOUNDARY WEST OF THE AREA...BUT
DUE TO SCATTERED NATURE...HAVE NOT INCLUDED IN THE TAF. LARGER
SYSTEM WILL DEVELOP AROUND MIDNIGHT...AND HAVE INCLUDED VCSH/TEMPO
TSRA GROUPS AT KOMA AND KLNK...BUT LEFT AS PROB30 AT KOFK. DEPENDING
ON WHERE CONVECTION SETS UP...TAFS WILL HAVE TO BE AMENDED...BUT
TEMPO GROUPS DO INCLUDE IFR CIGS.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$
WFOOAX