FXUS63 KOAX 150811
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
311 AM CDT MON AUG 15 2011
.DISCUSSION...
...MAIN CHALLENGE IS DETERMINING RAIN CHANCES THROUGH THE WEEK...
UPPER RIDGE PATTERN OVER THE CENTRAL US REMAINS IN PLACE PER WATER
VAPOR IMAGERY AND 00Z UPPER AIR OBSERVATIONS. HOWEVER ILL-DEFINED
SHORTWAVES ARE EVIDENT ON WEST SIDE OF RIDGE AND SUB TROPICAL
MOISTURE REMAINS IN PLACE THROUGHOUT THE RIDGE. THIS SYNOPTIC
PATTERN IS SUPPORTIVE OF WEAKLY FORCED MOIST CONVECTION WHICH IS
TYPICALLY POORLY RESOLVED BY NUMERICAL MODELS USING CONVECTIVE
PARAMETERIZATION SCHEMES...LEADING TO LOW CONFIDENCE POP FORECASTS.
REGIONAL RADAR MOSAIC SHOWED A SLOW MOVING MCS OVER NEBRASKA AND
NORTHERN KANSAS EARLY THIS MORNING...DRIFTING INTO EASTERN NEBRASKA
AND WEAKENING. STRONGER CONVECTION HAD BEEN OVER CENTRAL NEBRASKA
WHERE THE 30 KNOT LOW LEVEL JET CORE WAS LOCATED PER KUEX VWP. THE
6-HOUR PROG FROM THE 00Z NAM NEARLY MISSED THIS MCS ENTIRELY. THE
GFS WAS BETTER BUT PLACEMENT WAS POOR. THE ASSIMILATION OF
REFLECTIVITY DATA BY THE CONVECTION-ALLOWING HIGH RESOLUTION RAPID
REFRESH MODEL...HRRR...RESULTED IN THE 05Z RUN OF THE HRRR
REPRESENTING THE MCS REASONABLY WELL. THE HRRR IS CONSISTENT WITH
RECENT TRENDS IN KEEPING THE CONVECTION MORE ANCHORED OVER OUR
WESTERN COUNTIES AND CONNECTED TO THE THETA-E ADVECTION MAXIMUM AS
PROVIDED BY THE LOW LEVEL JET. THEREFORE A POP GRADIENT FROM WEST
TO EAST WILL BE NECESSARY THIS MORNING/TODAY RANGING FROM 90-100
PERCENT WEST TO 30-50 PERCENT OVER IOWA. SEE RECENT SWOMCD FOR
ADDITIONAL DETAILS AND CONCERNS FOR HEAVY RAIN POTENTIAL.
NEXT DECENT CHANCE FOR THUNDERSTORM ACTIVITY APPEARS TO BE TUESDAY
NIGHT. A STRONG SHORTWAVE MOVES THROUGH SOUTHERN CANADA
TUESDAY NIGHT AND LOWERS HEIGHTS A FEW METERS OVER THE CENTRAL
PLAINS. SURFACE LOW AND ATTENDANT COLD FRONT SWEEPS THROUGH
NEBRASKA/IOWA TUESDAY NIGHT AND MOST MODELS AGREE ON THIS TIMING.
DUE TO MODEL AGREEMENT WE INCREASED POPS AND RAINFALL AMOUNTS FOR
TUESDAY NIGHT.
BY THURSDAY NIGHT... THE SURFACE HIGH THAT MOVES IN ON WEDNESDAY
BEHIND THE COLD FRONT WILL BE MOVING EAST AND ALLOWING FOR ANOTHER
REGIME SIMILAR TO WHAT IS CURRENTLY IN PLACE...THAT OF STRONG
ISENTROPIC LIFT ASSOCIATED WITH THE LOW LEVEL JET. CURRENT POP
FORECAST HAS THIS SCENARIO REPRESENTED SO MADE FEW CHANGES TO POPS
BEYOND WEDNESDAY.
CLOUD COVER TODAY SHOULD LIMIT HEATING AND KEEP HIGH TEMPERATURES
FROM EXCEEDING THE LOWER 80S. SLIGHTLY WARMER HIGHS EXPECTED FOR
THE REMAINDER OF THE WEEK BUT STILL CONFINED TO THE 80S.
&&
.AVIATION...
TAF SITES KOFK/KOMA/KLNK
06Z ISSUANCE.
TEMPO GROUPS IN PLACE AT ALL TERMINALS BTWN 09Z-13Z IN ASSOCIATION
WITH SCT SHRA ACTIVITY MOVING SWD THRU ERN NEB THIS MORNING. VFR
CONDITIONS THEN EXPECTED TO PREVAIL THE REST OF THE FCST.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$
NIETFELD/DEE