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000
FXUS63 KOAX 260843
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
343 AM CDT SUN MAY 26 2013

.DISCUSSION...
IT APPEARS THUNDERSTORM ACTIVITY WILL CONTINUE TO FAVOR THE
OVERNIGHT HOURS THE NEXT FEW DAYS BEFORE AFTERNOON CONVECTION
BECOMES MORE LIKELY WITH APPROACH OF FRONTAL SYSTEM AND UPPER LOW.
THAT UPPER LOW WAS STILL SPINNING OVER SOUTHWEST CANADA AND THE
NORTHWEST CONUS THIS MORNING...AND IS FORECAST TO REFORM IN THE GULF
OF ALASKA LATER TONIGHT WITH TROUGH EXTENDING INTO THE SOUTHWEST
U.S. THE TROUGH WILL THEN ROTATE NORTHEAST TOWARD THE PLAINS
WEDNESDAY AND THURSDAY BEFORE CUTTING OFF AS AN UPPER LOW IN THE
NORTHERN PLAINS LATE IN THE WEEK.

AHEAD OF THIS SYSTEM...CONTINUED SOUTHWESTERLY FLOW ALOFT WILL
MAINTAIN QUASI-STATIONARY SURFACE TROUGH IN THE HIGH PLAINS WHICH
WILL KEEP MOIST SOUTHERLY FLOW GOING OVER THE REST OF THE PLAINS.
SURFACE DEW POINTS WERE IN THE 60S IN OUR SOUTHERN CWA...AND WILL
OVERSPREAD ALL OF THE AREA TODAY. 850 DEW POINTS WERE ALREADY IN THE
10 TO 15C RANGE AND WILL LINGER THROUGH THE WEEK. DEEPER MOISTURE
WAS RUNNING WELL ABOVE NORMAL FOR THIS TIME OF YEAR AS NOTED BY
PRECIPITABLE WATER VALUES NEAR OR ABOVE 1.5 INCHES. MEANWHILE HIGH
FREEZING LEVELS AT OR ABOVE 13000FT SUGGESTS DEEP WARM CLOUD LAYER
AND EFFICIENT PRECIPITATION PRODUCTION. SO HEAVY RAIN IS LIKELY WITH
ANY STORMS THAT FORM ACROSS OUR AREA THE NEXT SEVERAL DAYS.

EXACT LOCATION OF THAT HEAVY RAIN WILL BE CONDITIONAL ON SUBTLE
BOUNDARIES AT THE SURFACE AND 850...BUT WILL MOSTLY ALIGN NORTH AND
NORTHEAST OF LOW LEVEL JET CONVERGENCE. MODELS DIFFER ON WHERE THIS
WILL SET UP EACH NIGHT...BUT GFS AND ECMWF DO SHOW SOME OVERLAP IN
850 WIND FIELDS AND SUBSEQUENT MOISTURE CONVERGENCE. SO WILL FOLLOW
A BLEND OF THESE MODELS FOR THIS FORECAST.

FIRST OF ALL...CURRENT FLASH FLOOD WATCH FOR A SMALL PART OF WEST
CENTRAL IOWA WILL BE CANCELLED THIS MORNING AS STORMS HAVE LIFTED
WELL NORTHEAST OF THIS AREA. SOME REFORMATION OF CONVECTION TO THE
SOUTHWEST OF CURRENT CONVECTION COULD SWEEP THROUGH OUR FAR
NORTHEAST CWA DURING THE MORNING...BUT WILL ONLY AFFECT A SMALL PART
OF OUR AREA. SUBSEQUENT FLASH FLOOD WATCHES WILL LIKELY BE NEEDED
TONIGHT AND MONDAY NIGHT...BUT WILL ALLOW LATER SHIFTS TO LOOK AT
ANOTHER MODEL RUN AND AFTERNOON OBSERVATIONAL DATA TO FINE TUNE
AREAS MOST UNDER THE GUN. IT LOOKS LIKE SIMILAR AREAS TO THIS
MORNING ARE IN LINE FOR HEAVIEST RAINS TONIGHT...NAMELY NORTHEAST
NEBRASKA AND WEST CENTRAL IOWA WHERE ECMWF PAINTS HEAVIEST QPF. GFS
SUGGESTS ANOTHER AREA OVER OUR CENTRAL AND SOUTHERN CWA COULD SEE
HEAVY RAIN AS WELL. THEN MONDAY NIGHT...LOW LEVEL JET POINTS TO
SOUTHEAST NEBRASKA AND SOUTHWEST IOWA INTO NORTHWEST MISSOURI HAVING
THE HIGHEST POTENTIAL FOR HEAVY RAIN.

SEVERE RISK THROUGH THIS PERIOD WILL BE RELATIVELY LOW GIVEN ONLY
MODEST INSTABILITY AND SHEAR...BUT A FEW STORMS COULD APPROACH
SEVERE. TUESDAY AFTERNOON MAY PRESENT A BETTER CHANCE FOR SEVERE
WITH INSTABILITY AXIS SHIFTING OVER OUR WESTERN CWA...BUT LOW LEVEL
CONVERGENCE IS RATHER BENIGN.

OUR BEST CHANCES FOR SEVERE STORMS WILL COME MID WEEK AS UPPER
TROUGH/LOW MOVES CLOSER AND MID LEVEL WINDS AND DEEP LAYER SHEAR
INCREASE MARKEDLY. GFS SHOWS 0-6KM BULK SHEAR APPROACHING 50KT IN
OUR WEST AND SOUTHWEST WEDNESDAY AFTERNOON...BUT FRONTAL SYSTEM IS
STILL TO THE WEST. THURSDAY AND FRIDAY APPEAR TO OFFER THE BEST
SEVERE RISK WHEN INSTABILITY...SHEAR AND SURFACE CONVERGENCE ALL ARE
MAXIMIZED ACROSS EASTERN NEBRASKA AND WESTERN IOWA.

DERGAN

&&

.AVIATION...06Z TAFS FOR KOMA...KLNK AND KOFK.

THOUGHT CHANCES WERE TOO LOW TO INCLUDE ANY MENTION OF TSTMS AT
ANY OF THE TAF POINTS OVERNIGHT...AND ALSO FELT CHANCES WERE LOW
ENOUGH TO LEAVE A PROB30 GROUP OUT FOR SUNDAY AFTERNOON.

OVERNIGHT...CEILINGS SHOULD LOWER A BIT...INTO MAINLY THE MVFR
CATETORY BUT POSSIBLY TO IFR. IFR CONDITIONS WOULD BE MOST LIKELY
09Z-14Z. CEILINGS SHOULD TEND TO IMPROVE TOWARD VFR BY LATE
MORNING OR EARLY AFTERNOON.

MILLER

&&

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

$$