FXUS63 KOAX 121639
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
1139 AM CDT THU MAY 12 2011
.UPDATE...
HAVE UPDATED THE FORECAST FOR PRECIP/THUNDER EVOLUTION THIS
AFTERNOON THROUGH TONIGHT.
&&
.DISCUSSION...
HAVE MADE SEVERAL CHANGES TO THE POPS/WX FORECAST IN PARTICULAR
FOR THE REST OF TODAY THROUGH TONIGHT. SUBJECTIVE 12Z UPPER AIR
ANALYSIS INDICATES UPPER LOW CENTERED IN NORTHEAST CO/SOUTHWEST
NEB...WITH 500MB HEIGHT FALLS ACROSS NEB/KS/MO/IA INDICATING THAT
THE LOW IS BEGINNING TO PROGRESS EASTWARD. 850MB LOW WAS CENTERED
IN NORTHWEST CO...WITH SECONDARY LOW CENTERED IN WESTERN ONT.
TROUGH/COLD FRONT EXTENDED BETWEEN THE TWO LOWS...WITH COLD FRONT
EXTENDING SOUTHWARD FROM THE MAIN LOW THROUGH TX. MOISTURE AXIS
EXTENDED FROM THE TX GULF COAST THROUGH EASTERN OK/WESTERN MO INTO
IA...WITH A NOSE OF MOISTURE BACK WESTWARD INTO CENTRAL/WESTERN
NEB. SURFACE LOW AT 16Z WAS CENTERED IN SOUTH CENTRAL NEB/NORTH
CENTRAL KS...WITH LINGERING SURFACE BOUNDARY FROM THE LOW THROUGH
KGRI-KBVN-KSLB-KRST. VIS SATELLITE IMAGERY INDICATES CLEAR SLOT
AHEAD OF THE LOW IN CENTRAL KS/SOUTH CENTRAL NEB...WITH CLOUD DECK
OVER THE CWA BECOMING MORE BROKEN THROUGH THE MORNING.
MAIN FORECAST CONCERN IS THE POTENTIAL FOR THUNDERSTORMS THIS
AFTERNOON THROUGH THIS EVENING...INCLUDING POSSIBLE SEVERE
THUNDERSTORMS. AXIS OF MLCAPE >500 J/KG IS IN PLACE ACROSS
CENTRAL TO EAST CENTRAL NEB INTO SOUTHWEST IA...AND IS MOSTLY
STILL CAPPED...WITH SBCAPE SLIGHTLY HIGHER AND MORE EXTENSIVE.
EFFECTIVE BULK SHEAR IS STRONGER TODAY THAN YESTERDAY...THOUGH NOT
SUBSTANTIAL...AT AROUND 25-30KT. 0-1KM SHEAR IS MAXIMIZED CLOSER
TO THE SURFACE LOW...THOUGH EFFECTIVE SRH OF 50-100 M2/S2 IS IN
PLACE ACROSS CENTRAL TO EAST CENTRAL NEB.
WITH EARLY INSTABILITY WEAKER TODAY...AS WELL AS MORE CAPPING IN
PLACE...EXPECT STORMS TO DEVELOP THIS AFTERNOON ACROSS CENTRAL
NEB...AS WELL AS DOWN INTO KS. WITH HIGHER SHEAR VALUES AND LOWER
FREEZING LEVELS...HAIL MIGHT BE MORE OF A THREAT THAN YESTERDAY.
ALSO...WITH HIGHER LOW-LEVEL SHEAR...WILL NEED TO BE COGNIZANT OF
TORNADO THREAT NEAR THE BOUNDARY AS WELL AS UNDER THE UPPER LOW AS
IT EJECTS ACROSS THE AREA TODAY/THIS EVENING.
HAVE INCREASED PRECIP MENTION THIS EVENING AND TONIGHT FOR HIGHER
COVERAGE...BUT ALSO LOWERED THUNDER WORDING AS INSTABILITY WEAKENS
QUICKLY IN WAKE OF THE LOW MOVING ACROSS THE AREA. THINK THREAT
FOR MUCH IF ANY THUNDER WILL BE DONE AFTER 06Z...THOUGH RAIN WILL
PERSIST OVERNIGHT. NUDGED UP DEWPOINTS THROUGH THE DAY AND INTO
TONIGHT IN RAINY AIR...AND ALSO NUDGED UP MINS SLIGHTLY IN THE
SOUTH AS LINGERING RAIN SHOULD KEEP TEMPERATURES FROM FALLING OFF.
UPDATED GRIDS/ZFP ALREADY SENT.
MAYES
&&
.PREV DISCUSSION... /ISSUED 302 AM CDT THU MAY 12 2011/
DISCUSSION...TODAY THROUGH SATURDAY NIGHT.
WV IMAGERY/PROFILER NETWORK THIS MORNING SHOWING CLOSED UPPER LOW
SITUATED OVER CO WITH WEDGE OF DRY AIR WRAPPING AROUND THE
CIRCULATION...LIFTING UP THRU KS AND INTO SRN NEB. ILL-DEFINED SFC
REFLECTION WAS CENTERED IN KS WITH ATTENDANT STATIONARY FRONT
EXTENDING THRU NERN NEB TO ERN MN WITH DRY LINE EXTENDING ALONG THE
HIGH PLAINS.
EXPECT NEXT ROUND OF CONVECTION WILL DEVELOP THIS AFTN ALONG
INSTABILITY/MOISTURE CONVERGENCE AXIS CUTTING E-W THRU THE CWA.
MODELS SLOWLY PUSH THE SFC BNDRY SOUTH THRU TONIGHT...WITH
NAM/GFS/ECM ALL INDICATING FRONT EXITING THE SRN CWA BY 12Z FRIDAY.
LARGE SCALE FLOW THEN BEGINS TO TRANSITION FROM BLOCKING PATTERN TO
MORE PROGRESSIVE WHEN ERN CONUS RIDGE BEGINS KICKING UPPER LOW
PRESSURE OFF EAST COAST EASTWARD. AS THIS OCCURS...MODELS ADVERTISE
A VORT MAX DROPPING OUT OF CANADA INTO THE LOWER 48 SAT MORNING. NOT
TOO IMPRESSED WITH PCPN POTENTIAL...AND WILL KEEP TOKEN 20 POPS
NORTH. MEANWHILE ACCOMPANYING AIRMASS FILTERING INTO THE CNTRL PLAINS
PROGGED TO BE QUITE COLD FOR THIS TIME OF THE YEAR. AS A MATTER OF
FACT...850MB 0C ISOTHERM WILL APPROACH THE NRN CWA LATE FRIDAY
NIGHT. HAVE DECIDED TO USE BLEND OF COLDER MET/WARMER MAV WITH
LOWS GENERALLY IN THE LOW 40S SAT/SUN MORNING.
DEE
AVIATION...
TAF SITES KOFK/KOMA/KLNK
06Z TAFS
FAIRLY COMPLEX SURFACE PATTERN IS IN PLACE ACROSS THE CENTRAL PLAINS
THIS MORNING. MAIN AREA OF SHOWERS AND THUNDERSTORMS SHOULD BE
ACROSS NORTHEAST NEBRASKA THIS MORNING. IFR CEILINGS EXPECTED AT
KOFK FOR AT LEAST PART OF THE EARLY AND MID MORNING HOURS...THEN
CEILINGS SHOULD LIFT INTO THE MVFR CATEGORY AND POSSIBLY VFR. AT
LEAST TEMPORARY MVFR CEILINGS ARE POSSIBLE THIS MORNING AT KOMA AND
KLNK.
TIMING THUNDERSTORM ACTIVITY WILL BE DIFFICULT AGAIN TODAY. ACTIVITY
AROUND KOFK EARLY THIS MORNING SHOULD END MAINLY BY 12Z...AND THEN
CHANCES INCREASE AGAIN AFTER 21Z. THUNDERSTORM CHANCES AT KOMA AND
KLNK APPEAR HIGHEST AFTER 00Z.
MVFR CEILINGS ARE EXPECTED TO SPREAD INTO KOMA AND KLNK THIS EVENING
AS WINDS SHIFT TO THE NORTH. CEILINGS COULD DROP DOWN INTO THE IFR
CATEGORY AT KOFK AFTER ABOUT 03Z.
MILLER
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$