FXUS63 KOAX 132043
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
343 PM CDT WED APR 13 2011
.SHORT TERM...TONIGHT.
UNSETTLED AND COOLER WEATHER IS LURKING FOR THE AREA. SUBJECTIVE
12Z UPPER AIR ANALYSIS INDICATES UPPER-LEVEL TROUGH DIGGING INTO
THE WESTERN US. 850MB LOW WAS DEVELOPING IN NORTHWEST KS/SOUTHWEST
NEB...WITH INVERTED TROUGH EXTENDING THROUGH CENTRAL NEB TOWARD
SOUTHEAST SD...AND WITH TRAILING COLD FRONT THROUGH THE TX/OK
PANHANDLES AND TOWARD SOUTHERN NM. STEEP 700-500MB LAPSE RATES
WERE NOTED ACROSS NEB AND WESTERN KS INTO CO. MOISTURE WAS LACKING
AT 850MB...WITH NO RAOB SITES IN THE CENTRAL OR WESTERN US WITH A
GREATER DEWPOINT THAN 3C AT KLBF. SURFACE LOW AT 18Z WAS CENTERED
IN SOUTH CENTRAL KS...WITH SURFACE WARM FRONT EXTENDING FROM NEAR
BELOIT KS TO KJYR TO KLNK TO KDSM.
MAIN FORECAST CONCERN IS POTENTIAL FOR SHOWERS OR THUNDER THIS
EVENING AND TONIGHT. OVERALL...THINK CHANCES FOR PRECIP THIS
EVENING LOOK PRETTY SLIM...AS LOW-LEVEL MOISTURE PROFILE REMAINS
LIMITED. HAVE SCALED BACK POPS...THOUGH NOT QUITE CONFIDENT ENOUGH
TO ELIMINATE ALTOGETHER. LIMITED THE ISOLATED THUNDER MENTION TO
SOUTHEAST NEB...WHERE LAPSE RATES ARE STEEPEST...BUT OVERALL THREAT
IS PRETTY LOW. ALSO CUT THUNDER MENTION AFTER MIDNIGHT...WITH RAIN
MENTION FOCUSED ON THE NORTHERN CWA WHERE 850MB FRONTOGENESIS IS
MAXIMIZED AND WHERE 290-305K ISENTROPIC LIFT IS BOTH STRONGER AND
ACCOMPANIED BY LOWER COND PRES DEFS...BUT ALSO DID PULL BACK POPS
FOR TONIGHT AS WELL...ESPECIALLY IN THE CENTRAL CWA. NUDGED UP
TEMPS IN THE SOUTH/SOUTHEAST CWA AS THE COLD SIDE OF THE BOUNDARY
LIKELY WILL NOT MAKE IT THROUGH THE CWA BY MORNING.
MAYES
.LONG TERM...THURSDAY THROUGH WEDNESDAY.
INCREASING PRECIPITATION CHANCES AND TYPES THROUGH FRIDAY ARE THE
PRIMARY FORECAST CONCERNS.
A MID LEVEL LOW PRESSURE AREA IS FORECAST TO EJECT FROM UPPER TROUGH
ALONG THE WEST COAST...ENTERING THE PLAINS AND STRENGTHENING OVER
KANSAS THURSDAY AFTERNOON...THEN GRADUALLY DRIFTING EAST OF OUR AREA
BY SATURDAY MORNING. RAIN CHANCES WILL INCREASE MARKEDLY AS THIS LOW
APPROACHES...WITH A MIX WITH OR CHANGEOVER TO SNOW LIKELY AS COLD
AIR SPILLS SOUTH ON THE BACK SIDE FRIDAY. MODELS ARE GENERALLY IN
DECENT AGREEMENT WITH THE MAJOR FEATURES OF THE FORECAST...WITH ONLY
SMALL DIFFERENCES IN REGARDS TO TIMING OF MAXIMUM PRECIP POTENTIAL.
THE SPEED AND MAGNITUDE OF COLD AIR MOVING INTO THE WESTERN CWA IS
ALSO SLIGHTLY DIFFERENT BETWEEN MODELS.
SURFACE LOW WILL DEVELOP IN CENTRAL KANSAS THURSDAY AFTERNOON AS
UPPER LOW APPROACHES AND DEEPENS. ISENTROPIC UPGLIDE IS MAXIMIZED
THROUGH MUCH OF THE DAY IN THE NORTHERN CWA...BUT BACKING FLOW IN
SURFACE TO 850 LAYER WILL PROVIDE LIFT IN CENTRAL NEBRASKA DURING
THE AFTERNOON. 850 WARM FRONT WILL ALSO COME INTO PLAY THURSDAY
AFTERNOON AS IT ROTATES NORTH TO THE KANSAS NEBRASKA BORDER WITH 45
TO 50KT JET PUMPING HIGHER THETA-E AIR INTO SOUTHEAST NEBRASKA. THUS
WILL CONTINUE LIKELY POPS IN OUR NORTH IN THE MORNING WITH ONLY
SLIGHT CHANCES IN THE SOUTHEAST...THEN INCREASE CHANCE ACROSS THE
BOARD IN THE AFTERNOON. STILL THINK WESTERN IOWA AND EAST CENTRAL
NEBRASKA WILL HAVE LOWEST CHANCES AS FOCUSING MECHANISMS REMAIN
NORTHWEST AND SOUTH OF THAT AREA. ALSO...GIVEN STRENGTH OF THETA-E
ADVECTION...NEGATIVE 850 LIFTED INDICES...STEEP MID LEVEL LAPSE
RATES...STRONG CONVECTION IS POSSIBLE IN THE SOUTH NEAR 850 FRONT.
SPC DAY 2 OUTLOOK STILL PAINTS A SLIGHT RISK FOR SEVERE THERE...AND
WILL RE-EVALUATE WITH LATER FORECASTS AS THINGS START TO UNFOLD
TONIGHT/THURSDAY.
SAME FORCING MECHANISMS WILL CONTINUE TO GENERATE PRECIPITATION
THURSDAY NIGHT...BUT WILL BE SHIFTING EAST AND NORTHEAST WITH
TIME...FOCUSING ON OUR CWA. CONVECTION POTENTIAL WILL ROTATE THROUGH
SOUTHEAST NEBRASKA AND SOUTHWEST IOWA AS 850 FRONT LIFTS NORTH.
ISENTROPIC UPGLIDE IS STILL POTENT AS MOISTURE IS LIFTED NORTH THEN
WEST ACROSS OUR AREA. ALL OF THE CWA SHOULD SEE PRECIPITATION
THURSDAY NIGHT WITH PRECIP AMOUNTS WELL OVER A HALF INCH POSSIBLE
OVER A WIDE AREA. COLDER AIR WILL BEGIN TO FUNNEL SOUTH INTO CENTRAL
NEBRASKA AFTER MIDNIGHT THURSDAY NIGHT BEHIND INVERTED SURFACE
TROUGH. HOWEVER FORECAST SOUNDINGS AND THICKNESS PROFILES SUGGEST
ALL RAIN ACROSS OUR CWA THROUGH 12Z FRIDAY. LOW LEVEL COOLING BEGINS
FRIDAY MORNING IN THE NORTHWEST...WITH INCREASINGLY MORE SHALLOW
SURFACE LAYER OF ABOVE FREEZING AIR. THUS EXPECT A MIX WITH SNOW
THERE FRIDAY MORNING...THEN ALL SNOW IN THE AFTERNOON AS COLD AIR
CONTINUES TO SPILL INTO THE AREA. SNOW ACCUMULATIONS SHOULD BE
MINIMAL GIVEN RELATIVELY WARM GROUND AND DAYTIME SNOW...BUT A COUPLE
OF INCHES IS DEFINITELY POSSIBLE. HAVE PAINTED A STRIPE OF 1 TO 3
INCHES NORTHWEST OF THE NORFOLK AREA DURING THE DAY. A RAIN SNOW MIX
IS ALSO LIKELY AS WE HEAD THROUGH THE AFTERNOON...BUT LOW LEVEL
TEMPERATURE PROFILE SUGGESTS MOSTLY RAIN UNTIL THE EVENING WHEN
INSOLATION ENDS.
PRECIPITATION WILL GRADUALLY END FRIDAY NIGHT AS UPPER LOW SHIFTS
EAST. ANY LINGERING PRECIP SHOULD FAVOR A MIX OF RAIN AND SNOW...BUT
LITTLE IF ANY ACCUMULATION AS TEMPERATURES REMAIN ABOVE FREEZING.
DECREASING CLOUDS SATURDAY WILL ALLOW TEMPS TO REBOUND INTO THE 50S
WITH 60S LIKELY ON SUNDAY.
BROAD UPPER AIR TROUGH REMAINS OVER MIDDLE AMERICA THROUGH WEDNESDAY
OF NEXT WEEK...WITH A SHARPER TROUGH ENTERING OUR AREA ON TUESDAY.
AGAIN PRECIP CHANCES WILL INCREASE WITH THIS FEATURE AND SURFACE
FRONT SETTLES ACROSS MID AMERICA. WILL CONTINUE WITH CHANCE POPS
TUESDAY AND WEDNESDAY WITH TEMPERATURES GENERALLY IN THE 40S AND 50S.
DERGAN
&&
.AVIATION...
TAF SITES KOFK/KOMA/KLNK
18Z TAFS
VFR CONDITIONS ARE EXPECTED TO CONTINUE THROUGH THE TAF CYCLE.
MID-LEVEL CLOUDS WILL CONTINUE TO STREAM THROUGH THE AREA...AND KOFK
MAY FLIRT WITH MVFR CIGS AFTER 12Z...BUT LOW LEVELS LOOK DRY ENOUGH
TO KEEP THEM OUT FOR NOW. DID NOT INCLUDE PRECIP AT ANY TAF
SITES...THOUGH AN ISOLATED SHOWER MAY MOVE NEAR ANY OF THE SITES
THIS EVENING THROUGH MIDDAY THURSDAY...WITH GREATEST RISK AT KOFK.
WINDS AT ALL SITES WILL REMAIN GUSTY OVERNIGHT...WITH NORTHEAST TO
EAST WINDS AS THE SURFACE LOW MOVES ACROSS KANSAS.
MAYES
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$
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