000
FXUS63 KOAX 171821
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
121 PM CDT FRI MAY 17 2013

.UPDATE...
A FEW UPDATES TO THE CLOUDS FORECAST AND ADDED ISOLATED SHOWERS
AND THUNDERSTORMS TO THE NORTHEAST PART OF THE FORECAST AREA.

&&

.DISCUSSION...
SURFACE WARM FRONT HAS LIFTED TO THE NORTH OF THE FORECAST
AREA...WITH SURFACE DEWPOINTS IN THE 60S. HEATING TODAY TO WARM
TEMPERATURES INTO THE MID AND UPPER 80S AND CONVECTIVE
TEMPERATURES MAY BE REACHED WITH MU CAPES AROUND 2000 J/KG AND
LITTLE OR NO CIN.  BEST MOISTURE SEEMS TO BE IN THE NORTHEAST AND
PARTS OF WRN IOWA. WITH SUBTLE UPPER LEVEL WAVE IN THE
VICINITY...COULD SEE WEAK ELEVATED SHOWERS INCREASE TO ISOLATED
THUNDERSTORMS SO INCLUDED MENTION IN PARTS OF WESTERN IOWA.

&&

.AVIATION...
18Z TAFS FOR KOMA...KLNK...AND KOFK.
MAY SEE ELEVATED SHOWERS OR AN ISOLATED TSRA EAST OF THE TAF SITES
THROUGH EARLY THIS EVENING WITH HEATING DURING THE DAY...LINGERING
MOISTURE...AND A WEAK UPPER LEVEL WAVE.  THE FOCUS FOR CONVECTION
TONIGHT SHOULD BE ACROSS SOUTH DAKOTA IN THE VICINITY OF THE FRONT
AND THE AREA OF LOW PRESSURE. THERE IS A SECONDARY AREA OVER
PARTS OF KANSAS INTO CENTRAL NEBRASKA WITH THE RETURN OF DEEPER
MOISTURE. CONVECTIVE DEBRIS WILL LIKELY SPREAD INTO THE AREA
OVERNIGHT WITH VFR CIGS DEVELOPING. SOUTH WINDS 10 TO 14KTS
TODAY...SHOULD DECREASE TO UNDER 10KTS TONIGHT AND THEN INCREASE
AGAIN ABOVE 12KTS AFTER 15Z SATURDAY. THE LOW LEVEL JET WILL
INCREASE AT KOFK AND MAY NEED TO ADD TO THE TAF FORECAST. WILL
NEED TO WATCH LOW LEVEL MOISTURE RETURN FOR SATURDAY MORNING. DO
HAVE SOME MVFR VSBYS DESPITE THE CLOUD COVER AND COULD SEE SOME
MVFR CIGS TRY TO DEVELOP.

&&

.PREV DISCUSSION... /ISSUED 349 AM CDT FRI MAY 17 2013/

DISCUSSION...

SYNOPSIS...00Z UPPER AIR ANALYSIS INDICATED 70 KT H3 JET MOVING
INTO THE GREAT BASIN ASSOCIATED WITH A SEASONABLY STRONG H5
TROUGH WITH A 50 M H5 HEIGHT FALL AT KOAK. DOWNSTREAM A FLAT
SHORTWAVE RIDGE EXTENDED OVER THE HIGH PLAINS WITH A WEAK
SHORTWAVE TROUGH NOTED IN THE MID MO RIVER VALLEY. AT H85 QUALITY
MOISTURE WAS PRESENT FROM SRN KS INTO TX WITH DEW POINTS OF 10 TO
15 C. THE 08Z SFC ANLYS INDICATED WEAK LOW PRESSURE OVER NE NEB
WITH A WARM FRONT INTO CNTRL IA.

FORECAST...FOR TODAY THE UPSTREAM HIGH PLAINS SHORTWAVE RIDGE WILL
ADVANCE EWD WITH H5 HEIGHT RISES OF 30 TO 40 M OVER THE FA TODAY
LEADING TO FORCING FOR LARGE-SCALE SUBSIDENCE. THE SURFACE WARM
FRONT WILL LIFT NORTH THIS MORNING INTO SODAK WITH LITTLE SENSIBLE
WX EXPECTED FOR OUR CWA THROUGH TONIGHT. ON SAT THE GREAT BASIN
SHORTWAVE TROUGH WILL START TO ADVANCE ONTO THE HIGH PLAINS
LEADING TO CO CYCLOGENESIS AND INCREASING SOUTHERLY WINDS. THE
EML OVER THE HIGH PLAINS /CHARACTERIZED BY H7 TO H5 DELTA-T VALUES
OF +23 C ON THE 00Z UPPER AIR ANALYSIS/ WILL ADVANCE EWD OVER THE
CWA EFFECTIVELY CAPPING THE FA THROUGH THE DAY AND WE HAVE
REMOVED ANY DAY TIME POPS FROM THE FORECAST. AS THE TROUGH
ADVANCES EAST ON SAT A COLD FRONT WILL DROP SOUTHEAST INTO NE NEB
BY EARLY EVENING AND THIS WILL LIKELY BE OUR FIRST CHANCE AT
CONVECTION AFTER 00Z SUN. MODELS ARE CONSISTENT IN INDICATING
INCREASING INSTABILITY ON SAT WITH 2000-3000 J/KG OF MLCAPE BY 00Z
SUN OVER THE CWA. THIS COUPLED WITH AROUND 30-35 KT OF EFFECTIVE
SHEAR SHOULD ALLOW FOR SOME ORGANIZATION AND POTENTIAL FOR ISO
SVR WX WITH A WIND AND HAIL THREAT GIVEN THE INSTABILITY. OTHER
STORMS ARE LIKELY TO DEVELOP FARTHER SOUTH IN WRN NEB/KS ALONG THE
DRY LINE AND WILL START TO ADVANCE EWD ON SAT EVENING. THE CHANCES
OF THESE STORMS MAKING IT INTO OUR CWA ARE HIGHEST IN THE NE NEB
NEAR THE SURFACE BOUNDARY...BUT DECREASE THE FARTHER SOUTH DUE TO
INCREASING MLCIN THROUGH THE EVENING AS THE BOUNDARY LAYER COOLS
IN THE WARM SECTOR...BUT SOME POPS TO THE KS BORDER APPEAR
WARRANTED.

SOME LEFT-OVER CONVECTION MAY STILL BE HANGING AROUND ON SUN
MORNING...MOST LIKELY IN WRN IA AND NE NEB. THIS WILL LIKELY
QUICKLY CLEAR OUT OF THE FA BY MID TO LATE MORNING. AT THE SAME
TIME THE MODELS INDC A 80 KT H3 JET WILL PUNCH THROUGH KS WITH
SIGNIFICANT HEIGHT FALLS CROSSING INTO THE WARM SECTOR AS LOW
PRESSURE MOVES THROUGH CENTRAL NEB TOWARD SE SD ACCOMPANIED WITH A
TRAILING COLD FRONT INTO ERN NEB DURING PEAK HEATING. MID LEVEL
LAPSE RATES ARE EXPECTED TO RECOVER ON SUN CAPPING A MOIST
BOUNDARY LAYER CHARACTERIZED BY DEW POINTS IN THE LOWER TO MID
60S. THIS WILL LIKELY CREATE A MODERATELY TO STRONGLY UNSTABLE
ATMOSPHERE BY EARLY AFTERNOON WITH MLCAPE OF NEAR 3000 J/KG. WITH
THE SIGNIFICANT HEIGHT FALLS OVERSPREADING THE WARM SECTOR AND
SUPPORT FOR ASCENT IN THE LEFT EXIT OF THE BEFORE MENTIONED
JET...THE CAP SHOULD WEAKEN SUFFICIENTLY BY MID AFTERNOON FOR
SURFACED-BASED CONVECTION. SVR WX CERTAINLY SEEMS POSSIBLE...BUT
THE ORGANIZATION OF SAID SVR WX IS A BIT IN DOUBT ATTM. THE BEST
SHEAR PROFILES ARE WELL SOUTH OF THE CWA WITH HODOGRAPHS IN ERN
NEB/WRN IA INDICATING A VEERING LOW LEVEL PROFILE THAT BACKS
ABOVE 400 MB AS THE UPPER LEVEL BUCKLES. THIS HODOGRAPH SHAPE MAY
LEAD TO SOME MESSY STORM MORPHOLOGY ON SUNDAY. NEVERTHELESS GIVEN
THE INSTABILITY AND SOME SHEAR IN THE LOW TO MID LEVELS ISO TO SCT
SVR WX APPEARS LIKELY WITH A WIND AND HAIL THREAT. STORMS WILL
START TO SHIFT E OF THE AREA ON SUNDAY EVENING WITH THINGS
QUIETING DOWN.

AS MORE HEIGHT FALLS MOVE INTO THE BASE OF THE DEVELOPING CENTRAL
US TROUGH ON MONDAY THE UPPER LEVEL LOW OVER THE DAKOTAS IS
EXPECTED TO LINGER IN THE AREA THROUGH MID WEEK WITH A CONTINUED
SCHC/CHC OF SHOWERS...MAINLY IN THE NRN CWA AND COOLER
TEMPERATURES. THIS SYSTEM WILL FINALLY SHIFT E OUT OF THE AREA AND
WILL END THE EXTENDED DRY.

BOUSTEAD

&&

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

$$

ZAPOTOCNY