FXUS63 KOAX 190823
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
323 AM CDT SUN JUN 19 2011
.DISCUSSION...
MAIN CONCERN OVER THE NEXT 60 HOURS IS SEVERE WEATHER.
SYNOPSIS...00Z UPPER AIR ANALYSIS INDICATED A 130 KT 300 MB JET
DIVING INTO THE PACIFIC NORTHWEST. THIS WAS ALSO ASSOCIATED WITH
60 M 500 MB HEIGHT FALLS OVER WA/OR. DOWNSTREAM FROM THIS POTENT
SYSTEM...SHORTWAVE TROUGH WAS NOTED OVER NE NV/UT ASSOCIATED WITH
A MID-LEVEL COOL POCKET AND WEAK HEIGHT FALLS. OVER THE PLAINS THE
EML HAD BEEN PUSHED SOUTH...BUT STEEP MID-LEVEL LAPSE RATES WERE
NOTED FROM KRAP TO KAMA AND POINTS WEST. SEASONABLY DEEP MOISTURE
WAS NOTED AT 850 MB WITH AN AXIS OF +15 C DEWPOINTS FROM NORTHWEST
KS INTO THE LOWER MS RIVER VALLEY.
FORECAST...WE SHOULD START OFF THE DAY DRY WITH THE ORGANIZED MCS
ACTIVITY NOW WELL SE OF OUR FA. THIS SHOULD ALLOW FOR SIGNIFICANT
RECOVERY OF THE BOUNDARY LAYER TODAY OVER KS. WITH THE FLOW
INCREASING ACROSS THE ROCKIES TODAY...SURFACE PRESSURES SHOULD
FALL OVER THE WESTERN HIGH PLAINS AND PRODUCE A SIGNIFICANT LOW-
LEVEL RESPONSE OVER THE CENTRAL PLAINS. THE WARM FRONT OVER KANSAS
WILL ATTEMPT TO LIFT NORTH...AND SHOULD GET TO AT LEAST HIGHWAY
36 IN NORTHERN KS BY LATE AFTERNOON. THE STEEP MID-LEVEL LAPSE
RATES OVER THE WESTERN HIGH PLAINS WILL SHIFT EASTWARD AND
EFFECTIVELY CAP THE WARM FRONT NEAR THE KS/NEB BORDER FOR MOST OF
THE DAY...THOUGH THE ATMOSPHERE NEAR THE WARM FRONT SHOULD BE
STRONGLY TO EXTREMELY UNSTABLE WITH 4000-5000 J/KG OF MLCAPE. HAVE
REMOVED POPS THROUGH THE DAY TODAY DUE TO THE PRESENCE OF THE CAP.
WITH EASTERLY LOW LEVEL FLOW...HAVE ALSO LOWERED GOING HIGHS MOST
AREA ONE CATEGORY. THINGS START TO GET MORE INTERESTING AFTER 00Z
AS CONVECTIVE CHANCES INCREASE. THE HIGHEST PROBABILITY OF
CONVECTION WILL BE OVER THE HIGH PLAINS ASSOCIATED WITH THE LARGE-
SCALE FORCING FOR ASCENT FROM THE UT LEAD SHORT-WAVE TROUGH. THIS
WILL QUICKLY GROW UPSCALE AND SHIFT E-NE THROUGH THE EVENING
POSSIBLY REACHING OUR NW FA AS SOON AS 03Z. GIVEN THE 40-50 KT OF
EFFECTIVE SHEAR AND THE INSTABILITY...SEVERE FORWARD PROPAGATING
MCS WITH A SIGNIFICANT WIND DAMAGE THREAT MAY DEVELOP AS THIS MCS
TRACKS EASTWARD. THE OTHER AREA OF CONCERN WILL BE NEAR THE WARM
FRONT AFTER 23Z. POINT FORECAST SOUNDINGS INDC THAT THE CAP WILL
WEAKEN NEAR THE WARM FRONT...AND WITH SUSTAINED CONVERGENCE AS
WELL AS AN INCREASE IN THE LOW-LEVEL JET TOWARD EVENING...MAY SEE
ISOLATED DEVELOPMENT HERE OF AT LEAST NEAR SURFACED-BASED STORMS.
IF STORMS ARE ABLE TO DEVELOP IN THIS AREA...GENERALLY SOUTH OF
I-80 AND WEST OF I-29...SIGNIFICANT SEVERE WEATHER WOULD BE
POSSIBLE AS STORMS SHIFT EAST. CONVECTION WILL TEND TO DIMINISH
AFTER 09Z AS ALL MODELS INDICATE VERY WARM MID-LEVEL TEMPERATURES
MOVING INTO THE CWA.
THE MAIN UPPER LEVEL SYSTEM /CURRENTLY OVER WA-OR/ WILL THEN EJECT
INTO THE PLAINS ON MONDAY. THE MODELS CONTINUE TO SHOW SOME
DISAGREEMENT IN TIMING AND PLACEMENT OF SOME OF THE FEATURES...BUT
MOST MODELS INDICATE THE SURFACE LOW WILL BE MOVING NORTHEAST
THROUGH EASTERN NEBRASKA DURING THE AFTERNOON...WITH THE SURFACE WARM
FRONT MOVING TO NEAR HIGHWAY 20 BY 00Z TUE. PACIFIC FRONT WILL
THEN SWEEP EAST INTO OUR WESTERN FA BY EVENING. SYNOPTIC
SITUATION WOULD SEEM TO INDICATE A SIGNIFICANT THREAT OF SEVERE
WEATHER...AND THIS MAY UNFOLD...BUT THERE ARE SOME CONCERNS.
THE MAIN CONCERN IS THE UPPER LEVEL JET EJECTS ACROSS THE FA
DURING THE AFTERNOON LEADING TO FORCING FOR LARGE-SCALE SUBSIDENCE
SEEN IN THE 500-300 MB DIV-Q. THIS WILL LIKELY CAP THE WARM SECTOR
THROUGH AT LEAST 23Z MON. ONE AREA OF AFTERNOON DEVELOPMENT MAY BE
NORTHEAST OF THE SURFACE LOW FROM FAR NORTHEAST NEB INTO WEST
CENTRAL IOWA WHERE THE SUBSIDENCE IS WEAKER...AND WILL INCLUDE
SOME AFTERNOON CHC POPS THERE. IF STORMS ARE ABLE TO DEVELOP
NORTHEAST OF THE SURFACE LOW...SHEAR PROFILES INDICATE SIGNIFICANT
SUPERCELLS WOULD BE THE RESULT. FARTHER SOUTH...GENERALLY ALONG
AND SOUTH OF I-80...CONVECTION APPEARS MORE LIKELY TO DEVELOP IN
THE DEEPLY MIXED BOUNDARY LAYER AIR OVER EASTERN KS TO THE SOUTH
OF THE STRONG SUBSIDENCE....AND LIFT QUICKLY NORTHEAST THROUGH
THE EVENING. ALTHOUGH SEVERE WEATHER SEEMS LIKELY WITH THIS
ACTIVITY AS WELL...HIGHER DEWPOINT-TEMPERATURE SPREADS WILL
LIKELY LEAD TO A MAINLY WIND/HAIL THREAT. CONVECTION SHOULD
GENERALLY EXIT THE FORECAST AREA AFTER MIDNIGHT.
THE UPPER LEVEL LOW WILL THEN CLOSE OFF OVER SD AND SLOWLY MOVE
INTO MN FROM TUE/WED WITH A GOOD CHANCE OF SHOWERS IN THE NORTH.
GOING FORECAST PAST TUES WAS GENERALLY UNCHANGED.
BOUSTEAD
&&
.AVIATION...
TAF SITES KOFK/KOMA/KLNK
06Z TAFS
MVFR CIGS AND VIS MAY SNEAK INTO KOMA THIS MORNING...BUT SHOULD
CLEAR BY MID-MORNING AS MIXING INCREASES...WITH SOUTHEAST WINDS
INCREASING INTO THE 10-15KT RANGE. SHRA/TSRA ARE EXPECTED TO
DEVELOP IN THE REGION AND MOVE ACROSS THE AREA FROM LATER THIS
AFTERNOON THROUGH THE EVENING HOURS. TIMING IS UNCERTAIN...AND THUS
MENTION IS LIMITED TO PROB30 FOR NOW. ANY CONVECTION WOULD BRING
THE POTENTIAL FOR IFR-RANGE CIGS AND VIS AND VARIABLE GUSTY WINDS.
MAYES
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$