FXUS63 KOAX 210838
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
338 AM CDT SUN AUG 21 2011
.DISCUSSION...
THUNDERSTORM CHANCES TONIGHT INTO MONDAY ARE THE PRIMARY FORECAST
CONCERNS...WITH WARMER A SECONDARY ISSUE.
THE COMBINATION OF DEEP UPPER LEVEL LOW PRESSURE OVER JAMES BAY AND
WEAK RIDGING OVER THE ROCKIES WAS MAINTAINING NORTHWEST FLOW ALOFT
ACROSS THE CENTRAL AND NORTHERN PLAINS. ONLY MINOR CHANGES IN THIS
FLOW PATTERN IS EXPECTED OVER THE NEXT SEVERAL DAYS ACROSS OUR PART
OF THE WORLD. A STRONG SHORTWAVE MOVING ALONG THE CANADIAN BORDER AT
MID WEEK WILL DRIVE A COLD FRONT THROUGH THE CWA ON WEDNESDAY...BUT
UNTIL THEN...WARMER TEMPERATURES AND SPORADIC THUNDERSTORM CHANCES
WILL BE IN THE FORECAST.
SURFACE HIGH PRESSURE WAS OVER THE REGION THIS MORNING WITH
ATTENDANT LIGHT WINDS. WINDS WERE BECOMING SOUTH OR SOUTHEASTERLY IN
THE HIGH PLAINS ON THE BACK SIDE OF THE HIGH...WITH THIS FLOW
EXPECTED IN OUR AREA LATER TODAY. WITH THAT...INCREASING LOW LEVEL
MOISTURE IS EXPECTED TO DRIVE DEW POINTS FROM THE UPPER 50S TO
MIDDLE 60S CURRENTLY TO NEAR OR ABOVE 70 LATER TONIGHT AND MONDAY.
STRONG LOW LEVEL JET IS ALSO FORECAST TO DEVELOP IN WESTERN KANSAS
AND NEBRASKA TONIGHT...AND EVENTUALLY TURNING SOUTHWESTERLY AFTER
MIDNIGHT OVER EASTERN NEBRASKA AHEAD OF WEAK MID LEVEL WAVE DROPPING
SOUTHEAST. SPEED CONVERGENCE IS NOTED ALONG OUR WESTERN CWA WITH
ISENTROPIC UPGLIDE/WARM ADVECTION OCCURRING ABOVE 850MB. GFS
FORECAST SOUNDINGS ALONG THE MISSOURI RIVER SHOW NEARLY 1500 J/KG OF
ELEVATED CAPE WITH MINIMAL CINH. NAM IS NOT AS ROBUST BUT STILL
SHOWS SOME INSTABILITY ABOVE 700 MB. ALREADY HAVE A CHANCE FOR
STORMS GOING TONIGHT...SO WILL INCREASE TO OR ABOVE 50 PERCENT AND
REALIGN AXIS OF HIGHEST CHANCES ALONG THE MISSOURI RIVER.
COULD HAVE LINGERING PRECIP MONDAY MORNING...BUT THE MAJORITY OF
MORNING AND EARLY AFTERNOON LOOKS DRY. SOUTHERLY LOW LEVEL FLOW WILL
ALLOW MOISTURE TO REMAIN/RETURN TO OUR CWA...AND ALSO PUSH
TEMPERATURES INTO THE UPPER 80S OR LOWER 90S FOR MUCH OF THE AREA.
BOTH NAM AND GFS SOUNDINGS SHOW AFTERNOON MUCAPE VALUES TOPPING 3000
J/KG...BUT MODEST CINH SUGGESTS STORMS MAY NOT OCCUR. LACK OF
SYNOPTIC AND OBVIOUS MESOSCALE TRIGGERS ALSO POINTS TO LOW
PROBABILITY OF STORMS. HOWEVER...GIVEN THE POTENTIAL FOR STORMS
EARLIER IN THE DAY LAYING DOWN OUTFLOW BOUNDARIES FOR FOCUSING
MECHANISMS...AND VERY MOIST ATMOSPHERE...WILL CONTINUE WITH A CHANCE
FOR STORMS MONDAY AFTERNOON AND EVENING...ESPECIALLY IN OUR SOUTHERN
CWA. 30 TO 35KTS OF 0-6KM SHEAR WILL COINCIDE WITH HIGH INSTABILITY
TO SUGGEST SOME SUPERCELL STORMS ARE POSSIBLE IF THINGS GET GOING.
SPC HAS NOT OUTLOOKED OUR AREA IN THEIR DAY 2 DISCUSSION GIVEN THE
ABOVE NEGATIVES...BUT IS STORMS DO FIRE...LARGE HAIL AND DAMAGING
WINDS WILL BE POSSIBLE.
SIMILAR AIRMASS WILL BE IN PLACE LATE MONDAY NIGHT INTO TUESDAY.
SHORTWAVE MOVING THROUGH THE NORTHERN PLAINS WILL LIKELY SPARK
CONVECTION LATE MONDAY NIGHT NORTH OF OUR AREA...AND MAY SKIRT OUR
NORTH OR NORTHEAST CWA. WARMER MID LEVEL TEMPERATURES TUESDAY
AFTERNOON SHOULD CAP ANY CONVECTION THEN...SO WILL LOWER OUR CHANCE
POPS DOWN A BIT. STILL VERY UNSTABLE WITH DEEP MOISTURE...SO CAN NOT
TOTALLY RULE OUT A STRAY STORM. THEN TUESDAY NIGHT...UPPER WAVE WILL
BE MOVING WELL AWAY FROM OUR AREA DESPITE SURFACE FRONT APPROACHING
OUR NORTHWEST.
TEMPERATURES WILL BE WARMER TODAY...REACHING THE LOW TO MID 80S
ACROSS THE BOARD. THEN EVEN WARMER AND MORE HUMID CONDITIONS WILL
PREVAIL MONDAY AND TUESDAY AS SOUTHERLY LOW LEVEL FLOW AND
INCREASING 850 TEMPS PUSH HIGHS TO BETWEEN 85 AND 90 MONDAY...THEN
INTO THE LOWER 90S TUESDAY.
WILL NOT MAKE ANY CHANGES TO THE FORECAST BEYOND TUESDAY NIGHT.
TEMPERATURES WILL STILL BE WARM WEDNESDAY AS THE COLD FRONT LIMPS
THROUGH THE AREAS. HIGHS NEAR 90 ARE LIKELY. THEN 80S AND DRY
CONDITIONS ARE EXPECTED THURSDAY THROUGH SATURDAY.
DERGAN
&&
.AVIATION...
FOR THE 06Z TAFS...
VARIABLE CONDITIONS LIKELY THROUGH 15Z WITH POSSIBLE FOG AND IFR
CIGS IN AREAS THAT REMAIN CLEAR THE LONGEST. MVFR CIGS SLOWLY
WORKING SOUTH FROM NORTHEAST NEBRASKA EXPECTED TO LINGER IN THE KOFK
AREA AND LIMIT FOG DEVELOPMENT THERE. INCREASING CHANCE OF
THUNDERSTORMS AFTER 00Z.
FOBERT
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$