FXUS63 KOAX 090243
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
943 PM CDT SUN MAY 8 2011
.DISCUSSION...
TORNADO WATCH THAT WAS ISSUED EARLIER HAS BEEN CANCELLED FOR ALL
OF NORTHEAST NEBRASKA. WHILE THERE WAS SOME POTENTIAL FOR AN HOUR
OR SO BEFORE SUNSET...THE CAP WAS JUST TOO STRONG ACROSS
NEBRASKA...WITH STILL 75 TO 100 J/KG OF CIN TO OVERCOME. A COUPLE
OF CELLS TRIED TO INITIATE...BUT CONVERGENCE WASNT STRONG ENOUGH.
THERE WAS ALSO SOME CONCERN THAT THE CELLS HUGGING THE SOUTH
DAKOTA BORDER COULD TURN RIGHT...BUT THE SEVERE THREAT SHOULD BE
NORTH OF OUR AREA IN SOUTH DAKOTA.
NOW...WHAT HAPPENS FOR THE REMAINDER OF THE NIGHT IS STILL IN
QUESTION. BASE FEELING IS THAT IT WILL PROBABLY REMAIN DRY...BUT
STRENGTHENING LOW LEVEL JET STILL BOTHERS ME JUST A BIT...THUS
LEFT IN SOME SMALL CHANCE POPS FOR AREAS NORTH OF INTERSTATE
80...BUT CONFIDENCE IS VERY LOW. OTHERWISE...STILL EXPECTING A
STRATUS DECK TO DEVELOP OVERNIGHT...AND WOULD NOT EVEN BE SURPRISED
TO SEE SOME SPOTTY DRIZZLE OR AREAS OF FOG AROUND SUNRISE AS WELL.
DEWALD
&&
.PREV DISCUSSION... /ISSUED 323 PM CDT SUN MAY 8 2011/
SHORT TERM...TONIGHT.
QUESTIONS STILL REMAIN ABOUT WHETHER CONVECTION WILL DEVELOP WITH
THE RETREATING MOISTURE IN OUR FA OR NOT. LATEST RUC ANALYSIS
WOULD INDICATE THAT THE CAP IS WEAKENING ACROSS CENTRAL AND NORTH
CENTRAL NEB WHERE EARLIER SHORT RANGED HI-RES MODELS INDICATED
CONVECTION WOULD DEVELOP. 18Z SURFACE ANALYSIS INDICATED LOW
PRESSURE OVER NORTHEAST CO WITH A WEAKLY DEFINED WARM FRONT FROM
CENTRAL NEB INTO CENTRAL MO. THIS BOUNDARY MAY MAKE A LITTLE MORE
PROGRESS NORTHWARD THIS AFTERNOON...BUT THEN STALL THROUGH THE
OVERNIGHT HOURS. PERSISTENT PRESSURE FALLS OVER THE WESTERN HIGH
PLAINS IS KEEPING CONVERGENCE ALONG THIS BOUNDARY WEAK AND THIS
ISN'T EXPECTED TO CHANGE THROUGH THE AFTERNOON. SHORTWAVE TROUGH
MENTIONED IN THE MORNING UPDATE AFD APPEARED TO BE LOCATED AT 19Z
/PER WATER VAPOR/ OVER CENTRAL NEBRASKA. THIS WILL CONTINUED TO
LIFT SLOWLY NORTHEAST WHILE WEAKENING AS IT MOVES INTO THE MEAN
RIDGE. THUS LITTLE IN THE WAY OF LARGE-SCALE FORCING CONTINUES TO
BE EXPECTED WITH THIS WAVE. LATEST SHORT RANGE CONVECTION ALLOWING
MODELS CONTINUE TO TOSS SOME DOUBT AS WELL WHICH NOW INDICATE THAT
WE WILL STAY CONVECTION FREE. GIVEN ALL THE ABOVE FACTORS...WE ARE
STILL UNSURE IF CONVECTION WILL DEVELOP. THUS WILL MAINTAIN SOME
CHC POPS THROUGH THE EVENING HOURS...MAINLY IN THE NORTHERN FA.
IF CONVECTION DOES DEVELOP...SEVERE WEATHER CHANCES SEEM PRETTY GOOD
GIVEN THE CAPE AND SHEAR PROFILES. VERY LARGE HAIL STILL LOOKS TO BE
THE MAIN THREAT WITH AN OUTSIDE CHANCE OF A TORNADO. WIND WOULD ALSO
BE A CONCERN AS STORM MODE WOULD FAVOR MORE HP TYPE SUPERCELLS GIVEN
THE WEAK MID AND UPPER LEVEL STORM RELATIVE FLOW. OTHERWISE
CONVECTION CHANCES SHOULD DIMINISH BY LATE EVENING WITH THE FOCUS
SHIFTING NORTHWARD TOWARD THE 850 MB WARM FRONT AND THUS WILL END
PRECIP CHANCES SHORTLY AFTER MIDNIGHT. WITH CONTINUED SOUTHERLY FLOW
OVERNIGHT...AND INCREASING LOW CLOUDS...WE SHOULD SEE A MILD NIGHT
ACROSS THE AREA WITH LOWS IN THE MID 60S.
LONG TERM...MONDAY THROUGH SUNDAY.
VERY WARM AIR WILL BE IN PLACE ACROSS THE FORECAST AREA MONDAY WITH
THE OVERNIGHT CONVECTION HAVING MOVED NORTH AND EAST OF THE AREA.
LOW LEVEL MOISTURE AND LOW CLOUDS WILL BE IN PLACE EARLY ON. THE NAM
(NORTH AMERICAN MESOSCALE MODEL) HOLDS ON TO THESE CLOUDS AND HOLD
BACK TEMPERATURES ...HOWEVER THE GFS BREAKS THEM UP AND ALLOWS
TEMPERATURES TO WARM WELL INTO THE 80S. AM COUNTING ON THE CLOUDS
TO BREAK UP WITH DRIER AIR WORKING IN FROM THE SOUTHWEST. HIGHS IN
THE SOUTH SHOULD RANGE FROM THE MID 80S TO THE LOWER 90S.
NORTHEAST NEBRASKA SHOULD HOLD ON TO THE CLOUDS LONGER AND HAVE
HIGHS MOSTLY FROM 80 TO 85 THERE.
TUESDAY THE CLOSED MID TROPOSPHERIC LOW OVER SOUTHERN CALIFORNIA WILL
ELONGATE NORTHEASTWARD WITH ONE AREA OF CLOSED LOW PRESSURE OVER
MONTANA/THE WESTERN DAKOTAS AND THE OTHER OVER ARIZONA. THE SHORT RANGE
MODELS ARE IN GOOD AGREEMENT WITH THIS AND BRING A DRY COLD FRONT
INTO THE FORECAST AREA. THE THERMAL AXIS STARTS OUT OVER THE
FORECAST AREA EARLY TUESDAY THEN SHIFTS INTO KANSAS AND MISSOURI
BY EVENING. WITH SUNSHINE AND DRIER DEWPOINTS TO WORK WITH
TEMPERATURES SHOULD WARM AGAIN INTO THE 80S TO LOWER 90S.
TUESDAY NIGHT INTO WEDNESDAY THE SURFACE FRONT REMAINS DRAPED OVER
THE FORECAST AREA AND AS THE SOUTHERN STREAM MID LEVEL LOW ORGANIZES
OVER EASTERN COLORADO...DEEPER MOISTURE ON A STRENGTHENING LOW LEVEL
JET IS DRAWN BACK NORTHWARD. SHOWERS AND THUNDERSTORMS SHOULD
BEGIN TO INCREASE OVERNIGHT TUESDAY INCREASING IN COVERAGE FOR WEDNESDAY.
FOR THE WEDNESDAY NIGHT AND THURSDAY PERIOD...THE GFS HAS THE
CANADIAN LOW BECOMING STRONGER AND ROTATING INTO NORTH DAKOTA. THE
ECMWF (EUROPEAN CENTRE FOR MEDIUM RANGE FORECAST) KEEPS THE CANADIAN
LOW IN CANADA AND DEVELOPS A STRONGER LOW OVER NEBRASKA. BOTH THE
GFS/ECMWF HAVE MORE WIDESPREAD PRECIPITATION WEDNESDAY EVENING. THIS
ALSO AFFECTS THE PRECIPITATION PATTERN IN THAT THE GFS DIMINISHES
THE PRECIPITATION THURSDAY...WHILE THE ECMWF IS STIL TO THE WEST
OF THE AREA AND HOLDS ONTO THE PRECIPITATION THURSDAY THROUGH
SATURDAY FOR PARTS OF THE FORECAST AREA. THE GFS IS MOSTLY DRY
THURSDAY AFTERNOON THROUGH FRIDAY NIGHT WITH INSTABILITY SHOWERS
SATURDAY. THE GFS HAS TRENDED MORE TOWARD THE ECMWF FOR
WEDNESDAY...AND HPC IS USING A 20/80 BLEND OF THE ECMWF AND THE
ECMWF ENSEBLE MEAN. THUS HAVE ADJUSTED THE FORECAST TO BE MORE
PESSIMISTIC WITH HIGHER RAIN CHANCES FOR WEDNESDAY NIGHT AND THE
REST OF THE WEEK INTO SATURDAY.
AVIATION...
TAF SITES KOFK/KOMA/KLNK
18Z TAFS
CONDITIONS WILL REMAIN VFR THROUGH A GOOD PART OF THE AFTERNOON OVER
THE TERMINALS WITH CU DEVELOPING AT LNK AND OFK BY LATE AFTERNOON
AOA 3 K FT. IF CONVECTION DEVELOPS ALONG THE NORTHWARD MOVING WARM
FRONT...IT APPEARS OFK AND MAYBE OMA WOULD HAVE THE BEST SHOT AT
SEEING THIS ACTIVITY WITH MVFR CONDITIONS LIKELY IN CONVECTION. AS
LOW LEVEL MOISTURE CONTINUES TO STREAM NORTH OVERNIGHT...WILL LIKELY
SEE A MVFR/IFR STRATUS DECK AT ALL TAF SITES...BUT ESPECIALLY
OMA/OFK.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$
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