000
FXUS63 KOAX 130453
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
1153 PM CDT SUN MAY 12 2013

.AVIATION...06Z TAFS FOR KOFK...KLNK AND KOMA.

VFR CONDITIONS WILL PREVAIL THROUGH MONDAY EVENING. SCATTERED TO
BROKEN MID AND HIGH CLOUDS STREAMING NORTH TO SOUTH WILL BE OVER
TAF SITES THROUGH MONDAY AFTERNOON. OTHERWISE SOUTHEAST WINDS
OVERNIGHT WILL BECOME SOUTH AND INCREASE INTO THE 15 TO 25KT RANGE
BEFORE 18Z.

DERGAN

&&

.PREV DISCUSSION... /ISSUED 316 PM CDT SUN MAY 12 2013/

DISCUSSION...
TEMPERATURES HAVE RECOVERED NICELY FROM RECORD MORNING LOWS TODAY
UNDER PARTLY CLOUDY SKIES SOUTH OF I-80 IN NEB AND CLEAR SKIES
ELSEWHERE.  SUBJECTIVE 12Z UPPER AIR ANALYSIS INDICATES UPPER LOW
TRAVERSING THE EASTERN US...WITH CENTER IN EASTERN ONT AND 500MB
HEIGHT FALLS MAXIMIZED IN THE EASTERN GREAT LAKES.  UPPER-LEVEL HIGH
WAS CENTERED NEAR THE CA/NV BORDER...WITH NORTHWESTERLY FLOW ACROSS
THE CENTRAL US.  UPPER-LEVEL JET WAS SEASONALLY STRONG...WITH 120KT
JET STREAK BEHIND THE UPPER LOW AND 130KT ROUNDING ITS BASE...WHILE
130KT JET STREAK WAS COMING ASHORE IN BC.  DRY AIR WAS ENTRENCHED
ACROSS MOST OF THE CONUS AT 850MB...WITH 8C+ DEWPOINTS LIMITED TO
EXTREME SOUTH TX AND ALONG THE EAST COAST.  POOL OF SUB-0C
TEMPERATURES AT 850MB WAS LOCATED OVER THE GREAT LAKES AND AS FAR
WEST AS SD/IA/MO/TN.

MAIN FORECAST CONCERNS ARE DRY/HOT WEATHER ON TUESDAY...AND
INTERMITTENT CHANCES OF THUNDERSTORMS WEDNESDAY NIGHT THROUGH
SUNDAY.  AS UPPER-LEVEL FLOW TRANSITIONS TO ZONAL...WILL SEE MID-
LEVEL WARM AIR ADVECTION AND SOUTH TO SOUTHEAST WINDS BRING MUCH
WARMER TEMPERATURES MONDAY AND ESPECIALLY TUESDAY.  HAVE BOOSTED
TEMPS IN THE NORTHWEST TO NEAR 90 ON MONDAY...WHERE MIXING WILL BE
STRONGEST.  ALSO BOOSTED TEMPS EVERYWHERE BUT THE NORTHWEST FOR
TUESDAY...GIVEN MIXING UP TO AROUND 750MB AT LEAST...COMBINED WITH
DRY LOW-LEVEL PROFILE.  RAISING TEMPS ON TUESDAY PUTS SOME LOCATIONS
BACK TO NEAR-RECORD READINGS AND REFLECTS WARMING TREND IN MID-LEVEL
TEMPS PROGS.  HAVE TRENDED MIN TEMPS AND DEWPOINTS CLOSER TO MOS
GUIDANCE THROUGH WEDNESDAY...WHICH IS COOLER/LOWER THAN RAW GUIDANCE
AND HAS BEEN VERIFYING MORE ACCURATELY LATELY.  ALSO USED MIX-DOWN
TOOLS TO HELP REFINE DEWPOINT FORECAST.  THE COMBINATION DOES BRING
PREDICTED RH ON TUESDAY TO NEAR THE 20% THRESHOLD.  WINDS SHOULD BE
OUT OF THE SOUTHWEST AT AROUND 15-20 MPH...AND THUS THE AREA WILL BE
BORDERLINE FOR RED FLAG CONDITIONS.  GROUND IS QUITE GREEN NOW
THOUGH...AND GIVEN MARGINAL/BORDERLINE FIRE WEATHER FORECAST RIGHT
NOW...HAVE OPTED TO HOLD OFF ON A FIRE WEATER WATCH.

KEPT PRECIP MENTION OUT OF THE AREA DURING THE DAY ON TUESDAY WITH
STRONG CAPPING.  LATER IN THE EVENING/TUESDAY NIGHT...AS A WEAK
FRONT MOVES THROUGH THE CWA AND LOW-LEVEL JET INCREASES...A FEW
SHOWERS/THUNDERSTORMS MIGHT BE ABLE TO DEVELOP BEHIDN THE FRONT.
WITH SUCH LIMITED MOISTURE...CONFIDENCE IS VERY LOW...AND HAVE
PULLED BACK POPS SIGNIFICANTLY.  ALSO KEPT WEDNESDAY DRY AS
SHOWERS/THUNDERSTORMS MAY FESTER ALONG THE WEAKENING FRONT IN KS/MO.
 MODELS HINT THAT FRONT MAY RETREAT INTO THE SOUTHEAST CWA ON
WEDNESDAY NIGHT...AND HAVE INCLUDED A CHANCE OF
SHOWERS/THUNDERSTORMS THERE.

DESPITE MODEL BLENDS WEIGHTED BY OVER-QPF-ING MODELS...DO BELIEVE
THURSDAY WILL BE LARGELY DRY ACROSS THE CWA.  CAPPING WILL BE IN
PLACE DURING THE DAY...AND WITH 500MB HEIGHTS RISING AND 850MB FLOW
REGROUPING...SEE NOTHING THAT WOULD FORCE THUNDERSTORMS TO DEVELOP
IN THIS AREA BEFORE 00Z FRIDAY.  DO THINK STORMS WILL FIRE ALONG THE
DRYLINE WELL WEST OF THE AREA...AND THESE STORMS MAY WORK ACROSS THE
REGION OVERNIGHT THURSDAY NIGHT.  SIMILARLY THINK MUCH OF FRIDAY
DAYTIME MAY BE DRY AS OVERNIGHT CONVECTION MOVES AWAY...WHILE
INSTABILITY BUILDS DURING THE DAY.  STORMS ONCE AGAIN SHOULD FIRE
WEST OF THE CWA...THOUGH A LITTLE CLOSER THIS TIME...AND WORK ACROSS
THE REGION THROUGH THE EVENING/OVERNIGHT.  BY SATURDAY...UPPER-LEVEL
TROUGH APPROACHES THE REGION MROE CLOSELY...AND SURFACE LOW SHOULD
BE TRACKING INTO THE MISSOURI VALLEY REGION.  ONCE AGAIN...SHOULD
SEE STORMS DEVELOP DURING THE AFTERNOON ALONG THE FRONT...THEN PUSH
ACROSS THE AREA IN THE EVENING.  CURRENTLY THINK THE SYSTEM WILL
MOVE TO THE EAST BY SUNDAY...LEAVING CWA MORE IN A CHANCE FOR
SHOWERS THAN THUNDERSTORMS IN THE COOLER NORTHWEST FLOW BEHIND THE
SYSTEM.  WOULD THINK POTENTIAL FOR SEVERE WEATHER WOULD BE GREATEST
ON FRIDAY/SATURDAY AS THE CWA IS CLOSER TO CONVECTIVE
INITIATION...BUT MANY DETAILS NEED TO WORK THEMSELVES OUT BETWEEN
NOW AND THEN TO BE MORE CONFIDENT.  GFS/ECMWF ARE STILL EXHIBITING
SOME TIMING DIFFERENCES IN THE EXTENDED RANGE REGARDING THE PASSAGE
OF THE SURFACE LOW...WHICH AFFECTS THE THUNDERSTORM POTENTIAL IN ANY
GIVEN PERIOD.  OVERALL...IN COORDINATION WITH NEIGHBORS...MADE
SEVERAL SIGNIFICANT CHANGES TO EXTENDED FORECAST BEYOND MODEL
BLENDS...INCLUDING SUBSTANTIAL REDUCTIONS TO DAYTIME POPS ON BOTH
THURSDAY AND FRIDAY...AS WELL AS NUDGING MIN TEMPS AND DEWPOINTS
TOWARD MOS GUIDANCE THROUGHOUT THE EXTENDED.

MAYES

&&

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

$$