Dense Fog in Kansas, May 3, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
355 AM CDT THU MAY 3 2007

.DISCUSSION...
PRECIP CHANCES THROUGHOUT THE FORECAST CONTINUES TO BE THE MAIN
FORECAST PROBLEM.

08Z WATER VAPOR IMAGERY SHOWS AN UPPER LOW MOVING ACROSS WEST TEXAS
WITH VORT MAXIMUM ROTATING NORTH INTO SOUTHEASTERN KS. RADAR SHOWS
SHOWERS DEVELOPING ACROSS SOUTHEAST KS IN RESPONSE TO THE VORT MAX.
SFC OBS SHOW AN EASTERLY WIND CONTINUES TO ADVECT MOISTURE INTO
EASTERN KS. THIS HAS CAUSED LOW STRATUS AND PATCHY FOG TO BECOME
WIDESPREAD ACROSS THE FORECAST AREA.

MAIN DIFFICULTY IN THE FORECAST IS NAILING DOWN THE SMALL SCALE
DETAILS. MODELS SHOW THERE TO BE PLENTY OF MOISTURE AROUND THROUGH
THE DAY. AND IF WE ARE ABLE TO BREAK OUT WITH SOME SUN THERE COULD
BE SOME INSTABILITY DEVELOP. HOWEVER THE MODELS ARE SUFFERING FROM
FEEDBACK ISSUES AND THE NAM CONTINUES TO BE AN OUTLIER WITH THE SFC
TROUGH/DRYLINE MIXING INTO CENTRAL KS BY THE END OF THE WEEK. WITH
SUCH LOW CONFIDENCE IN THE OPERATIONAL MODELS...RELIED MORE ON THE
00Z GFS ENSEMBLE AND SREF ENSEMBLE MEAN FOR THE FORECAST. THIS ALSO
MAINTAINS SOME CONTINUITY WITH THE PREVIOUS FORECAST.

FOR TODAY EASTERLY SFC WINDS ARE EXPECTED TO CONTINUE THROUGH THE
DAY AS THE SFC REFLECTION OF THE UPPER LOW REMAINS ACROSS OK. THIS
SHOULD KEEP THE STRATUS IN ACROSS THE AREA...ESPECIALLY ACROSS
NORTHERN SECTIONS. THOUGH THERE MAY BE SOME BREAKS IN THE CLOUDS
THIS AFTERNOON ACROSS EAST CENTRAL KS. WITH THIS IN MIND...TWEAKED
MAX TEMPS DOWN A DEGREE. THE CLOUD COVER WOULD ALSO INHIBIT THE
DEVELOPMENT OF SFC BASED INSTABILITY. MODEL GUIDANCE COMING IN WITH
CATEGORICAL POPS MAY BE BASED ON THEIR INSTABILITY PROGS. WHILE
THERE WILL BE SCATTERED TO NUMEROUS SHOWERS AROUND TODAY...DID NOT
FEEL LIKE COVERAGE WOULD BE GREAT ENOUGH FOR CATEGORICAL POPS WITH
NO REAL FEATURE TO FOCUS FORCING FOR PRECIP. THEREFORE WENT BELOW
GUIDANCE AND KEPT POPS IN THE LIKELY CAT FOR THE EASTERN HALF OF THE
FORECAST AREA.

UPPER LEVEL VORT MAXIMUM BEGIN TO LIFT EAST AND NORTHEAST TONIGHT...
AND SHOULD TAKE THE BULK OF THE PRECIP WITH IT. LEFT SOME CHANCE
POPS IN AS 850 WINDS VEER AND DEVELOP A WAA PATTERN OVER THE
RETREATING BOUNDARY. FOR FRIDAY THROUGH SUNDAY...MODELS SHOW THE
ATMOSPHERE BECOMING VERY UNSTABLE MAINLY DO TO THE ADVECTION OF
UPPER 60 DEWPOINTS INTO THE REGION. THIS REMAINS TO BE SEEN BUT HAVE
TRENDED DEWPOINTS UP WITH MODELS SHOWING SOME CONSISTENCY HERE. THE
MEAN UPPER LEVEL TROUGH REMAINS TO THE WEST THROUGH THE PERIOD WITH
SHORTWAVE RIDGING ALONG THE KS/MO STATE LINE...SO FORCING LOOKS
LIMITED AND FORECAST SOUNDINGS HAVE AN EML CAPPING THE BOUNDARY
LAYER. LEFT SOME SLIGHT CHANCE POPS IN FOR FRIDAY MAINLY BECAUSE OF
THE MODEL PROGS OF INSTABILITY. THE SREF AND GFS ENSEMBLE BOTH
SUPPORT THE IDEA OF CONVECTION BACK BUILDING SOUTH TOWARDS THE
NEB/KS STATE LINE FRIDAY EVENING...BUT NOT NEARLY AS AGGRESSIVE AS
THE NAM. THEREFORE INCREASED POPS INTO THE CHANCE CAT FOR NORTH
CENTRAL ZONES AND ALONG THE STATE LINE. FOR SATURDAY AND
SUNDAY...THE DRYLINE IS EXPECTED TO EVENTUALLY MIX OUT INTO THE
PLAINS. THE GFS ENSEMBLE HINTS MORE FOR SUNDAY. NEVERTHELESS SHOW
POPS GRADUALLY MOVING EAST FROM SATURDAY THOUGH SUNDAY. SINCE THE
ENSEMBLE DATA WAS USED MORE...IT IS MORE DIFFICULT TO NAIL DOWN THE
TIMING. WILL NEED TO WATCH LATER MODEL RUNS AND FINE TUNE THE
FORECAST. SUSTAINED SOUTHERLY WINDS BRINGING WARM AIR NORTH AND SOME
SUNSHINE FOR FRIDAY AND SATURDAY ARGUE FOR A WARM UP. 850 TEMPS
SUPPORT GOING FORECAST OF LOWER 80S AND ONLY MADE SOME COSMETIC
CHANGES.

DID NOT MAKE ANY CHANGES TO THE FORECAST BEYOND SUNDAY. MEDIUM RANGE
MODELS CONTINUE TO SHOW AN UPPER LOW TO THE WEST OF THE FORECAST
AREA FOR THE FIRST HALF OF NEXT WEEK. THERE ARE SOME TIMING
DIFFERENCES IN LIFTING AN UPPER LEVEL SHORTWAVE TROUGH ACROSS THE
PLAINS. OTHERWISE GOING FORECAST LOOKS PLAUSIBLE.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...NONE.

&&

WOLTERS

HAZARDOUS WEATHER OUTLOOK...CORRECTED
NATIONAL WEATHER SERVICE TOPEKA KS
503 AM CDT THU MAY 3 2007

KSZ008>012-020>024-026-034>040-054>056-058-059-041015-
REPUBLIC-WASHINGTON-MARSHALL-NEMAHA-BROWN-CLOUD-CLAY-RILEY-
POTTAWATOMIE-JACKSON-JEFFERSON-OTTAWA-DICKINSON-GEARY-MORRIS-
WABAUNSEE-SHAWNEE-DOUGLAS-LYON-OSAGE-FRANKLIN-COFFEY-ANDERSON-
503 AM CDT THU MAY 3 2007

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST CENTRAL...NORTH
CENTRAL AND NORTHEAST KANSAS.

.DAY ONE...TODAY AND TONIGHT

A FEW THUNDERSTORMS ARE POSSIBLE TODAY AND TONIGHT. OTHERWISE
PATCHY MORNING FOG COULD TEMPORARILY REDUCE LOCAL VISIBILITIES
BELOW A MILE.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

ISOLATED THUNDERSTORMS ARE POSSIBLE FRIDAY THROUGH SATURDAY MAINLY
DURING THE AFTERNOON AND EVENING. THE BETTER CHANCE FOR
THUNDERSTORMS SHOULD BE ACROSS NORTH CENTRAL KANSAS. THERE IS THE
POSSIBILITY FOR THE THUNDERSTORMS TO PRODUCE LARGE HAIL AND
DAMAGING WINDS.

THUNDERSTORM CHANCES SPREAD EAST TO INCLUDE ALL OF THE OUTLOOK
AREA FOR SUNDAY THROUGH WEDNESDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS SHOULD NOT BE NEEDED TODAY OR TONIGHT.

WOLTERS