Flash Flooding and Heavy Rain in Nebraska, August 4 to 5, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
358 AM CDT THU AUG 4 2011

.SYNOPSIS...

H5 PATTERN REMAINS RELATIVELY SIMILAR TO LAST NIGHT...AT LEAST IN
TERMS OF THE FLAT RIDGE ENCOMPASSING MOST OF THE SOUTHERN UNITED
STATES...WITH QUASI-ZONAL FLOW ACROSS MUCH OF THE CENTRAL PLAINS.
JUST NORTH OF THE STAGNANT RIDGE...THE PATTERN REMAINS FAIRLY ACTIVE
AS ANOTHER SHORTWAVE DISTURBANCE PUSHED EAST FROM NORTHEASTERN
COLORADO INTO CENTRAL NEBRASKA.

PRECIPITATION CONTINUES TO BE WELL SAMPLED BY AREA RADARS WITH TWO
MAIN CLUSTERS NOTED.  ONE ACROSS NORTHWESTERN PORTIONS OF THE
CWA...AND A SECOND EXTENDING FROM SOUTHEASTERN KANSAS...NORTH TO SOUTH
CENTRAL NEBRASKA.  A QUICK HAND ANALYSIS OF THE 03Z SURFACE REVEALS
A STATIONARY BOUNDARY ACROSS SOUTHERN OKLAHOMA...EXTENDING
WEST...THEN NORTH ALONG THE HIGHER TERRAIN OF EASTERN COLORADO AND
WYOMING.  A COLD FRONT WAS ANALYZED ALONG THE INTERNATIONAL BORDER
OF CANADA.

&&

.DISCUSSION...

H5 VORT MAX CONTINUES TO PUSH EAST EARLY THIS MORNING...WITH A PV
ANOMALY NOTED ACROSS EASTERN WYOMING. SHOWERS AND THUNDERSTORMS HAVE
BEEN ONGOING FOR MUCH OF THE OVERNIGHT...WITH THE MOST RECENT ECHOS
SHOWING UP ACROSS CENTRAL KEITH COUNTY.  AS BEEN THE CASE OVER THE
LAST COUPLE NIGHTS...THE MODEL SOLUTIONS SEEM TO BE STRUGGLING WITH
THE TIMING OF THE WAVES AND THE ASSOCIATED PRECIPITATION.  EARLY
THIS MORNING...CERTAINLY HAS NOT BEEN AN EXCEPTION.  HAVE KEPT THE
POPS HIGHEST FOR THE EARLY MORNING HOURS OVER THE FAR SOUTHEASTERN
ZONES AND ACROSS THE WEST...WITH PRECIPITATION ENDING BY 12Z FOR THE
CWA.  THIS MAY NEED TO BE ADJUSTED GIVEN THE CURRENT TRENDS.  OTHER
THAN PRECIPITATION CHANCES...FOG DEVELOPMENT IS POSSIBLE.  LIGHT
SOUTHEASTERLY FLOW WITH AN ABUNDANTLY MOIST BOUNDARY LAYER WILL
POTENTIALLY LOWER VISIBILITIES AOB 1SM FOR FOG FAVORED LOCATIONS
SOUTH OF HIGHWAY TWO.  GIVEN THE PATCHY NATURE OF THE FOG...WILL
FORGO A HEADLINE AT THIS TIME.

THE PATTERN REMAINS ACTIVE TODAY AND TONIGHT...WITH THE NEXT
DISTURBANCE ON TIME FOR ARRIVAL.  SHOWERS AND THUNDERSTORMS ARE ONCE
AGAIN EXPECTED ACROSS THE WEST THIS AFTERNOON...THEN POSSIBLY
SHIFTING EAST OVERNIGHT.  AS EXPECTED...MODELS GENERATED A GOOD
CONVECTIVE CLUSTER SOMEWHERE ACROSS THE REGION...BUT DISAGREE ON
TIMING AND LOCATION.  GFS AND NAM ARE FURTHER SOUTH WHERE THE NOSE
OF LLJ AND STRONGEST THETA-E ADVECTION WILL BE.  THE EURO BRINGS THE
COMPLEX OVER MUCH OF THE CWA.  FOR THE FORECAST...TRENDED TOWARD THE
GFS AND NAM WITH THE HIGHEST POPS OVER THE WESTERN AND SOUTHERN
COUNTIES OF THE LBF CWA...BUT DID KEEP SLIGHT CHANCE POPS ELSEWHERE
TONIGHT AS FORECAST CONFIDENCE REMAINS LOW.  WITH THE BEST
INSTABILITY EXPECTED SOUTH OF THE CWA...SEVERE WEATHER WILL NOT BE
MUCH OF A CONCERN.  BUT...HEAVY RAINFALL WILL REMAIN A
THREAT...WITH RAIN POTENTIAL OF ONE TO TWO INCHES AN HOUR.
BUFER SOUNDINGS INDICATE WARM CLOUD PROCESSES IN PLACE...WITH SKINNY
CAPE...PLENTIFUL PWATS OF GREATER THAN AN INCH AND A HALF...SLOW TO
MODERATE STORM MOTIONS AND CORRESPONDING K-INDEX VALUES PUSHING 40
AT TIMES...HEAVY RAIN MAY BE A CONCERN.

FRIDAY INTO THE WEEKEND...SHORTWAVE TROUGH SLIDES ACROSS THE
US/CANADIAN BORDER WITH A WARM FRONT LIFTING NORTH ACROSS THE
DAKOTAS.  SURFACE LOW PRESSURE WILL SHIFT EAST FROM THE HIGH PLAINS
OF NORTHEASTERN WYOMING...DRAGGING A SURFACE TROUGH AND EVENTUALLY A
COOL FRONT ACROSS THE REGION.  BESIDES A CONTINUED SLIGHT CHANCE OF
PRECIPITATION...TEMPERATURES SHOULD COOL A FEW DEGREES...ESPECIALLY
FOR SUNDAY AS SURFACE HIGH SETTLES OVER EASTERN NEBRASKA.  HOWEVER
THE COOL DOWN WILL BE BRIEF AS THE FRONT WILL FAIL TO EFFECTIVELY
SCOUR OUT LOW LEVEL MOISTURE AND EASTERLY FLOW RETURNS. A NOTICEABLE
PATTERN SHIFT DEVELOPS FOR LATE IN THE WEEKEND...WITH NORTHWESTERLY
FLOW RETURNING TO WESTERN NEBRASKA.  FOR THE START OF THE WORK
WEEK...MODELS INDICATE THE POTENTIAL FOR CONVECTIVE DEVELOPMENT AS A
COOL FRONT QUICKLY PUSHES THROUGH THE REGION.  TEMPERATURES LOOK TO
COOL BELOW CLIMO BEHIND THE FRONT AND SEVERAL DISTURBANCES RIDING
THROUGH THE NORTHWESTERLY FLOW WILL BRING NEAR DAILY PRECIPITATION
CHANCES FOR MONDAY AND BEYOND.  MADE NO MAJOR CHANGES TO THE
EXTENDED GIVEN THE RECENT PERFORMANCE OF THE SOLUTIONS.

&&

.AVIATION...

MVFR/IFR/LIFR CONDITIONS SOUTH OF NEBRASKA HIGHWAY 2 SHOULD IMPROVE
TO VFR AROUND 15Z AS STRATUS DECK LIFTS AND MIXES OUT. VFR IS
EXPECTED ALL AREAS AFTER 15Z.

SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO CONTINUE MOVING
EAST THROUGH PARTS OF THE FCST AREA EARLY THIS MORNING WITH ACTIVITY
BECOMING ISOLATED AFTER SUNRISE.

SCATTERED THUNDERSTORMS MAY REDEVELOP LATE THIS AFTERNOON AND
TONIGHT FROM WEST TO EAST. GENERALLY VFR IS EXPECTED THIS AFTERNOON
THROUGH 06Z TONIGHT. AFTER 06Z...STRATUS AND FOG MAY REDEVELOP ONCE
AGAIN ALONG AND SOUTH OF NEBRASKA HIGHWAY 2 AND ACROSS AREAS ALONG
AND EAST OF HIGHWAY 83.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...NONE.
&&

SYNOPSIS/SHORT TERM/EXTENDED...JACOBS
AVIATION...CDC

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE NORTH PLATTE NE
443 AM CDT THU AUG 4 2011

NEZ004>010-022>029-035>038-056>059-069>071-094-050945-
SHERIDAN-EASTERN CHERRY-KEYA PAHA-BOYD-BROWN-ROCK-HOLT-GARDEN-
GRANT-HOOKER-THOMAS-BLAINE-LOUP-GARFIELD-WHEELER-ARTHUR-MCPHERSON-
LOGAN-CUSTER-DEUEL-KEITH-PERKINS-LINCOLN-CHASE-HAYES-FRONTIER-
WESTERN CHERRY-
443 AM CDT THU AUG 4 2011 /343 AM MDT THU AUG 4 2011/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF WESTERN AND
NORTH CENTRAL NEBRASKA.

.DAY ONE...TODAY AND TONIGHT.

AN ISOLATED SEVERE THUNDERSTORM IS POSSIBLE ACROSS WESTERN
NEBRASKA LATE THIS AFTERNOON OR EARLY THIS EVENING. LARGE HAIL AND
WIND DAMAGE ARE THE CONCERN. EAST WINDS...INCREASING UPSLOPE
MOISTURE...STRONG DAYTIME HEATING AND A WEAK UPPER LEVEL
DISTURBANCE MOVING THROUGH WYOMING ARE EXPECTED TO BE THE CATALYST
FOR STORM DEVELOPMENT.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY.

FRIDAY...MOISTURE POOLING ALONG A DEVELOPING WARM FRONT ACROSS
NORTHERN NEBRASKA MAY BE SUFFICIENT FOR ISOLATED SEVERE
THUNDERSTORM DEVELOPMENT ACROSS NORTHWEST NEBRASKA. LARGE HAIL AND
WIND DAMAGE ARE THE CONCERN LATE IN THE AFTERNOON THROUGH EARLY EVENING.

SATURDAY...A COLD FRONT WILL MOVE INTO NORTH CENTRAL NEBRASKA LATE
IN THE AFTERNOON. STRONG DAYTIME HEATING AND MOISTURE POOLING
AHEAD OF THE COLD FRONT MAY BE SUFFICIENT FOR ISOLATED SEVERE
STORM DEVELOPMENT ALONG AND EAST OF HIGHWAY 83. WARMING IN THE MID
LEVELS OF THE ATMOSPHERE AHEAD OF THE COLD FRONT IS EXPECTED TO
LIMIT STORM COVERAGE. LARGE HAIL AND WIND DAMAGE ARE THE CONCERN.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED THROUGH TONIGHT.

&&

THIS PRODUCT IS NOW AVAILABLE...ALONG WITH OTHER WEATHER...
HYDROLOGICAL AND CLIMATOLOGICAL INFORMATION...AT
HTTP://WWW.WEATHER.GOV/NORTHPLATTE

CDC