Area Forecast Discussion
Issued by NWS Hastings, NE

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000
FXUS63 KGID 220522
AFDGID

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HASTINGS NE
1222 AM CDT FRI AUG 22 2014

.UPDATE...
ISSUED AT 700 PM CDT THU AUG 21 2014

THE 18Z NAM HAS FAILED TO CAPTURE THE ONGOING CONVECTION ACROSS
OUR SOUTHEASTERN FORECAST AREA AND IS ESSENTIALLY DRY THROUGH
MIDNIGHT. HOWEVER...THE HRRR MODEL SEEMS TO BE CATCHING ONTO
THINGS AND HAS BEEN GIVING FAIRLY REALISTIC SCENARIOS FOR HOW
THUNDERSTORMS WILL EVOLVE THIS EVENING. BASED ON RADAR AND THE
HRRR HAVE INCREASED POPS INTO THE LIKELY CATEGORY FOR MOST OF OUR
KANSAS COUNTIES INTO NUCKOLLS...THAYER...AND FILLMORE COUNTIES.
ALSO SLIGHTLY INCREASED POPS NORTH OF THE RADAR FINE LINE BOUNDARY
THAT AT 7 PM WAS RUNNING FROM PHILLIPSBURG...TO BLUE HILL. THE LOW
LEVEL JET WILL INCREASE THIS EVENING WITH THE NOSE OF THE JET
RUNNING INTO OUR SOUTHERN FORECAST AREA. THE HRRR INDICATES THAT
THUNDERSTORMS COULD FORM NORTH OF THE EXISTING THUNDERSTORMS LATER
THIS EVENING IN PLACES LIKE HASTINGS AS THE LOW LEVEL JET
INCREASES...BUT CONFIDENCE IN THIS IS STILL LESS THAN 50 PERCENT.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 341 PM CDT THU AUG 21 2014

MAP ANALYSIS INDICATES AN UPPER TROPOSPHERIC RIDGE OVER THE
CENTRAL CONUS...WITH TROUGHS OVER THE WESTERN AND EASTERN CONUS.
MAP ANALYSIS ALSO SHOWS A CLOSED UPPER TROPOSPHERIC LOW EMBEDDED
WITHIN THE BASE OF THE WESTERN CONUS TROUGH. ENHANCED UPPER
TROPOSPHERIC ENERGY EXTENDS FROM NORTH TO SOUTH ALONG THE WESTERN
CONUS COAST...THEN NORTHEAST INTO THE NORTHERN PLAINS...AND
FINALLY BACK TO THE SOUTHEAST ACROSS THE GREAT LAKES REGION. THAT
BEING SAID...UPPER TROPOSPHERIC FLOW OVER OUR AREA REMAINS FAIRLY
WEAK...ONLY MAXING OUT AT AROUND 35KTS NEAR 38000FT AGL PER RAP
ANALYSIS DATA AT 12Z. WATER VAPOR IMAGERY ALSO SHOWS THE
AFOREMENTIONED RIDGE AND TROUGHS...AS WELL AS ENHANCED UPPER
TROPOSPHERIC MOISTURE EXTENDING FROM HURRICANE LOWELL INTO THE
SOUTHWESTERN CONUS. THIS TROPICAL MOISTURE HAS YET TO REACH THE
CENTRAL PLAINS HOWEVER. AT THE SURFACE AN AREA OF LOW BAROMETRIC
PRESSURE EXISTS OVER SOUTHWESTERN MINNESOTA...AND AN ASSOCIATED
SURFACE TROUGH EXTENDS SOUTHWEST FROM THE LOW INTO NEBRASKA AND
KANSAS. AS OF 18Z THIS TROUGH WAS NOTED EXTENDING FROM NEAR
KODX...TO NEAR KHDE...TO NEAR KHLC. THE RESULTANT LOWER
TROPOSPHERIC WIND FIELD ACROSS OUR AREA REMAINS FROM THE SOUTH
ACROSS EASTERN PORTIONS OF OUR CWA...BUT LOCATIONS FARTHER
WEST/NORTHWEST...BEHIND THE TROUGH...ARE NOW REPORTING A NORTHERLY
COMPONENT TO THE LOWER TROPOSPHERIC WIND FIELD.

GUIDANCE SUGGESTS THE CLOSED UPPER TROPOSPHERIC LOW OVER THE
WESTERN CONUS WILL EJECT FROM THE BASE OF THE LONG WAVE TROUGH AS
A SHORT WAVE TONIGHT INTO FRIDAY...LIKELY MOVING INTO THE FOUR
CORNERS REGION BY 00Z SATURDAY. AS A RESULT...SURFACE CYCLOGENESIS
THEN EXPECTED OVER WESTERN KANSAS FRIDAY AFTERNOON. SO ALTHOUGH
THE SURFACE TROUGH...CURRENTLY LOCATED OVER OUR AREA...WILL MAKE
AN ATTEMPT TO MOVE EAST ACROSS THE AREA TONIGHT...THE TROUGH
SHOULD EVENTUALLY BECOME STATIONARY IF NOT RETROGRADE SOMEWHAT AS
IT STRENGTHENS INTO A WARM FRONT IN RESPONSE TO THE WESTERN KANSAS
CYCLOGENESIS. THE LOWER TROPOSPHERIC WIND FIELD ACROSS THE
SOUTH/SOUTHEASTERN ONE-HALF OF THE CWA WILL LIKELY REMAIN FROM THE
SOUTH/SOUTHEAST THROUGH THE NEXT 24 HOURS...BUT LOCATIONS FARTHER
NORTHWEST WILL LIKELY EXPERIENCE MORE OF A NORTHEASTERLY WIND
FIELD.

ANY OMEGA DERIVED FROM UPPER TROPOSPHERIC KINEMATICS SHOULD
REMAIN ON THE WEAK SIDE THROUGH MUCH OF THE SHORT TERM FORECAST
PERIOD. THAT BEING SAID...GUIDANCE DOES SUGGEST THE AXIS OF A
~50KT LOWER TROPOSPHERIC JET STREAK JUST ABOVE THE BOUNDARY LAYER
WILL DEVELOP FROM CENTRAL KANSAS INTO SOUTHEASTERN NEBRASKA
TONIGHT...BEFORE SHIFTING OFF TO THE EAST SOMEWHAT BY DAYBREAK
FRIDAY. THERMAL ADVECTION ALONG THIS AXIS...AS WELL AS MOISTURE
CONVERGENCE NEAR THE NOSE OF THE JET STREAK...SHOULD BE SUFFICIENT
FOR PRECIPITATION PRODUCTION...ESPECIALLY ACROSS OUR SOUTHEASTERN
CWA...A SOLUTION SUPPORTED BY QPF FIELDS FROM THE
NAM...OPERATIONAL GFS AND EC...AS WELL AS SIMULATED REFLECTIVITY
FROM THE HRRR. GIVEN ALL THIS...WENT AHEAD WITH 20-30% POPS ACROSS
MUCH OF THE CWA FOR TONIGHT...WITH THE HIGHEST POPS RELEGATED TO
THE SOUTHEASTERN CWA.

ANY PRECIPITATION THAT DOES DEVELOP TONIGHT SHOULD MOVE OFF TO
THE EAST BY SUNRISE FRIDAY AS THE AXIS OF THE LOWER TROPOSPHERIC
JET STREAK DOES THE SAME. THIS SHOULD PROVIDE A BREAK IN THE
PRECIPITATION ACROSS OUR AREA FRIDAY MORNING INTO LATE FRIDAY
AFTERNOON.

BY LATE FRIDAY AFTERNOON AND INTO FRIDAY EVENING
HOWEVER...THERMAL ADVECTION AHEAD OF THE APPROACHING UPPER
TROPOSPHERIC SHORT WAVE SHOULD PROMOTE INCREASING OMEGA ACROSS THE
REGION. THIS OMEGA...WORKING IN CONCERT WITH ENHANCED LOWER
TROPOSPHERIC CONVERGENCE ALONG THE STRENGTHENING BAROCLINIC
ZONE...MAY BE SUFFICIENT FOR THE DEVELOPMENT OF ISOLATED TO
PERHAPS SCATTERED SHOWER AND THUNDERSTORM ACTIVITY. THIS IS A
SOLUTION SUPPORTED BY QPF FIELDS FROM THE NAM...OPERATIONAL GFS
AND EC. GIVEN ALL THIS..WENT AHEAD WITH 20-50% POPS ACROSS THE CWA
FRIDAY AFTERNOON AND EVENING...WITH THE HIGHEST POPS RELEGATED TO
CENTRAL AND NORTHERN PORTIONS OF THE CWA IN CLOSEST PROXIMITY TO
THE LOWER TROPOSPHERIC BAROCLINIC ZONE.

FORECAST PROXIMITY SOUNDINGS FROM THE ACROSS THE CWA...PER THE
NAM AND OPERATIONAL GFS...SUGGEST PARCELS ROOTED TO AROUND 800MB
SHOULD HAVE 500-1000J/KG WITH ANY CONVECTION THAT IS REALIZED
TONIGHT. GIVEN THIS...WILL GO AHEAD AND OUTLOOK THE POSSIBILITY
FOR LARGE HAIL AND STRONG WIND GUSTS IN THE HWO FOR TONIGHT.
TURNING TO FRIDAY AFTERNOON AND EVENING...THE NAM...OPERATIONAL
GFS AND EC SUGGEST 0-1KM MLCAPE VALUES OF 1000-3000J/KG WILL BE IN
EXISTENCE WITH DEEP-LAYER BULK SHEAR VALUES OF 15-30KTS. GIVEN
THIS...SEVERE WEATHER IS A DEFINITE POSSIBILITY WITH ANY
THUNDERSTORM THAT DOES DEVELOP AND AS A RESULT...WILL GO AHEAD AND
OUTLOOK LARGE HAIL AND STRONG WIND IN THE HWO FOR LATE FRIDAY
AFTERNOON AND FRIDAY EVENING. ALSO...LOCALLY ENHANCED LOWER
TROPOSPHERIC HORIZONTAL VORTICITY ALONG THE AXIS OF THE BAROCLINIC
ZONE COULD PROMOTE A THREAT FOR ISOLATED TORNADOES WITH ANY STORM
THAT CAN LATCH ONTO THE BOUNDARY. GIVEN THIS...WILL ALSO OUTLOOK
THE THREAT FOR ISOLATED TORNADIC ACTIVITY.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 341 PM CDT THU AUG 21 2014

FRIDAY EVENING THROUGH THURSDAY. FORECAST CONCERN IN THE EXTENDED
CENTERS ON CONTINUING RAIN CHANCES ALONG WITH SLIGHT COOLING
TREND.

BEGINNING FRIDAY EVENING...MODELS CONSISTENT WITH BIG PICTURE AS
THEY HAVE AN UPPER LEVEL RIDGE OVER THE MISSISSIPPI RIVER VALLEY
AND A LOW CENTERED OVER NORTH CENTRAL IDAHO. THE LOW OVER SOUTHERN
CALIFORNIA AT PRESENT IS FORECAST TO EJECT OUT AHEAD OF THE MAIN
PACIFIC NW CLOSED LOW AS A SHORTWAVE TROUGH AND SHOULD MOVE
NORTHEAST AFFECTING THE CENTRAL PLAINS LATE FRIDAY EVENING. IT
SHOULD HELP LIFT A SURFACE LOW AND ASSOCIATED WARM FRONT NORTH
THROUGH NEB OVERNIGHT. THE NAM AND GFS STILL DIFFER SOME ON THE
LOCATION BUT ARE SIMILAR IN LIFTING THE PRECIPITATION FROM OUR CWA
INTO NORTHERN NEB OVERNIGHT. HEAVY RAIN IS POSSIBLE AS THE SYSTEM
MOVES SLOWLY NORTH WITH PLENTY OF MOISTURE AVAILABLE. THE KS
PORTION OF OUR CWA MAY REMAIN CAPPED AND MISS OUT ON THE
ACTION...DEPENDING WHERE THE THUNDERSTORMS FIRST FIRE UP. ML-CAPE
AND DEEP LAYER SHEAR APPEAR HIGH ENOUGH FOR SEVERE STORMS INTO THE
EVENING...ALTHOUGH BETTER SHEAR PROGGED TO BE IN THE WESTERN PART
OF NEB AS OF NOW. DECENT LOW LEVEL JET OF 30-40 KT ALSO FORECAST
TO DEVELOP AND RIDE OVER WARM FRONT WHICH SHOULD HELP SUSTAIN
STORMS. PLAN TO TRIM POPS FROM SOUTH TO NORTH OVERNIGHT.

RAIN CHANCES SHOULD CONTINUE FOR THE WEEKEND WITH THE BEST TIME
FRAME FOR RAIN BEING LATE AFTERNOON INTO THE NIGHT. THE UPPER
TROUGH IS EXPECTED TO MOVE A BIT EASTWARD PUTTING US IN SOUTHWEST
FLOW. MEANWHILE A COLD FRONT SHOULD STALL OUT AS IS BECOMES
PARALLEL TO THE UPPER FLOW AND SHOULD BE SITUATED FROM THE EASTERN
DAKOTAS TO SOUTHWEST KANSAS. RAIN CHANCES WILL DEPEND ON SEVERAL
FACTORS INCLUDING FRONTAL CONVERGENCE...LOW LEVEL JET
DEVELOPMENT...SHORTWAVE TROUGHS MOVING THROUGH...ETC. ONE THING
THAT WILL NOT BE A CONCERN IS MOISTURE AS PRECIPITABLE WATER
VALUES AVERAGE 150 PERCENT OF NORMAL DUE TO A GOOD SUBTROPICAL
TAP.

AS NOTED IN PREVIOUS AFD...RAIN CHANCES CONTINUE INTO THE EARLY
PART OF NEXT WEEK AS THE UPPER TROUGH REMAINS WEST OF US AND
VARIOUS SURFACE BOUNDARIES STALL OUT OVER THE AREA. THE LATEST GFS
OPERATIONAL RUN IS MOVING IT THROUGH A LITTLE FASTER AS IT NOW HAS
THE 500 MB TROUGH AXIS PASSING OUR CWA NEXT WED AFTERNOON. EC HAS
ALSO COME IN LINE WITH THIS SOLUTION AND IS ACTUALLY ABOUT 12
HOURS FASTER THAN THE GFS. THIS A QUITE A DIFFERENCE FROM PREVIOUS
EC WHICH DROPPED A SECOND LOW SOUTH BEHIND THE FIRST ONE AND DIDNT
CLEAR THE SECOND LOW UNTIL NEXT SATURDAY. WILL HAVE TO KEEP AN EYE
ON HOW THIS CHANGES OVER THE NEXT FEW DAYS...BUT IF LATEST
SOLUTIONS ARE ON TRACK...COULD SEE THINGS DRY OUT A BIT NEXT WED
INTO AT LEAST FRIDAY WHICH WOULD BE WELCOME NEWS FOR NEB STATE
FAIR ATTENDEES.

REGARDING TEMPERATURES...SOME COOLING EXPECTED ON SUNDAY WITH
PASSAGE OF WEAK COLD FRONT AND THEN AGAIN ON WEDNESDAY AS MAIN
TROUGH AND ANOTHER FRONT MOVES THROUGH. EXPECT HIGH TO BE IN THE
LOWER 80S NORTH TO LOWER 90S SOUTH ON AVERAGE...ONCE AGAIN
DEPENDING ON WHERE VARIOUS FRONTS STALL OUT.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1216 AM CDT FRI AUG 22 2014

AT FIRST GLANCE...CONVECTION DURING THE REMAINDER OF THE NIGHT
SHOULD REMAIN TO THE EAST OF THE TERMINALS BUT A HIT OR MISS STORM
MAY STILL DEVELOP PRIMARILY TOWARDS KGRI IN THE VCNTY OF A LLVL
BOUNDARY. WITH FAIRLY LIGHT WINDS AND IN PRESENCE OF LLVL MOISTURE
FOG DEVELOPMENT IS POSSIBLE TOWARD MORNING WITH THE HRRR THE MOST
ROBUST WITH DEVELOP ALONG THE PLATTE RIVER AND MORE SO FOR KGRI VS
KEAR. WILL CONTINUE TO MONITOR TRENDS FOR THIS. A WARM FRONTAL
BOUNDARY IS PROGGED TO STALL SOUTH OF THE TERMINALS THIS AFTERNOON
THEN LIFT NORTHWARD THIS EVENING AND TONIGHT. THE FRONT WILL AGAIN
BE THE FOCUS FOR SHOWERS AND STORMS AND SEVERE WEATHER IS
POSSIBLE. BEST TIMING FOR CONVECTION IS DURING THE LATTER TAF
HOURS.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.

&&

$$

UPDATE...WESELY
SHORT TERM...BRYANT
LONG TERM...EWALD
AVIATION...FAY


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