Area Forecast Discussion
Issued by NWS Hastings, NE

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000
FXUS63 KGID 241050
AFDGID

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HASTINGS NE
550 AM CDT SUN AUG 24 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 400 AM CDT SUN AUG 24 2014

CONVECTION DEVELOPED DURING THE OVERNIGHT HOURS IN WAA/ISENTROPIC
LIFT AS INDICATED ON THE 315K SURFACE AHEAD OF AN UPPER LOW PRESSURE
SYSTEM CENTERED IN MT/WY AND IN ADVANCE OF A COOL FRONT ACROSS
WESTERN NEB. FOR THE MOST PART THE CONVECTION IS LIFTING NORTHEAST
INTO NORTHERN NEB BUT WE COULD STILL SEE ISOLATED DEVELOPMENT THE
NEXT SEVERAL HOURS UNTIL THE ISENTROPIC LIFT SHIFTS EAST ON NOSE
OF LLVL JET.

AS WE HEAD THROUGH THE DAY TODAY THE UPPER LOW PRESSURE SYSTEM WILL
LIFT NORTHEAST INTO NORTH DAKOTA...AND THE SURFACE BOUNDARY TREKKING
ACROSS THE CENTRAL PLAINS WILL STALL OUT FM SOUTHEAST NEB TO WESTERN
KS THIS AFTERNOON.  AHEAD OF THE FRONT...TEMPS WILL BE WARM AGAIN
ACROSS OUR SOUTHEAST ZONES WITH HIGHS IN THE 90S...WITH 80S TO THE
NORTH OF THE BOUNDARY. THE MAIN DIFFERENCE WILL BE SOME NOTICEABLY
DRIER AIR WHICH ADVECTS IN FOLLOWING THE BOUNDARY TODAY WITH DPS
DROPPING INTO THE 50S FOR AT LEAST THE WESTERN HALF OF THE CWA.
THE BOUNDARY POSITION WILL BE KEY IN WHETHER OR NOT WE WILL SEE
THE RETURN OF EVENING CONVECTION AS THE PROGGED BOUNDARY POSITION
WILL BE NEAR MITCHELL COUNTY KS AND THAYER COUNTY NEB. HAVE
CARRIED LOW POPS FOR THIS EVENING FOR THIS AREA...AND EXPANDED
POPS FOR OUR SOUTHERN ZONES INTO THE OVERNIGHT HOURS AS THE LLVL
STRENGTHENS TO 30 TO 40KTS AND LIFT OVER THE FRONT MAY GENERATE
ISOLATED/SCATTERED STORMS. ALSO TO OUR WEST...ANOTHER ROUND OF
CONVECTION IS EXPECTED TO INITIATE ALONG THE HIGH PLAINS NORTH OF
THE SFC LOW IN COLORADO...WHILE A MID LEVEL SHORTWAVE TROUGH LIFTS
OUT OF THE ROCKIES AND A STRONGER FRONT ENTERS THE PANHANDLE.
THERE ARE SOME MODEL DIFFERENCES ON COVERAGE ON STORMS AND HOW FAR
EAST THE ACTIVITY WILL GET OVERNIGHT BUT OUR WESTERN ZONES SHOULD SEE
INCREASING CHANCES FOR PCPN HEADING INTO MONDAY MORNING.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 400 AM CDT SUN AUG 24 2014

MULTIPLE EPISODES OF HEAVY RAIN MON NIGHT-THU...ESPECIALLY FOR S-
CNTRL NEB. EXCESSIVE RAINFALL AMOUNTS AND POTENTIAL FLOODING ARE
POSSIBLE N OF I-80.

ALOFT: LITTLE HAS CHANGED FROM THE FCST REASONING OF THE PREVIOUS 2
NIGHT SHIFTS. WATER VAPOR IMAGERY SHOWS A CLOSED LOW OVER WY LIFTING
NE OUT OF THE WRN USA TROF. THE NEXT SHORTWAVE TROF WAS DIVING S
ALONG THE W COAST OF CANADA. HEIGHTS WILL FALL ANEW IN THE WRN
PORTION OF THE WRN USA TROF WITH A CUT-OFF LOW DEVELOPING MON. THIS
WILL MAINTAIN SW FLOW OVER THE CNTRL PLAINS WITH THE MAIN BELT OF
WESTERLIES REFORMING OVER SRN CANADA TUE-WED. IN THE MEANTIME...THE
LOW WILL DRIFT E AND BE OVER WY/CO BY 00Z/THU. THE CONSENSUS OF THE
EC/GEM/UKMET REMAIN CONSISTENT ON THIS EVOLUTION. THE 18Z GFS
FINALLY FELL INTO LINE...BUT THE 00Z RUN WAS BACK TO BEING TOO
PROGRESSIVE. THE 00Z GFS DID NOT HAVE ANY WEIGHTING IN THIS FCST
BEYOND 12Z/TUE. IT`S EVEN FASTER THAN ITS OWN ENSEMBLE MEAN. THIS
TROF MOVES OVERHEAD THU WITH DISAGREEMENT FRI ON IF IT CONTS E OR
REMAINS A SLOW MOVER. THE MODEL CONSENSUS INDICATES NW FLOW AND
RIDING HEIGHTS SAT AS THE NEXT TROF MOVES ONSHORE IN THE W.

SURFACE: THE COOL FRONT CURRENTLY MOVING INTO THE FCST AREA WILL
BECOME QUASI-STATIONARY OVER NRN KS MON AND REMAIN THERE THRU WED.
THIS FRONT WILL BE CONVECTIVELY ACTIVE AND BE REINFORCED BY OUTFLOWS
AND DIFFERENTIAL HEATING. LOW PRES WILL FORM ON THE FRONT WED AND
HEAD INTO THE MID MS VALLEY THU OR FRI DEPENDENT ON THE SPEED OF THE
TROF. HIGH PRES SHOULD CREST OVER THE REGION SAT.

HAZARDS: DAILY CHANCES FOR TSTMS THRU THU. FLOODING COULD BE A
PROBLEM...AND IT COULD BE SERIOUS WORST CASE. BELIEVE THERE IS LEGIT
POTENTIAL FOR ISOLATED POINT RAINFALL OF 6+" SOMEWHERE OVER CNTRL OR
NRN NEB.

HEAVY RAIN: CONDITIONS LOOK FAVORABLE FOR MULTIPLE TSTM CLUSTERS
PRIMARILY IN THE EVENING/OVERNIGHT HRS MON-THU. WE ARE SEEING LOTS
OF CLUES THAT PARTS OF THE FCST AREA COULD BE IN TROUBLE. IF ONE OR
MORE OF THESE DUMP HEAVY RAIN OVER THE SAME AREAS...WE COULD BE
LOOKING AT HYDRO/FLOODING CONCERNS WITH SOME EXTREMELY IMPRESSIVE
RAINFALL AMTS. THE LAST 2 RUNS OF THE EC OUTPUT A SWATH OF 2-5" N OF
I-80 WITH THE 00Z GFS 3-7". IF THE MODELS ARE INDICATING THESE KINDS
OF TOTALS...REALITY COULD BE EVEN GREATER GIVEN THE POOR
PREDICABILITY OF MODEL QPF. WE HAVE NOTED THE EC/GFS ENSEMBLE
PROBABILITIES FOR 4+ INCHES AND THAT IS CONCERNING.

WE HAVE SEEN THE WPC EXCESSIVE RAINFALL OUTLOOK. S-CNTRL NEB IS
OUTLOOKED IN A SLIGHT RISK FOR MON NIGHT AND TUE NIGHT.

FLOODING: THIS LOOKS LIKE A MULTI-DAY MADDOX "FRONTAL EVENT" TYPE
FOR EXCESSIVE RAINFALL MON-WED...POSSIBLY TRANSITIONING TO A
SYNOPTIC TYPE EVENT THU. QUASI-STATIONARY FRONT EMBEDDED WITHIN LOW-
LVL DEFORMATION AND THE LLJ SUPPLYING A SWATH OF RICH MOISTURE INTO
THE FRONT ALONG WITH ASSOCIATED WARM AIR ADVECTION AND
FRONTOGENESIS.

THE COLD POOL GENERATED BY EACH MCS WILL DICTATE WHERE EACH ONE
TRACKS AND ACCURATE MODEL DEPICTION OF THIS IS NOT GOOD GIVEN THE
INHERENT UNCERTAINTY IN QPF PREDICTION. WHILE PROBABILITIES ARE HIGH
FOR MULTI-NIGHT MCS ACTIVITY...THERE ARE NO GUARANTEES EACH ONE
TRACKS WHERE ITS PREDECESSOR DID. THE MAIN POINT IS THE INGREDIENTS
FOR EXCESSIVE RAINFALL WILL BE THERE. SUGGEST VIGILENCE AS WE WATCH
HOW THINGS UNFOLD THIS WEEK.

CONFIDENCE IN FCST DAYTIME HIGH TEMPS IS LOW MON-THU AS UNCERTAINTY
IS ABOVE AVERAGE...ESPECIALLY OVER S-CNTRL NEB WHERE CLOUDS/RAIN
COULD KEEP TEMPS SIGNIFCANTLY DEPRESSED. THIS IS ESPECIALLY TRUE IF
STRATUS BECOMES TRAPPED UNDER THE FRONTAL INVERSION.

THE DAILY DETAILS...

MON: A FEW SHWRS/TSTMS COULD STILL BE ON-GOING. LEFTOVERS FROM
OVERNIGHT DEVELOPMENT. WHILE A DECREASE IS EXPECTED DURING THE DAY
...THE FCST AREA WILL BE IN THE RIGHT REAR QUADRANT OF A 70 KT ULJ
STREAK. SO RENEWED/SCATTERED TSTM DEVELOPMENT IS LIKELY AFTER 4 PM.
MLCAPE IS FCST AS HIGH AS 2000 J/KG WITH 30-40 KTS OF DEEP LAYER
SHEAR COULD RESULT IN SVR TSTMS.

MON NIGHT: TSTM COVERAGE SHOULD INCREASE AS THE LLJ STRENGTHENS.
UPSCALE GROWTH INTO AN MCS APPEARS LIKELY ESPECIALLY N OF I-80.
WHILE THE COLD POOL SHOULD ALLOW FOR PROPAGATION AWAY FROM THE FCST
AREA...CORFIDI VECTORS SUGGEST BACKBUILDING IS POSSIBLE AS LONG AS
THE LLJ CONTINUES TO INITIATE TSTMS.

TUE: AN MCS SHOULD BE EXITING TO THE E...THEN A LULL IS EXPECTED
BEFORE SCATTERED REDEVELOPMENT AFTER 4 PM. THE THREAT FOR SVR TSTMS
IS LESS CERTAIN WITH MLCAPE UP TO 1500 J/KG AND 30 KTS OF DEEP LAYER
SHEAR. IT CANT BE RULED OUT ENTIRELY.

TUE NIGHT: ANOTHER MCS IS EXPECTED. THE 500 MB RIDGE WILL BE
OVERHEAD. THIS CAN BE AN INDICATION OF TROUBLE FOR FLOODING WITH
WEAK STEERING FLOW ALOFT AND REGENERATION VIA THE LLJ.

WED: PROBABLY ANOTHER LULL AS THE MCS DEPARTS TO THE E.

WED NIGHT: ANOTHER MCS. THE APPROACH OF THE UPPER TROF COULD SHOVE
THE FRONT N...WITH THE RESULTING MCS ENDING UP FURTHER N OVER THE
SANDHILLS.

THU: THIS PERIOD WAS INITIALLY DRY A COUPLE DAYS AGO. BUT THE SLOWER
MOVEMENT OF THE TROF NOW NECESSITATES POPS AND WE ARE PROBABLY TOO
LOW. MORE TSTMS APPEAR LIKELY.

A SLOW COOL FRONTAL PASSAGE WILL OCCUR THU-FRI.

FRI: THE FCST IS CURRENTLY DRY. BUT WOULD NOT BE SURPRISED IF WE DO
END UP NEEDED POPS. THE 00Z GEM/EC SUGGEST THE TROF COULD BE SLOW
ENOUGH.

SAT: PROBABLY DRY WITH SOME RECOVERY IN TEMPS...BACK TO NEAR NORMAL.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 547 AM CDT SUN AUG 24 2014

WINDS WILL BE FAIRLY LIGHT TODAY WITH SURFACE BOUNDARY IN THE
VICINITY. CLOUDS WILL BE LIMITED TO MID/HIGH LEVELS AND WILL
INCREASE IN COVERAGE OVERNIGHT.

&&

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

&&

$$

SHORT TERM...FAY
LONG TERM...HALBLAUB
AVIATION...FAY



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