Area Forecast Discussion
Issued by NWS Hastings, NE

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000
FXUS63 KGID 281045
AFDGID

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HASTINGS NE
545 AM CDT THU AUG 28 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 545 AM CDT THU AUG 28 2014

UNFORTUNATELY RUNNING LATER THAN USUAL THIS MORNING DUE TO A
CHALLENGING NIGHT OF SHOWER/THUNDERSTORM TIMING...THE POSSIBILITY
OF AT LEAST A FEW SEVERE STORMS...AND ESPECIALLY HEAVY RAINFALL
CONCERNS.

NEEDLESS TO SAY...WE HAVE BEEN TALKING ABOUT HEAVY RAIN POTENTIAL
FOR SEVERAL DAYS NOW...AND AT LEAST IN TERMS OF THE WIDESPREAD
COVERAGE OF 1+ INCH AMOUNTS ACROSS THE MAJORITY OF THE CWA...THESE
PAST 12 HOURS HAVE PROVEN TO BE THE MAIN SHOW SO FAR THIS WEEK.
THE ONLY AREAS THAT HAVE TRULY FALLEN WELL SHORT OF 1 INCH
OVERNIGHT HAVE MAINLY RESIDED WITHIN FAR NORTHERN COUNTIES SUCH AS
GREELEY/SHERMAN/VALLEY/ AND ALSO FAR SOUTHEAST AREAS IN/NEAR
MITCHELL COUNTY KANSAS. BY FAR THE MAIN CORRIDOR OF HEAVY...LIKELY
2-4+ INCH RAINFALL OVERNIGHT CONCENTRATED WITHIN A ROUGHLY 20 MILE
WIDE CORRIDOR EXTENDING FROM NORTHERN ROOKS/SOUTHERN PHILLIPS
COUNTY ON ONE END OF THE CWA...THEN NORTHEASTWARD THROUGH THE RED
CLOUD-CLAY CENTER-SOUTHERN YORK/NORTHERN FILLMORE COUNTY AREA.
ALTHOUGH GROUND-TRUTH REPORTS OF FLOODING ARE VERY LIMITED SO FAR
THIS MORNING...POINT RIVER WARNINGS FOR AUTOMATED GAUGES CONTINUE
FOR THE BOW CREEK NORTH OF STOCKTON KS AND FOR THE LITTLE BLUER
RIVER NEAR DEWEESE ON THE NEB SIDE. OBVIOUSLY THE NEXT 2-4 HOURS
WILL SHED CONSIDERABLY MORE LIGHT ON WHETHER MORE WIDESPREAD LOW-
LYING AREA/STREAM FLOODING MAY BE HAPPENING ACROSS THE AREA THAN
CURRENTLY THOUGHT...BUT FORTUNATELY A GOOD CHUNK OF THE OVERNIGHT
RAIN FELL ON AREAS THAT HAD NOT OBSERVED NOTABLE AMOUNTS DURING
THE PAST FEW DAYS.

AS FOR THE FLASH FLOOD WATCH...KEPT IT INTACT/UNCHANGED THROUGH
15Z/10AM...AND ALTHOUGH MOST FLOODING ISSUES THAT ARE OUT THERE
ARE LIKELY ALREADY ATTRIBUTED TO RAIN THAT HAS ALREADY
FALLEN...WANT TO GIVE DAY SHIFT A FEW HOURS TO DECIDE IF ANOTHER
POSSIBLE EXTENSION IN TIME MAY BE WARRANTED TO ACCOUNT FOR LATER
DAY/EVENING CONVECTION WHICH COULD EASILY DUMP ANOTHER QUICK INCH
OR SO IN SOME PLACES.

TURNING TO THE HERE AND NOW AS OF 10Z/5AM...FORTUNATELY THE BULK
OF STEADY MODERATE TO HEAVY RAIN HAS SHIFTED EAST OF THE LOCAL
AREA INTO EASTERN NEB...BUT ISOLATED TO SCATTERED SHOWERS WITH A
FEW THUNDERSTORMS CONTINUE TO FLARE UP ACROSS THE CWA IN THE VERY
MOIST AIRMASS CHARACTERIZED BY IMPRESSIVE PRECIPITABLE WATER
VALUES GENERALLY IN THE 1.6-2.0 INCH RANGE. PER WATER VAPOR
IMAGERY AND MODEL DATA...THE LARGE-SCALE DRIVING FORCE BEHIND THE
WETNESS IS A SEASONABLY STRONG CLOSED MID LEVEL LOW PRESSURE
SYSTEM SLOWLY BUT STEADILY APPROACHING THE LOCAL AREA FROM ITS
CURRENT POSITION CENTERED OVER THE NORTH CENTRAL CO/WY BORDER
AREA. OUT AHEAD OF THIS SYSTEM...LARGE SCALE LIFT AND IMPRESSIVE
LOW LEVEL MOISTURE TRANSPORT ALONG THE AXIS OF A HEALTHY 30-40KT
LOW LEVEL JET HAVE RESULTED IN THE WIDESPREAD CONVECTION
OVERNIGHT...WITH THE GRADUAL VEERING OF THE LOW LEVEL JET RECENTLY
STEERING THE HEAVIEST RAINS OUT OF THE LOCAL AREA TO THE EAST.

FOR TODAY...AND STARTING WITH THE BIG PICTURE...THE SLOW-MOVING
MID-UPPER TROUGH WILL CONTINUE TO SLIDE EAST...WITH ITS AXIS
ALIGNED FROM FAR WESTERN KS TO NORTH CENTRAL NEB BY SUNSET.
MEANWHILE AT THE SURFACE...A FAIRLY WEAK COLD FRONT/TROUGH AXIS
WILL SLIDE EAST INTO AT LEAST WESTERN PORTIONS OF THE CWA AS THE
DAY GOES ON. ALTHOUGH AT LEAST A ROGUE/SPOTTY SHOWER IS ALMOST
IMPOSSIBLE TO RULE OUT AT ANY POINT TODAY...THE GENERAL
EXPECTATION BASED ON SIMULATED REFLECTIVITY FROM THE 00Z 4KM WRF-
NMM AND 4KM NSSL WRF IS FOR PRECIPITATION TO GRADUALLY DIMINISH IN
COVERAGE THIS MORNING AND LIKELY RESULT IN A MOSTLY DRY PERIOD
FROM MID-MORNING THROUGH MID-AFTERNOON. THEN...AS LIKELY AT LEAST
PARTIAL CLEARING/SUNSHINE ACTS TO DESTABILIZE THE AIRMASS OUT
AHEAD OF THE UPPER SYSTEM AND NEAR/AHEAD OF THE SURFACE
TROUGH...THE MID AFTERNOON INTO THE EVENING HOURS SHOULD FEATURE
AT LEAST A MODEST/SCATTERED REDEVELOPMENT OF SHOWERS/STORMS...SOME
OF WHICH COULD BE AT LEAST MARGINALLY SEVERE GIVEN THE POSSIBILITY
OF AROUND 2000 J/KG MIXED LAYER CAPE BUT FAIRLY WEAK 20-25KT DEEP
LAYER SHEAR AND STILL-FAIRLY WEAK MID LEVEL LAPSE RATES. AGREE
WITH SPC IN ADVERTISING BASELINE 5 PERCENT WIND/HAIL PROBS ACROSS
MOST OF THE CWA. AGAIN...ANY SEVERE RISK WILL BE HIGHLY DEPENDENT
UPON GETTING SOME LOW LEVEL DESTABILIZATION...WHICH GENERALLY
APPEARS MORE LIKELY THAN YESTERDAY AT THIS POINT DESPITE THE OTHER
LIMITING FACTORS.

FOR THIS EVENING/TONIGHT...THE BIG PICTURE INVOLVES THE CONTINUED
EASTWARD PROGRESSION OF THE MID-UPPER TROUGH AXIS...WHICH SHOULD
BE RIGHT OVER THE HEART OF THE CWA AT NIGHTS END. AGAIN...ITS
ALMOST IMPOSSIBLE TO RULE OUT AT LEAST AN ISOLATED SHOWER/WEAK
STORM AT ANY POINT TONIGHT...BUT IN GENERAL EXPECT A GRADUAL WEST-
TO-EAST DECREASE IN CONVECTIVE INTENSITY/COVERAGE AS THE
EVENING/OVERNIGHT HOURS WEAR ON. PER THE MAJORITY OF MODEL
DATA...THE BULK OF THE CWA SHOULD PROBABLY DRY OUT COMPLETELY
POST-MIDNIGHT...BUT THE LATEST 06Z GFS IS A BIT MORE AGGRESSIVE IN
KEEPING A BIT GREATER COVERAGE GOING...SO THUS WHY AT LEAST A
SLIGHT CHANCE MENTION PERSISTS THROUGH THE NIGHT...BUT WITH ANY
LIKELY 60+ POPS CONFINED TO THE EVENING HOURS AND MAINLY EAST OF
THE HIGHWAY 281 CORRIDOR. ANY POSSIBLE SEVERE WEATHER THREAT
WOULD LIKELY DIMINISH BY 10 PM OR SO.

TEMPERATURE-WISE...ASSUMING THAT TODAY FEATURES MORE BREAKS IN THE
CLOUDS THAN YESTERDAY DID...MOST AREAS SHOULD JUMP A FEW DEGREES
WARMER...AND AGAIN WENT WITH A FAIRLY STANDARD MULTI-
GUIDANCE/MODEL BLEND TO AIM MOST OF THE CWA INTO THE LOW
80S...WITH MID 80S MORE COMMON NEAR/SOUTH OF THE STATE LINE. MADE
VERY LITTLE CHANGE TO TONIGHTS LOWS...AIMING FOR LOW-MID 60S MOST
AREAS AND MAYBE A FEW UPPER 50S MAINLY FAR WEST.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 545 AM CDT THU AUG 28 2014

PROGRESSIVE WEST SOUTHWEST FLOW CONTINUES INTO FRIDAY. I FAVOR
ENSEMBLES FROM SREF FOR PRECIPITATION CHANCES. THIS LEADS TO A GOOD
CHANCE OF RAIN BY AFTERNOON AS THE PASSAGE OF AN UPPER LEVEL TROUGH
AXIS IS STILL IN QUESTION. ALTHOUGH OPERATIONAL RUNS OF MOST MODELS
PLACE THE TROUGH AXIS EAST OF THE CWA BY FRIDAY
AFTERNOON...ENSEMBLES LAG THE TROUGH BEHIND A BIT...THEREFORE I AM
KEEPING HIGHER CHANCES OF SHOWERS AND THUNDERSTORMS. SEVERE
PARAMETERS REVEAL THAT WE COULD GET SOME STRONG STORMS...AS BOTH
INSTABILITY AND SHEAR WILL BE MARGINAL.

TRYING TO PICK A DRY PERIOD IS RATHER DIFFICULT WITH THIS
PATTERN...BUT SATURDAY DOES LOOK LARGELY DRY DURING THE DAY...AS WE
SHOULD BE UNDER THE INFLUENCE PRIMARILY FROM SHORTWAVE
RIDGING...BEHIND THE TROUGH GOING THROUGH FROM THE PREVIOUS DAY.
HOWEVER...BY VERY LATE SATURDAY NIGHT...THE AXIS OF A STRONG LOW-
LEVEL JET SHOULD MAKE ITS WAY ACROSS THE AREA IN ADVANCE OF THE NEXT
MID-UPPER LEVEL TROUGH AND GIVE US ANOTHER SHOT AT SOME SHOWERS AND
THUNDERSTORMS. SEVERE WEATHER DOES NOT APPEAR TO BE MUCH OF AN ISSUE
AS MID-LEVEL LAPSE RATES SHOULD BE POOR SUPPORT FOR ANYTHING OF THAT
NATURE.

AS THE AFOREMENTIONED BROAD UPPER TROUGH MOVES INTO THE CENTRAL
PLAINS SUNDAY WITH AN ASSOCIATED COLD FRONT INTRODUCING A STRONG
BAROCLINIC ZONE INTO THE AREA. LARGE HAIL AND DAMAGING WINDS ARE
LOOKING VERY POSSIBLE...ESPECIALLY FOR SUNDAY EVENING...WITH PLENTY
OF INSTABILITY AND SHEAR FOR SUPPORT EXPECTED. THE HWO IS ALREADY
STRONGLY WORDED AND AT THIS TIME...I DO NOT SEE A REASON TO DEVIATE
FROM THIS.

WE COULD GET ENOUGH LOW-LEVEL CONVERGENCE FOR MONDAY NIGHT AND
TUESDAY NIGHT IN OUR FAR SOUTH/SOUTHEAST TO KEEP CHANCES OF SHOWERS
AND THUNDERSTORMS IN THE FORECAST. SEVERE CHANCES LOOK RATHER SLIM
AS THERE DOES NOT APPEAR TO BE MUCH SUPPORT IN MID-LEVELS FOR
PARTICULARLY STRONG CONVECTION.

THERE IS GENERAL AGREEMENT THAT BY WEDNESDAY WE WILL BE WITHIN
SOUTHWEST FLOW...ON THE NORTHWEST SIDE OF A SUBTROPICAL RIDGE
ANCHORED ACROSS THE SOUTH. WE SHOULD HAVE ENOUGH OF A CAP TO
PRECLUDE PRECIPITATION FOR DAYTIME WEDNESDAY...BUT I WOULD NOT BE
SURPRISED OF SOME SHOWERS AND THUNDERSTORMS TO DEVELOP WEDNESDAY
NIGHT AS A LOW-LEVEL JET DEVELOPS.

TEMPERATURES WERE CHANGED LITTLE FROM THE PREVIOUS FORECAST.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 106 AM CDT THU AUG 28 2014

THIS IS A RATHER DIFFICULT TAF PERIOD TO FORECAST. OVERALL
CONFIDENCE IS LOW TO MODERATE FOR THIS PERIOD. THUNDERSTORMS
CONTINUE ACROSS THE FORECAST AREA...CURRENTLY IMPACTING BOTH
TERMINAL SITES. IFR CONDITIONS FOR LOW CEILINGS ARE CURRENTLY
FORECAST AT BOTH TAF SITES FOR AT LEAST THE NEXT 3 TO 4 HOURS...OR
BASICALLY UNTIL WE CAN GET THESE THUNDERSTORMS TO ROLL THROUGH THE
AREA. THE BACK EDGE OF THE PRECIPITATION SHOULD REACH THE KEARNEY
TAF SITE FIRST...WHILE THE GRAND ISLAND TAF SITE MAY BE IMPACTED
ABOUT AN HOUR LONGER. VISIBILITIES MAY NOT BE LOW ENOUGH IN THE
CURRENT TAF...BUT WITHIN THE HEAVIER RAIN THE VISIBILITIES MAY BE
CLOSER TO MVFR. THERE SHOULD BE A LULL IN THE PRECIPITATION
BETWEEN LATER THIS MORNING AND LATER THIS AFTERNOON...DURING
WHICH TIME WE WILL HAVE VFR CONDITIONS. THERE SHOULD BE A
BREAK...BUT THE TIMING OF THIS BREAK IN PRECIPITATION WILL BE THE
DIFFICULT PART OF THIS FORECAST. WITH THAT BEING SAID...I AM
EXPECTING ANOTHER ROUND OF CONVECTION LATER THIS AFTERNOON AS WE
REACH PEAK HEATING. AT THIS TIME...CONDITIONS WILL LIKELY RETURN
TO MVFR OR IFR.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...FLASH FLOOD WATCH UNTIL 10 AM CDT THIS MORNING FOR NEZ039>041-
     046>049-061>064-073>077-082>086.

KS...FLASH FLOOD WATCH UNTIL 10 AM CDT THIS MORNING FOR KSZ005>007-
     017-018.

&&

$$

SHORT TERM...PFANNKUCH
LONG TERM...HEINLEIN
AVIATION...GUERRERO


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