Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 190513
AFDGID

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HASTINGS NE
1113 PM CST THU DEC 18 2014

.UPDATE...
ISSUED AT 737 PM CST THU DEC 18 2014

DECIDED TO PULL THE SLIGHT CHANCE OF FREEZING DRIZZLE TONIGHT OUT
OF THE FORECAST. THE SATURATED CLOUD LAYER DEPTH IS LESS THAN 1KM
AND THE LOW LEVEL MIXING AS INDICATED BY THE LOW LEVEL BULK SHEAR
IS AROUND OR LESS THAN 10 KTS. THE ONLY MODEL STILL HINTING AT
DRIZZLE WAS THE 18Z NAM...OTHERWISE IT JUST APPEARS RATHER
UNLIKELY. OUR PRIMARY CONCERN WILL CENTER AROUND THE POSSIBILITY
OF DENSE FOG ACROSS OUR FAR WESTERN FORECAST AREA NEAR THE EDGE OF
THE STRATUS DECK. CONFIDENCE IS NOT HIGH ENOUGH TO ISSUE ANY KIND
OF ADVISORY AT THIS POINT IN TIME...BUT AREAS WEST OF HWY 183 WILL
NEED TO POSSIBLY WATCH OUT FOR LOCALLY DENSE FOG LATER TONIGHT.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 300 PM CST THU DEC 18 2014

DRIER AIR HAS BEGUN TO MOVE TO IN ALOFT ACROSS THE REGION THIS
AFTERNOON BEHIND THE DEPARTING DISTURBANCE WHICH BROUGHT SOME LIGHT
SNOW TO THE REGION EARLY THIS MORNING. WITH THIS DRIER AND WARMER
AIR MOVING IN AT MID LEVELS...THE SURFACE INVERSION HAS ONLY
STRENGTHENED THE PAST FEW HOURS...AND LITTLE TO NO MIXING HAS
OCCURRED...PREVENTING THE LOW LEVEL STRATUS DECK FROM ERODING. AS
A RESULT...OVERCAST SKIES HAVE ONCE AGAIN BEEN THE RULE...WITH
TEMPERATURES STRUGGLING TO CLIMB INTO THE UPPER 20S AND LOWER 30S
ACROSS THE LOCAL AREA. WITH VERY LIGHT WINDS IN PLACE AND NO
SIGNIFICANT CHANGE IN THE GENERAL AIRMASS...SEE NO REASON WHY THIS
STRATUS DECK WILL NOT CONTINUE TO PREVAIL THROUGH THE SHORT TERM
PERIODS. CONSEQUENTLY...EXPECT THE INSULATING CLOUD COVER TO HELP
HOLD TEMPERATURES UP A FEW DEGREES OVERNIGHT...AND ONCE AGAIN KEEP
AFTERNOON TEMPS A LITTLE BIT COOLER THAN THEY OTHERWISE WOULD BE
TOMORROW AFTERNOON.

DESPITE THESE COOL AND CLOUDY CONDITIONS...GENERALLY LIGHT SOUTHERLY
WINDS WILL HELP MAKE IT FEEL A LITTLE MORE PLEASANT THAN IT OTHERWISE
COULD FEEL...AS THE PRESSURE GRADIENT NEAR THE SURFACE WILL REMAIN
WEAK WITH A BROAD AREA OF SURFACE HIGH PRESSURE ACROSS THE
MIDWEST AND A BROAD AREA OF LOW PRESSURE ACROSS THE ROCKIES. ALL
THIS SAID...THE MAIN QUESTION THROUGH THE SHORT TERM PERIODS LIES
AROUND THE POTENTIAL FOR SOME LIGHT FREEZING DRIZZLE OR FOG
OVERNIGHT THROUGH EARLY FRIDAY MORNING...AS OTHERWISE PERSISTENCE
IS EXPECTED FOR BOTH TEMPERATURES AND WINDS THROUGH THE PERIOD.

GIVEN THE MODELED SOUNDINGS INDICATING SOMEWHAT FAVORABLE
CONDITIONS FOR THE FORMATION OF DRIZZLE COMBINED WITH MODEST BULK
SHEAR VALUES FORECAST IN THE LOWEST LAYER OF THE ATMOSPHERE...HAD
A DIFFICULT TIME REMOVING THE MENTION OF FREEZING DRIZZLE FROM THE
FORECAST DESPITE ITS APPARENT LACK OF ITS APPEARANCE UNDER SIMILAR
CONDITIONS THE PAST FEW DAYS. THAT SAID...THE QPF FIELDS FROM THE
NAM THIS AFTERNOON AS WELL AS THE RAW VALUES OF BULK SHEAR ARE A
LITTLE MORE FAVORABLE THAN THE PAST TWO DAYS...SO KEPT THE SMALL
POTENTIAL IN THE FORECAST DESPITE ITS SEEMINGLY LOW PROBABILITY.
DID...HOWEVER...FINE TUNE THE TIMING AND LOCATION A BIT PER LATEST
MODEL GUIDANCE.

OTHERWISE...THERE IS ALSO A MODEST POTENTIAL FOR SOME FOG FORMATION
ACROSS THE WESTERN FRINGES OF THE AREA OVERNIGHT...AS THIS AREA WILL
BE CLOSER TO THE EDGE OF THE LOW LEVEL STRATUS TO OUR WEST. BOTH
RAP/HRRR GUIDANCE SUGGEST THE WESTERN EDGES OF OUR FORECAST AREA
AT LEAST HAVE THE POTENTIAL TO SEE SOME PATCHY LOCALLY DENSE FOG
TOWARDS EARLY FRIDAY MORNING...SO OPTED TO KEEP MENTION OF PATCHY
FOG IN THE FORECAST...WITH NO MENTION OF ANY DENSE FOG AS THINK
THE EDGE OF THE STRATUS WILL REMAIN FURTHER WEST THAN CURRENTLY
MODELED.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 300 PM CST THU DEC 18 2014

PATTERN: THIS FCST MAINTAINS EXCELLENT CONTINUITY WITH 24 HRS AGO.
THE UKMET/GEM/GFS/EC AND THE GEM/GFS/EC ENSEMBLE MEANS CONT IN
UNISON ON THE LONGWAVE FLOW. AMPLIFICATION WILL OCCUR OVER THE PAC
THE NEXT SEVERAL DAYS AND DOWNSTREAM INTO N AMERICA. A LONGWAVE TROF
WILL EVOLVE NEAR THE DATELINE...AND THIS WILL FORCE A PIECE OF THE
SUBTROPICAL HIGH TO BREAK OFF AND SETUP SW OF CA. THIS WILL RAISE
HEIGHTS ALONG THE W COAST AND RESULT IN A LONGWAVE TROF OVER THE
CNTRL/ERN USA.

A POTENTIAL FCST PROBLEM IS THE MAGNITUDE OF THE HEIGHT FALLS OVER
THE WRN USA CHRISTMAS DAY. THE PAST 3 RUNS OF THE EC /PRIOR TO ITS
12Z RUN/ AND ITS ENSEMBLE MEAN ARE MUCH DEEPER WHILE THE GFS/GEM ARE
FLATTER...A DIFF OF 250-300 METERS. THIS COULD BE GFS/EC BOTH
EXHIBITING THEIR BIASES. THIS WILL NEED TO BE WATCHED BECAUSE IT
WILL DETERMINE THE STRENGTH OF LEE CYCLOGENESIS JUST AFTER
CHRISTMAS. FOR WHAT ITS WORTH...THE 12Z EC CAME IN FLATTER LIKE THE
GFS BUT PROBABLY IS A ONE-RUN ABERRATION.

ALOFT: LOW AMPLITUDE FLOW WILL REMAIN OVERHEAD THRU SUN WITH SOME
INCONSEQUENTIAL RIPPLES PASSING THRU...AND SLOWLY RISING HEIGHTS
ALONG THE W COAST. SUN A STRONG SHORTWAVE TROF WILL CREST THE RIDGE
IN THE EXIT REGION OF A 175 KT ANTICYCLONICALLY-CURVE JET MAX. THIS
TROF WILL DIVE SE INTO THE CNTRL/NRN PLAINS AND CLOSE OFF MON. NW
FLOW FOLLOWS IN ITS WAKE TUE-WED. HEIGHTS RISE WED WITH A STRONG
SHORTWAVE TROF DIGGING OVER THE WRN USA. THE DEPTH/STRENGTH WILL
DETERMINE OUR SENSIBLE WX CHRISTMAS DAY...IE A SLOWER OR FASTER
SOLUTION. ALSO OF IMPORTANCE IS WHERE WILL THE LEADING EDGE OF THE
COLDER AIR BE? THIS WILL DETERMINE WHERE LEE CYCLOGENESIS OCCURS.

SURFACE: A WARM FRONT WILL FORM SAT-SUN AS LOW PRES ORGANIZES OVER
ALBERTA. THE LOW WILL DIVE SE INTO NRN PLAINS SUN NIGHT AND DRIFT
INTO IA MON BEFORE HEADING INTO THE GREAT LAKES TUE. WEAK HIGH PRES
WILL SPREAD OVER THE PLAINS WED. A WARM FRONT WILL FORM OVER THE SRN
PLAINS CHRISTMAS WITH LEE CYCLOGENESIS ENSUING.

THE DAILY DETAILS...

FRI NIGHT: DIFFICULT TO KNOW WHAT HAPPENS WITH THE STRATUS.
EC/GFS/NAM CROSS SECTIONS SUGGEST IT WILL DECREASE...BUT A WARM
FRONT IS FCST TO DEVELOP AND STRATUS WOULD BE SUPPORTED ON THE
STABLE/COOL SIDE. FOG COULD BE A PROBLEM NEAR THE EDGE OF THE
STRATUS. THE SKY FCST IS TROUBLESOME AND COULD RESULT IN LARGE
ERRORS IN TEMPS...WHICH HINGE ON SKIES CLEARING W OF HWY 281. USED
BIAS CORRECTED MET GUIDANCE WHICH REALLY DROPPED TEMPS OUT W.

SAT: ALL DEPENDS ON WHERE THE STRATUS IS. CLOUDY VS SUNNY. COLD VS
WARM. CONFIDENCE VERY LOW.

SUN: PROBABLY MOSTLY CLOUDY WITH MULTI-LAYERED MID-HIGH CLOUDS...
IF STRATUS IS NOT A LINGERING ISSUE. A FEW SPRINKLES POSSIBLE OVER S-
CNTRL NEB?

SUN NIGHT: THE LEE TROF HEADS E ACROSS THE FCST AREA AS THE LOW
DIVES INTO MN. THIS COULD PRODUCE SOME SPRINKLES OR A COUPLE LIGHT
SHWRS.

MON: COLD FRONTAL PASSAGE. POSSIBLY A FEW WRAP AROUND SHWRS?

TUE: COLD SECTOR. NOT LOOKING QUITE AS WINDY AS 24 HRS BECAUSE HOW
THE MODELS ARE HANDLING THE STRENGTH OF THE GREAT LAKES LOW.

WED: AM NOT BUYING THE GFS TAKING A CLIPPER TO THE N OF THE FCST
AREA...BUT THE EC SNEAKING SOMETHING DOWN THE FRONT RANGE LOOKS FROM
PLAUSIBLE AND THIS COULD BRING A TOUCH OF LIGHT SNOW TO PARTS OF THE
REGION. LOTS OF UNCERTAINTY...SO THIS IS NOT A LOCK.

CHRISTMAS DAY: LEE CYCLOGENESIS WITH A WARM FRONT FORMING/
STRENGTHENING. EXPECT A WAA PATTERN TO DEVELOP...BUT TIMING REMAINS
UNCERTAIN AND LOCATION OF THE LOW/FRONT WILL BE KEY IN SUBSEQUENT
SENSIBLE WX. SUGGEST ALL WITH TRAVEL PLANS KEEP AN EYE ON THE FCST.

MODELS AND ENSEMBLES CONT TO INDICATE A TRANSITION BACK TO THE
PATTERN OF NOV LATE MONTH...WITH A RIDGE OVER AK AND ARCTIC CHILL
RETURNING. IT WILL BE TURNING COLDER AFTER CHRISTMAS.

&&

.AVIATION...(FOR THE 06Z KGRI/KEAR TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1113 PM CST THU DEC 18 2014

MVFR TO IFR CONDITIONS EXPECTED TO START THE TAF PERIOD...WITH
VFR CONDITIONS CURRENTLY FORECAST AT KEAR BY 15Z...AND AT KGRI BY
03Z.

STRATUS PERSISTS ACROSS THE REGION AS OF 05Z AND THIS IS A TREND
WHICH IS EXPECTED TO CONTINUE THROUGH TONIGHT AND INTO THE DAY
FRIDAY. AN MVFR CEILING IS CURRENTLY IN EXISTENCE AT BOTH TAF
SITES...BUT GUIDANCE SUGGESTS AN IFR CEILING WILL MOVE IN FROM THE
WEST LATER TONIGHT AND PERSIST UNTIL VFR CONDITIONS ARE REALIZED
DURING THE DAY FRIDAY. THE SURFACE WIND WILL REMAIN FAIRLY LIGHT
DURING THE TAF PERIOD...SUSTAINED FROM THE SOUTH/SOUTHWEST AT
5-8KTS. SOME LOCATIONS MAY OBSERVE FOG TONIGHT UNTIL JUST AFTER
SUNRISE FRIDAY...WITH VISIBILITY RESTRICTION TO AROUND 6SM
CURRENTLY FORECAST.

&&

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

$$

UPDATE...WESELY
SHORT TERM...ROSSI
LONG TERM...HALBLAUB
AVIATION...BRYANT



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