Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 291727
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1227 PM CDT FRI APR 29 2016

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 350 AM CDT FRI APR 29 2016

TODAY AND TONIGHT...THE RAP IS TRACKING THE POWERFUL UPPER LOW
ACROSS THE 4 CORNERS REGION AND BRINGING RAIN AND SNOW INTO SWRN NEB
BY LATE AFTERNOON. THIS IS CLOSE TO THE COOLER NAM SOLN. IN FACT THE
RAP SHOWS RAIN AND SNOW EAST OF HIGHWAY 83 AT 00Z THIS EVENING WITH
ALL SNOW ACROSS SWRN NEB. DESPITE THIS THE RAP KEEPS ACCUMULATING
SNOW ACCUMULATIONS LIGHT...WEST OF HIGHWAY 61 BUT WITH HEAVY
ACCUMULATIONS OVER THE COLORADO PLAINS. THE FORECAST TODAY FOLLOWS A
BLEND OF THE RAP AND 4 BIAS CORRECTED GUIDANCE DATASETS FOR HIGHS IN
THE 40S.

THE BLEND OF 4 BIAS CORRECTED GUIDANCE DATASETS PRODUCES LOWS IN THE
30S TO NEAR 40 TONIGHT. IF THIS TEMPERATURE FORECAST IS CLOSE...THEN
SNOW SHOULD BECOME WIDESPREAD ACROSS THE CNTL AND WRN SANDHILLS.
NOTE THE RAP IS FORECASTING VSBY LESS THAN 1/4 MILE AT 00Z AND THIS
IS DISTURBING AS IT REPRESENTS HEAVY SNOW. IT MIGHT BE BEST TO
REVISIT THE RAP MODEL AFTER THE 12Z UPPER AIR DATA INGEST IS
COMPLETE AROUND 13Z OR 14Z.

A WINTER WEATHER ADVISORY IS IN PLACE FOR THE SANDHILLS TONIGHT AND
SATURDAY. SNOW IS UNDERWAY IN LIMON THIS MORNING AND SNOW LEVELS
ACROSS THE SANDHILLS SHOULD FALL TO AROUND 3500 FEET TONIGHT.

HEAVY RAIN IS FORECAST FOR TONIGHT FOR AREAS EAST OF HIGHWAY 83. THE
BLENDED SOLN PRODUCES AROUND 1.5 INCHES OF RAINFALL IN 12 HOURS
TONIGHT WHICH MAY PRODUCE MINOR FLOODING. THE DOWN-SCALED NAM AND TO
A LESSER EXTENT THE ARW AND NMM REFLECTIVITY PRODUCTS SHOW
CONVECTION JUST EAST OF THE FCST AREA TONIGHT. THE NAM12 INDICATES
ELEVATED CAPE ACROSS SCNTL NEB EAST OF THE FCST AREA ALSO. ALL OF
THIS CONVECTION WILL BE FEEDING NORTHWEST INTO A DEFORMATION ZONE
ACROSS THE SANDHILLS TONIGHT.

LASTLY...A FAIRLY WIDESPREAD SEVERE WEATHER EVENT IS EXPECTED ACROSS
THE MID SOUTH WHICH SHOULD MOMENTARILY BLOCK OR DEFLECT MOISTURE
TRANSPORT INTO THE STORM ACROSS NEB. THE MODELS TEND TO MIS-FORECAST
THIS FEATURE AND CONTINUE TO FORECAST HEAVY RAIN OR SNOW FARTHER
NORTH WHICH SOMETIMES DOES NOT MATERIALIZE. THUS THE PROSPECT OF
HEAVY RAIN AND SNOW ACROSS THE FCST AREA IS SOMEWHAT UNCERTAIN.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 350 AM CDT FRI APR 29 2016

MID RANGE...SATURDAY AND SUNDAY... MAIN FORECAST CHALLENGES ARE
TEMPERATURES AND PRECIPITATION AS THE POTENT UPPER LOW SLOWLY
CROSSES THE CENTRAL PLAINS.

SATURDAY... LOWERED MAX TEMPS ANOTHER DEGREE OR SO AS GUIDANCE HAS
BEEN OVERSHOOTING TEMPS LATELY. CURRENT FORECAST HIGHS ARE NOW NEAR
40F WEST AND LOWER/MID 40S EAST... WHICH IS ABOUT 5 DEGREES BELOW
MAV/MET BUT SLIGHTLY ABOVE ECS. WENT AHEAD AND INTRODUCED ALL SNOW
FOR THE PANHANDLE AND FAR WESTERN SANDHILLS THROUGH 18Z. NAM AND GFS
FORECAST SOUNDINGS AGREE ON SATURATION IN THE DGZ THROUGHOUT THE
MORNING... INDICATING ICE INITIATION IN THE CLOUD LAYER. NAM KEEPS
VIRTUALLY THE ENTIRE TEMP PROFILE AT OR BELOW FREEZING AT KAIA AND
KOGA... WHICH SUGGESTS LITTLE TO NO MELTING. IN ADDITION...
APPRECIABLE LIFT EXISTS AS SHOWN BY NEGATIVE OMEGA IN SOUNDINGS...
ISENTROPIC UPGLIDE AT 295K AND 300K... AND NEARLY UPRIGHT AGEO
CIRCULATION IN CROSS SECTIONS OF THE SANDHILLS. THE H3 JET IS ALSO
NEARBY... PROVIDING EXTRA DIVERGENCE ALOFT. THE POTENTIAL FOR
MODERATE SNOW EXISTS... BUT THE QUESTION IS HOW MUCH SNOW ACTUALLY
ACCUMULATES DUE TO RELATIVELY WARM GROUND TEMPS. CONFIDENCE IS LOW
FOR HEAVY SNOW... OR AT LEAST HEAVY ENOUGH TO COMPENSATE AND PILE UP
ON NON GRASSY SURFACES. FARTHER EAST ALONG THE HWY 83 CORRIDOR...
TEMP PROFILES HUG THE FREEZING LINE FOR THE LOWEST 200HPA... RAISING
THE POSSIBILITY OF MELTING SNOW. GIVEN SLIGHTLY WARMER MIN TEMPS...
KEPT PTYPE AS RASN. ENOUGH LOW LEVEL WARMING SHOULD TAKE PLACE
AFTN/EVE TO SWITCH PRECIP TO ALL RAIN FOR THE ENTIRE CWA. FLIPPED
BACK TO RASN SAT NIGHT ACROSS THE WEST AND SNOW IN THE PANHANDLE.
MOISTURE CONTENT WILL BE LOWER AND THE FORCING WEAKER... SO
ACCUMULATING SNOW IS NOT AS BIG A CONCERN AS SAT AM.

SUNDAY... MADE LITTLE CHANGE TO MAX TEMPS AS WEAK WAA RESUMES.
HOWEVER... CONTINUED BKN/OVC CONDITIONS AND NORTH/NORTHEAST WINDS
WILL STILL LIMIT HIGHS TO THE LOWER 50S. CUT POPS BACK AS THE MID
LEVELS START TO DRY OUT. SOME LIFT AND RELATIVELY STEEP LAPSE RATES
STILL EXIST IN THE LOW LEVELS AND SOME WEAK FGEN FORCING AT H7
REMAINS... SO CANT ENTIRELY RULE OUT A SHOWER... MAINLY SOUTHERN AND
WESTERN PORTIONS OF THE CWA.

LONG RANGE...MONDAY THROUGH THURSDAY... A WEAK SHORTWAVE TRAVERSES
THE AREA MONDAY... BUT THE BEST MOISTURE IS ACROSS SOUTHWEST
NEBRASKA. SCHC POPS CONFINED GENERALLY ALONG/SOUTH OF I-80 AM/EARLY
PM. MIDWEEK... AN UPPER LEVEL RIDGE AND SURFACE HIGH PRESSURE
CONTROL THE PATTERN OVER THE ROCKIES AND PLAINS. SIGNIFICANT WARMING
IS DUE WITH DOWNSLOPE FLOW ON TUESDAY AND A THERMAL RIDGE
APPROACHING THE AREA WEDNESDAY. H85 TEMPS EXCEED 10C FOR WESTERN AND
CENTRAL NEB WED AND CLOSE TO 15C PANHANDLE. THE UPPER RIDGE AXIS IS
ON OUR DOORSTEP THURSDAY WHILE THE H85 RIDGE AXIS BISECTS THE
AREA... FLIPPING THE FLOW TO SOUTHERLY. GFS A LITTLE QUICKER AND
WARMER THAN EURO WITH THIS FEATURE... BUT HIGHS SHOULD HAVE NO
PROBLEM REACHING THE 70S ONCE AGAIN.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1222 PM CDT FRI APR 29 2016

MODELS ARE IN GOOD AGREEMENT AND CONFIDENCE IS INCREASING WHERE A
PROLONGED SLOW MOVING SPRING STORM WILL BRING A MIXTURE OF RAIN
AND SNOW THROUGH 18Z SATURDAY. MARGINAL VFR CONDITIONS WILL LOWER
TO IFR CONDITIONS THIS EVENING...AND DOWN TO LIFR FLIGHT
CATEGORIES FOR OVERNIGHT AND BEYOND.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM 7 PM CDT /6 PM MDT/ THIS EVENING TO
7 PM CDT /6 PM MDT/ SATURDAY FOR NEZ004-022>024-035-036-056-094.

&&

$$

SHORT TERM...CDC
LONG TERM...SNIVELY
AVIATION...KECK



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