Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 310605
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1205 AM CST SAT JAN 31 2015

.SYNOPSIS...
ISSUED AT 330 PM CST FRI JAN 30 2015

HIGH PRESSURE DOMINATES THE MISS RVR VALLEY THIS AFTERNOON.
SOUTHERLY FLOW ON THE BACK SIDE OF THE HIGH ACROSS THE REGION...WITH
LOCALLY SOME BREEZY CONDITIONS WITH WIND GUSTS OF 20 TO 30 MPH.
MEANWHILE A LOW PRESSURE SYSTEM IS LOCATED ACROSS THE DESERT
SOUTHWEST. A GOOD FETCH OF PACIFIC MOISTURE IS BRING DRAWN NORTHWARD
AHEAD OF THE LOW PRESSURE...RESULTING IN DENSE CIRRUS STRATUS.
BOUNDARY LAYER MIXING WAS LIMITED AS A RESULT OF THE HIGH CLOUDS AND
AFTERNOON TEMPS ONLY MANAGED TO WARM TO AROUND 50 DEGREES...ALTHOUGH
THIS IS ABOVE NORMAL FOR LATE JANUARY.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 330 PM CST FRI JAN 30 2015

THE LOW PRESSURE SYSTEM WILL SLIDE SLOWLY ACROSS THE DESERT
SOUTHWEST OVER THE NEXT 24 HOURS. THIS WILL ALLOW FOR CONTINUED
SOUTHERLY MOIST FLOW FROM THE PACIFIC. AS THE SYSTEM MOVES TOWARDS
THE SOUTHERN ROCKIES...A DISTURBANCE AHEAD OF THE SYSTEM WILL PUSH
ACROSS KS/SRN NEB. SOUNDINGS SHOW A VERY DRY LAYER WHICH WILL LIMIT
PRECIP INITIALLY FROM REACHING THE GROUND. ISENTROPIC LIFT BEST FROM
285K TO 295K AND SHOULD BE ABLE TO EVENTUALLY SATURATE THE LOWER
LEVELS. MARGINAL LIFT ON THE NW SIDE OF THE LOW AND DELAYED PRECIP
REACHING THE GROUND SHOULD RESULT IN PRECIP TOTALS BEING ON THE
LIGHT SIDE. THIS IS WHY THE FORECAST REMAINS CHANCE POPS.

ANOTHER CONCERN WILL BE PRECIP TYPE. COOLER AIR FROM THE NORTHERN
SYSTEM DRIFTS SOUTH...WHICH MODELS SHOW IN DECENT AGREEMENT. 850 MB
TEMPS AROUND ZERO BY MORNING AND SLOWLY FALL DURING THE DAY. TEMPS
REMAIN MILD TONIGHT DUE TO THE CLOUDS AND SHOULD FALL ONLY INTO THE
20S...MAYBE HOLDING CLOSE TO FREEZING IN THE SOUTHWEST. THIS WILL
ALLOW FOR A SLIGHT REBOUND INTO THE LOWER AND MID 30S IN THE
MORNING. WHILE GENERALLY SNOW WILL BE THE PRIMARY P TYPE...WHILE
TEMPS WARM ABOVE 35 DEGREES COULD SEE SOME MIX OF RAIN AND SNOW OR
EVEN A BRIEF PERIOD TO ALL RAIN. BY LATE AFTERNOON 850MB TEMPS TO
-2C OR COLDER AND TEMPS SHOULD BE FALLING AT THE SURFACE...THUS
EVENTUALLY THE THREAT FOR A MIX IS ELIMINATED.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 330 PM CST FRI JAN 30 2015

SOME WEAK ELEVATED ISENTROPIC LIFT CONTINUES SATURDAY EVENING AND
OVERNIGHT IN THE 285-300K LAYER OVER NORTH CENTRAL AND NORTHEAST
NEBRASKA ALONG WITH WEAK FRONTOGENESIS. IN ADDITION...THE LIFT
WILL BE ENHANCED IN THE RIGHT REAR QUADRANT OF THE JET STREAK. THE
FORECAST SOUNDING LOCATED NEAR ONEILL INDICATES A SATURATED
ISOTHERMAL LAYER 850-700MB WITH A TEMPERATURE OF -10C TO -8C. THE
GFS AND THE NAM INDICATE THAT THE 1200M THICK DENDRITIC LAYER IS
SUPER- SATURATED (WITH RESPECT TO ICE) AND HAS UPWARD MOTION OF
2-6 MICROBARS/SEC. THE FORECAST SOUNDINGS APPEAR TO SUPPORT A SNOW
TO LIQUID RATIO OF 10:1 INITIALLY AND 14:1 BY 06Z. SINCE THE
FORECAST AMOUNTS ARE FAIRLY SMALL...THE DIFFERENCE BETWEEN THE TWO
IS NOT BIG AND A 12-13:1 RATIO WOULD WORK FOR THE 12 HOUR PERIOD
00-12Z. THE SYNOPTIC FORCING WOULD THEN SUPPORT SNOWFALL AMOUNTS
OF AN INCH OR TWO. HOWEVER...A CROSS-SECTION OF EQUIVALENT
POTENTIAL VORTICITY AND THETA-E INDICATE THE POTENTIAL FOR
CONVECTIVE ENHANCEMENT IN THE 700-500MB LAYER. THAT IS SUPPORTED
BY THE NEARLY PSEUDO-ADIABATIC LAPSE RATE SIGNALED IN THE
FORECAST SOUNDINGS. THE FAVORABLE PARAMETERS THEN SHIFT GRADUALLY
TO THE EAST AND END BY 12Z.

IN CENTRAL AND SOUTH CENTRAL NEBRASKA...THE FRONT-RELATIVE LIFT
SHIFTS TO THE SOUTHEAST RATHER QUICKLY. THERE IS A DIFFERENCE IN THE
TIMING OF THAT SHIFT INDICATED IN THE MODELS.

THE NEXT CHANCE FOR PRECIPITATION LOOKS TO BE TUESDAY NIGHT AND
WEDNESDAY. AS A FRONT SLIDES SOUTH...SYSTEM-RELATIVE LIFT IN THE
290-300K LAYER SETS THINGS UP FOR LIGHT SNOW. THE FRONT STALLS OVER
CENTRAL KANSAS AND SOME WEAK ISENTROPIC UPGLIDE COULD LIFT MOIST AIR
INTO SOUTH CENTRAL AND SOUTHWEST NEBRASKA. AT THAT TIME RANGE...IT
IS PROBABLY A LITTLE TOO EARLY TO PIN DOWN THE LOCATION AND AMOUNTS
OF PRECIPITATION OR EVEN THE PHASE. LOOKING AT THE GFS, GEM AND
ECM...THIS EVENT APPEARS TO BE PRIMARILY WARM ADVECTION OVER A
SHALLOW-SLOPED FRONT. A CROSS-SECTION OF WIND AND AGEOSTROPHIC
VERTICAL CIRCULATION IS SIGNALING ISENTROPIC UPGLIDE AND
FRONTOGENESIS IN THE 291-306K LAYER WITH NEGATIVE TO ZERO THETA-E
LAPSE RATES (NEUTRAL TO FOLDED THETA-E).

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1205 AM CST FRI JAN 30 2015

A STORM SYSTEM FROM THE SOUTHWESTERN U.S WILL LIFT INTO WESTERN
NEBRASKA SATURDAY AND BRING IFR CEILINGS AND AREAS OF SNOW. THE
SNOW SHOULD BEGIN AT KLBF AFTER 14Z AND AT KVTN AFTER 21Z. WHILE
LOWEST VISIBILITY IS FORECAST AT 3SM...LOWER VISIBILITIES OF A
MILE OR LESS ARE POSSIBLE.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SYNOPSIS...MASEK
SHORT TERM...MASEK
LONG TERM...SPRINGER
AVIATION...ROBERG











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