FXUS63 KOAX 181647
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
1047 AM CST SAT DEC 18 2010
.UPDATE...
INCREASED POPS AND SNOW TOTALS IN SOUTHEAST NEBRASKA.
&&
.DISCUSSION...
INTENSE SHORTWAVE AND MID-LEVEL FRONTOGENESIS CONTINUE TO SUPPORT
A BAND OF SNOW FROM SOUTH CENTRAL TO SOUTHEAST NEBRASKA. INCREASED
POPS TO CATEGORICAL THROUGH THIS AFTERNOON A COUPLE OF UPDATES
AGO...AND ALSO INCREASED SNOW AMOUNTS TO UP TO 2 INCHES UNDER THE
MOST INTENSE BANDING WITH AN INCH ALREADY REPORTED AND SNOW
EXPECTED TO CONTINUE FOR ANOTHER COUPLE OF HOURS. SHORTWAVE IS
FAIRLY FAST-MOVING..AND SHOULD SEE BAND DISSIPATE THIS AFTERNOON
AS IT PASSES BY.
UPDATED GRIDS/ZFP SENT.
&&
.PREV DISCUSSION... /ISSUED 847 AM CST SAT DEC 18 2010/
UPDATE...
ADDED SLIGHT CHANCE OF SNOW IN THE SOUTHERN CWA.
DISCUSSION...
WEAK SHORTWAVE APPARENT IN WV IMAGERY AND 1.5PVU PRESSURES...ALONG
WITH BAND OF MID- LEVEL FRONTOGENESIS...IS JUST ENOUGH TO ALLOW AN
AREA OF LIGHT SNOW TO DEVELOP AND MOVE FROM CENTRAL NEB INTO SRN
NEB/NRN KS THIS MORNING. WITH VIS DOWN TO 1.5 SM AT KCNK AND A
DUSTING REPORTED...HAVE OPTED TO ADD A SLIGHT CHANCE MENTION FOR
SNOW IN THE SRN CWA THIS MORNING WITH THE POTENTIAL FOR JUST
ENOUGH SNOW TO MEASURE. HAVE ALSO INCREASED CLOUDS TO OVERCAST
CATEGORY TO CORRESPOND WITH CLOUDS MOVING INTO THE SRN CWA...AND
LOWERED TEMPS THERE A FEW DEGREES.
UPDATED GRIDS/ZFP ALREADY SENT.
PREV DISCUSSION... /ISSUED 330 AM CST SAT DEC 18 2010/
DISCUSSION...
SNOW CHANCES SUNDAY INTO MONDAY ARE THE PRIMARY FORECAST CONCERNS.
PRECIPITATION TYPE MONDAY IS ALSO A CONCERN.
UPPER LOW OFF THE NORTHERN PACIFIC COAST WILL SEND A COUPLE OF
SHORTWAVES THROUGH THE WESTERN STATES AND ROCKIES AND INTO THE
PLAINS TONIGHT THROUGH MONDAY. THE FIRST WAS MOVING THROUGH NORTHERN
CALIFORNIA THIS MORNING AND WILL ENTER OUR AREA LATE TONIGHT AND
SUNDAY. THIS IS THE WEAKER OF THE TWO AND MODELS SHOW LITTLE IN THE
WAY OF SURFACE REFLECTION. MAINLY A MID LEVEL WARM ADVECTION
SCENARIO WITH LIMITED LOW LEVEL MOISTURE. HOWEVER MODEL CONSISTENCY
FROM RUN TO RUN OVER THE LAST COUPLE OF DAYS SUGGESTS LIGHT SNOW
WILL BREAK OUT AFTER MIDNIGHT TONIGHT IN NORTHEAST NEBRASKA AND
SPREAD EAST THROUGH NOON SUNDAY. INCREASING SPECIFIC HUMIDITY ALONG
295K THETA SURFACE SUGGESTS A HALF INCH OR SO OF SNOW IS POSSIBLE
DURING A 6 HOUR WINDOW IN ANY ONE LOCATION BEGINNING IN OUR
WESTERN CWA LATE TONIGHT AND ENDING SUNDAY AFTERNOON IN THE EAST.
BEST SNOW CHANCES WILL REMAIN NORTH OF INTERSTATE 80...AND MORE
LIKELY FROM NORTHEAST NEBRASKA INTO WEST CENTRAL IOWA.
OUR NEXT AND MORE IMPRESSIVE SYSTEM WAS SPINNING SOUTH ON WEST SIDE
OF UPPER LOW IN THE PACIFIC...AND WAS CLEARLY EVIDENT ON WATER VAPOR
IMAGERY. GFS TRACKS THIS WAVE INTO THE PLAINS LATE SUNDAY NIGHT AND
MONDAY...AND WAS A LITTLE FARTHER SOUTH THAN NAM AND ECMWF. GFS HAS
BEEN RELATIVELY CONSISTENT IN PAINTING AXIS OF HIGHEST QPF NEAR AND
JUST NORTH OF THE NEBRASKA SOUTH DAKOTA BORDER OVER THE LAST FEW
DAYS...BUT WILL BE CURIOUS HOW MODELS REACT WHEN BETTER SOUNDING
SAMPLING OCCURS OVER LAND. IT SURE LOOKS LIKE THIS WAVE WILL DIVE A
BIT SOUTH OF ADVERTISED LANDFALL...SO HAVE PLACED MORE CONFIDENCE IN
GFS SOLUTION. STRONG ISENTROPIC UPGLIDE WILL ENSUE SUNDAY NIGHT
ALONG 300K THETA SURFACE WITH BROAD AREA OF LIGHT SNOW DEVELOPING BY
12Z MONDAY OVER MUCH OF THE CWA. UPGLIDE STRENGTHENS THROUGH THE
MORNING AND IS MAXIMIZED OVER OUR NORTHERN CWA AT NOON MONDAY.
ADVECTING MIXING RATIOS FROM SOUTHERN NEBRASKA INTO NORTHERN CWA AND
SOUTHEAST SOUTH DAKOTA SUGGEST MAXIMUM SNOW AMOUNTS COULD TOTAL 4 TO
6 INCHES BEFORE SNOW TAPERS MONDAY EVENING. ALSO...STRONG SOUTH
WINDS OVER OUR SOUTHERN CWA WILL DRIVE TEMPERATURES WELL INTO THE
30S IN OUR SOUTH...AND FORECAST SOUNDINGS SUGGEST A MIX OF
PRECIPITATION IS LIKELY SOMEWHERE NEAR INTERSTATE 80 OR THE PLATTE
RIVER IN NEBRASKA MONDAY AFTERNOON. SNOW AMOUNTS WILL TAPER NEAR AND
SOUTH OF THIS TRANSITION ZONE...SO WILL HAVE TO FINE TUNE THIS WITH
LATER FORECASTS.
THE REST OF THE FORECAST WAS LEFT BASICALLY UNCHANGED. COOLER
TEMPERATURES ARE EXPECTED BEHIND THIS EXITING WAVE FOR TUESDAY.
LINGERING LOW LEVEL MOISTURE AND WEAK WARM ADVECTION BELOW 850MB
COULD LEAD TO PATCHY DRIZZLE OR FREEZING DRIZZLE FROM TIME TO TIME
TUESDAY AND WEDNESDAY. THEN A MORE SIGNIFICANT SYSTEM IS FORECAST
THURSDAY WITH GFS AND ECMWF CONVERGING ON PRECIP CHANCES THEN.
DERGAN
AVIATION...
TAF SITES KOFK/KOMA/KLNK
06Z TAFS
VFR CONDITIONS EXPECTED THROUGH THE PERIOD AT ALL THREE TAF
SITES. SMALL BAND OF SC OVC ACROSS SOUTH CENTRAL IOWA WILL
CONTINUE MOVING EAST OUT OF THE KOMA AND KLNK AREA THROUGH 12Z.
MID LEVEL CIGS HOWEVER EXPECTED TO INCREASE AFTER 12Z AS 850-700MB
WARM ADVECTION DEVELOPS IN ADVANCE OF WEAK WAVE MOVING OUT OF
COLORADO. HIGH PRESSURE REMAINS IN PLACE AT THE SURFACE WITH WINDS
REMAINING LIGHT DURING THE PERIOD.
FOBERT
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$
MAYES