FXUS63 KOAX 182055
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
255 PM CST FRI FEB 18 2011
.SHORT TERM...TONIGHT THROUGH MONDAY
NEAR-SPRING WEATHER WILL BRING A RANGE ACROSS THE AREA FROM
THUNDERSTORMS TO ICE AND SNOW THIS WEEKEND. SUBJECTIVE 12Z UPPER
AIR ANALYSIS INDICATES UPPER-LEVEL TROUGH DIGGING OFF THE PACIFIC
COAST...WITH A MORE COMPACT UPPER LOW MOVING ACROSS THE NORTHERN
GREAT LAKES. DRY PROFILE CONTINUES IN THE CENTRAL US PER 12Z
RAOBS...PARTICULARLY IN THE LOWER TO MID LEVELS. SHARP 850MB
TEMPERATURE GRADIENT WAS NOTED IN THE NORTH CENTRAL US...WITH -25C
AT KINL TO -5C AT KMPX TO 1C AT KOAX...IN WAKE OF THE GREAT LAKES
LOW. SURFACE RIDGE AT 20Z EXTENDED FROM CENTRAL ND THROUGH EASTERN
SD AND WESTERN IA INTO NORTHERN MO.
MAIN FORECAST CONCERNS ARE LINKED TO WEEKEND SYSTEM AS WESTERN US
LOW EJECTS ACROSS THE CENTRAL PLAINS. HAVE KEPT DRY FORECAST FOR
TONIGHT THROUGH SATURDAY MIDDAY...WITH DRIZZLE DEVELOPING IN THE
SOUTHERN CWA BY LATE AFTERNOON AS STRONG MID-LEVEL THETA-E ADVECTION
MOISTENS THE PROFILE. PRECIP SHOULD TRANSITION TO A MEASURABLE
LIGHT RAIN THROUGH THE EVENING. AN ISOLATED RUMBLE OF THUNDER IS
POSSIBLE IN THE EVENING...BUT MOST OF THE ELEVATED INSTABILITY AND
CONVERGENCE ON THE NOSE OF THE LOW-LEVEL JET WILL REMAIN WEST OF THE
CWA BEFORE 06Z. THUS...HAVE PULLED BACK THUNDER MENTION IN THE TO
JUST THE SOUTHWEST...THOUGH DID INCREASE POPS. BEST THUNDER THREAT
LOOKS TO BE AROUND 08-12Z...FOCUSED ON THE SOUTHERN TO SOUTHEASTERN
CWA AS THE LOW-LEVEL JET VEERS THROUGH THE NIGHT. HAVE INCREASED
THUNDER COVERAGE IN EXTREME SOUTHEAST NEB...BUT AGAIN...PULLED IT
OUT OF THE NORTHERN CWA...AS MODELS HAVE TRENDED FURTHER SOUTH WITH
THE SURFACE LOW AND THAT AREA LOOKS TO REMAIN OUT OF THE INSTABILITY
AXIS. AN ISOLATED RUMBLE MAY LINGER MAINLY IN SOUTHWEST IA AFTER
12Z...BUT ELEVATED INSTABILITY WANES RAPIDLY AS MID-LEVEL
SATURATION DECREASES...WITH DRY SLOTTING MOVING INTO THE SOUTHERN
CWA THROUGH THE MORNING.
DID KEEP TEMPS AT OR ABOVE FREEZING THROUGH 12Z SUNDAY ACROSS THE
CWA...THOUGH IT WILL BE CLOSE IN THE EXTREME NORTHWESTERN CWA.
MODEL SOUNDINGS STILL INDICATE A TRANSITION FROM RAIN TO FREEZING
RAIN TO SNOW IN THAT AREA ON SUNDAY AS A MUCH COLDER AIRMASS
UNDERCUTS A MID-LEVEL WARM NOSE. MODELS HAVE TRENDED COLDER WITH
THE INCOMING AIRMASS...WITH A MORE RAPID TRANSITION TO SNOW ON
SUNDAY. STRONG LOW TO MID-LEVEL FRONTOGENESIS PROVIDING
CONCENTRATED LIFT IN THE NORTHWESTERN CWA...ALONG WITH THE POTENTIAL
FOR CONVECTIVE INSTABILITY TO CONTRIBUTE TO PRECIPITATION
TOTALS...SHOULD PRODUCE FAIRLY SIGNIFICANT LIQUID EQUIVALENTS.
CONSIDERABLE UNCERTAINTY EXISTS IN THE TRANSITION BETWEEN
PRECIPITATION TYPES...BUT LIKELIHOOD/CONFIDENCE OF WARNING
QUANTITIES OF ANY WINTRY TYPES IS LOW DUE TO THE TRANSITIONS.
ADDITIONALLY...IF SURFACE TEMPS HOVER NEAR FREEZING...MODERATE
RAIN FALLING THROUGH A STRONG WARM NOSE TENDS TO WARM THE PROFILE
SLIGHTLY AND KEEP THE ICE TOTALS DOWN. STILL...COULD SEE A COUPLE
OF A TENTHS OF ICING IN THE EXTREME NORTHWESTERN CWA DEPENDING ON
HOW QUICKLY SURFACE TEMPERATURES FALL BELOW FREEZING...ALONG WITH
GUSTY WINDS THAT COULD EXACERBATE ANY ICING HEADACHES...AND A
CLOSING INCH OR TWO OF SNOW TO ADD TO THE TROUBLES. CONSIDERED
WINTER STORM WATCH FOR ICE IN THE EXTREME NORTHWEST...WITH
SIGNIFICANT SNOWFALL REMAINING NORTH...BUT AFTER MUCH
CONSIDERATION HAVE OPTED TO HOLD OFF...GIVEN FINE LINES BETWEEN
RAIN/ICE/SNOW AND ASSOCIATED UNCERTAINTY. WILL INSTEAD STRENGTHEN
WORDING IN HWO TO EMPHASIZE POSSIBLE THREATS.
PRECIPITATION WILL END RAPIDLY FROM SOUTHWEST TO NORTHEAST ON SUNDAY
INTO SUNDAY EVENING AS STATIC STABILITY INCREASES RAPIDLY. HAVE
SPED TIMING OF PRECIP ENDING ACROSS THE CWA...WITH JUST A SLIGHT
CHANCE OF SNOW LINGERING IN THE EXTREME NORTH ON SUNDAY NIGHT AND
MONDAY AS A SECOND SHORTWAVE SLIDES ACROSS THE DAKOTAS INTO
MINNESOTA/IOWA.
.LONG TERM...MONDAY NIGHT THROUGH FRIDAY
INDIVIDUAL MODELS AS WELL AS ENSEMBLE MEMBERS SEEM TO BE IN DECENT
AGREEMENT STARTING THE EXTENDED PERIOD OFF WITH A LONGWAVE UPPER
TROF IN THE VICINITY OF THE WEST COAST. THROUGHOUT THE
WEEK...VARIOUS SHORTWAVES ARE PROGGED TO MIGRATE FROM THE LONGER
WAVE TROF AND INTO THE PLAINS...AND MODEL AGREEMENT DECREASES OVER
TIME WITH THE DETAILS OF THESE WAVES. IN ADDITION...AS MEAN UPPER
TROF AXIS MOVES EAST AND THE PLAINS END UP IN NORTHWEST FLOW... AN
ARCTIC FRONT IS ADVERTISED BY THE ECMWF TO MOVE THROUGH THE FORECAST
AREA WEDNESDAY NIGHT. THE ECMWF TIMING CONTINUITY FROM THE 00Z RUN
TO THE 12Z RUN WAS NEARLY IDENTICAL. THE OPERATIONAL GFS IS MUCH
LATER WITH THE ARCTIC AIR...CLOSER TO THE FRIDAY NIGHT/12Z SATURDAY
TIME FRAME. AHEAD OF THIS FRONT...MODELS AGREE IN SPINNING UP A
SURFACE LOW OVER THE HIGH PLAINS. THIS SHOULD RESULT IN MOIST
SOUTHERLY FLOW INTO THE REGION WITH PRECIPITATION CHANCES FROM
WEDNESDAY NIGHT INTO FRIDAY. REGARDING PRECIPITATION TYPE...THERE
IS ANOTHER CHANCE FOR FREEZING RAIN WITH WARMER 850 TEMPERATURES AND
SUB-FREEZING SURFACE TEMPERATURES MAINLY EARLY THURSDAY MORNING.
HAVE HINTED AT THIS IN OUR SOUTHERN COUNTIES.
&&
.AVIATION...
TAF SITES KOFK/KOMA/KLNK
18Z TAFS
VFR CONDITIONS ARE EXPECTED THROUGH MUCH OF THE PERIOD. LOW LEVEL
MOISTURE IS FORECAST TO SPREAD NORTH TONIGHT AND SHOULD BEGIN
REACHING THE TAF SITES AFTER 12Z WITH MVFR CIGS DEVELOPING.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$
MAYES/NIETFELD/FOBERT