FXUS63 KGID 080525
AFDGID
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HASTINGS NE
1125 PM CST MON DEC 7 2009
.AVIATION...06Z KGRI TAF. TROUBLING FLIGHT CONDITIONS CONTINUE TO
LOOK LIKELY...ESPECIALLY BY MID TO LATE MORNING INTO TUESDAY
NIGHT. LIGHT SNOW WILL CONTINUE TO SPREAD ACROSS SOUTH CENTRAL
NEBRASKA DURING THE EARLY MORNING HOURS. CEILINGS HAVE ALREADY
FALLEN INTO THE MVFR RANGE AND WILL CONTINUE TO LOWER TOWARDS
DAYBREAK AS SNOW INCREASES. CONDITIONS WILL CONTINUE TO
DETERIORATE ESPECIALLY BY LATE MORNING INTO THE AFTERNOON AS THE A
POTENT STORM SYSTEM MOVES INTO THE CENTRAL AND SOUTHERN PLAINS.
EXPECT A DROP IN CEILINGS TO AROUND 200 FT WITH VISIBILITIES NEAR
1/2SM IN SNOW DURING MUCH OF THE DAY...POSSIBLY LOWER BY LATE
AFTERNOON. THE POOR CONDITIONS WILL THEN CONTINUE PAST THE END OF
THE 06Z TAF PERIOD AS THE WINDS REALLY INCREASE DURING THE EVENING
AND OVERNIGHT HOURS TO INCREASE BLOWING AND DRIFTING OF THE SNOW
THAT WILL HAVE ALREADY FALLEN.
&&
.PREV DISCUSSION... /ISSUED 957 PM CST MON DEC 7 2009/
UPDATE...00Z GFS AND NAM MODELS CONTINUE ON NEARLY UNCHANGED FROM
PREVIOUS RUNS. THERE WAS A SLIGHT REDUCTION IN QPF ON THE
GFS...BUT NOT SIGNIFICANT. THEREFORE...WILL CONTINUE ONWARD WITH
PREVIOUS FORECAST AT THIS TIME. WILL REALLY NEED TO WATCH THE
WINDS LATE TUESDAY AFTERNOON INTO TUESDAY EVENING FOR SUBSTANTIAL
BLOWING AND DRIFTING SNOW...ALONG WITH NEAR WHITE OUT CONDITIONS
AT TIMES IN RURAL AREAS.
PREV DISCUSSION... /ISSUED 338 PM CST MON DEC 7 2009/
SHORT TERM...TONIGHT THROUGH SUNRISE WEDNESDAY. OBVIOUS FORECAST
CONCERN WILL BE APPROACHING WINTER STORM.
AT PRESENT IT IS THE CALM BEFORE THE STORM AS YESTERDAYS DISTURBANCE
THAT PRODUCED 1 TO 5 INCHES OF SNOW HAS EXITED THE PLAINS AND
UPSTREAM MID LEVEL TROUGH FROM MONTANA TO NORTHERN CALIFORNIA
CONTINUES TO DIG. MEANWHILE WE SIT UNDER HIGH PRESSURE AT THE
SURFACE.
RIGHT UP FRONT MIGHT AS WELL STATE THAT MODEL CONSISTENCY CONTINUES
TO BE REMARKABLY SIMILAR AND DO NOT PLAN TO MAKE MANY CHANGES FROM
ONGOING FORECAST. LOOKS LIKE FIRST ROUND OF SNOW STILL ON TRACK TO
BEGIN THIS EVENING AS WARM ADVECTION SETS UP AHEAD OF WAVE. ACTUALLY
MAY GET SOME LIGHT SNOW THIS AFTERNOON AS VERY WEAK RETURNS ALREADY
SHOWING UP ON THE 88D. WARM ADVECTION PATTERN WILL BE PROLONGED AS
NOTED ON 290K ISENTROPIC SURFACE. AVERAGE MIXING RATIOS DURING THAT
TIME TO RANGE FROM 2.0 GM/KG IN THE NORTH TO 3 IN THE SOUTH. THAT
ALONE WOULD RESULT IN 6 TO 12 INCHES OF SNOW USING THE GARCIA METHOD
AND ACCOUNTING FOR A DURATION OF CLOSE TO 24 HOURS.
IMPRESSIVE DYNAMICS MOVE INTO THE REGION ON TUESDAY NOTED BY Q
VECTORS AND JET POSITION WITH OUR CWA IN FAVORABLE LEFT EXIT REGION.
TOOK A CROSS SECTION NORTH TO SOUTH ACROSS ACROSS OUR CWA AND NOTED
ABUNDANT MOISTURE...STRONG OMEGA IN THE DENDRITIC ZONE WHICH IS
PERSISTENT AND WIDESPREAD. STILL A QUESTION MARK OF EXACTLY WHERE
THE HEAVIEST SWATH OF SNOW FALLS BUT AT THIS POINT 700 MB LOW TRACK
AND OTHER PARAMETERS WOULD CONFIRM ORIGINAL THINKING THAT IT WOULD
BE IN THE SOUTHEAST THIRD OF THE CWA. HOWEVER STILL BELIEVE THE
MAJORITY OF THE CWA WILL REACH WARNING CRITERIA WITH THE BIGGEST
QUESTION MARK BEING IN THE EXTREME NORTHWEST.
WILL GO AHEAD AND USE LIQUID TO SNOW RATIO OF AROUND 15-17 TO 1 IN
THE NORTH AND AROUND 12 TO 1 IN THE SOUTH BASED ON MODEL OUTPUT AND
RESULTS FROM THE COBB AND ROEBBER METHODS.
FORECAST TRACK AND INTENSITY OF THE SURFACE LOW SHOULD RESULT IN
STRONG NORTHWEST WINDS BEGINNING MID TO LATE AFTERNOON TUESDAY AND
CONTINUING OVERNIGHT. MAY HAVE TO EVENTUALLY UPGRADE TO A BLIZZARD
WARNING BUT WILL CONTINUE WITH WINTER STORM WARNING FOR NOW.
LONG TERM...12Z WEDNESDAY THROUGH MONDAY. WEDNESDAY SHOULD BE DRY
AS THE STORM SYSTEM CONTINUES TO DEPART...HOWEVER SOME BLOWING SNOW
COULD LINGER DURING THE MORNING HOURS. THE WINDS APPEAR STRONGER IN
THE EASTERN HALF OF THE FORECAST AREA AS SURFACE HIGH PRESSURE
BUILDS INTO THE CENTRAL PLAINS...BUT FOR NOW WILL NOT GET TOO FANCY
IN THE GRIDS AND JUST LINGER BLOWING SNOW ACROSS THE ENTIRE FORECAST
AREA DURING THE MORNING. IT SHOULD THEN BE COLD AND DRY FOR THE END
OF THE WEEK WITH SNOW PACK ACROSS THE AREA HELPING KEEP TEMPERATURES
AT OR BELOW GUIDANCE. ONE CAVEAT TO THE DRY FORECAST IS THAT THE
06Z GFS DID BRING A WAVE ACROSS KANSAS FOR THURSDAY NIGHT INTO
FRIDAY WITH INCREASING ISENTROPIC LIFT (280K). THE 00Z ECMWF AND
12Z GFS ALSO SHOW THIS...BUT ARE FARTHER SOUTH IN THEIR HANDLING OF
THE UPPER LEVEL ENERGY. AGAIN...HAVE KEPT IT DRY DURING THAT
PERIOD...BUT ITS SOMETHING TO WATCH.
AN UPPER RIDGE ACROSS THE WESTERN UNITED STATES WILL THEN HELP
HEIGHTS RISE ACROSS THE CENTRAL PLAINS THIS WEEKEND. THIS SHOULD
BRING SOME MODERATION TO TEMPERATURES WITH HIGHS PERHAPS RISING TO
NEAR FREEZING IN SOME SPOTS FOR SUNDAY. ANOTHER WAVE THEN PUSHES
ACROSS ANOTHER COLD FRONT EARLY NEXT WEEK. THERE IS STILL SOME
DIFFERENCES IN THE MODELS WITH THIS...HOWEVER HPC GUIDANCE IS GIVING
SMALL SNOW CHANCES FOR MONDAY...AND SEE NO REAL REASON TO DEVIATE
FROM THAT AT THE MOMENT.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...WINTER STORM WARNING UNTIL 6 AM CST WEDNESDAY FOR NEZ039>041-
046>049-060>064-072>077-082>087.
KS...WINTER STORM WARNING UNTIL 6 AM CST WEDNESDAY FOR KSZ005>007-
017>019.
&&
$$
