FXUS63 KGID 042303
AFDGID

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HASTINGS NE
503 PM CST FRI DEC 4 2009

.AVIATION...00Z KGRI TAF. VFR CONDITIONS TO CONTINUE AT THE KGRI TERMINAL
THROUGH 00Z SUNDAY. HIGH LEVEL SCATTERED CLOUDS WILL BE POSSIBLE
SATURDAY WITH VISIBILITIES REMAINING UNRESTRICTED. A FRONTAL
BOUNDARY...CURRENTLY OVER WESTERN NEBRASKA THIS EVENING...WILL PUSH
EASTWARD DURING THE FORECAST PERIOD...THUS ALLOWING SURFACE WINDS
AT KGRI TO TRANSITION FROM THE SOUTH / SOUTHWEST TO MORE OF A
NORTH / NORTHWESTERLY DIRECTION BY LATE MORNING OR EARLY AFTERNOON
SATURDAY.

&&

.PREV DISCUSSION... /ISSUED 328 PM CST FRI DEC 4 2009/ 

SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT.  THE SHORT TERM 
PERIODS WILL EXPERIENCE JUST A SLIGHT MODERATION IN TEMPERATURES 
BEFORE AN ANOTHER ARCTIC SURGE ARRIVES SATURDAY NIGHT.  THE PATTERN 
CONTINUED TO REFLECT A LONGWAVE TROUGH FROM MANITOBA/ONTARIO SOUTH 
THRU TEXAS.  THE BRUNT OF THE ARCTIC AIR OR AT LEAST THE AIRMASS 
WHICH WAS IN PLACE ACROSS OUR REGION THE LAST COUPLE OF DAYS HAD 
SHIFTED JUST EASTWARD WITH SOME RISING HEIGHTS/THICKNESSES ACROSS 
OUR REGION.  THIS SLIGHT MODIFICATION IN THE AIRMASS HAS ALLOWED 
TEMPS TO MAKE A RUN TOWARD READINGS AROUND THE FREEZING MARK 
TODAY.  MAINLY CLEAR SKIES TONIGHT AND GOOD RADIATIONAL CONDITIONS 
WILL ALLOW TEMPS TO PLUMMET AFTER DARK AND LOWS ARE EXPECTED TO BE 
IN THE 10 TO 15 DEGREE RANGE.  

THE PSEUDO MILDER WEATHER WILL LINGER INTO THE FIRST PART OF 
SATURDAY THEN ANOTHER SHOT OF COLD AIR POISED WITH A COUPLE OF POLAR 
VORTICES ACROSS THE NORTHERN PLAINS WILL BEGIN TO ADVECT SOUTH 
FOLLOWING A COLD FRONTAL PASSAGE SATURDAY AFTERNOON AND NIGHT.  
AFTER AN H85 TEMP CLIMB TO AROUND -3C EARLY SATURDAY...READINGS 
RAPIDLY DROP TO AROUND -10C BY 12Z SUNDAY.  THE QUICKER PASSAGE OF 
THE FRONT ON SATURDAY HAS LED TO A DROP IN MAX TEMPS SATURDAY 
AFTERNOON BY A FEW DEGREES.  THE SURGE OF COLD AIR SATURDAY NIGHT 
COMBINED WITH INCREASING FRONTOGENETIC FORCING WITH LIFT/MOISTURE IN 
THE DENDRITIC LAYER MAY LEAD TO SOME FLURRIES IN OUR NORTHERN ZONES.

LONG TERM...12Z SUNDAY THROUGH FRIDAY. BIGGEST FORECAST CHALLENGE 
WILL BE SNOW AMOUNTS FOR LATE MONDAY NIGHT THROUGH TUESDAY NIGHT.

TWO WAVES WITHIN PROGRESSIVE FLOW ARE THE MAIN CONCERN FOR THE 
EXTENDED FORECAST. THE FIRST WAVE ON SUNDAY AND SUNDAY NIGHT 
CONTINUES TO BE FORECAST BY MODELS AS RELATIVELY MINOR AND 
SHALLOW...PERHAPS PRODUCING ADVISORY TYPE SNOW AMOUNTS. THE SECOND 
WAVE FROM MONDAY NIGHT THROUGH TUESDAY NIGHT WILL BE STRONGER AND 
POSES POTENTIALLY MORE OF A PROBLEM. 

THE FIRST WAVE IS CONSISTENTLY FORECAST FOR SUNDAY/SUNDAY NIGHT. 
MODELS ARE TRENDING HIGHER WITH QPF...ESPECIALLY THE CANADIAN. THE 
SYNOPTIC SCALE LIFT LOOKS FAIRLY GOOD WITH THIS WAVE AS 
WELL...HOWEVER IT CONTINUES TO LOOK QUITE PROGRESSIVE...SO IT SHOULD 
NOT STICK AROUND LONG ENOUGH TO BE TOO MUCH OF AN ISSUE. I HAVE 
LOWERED TEMPERATURES FOR HIGHS AS CLOUDS AND COLD AIR ADVECTION WILL 
KEEP US FROM WARMING MUCH AT ALL DURING THE DAY. SNOW RATIOS WILL BE 
HIGHER DUE TO COLDER AIR...SO I BUMPED UP SNOW ACCUMULATIONS TO ONE 
TO THREE INCHES FROM THE PREVIOUS ONE INCH.

MODELS ARE CONSISTENT WITH TIMING WITH THE NEXT WAVE MOVING IN 
MONDAY NIGHT...BUT TRENDING TOWARD A CLOSED 700 MB LOW AND HIGHER 
QPF AMOUNTS. THERE ARE DIFFERENCES AMONG MODELS WITH THE TRACK OF 
THIS LOW...BUT GENERAL CONSENSUS IS THAT WE STAND A FAIR CHANCE AT 
GETTING SEVERAL INCHES OF SNOW HERE. THE ECMWF IS TRENDING FARTHER 
SOUTH WITH THE HEAVIER SNOW BAND...BUT THE GFS DIVE BOMBS OUR CWA 
WITH HIGHER QPF AND IS THE WORST CASE SCENARIO...SIMILAR TO THE 
ECMWF FROM YESTERDAY. IF THE GFS PANS OUT...WE COULD GET OVER A FOOT 
OF SNOW IN OUR CWA ON TUESDAY. THIS IS AN EXTREME OUTLIER RIGHT NOW 
AND HAVE SETTLED ON 5 TO 7 INCHES AS MY BEST GUESS FOR MONDAY NIGHT 
THROUGH TUESDAY NIGHT FOR NOW. LOOKS LIKE THERE COULD BE QUITE A 
GOOD MID-LEVEL FRONTOGENETIC BAND HERE...BUT STILL DIFFICULT TO TELL 
EXACTLY WHERE IT WILL SET UP. MY GUESS WOULD BE TOWARD THE SOUTHERN 
CWA CONSIDERING GENERAL TRENDS. THE SYNOPTIC SCALE LIFT PRETTY GOOD 
WITH THIS WAVE AS WELL. THE POTENTIAL SURFACE PRESSURE GRADIENT 
LOOKS MUCH STRONGER NOW AS THE ASSOCIATED SURFACE LOW MOVES THROUGH 
KANSAS...WITH NORTH WIND OF 20 TO 30 MPH...WITH GUSTS OF 30 TO 40 
MPH LOOK REASONABLE. NOT THE GREATEST COMBINATION WITH SEVERAL 
INCHES OF SNOW. 

I GENERALLY LOWERED TEMPERATURES AND WENT BELOW GUIDANCE 
VALUES...AND SOMETIME WELL BELOW GUIDANCE VALUES DUE TO ANTICIPATED 
SNOW COVER AND COLD AIR ADVECTION...ESPECIALLY FOR WEDNESDAY HIGHS. 

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&

$$