FXUS63 KEAX 040547
AFDEAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
1147 PM CST THU DEC 3 2009
...UPDATED AVIATION DISCUSSION...
.DISCUSSION...
ONLY MINOR CONCERNS IN THE SHORT TERM AS MUCH OF THE FCST FOCUS
REMAINS IN THE MEDIUM RANGE...WITH VERY FEW CHANGES MADE TO THE
ONGOING FCST. THIS AFTN...WV IMAGERY DEPICTS LARGE SCALE UPR
TROUGHING ACROSS THE CENTRAL CONUS...WITH CORE OF 500 MB HEIGHTS
CENTERED IN NORTHERN IA. ALMOST DUE MERIDIONAL FLOW CONTINUES ACROSS
THE HEART OF COUNTRY PULLING ADDITIONAL COLD AIR INTO THE REGION
FROM THE CANADIAN PROVINCES. THE END RESULT IS WIDESPREAD
DEVELOPMENT OF STRATO-CU ACROSS THE MIDWEST WITH TEMPS STRUGGLING TO
REACH 30 DEGREES IN MOST LOCATIONS. IN ADDITION...NUMEROUS REPORTS
OF WAFTING FLURRIES WERE COMMON IN THIS STRATO-CU FIELD.
FOR TONIGHT...UPSTREAM AIR MASS TRAJECTORIES SUGGEST COLDEST CORE OF
LOW- LVL AIR ALONG WITH LOWEST DEW POINTS WILL ADVECT INTO THE AREA.
CURRENTLY PORTIONS OF WESTERN NE/SD ARE ONLY SITTING IN THE UPR TEENS
TO LOWER 20S. SOME QUESTIONS EXIST AS TO HOW FAST STRATO-CU WILL
DISSIPATE AFTER SUNSET. HOWEVER GIVEN THE LOWER DEW POINTS IN THE
SINGLE DIGITS AND LOWER TEENS ALONG WITH THE POTENTIAL FOR CLEARING
SKIES...EXPECTING LOW TEMPS TO FALL INTO THE LOWER TO MIDDLE TEENS IN
MOST LOCATIONS. GUIDANCE SUGGESTS ADDITIONAL CLOUD REDEVELOPMENT WILL
REMAIN OVER NE/IA AS WELL AS NORTHERN MO...WITH THIS CLOUD COVER ALSO
HOLDING THE POTENTIAL FOR ADDITIONAL FLURRY ACTIVITY.
EXPECTING LITTLE CHANGE FOR FRIDAY...AS LOW LVL TEMPS CHANGE VERY
LITTLE IN THE NEXT 24 HOURS. GIVEN A COLD START...HIGH TEMPS MAY ONCE
AGAIN STRUGGLE TO REACH 30 IN SOME LOCATIONS. IN ADDITION...WOULDN'T
BE SURPRISED TO SEE FLURRIES ONCE AGAIN REPORTED IN NORTHERN MO.
STILL EXPECTING A BRIEF WARMUP...IN RESPECT TO CURRENT
CONDITIONS...FOR SATURDAY. LOW-LVL TRAJECTORIES SUGGEST AN INCREASING
AMOUNT OF WARM AIR ADVECTION ALOFT...WITH A RATHER STIFF SSW BOUNDARY
LAYER WIND. SOUNDINGS CONTINUE TO SUPPORT LOWER 40S FOR HIGHS...AND
WILL CONTINUE TO ADVERTISE TEMPS AT THE HIGHER SPECTRUM OF ENSEMBLE
MODELS.
DUX
MEDIUM RANGE (SUN-WED)...
MAIN CONCERN FOR THE MEDIUM RANGE DEALS WITH A MORE ACTIVE WEATHER
PATTERN WITH THE POTENTIAL OF A WINTER STORM FOR TUESDAY INTO
WEDNESDAY.
SUNDAY - MONDAY:
A FAST MOVING PV ANOMALY WILL MOVE THROUGH THE AREA SUNDAY
AFTERNOON/EVENING. WITH FAVORABLE JET DYNAMICS IN THE FORM OF A
NEARLY COUPLED JET STRUCTURE...A DECENT LOOKING MID/UPPER LEVEL
FRONTOGENESIS BAND SETS UP ACROSS NORTHERN/NORTHWEST MISSOURI. THIS
BAND SHOULD FORM IN AN AREA OF FAVORABLE SNOW GROWTH. THAT IS WHAT
LOOKS FAVORABLE WITH THIS SYSTEM. ON THE NEGATIVE SIDE...FORECAST
SOUNDINGS SHOW A FAIRLY DEEP DRY LAYER OF NEARLY 200MB. THIS DRY
LAYER MAY BE DEEP ENOUGH THAT SNOW CRYSTALS MAY NOT BE ABLE TO
SATURATE AND/OR FALL INTO THE NEXT SATURATED LAYER. IN SHORT...IT IS
PUSHING THE LIMITS OF SEEDER/FEEDER THRESHOLDS. IN THE LOW LEVELS
THERE IS ANOTHER LAYER OF DRY AIR FOR POSSIBLE PRECIPITATION TO TRY
AND OVERCOME. SURFACE TEMPERATURES SHOULD BE IN THE MID TO UPPER
20S...ESPECIALLY ACROSS OUR NORTHERN ZONES. THIS WOULD IMPLY THAT
ANYTHING THAT HITS THE GROUND WOULD BE IN THE FORM OF SNOW.
HOWEVER...WITH THE LOWER LEVEL SATURATED AREA NOT LIKELY TO BE ABLE
TO PRODUCE ICE CRYSTALS IT WILL DEPEND ON THE ABILITY OF THE
SEEDER/FEEDER MECHANISM TO INTRODUCE ICE CRYSTALS FROM ALOFT. THUS
PRECIPITATION WOULD BE EITHER IN THE FORM OF SNOW OR SNOW/FREEZING
DRIZZLE. DUE TO SIGNIFICANT UNCERTAINTY WILL JUST CARRY LOW END
CHANCE CATEGORY POPS AND MENTION ONLY SNOW AT THIS POINT.
ACCUMULATIONS SHOULD BE LIGHT GIVEN THE RAPID MOTION OF THE
SHORTWAVE AND THE SIGNIFICANT NEGATIVE FACTORS WITH THIS SYSTEM.
TUESDAY - WEDNESDAY:
A MUCH MORE SIGNIFICANT SYSTEM IS FORECAST TO IMPACT THE CENTRAL
PORTIONS OF THE CONUS FOR THIS PERIOD. THERE ARE MAJOR DIFFERENCES
IN THE VARIOUS MODEL SOLUTIONS REGARDING THIS EVENT WITH THE ECMWF
MUCH FURTHER NORTH THAN THE GFS. THIS NORTHWARD SHIFT ALSO LIFTS THE
THERMAL PROFILE TO THE NORTH BRINGING A POSSIBLE RAIN SNOW MIX INTO
THE METRO AREA BEFORE CHANGING OVER TO ALL SNOW AS COLD AIR SETTLES
INTO THE REGION. BY CONTRAST THE GFS IS FURTHER SOUTH AND INDICATES
THAT MOST OF THE FORECAST AREA WOULD BE ALL SNOW FOR THE DURATION OF
THE EVENT. THERE ARE REASONS TO NOT LIKE EITHER MODEL BUT PREFERENCE
FOR THIS PACKAGE IS SKEWED TO THE GFS AS IT HAS HAD BETTER
CONSISTENCY OVER THE LAST FEW RUNS. WITH THAT SAID...THE GFS DEPICTS
A SOMEWHAT NON-TYPICAL WINTER WEATHER EVENT. THE PV ANOMALY THAT
WILL DRIVE THIS STORM DOES NOT LOOK PARTICULARLY INTENSE AND APPEARS
SOMEWHAT BROAD OVER THE CENTRAL PORTIONS OF THE CONUS. COUPLED
FORCING IS MODEST WITH THE STRONGEST QG FORCING TO OUR SOUTH.
HOWEVER THERE DOES APPEAR TO BE SOME JET COUPLING WHICH WILL ENHANCE
THE DYNAMICS. WITH THE PRIMARY MECHANISM FOR THIS EVENT BEING
PROLONGED LIFT THERE REALLY IS NO INDICATION OF A TROWAL AND
INSTABILITY LOOKS LIMITED FROM PLOTS OF -EPV. FORECAST SOUNDINGS DO
SHOW STEEP UPPER LEVEL LAPSE RATES SO THERE WILL LIKELY BE SOME
INSTABILITY FOR THE SYSTEM TO WORK WITH. WHAT LOOKS TO REALLY DRIVE
UP POTENTIAL SNOW AMOUNTS IS VERY FAVORABLE SNOW GROWTH OVER A 12 TO
18 HOUR TIME FRAME FROM TUESDAY TO TUESDAY NIGHT. WHILE FINE DETAILS
ARE UNRESOLVED AT THIS POINT IN TIME THERE IS INCREASING CONFIDENCE
IN A POTENTIAL WINTER STORM EVENT FOR NORTHWEST MISSOURI AND EASTERN
KANSAS.
CDB
&&
.AVIATION...
EXTENSIVE BAND OF VFR STRATO-CU ABOUT TO EXIT EAST OF THE TERMINALS
OVER THE NEXT HOUR...LEAVING CLEAR SKIES OVERNIGHT. SOUNDINGS SHOW
THAT MIXING SHOULD YIELD AN ABUDANCE OF STRATO-CU BY LATE MORNING.
SKIES SHOULD CLEAR QUICKLY WITH THE LOSS OF DAYTIME HEATING...IN A
RELATIVE SENSE.
NORTHWEST WINDS WILL GRADUALLY SHIFT TOWARD THE WEST AND SOUTHWEST
WITH SPEEDS GENERALLY AT OR BELOW 10 KNOTS.
BOOKBINDER
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.
&&
$$
