FXUS63 KDMX 120539 AAA
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1138 PM CST FRI DEC 11 2009

...UPDATED AVIATION DISCUSSION...

.NEAR TERM /TONIGHT/...
LITTLE SENSIBLE WX INTO TOMORROW OUTSIDE OF CONTINUED FAIR AND COLD 
WEATHER.  MINOR SHORT WAVES ARE TRAVERSING NW FLOW BUT ARE MOISTURE 
STARVED WITH LITTLE CLOUD COVER.  BROAD BUT WEAK WARM ADVECTION 
CONTINUES AND WILL PUSH LOWS A CATEGORY TO TWO ABOVE LAST 
NIGHT...BUT STILL TOWARD THE COOL END OF GUIDANCE.

.SHORT TERM /SAT THROUGH MON/...
SHIFT IN THE WEATHER WILL TAKE PLACE THIS WEEKEND AND INTO EARLY 
NEXT WEEK WITH A PARADE OF PACIFIC SHORT WAVES AFFECTING IA.  
SEVERAL WEAK WAVES ARE NOW COMING ONSHORE INTO CA AND WILL QUICKLY 
CROSS THE ROCKIES INTO THE MO VALLEY BY MIDDAY SAT.  THIS WILL 
CONTINUE TO INCREASE MOISTURE...ESPECIALLY IN LOW LEVELS...WITH 
PERIOD OF RETURN FLOW.  THIS SHOWS UP QUITE WELL IN 285-295K ISENT 
DIAGS WITH BEST POTENTIAL EITHER SIDE OF 00Z SUN AS IT BRUSHES SE 
SECTIONS.  OTHERWISE...MOISTURE IS SHALLOW /0.5-1.5KM/ AND MORE 
CONDUCIVE TO FREEZING DRIZZLE OR LIGHT FREEZING RAIN WITH LITTLE RH 
COOLER THAN -8C.  THUS HAVE RAISED POPS SOMEWHAT TO OCCUR FOR 
GREATER MEASURABLE THREAT...AND ALSO SWITCHED TO LIGHT FREEZING RAIN 
FROM FREEZING DRIZZLE DUE TO SATURATION UP TO 1.5KM AT TIMES.  

SHOULD SEE A BREAK BETWEEN SYSTEMS SUN FOLLOWED BY ANOTHER STRONGER 
SHORT WAVE...CURRENTLY WELL OUT IN THE PACIFIC APPROACHING 40N 
140W...WHICH SHOULD ARRIVE TO MO VALLEY EARLY MON.  MODELS HAVE 
INTENSIFIED WITH THIS SYSTEM SINCE YESTERDAY.  ALTHOUGH BETTER 
CHANCES ARE TO OUR NORTH...HAVE STILL RAISED POPS THROUGH THE CHANCE 
CATEGORY WITH 280-290K ISENT LAYER SHOWING GOOD MOISTURE AND UVM 
SIGNALS FOR MEASURABLE PRECIP NE.  MUCH LIKE EARLIER SYSTEM...COLUMN 
SATURATION FOLLOWED BY MORE SHALLOW MOISTURE NO DEEPER THAN -8C SO 
HAVE BLENDED WITH MORE FREEZING DRIZZLE WORDING AS WELL.

WITH CYCLES OF WARM AND COOL ADVECTION...SEVERAL PERIODS WILL END UP 
WITH NON-DIURNAL TRENDS.  WARMING AT NIGHT AND/OR DAYTIME COOLING.  
FOG AND STRATUS WILL HAVE AN INFLUENCE TOO SO HAVE OPTED TO SHRINK 
THE DIURNAL RANGE LEANING TOWARD THE WARM END OF MINS AND COOL END 
OF HIGHS.  CONFIDENCE IN DETAILS NOT THE BEST HOWEVER DUE TO 
INFLUENCE OF DEEP SNOW PACK.

.LONG TERM /MON NIGHT THROUGH FRI/...
MOST SIGNIFICANT ISSUE IN THIS PERIOD WILL BE TEMPS.  ANOTHER ROUND 
OF ARCTIC AIR SPILLS INTO THE PLAINS BEHIND THE MON SYSTEM WITH 
STRONG HIGH PRESSURE INTO IA/MO BY 12Z WED.  HAVE GONE AT OR BELOW 
THE COOLEST ENSEMBLE MOS TUE INTO WED.  MODERATION THEN QUICKLY 
RETURNS AS AMPLITUDE LESSENS.  MODELS HAVE CONTINUED TO SUGGEST SOME 
WEAK NW FLOW WAVE AROUND THU OR FRI BUT ARE FLIP-FLOPPING ON 
TIMING.  ALTHOUGH 12Z GFS/ECMWF NO LEAN TOWARD FRI...THAN CONSENSUS 
DID NOT ARRIVE EARLIER ENOUGH IN THE PROCESS TO BE INCORPORATED SO 
THU SLIGHTS CONTINUE TO RIDE FOR NOW.

&&

.AVIATION...
12/06Z...VFR CONDITIONS WILL CONTINUE TO PERSIST THROUGH MID 
AFTERNOON. MOISTURE WILL LIFT NORTH DURING THE DAY ON SATURDAY AND 
EXPECT WIDESPREAD STRATUS TO DEVELOP. THE LOW LEVEL SATURATION AND 
STRATUS DEVELOPMENT IS EXPECTED TO OCCUR AROUND 21Z SATURDAY OR 
AFTER. EXPECT IFR TO LIFR CIGS TO DEVELOP MOST LOCATIONS AFTER THIS 
TIME. AREAS OF FREEZING DRIZZLE ARE ALSO POSSIBLE MOST LOCATIONS 
AFTER 00Z THOUGH KOTM MAY WARM SLIGHTLY ABOVE FREEZING...CHANGING 
THE PRECIPITATION TO DRIZZLE.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM/LONG TERM...KLP/BSS
AVIATION...DONAVON