FXUS63 KDMX 050539 AAB
AFDDMX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
1140 PM CST FRI DEC 4 2009
...UPDATED AVIATION DISCUSSION...
.SHORT TERM /TONIGHT/...
STRATOCUMULUS CLOUDS HAVE BEEN GENERATED ACROSS OUR ENTIRE AREA
DURING PEAK HEATING HOURS THIS AFTERNOON...WITH SCATTERED FLURRIES
OCCASIONALLY REDUCING VISIBILITY TO BELOW 2 MILES BUT NO
ACCUMULATION REPORTED. EXPECT THE STRATOCU TO STEADILY BREAK UP
AROUND/AFTER SUNSET AND MOVE OFF TO THE EAST AND NORTHEAST IN THE
FLOW. MEANWHILE SOME HIGH CIRRUS IS SEEN ON VISIBLE SATELLITE MOVING
ACROSS NORTHERN AND NORTHEASTERN IOWA FROM MINNESOTA...AND MODEL
MOISTURE FIELDS INDICATE THAT THIS CIRRUS MAY PERSIST ACROSS OUR
NORTHEASTERN AREAS WELL INTO TONIGHT. WILL INCLUDE A PRE FIRST
PERIOD IN THE AFTERNOON FORECAST PACKAGE TO ACCOUNT FOR CLOUD/FLURRY
TRENDS LATE THIS AFTERNOON AND EVENING.
MEANWHILE...SURFACE HIGH PRESSURE WILL BE SQUEEZED TO THE SOUTHEAST
INTO THE OHIO RIVER VALLEY TONIGHT AS ANOTHER BROAD TROUGH OF LOW
PRESSURE TAKES SHAPE ALONG THE LEE OF THE ROCKIES. AS A RESULT OUR
WINDS WILL LIGHTEN AFTER SUNSET AND TURN TO SOUTHWEST THEN SOUTH
OVERNIGHT WITH A MODEST WARM AIR ADVECTION REGIME KICKING IN.
THIS...ALONG WITH POTENTIAL HIGH CLOUD COVER...COMPLICATES THE LOW
TEMPERATURE FORECAST FOR TONIGHT. IN THE NORTHEAST WHERE IT APPEARS
CLOUD COVER IS MOST LIKELY TO LINGER HAVE STUCK CLOSE TO MOS ON MIN
TEMPS...HOWEVER IN THE WEST AND SOUTHWEST HAVE LOWERED MIN TEMPS AS
IT SEEMS LIKELY THAT ATMOSPHERIC DECOUPLING WILL NEGATE ANY MODEST
WAA ALOFT AND MOSTLY CLEAR SKIES WILL ALLOW TEMPERATURES TO BOTTOM
OUT AGAIN AS THEY DID LAST NIGHT.
.LONG TERM /SATURDAY THROUGH FRIDAY/...
AN INTERESTING SCENARIO IS BEGINNING TO PLAY OUT IN THE NEXT SEVEN
DAYS AS A POTENTIAL SIGNIFICANT WINTER STORM MOVES THROUGH THE CWA
TUESDAY INTO WEDNESDAY. MODELS ARE CONVERGING ON A SOLUTION FOR THE
UPPER TROF DIGGING INTO THE PAC NW THIS EVENING. AN INITIAL VORT
LOBE WILL SPIN OFF THAT SYSTEM THROUGH THE UPPER MIDWEST SUNDAY INTO
MONDAY. SNOW CHANCES WILL INCREASE DURING THAT TIME WITH LITTLE
ACCUMULATION...BUT A MORE ROBUST WEATHER SYSTEM WILL DEVELOP OVER
THE FRONT RANGE BY TUESDAY. A 985MB LOW WILL PASS THROUGH CENTRAL
MISSOURI TUESDAY NIGHT AND WILL END UP OVER NORTHERN INDIANA ON
WEDNESDAY AND CONTINUE TO DEEPEN. A TIGHT PRESSURE GRADIENT WILL
DEVELOP OVER CENTRAL IOWA TUESDAY AND LAST INTO WEDNESDAY AFTERNOON.
BASED ON THE LOW TRACK...THE HEAVIEST SNOWFALL WITH THIS SYSTEM
SHOULD BE OVER SOUTHERN IOWA. THE 12Z GFS AND 00Z GEM DEVELOP A
CLOSED 500MB CIRCULATION OVER MISSOURI TUESDAY NIGHT WHILE THE 12Z
ECMWF MAINTAINS THE SYSTEM AS A SHORTWAVE TROUGH.
THE SYSTEM MOVING THROUGH ON MONDAY IS HANDLED FAIRLY CONSISTENTLY
WITH THE MODELS AS MOST OF THE PRECIP SHOULD REMAIN OVER THE
SOUTHERN PART OF THE CWA. THUS...REDUCED POPS ALONG NORTHERN BORDER.
GFS PULLS THE PRECIP OUT OF THE AREA BY 12Z MONDAY WHILE HIGH
PRESSURE CLEARS THINGS OUT A BIT MONDAY NIGHT BEFORE THE WEATHER
SYSTEM ENTERS THE AREA TUESDAY AFTERNOON. ANOTHER WAVE IS EXPECTED
TO MOVE OFF THE FRONT RANGE LATE IN THE WEEK AND SHOULD FOLLOW THE
SAME TRACK AS THE TUESDAY/WEDNESDAY STORM...BUT DOES NOT LOOK AS
INTENSE AT THIS POINT.
&&
.AVIATION...
05/06Z...RAPID CLEARING GOING ON ACROSS CENTRAL IOWA THIS EVENING.
KALO STILL HANGING ON TO SOME CLOUD COVER THOUGH THEY TOO WENT VFR
OVER THE PAST HOUR. CLR SKY AND SRLY WIND 5-10 KT THROUGH 12Z. THE
SRLY FLOW WILL BRING IN SOME MID MOISTURE ON SATURDAY AFT 15Z AND A
MID DECK OF CLOUDS SHOULD PRODUCE SOME VFR CIGS AFT 18Z. THE MID
DECK WILL REMAIN IN THE FORECAST THROUGH 06/06Z AS LOW PRESSURE OVER
THE PLAINS NEARS THE STATE.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
SHORT TERM/AVIATION...FAB
LONG TERM...HINSBERGER
