FXUS63 KDMX 251741 AAB
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1142 AM CST FRI DEC 25 2009
...UPDATED AVIATION AND PUBLIC DISCUSSIONS...
.SHORT TERM.../TODAY/
HAVE TRIMMED BACK THE WARNING AREA AND REPLACED WITH A WINTER
WEATHER ADVISORY. WILL BE MAKING FURTHER ADJUSTMENTS OVER THE NEXT
FEW UPDATES...AS CONDITIONS IMPROVE. RAIN HAS BEEN CHANGING BACK TO
SNOW NORTH SECTIONS AND EXPECT LIGHT SNOW TO CONTINUE OVER MUCH OF
THE REGION THROUGH SATURDAY. WORST CONDITIONS TO REMAIN OVER THE
WEST...THOUGH EVEN WITH THAT SAID...WINDS BEGINNING TO DIE DOWN AND
THE PEAK OF THE STORM HAS PASSED./REV
.PREVIOUS SHORT TERM.../TODAY/
SFC LOW PRESSURE HAS LIFTED INTO FAR NORTHEAST MISSOURI AND WILL BE
OVER SOUTHEAST IOWA BY 12Z. INVERTED TROUGH HAS PUSHED EAST TO JUST
EAST OF INTERSTATE 35 OVERNIGHT WITH A TIGHT THERMAL GRADIENT ALONG
IT. TEMPERATURES ARE IN THE LOW TO MID 30S TO THE EAST WITH LOWER
TEENS TO LOWER 20S TO THE WEST. POLAR UPPER LOW PRESSURE IS NOW OVER
WRN NEBRASKA WITH ANOTHER YET WEAKER SRN STREAM CLOSED LOW OVER
CNTRL MISSOURI. THE SOUTHERN STREAM SYSTEM IS BEGINNING TO ROTATE
SLIGHTLY BACK TO THE NORTHWEST AS IT BECOMES ASSIMILATED BY THE
POLAR SYSTEM.
DRY SLOT ASSOCIATED WITH SOUTHERN STREAM UPPER LOW IS NOW MOVING
INTO SOUTHEAST AND IT WILL AFFECT PRECIPITATION AMOUNTS OVER THE
SOUTHEAST...POSSIBLY STRETCHING INTO CNTRL IA NEAR THE DSM METRO.
KINEMATIC FORCING AND ASSOCIATED VERTICAL MOTION FROM POLAR LOW WILL
LIFT BACK INTO THE SOUTH AND SHOULD FILL A PORTION OF THE DRY SLOT
BACK IN. FARTHER TO THE NORTHEAST IN THE WATERLOO AREA...THE
PRECIPITATION WILL LIKELY REMAIN NEARLY ALL RAIN THROUGH 18Z BEFORE
SWITCHING OVER. BY THIS TIME...PRIMARY PRECIPITATION BAND SHOULD
HAVE MOVED THROUGH AND ELIMINATING THE CHANCE FOR WARNING CRITERIA
SNOWFALL. WILL BE DOWNGRADING BLACK HAWK...TAMA AND BREMER
COUNTIES. COUNTIES JUST TO THE WEST HAVE BEEN LEFT IN THE
WARNING MAINLY DUE TO NEAR WARNING CRITERIA SNOWFALL IN THE
WESTERN PORTIONS OF THEIR COUNTIES.
TEMPERATURES TODAY WILL BE QUITE UNIQUE. THE POLAR AIR WILL SWEEP IN
TO THE SOUTHWEST HALF WHILE WARMER TEMPERATURES WRAP BACK AROUND
OVER THE NORTH.
.LONG TERM /TONIGHT THROUGH TUESDAY/...MAJOR WINTER STORMS BEGINS
TO WIND DOWN DURING THE EARLY PART OF THE HOLIDAY WEEKEND AS IT
FINALLY PUSHES EAST INTO THE GREAT LAKES BY SUNDAY. MODELS HAVE
COME INTO BETTER AGREEMENT WITH THE EVOLUTION OF THIS STRONG UPPER
LOW TONIGHT THROUGH SUNDAY. NAM STILL THE COLDER SOLUTION AS IT
PULLS THE UPPER LOW A LITTLE FURTHER NORTHEAST. GFS/ECMWF HAVE THE
UPPER LOW RETROGRADE BACK SOUTH AND WEST INTO EASTERN IOWA LATE
SATURDAY NIGHT INTO SUNDAY MORNING. THE MAJORITY OF THE CWA
REMAINS IN THE CAA REGIME THROUGH SUNDAY.
TONIGHT INTO SUNDAY...ISENTROPIC LIFT SLOWLY DIMINISHES OVERNIGHT
TONIGHT THROUGH SATURDAY...AT LEAST THE GOOD DENDRITIC SNOW IS NOT
EXPECTED WITH THE MAX OMEGA BELOW THE SNOW GROWTH ZONE. LOWERED
QPF AMOUNTS...HENCE LOWERED SNOW AMOUNTS OVERNIGHT INTO SATURDAY.
STILL MAY SEE A FEW SPOTS ACROSS THE WEST WITH AN ADDITIONAL 1-2
INCHES OVERNIGHT WITH THE DEFORMATION ZONE SETTING UP ON THE
WESTERN EDGE OF THE SURFACE LOW. THE SYSTEM BEGINS TO DRY OUT BY
LATE SATURDAY MORNING WITH BUFR SOUNDINGS LOSING THE DEEP MOISTURE
AS STRONG CAA BRINGS IN DRIER AIR ALOFT. STILL COULD SEE SOME
ADDITIONAL ACCUMULATING SNOW THROUGH MIDDAY SATURDAY...BUT
DECREASED AMOUNTS SLIGHTLY AS CONFIDENCE WAS LOW WITH GETTING
ANYTHING OVER A HALF INCH ON SATURDAY.
BY SATURDAY NIGHT...GFS WANTS TO INCREASE THE ISENTROPIC LIFT INTO
SUNDAY MORNING WHICH COINCIDES WELL WITH THE BUFR SOUNDINGS BECOMING
SATURATED ACROSS THE CENTRAL TO NORTHERN SECTIONS OF THE CWA. MAY
SEE A FEW SPOTS ACROSS THE NORTH WITH AROUND A HALF INCH OR SO BY
MIDNIGHT SATURDAY NIGHT.
HIGH PRESSURE FINALLY SETTLES INTO THE REGION BY SUNDAY NIGHT AND
DOMINATES THROUGH THE MIDDLE OF THE WORK WEEK. SURFACE HIGH
CENTERS ITSELF OVER THE STATE BY MONDAY NIGHT INTO TUESDAY. VERY
DRY AND COLD AIR MASS ASSOCIATED WITH THIS HIGH PRESSURE...SO
DROPPED CLOUD COVER...WINDS...AND TEMPERATURES TUESDAY MORNING.
TUESDAY MORNING LOWS DROPPED CONSIDERABLY FROM PREVIOUS FORECAST
ACROSS THE NORTHWEST WITH THE FRESH SNOW PACK AND RADIATIONAL
COOLING. ONE THING TO CONSIDER FOR NEXT FORECAST ISSUANCE IS THAT
THE ECMWF/GFS HAS A WEAK SYSTEM BY WEDNESDAY INTO THURSDAY.
&&
.AVIATION...
25/18Z...HAVE UPDATED THE PACKAGE TO REFLECT THE CURRENT TRENDS.
COMPLEX LOW TO SPIN OVER THE REGION THROUGH SATURDAY. THUS...CIGS
AND VSBYS AND PTYPE WILL BE QUITE VARIABLE AT TIMES...WITH THE
LOWEST CIGS BENEATH THE H500 LOW. CONSEQUENTLY...LOTS OF CATEGORY
CHANGES FOR THE NEXT 24 HOURS...WITH IFR TO MVFR TO PREDOMINATE.
SOME LIGHT RA AND FZRA AND PL WILL OCCUR YET TODAY...MIXING TO SNOW.
BY TONIGHT...ALL SNOW SHOULD OCCUR./REV
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 6 AM CST SATURDAY FOR
ADAIR-ADAMS-AUDUBON-BOONE-CALHOUN-CARROLL-CASS-CLARKE-
CRAWFORD-DALLAS-DECATUR-EMMET-GREENE-GUTHRIE-HAMILTON
-HANCOCK-HUMBOLDT-KOSSUTH-MADISON-PALO ALTO-POCAHONTAS-
POLK-RINGGOLD-SAC-STORY-TAYLOR-UNION-WARREN-WEBSTER-
WINNEBAGO-WORTH-WRIGHT.
WINTER WEATHER ADVISORY UNTIL 6 AM CST SATURDAY FOR APPANOOSE-BLACK
HAWK-BREMER-BUTLER-CERRO GORDO-DAVIS-FRANKLIN-HARDIN-GRUNDY-JASPER-
LUCAS-MAHASKA-MARION-MARSHALL-MONROE-POWESHIEK-TAMA-WAPELLO-WAYNE
-WORTH.
&&
$$
SHORT TERM...DONAVON/REV
LONG TERM...PODRAZIK
AVIATION...REV
