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000
FXUS63 KDMX 100251 AAB
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
851 PM CST TUE FEB 9 2010

.PUBLIC DISCUSSION UPDATED.

.SHORT TERM /TONIGHT/...
PATCHY CLOUDS REMAIN BUT CLEARING ON THE WAY FOR MOST OF THE AREA BY
12Z. THUS...TEMPS WILL CRASH OVER THE NORTHWEST AND HAVE LOWERED
READINGS TO NEAR 10 BELOW IN THE FAR NORTHWEST...NEARER THE RIDGE
AXIS BY MORNING.  EAST AND SOUTHEAST WILL NOSEDIVE BY SUNRISE AS
WELL...BUT REMAIN ABOVE FREEZING. CENTRAL IOWA WILL BE AROUND 5
ABOVE. WINDS BEGINNING TO RELAX WEST ALREADY AND ONLY PATCHY BLOWING
SNOW REMAINS EAST. FORECAST FOR WED LOOKS ON TRACK...NO CHANGES
NEEDED THERE. /REV

.PREVIOUS SHORT TERM /TONIGHT/...
LOW PRESSURE AREA PULLING AWAY TO THE EAST LATE THIS AFTERNOON.
LIGHT SNOWFALL HAS GREATLY DIMINISHED...BUT OCNL LIGHT SNOW OR
FLURRIES WILL BE POSSIBLE INTO THE EARLY EVENING HOURS...ESPECIALLY
EAST OF INTERSTATE 35. LITTLE IF ANY ADDITIONAL ACCUMULATION IS
EXPECTED. PRESSURE GRADIENT HAS INCREASED AS EXPECTED AND MAX MIXED
LAYER WINDS APPEAR TO BE 30 TO 32 KTS. THIS HAS TRANSLATED INTO A
GENERAL SUSTAINED WIND FIELD OF 20 TO 25 MPH WITH GUSTS AROUND 30
MPH. SOUNDINGS INDICATE THE DEEPER MIXING GOES AWAY EARLY THIS
EVENING...SO EXPECT THE GUSTINESS TO COME DOWN BY 9 PM...AND WINDS
IN GENERAL TO SLOWLY SUBSIDE OVERNIGHT. WINDS WILL PROBABLY GO
NEARLY CALM IN THE WEST LATE TONIGHT AS ARCTIC HIGH PRESSURE RIDGE
BUILDS ACROSS THAT PART OF THE REGION. MANY REPORTS FROM THE
OUTLYING AREAS CORROBORATE CURRENT AUTOMATED VSBY MEASUREMENTS. SNOW
NOT BEING LOFTED ALL THAT MUCH AND HORIZONTAL VSBY IS LARGELY
GREATER THAN 1-2 MILES. LOW DRIFTING A BIGGER ISSUE. WITH FALLING
SNOW MOVING OUT OF THE PICTURE...AND WINDS NOT EXPECTED TO GET MUCH
STRONGER THAN THEY CURRENTLY ARE...DO NOT EXPECT WIDESPREAD 1/4 MILE
OR LESS VSBY RESTRICTIONS. SO WILL CANCEL THE WINTER WEATHER
ADVISORY AND WINTER STORM WARNING. THAT BEING SAID...ISOLATED AREAS
OF VERY LOW VSBY IN OPEN AREAS...AND CONSIDERABLE DRIFTING WILL
CONTINUE. SO TRAVEL WILL STILL BE IMPACTED IN SOME AREAS. TEMPS
TONIGHT BECOME COLDEST...SEVERAL DEGREES BELOW ZERO ACROSS THE
NORTHWEST WHERE CLEAR AND LIGHT WIND CONDITIONS WILL MOVE IN
SOONEST. OVERALL...WENT BELOW GUIDANCE EVERYWHERE.

.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
A RELATIVELY COLD AND ACTIVE PATTERN WILL PERSIST THROUGH MOST IF
NOT ALL OF THE NEXT SEVEN DAYS...WITH NORTHWESTERLY FLOW ALOFT
BRINGING A SERIES OF CLIPPER SYSTEMS NEAR OR ACROSS OUR AREA.

WEDNESDAY AND WEDNESDAY NIGHT WILL BE QUIET WITH A RIDGE OF HIGH
PRESSURE MOVING IN FROM WESTERN IOWA AND SETTLING ACROSS OUR EASTERN
COUNTIES BY WEDNESDAY NIGHT. THIS MAKES FOR A PROBLEMATIC
TEMPERATURE FORECAST AS WINDS WILL BE VERY LIGHT TO CALM ON TOP OF
FRESH DEEP SNOW COVER...BUT AT THE SAME TIME A MODICUM OF MID/UPPER
CLOUDS MAY MOVE IN MITIGATING RADIATIONAL COOLING SOMEWHAT. HAVE
ESSENTIALLY HELD WEDNESDAY NIGHT MIN TEMPS AT THE LEVEL OF THE
PREVIOUS FORECAST PACKAGE...WHICH IS WELL BELOW GUIDANCE ESPECIALLY
ACROSS OUR NORTHERN AND EASTERN ZONES.

MEANWHILE A MID/UPPER LOW OVER FAR NORTHERN MANITOBA WILL DRIFT
SLOWLY SOUTHWARD OVER THE NEXT SEVERAL DAYS...EJECTING A SERIES OF
SHORTWAVES THAT WILL BRING INTERMITTENT PRECIP CHANCES AND WIND
SHIFTS ACROSS THE REGION. MODELS ARE STILL HAVING DIFFICULTY
RESOLVING THE TIMING AND TRACK OF THESE WAVES AND OF THE LARGER
PARENT LOW...HOWEVER A GENERAL SCENARIO IS BEGINNING TO COME INTO
FOCUS. IT APPEARS THAT A LEADING SUBTLE SHORTWAVE WILL TRAVERSE THE
AREA LATE THURSDAY...BUT MOISTURE IS LIMITED AND SOME OF THE
FORECAST SOUNDINGS SHOW GOOD SATURATION ONLY UP TO ABOUT 5000
FT/-10C. HAVE INCLUDED SLIGHT POPS FOR THURS AFTERNOON THOUGH THURS
NIGHT WITH PATCHY FZDZ THROWN IN DURING THE AFTERNOON AND EVENING.
IN ANY EVENT THE POPS AND QPFS ARE LOW FOR THIS INITIAL WAVE.

BY FRIDAY THE LARGE MID/UPPER LOW WILL HAVE SUNK INTO WESTERN OR
SOUTHWESTERN MANITOBA AND A SOMEWHAT STRONGER SHORTWAVE AHEAD OF IT
WILL CROSS OUR AREA...BUT EVEN THIS WAVE WILL NOT BE CLOSED AND WILL
LIKELY RESULT IN A HIGH POP/LOW QPF SCENARIO WITH ALL SNOW EXPECTED
AS SATURATION SHOULD BE DEEPER THAN WITH THE FIRST WAVE LATE
THURSDAY. HAVE INCREASED TO CHANCE POPS FOR NOW ON FRIDAY.

THE MOST SIGNIFICANT PRECIP CHANCES DURING THE FORECAST PERIOD WILL
COME AS THE PARENT LOW FINALLY NEARS OR CROSSES OUR AREA THIS
WEEKEND...HOWEVER THE LONG RANGE MODELS ARE STILL HAVING A LOT OF
DIFFICULTY WITH THE TIMING AND TRACK OF THE LOW. PREVIOUSLY THE GFS
HAD BEEN THE FASTEST TO BRING IT THROUGH...HOWEVER THE 12Z ECMWF HAS
ROCKETED AHEAD OF IT AND NOW HAS THE LOW OVER EASTERN SDAK BY 12Z
SATURDAY WHEREAS THE GFS AND GEM KEEP IT BACK AROUND GRAND FORKS.
THEN DESPITE GOOD AGREEMENT IN TIMING OF ITS PASSAGE THE GFS AND GEM
TAKE THE LOW ON DIFFERENT TRACKS...WITH THE GEM SWINGING IT MUCH
FURTHER TO THE WEST AND NOT DEEPENING IT AS THE OTHER MODELS DO.
WITH SUCH A HIGH AMOUNT OF SPREAD AND LACK OF RUN-TO-RUN CONSISTENCY
AMONG THE MODELS IT IS DIFFICULT TO HANG YOUR HAT ON ANY PARTICULAR
PERIOD OR PORTION OF THE CWA FOR HIGHEST POPS...HOWEVER IN GENERAL
THE FOCUS POINT SEEMS TO BE FROM SATURDAY AFTERNOON INTO SATURDAY
NIGHT AND HAVE ADJUSTED POPS UP TO CHANCE DURING THIS TIME.
DEPENDING ON HOW THIS SYSTEM EVENTUALLY DOES EVOLVE...IT HAS THE
POTENTIAL TO PRODUCE ANOTHER MODERATE ACCUMULATION SNOW FOLLOWED BY
BLOWING SNOW EVENT OVER THE WEEKEND. THIS WILL BEAR CLOSE MONITORING
ON SUBSEQUENT SHIFTS.

IN THE LONG RANGE IT APPEARS HIGH PRESSURE WILL PROVIDE A BRIEF
RESPITE AROUND SUNDAY AND MONDAY...HOWEVER CONTINUING NORTHWESTERLY
FLOW ALOFT WILL LIKELY ENSURE THAT THIS LULL IS BRIEF AND THE ACTIVE
WEATHER PATTERN WILL LIKELY CONTINUE WELL INTO NEXT WEEK.

&&

.AVIATION...
10/00Z...TROUGH STILL SWINGING THROUGH THE AREA TONIGHT AS WINDS
BEGIN TO DROP OFF. STILL A DECENT GRADIENT OVER THE NORTH AND EAST
AND EXPECT SOME MINOR VSBY REDUCTIONS FOR THE NEXT SEVERAL HOURS.
CIGS STILL MVFR EAST/SOUTH WITH WEST AREAS ERODING FROM MVFR TO
POCKETS OF VFR. THAT TREND WILL CONTINUE WITH KFOD AND KDSM SEEING
VFR CIGS BY 02 TO 05Z. EAST SITES WILL HAVE LONGER...AFT 04-08Z.
SCT020 ON THE WAY FOR DAY PART HOURS WED AS SOUNDINGS CONTINUE TO
SHOW SOME CLOUDS. OTHERWISE...LIGHT WIND DAY WITH VFR CIGS EXPECTED
FOR THE AREA. /REV

&&

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

$$

SHORT TERM...MOYER/REV
AVIATION...REV
LONG TERM...LEE