HAMweather.com Area Forecast Discussion for County Warning Area DMX

Thu, 16 Feb 2012 05:52:00 GMT
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
1150 PM CST WED FEB 15 2012

.UPDATED 16/06Z AVIATION DISCUSSION...

.SHORT TERM /TONIGHT/...
MAIN FORECAST CONCERN IS WITH WEAK SHORTWAVE EXPECTED TO MOVE ACROSS 
MISSOURI THROUGH THE EVENING HOURS AND PROVIDE SOME LIGHT RAIN 
ACROSS SOUTHERN IOWA. SYSTEM IS LACKING SIGNIFICANT LIFT AND 
MOISTURE TO PRODUCE MUCH MORE THAN SOME LIGHT RAIN THROUGH THIS 
EVENING. BEST ISENTROPIC LIFT REMAINS CONFINED TO NORTHERN MISSOURI 
AND FAR SOUTHERN IOWA ALONG THE 290-300K SURFACE AND QUICKLY 
DIMINISHES BY 03Z THURSDAY.  COLD FRONT LOOKS TO ENTER THE FORECAST 
AREA LATE THIS EVENING AND COMPLETELY CLEAR THE STATE BEFORE 12Z 
THURSDAY. WITH THE DRIER AND COLDER AIR ADVECTING INTO THE 
STATE...NOT EXPECTING MUCH PRECIP PAST 06Z. BUFR SOUNDINGS REALLY 
DRY OUT BY THEN AND LOOKS LIKE ANY RAIN FALLING WILL BE HIGH BASED. 
DSM BUFR SOUNDINGS DEPICTING A DECENT DRY LAYER B/T 900-700MB 
THROUGH THIS EVENING...SO HAVE LOW CONFIDENCE WITH ANY RAINFALL 
NORTH OF I-80. 

.LONG TERM /THURSDAY THROUGH WEDNESDAY/... 
MAINLY DRY FORECAST FOR BEGINNING OF THE EXTENDED PERIOD WITH
SPLIT FLOW ACROSS THE CWA AS THE NORTHERN STREAM REMAINS ACROSS
MINNESOTA...WITH THE SOUTHERN STREAM AND CUTOFF LOWS TRACKING FROM
THE DESERT SOUTHWEST ACROSS THE OZARK MOUNTAINS. RAISED HIGH TEMPS
ABOUT 5 DEGREES ON THURSDAY AND FRIDAY WITH WEST/SOUTHWEST FLOW
AND WEAK WARM AIR ADVECTION...BUT THESE MAY STILL NEED TO BE
ADJUSTED UP.

ACTIVE NORTHWEST FLOW WILL CAUSE A SERIES OF SHORTWAVES IN CENTRAL 
CANADA TO DIVE SOUTHEAST OVER THE GREAT LAKES REGION...ONE OF WHICH 
WILL SCRAPE ACROSS NORTHERN IOWA ON FRIDAY AS A POSITIVELY TILTED 
LONG WAVE TROUGH TRAVERSES THE CENTRAL US. LITTLE INFLUENCE IN THE 
OBSERVED WEATHER IS EXPECTED...OTHER THAN INCREASING MID LEVEL 
CLOUDS AND SHIFT IN THE WIND FROM SOUTHWESTERLY TO NORTHWESTERLY 
WITH THE PASSAGE OF A WEAK FRONTAL BOUNDARY. THERE IS A MINUSCULE 
CHANCE FOR A FEW SPRINKLES OR FLURRIES ACROSS THE NORTHEAST FRIDAY 
AFTERNOON...BUT FOR NOW HAVE THAT PERIOD DRY. AT THE SAME 
TIME...CUTOFF LOW CURRENTLY LOCATED OVER SOUTHERN CALIFORNIA WILL 
SWING ACROSS THE SOUTHERN US TOWARDS TEXAS...AND SPREAD SHOWERS AND 
THUNDERSTORMS OVER THE SOUTHERN PLAINS THROUGH SATURDAY. THIS AREA 
OF PRECIP WILL REMAIN WELL TO THE SOUTH AND EAST OF CENTRAL IOWA. 

ON SATURDAY NIGHT...GFS 15.12 TRIES TO BRING ANOTHER WEAK UPPER 
LEVEL SHORTWAVE ACROSS NORTHEAST IOWA...BUT MODELS SHOW CONSIDERABLE 
DISAGREEMENT WITH BOTH THE TIMING AND PLACEMENT. CHOSE NOT TO STRAY 
FROM BLENDED GUIDANCE AS CONFIDENCE AND UNCERTAINTY IS HIGH. 
SWITCHING ATTENTION BACK TO THE SOUTHWEST...THE ANOTHER WAVE 
CURRENTLY APPROACHING THE DATELINE IN THE NORTHERN PACIFIC WILL 
IMPACT THE NORTHWESTERN UNITED STATES THIS WEEKEND...CROSS THE 
SOUTHERN ROCKIES ON SUNDAY...AND HEAD TOWARDS THE MIDWEST EARLY NEXT 
WEEK. LATEST GFS MODEL HAS SLOWED DOWN THE TIMING OF THE MAIN WAVE 
CONSIDERABLY IN COMPARISON TO THE 06Z RUN...BUT EJECTS A SHORTWAVE 
ACROSS THE MISSOURI RIVER VALLEY MONDAY EVENING SIMILAR TO TO THE 
ECMWF 15.12. THEREFORE ALSO FELT THE MODEL BLEND WAS 
SUFFICIENT...WITH ROUGHLY 30 POPS.

.AVIATION...16/06Z
HIGH PRESSURE IS BUILDING IN FROM THE WEST AS THE WEAK SYSTEM THAT 
BROUGHT LIGHT RAIN TO PARTS OF SOUTHERN IOWA IS DEPARTING.  
SATELLITE SHOWING STRATUS BREAKING UP AT THE MOMENT BUT FORECAST 
SOUNDINGS ARE PRETTY ADAMANT THAT THE LOW LEVEL MOISTURE IN PLACE 
WILL DEVELOP PATCHY FOG AND THE STRATUS WILL LIKELY FILL BACK IN.  
WROTE TAFS PESSIMISTICALLY AS THIS SCENARIO SEEMS LIKELY.  

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