000
FXUS63 KDMX 160449
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1149 PM CDT WED MAY 15 2013

.SHORT TERM.../TONIGHT /...
ISSUED AT 400 PM CDT WED MAY 15 2013

MAIN FORECAST CONCERNS FOR TONIGHT WILL BE PRECIPITATION CHANCES.
WEAK SHORTWAVE AND THETA-E ADVECTION BAND ACROSS NORTHERN IOWA WILL
CONTINUE TO WEAKEN IN THE LATE AFTERNOON HOURS...WITH ONLY SLIGHT
CHANCES OF LIGHT RAIN AND MAYBE SOME EMBEDDED THUNDER. FURTHER SOUTH
FRONTAL BOUNDARY REMAINS ACROSS NORTHERN MISSOURI...WITH WEAK
DEVELOPMENT ALONG BOUNDARY IN EASTERN IOWA. DYNAMICS ARE WELL SOUTH
OF IOWA INTO MISSOURI...AND STORMS HAVE BEEN BRIEF. ADDITIONAL
THETA-E ADVECTION PROGGED TO LIFT NORTH ACROSS SOUTHERN IOWA
OVERNIGHT...AND HAVE KEPT POPS GOING ACROSS THE SOUTH AND SOUTHWEST
THROUGH THE OVERNIGHT. SOME UNCERTAINTY AGAIN GIVEN THE VERY DRY
ENVIRONMENT. HAVE KEPT LOWS ABOVE GUIDANCE WITH CLOUDS INCREASING AND
WEAK WAA THROUGH MUCH OF THE NIGHT.

.LONG TERM.../THURSDAY THROUGH WEDNESDAY/...
ISSUED AT 400 PM CDT WED MAY 15 2013

WEAK SURFACE BOUNDARY OVER NORTHERN MISSOURI WILL START LIFTING
BACK INTO IOWA TOMORROW MORNING AS HIGH PRESSURE OVER THE WESTERN
GREAT LAKES BEGINS PULLING OFF TO THE EAST. PRECIP CHANCES ALONG
THE FRONT WILL BE QUITE LIMITED IN THE MORNING WITH LITTLE IN THE
WAY OF ANY SYNOPTIC OR SIGNIFICANT MESOSCALE FORCING AND WEAK
ELEVATED INSTABILITY. UNCAPPED SBCAPE VALUES ALONG AND SOUTH OF
THE WARM FRONT INCREASE TO AROUND 1000 TO 1500 J/KG BY THE EARLY
AFTERNOON AS GULF MOISTURE CREEPS BACK INTO THE STATE. THETA-E
ADVECTION ALONG THE FRONT IN WESTERN IOWA INCREASES AS WELL
DURING THE AFTERNOON...BUT WITH DEEP LAYER SHEAR OF 15 KTS OR
LESS...ONLY EXPECTING SCATTERED SHORT-LIVED THUNDERSTORMS INVOF
AND BEHIND THE FRONT. LEANED TOWARDS THE DRIER NAM FOR POPS AND
PRECIP COVERAGE.

CURRENT WATER VAPOR IMAGERY DENOTES AN UPPER LEVEL LOW TRANSITING
THROUGH UTAH. THIS VORT MAX AND ASSOCIATED SHORTWAVE TROUGH WILL
PROPAGATE TO THE ENE IN THE WESTERLIES AND MOVE INTO EASTERN SD
AND NE BY 06Z FRI. MODELS ARE CONSISTENT IN BRINGING A COMPLEX OF
THUNDERSTORMS OUT OF NEBRASKA WITH THIS WAVE AND ALONG THE NEAR-
SURFACE WARM FRONT. THE NAM TAKES THIS COMPLEX ALMOST COMPLETELY
INTO CENTRAL MN WHILE THE GFS HANGS A CONSIDERABLE AMOUNT OF
ACTIVITY INTO CENTRAL IOWA. THE EC OFFERED A NICE COMPROMISE
BETWEEN THESE TRACKS...TAKING THE COMPLEX THROUGH NORTHERN IOWA
ALONG THE INSTABILITY GRADIENT DURING THE MORNING HOURS ON
FRIDAY.

UPPER LEVEL PATTERN BECOMES QUITE AMPLIFIED ACROSS THE WESTERN
CONUS ON FRIDAY AS A DEEP LONGWAVE TROUGH PUSHES ONTO THE PACIFIC
COAST. SUCCESSIVE MODEL RUNS HAVE BEEN CONSISTENTLY SLOWER WITH
THE PROGRESSION OF THIS WAVE OVER THE LAST SEVERAL DAYS AND THE
LATEST 12Z RUNS HAVE NOT DEVIATED FROM THIS TREND. THE UPPER
LEVEL TROUGH BECOMES NEGATIVELY TILTED AS IT CLEARS THE ROCKIES
AROUND 06Z SUNDAY AND DEVELOPS INTO A CLOSED LOW OVER NEBRASKA
SUNDAY AFTERNOON. SATURDAY LOOKS TO REMAIN DRY WITH THE STATE IN
THE WARM SECTOR...WITH THE BEST SHOT OF STRONG TO SEVERE
THUNDERSTORMS DURING THE AFTERNOON ON SUNDAY AND POSSIBLY AGAIN
ON MONDAY. THE CLOSED LOW LOOKS TO SPIN ACROSS THE UPPER MIDWEST
INTO THE MIDDLE PART OF NEXT WEEK...BRINGING COOLER AND WETTER
WEATHER.

&&

.AVIATION...16/06Z
 ISSUED AT 1148 PM CDT WED MAY 15 2013

VFR CONDITIONS WILL PREVAIL THROUGH THE TAF PERIOD. SMALL SHOWERS
AND THUNDERSTORMS ARE DEVELOPING ACROSS SOUTHERN IOWA AND WILL
PERSIST INTO THE EARLY MORNING HOURS...AND POSSIBLY AT INTERVALS
ON THURSDAY. HOWEVER...THE RELATIVELY LOW PROBABILITY OF A
THUNDERSTORM STRIKING KDSM/KOTM...AND MORE SO THE BRIEF DURATION
OF ANY LOWERED CIGS/VSBYS THAT WOULD OCCUR...PRECLUDE ADVERTISING
A LONG PERIOD OF VCTS IN THE 06Z TAFS. WINDS WILL BE EAST TO
SOUTHEAST AND LIGHT THROUGH THURSDAY NIGHT.

&&

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

&&

$$

SHORT TERM...AWB
LONG TERM...SKOW
AVIATION...LEE