Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 260000
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
700 PM CDT TUE AUG 25 2015

...UPDATED FOR AVIATION DISCUSSION...

.SHORT TERM /TONIGHT/...
ISSUED AT 347 PM CDT TUE AUG 25 2015

ANOTHER TRANQUIL AND COOL NIGHT IS IN STORE FOR CENTRAL IOWA AS
SURFACE HIGH PRESSURE GRADUALLY SLIDES INTO THE CWA. GIVEN THE
EXCELLENT RADIATIONAL COOLING SETUP TONIGHT...HAVE DROPPED LOWS
ABOUT 3 TO 4 DEGREES LOWER THAN MOST GUIDANCE SOLUTIONS. THIS LINES
UP WELL WITH LAST NIGHT`S MIN TEMPS ACROSS WESTERN IOWA...WHICH
RANGED FROM 39 TO 46 DEGREES. ADDED PATCHY FOG IN RIVER VALLEYS
AFTER 08Z IN THE CENTRAL AND WESTERN PARTS OF THE CWA UNDER THE
RIDGE AXIS. DESPITE THE LACK OF CLOUDS...SMOKE ADVECTING IN FROM THE
WESTERN US WILDFIRES MAY GIVE THE SKY A HAZY APPEARANCE THIS EVENING
AND TONIGHT.

.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
ISSUED AT 347 PM CDT TUE AUG 25 2015

MAIN FOCUS DURING THE LONG TERM WILL REMAIN ON SYSTEM PASSING
THROUGH THE STATE THURSDAY/FRIDAY TIMEFRAME. QUIET WEATHER WILL
PERSIST INTO WEDNESDAY AS SURFACE RIDGE BEGINS TO PULL EAST OF THE
STATE. WARM ADVECTION WILL INCREASE BY LATER IN THE DAY WITH
SOUTHERLY WINDS STRENGTHENING ON THE BACKSIDE OF THE HIGH.
HOWEVER...THE BIGGER CHANGES ARRIVE ON THURSDAY AS INCREASING
850MB FLOW FROM THE SOUTH/SOUTHWEST TRANSPORTS MOISTURE BACK INTO
THE STATE. WILL BEGIN TO SEE SOME INSTABILITY ALONG WITH LIFT
LEADING TO A THREAT OF SCATTERED STORMS IN THE FAR WEST BY
AFTERNOON. THE INITIAL CHANCE OF PRECIPITATION WILL MAINLY BE
DRIVING BY THERMODYNAMIC FORCING INTO THURSDAY EVENING...HOWEVER
THE UPPER SYSTEM WILL APPROACH BY THURSDAY NIGHT WITH STRONG
KINEMATIC FORCING SPREADING INTO CENTRAL IOWA. CROSS SECTIONS
INDICATE DEEP FORCING AND ALONG WITH DEEP WARM LAYER. INSTABILITY
IS NOT REAL STRONG AND PWATS WILL GENERALLY BE FROM 1.5-1.75
INCHES. WARM CLOUD PROCESSES WILL LIKELY LEAD TO MODERATE TO HEAVY
RAINFALL ACROSS PORTIONS OF THE STATE WITH GFS FARTHER NORTH THAN
EURO AT THIS POINT. IN EITHER CASE...RAIN APPEARS WIDESPREAD FOR
MUCH OF CENTRAL IOWA LATE THURSDAY NIGHT INTO FRIDAY MORNING AND
HAVE INCREASED POPS INTO LIKELY AND CATEGORICAL LEVELS. BOTH GFS
AND EURO HAVE THE SYSTEM DEPARTING BY FRIDAY NIGHT WITH POPS
ENDING FROM WEST TO EAST. THEREAFTER...UPPER RIDGING BUILDS ACROSS
THE CENTRAL UNITED STATE WITH DRIER AND WARMER WEATHER INTO THE
LATER HALF OF THE WEEKEND INTO EARLY NEXT WEEK.

&&

.AVIATION...26/00Z
ISSUED AT 638 PM CDT TUE AUG 25 2015

BIGGEST FCST DECISION IS WHAT TO DO WITH FOG POTENTIAL FOR
TONIGHT. WITH HIGH PRESSURE APPROACHING OVERHEAD FROM THE
WEST WINDS SHOULD BECOME VERY LIGHT...UPPER LEVELS DRY OUT...AND
SUBSIDENCE BE PRESENT...MAKING RADIATIONAL FOG VERY PLAUSIBLE FOR
KFOD AND KMCW. KALO IS THE OTHER SITE THAT MAY SEE FOG. WILL
MONITOR WINDS/TEMP TREND AND MAY ADD FOG TO KALO WITH 06Z TAF
PACKAGE. MAY ALSO LOWER VSBYS AT KFOD AND KMCW IF CONFIDENCE
INCREASES FOR FOG DEVELOPMENT. VFR CONDITIONS AT ALL TAF SITES
AFTER 14Z WED.

&&

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

$$

SHORT TERM...SKOW
LONG TERM...COGIL
AVIATION...KOTENBERG


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