Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 052332
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
632 PM CDT THU MAY 5 2016

.SHORT TERM.../TONIGHT/
ISSUED AT 250 PM CDT THU MAY 5 2016

BENIGN FORECAST TONIGHT.  THE MOST INTERESTING PART OF THE FORECAST
TONIGHT WILL BE TEMPERATURES.  ALOFT WE HAVE AN ENORMOUS RIDGE OVER
THE ROCKIES INTO THE UPPER MIDWEST. AT THE SURFACE A RIDGE OF HIGH
PRESSURE WILL BE CENTERED OVER THE UPPER MIDWEST. THE RESULT WILL BE
CLEAR OR MOSTLY CLEAR SKIES AND LIGHT WINDS TONIGHT.

TEMPS WILL BE WARMER OVER THE CENTRAL AND WESTERN PORTION OF IOWA...
ALONG AND WEST OF THE SURFACE RIDGE AXIS WHERE WINDS WERE SOUTHWESTERLY
ALL DAY TODAY AND DAYTIME HIGHS WERE 6 TO 10 DEGREES WARMER THAN
IN THE EAST. EASTERN IOWA BEING ON THE FRINGE BETWEEN THE UPPER
RIDGE TO THE WEST AND A DEEP UPPER TROUGH OVER THE EASTERN U.S. AS
WELL AS BEING EAST OF THE SURFACE RIDGE AXIS HAD WINDS OUT OF THE
NORTH DURING THE DAY TODAY. WEAK PASSING DISTURBANCES HAD PRODUCED
SOME CLOUDS AND ISOLATED LIGHT SHOWERS. ALL OF THIS HAS CAUSED
HIGHS OVER EASTERN IOWA TO BE CONSIDERABLY COOLER THAN LOCATIONS
IN CENTRAL AND WESTERN IOWA. TONIGHT AS THE SURFACE RIDGE SINKS
SOUTH AND THE UPPER RIDGE SHIFTS MORE INTO THE UPPER MIDWEST WINDS
WILL BECOME SOUTHWESTERLY OVER THE ENTIRE FORECAST AREA. HOWEVER
THEY WILL BE FAIRLY LIGHT AND WITH LITTLE MIXING AND A COOLER
START TO THE EVENING...OVERNIGHT LOWS ACROSS THE EASTERN PORTION
OF THE FORECAST AREA WILL BE SOME 5 OR SO DEGREES COOLER THAN THE
REST OF THE STATE.

.LONG TERM.../FRIDAY THROUGH THURSDAY/
ISSUED AT 250 PM CDT THU MAY 5 2016

WARM AND BREEZY CONDITIONS TO BEGIN THE EXTENDED PERIOD. RIDGE OF
HIGH PRESSURE WILL BE EAST OF IOWA ON FRIDAY WITH SOUTHERLY WINDS
RETURNING TO THE REGION. AS PER ADVERTISED THE PAST SEVERAL DAYS...
THICKNESS/H850 TEMPS WILL BE WARMING SIGNIFICANTLY BY LATE DAY WITH
80S LIKELY OVER MUCH OF THE AREA...HEAT ISLAND OVER METRO WILL YIELD
HIGHS IN THE MID 80S WITH MID 80S ALSO LIKELY OVER THE NORTHWESTERN
AREAS WHERE THERMAL RIDGE WILL FOCUS THE WARM AIR ADVECTION ACROSS
NORTHERN IOWA AND INTO SOUTHERN MN. SOME CLOUDS WILL RETURN IN THE
NORTH BY MID TO LATE AFTERNOON AS COOL FRONT APPROACHES FROM THE
NORTHWEST. FORCING REMAINS LIMITED AND DRY CONDITIONS WILL BE THE
RULE FOR THE DAY. AS THE COOL FRONT DRIVES SOUTH FRIDAY NIGHT WEAK
CONVERGENCE AND INSTABILITY WILL COMBINE TO PROMOTE WIDELY
SCATTERED SHOWERS AND THUNDERSTORMS MOVING INTO NORTHERN IOWA
PRIOR TO 12Z SATURDAY. SOME CHALLENGES REMAIN FOR SATURDAY REGARDING
COVERAGE OF SHOWERS AND THUNDERSTORMS. THE EURO DEVELOPS A STRONGER
H500 VORT MAX THAT MOVES ALONG THE BOUNDARY WHILE THE GFS SHOWS
WEAKER DEVELOPMENT...WEAKER FORCING AND LESS COVERAGE OF PRECIPITATION.
NONE THE LESS...CHANCE POPS AT LEAST FOR NOW. INSTABILITY REMAINS
MARGINAL SO HAVE TRIMMED BACK TO ISO THUNDER. PER PREVIOUS FORECASTS
THE BOUNDARY WILL EVENTUALLY DRIFT SOUTH OF THE REGION BY SATURDAY
NIGHT WITH SOME RETURN FLOW ALOFT THE BOUNDARY OVERNIGHT SATURDAY
NIGHT INTO SUNDAY. THE FIRST IN A SERIES OF SHORTWAVES WILL ADVANCE
NORTHEAST TOWARD IOWA SUNDAY AS THE STRONGER UPPER LEVEL TROUGH TO
OUR WEST BECOMES MORE ESTABLISHED OVER THE CENTRAL PLAINS. THIS
WILL RESULT IN MORE WIDESPREAD RAINFALL OVER SOUTHERN IOWA SUNDAY
NIGHT AND ACROSS MOST OF THE AREA MONDAY. AS WARM FRONT LIFTS
NORTHEAST DEW POINTS WILL RISE INTO THE LOWER 60S BY MIDDAY MONDAY
RESULTING IN MUCAPE ABOVE 1500 J/KG AS THE WARM SECTOR OVERTAKES
MOST OF THE CENTRAL AND SOUTH. A DRY LINE PUSHING AS FAR NORTHEAST
AS EASTERN KS/SOUTHEAST NE SHOULD BE THE FOCUS FOR THUNDERSTORM
DEVELOPMENT WITH A LINE OF STORMS THEN MOVING NORTHEAST INTO THE
EVENING HOURS. BULK SHEAR/WIND FIELDS REMAIN SUPPORTIVE OF SVR
DEVELOPMENT MONDAY AND POTENTIALLY INTO TUESDAY. MODELS BEGIN TO
DIVERGE ON SOLUTIONS BY TUESDAY WITH GFS HOLDING ONTO THE MAIN
SYSTEM OVER IOWA WHILE THE EURO IS SLIGHTLY FASTER IN SHIFTING THE
FORCING INTO EASTERN IOWA BY AFTERNOON WITH BETTER CHANCES FOR
STRONG THUNDERSTORMS THERE. STILL...THERE MAY BE A RESIDUAL RISK
OF SOME SEVERE STORMS IN EITHER CASE BUT UNCERTAINTY REMAINS FOR
NOW. RAINFALL TOTALS WILL AGAIN RAMP UP AFTER SUNDAY NIGHT...AND
PEAK FROM SUNDAY NIGHT THROUGH TUESDAY. SIMILAR TO YESTERDAY TOTALS
LOOK TO RANGE FROM 1 TO 2 INCHES ON AVG WITH HIGHER AMOUNTS POSSIBLE
IN HEAVIER CORRIDORS. GIVEN THE BETTER LIKELIHOOD OF RAIN CHANCES
AND CLOUD COVER...HIGHS FOR THE PERIOD FROM SUNDAY THROUGH WEDNESDAY
WILL REMAIN IN THE 60S/70S WITH LOWS MAINLY IN THE 50S UNTIL LATER
IN THE WEEK WHEN THE H500 PARENT CIRCULATION FINALLY PULLS EAST OF
THE REGION. THE OTHER COOL START TO THE DAY WILL BE SUNDAY OVER
THE NORTH WHEN A BRIEF BREAK FROM CLOUDS AND RAINFALL WILL BE SEEN
OVER THE NORTHERN PORTIONS OF THE FORECAST AREA.

&&

.AVIATION.../FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING/
ISSUED AT 632 PM CDT THU MAY 5 2016

NEARLY CLEAR SKIES ARE FORECAST THROUGH THE TAF PERIOD. LIGHT
VARIABLE OR SOUTHWEST WINDS OVERNIGHT WILL PICK UP A BIT ON FRIDAY
BUT REMAIN AROUND 12 KT OR LESS. NO OBSCURATIONS OR PRECIPITATION
ARE ANTICIPATED.

&&

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

&&

$$

SHORT TERM...FAB
LONG TERM...REV
AVIATION...LEE



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