Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 220903
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
403 AM CDT FRI MAY 22 2015

.SHORT TERM /TODAY/...
ISSUED AT 403 AM CDT FRI MAY 22 2015

OUR LAST SEMI NICE DAY FOR A WHILE. SFC RIDGE NEAR GREEN BAY EAST
TODAY WITH UPPER LEVEL RIDGE PROGRESSING ACROSS THE AREA AS WELL.
AS LEE SIDE TROUGH DEVELOPS AND WARM AIR ADVECTION RETURNS TO THE
WESTERN PLAINS...THETAE ADVECTION WILL REALLY KICK IN BY 00Z WITH
MID TO HIGH LEVEL CLOUDS BUILDING IN FROM THE SOUTHWEST TODAY.
ALREADY AT 06Z...SOME THIN HIGH LEVEL CLOUDS SHOWING UP OVER SW IA
WHICH SHOULD SPREAD EAST WITH TIME. H850 TEMPS REMAIN MILD THIS
AFTERNOON AND WITH PLENTY OF SUNSHINE UNTIL MID AFTERNOON...SHOULD
SEE HIGHS RECOVER NICELY TODAY. BY 00Z H850 TEMPS RANGE FROM NEAR
10C NORTH TO ABOUT 8C CENTRAL. HAVE KEPT SW HIGHS A BIT COOLER
WITH EVENTUAL CLOUDS...NEAR 70 WITH CENTRAL AREAS AT MID 70S AND
NORTHERN AREAS ALSO NEAR 75 DEGREES. WINDS SHOULD REMAIN WESTERLY
BUT BEGIN TO SWING AROUND TO THE SOUTH SOUTHWEST BY 18 TO 20Z.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
ISSUED AT 403 AM CDT FRI MAY 22 2015

SEVERAL CONCERNS OVER THE EXTENDED PERIOD AS A VERY ACTIVE
WEATHER PATTERN SETS UP ACROSS THE REGION WITH SOUTHWEST FLOW
ALOFT DEVELOPING THIS WEEKEND AND LASTING THROUGH THE MIDDLE OF
NEXT WEEK. WIDESPREAD RAIN ANTICIPATED LATE SATURDAY NIGHT INTO
SUNDAY...THEN A HINT OF SEVERE WEATHER POTENTIAL ON MONDAY ACROSS
PORTIONS OF THE FORECAST AREA. OVERALL...LEANED TOWARD A NAM/ECMWF
BLEND.

TONIGHT THROUGH SUNDAY NIGHT...VERY LARGE AND STUBBORN SURFACE
HIGH PRESSURE SLOWLY MEANDERS EASTWARD TONIGHT INTO SATURDAY. AS
PER PREVIOUS MODEL RUNS...THE 00Z RUNS ARE NO DIFFERENT IN SLOWING
DOWN PRECIPITATION CHANCES ACROSS CENTRAL IOWA UNTIL LATE SATURDAY
NIGHT INTO SUNDAY. CUT BACK CONSIDERABLY WITH TIMING TONIGHT INTO
SATURDAY...EVEN WITH THE WEAK MID-LEVEL THETA-E ADVECTION MOVING
INTO SOUTHWEST IOWA SATURDAY MORNING. THERE IS PLENTY OF DRY AIR
TO CONTEND WITH NEAR THE SURFACE AND HAVE LOW CONFIDENCE WITH MUCH
OF THE WAY OF MEASURABLE PRECIPITATION UNTIL SATURDAY NIGHT WHEN A
500MB VORT MAX PUSHES NORTHEAST ACROSS THE STATE INTO SUNDAY. WENT
SLIGHTLY WARMER ON SATURDAY PER THE DRIER FORECAST AND ENOUGH
MIXING TO DEVELOP.

THE BETTER LARGE SCALE FORCING REMAINS TO THE SOUTH SATURDAY NIGHT
INTO SUNDAY MORNING...BUT THERE IS PLENTY OF MOISTURE TRANSPORT
AND THETA-E ADVECTION INTO THE FORECAST AREA DURING THIS TIME
FRAME. ENOUGH OMEGA PRESENT FROM 06Z TO 18Z SUNDAY TO KEEP WITH
THE HIGH POPS ACROSS CENTRAL IOWA BUT NOT ANTICIPATING A
CONTINUOUS RAIN AND HAVE MENTION OF PERIODS OF TSRA. INSTABILITY
AND SHEAR REMAIN LIMITED AND HAVE LOW CONFIDENCE IN ANY SEVERE
POTENTIAL SATURDAY NIGHT INTO SUNDAY. ANOTHER SHORTWAVE MOVES
NORTHEAST RIDING THE WINDWARD SIDE OF THE UPPER RIDGE LATE SUNDAY
AND WILL PROVIDE ENOUGH LIFT TO KEEP THE PERIODIC THUNDERSTORMS
CHANCES GOING SUNDAY NIGHT.

MONDAY...TIMING WILL BE KEY ON MONDAY FOR SEVERE WEATHER
POTENTIAL. STILL SOME BIG UNCERTAINTIES BETWEEN MODEL SOLUTIONS.
THE GFS WANTS TO MOVE TWO QUICK MOVING SHORTWAVES ACROSS THE
STATE MONDAY WHILE THE ECMWF FORECASTS ONLY ONE.
REGARDLESS...INSTABILITY BUILDS BACK INTO THE STATE DURING THE
DAY MONDAY WITH THE GREATEST SURFACE BASED CAPE VALUES OF
1500-3000 J/KG ACROSS THE SOUTHERN HALF OF THE STATE BY 00Z
TUESDAY. DEEP LAYER SHEAR SEEMS SUFFICIENT ENOUGH TO SUPPORT
UPDRAFT DEVELOPMENT AND GFS IS A SLIGHTLY HIGHER THAN THE ECMWF
WITH THE 0-1KM SHEAR...BUT STILL IN THE 10-20 KNOT RANGE BY 00Z
TUESDAY. CERTAINLY HAIL AND WIND LOOK TO BE A THREAT AND SHOULD
THE MODELS TREND TOWARD JUST ONE STRONG SHORTWAVE MOVING THROUGH
DURING THE PEAK HEATING...PROVIDING MORE INSTABILITY AND
POTENTIALLY LEADING TO A BETTER TORNADIC THREAT. SOMETHING TO
CONTINUE TO MONITOR OVER THE HOLIDAY WEEKEND. ON A SIDE
NOTE...EVEN WITH CONVECTION ANTICIPATED ON MONDAY...TEMPS SHOULD
RISE WELL INTO THE 70S TO LOWER 80S AND RAISED MAX TEMPS FOR
MONDAY.

TUESDAY THROUGH THURSDAY...HIGHER CONFIDENCE IN DRY CONDITIONS
WITH STRONG SUBSIDENCE BUILDING INTO THE STATE AND TRENDED DRIER
ON TUESDAY AND TUESDAY NIGHT WITH SOME LINGERING POPS ACROSS THE
SOUTHEAST. GFS WANTS TO PUNCH A FAIRLY STRONG SHORTWAVE ACROSS
MINNESOTA TUESDAY NIGHT INTO WEDNESDAY BUT THE ECMWF BRINGS IN A
DECENT SURFACE RIDGE AND LEANED TOWARD THE DRY ECMWF SOLUTION
ATTM.

&&

.AVIATION...22/06Z
ISSUED AT 1146 PM CDT THU MAY 21 2015

VFR CONDITIONS THROUGH THE PERIOD WITH CLEAR SKIES AND LIGHT WINDS
INTO FRI MORNING. WINDS WILL SLOWLY BECOME SLY BY MIDDAY WITH
GRADUALLY INCREASING MID CLOUDS SW TO NE LATE.


&&

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

&&

$$

SHORT TERM...REV
LONG TERM...PODRAZIK
AVIATION...SMALL



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