Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 030312
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1012 PM CDT SAT MAY 2 2015

.UPDATE...
ISSUED AT 957 PM CDT SAT MAY 2 2015

UPDATE MADE TO THE FORECAST FOR THE EVENING CONCERNS PRECIP
UNCERTAINTIES FOR THE OVERNIGHT. THE HI-RES MODELS ALL PICK UP ON
SOME ELEVATED INSTABILITY DRIBBLING ACROSS THE FORECAST AREA
TONIGHT WHILE THE OTHER MODELS KEEP US DRY. WATER VAPOR SHOWS A
VORT MAX AND A SECONDARY SHORTWAVE PUSHING EAST OUT OF OMAHA WHICH
THE HRRR BRINGS ACROSS IOWA THROUGH THE OVERNIGHT. CERTAINLY THE
STORMS OVER EASTERN NEBRASKA HAVE HELD TOGETHER AS THEY CROSSED
INTO IOWA AND ADDITIONAL SHOWERS/STORMS ARE CURRENTLY RE-
DEVELOPING ACROSS OUR WESTERN FORECAST AREA. THE UPDATE BROUGHT
PRECIP BACK INTO THE WEST THIS EVENING INTO THE OVERNIGHT BUT JUST
HOW LONG IT WILL PERSIST IS THE QUESTION. DESPITE THE HI-RES
MODELS SOLUTION...THE STORMS OUT WEST ARE DYING THE FURTHER EAST
THEY COME AND WE ARE FORECAST TO LOSE AT LEAST SOME OF OUR
INSTABILITY OVERNIGHT. ANY SHOWERS THAT WOULD HAPPEN WOULD BE VERY
HIT OR MISS IN POCKETS OF RESIDUAL INSTABILITY WHICH ARE JUST TOO
HARD TO FORECAST AND CERTAINLY NOT WORTH PAINTING SLIGHT CHANCE
POPS ACROSS OUR ENTIRE FORECAST AREA...AT LEAST AT THIS POINT. IF
WE SEE BETTER EVIDENCE OF MORE WIDESPREAD INSTABILITY TO COINCIDE
WITH THE HRRR`S WEAK SHORTWAVE AND VORT MAX DRIFTING ACROSS THE
CWA OVERNIGHT WE MAY NEED TO ADD A LITTLE MORE WIDESPREAD SLIGHT
CHANCE POPS TO THE GRIDS. CERTAINLY AN INTERESTING AND NOT CLEAR
CUT FORECAST TONIGHT.

&&

.SHORT TERM /TONIGHT/...
ISSUED AT 310 PM CDT SAT MAY 2 2015

AREA OF SHOWERS AND A FEW THUNDERSTORMS HAS SLOWLY PROGRESSED
EASTWARD ACROSS THE SOUTHERN HALF OF IOWA TODAY. THIS ACTIVITY IS
IN AN AREA OF MID LEVEL THETA-E ADVECTION AND WARM ADVECTION AHEAD
OF A WEAK SHORTWAVE THAT IS QUITE EVIDENT IN THE WATER VAPOR
IMAGERY. THIS ACTIVITY WILL CONTINUE TO PROGRESS EASTWARD THIS
EVENING WITHOUT AND EVENTUALLY EXIT THE EAST LATER THIS EVENING AS
SUBSIDENCE INCREASES FROM THE WEST BEHIND THE WAVE. OVERNIGHT WILL
BE RELATIVELY QUIET WITH MODEST SOUTHERLY SURFACE WINDS AND
GENERALLY CLEAR TO PARTLY CLOUDY SKIES. HAVE KEPT TEMPERATURES AT
OR SLIGHTLY ABOVE GUIDANCE GIVEN THE ONGOING WARM ADVECTION
OVERNIGHT AND INCREASING MOISTURE.

.LONG TERM /SUNDAY THROUGH SATURDAY/...
ISSUED AT 310 PM CDT SAT MAY 2 2015

ACTIVE WEATHER PATTERN SETS UP ACROSS THE REGION SUNDAY NIGHT AND
LASTS THROUGHOUT MUCH OF THE WEEK. SEVERE POTENTIAL SUNDAY LATE
AFTERNOON INTO THE EVENING OVER THE NORTH BUT NO OTHER CLEAR CUT
TIME FRAME FOR SEVERE WEATHER THE REMAINDER OF THE WEEK. LEANED
TOWARD A BLEND OF THE NAM12/ECMWF FOR TEMPS AND POPS THROUGH
TUESDAY...THEN A GFS/ECMWF BLEND THROUGH THE REST OF THE WEEK.

SUNDAY INTO TUESDAY...GOOD SURGE OF WAA ACROSS THE STATE WILL PUSH
MAX TEMPS WELL INTO THE 80S ACROSS CENTRAL IOWA. BUMPED UP MAX TEMPS
UP A COUPLE DEGREES AS WELL AS WINDS DURING THE AFTERNOON WITH THE
STRONG SOUTHWEST FLOW AND MIXING TO AROUND 900MB. BOUNDARY SAGS SOUTH
INTO NORTHERN IOWA SUNDAY EVENING AND HELPS WEAKEN THE CAP OVER
NORTHERN IOWA PAST 22Z SUNDAY. MUCAPE INCREASES TO 1500-2200 J/KG
LATE IN THE AFTERNOON INTO THE EVENING WITH DEEP LAYER SHEAR STRONG
ENOUGH TO SUPPORT UPDRAFTS FOR A CONSIDERABLE TIME FRAME. LOW LEVEL
SHEAR IS WEAK...SO MAINLY LOOKING AT ELEVATED HAIL OVER THE
NORTHERN SECTIONS OF THE FORECAST AREA WITH A SECONDARY THREAT OF
DAMAGING WINDS PER LOW VALUES OF DCAPE PRESENT. TEMPERATURES MONDAY
WILL BE COOLER WITH THE BOUNDARY STALLING ACROSS CENTRAL IOWA FROM
WEST TO EAST...BASICALLY ALONG INTERSTATE 80 TO HIGHWAY 30 CORRIDOR
THROUGH MONDAY EVENING. THUNDERSTORMS CHANCES CONTINUED SOUTH OF THE
BOUNDARY DURING THE DAY MONDAY AND BY MONDAY NIGHT INTO
TUESDAY...THE WARM FRONT SURGES BACK NORTHWARD AND HAVE LIKELY POPS
GOING ACROSS THE ENTIRE FORECAST AREA THROUGH TUESDAY MORNING WITH
FORCING AND MOISTURE TRANSPORT INTO THE STATE DURING THIS TIME.
SEVERE THREAT LOOKS MINIMAL ATTM WITH THE LACK OF SIGNIFICANT
INSTABILITY AND SHEAR PRESENT.

THE WARM FRONT CONTINUES TO SURGE NORTH INTO SOUTHERN MINNESOTA ON
TUESDAY AND PLACES THE FORECAST AREA WELL INTO THE WARM SECTOR. THE
850MB TEMPS WARM TO +12C TO +14C AND BUMPED UP MAX TEMPS
CONSIDERABLY...ESPECIALLY OVER NORTHERN IOWA FOR TUESDAY. THE
ATMOSPHERE BECOMES STABILIZED BY TUESDAY NIGHT INTO WEDNESDAY...AND
WENT COMPLETELY DRY ACROSS MUCH OF THE FORECAST AREA DURING THIS
TIME. MODELS ARE IN GOOD AGREEMENT WITH THIS DRY PERIOD.

WEDNESDAY THROUGH SATURDAY...MORE PERIODIC RAIN CHANCES DURING THIS
TIME FRAME WITH THE BEST POTENTIAL LOOK TO BE LATE WEDNESDAY INTO
THURSDAY AS A DECENT SHORTWAVE EJECTS OUT OF THE CENTRAL ROCKIES
INTO WESTERN IOWA. AFTER THURSDAY...DEPENDING ON WHICH MODEL...THERE
IS THUNDERSTORM CHANCES EACH PERIOD THROUGH NEXT WEEKEND.

&&

.AVIATION...03/00Z
ISSUED AT 635 PM CDT SAT MAY 2 2015

UPPER LEVEL WAVE MOVING ACROSS CENTRAL IOWA THIS EVENING AND
PRODUCING SCT SHRA WITH ISOLD TSRA MAINLY AFFECTING KDSM AND KOTM.
THIS WAVE SHOULD PASS EAST BY 03Z OR SO DIMINISHING ANY THREAT FOR
PRECIP THOUGH THERE IS SOME SUGGESTION THAT A MOISTENING MID LAYER
COULD PRODUCE SOME ISOLD SHRA NEAR KALO BEFORE 06Z AS WELL BEFORE
THE WAVE FINALLY EXITS.  VFR CIGS EXPECTED THROUGH THE TAF PERIOD
AND SOUTHERLY SFC WIND WILL DIMINISH TO AROUND 10-15KT THROUGH 12Z
THEN INCREASE ONCE AGAIN TO 15G25KTS AFT 16-18Z.


&&

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

$$

UPDATE...FAB
SHORT TERM...COGIL
LONG TERM...PODRAZIK
AVIATION...FAB



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