Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 050902
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
402 AM CDT WED AUG 5 2015

.SHORT TERM /TODAY/...
ISSUED AT 351 AM CDT WED AUG 5 2015

HAVE HAD AN AREA OF SHOWERS AND ISOLATED THUNDERSTORMS STRETCHING
ACROSS THE CWA FROM WEST CENTRAL IOWA TO THE SOUTHEASTERN CWA. THIS
LINE AS BEEN SLOWLY DIMINISHING WITH TIME AND A FEW ISOLATED SHOWERS
HAVE REDEVELOPED ACROSS THE SOUTHWESTERN CWA IN THE PAST HOUR.
EXPECT TO SEE THIS ACTIVITY FESTER THROUGH THIS MORNING AND SLOWLY
DIMINISH TOWARD MID/LATE MORNING AS THE THETA-E ADVECTION ALOFT
DIMINISHES. UPPER LEVEL SPINNING ACROSS SC NE TO PUSH ESE
TODAY...WITH ADDITIONAL SHOWER/THUNDERSTORM DEVELOPMENT POSSIBLE
THIS AFTERNOON. HOWEVER DO EXPECT MUCH OF THE ACTIVITY CLOSER TO THE
ENERGY ALOFT WHICH WILL REMAIN TO THE SOUTH/SOUTHWEST OF THE CWA
WITH LOW LEVEL FLOW COMING MORE OFF THE DRY AREA OF HIGH PRESSURE
OFF TO THE ENE. THEREFORE HAVE REDUCED POPS QUITE A BIT ACROSS THE
CWA TODAY AND CONFINED THE ACTIVITY TO THE WESTERN/SOUTHERN PORTIONS
OF THE CWA FOR THE MOST PART. FAIRLY DENSE CIRRUS SHIELD IN PLACE
CURRENTLY AND EXPECT THE HIGH CLOUD COVER TO REMAIN FAIRLY
ENTRENCHED ACROSS THE CWA TODAY...SO HAVE KNOCKED HIGHS DOWN A BIT
TO VALUES SIMILAR TO READINGS FROM TUESDAY.

.LONG TERM /TONIGHT THROUGH TUESDAY/...
ISSUED AT 351 AM CDT WED AUG 5 2015

LONG TERM PERIOD STARTS OFF WITH A LOW THAT SHOULD BE SE OF THE
DMX CWA AND A SFC HIGH THAT WILL BE OVER THE GREAT LAKES. NET
RESULT IS THE AFTERNOON SHOULD BE VERY QUIET IN TERMS OF SENSIBLE
WEATHER WITH S/SE FLOW EXPECTED. 850MB TEMPS FOR THURSDAY SIMILAR
TO WEDNESDAY/S...PERHAPS A DEGREE OR TWO WARMER. BASED ON
SATELLITE IMAGERY...MODELS MAY BE INITIALIZING A LITTLE HEAVY ON
MID TO UPPER LEVEL CLOUD COVER FOR THURSDAY. THEREFORE STARTED
NEAR PERSISTENCE AND NUDGED TEMPS UP A FEW DEGREES. SFC LOW
EXPECTED TO DEVELOP OVER THE DAKOTAS DURING THE DAYTIME WILL HELP
USHER IN POTENTIALLY ACTIVE WX OVERNIGHT.

MODELS STILL ON TRACK WITH BRINGING SFC LOW/SHORTWAVE THROUGH THE
UPPER MIDWEST. THE NAM IS AN OUTLIER WITH THIS 00Z RUN AS IT PUTS
THE LOW ALONG THE CANADA/US BORDER. THE GFS AND GEM HAVE THE LOW
PROPAGATING THROUGH SOUTH CENTRAL MINNESOTA. THE EURO IS IN BETWEEN
THE NAM AND THE GFS BUT...BUT CLOSER TO THE GFS. WILL LEAN TOWARDS
THE EURO HERE AND TOSS OUT THE NAM. LOW SHOULD BE INTO MINNESOTA BY
06Z WITH AN ATTENDANT WARM FRONT TO HELP PROVIDE LIFT FOR STORMS
ACROSS NORTHERN IOWA. SYNOPTIC SETUP ALSO FEATURES A MID-LEVEL JET
AND SOUTHERLY MOIST FLOW. SHEAR UPWARDS OF 40KTS SHOULD BE ENOUGH TO
HELP ORGANIZE STORMS. 0 TO 6 KM MUCAPES LOOK TO BE MINIMAL WITH
VALUES AROUND 1000 J/KG. DCAPES LOOK TO BE OVER 1500 J/KG. MID LEVEL
LAPSE RATES STEEPENING TO AROUND 7 C/KM WILL HELP PROVIDE SOME
INSTABILITY. GIVEN TIMING OF SYSTEM AND ORIENTATION OF SFC MOISTURE
CONVERGENCE...LINEAR MODE OF CONVECTION WITH DAMAGING WINDS SEEMS
MOST LIKELY. PWATS SHOULD BE AROUND 1.5 WHICH IS LOW ENOUGH TO
PREVENT WATER LOADING OF UPDRAFTS...SOMETHING WHICH HAS GENERALLY
INHIBITED HAIL WITH MOST OF OUR ACTIVE WEATHER EVENTS OVER THE PAST
MONTH OR SO IN IA. THUS HAIL IS POSSIBLE...THOUGH DAMAGING WINDS
REMAIN THE MAIN THREAT. IN THIS TYPE OF SETUP...DIURNAL HEATING IS
NOT NECESSARY...SO CONVECTION SHOULD CONTINUE OVERNIGHT.

FCST REMAINS CONSISTENT WITH PUSHING HIGH PRESSURE THROUGH NEBRASKA
AND INTO WESTERN IOWA FRIDAY AFTERNOON/EVENING. AT +17C IN OUR NE
AND +20C IN OUR SW...850MB TEMPS HAVE BEEN TRENDING UPWARDS THE PAST
FEW RUNS. THUS HAVE KEPT MID 80S IN THE FCST. ALSO KEPT STRONGER
WINDS AS FCST SOUNDINGS SHOW WINDS OF AROUND 25 KTS AT THE TOP OF
THE MIXED LAYER WHICH SHOULD BE ABLE TO MIX DOWN TO THE SFC.

BY THIS WEEKEND...A LARGE UPPER LEVEL HIGH WILL ESTABLISH ITSELF
NEAR THE TX/OK PANHANDLE. THIS WILL PLACE THE DMX CWA INTO W/NW FLOW
ALOFT. SUBSEQUENTLY...MODELS TRY TO PUSH A SERIES OF SHORTWAVES
THROUGH THE REGION SATURDAY THROUGH TUESDAY. MODELS HINT AT A MCS
OVER EASTERN NE/WESTERN IA SATURDAY MORNING. WITH A LOT OF TIME IN
BETWEEN NOW AND THEN...CONFIDENCE NOT GREAT IN THIS
SOLUTION...ESPECIALLY WITH A SFC HIGH EXPECTED TO BE TO OUR N/NE
SATURDAY MORNING. THUS...HAVE LOWERED POPS SLIGHTLY DURING THIS
TIME. KEPT BROAD-BRUSHED POPS FOR REST OF EXTENDED AS CONFIDENCE
NOT HIGH ENOUGH TO MODIFY OTHERWISE. 850MB TEMPS APPEAR TO REMAIN
IN THE +18C TO +21C RANGE...WHICH REMAINS PERSISTENT WITH REST OF
LONG TERM. THEREFORE...HELD MAX TEMPS IN THE LOW TO MID 80S AND
MIN TEMPS IN THE MID TO UPPER 60S.

&&

.AVIATION...05/00Z
ISSUED AT 624 PM CDT TUE AUG 4 2015

EXPECT VFR CONDITIONS AT SITES THROUGH PERIOD. MAY SEE SHRA OR
TSRA AT SITES AFTER 06Z...WITH THE BEST CHANCES AT KOTM...KDSM AND
KFOD. HOWEVER...DO NOT HAVE ENOUGH CONFIDENCE TO INCLUDE MENTION
ATTM...WITH ONLY VCSH MENTION AT KDSM NEAR 12Z. WINDS WILL BE
GENERALLY VARIABLE...BECOMING SE THROUGH THE DAY WEDNESDAY.


&&

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

$$

SHORT TERM...BEERENDS
LONG TERM...KOTENBERG
AVIATION...AWB



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