Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 050857
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
357 AM CDT SAT SEP 5 2015

.SHORT TERM /TODAY/...
ISSUED AT 356 AM CDT SAT SEP 5 2015

ONGOING PRECIPITATION ACROSS WESTERN CWA WILL PERSIST THROUGH THE
EARLY MORNING HOURS AS FORCING REMAINS MAXIMIZED. FORCING WILL BEGIN
TO LIFT NORTH AND DIMINISH AFTER SUNRISE WITH DECREASING SUPPORT
FROM LLJ...AND EXPECT PRECIPITATION TO BEGIN TO DIMINISH AS WELL.
HIGH RES MODELS KEEP PRECIPITATION ACROSS NORTHERN CWA THROUGH ABOUT
18Z...AND HAVE HELD ONTO CHANCE POPS ACROSS THE AREA A BIT LONGER.
OTHERWISE...EXPECT PRECIPITATION CHANCES TO REMAIN WEST OF CWA...AND
HAVE LEFT FORECAST DRY THROUGH THE AFTERNOON.

WILL SEE ANOTHER HOT AND HUMID DAY ACROSS THE AREA. TEMPERATURES
WILL BE SIMILAR TO YESTERDAY...WITH SLIGHTLY COOLER TEMPS IN THE
NORTH AND NORTHEAST WHERE CLOUDS WILL HELP KEEP TEMPERATURES DOWN.
HOWEVER...WITH HUMIDITY WILL SEE HEAT INDEX VALUES ONCE AGAIN IN THE
90S...WITH WARMER READINGS IN THE SOUTH.

.LONG TERM /TONIGHT THROUGH FRIDAY/...
ISSUED AT 356 AM CDT SAT SEP 5 2015

THUNDERSTORM CHANCES SUNDAY INTO MONDAY AND TUESDAY ARE THE PRIMARY
FOCUS THROUGH THE PERIOD. THE PACIFIC NORTHWEST UPPER LOW HAS BEEN
TRENDING FURTHER NORTH AS IT EJECTS OUT TO THE EAST/NORTHEAST. THE
IMPACT OF THIS IS THE SUBTROPICAL HIGH BUBBLE WILL NOT BE SUPPRESSED
AS FAR SOUTH AS PREVIOUSLY EXPECTED BY MONDAY WITH THE SFC BOUNDARY
LIKELY TO STALL OVER CENTRAL TO SOUTHERN IOWA. THE BOUNDARY WILL
LIFT BACK NORTH A BIT ON MONDAY BEFORE A COLD FRONT MOVES THROUGH
MONDAY NIGHT INTO TUESDAY.

THE TROPICAL CONNECTION HAS BEEN STRENGTHENING THIS MORNING WITH MID
LEVEL MOISTURE ADVECTION SURGING NORTH IN THE INCREASING MONSOONAL
FLOW. THE INITIAL SURGE OF THIS MOISTURE WILL PASS JUST NORTHWEST OF
THE FORECAST AREA LATE THIS AFTERNOON AND TONIGHT. THIS FLOW WILL
VEER SUNDAY INTO SUNDAY NIGHT AND BECOME MORE FOCUSED INTO CENTRAL
IOWA. IN ADDITION...LOWER LEVEL GULF MOISTURE WILL BE STREAMING
NORTH INTO THE STATE DURING THIS PERIOD AND THE COMBINATION OF THE
PACIFIC AND GULF MOISTURE WILL PUSH PWAT VALUES IN EXCESS OF 2
INCHES LATE SUNDAY INTO MONDAY. THE PWATS IN CONJUNCTION WITH DEEP
WARM CLOUD DEPTHS AND STORM MOTIONS OF 25 KTS OR LESS WILL BE
FAVORABLE FOR EFFICIENT RAIN PRODUCING STORMS. STORM MOTIONS NEARLY
PARALLEL TO THE BOUNDARY WILL LEAD TO POTENTIAL TRAINING STORMS. THE
GREATEST THREAT WITH THIS SYSTEM IS SWITCHING TO A HEAVY TO VERY
HEAVY RAIN THREAT. SEVERE WEATHER IS ALSO POSSIBLE ESPECIALLY WITH
PEAK HEATING STORMS AS MLCAPES OF 2500 J/KG OR GREATER DEVELOP. A
FEW SUPERCELLS MAY DEVELOP WITH THE INITIAL ACTIVITY SUNDAY
AFTERNOON WITH EFFECTIVE SHEAR VALUES OF 30 TO 35 KTS. THE EFFECTIVE
SRH IS NOT PROJECTED TO BE AS HIGH AS THE PREVIOUS NIGHTS GUIDANCE
THUS THE PRIMARY THREATS WILL BE LARGE HAIL AND DAMAGING WIND GUSTS
WITH UPPER LEVEL WIND PROFILES BECOMING UNIDIRECTIONAL. THE BOUNDARY
WILL PUSH SOUTH MONDAY NIGHT THOUGH A FEW THUNDERSTORMS WILL LINGER
INTO SOUTHERN IOWA ON TUESDAY. ANOTHER SYSTEM ARRIVES THURSDAY WITH
ANOTHER CHANCE FOR SHOWERS AND THUNDERSTORMS. THIS SYSTEM WILL DRIVE
EVEN COOLER WEATHER INTO THE AREA WITH HIGHS IN THE 60S TO LOWER 70S
BY FRIDAY WHICH IS A BIG SWITCH FROM THE 80S TO LOWER 90S EXPECTED
ON SUNDAY.

&&

.AVIATION...04/18Z
ISSUED AT 1154 PM CDT FRI SEP 4 2015

WEAK ELEVATED CONVECTION WILL PERSIST OVER NRN SITES
/KFOD/KMCW/KALO/ INTO THE EARLY MORNING HOURS BUT FAIRLY HIGH
CONFIDENCE THAT THEY WILL REMAIN VFR. THERE COULD BE ANOTHER BRIEF
PERIOD OF RADIATION FOG NEAR KMCW AS WELL...POSSIBLY DOWN TO IFR FOR
AN HOUR OR TWO.  OTHERWISE EXPECT CONTINUED VFR CONDITIONS AT
KDSM/KOTM WITH MAINLY SCT/BKN MID CLOUDS AND WEAK GUSTS.


&&

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

$$

SHORT TERM...AWB
LONG TERM...DONAVON
AVIATION...SMALL


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