Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 252051
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
351 PM CDT SAT JUL 25 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 309 PM CDT SAT JUL 25 2015

MAIN CONCERN INTO THE NIGHT WILL CONTINUE TO BE CONVECTIVE TRENDS.
SEPARATE NRN AND SRN STREAM SHORT WAVES PRODUCED MCSS OVER SD AND
NE/KS EARLIER TODAY WITH RESULTANT CLUSTERS SUSTAINING THEMSELVES TO
VARIED DEGREES AS THEY CROSSED THE MO RIVER INTO IA. THE
THERMODYNAMIC ENVIRONMENT IS QUITE VARIED DOWNSTREAM IN TERMS OF
BOTH MLCAPE AND MLCIN WITH SIOUXLAND CLUSTER HAVING MORE FAVORABLE
CONDITIONS AND BETTER EFFECTIVE SHEAR AS WELL. CLUSTER HAS WEAKENED
RECENTLY HOWEVER SO IT MAY BE MAINTAINING ITS MORE
KINEMATIC/ELEVATED ORIGINS RATHER THAN TRYING TO BE ROOTED LOWER AND
BECOME MORE SURFACE BASED. THUS...FOR THE TIME BEING...NEITHER AREA
IS OF TOO MUCH CONCERN FOR INTENSIFICATION WITH DOWNSTREAM
CONVERGENCE LACKING. WOULD TAKE AWHILE TO REALIZE THE EXTREME
UNCAPPED INSTABILITY NEAR THE QUAD CITIES.

CONFIDENCE IS SLIGHTLY BETTER UPSTREAM HOWEVER. CONDITIONS SEEM
FAVORABLE FOR DEVELOPMENT ACROSS SD WITH 0-1KM MOISTURE
CONVERGENCE...BACK EDGE OF SYNOPTIC SCALE LIFT AND MLCAPE/MLCIN ALL
APPEARING TO BE PHASED AND READY TO TRIGGER DEVELOPMENT...WHICH HAS
INDEED RECENTLY OCCURRED NORTH. THUS CANNOT ARGUE WITH NAM AND
SEVERAL CONVECTION ALLOWING MODELS WHICH FIRE SD MCS AND DROP IT
INTO IA EARLY SUN MORNING PER FORWARD PROPAGATING MCS VECTORS.
CURRENT KS/NE/SD MOISTURE TRANSPORT DOES WEAKEN SOMEWHAT AS IT VEERS
INTO IA OVERNIGHT...BUT SHOULD STILL BE SUFFICIENT TO SUSTAIN MCS.
INSTABILITY AND SHEAR WILL NOT BE EXTREME INTO IA...BUT MAY STILL BE
SUFFICIENT FOR SEVERE POTENTIAL TO EXTENT BEYOND CURRENT SPC DAY 1
OUTLOOK FOR EARLY SUN MORNING.


.LONG TERM /SUNDAY THROUGH SATURDAY/...
ISSUED AT 309 PM CDT SAT JUL 25 2015

BEGINNING OF EXTENDED WILL BE MARKED BY LARGE RIDGE BUILDING INTO
NORTHERN PLAINS. EXPECT ANY PRECIPITATION ONGOING SUNDAY MORNING
TO PUSH QUICKLY EAST. HOWEVER...MAY SEE ADDITIONAL THUNDERSTORM
CHANCES IN THE AFTERNOON WITH BAND OF FORCING PUSHING EAST. MODELS
ARE NOT IN GOOD AGREEMENT WITH AMOUNT OF INSTABILITY AND
SHEAR...WITH NAM SIGNIFICANTLY MORE AGGRESSIVE THAN GFS...THOUGH
BOTH ARE SUFFICIENT TO WARRANT THUNDERSTORM POTENTIAL AND CHANCES
FOR ISOLATED SEVERE IN THE AFTERNOON. HAVE KEPT FORECAST DRY FOR
LATE SUNDAY NIGHT...EXPECTING SYSTEM TO PUSH EAST.
HOWEVER...CHANCES FOR THUNDERSTORMS WILL CONTINUE THROUGH MONDAY
AND TUESDAY AS LARGE LOW PRESSURE SYSTEM DEVELOPS IN THE NORTHWEST
TO HELP PUSH RIDGE EAST. WAVE PUSHING THROUGH MONDAY MAY BRING
PRECIPITATION TO THE SOUTH LATE IN THE DAY...THOUGH BEST FORCING
IS PRIMARILY TO THE WEST OF IOWA. BEST CHANCES FOR PRECIPITATION
BEGIN MONDAY NIGHT AND BOUNDARY PUSHES INTO MISSOURI RIVER VALLEY
WITH SURFACE LOW LIFTING NORTHEAST. MONDAY NIGHT PRECIPITATION
CONTINUES TO BE CONFINED PRIMARILY TO THE NORTH...NORTH OF IOWA.
HOWEVER...HAVE INCLUDED PRECIPITATION CHANCES FURTHER SOUTH GIVEN
MODEL UNCERTAINTY AND AMOUNT OF FORCING. HOWEVER...STRONG CAP
NOTED IN SOUNDINGS...ESPECIALLY IN THE NORTH AND MAY BE TOO
AGGRESSIVE WITH POPS MONDAY AND TUESDAY. BEST CHANCES FOR
PRECIPITATION WILL COME TUESDAY NIGHT AS BOUNDARY PUSHES SOUTH
ACROSS CENTRAL IOWA.

RIDGE WILL BRING CONTINUED HOT AND HUMID TEMPERATURES THROUGH
TUESDAY...WITH TUESDAY EXPECTED TO BE HOTTEST HOTTEST DAY AS RIDGE
SLIDES EAST. MAY NEED HEAT ADVISORY AT TIMES THROUGH
TUESDAY...ESPECIALLY IN THE SOUTH. WILL HOLD OFF ATTM WITH SOME
UNCERTAINTIES IN TEMPERATURES TRENDS DUE TO PRECIPITATION CHANCES
INTERFERING WITH HEATING. BEHIND BOUNDARY TUESDAY THROUGH END OF
THE PERIOD WILL SEE COOLER CONDITIONS...AND GENERALLY DRY.
TEMPERATURES WILL BE GENERALLY NEAR NORMAL.

&&

.AVIATION...25/18Z
ISSUED AT 1248 PM CDT SAT JUL 25 2015

CONFIDENCE ADMITTEDLY LOW THROUGH THE VALID PERIOD...MAINLY DUE TO
UNCERTAIN PRECIP TRENDS. CONVECTION OF VARIED STRENGTH WILL CROSS
THE MO RIVER INTO IA SHORTLY WHICH MAY BRING A PERIOD OF PRECIP TO
TAF SITES BUT COVERAGE AND AREAL EXTENT REMAINS QUESTIONABLE.
ADDITIONAL CONVECTION MAY ALSO DEVELOP FARTHER UPSTREAM IN THE
DAKOTAS REACHING IA DURING THE EARLY MORNING HOURS SUN. THUS HAVE
NOTHING MORE THAN VFR/VCSH WORDING FOR NOW UNTIL TRENDS IN LOWER
CONDITIONS AND THUNDER BECOME MORE CLEAR.


&&

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

&&

$$

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



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