Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 182340
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
640 PM CDT FRI JUL 18 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 338 PM CDT FRI JUL 18 2014

WIDESPREAD CU FIELD IN PLACE ONCE AGAIN THIS AFTERNOON WITH SOUTH
WINDS AS SURFACE RIDGE SLIDES ACROSS THE LOWER GREAT LAKES.  THIS CU
FIELD WILL DISSIPATE SOMEWHAT THIS EVENING...BUT MODEL SOUNDINGS
CONTINUE TO SHOW MOISTURE AROUND 5-8KFT.  ANTICIPATE AT LEAST SOME
SCATTERED CLOUDINESS TO PERSIST THROUGH THE NIGHT AS THE MOISTURE
REMAINS.  THE MORE EXTENSIVE CLOUDS ACRS NEBRASKA INTO WESTERN IOWA
SHOULD GRAZE THE FAR WEST BUT THE LOW CEILINGS ARE NOT EXPECTED TO
BE AN ISSUE WHEN LOOKING AT THE RELATIVELY DRY LOW LEVELS IN
FORECAST SOUNDINGS OVERNIGHT.  WINDS WILL DECOUPLE NICELY THIS
EVENING WITH LIGHT SOUTHEAST FLOW OVERNIGHT.  TEMPERATURES WILL
CONTINUE TO GAIN A FEW DEGREES TONIGHT...ESPECIALLY AS DEWPOINTS
COME UP BUT READINGS WILL STILL BE BELOW NORMAL FOR THIS TIME OF THE
YEAR.

.LONG TERM /SATURDAY THROUGH FRIDAY/...
ISSUED AT 338 PM CDT FRI JUL 18 2014

PRIMARY CONCERNS FOR THIS PERIOD REMAIN THE SAME AS PAST FEW
DAYS...TEMP/DEWPOINTS AND CONVECTIVE TRENDS INTO NEXT WEEK. LONG
WAVE PATTERN WILL BE IN TRANSITION THIS WEEKEND EVOLVING FROM
TRANSIENT ZONAL FLOW TO UPPER LEVEL RIDGE BUILDING FROM SWRN CONUS
INTO THE ROCKIES/HIGH PLAINS BY THE MIDDLE OF NEXT WEEK. TEMP AND
MOISTURE REBOUND WILL REMAIN SLOW TO START THE WEEKEND WITH
SPRAWLING ATYPICAL HIGH PRESSURE STILL AFFECTING THE ERN CONUS AND
KEEPING SIGNIFICANT RETURN FLOW AT BAY. INITIAL SURGE OF UPPER LEVEL
RIDGING WILL BUILD INTO THE MO VALLEY BY LATE SUN HOWEVER
INCREASING THETA-E ADVECTION INTO IA. THIS WILL RESULT IN M80S-
L90S HIGHS BY MON AND TUE...A TOUCH HIGHER THAN PREVIOUS
FORECAST...WITH HEAT INDICES WELL THROUGH THE 90S AND JUST
TOPPING 100F IN SPOTS THOSE DAYS.

THIS IS ALSO THE WINDOW WHERE PRECIP CHANCES COME INTO PLAY. WHAT
CONVECTIVE POTENTIAL THERE IS APPEARS TO BE ELEVATED INITIALLY WITH
LITTLE RUN TO RUN CONSISTENCY.  CONFIDENCE IS LOW WITH CONVECTIVE
PARAMETERIZATION SCHEMES LIKELY DEGRADING THE FORECAST AND NO
CONVECTION ALLOWING HI RES MODEL INPUT AT THIS TIME RANGE.
EXAMINATION OF GFS/ECMWF 310K ISENT SURFACES SHOW EITHER WEAK OR
NIL LIFT AND/OR BAROCLINICITY WITH LIMITED MOISTURE SO ONLY TOKEN
SLIGHT CHANCES ARE MENTIONED FAR NW LATE SAT NIGHT...AGAIN NE SUN
NIGHT...AND HAVE ALSO LOWERED POPS DUE TO SIMILAR THINKING MON
NIGHT. MOST APPRECIABLE CHANCES LOOK TO HOLD OFF UNTIL TUE OR TUE
NIGHT WHEN MORE SIGNIFICANT SHORT WAVE AND SYNOPTIC FORCING
ARRIVES AND MODIFIES THE AIRMASS. THIS FEATURE WILL ALSO INTRODUCE
SOME SURFACE CONVERGENCE...ALBEIT WEAK. THIS WILL ALSO BE A WINDOW
OF SEVERE WEATHER AND LOCALLY HEAVY RAINS. MUCAPES ARE EXTREME AND
ALTHOUGH 0-6KM SHEAR IS NOT TOO HIGH IT WOULD BE MORE THAN
ADEQUATE FOR SEVERE WEATHER. HEAVY RAIN EFFICIENCY WOULD ALSO BE
QUITE ELEVATED WITH OBVIOUS HIGH LEVELS OF PWS AND HIGH WARM CLOUD
DEPTHS CONSIDERING THE AIRMASS IN PLACE.

WEAK PRECIP CHANCES WILL LINGER EAST INTO WED MORNING WITH AIRMASS
MODIFYING SOMEWHAT BEHIND THE SYSTEM...BUT STILL STAYING SEASONAL.
AFTER A BREAK AROUND THU...ANOTHER WAVE LOOKS TO TOP THE RIDGE
INTRODUCING ANOTHER ROUND OF LOW CHANCES FOR THE NEW DAY 7 /FRI/.

&&

.AVIATION...19/00Z
ISSUED AT 640 PM CDT FRI JUL 18 2014

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH THE PERIOD. ANY
CIGS WILL GENERALLY BE BETWEEN 4 KFT AND 8 KFT. SOUTHERLY WINDS
WILL AGAIN BECOME BREEZY ON SATURDAY.

&&

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

$$

SHORT TERM...COGIL
LONG TERM...SMALL
AVIATION...DONAVON



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