Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 011740
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1240 PM CDT FRI AUG 1 2014

...UPDATED AVIATION DISCUSSION...

.SHORT TERM /TODAY/...
ISSUED AT 337 AM CDT FRI AUG 1 2014

NORTHWEST FLOW ALOFT ACROSS THE STATE WILL CONTINUE TO SHUTTLE
IMPULSES THROUGH THE AREA TODAY. THE INITIAL IMPULSE WILL PASS BY
EARLY THIS MORNING WITH SHOWERS ENDING NEAR THE MISSOURI BORDER.
ANOTHER IMPULSE ARRIVES BY LATE MORNING AND INTO THE AFTERNOON.
THE ASSOCIATED KINEMATICS SHOULD PROVIDE ENOUGH FORCING IN THE
WEAKLY CAPPED ENVIRONMENT TO GENERATE A FEW THUNDERSTORMS. SFC
BASED CAPES OF 1000-1500 J/KG ARE POSSIBLE BY THE AFTERNOON OVER
NORTHEAST IOWA. THE COOL TEMPERATURES ALOFT AND RESULTANT
SEASONALLY SHALLOW MELTING LEVELS IN ADDITION TO THE SFC
INSTABILITY WILL KEEP THE POTENTIAL FOR A LOCAL STORM TO PRODUCE
PENNY TO QUARTER SIZED HAIL. TEMPERATURES AGAIN WILL BE IN THE
UPPER 70S TO MID 80S WITH LIGHT WINDS EXPECTED.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
ISSUED AT 337 AM CDT FRI AUG 1 2014

FROM TONIGHT THROUGH SATURDAY A SURFACE HIGH PRESSURE AREA WILL
LIE ACROSS IOWA WITH RIDGING SLOWLY BUILDING ALOFT...LEADING TO A
CONTINUATION OF LIGHT WINDS AND GENERALLY QUIET AND DRY WEATHER. A
FEW SHOWERS OR STORMS WILL REMAIN POSSIBLE AT TIMES...BUT WOULD
BE SO ISOLATED THAT THE LOW AREAL COVERAGE AND PROBABILITY
PRECLUDE MENTION IN THE OUTGOING FORECAST. ON SATURDAY NIGHT THE
SURFACE HIGH WILL BEGIN TO MOVE OFF TO THE EAST BRINGING A RETURN
OF LIGHT SOUTHERLY FLOW ACROSS THE AREA. CONCURRENTLY...A WEAK 500
MB IMPULSE WILL OVERTOP THE RIDGE AND MOVE DOWN ACROSS THE DAKOTAS
AND MINNESOTA TOWARD IOWA. AS THIS SHORTWAVE MOVES OVER OUR
FORECAST AREA ON SUNDAY AND SUNDAY NIGHT IT MAY GENERATE MORE
SCATTERED THUNDERSTORMS AND POPS HAVE BEEN INCREASED A BIT
ACCORDINGLY.

FROM MONDAY THROUGH ABOUT THURSDAY A MUCH MORE ACTIVE WEATHER
PATTERN WILL DEVELOP...INITIALLY DUE TO ADDITIONAL MID LEVEL
IMPULSES ROUNDING THE RIDGE AND THEN FROM A DEEPER BUT NOT
PARTICULARLY ROBUST LONGWAVE TROUGH SWEEPING OVERHEAD AROUND
WEDNESDAY NIGHT AND THURSDAY. WITH THE FIRST COUPLE OF ROUNDS ON
MONDAY AND TUESDAY THERE IS SOME UNCERTAINTY REGARDING THE
PLACEMENT OF THE SO CALLED RING OF FIRE...WHICH THE LONGER RANGE
MODELS HAVE BEEN CONSISTENTLY PLACING ACROSS OUR NORTHEAST AND UP
INTO MINNESOTA AND WISCONSIN...BUT WHICH TONIGHTS 00Z GFS AND
ECMWF HAVE SUDDENLY SHIFTED SOUTHWARD MORE DIRECTLY ACROSS OUR
AREA. THIS WILL HAVE A SIGNIFICANT IMPACT ON POPS DURING THIS TIME
FRAME AS WELL AS TEMPERATURES...WHICH WILL OBVIOUSLY BE COOLER
WITHIN THE CONVECTIVE ZONE THAN IN THE CLEARER SOUTH SOUTHWEST
FLOW TO THE SOUTH OF THIS ZONE. FOR NOW HAVE STUCK WITH A MORE OR
LESS PERSISTENCE FORECAST DUE TO THE ABERRATIONAL NATURE OF THESE
TWO MODEL RUNS...BUT WILL NEED TO CLOSELY MONITOR THIS POSSIBILITY
OVER THE NEXT DAY OR TWO. THE WEDNESDAY TO THURSDAY PERIOD SEEMS
CLOSER TO A SLAM DUNK FOR RAINFALL WITH THE LONGWAVE TROUGH MOVING
THROUGH...AND HAVE CONTINUED LIKELY POPS ALTHOUGH THERE IS SOME
WIGGLE ROOM WITH REGARD TO TIMING AND INSTANTANEOUS COVERAGE. IN
ANY EVENT...IT APPEARS PROBABLE THAT MOST OF THE AREA WILL RECEIVE
SOME BENEFICIAL RAINFALL NEXT WEEK AND THE QUESTION IS LARGELY HOW
MUCH AND WHEN. BEHIND THE LONGWAVE TROUGH...TOWARD THE END OF
NEXT WEEK...THE OVERALL PATTERN APPEARS COOL AND DRY ONCE AGAIN.

&&

.AVIATION...01/18Z
ISSUED AT 1240 PM CDT FRI AUG 1 2014

HIGH PRESSURE WILL REMAIN IN CONTROL OF THE WEATHER THROUGH
SATURDAY. VERY DIFFICULT TO DISCERN A WIND DIRECTION/SPEED THROUGH
TOMORROW AND WITH SUBSIDENCE AND CLEAR SKIES TONIGHT...HAVE IFR
TO MVFR FOG MENTIONED AT ALL TAF SITES EXCEPT DSM. THERE IS A WEAK
SHORTWAVE LOOKS TO PASS ACROSS SOUTHERN IOWA AND MISSOURI TODAY
AND MAY SPAWN A FEW ISOLATED THUNDERSTORMS THIS AFTERNOON. HAVE
LOW CONFIDENCE WITH MENTIONING ANY TS IN TAFS WITH MINIMAL
COVERAGE AND PULSE NATURE STORMS.

&&

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

&&

$$

SHORT TERM...DONAVON
LONG TERM...LEE
AVIATION...PODRAZIK



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