000
FXUS63 KDMX 230814
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
314 AM CDT THU MAY 23 2013

.SHORT TERM.../TODAY /...
ISSUED AT 313 AM CDT THU MAY 23 2013

UPPER LOW WILL MOVE OUT OF THE AREA TODAY AS SURFACE TROUGH
EXTENDING FROM NRN IL INTO NWRN IA ROTATES SOUTH ACROSS THE STATE
THIS MORNING. ISOLATED TO SCATTERED SHOWERS OVER THE EAST HALF OF
THE CWA SHOULD COME TO AN END EARLY THIS MORNING AS DRIER AIR
BEGINS TO PUSH SOUTH BEHIND THE TROUGH. HIGH PRESSURE CENTERED
OVER NRN MANITOBA WILL PUSH SOUTH TODAY. THIS WILL BRING GRADUAL
CLEARING FROM THE NORTH TODAY. COOL H8 AIR FOR THIS TIME OF THE
YEAR WILL PUT A LIMIT ON THE HIGH TEMPS TODAY WITH PROGS OF +3 TO
+7 ACROSS THE STATE THIS AFTERNOON. SUNSHINE SHOULD OVERCOME THE
COLD AIR ADVECTION AND GIVE HIGHS IN THE 60S ACROSS THE CWA THIS
AFTERNOON.

.LONG TERM.../TONIGHT THROUGH TUESDAY/...
ISSUED AT 313 AM CDT THU MAY 23 2013

LITTLE HAS CHANGED IN OVERALL FORECAST THINKING THIS SHIFT.
TONIGHT AND FRIDAY WILL REMAIN DRY AND UNEVENTFUL WITH A LARGE
SURFACE HIGH PRESSURE CENTER SLIDING FROM THE ARROWHEAD OF
MINNESOTA ACROSS WISCONSIN AND INTO THE GREAT LAKES REGION. THIS
WILL RESULT IN NORTHEAST WINDS THIS EVENING BECOMING CALM OR LIGHT
AND VARIABLE...THEN TURNING AROUND TO SOUTH SOUTHEAST ON FRIDAY.
WITH CALM/LIGHT WINDS AND DRY AIR FILTERING OUT OF THE HIGH
PRESSURE AREA TEMPERATURES WILL DROP TO WELL BELOW SEASONAL LEVELS
TONIGHT ESPECIALLY ACROSS OUR NORTHEASTERN COUNTIES WHERE FRIDAY
MORNING LOWS IN THE UPPER 30S ARE FORECAST IN SOME AREAS.
HOWEVER...TEMPERATURES ARE NOT EXPECTED TO REACH LEVELS SUFFICIENT
FOR FROST FORMATION.

BY FRIDAY NIGHT THE AXIS OF THE CENTRAL U.S. 500 MB RIDGE WILL BE
LOCATED OVER IOWA...WHILE A LARGE 500 MB LOW CENTERED OVER THE
PACIFIC NORTHWEST WILL HAVE CARVED OUT A DEEP BUT BROAD TROUGH
DOWN THE WEST COAST. THIS GENERAL PATTERN WILL THEN REMAIN IN
PLACE THROUGH THE ENTIRE REMAINDER OF THE SEVEN DAY FORECAST. THIS
WILL LEAD TO AN OVERALL WET AND ACTIVE FORECAST FOR THE AREA THIS
WEEKEND AND THE FIRST HALF OF NEXT WEEK AS A TRAIN OF MID-LEVEL
IMPULSES MOVE UP THE SOUTHWESTERLY FLOW ON THE WESTERN FLANK OF
THE RIDGE AND OVER THE MIDWESTERN STATES. UNFORTUNATELY ANY
ATTEMPT TO PIN DOWN THE PRECISE TIMING AND LOCATION OF THESE
IMPULSES...MUCH LESS THE PRECIPITATION THEY PRODUCE WHICH WILL
ALSO BE DEPENDENT ON THE LOCATION OF SUBTLE SURFACE BOUNDARIES AND
OTHER DIFFICULT TO PREDICT FEATURES...IS FUTILE AT THIS POINT.
THEREFORE THE FORECAST REMAINS PEPPERED WITH POPS FOR THE
FORESEEABLE FUTURE. FROM FRIDAY NIGHT THROUGH SUNDAY HAVE
MAINTAINED POPS GENERALLY IN THE 40 TO 60 RANGE...WHICH THEN
DECREASE STEADILY INTO NEXT WEEK AS CONFIDENCE DECREASES FURTHER.
THE GOOD NEWS IS THAT THE OVERALL SYNOPTIC SET UP DOES NOT LEND
ITSELF WELL TO LARGE SEVERE WEATHER EVENTS...HOWEVER AT THIS TIME
OF YEAR SUCH A PROLONGED PERIOD OF THUNDERSTORM CHANCES IMPLIES
THAT SOME DEGREE OF SEVERE WEATHER WILL PROBABLY BE ACHIEVED AT
SOME POINT. IN ADDITION...HEAVY RAIN COULD RESULT IN LOCALIZED
FLASH FLOODING AND POSSIBLY LARGER SCALE AREAL FLOODING DEPENDING
ON WHETHER THUNDERSTORMS FORM OVER THE SAME AREAS DAY AFTER DAY OR
SHIFT AROUND THE REGION A BIT.

&&

.AVIATION...23/06Z
 ISSUED AT 1055 PM CDT WED MAY 22 2013

MAIN CONCERNS CONTINUE THROUGH 12Z WITH MVFR/IFR CIGS AND DZ/-SHRA
CROSSING THE AREA WITH LAST UPPER LEVEL TROUGH AND SFC TROUGH NOW
HEADING SOUTHEAST ACROSS CENTRAL IOWA. UPPER LEVEL SYSTEM OVER
KMKE BUT STILL HAS WRAP AROUND MOISTURE EXTENDING BACK INTO
SOUTHERN MN AND NORTHERN IA AFFECTING MOST OF THE EASTERN TAF
SITES INCLUDING KMCW...KALO...KOTM AND TO A LESSER EXTENT KFOD AND
KDSM THOUGH BOTH OF THOSE SITES WILL SEE PASSING -DZ OR -SHRA
THROUGH 12Z. FINALLY THE LOW DRIFTS EAST AND VFR CONDITIONS
EXPECTED TO RETURN TO AREA AFT 12-15Z AS WEAK RIDGE OF HIGH
PRESSURE BUILDS SOUTHEAST. SOME CONCERN WITH EXTENT OF
CLEARING...HOWEVER AS SUBJECTIVE H850 ANALYSIS SHOWS TROUGH AXIS
BACK TO NEXT UPSTREAM SYSTEM OVER UTAH. WITH BRIEF RETURN TO
NORTHWEST FLOW ALOFT...CLEARING STILL MORE LIKELY TO OCCUR THAN
NOT DUE TO LATE MAY SOLAR INFLUENCE.

&&

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

&&

$$

SHORT TERM...MS
LONG TERM...LEE
AVIATION...REV