000
FXUS63 KDMX 122330
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
630 PM CDT SUN MAY 12 2013

.SHORT TERM.../TONIGHT /...
ISSUED AT 304 PM CDT SUN MAY 12 2013

FEW CONCERNS FOR THE OVERNIGHT PERIOD. RIDGE WILL PASS EAST OF THE
REGION BY EARLY MORNING...MEANWHILE AIRMASS REMAINS QUITE DRY WITH
DEW POINTS IN THE TEENS AND 20S ONCE AGAIN THIS AFTERNOON. LOWS
TONIGHT WILL BE COOLER EAST IN THE CEDAR RIVER VALLEY...OTHERWISE
LOOKING FOR A MODERATION IN TEMPERATURES ACROSS THE FORECAST AREA
TONIGHT. WINDS WILL GO CALM AND THEN LIGHT WEST SOUTHWEST TOWARD
MORNING. SKIES WILL REMAIN CLEAR UNTIL LATE NIGHT WHEN INCREASING
HIGH CLOUDS APPROACH FROM THE WEST AHEAD OF THE NEXT UPSTREAM SHORT
WAVE.

.LONG TERM.../MONDAY THROUGH SUNDAY/...
ISSUED AT 304 PM CDT SUN MAY 12 2013

LONGWAVE 500 MB TROUGH WILL CONTINUE TO MOVE AWAY ACROSS THE
EASTERN U.S. ON MONDAY...WITH A DEEP THERMAL RIDGE BUILDING ACROSS
THE WESTERN HALF OF THE CONUS. AT THE SURFACE THIS WILL BE
REFLECTED IN THE COOL HIGH PRESSURE RIDGE THAT AFFECTED OUR AREA
THIS WEEKEND MOVING EASTWARD...BRINGING A RAPID RETURN TO
SOUTHERLY LOW LEVEL FLOW BY MIDDAY MONDAY. THE RESULT OF THIS
PATTERN WILL BE AN IMPRESSIVE WARMING TREND OVER THE NEXT COUPLE
OF DAYS CULMINATING ON TUESDAY. THE 500 MB RIDGE AXIS WILL MOVE
OVERHEAD DURING THE DAY ON TUESDAY CONCURRENT WITH SURFACE WINDS
TURNING TO NORTHWEST AND INCREASING AHEAD OF AN APPROACHING COLD
FRONT...MORE ON THAT BELOW. QUESTIONS REMAIN AS TO HOW WARM WE
WILL GET ON TUESDAY PARTICULARLY PERTAINING TO THE MIXING
DEPTH...HOWEVER FORECAST SOUNDINGS AND TEMPERATURES ALOFT COMBINED
WITH THE WIND DIRECTION AND SUNSHINE AT THIS TIME OF YEAR CONTINUE
TO SUPPORT A FORECAST ABOVE ALL GUIDANCE...ESPECIALLY WEST OF
INTERSTATE 35 WHERE MANY AREAS WILL APPROACH THE MID 90S. WILL
CONTINUE TO CARRY NEAR RECORD HIGHS WORDING AND HAVE BUMPED
TEMPERATURES UP ANOTHER DEGREE OR TWO OVER PREVIOUS FORECAST
PACKAGE. IN ADDITION TO THE HEAT...STRONG MIXING WILL PROMOTE
LOWER DEWPOINTS AT THE SURFACE AND RELATIVE HUMIDITY WILL DROP TO
AROUND 30 PERCENT IN SOME AREAS...COMBINING WITH STRONG AND GUSTY
WINDS TO PROMOTE AN ENHANCED FIRE DANGER ACROSS THE CWA. THIS WILL
BE FURTHER ADDRESSED AS TUESDAY DRAWS NEARER.

RETURNING TO THE SUBJECT OF THE APPROACHING COLD FRONT...A COMPACT
BUT ROBUST 500 MB SHORTWAVE WILL MOVE QUICKLY ALONG THE
CANADA/U.S. BORDER ON MONDAY AND NIGHT AND TUESDAY OVER THE TOP OF
THE DEEP LAYER RIDGE. A SURFACE LOW WILL DEVELOP RAPIDLY BENEATH
THIS FEATURE...AND PUSH A COLD FRONT INTO NORTHWESTERN IOWA BY
TUESDAY EVENING AND ACROSS THE REMAINDER OF THE STATE BY WEDNESDAY
MORNING. A CAPPING INVERSION AND LACK OF DEEP LIFT WITH THE LOW
MOVING BY FAR TO THE NORTH WILL LIMIT RAINFALL CHANCES...BUT A FEW
THUNDERSTORMS ARE POSSIBLE ALONG THE BOUNDARY EARLY TUESDAY NIGHT
AND HAVE MAINTAINED 20 POPS TO ACCOUNT FOR SUCH. THE AIRMASS
BEHIND THE FRONT WILL NOT BE PARTICULARLY COLD BUT WILL BE
SUFFICIENT TO HOLD DAYTIME TEMPERATURES IN THE 70S FOR THE LATTER
HALF OF THE WEEK.

IT APPEARS THAT THE AFOREMENTIONED COLD FRONT WILL STALL SOMEWHERE
NEAR THE IOWA/MISSOURI BORDER ON WEDNESDAY...WITH THE 500 MB FLOW
BECOMING ZONAL THROUGH AT LEAST FRIDAY AND THE BOUNDARY WOBBLING
AROUND OUR AREA THROUGH THAT TIME FRAME. THIS WILL PROMOTE SEVERAL
DAYS OF THUNDERSTORM CHANCES...PARTICULARLY IN THE EVENING AND
EARLY NIGHTTIME HOURS AND COINCIDENT WITH ANY SHORTWAVE RIPPLES
MOVING QUICKLY THROUGH THE ZONAL FLOW. HAVE TRENDED POPS SOMEWHAT
TOWARD THE DIURNALLY FAVORED TIMES...BUT KEPT THEM THROUGH THE
DAYTIME AS WELL DUE TO THE UNPREDICTABILITY OF THE DETAILS OF THE
SCENARIO AT THIS RANGE. IT DOES APPEAR THAT THUNDERSTORM AND
SEVERE WEATHER CHANCES WILL INCREASE SOMEWHAT TOWARD NEXT WEEKEND
AS A DEEP 500 MB TROUGH MOVES INTO THE WESTERN U.S. AND TOWARD THE
MIDWEST. THIS FEATURE WILL LIKELY EJECT STRONGER SHORTWAVE
IMPULSES OUT AHEAD OF IT...WITH SEVERAL ROUNDS OF THUNDERSTORMS
LIKELY FROM LATE FRIDAY THROUGH THE WEEKEND. THIS WILL BEAR CLOSE
MONITORING LATER THIS WEEK.

&&

.AVIATION...13/00Z
 ISSUED AT 623 PM CDT SUN MAY 12 2013

VFR CONDITIONS TO CONTINUE TONIGHT THROUGH MONDAY EVENING. CLEAR
SKIES WILL CONTINUE THROUGH THE EARLY MORNING HOURS...UNTIL
WIDESPREAD HIGH AND MID LEVEL CLOUDS MOVE INTO IOWA BY 14Z. WINDS
WILL BE LIGHT AND VARIABLE OVERNIGHT...AND THEN OUT OF THE SOUTH
AT AROUND 10 TO 15 KNOTS BY MONDAY AFTERNOON.

&&

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

$$

SHORT TERM...REV
LONG TERM...LEE
AVIATION...KOTENBERG