000
FXUS63 KDMX 140445
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1145 PM CDT MON MAY 13 2013

.SHORT TERM.../TONIGHT /...
ISSUED AT 315 PM CDT MON MAY 13 2013

FIRST WAVE OF WARM AIR ADVECTION HAS MOVED EAST WITH THERMAL TROUGH
WEST OF AREA RIGHT NOW. THOUGH WINDS WILL DECOUPLE THIS EVENING...
SOUTHWEST FLOW WILL KEEP OVERNIGHT MINS QUITE MILD OVER MOST OF THE
AREA. LOOKING FOR LOWS TO REMAIN IN THE LOWER 50S NORTHEAST TO THE
UPPER 50S WEST. FEW HIGH CLOUDS OVER THE AREA OTHERWISE SLOW
INCREASE IN DEW POINTS DURING THE OVERNIGHT HOURS AS WELL.

.LONG TERM.../TUESDAY THROUGH MONDAY/...
ISSUED AT 315 PM CDT MON MAY 13 2013

THE LONG TERM FORECAST REMAINS CONFUSING AND FRAUGHT WITH ISSUES.
TUESDAY STILL LOOKS HOT...DRY...AND WINDY WITH A DEEP THERMAL
RIDGE PASSING OVERHEAD AND STRENGTHENING SOUTH SOUTHWEST WINDS AT
THE SURFACE. SHORT RANGE FORECAST MODELS STILL REMAIN WAY TOO
MOIST WITH THEIR DEWPOINTS AS COMPARED TO FORECAST AND UPSTREAM
SOUNDINGS...AND HAVE CONTINUED TO CARRY VALUES FAR BELOW GUIDANCE
AND MORE CONSISTENT WITH THE DEGREE OF MIXING EXPECTED. PREDICTING
THE DEPTH OF THE MIXED LAYER ON TUESDAY AFTERNOON IS PROVING
DIFFICULT AND WILL HAVE IMPLICATIONS FOR WIND SPEEDS AND FIRE
WEATHER CONCERNS AS OUTLINED IN THAT SECTION BELOW.
REGARDLESS...TEMPERATURES ARE STILL EXPECTED TO RISE INTO THE 90S
ACROSS MOST OR ALL OF THE AREA WITH RECORD HIGHS AT SOME STATIONS.
DID NOT MAKE ANY APPRECIABLE CHANGES TO THAT SEGMENT OF THE FORECAST.

THE COLD FRONT ENTERING OUR NORTHWEST CORNER ON TUESDAY EVENING IS
STILL EXPECTED TO MOVE ACROSS THE CWA AND REACH THE MISSOURI
BORDER BY AROUND SUNRISE WEDNESDAY. THE DRY AIR IN PLACE AND LACK
OF UPPER LEVEL FORCING WILL LIMIT THUNDERSTORM POTENTIAL ALONG THE
BOUNDARY AND WAS TEMPTED TO GO WITH A DRY FORECAST...HOWEVER AT
PEAK HEATING CONVECTIVE TEMPERATURE MAY BE REACHED AND COMBINED
WITH LOW LEVEL CONVERGENCE ALONG THE FRONT AND THE FACT THAT
SLIGHT POPS WERE ALREADY IN THE FORECAST DECIDED TO KEEP THEM.
HOWEVER...ANY STORMS THAT DO DEVELOP SHOULD BE ISOLATED. BEHIND
THE FRONT SOMEWHAT COOLER TEMPERATURES WILL PREVAIL FOR THE
REMAINDER OF THE WEEK.

FROM WEDNESDAY THROUGH THURSDAY THE PRECIPITATION FORECAST WILL BE
HEAVILY DEPENDENT ON THE DEGREE TO WHICH THE SURFACE FRONT IS ABLE
TO MOVE SOUTH INTO MISSOURI...OR WHETHER IT SLIDES BACK UP INTO
IOWA. WITH NEARLY ZONAL FLOW ALOFT ANY SHORTWAVE RIPPLES THAT MOVE
OVERHEAD WILL LIKELY TRIGGER SOME STORMS IN THE DECAYING FRONTAL
ZONE BUT HAVE LIMITED POPS TO OUR SOUTHERN COUNTIES FOR NOW.

LATE ON THURSDAY A MORE VIGOROUS SHORTWAVE WILL MOVE THROUGH THE
500 MB FLOW...AND LIKELY PULL THE OLD FRONTAL BOUNDARY BACK
NORTHWARD ACROSS THE CWA AS A WEAK WARM FRONT. THIS WILL INITIATE
MORE WIDESPREAD SHOWER AND THUNDERSTORM DEVELOPMENT GIVEN AN
INCREASINGLY MOIST AND UNSTABLE AIRMASS...AND BEGIN A SLIGHT
WARMING TREND FOR FRIDAY AND SATURDAY. BY THE END OF THE WORK WEEK
A LONGWAVE 500 MB TROUGH WILL BE PUSHING ACROSS THE WESTERN U.S.
BUT OVER IOWA SENSIBLE WEATHER WILL LARGELY DEPEND ON HOW FAR
NORTH THE WARM FRONT AND ENSUING AIRMASS PROGRESS. IF IT PUSHES
CLEAR UP INTO MINNESOTA THEN WE COULD BE CAPPED OFF AND LARGELY
DRY AT THE END OF THE WEEK...BUT IF IT REMAINS NEARBY THEN SEVERAL
MORE ROUNDS OF THUNDERSTORMS WILL BE POSSIBLE. DECREASED POPS A
BIT DURING THIS TIME FRAME BUT KEPT THEM IN THE CHANCE CATEGORY AS
THERE IS A LOT OF UNCERTAINTY.

FINALLY...THE LONGWAVE TROUGH WILL MOVE ACROSS IOWA SLOWLY BETWEEN
LATE SATURDAY AND EARLY MONDAY. GIVEN THAT WE WILL LIKELY RESIDE
WITHIN THE WARM SECTOR BY SATURDAY...AT LEAST ACROSS A PORTION OF
THE CWA...THIS WILL SET UP A SEVERE WEATHER THREAT FROM PEAK
HEATING TIME INTO SATURDAY NIGHT. THE DETAILS REMAIN UNCLEAR...BUT
AS OF THIS WRITING IT APPEARS TO BE THE BEST SEVERE WEATHER
SCENARIO WE HAVE SEEN IN OUR AREA SO FAR THIS YEAR. STAY TUNED AS
THE WEEK PROGRESSES BECAUSE THINGS COULD STILL SHIFT QUITE A BIT
BEFORE SATURDAY ARRIVES...BUT ANYONE WITH ACTIVITIES PLANNED THIS
WEEKEND SHOULD REMAIN ESPECIALLY COGNIZANT OF THIS POSSIBILITY.
HIGH POPS WILL PERSIST INTO EARLY NEXT WEEK WITH THE LARGE TROUGH
NEARBY...BUT THE SEVERE WEATHER THREAT SHOULD GRADUALLY DIMINISH
AFTER SATURDAY NIGHT AS A SOMEWHAT COOLER AIRMASS WORKS INTO THE
AREA.

&&

.AVIATION...14/06Z
ISSUED AT 1145 PM CDT MON MAY 13 2013

VFR CONDITIONS THROUGH THE TAF PERIOD...WITH SOUTHERLY WINDS
INCREASING THROUGH THE DAY TUESDAY. WINDS TO BECOME MORE
SOUTHWESTERLY TO WESTERLY AS A FRONTAL BOUNDARY APPROACHES TUESDAY
EVENING. SCT-BKN150 HIGH CLOUDS POSSIBLE THROUGH THE PERIOD.

&&

.FIRE WEATHER...
ISSUED AT 315 PM CDT MON MAY 13 2013

THERE IS SOME UNCERTAINTY REGARDING THE DEPTH OF THE MIXED LAYER
DEVELOPING DURING THE DAY ON TUESDAY...ALONG WITH IMPLICATIONS FOR
WIND AND DEWPOINT/HUMIDITY FORECASTS. HOWEVER...IT APPEARS LIKELY
THAT RELATIVE HUMIDITY WILL DROP TO 25 PERCENT OR LESS ACROSS MUCH
OF NORTHERN AND WESTERN IOWA BY TUESDAY AFTERNOON...AND SOUTH
SOUTHWEST WINDS WILL BE SUSTAINED AT 20 TO 25 MPH WITH GUSTS TO
WELL OVER 30 MPH FOR MUCH OF THE AFTERNOON AND EVENING. THERE IS
ENOUGH OF AN ELEVATED FIRE DANGER TO JUSTIFY A FIRE WEATHER WATCH
BEING ISSUED THIS AFTERNOON...AND AN UPGRADE TO A RED FLAG WARNING
IS POSSIBLE BY TUESDAY MORNING AS CRUCIAL DETAILS OF THE FORECAST
BECOME CLEARER. REGARDLESS OF WHETHER A WATCH...WARNING...OR
SPECIAL WEATHER STATEMENT IS IN EFFECT...TUESDAY WILL BE A
HAZARDOUS FIRE WEATHER DAY AND A HIGH DEGREE OF CAUTION IS
ADVISED.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FROM TUESDAY AFTERNOON THROUGH TUESDAY
EVENING FOR ADAIR-ADAMS-AUDUBON-BOONE-CALHOUN-CARROLL-CASS-
CERRO GORDO-CRAWFORD-DALLAS-EMMET-FRANKLIN-GREENE-GUTHRIE-
HAMILTON- HANCOCK-HUMBOLDT-KOSSUTH-PALO ALTO-POCAHONTAS-SAC-
WEBSTER- WINNEBAGO-WORTH-WRIGHT.

&&

$$

SHORT TERM...REV
LONG TERM...LEE
AVIATION...BEERENDS
FIRE WEATHER...LEE