000
FXUS63 KDMX 131727
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1227 PM CDT MON MAY 13 2013

.UPDATE...
ISSUED AT 1201 PM CDT MON MAY 13 2013

WARM AIR ADVECTION LIGHT SHOWERS CONTINUE TO DEVELOP ACROSS
NORTHERN IOWA AND SOUTHERN MN HEADING SOUTHEAST WITH H700 FLOW.
HAVE UPDATED ZONES TO INCLUDE A FEW SPRINKLES OVER THE NORTHERN
SECTIONS FOR THE NEXT HOUR OR TWO.

&&

.SHORT TERM.../TODAY/
ISSUED AT 416 AM CDT MON MAY 13 2013

TEMPS AND SUBTLE PRECIP TRENDS WILL BE THE MAIN CONCERN THIS
MORNING. KINEMATIC FORCING ASSOCIATED WITH CANADIAN SHORT WAVE
STILL WELL REMOVED FROM U.S. BORDER WILL REMAIN TO OUR NORTH AND
EAST TODAY. HOWEVER STRONG THERMODYNAMIC FORCING AHEAD OF THIS
FEATURE AND ADVANCING UPPER LEVEL RIDGE IS CURRENTLY PRODUCING
SCATTERED HIGH BASED SHOWERS ACROSS THE DAKOTAS. MODELS SUGGEST
THIS STRONG THETA-E ADVECTION WILL BRUSH NERN IA AROUND MIDDAY.
THERE IS A DECENT AMOUNT OF DRY AIR BELOW 3KM ON THE MASON CITY
SOUNDING...HOWEVER IT IS SATURATED ABOVE AND UVM ASSOCIATED WITH
STRONG WARM ADVECTION OFTEN IS SUFFICIENT TO GET AT LEAST
SOMETHING TO THE SURFACE. FEEL MODEL QPF AND AREAL COVERAGE OF
MEASURABLE POTENTIAL IS OVERDONE...BUT CONFIDENCE IS THERE TO
INTRODUCE A SHORT PERIOD OF SPRINKLES NE CENTERED AROUND 18Z.
FORECAST SOUNDINGS ADJUSTED FOR RECENT MIXING SUGGEST SOMETHING
CLOSE TO A MOS BLEND FOR HIGHS TODAY...WHICH PERFORMED WELL
YESTERDAY.

.LONG TERM.../TONIGHT THROUGH SUNDAY/
ISSUED AT 416 AM CDT MON MAY 13 2013

MAIN FORECAST CONCERN IS WITH HOT TEMPERATURES AND FIRE WEATHER
ON TUESDAY...AND THUNDERSTORM CHANCES LATE IN THE WEEK. LEANED
TOWARD SREF TONIGHT INTO WEDNESDAY AS GFS/NAM/ECMWF ARE TOO COLD
FOR TEMPS TOMORROW.

TONIGHT THROUGH WEDNESDAY...WAA CONTINUES TONIGHT INTO TOMORROW
AHEAD A COLD FRONT AND AREA OF LOW PRESSURE SET TO MOVE ACROSS THE
FORECAST AREA TUESDAY NIGHT. GOOD MIXING TO 900MB TOMORROW AND
POSSIBLY EVEN HIGHER. THIS MAY TAP INTO THE VERY WARM 850MB TEMPS
RANGING FROM 22C TO 25C ACROSS IOWA. WINDS LOOK TO GUST TO AROUND
25-30 KNOTS ACROSS THE NORTH AND SLIGHTLY LESS FURTHER SOUTH. VERY
DRY AIR MASS MOVING INTO THE STATE FROM THE PLAINS AND MODELS NOT
CAPTURING THE CURRENT DEW POINTS TRENDS OVER THIS AREA. FELT
CURRENT FORECAST AND MODELS WERE TOO HIGH FOR SURFACE DEW POINTS
TONIGHT INTO TOMORROW. PLUS WITH THE GOOD MIXING...LEANED TOWARD
LOWERING DEW POINTS 4 TO 6 DEGREES TONIGHT INTO TOMORROW WHICH WAS
FAIRLY CLOSE TO THE 900MB FROM THE NAM12. WITH THE DRIER AIR NOW
FORECAST...LEANED TOWARD INCREASING MAX TEMPS FOR TUESDAY ROUGHLY
1-3 DEGREES ACROSS THE FORECAST AREA. IN SOME PLACES FORECASTING A
RECORD HIGH FOR TOMORROW.

COLD FRONT SHOULD ENTER THE NORTHWEST PORTIONS OF THE FORECAST AREA
BY AROUND 00Z WEDNESDAY AND CONTINUE TO TRACK SOUTH OVERNIGHT INTO
WEDNESDAY MORNING. LIMITED MOISTURE WITH FRONT BUT ENOUGH
INSTABILITY AND FORCING TO KEEP MENTION OF SLIGHT CHANCES GOING
TUESDAY INTO WEDNESDAY. FRONT WASHES OUT ACROSS NORTHERN MISSOURI
DURING THE DAY WEDNESDAY AND MAY SEE A STRAY THUNDERSTORM ALONG
THE BORDER.

THURSDAY THROUGH MONDAY...SURFACE HIGH PRESSURE MOVES BACK IN
OVER THE STATE FOR THURSDAY AND LOOKS TO BE STRONG ENOUGH TO KEEP
CONDITIONS DRY FOR AT LEAST NORTHERN IOWA. ECMWF TRIES TO BRING
MOISTURE NORTHWARD DURING THE DAY AND MAY SEE THUNDERSTORM
ACTIVITY ACROSS THE SOUTH. EXTENDED MODELS IN DECENT AGREEMENT
WITH A SLOW MOVING SURFACE LOW AND UPPER LEVEL TROUGH TO AFFECT
THE PLAINS AND INTO THE CORN BELT FRIDAY INTO THE WEEKEND. BEST
THUNDERSTORM CHANCES IS SATURDAY NIGHT INTO SUNDAY WITH LLJ
DEVELOPING AHEAD OF THE TROUGH.

&&

.AVIATION...13/18Z
 ISSUED AT 1226 PM CDT MON MAY 13 2013

MAIN CONCERNS THIS PERIOD AND JUST BEYOND WILL BE WINDS. SOME MID
TO HIGH LEVEL BKN CLOUDS ACROSS THE FORECAST AREA WILL MOVE ESE
THIS AFTERNOON. OTHER THAN A FEW SPRINKLES...NO ORGANIZED
CONVECTION EXPECTED WITH THIS PUSH OF WARM AIR. HOWEVER...WINDS
HAVE BEEN GUSTING NORTHWEST SITES AS MIXED LAYER INCREASES IN
DEPTH. EXPECT MOST SITES TO SEE GUSTS TO 20 TO 25 KTS THROUGH 01Z
WHEN DECOUPLING OCCURS. PUSH OF WARMER AIR TO ARRIVE TUESDAY AND
DEPTH OF MIXED LAYER INCREASES AGAIN AFT 18Z. MAY SEE SUSTAINED SFC
WINDS 20 TO 25 KTS WITH GUSTS 35 TO 40KTS...MAINLY NORTH SITES...AFT 19Z
TUESDAY AS MIXING MAXIMIZED DURING THE AFTERNOON HOURS.

&&

.FIRE WEATHER...
ISSUED AT 416 AM CDT MON MAY 13 2013

FIRE WEATHER CONCERNS ARE INCREASING SOMEWHAT TODAY WITH STRONGER
WIND AND LOW RH DUE TO MIXING.  LOCAL AND UPSTREAM SOUNDINGS
INITIALIZED TOO MOIST IN THE LOWEST 1.5KM AT 00Z IN MOST MODELS SO
HAVE DEWPOINTS BELOW MOS AND CONSENSUS.  RAP WAS THE DRIEST AND
CLOSEST TO REALITY.  DID NOT GO THAT LOW YET BUT LEANED IN THAT
DIRECTION.  THIS RESULTED IN MIN RH AROUND 25 PERCENT IN 5-6
COUNTIES W CENTRAL AND NW...BUT SUSTAINED WINDS WILL STAY JUST BELOW
RED FLAG WARNING CRITERIA /25 MPH/.  THUS NO HEADLINES TODAY...BUT
WILL MENTION IN HWO AND HIGHLIGHT IN FIRE WEATHER FORECAST.  DRYNESS
OF FUELS ALSO SOMEWHAT IN QUESTION OVER NRN IA.  USED AS A PROXY FOR
FARTHER WEST WHERE CLIMATE DATA IS MORE QUESTIONABLE...MASON CITY
HAS HAD WETTEST METEOROLOGICAL SPRING TO DATE.

TUESDAY LOOKS TO BE HOTTER AND MUCH DRIER THAN PREVIOUSLY
ANTICIPATED AS MODELS OVERDOING THE SURFACE DEW POINTS ACROSS
CENTRAL IOWA. MIXING UP TO 3000 TO 3500 FEET BY TUESDAY AFTERNOON
WILL RESULT IN DEW POINTS IN THE UPPER 40S TO THE LOWER 50S.
HENCE...RH VALUES ARE FORECAST TO DROP TO 25 PERCENT OR LESS
GENERALLY ALONG AND WEST OF INTERSTATE 35. TEMPS WILL RAPIDLY
INCREASE IN THE MORNING AND THE 25 PERCENT RH VALUES LOOK TO BE
REALIZED BY AROUND NOON. SOUTHWEST WINDS GUSTING TO 30 TO 35 MPH
BY THE AFTERNOON. SO WITH THE LOW RH...GUSTY WINDS...AND HOT
TEMPS...BORDERLINE POTENTIAL FOR A RED FLAG WARNING ACROSS WESTERN
PORTIONS OF THE FORECAST AREA.

&&

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

$$

UPDATE...REV
SHORT TERM...SMALL
LONG TERM...PODRAZIK
AVIATION...REV
FIRE WEATHER...SMALL/PODRAZIK