Area Forecast Discussion
Issued by NWS Des Moines, IA

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855
FXUS63 KDMX 172046
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
346 PM CDT SUN MAY 17 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 329 PM CDT SUN MAY 17 2015

PRECIP AND SIGNIFICANT WEATHER POTENTIAL SEEMS TO BE ENDING ACROSS
THE FORECAST AREA.  PARENT UPPER LOW ALONG DAKOTAS/MN BORDER
CONTINUES TO DRIFT AWAY WITH ATTENDANT 120KT SPEED MAX PUSHING DRY
SLOT THROUGH IA. LARGE SCALE QG FORCING ASSOCIATED WITH THE LOW
CONTINUES TO ARC FROM SYSTEM ACROSS WI AND IMMEDIATE MS
VALLEY...INCLUDING ERN IA.  HOWEVER DEEP MOISTURE CONVERGENCE IS
WELL PAST IA INTO IL SO EXPECT OUR ONLY REAL CONCERN TO BE
EXTRAPOLATION OF CURRENT NWRN IA CONVECTION.  MUCH OF THE 500 OR SO
UNCAPPED MLCAPES ARE WEIGHTED IN THE LOWEST 3KM WITH WEAK MID LEVEL
LAPSE RATES SO DO NOT EXPECT MUCH IN THE WAY OF A HAIL THREAT.
EFFECTIVE SHEAR IS SUFFICIENT FOR ORGANIZATION...BUT QUESTION HOW
MUCH DEEP CONVECTION CAN GET GOING. THE THREAT IS NOT TOO HIGH...BUT
THERMODYNAMICALLY WEIGHTED SHALLOW WEAK TORNADOES/FUNNELS CANNOT BE
RULED OUT DUE TO LOW LCLS AND OVER 150 J/KG 0-3KM CAPES. FAIRLY FAST
MOVEMENT...LITTLE FOCUS...AND LACK OF 0-1KM KINEMATICS WILL LIKELY
PRECLUDE MUCH POTENTIAL HOWEVER...ESPECIALLY IF IT HAS NOT SHOWN ITS
HAND YET.

MOST LIKELY FORECAST WILL BE SCATTERED NON-SEVERE CONVECTION EXITING
THE FORECAST AREA WITH PARENT LOW EARLY THIS EVENING FOLLOWED BY
CLEARING.  WINDS WILL REMAIN SOMEWHAT BRISK INTO THE NIGHT...BUT
LOSE A GOOD DEAL OF GUSTINESS WITH LOSS OF HEATING AND MIXING.  HAVE
COOLED LOW TEMPS A BIT WITH OVERNIGHT MINS NOW FROM 40 NW TO 55 SE
BASED ON CLEARING AND UPSTREAM OBS.

.LONG TERM /MONDAY THROUGH SUNDAY/...
ISSUED AT 329 PM CDT SUN MAY 17 2015

LARGE UPPER LEVEL LOW WILL CONTINUE TO PULL NORTHEASTWARD FOR THE
BEGINNING OF THE WORK WEEK. BEHIND THE LOW MUCH COOLER AIR WILL
PUSH IN...WITH MAIN CONCERN FOR BEGINNING OF PERIOD TEMPERATURES.
CAA AND SUBSIDENCE WILL PUSH IN BEHIND LOW WITH GUIDANCE GOING
MUCH COOLER THAN NORMAL ACROSS THE AREA. FEEL THAT GUIDANCE IS A
BIT AGGRESSIVE...AND HAVE GENERALLY KEPT TEMPERATURES ABOVE
GUIDANCE AND BUMPED UP A FEW DEGREES. HOWEVER...TEMPERATURES WILL
STILL BE AROUND 10 DEGREES BELOW NORMAL. CONCERN WILL COME WITH
COLD OVERNIGHT LOW TEMPERATURES...ESPECIALLY MONDAY NIGHT IN THE
NORTH. GUIDANCE CONTINUES TO KEEP LOWS NEAR FREEZING...AND MAY
SEE FROST OR BRIEF FREEZING TEMPERATURES. EXPECT WINDS TO REMAIN
UP OVERNIGHT AND CLOUDS ACROSS THE FAR NORTH...WHICH WILL HELP TO
LIMIT COOLING...THOUGH WITH HIGH PRESSURE AND DRY AIR IN
PLACE...WILL NEED TO BE MONITORED FOR FROST/FREEZE POTENTIAL IN
THE NORTH.

NEXT CONCERN WILL BECOME PRECIPITATION EXPECTED TO PUSH INTO
WESTERN IOWA AS WEAK LOW LIFTS NORTH IN MOSTLY ZONAL FLOW. MODELS
ARE IN DECENT AGREEMENT WITH TIMING AND PLACEMENT OF THIS
SYSTEM...THOUGH WITH WEAK FLOW DO NOT HAVE HIGH CONFIDENCE IN
TIMING OF ONSET OF PRECIPITATION...ESPECIALLY WITH HIGH PRESSURE
IN PLACE. ATTM INSTABILITY IS LIMITED AND HAVE THEREFORE KEPT
THUNDER MENTION OUT...THOUGH MAY SEE ISOLATED THUNDER IN THE
AFTERNOON WEDNESDAY. SYSTEM WILL DROP SOUTH AS ANOTHER HIGH PUSHES
IN FROM CANADA...AGAIN BRINGING COOLER TEMPERATURES...THOUGH ONLY
SLIGHTLY BELOW NORMAL THROUGH THE END OF THE WORK WEEK. MODELS
CONTINUE TO BRINGING ANOTHER LARGE AREA OF LOW PRESSURE ONSHORE
ACROSS CALIFORNIA BEGINNING FRIDAY...WITH SYSTEM EXPECTED TO PUSH
INTO IOWA SATURDAY AND SUNDAY. GFS CONTINUES TO BE MORE
AGGRESSIVE...BRINGING WELL DEFINED UPPER LEVEL LOW INTO NORTHERN
PLAINS WHILE ECMWF IS GENERALLY MORE OPEN WAVE...AND SYSTEM WILL
NEED TO BE MONITORED.

&&

.AVIATION...17/06Z
ISSUED AT 647 PM CDT SAT MAY 16 2015

AREAS OF MVFR CIGS SHOULD BECOME VFR BY MID MORNING AS THE DRY SLOT
FROM A LOW PRESSURE SYSTEM SHIFTS INTO IOWA.  A SURFACE LOW WILL
SHIFT INTO MN THIS AFTERNOON WITH A FRONTAL BOUNDARY EXTENDING FROM
IT INTO NE IA AND WISCONSIN.  ADDITIONAL STORMS COULD RE-FIRE NEAR
THE LOW AND FRONTAL BOUNDARY AND MAY IMPACT KMCW AND KALO.  AT THIS
POINT TOO MUCH UNCERTAINTY EXISTS AS TO THE EXTENT OF
DESTABILIZATION AND WHERE THE FRONT WILL BE THUS STORM COVERAGE AND
LOCATION IS TOO UNCERTAIN TO PUT IN TAFS AT THIS POINT.  WINDS WILL
BE INCREASING BY MID MORNING OUT OF THE SOUTH THEN TURNING MORE
WESTERLY AT SPEEDS OF 20G30KTS.


&&

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

$$

SHORT TERM...SMALL
LONG TERM...AWB
AVIATION...FAB



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