Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 312330
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
628 PM CDT MON AUG 31 2015

...UPDATED FOR 01/00Z AVIATION DISCUSSION...

.SHORT TERM /TONIGHT/...
ISSUED AT 312 PM CDT MON AUG 31 2015

HIGH REMAINS ANCHORED OVER THE OHIO RIVER VALLEY WITH RETURN
SOUTHEAST FLOW BEGINNING TO TAKE HOLD. ABUNDANT LOW LEVEL MOISTURE
CONTINUES TO PROP UP DEW POINTS...NOW IN THE LOWER 70S...WITH CU
FIELD ACROSS MOST OF THE FORECAST AREA AT THIS TIME.  DESPITE THE
CLOUDS TEMPERATURES HAVE CLIMBED INTO THE LOWER TO MID 80S PRIMARILY
DUE TO SLIGHTLY INCREASED AFTERNOON MIXING. SYNOPTIC MODELS AGAIN
SUGGEST A GENERAL RELAXATION OF THE SFC PRESSURE GRADIENT OVERNIGHT
WITH WINDS OF 6 TO 8 MPH BY 10-13Z. ITS LIKELY ONCE AGAIN THAT SOME
FOG WILL DEVELOP OVERNIGHT.  THOUGH WIDESPREAD DENSE FOG IS NOT
LIKELY THERE MAY BE A FEW POCKETS OF LOW VISIBILITY BY MORNING. FOR
NOW WILL GO PATCHY ACROSS THE BOARD. USING THE MET GUIDANCE
CROSSOVER TEMPERATURES SUGGEST ABOUT A 2-5 DEGREE SPREAD FROM
CURRENT DEW POINTS SO FOG SHOULD OCCUR ONCE THE WINDS DROP OFF
TOWARD DAWN. LOOKING MAINLY FOR 3-5SM ON AVERAGE WITH POCKETS OF 1-
2SM AND MAYBE A FEW SPOTS TO 1/4-1/2 MILE. OTHERWISE...LOWS IN THE
MID TO UPPER 60S WITH EITHER SOME STRATUS OR FOG OR BOTH REFORMING
OVERNIGHT.

.LONG TERM /TUESDAY THROUGH MONDAY/...
ISSUED AT 312 PM CDT MON AUG 31 2015

STILL LITTLE OVERALL CHANGE IN THE FORECAST FOR THE WEEK.
NORTHWEST IOWA WILL CONTINUE TO BE ON THE PERIPHERIES OF THE NE
STEERING FLOW ALOFT AND BE SUBJECTED TO MULTIPLE SHORT WAVES IN
THE MIDDLE OF THE WEEK. AFTER WHICH THE RIDGE WILL AMPLIFY INTO
THE WEEKEND AS A TROUGH DIGS INTO THE PACIFIC NORTHWEST AND
EVENTUALLY TREKS EASTWARD THROUGH THE WEEKEND AND BREAKING DOWN
THE RIDGE OVER IOWA.

TUESDAY TO THURSDAY...WHILE THE STATE GENERALLY REMAINS
UNDERNEATH THE RIDGE...THE NORTHWEST THIRD OF THE STATE WILL BE
WELL WITHIN REACH OF SHORTWAVES MOVING THROUGH THE UPPER LEVEL
FLOW. THE FIRST OF WHICH WILL MOVE THROUGH TUESDAY NIGHT/WEDNESDAY
MORNING FOLLOWED BY A SECOND WEDNESDAY NIGHT/THURSDAY MORNING.
FORCING APPEARS MOST ROBUST FOR THE CWA IN THE FORMER WITH MODELS
DEPICTING A FAIR AMOUNT OF ISENTROPIC LIFT ABOVE THE MORNING
INVERSION. HAVE CARRIED ONLY SLIGHT TO CHANCE POPS THROUGH DUE TO
OVERALL WEAKNESS AND MODELS NOT IN THE GREATEST CONSENSUS ON
EXTENT OR TIMING. TEMPS MAY ALSO BE A BIT WARM...NAMELY IN THE
NORTHWEST HALF OF THE STATE...ESPECIALLY IF CLOUD COVER OR PRECIP
COVERAGE ENDS UP GREATER THAN CURRENTLY EXPECTED.

FRIDAY TO MONDAY...MODELS CONTINUE TO AMPLIFY THE RIDGE TOWARDS THE
END OF THE WEEK AND INTO THE WEEKEND AS A TROUGH DIGS INTO THE
PACIFIC NORTHWEST.  AS A RESULT...SCANT PRECIP CHANCES WILL CONTINUE
TO CLIP THE NORTHWEST PORTIONS OF THE STATE...BUT SHOULD OVERALL
REMAIN DRY.  QUITE POSSIBLY THE WARMEST TEMPS OF THE WEEK MAY COME
ON FRIDAY WITH 850 TEMPS OF 20-21 DEG C IN THE AREA AND PRECIP
CHANCES OFF TO THE NORTHWEST. MODELS HAVE NOT BEEN IN CONSENSUS
WITH REGARD TO PROGRESSION OF THE WESTERN TROUGH THROUGH THE
WEEKEND...ESPECIALLY WITH THE MOST RECENT RUNS. EURO NOW SLOWS THE
PROGRESSION AND ACTUALLY PUSHES THE TROUGH UP INTO ALBERTA AND
SASKATCHEWAN WHILE GFS SKIRTS IT ALONG THE US/CANADA BORDER AND
DROPS A FRONT INTO THE REGION EARLY NEXT WEEK. AS A RESULT OF THE
LACK OF CONSENSUS...HAVE WARMED TEMPS A FEW DEGREES SAT AND SUN
OVER GUIDANCE...AND SLOWED POP PROGRESSION SUNDAY.

&&

.AVIATION...01/00Z
ISSUED AT 628 PM CDT MON AUG 31 2015

SIMILAR CONCERNS OF PAST FEW NIGHTS...ABUNDANT LOW LEVEL MOISTURE
WITH LIGHT WINDS OVERNIGHT. AS UPPER LEVEL TROUGH AND SFC
REFLECTION BOTH REMAIN NORTHWEST OF THE AREA TONIGHT/TUE
MORNING...WILL EXPECT TO SEE BR/POSSIBLE FG AGAIN DEVELOP AFT 06Z.
HAVE NOT HIT TERMINALS AS HARD WITH VSBY AS AIRMASS CONTINUES TO
WARM WHICH SHOULD OFFSET POTENTIAL FOR WIDESPREAD THICK FOG. EVEN
SO...HAVE LOWERED A FEW SPOTS TO 1SM...2SM BY 09-12Z. LIKELY THE
FOG/STRATUS LAYER WILL BE SHALLOWER THAN PAST NIGHTS. WIND OF LITTLE
CONCERN THOUGH SOME MIXING EXPECTED WEST TODAY/TOMORROW.

&&

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

&&

$$

SHORT TERM...REV
LONG TERM...CURTIS
AVIATION...ZOGG


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