Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 302337
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
637 PM CDT SAT MAY 30 2015

...UPDATED AVIATION DISCUSSION...

.SHORT TERM /TONIGHT/...
ISSUED AT 400 PM CDT SAT MAY 30 2015

BOUNDARY WILL CONTINUE TO PULL SOUTH OF IOWA WITH DECREASING
CLOUDS THROUGHOUT THE LATE AFTERNOON AND EVENING AS HIGH
PRESSURE WORKS IN ACROSS THE NORTH. FORECAST CONCERN WILL BECOME
AMOUNT OF COOLING OVERNIGHT AS SKIES CLEAR AND WINDS LIGHTEN.
HOWEVER...WINDS WILL STAY UP NEAR 5 KTS WHICH SHOULD BE SUFFICIENT
TO HELP LIMIT COOLING. IN ADDITION...WEAK WAA RETURNS IN THE WEST
LATE IN PERIOD. HAVE THEREFORE KEPT TEMPERATURES NEAR
GOING...THOUGH SLIGHTLY COOLER IN THE NORTH WHERE CLOUDS HAVE HUNG
AROUND THROUGHOUT THE DAY KEEPING HIGHS DOWN. HAVE GENERALLY
TRENDED TOWARDS GUIDANCE...THOUGH WARMER IN THE SOUTH WHERE EXPECT
SOME CLOUDS TO PERSIST THROUGH MUCH OF THE NIGHT HELPING TO KEEP
TEMPERATURES UP SLIGHTLY.

.LONG TERM /SUNDAY THROUGH SATURDAY/...
ISSUED AT 400 PM CDT SAT MAY 30 2015

THE COLD FROPA HAS DROPPED THE CURTAIN FOR LAST WEEK/S WEATHER
PATTERN OF CLOUDS AND RAIN. BROAD CYCLONIC FLOW ALONG THE ROCKIES
AND HIGH PRESSURE OVER THE NERN US WILL ACT TO KEEP IOWA IN
GENERAL SE/ERLY FLOW AND A RELATIVELY QUIET WEATHER PATTERN FOR
MUCH OF THIS WEEK.

STARTING OFF AT 12Z SUN...+1 TO +2 STD DEV HIGH PRESSURE WILL BE
ON THE CANADIAN SIDE OF THE GREAT LAKES. AS A RESULT...THE DMX
CWA WILL BE IN NE/ERLY FLOW FOR THE AFTERNOON AND KEEPING US DRY.
BY 00Z MON...MODELS TRY TO SQUEEZE OUT A FEW HUNDREDTHS OF RAIN
ACROSS OUR FAR NW AS THEY PASS A WEAK 500MB SHORTWAVE AND
ASSOCIATED VORTICITY LOBE THROUGH. HOWEVER...LOW LEVEL SUPPORT
WITH THIS FEATURE IS ESSENTIALLY NIL. PLUS...THERE IS A LOT OF DRY
AIR IN THE LOW LEVELS TO CONTEND WITH AS SFC DWPT DEPRESSIONS ARE
A SOLID 20F. THEREFORE WILL LEAVE OUT POPS AND ANTICIPATE VIRGA AT
WORST.

FOR MON AND TUE...LARGE SCALE SUBSIDENCE AND DRY AIR EXPECTED TO
BE IN PLACE WILL KEEP POPS AT BAY. THE AREA OF INFLUENCE FROM
GREAT LAKES SFC HIGH BEGINS TO MOVE EAST OF IOWA ON TUESDAY. AS TO
THE SPECIFICS...SLIGHT DISCREPANCIES EXIST WITH 850 MB TEMPS. FOR
850 MB TEMPS...THE 12Z NAM IS AROUND 4 TO 6C WARMER THAN THE
EURO...WITH THE GFS BEING IN THE MIDDLE OF THE TWO. INITIALIZED
TEMPERATURES FROM OUR SOURCE REGION OVER OK/KS...HOWEVER...WERE
MORE CONSISTENT AMONGST MODELS. THEREFORE KEPT TEMPS CLOSE TO
GUIDANCE BLEND TO IRON OUT OUTLIERS.

FOR WEDNESDAY...OUR WESTERN CWA WILL BE ON THE BACKSIDE OF A 500MB
RIDGE AXIS. MID LEVEL Q-VECTOR CONVERGENCE PRESENT TO SUPPORT
LIFT TO OUR WEST. AT 250 MB...UPPER LEVEL JET INTO CANADA SO NO
ADDTL SUPPORT THERE. SOME LOW LEVEL MOISTURE RETURNS SHOULD BE
GOOD ENOUGH TO GET PRECIP TO THE GROUND IN OUR WEST. AN 850MB
THERMAL RIDGE BUILDS TO OUR WEST AND SHOULD REMAIN THERE THROUGH
AT LEAST WED.

BIG DIFFERENCES BTX THE GFS AND THE EURO COME INTO PLAY FOR THU
INTO THE WKND. THE EURO BRINGS A DECENTLY STRONG 850 MB LOW
ALONG THE US/CANADA BORDER. WITH THIS LOW...THE EURO HAS A 25 TO
30KT JET TRANSPORTING MOISTURE INTO THE CWA. THE GFS...ON THE
OTHER HAND...IS MUCH WEAKER WITH THIS LOW...AND THUS MOISTURE
TRANSPORT. 850MB WINDS WITH THE GFS ARE FROM THE SOUTH AT AROUND
15 TO 20 KTS. EURO IS STRANGELY ABOUT 6 TO 12 HOURS FASTER THAN
THE GFS...USUALLY IT/S THE OTHER WAY AROUND THIS FAR OUT.
ADDITIONALLY...IT IS SOMEWHAT INTUITIVE THAT THE EURO SHOULD BE
SLOWER THIS FAR OUT GIVEN IT IS YIELDS THE STRONGER OUTPUT. FOR
NOW WILL STICK CLOSE TO GUIDANCE WITH UNDERSTANDING THAT POPS MAY
NEED TO BE PUSHED BACK TIMING-WISE. REGARDLESS OF
MODEL...CONTINUOUS SOUTHERLY FLOW HELPS PWAT VALUES RETURN TO .5
TO +1.5 STD DEV. BEST MOISTURE TRANSPORT REMAINS OVER WESTERN PART
OF CWA. BY FRIDAY INTO SATURDAY...0 TO 6 KM CAPE VALUES RETURN TO
1000-2000 J/KG AND CHANCES FOR STRONGER STORMS INCREASE.

&&

.AVIATION...31/00Z
ISSUED AT 633 PM CDT SAT MAY 30 2015

MVFR STRATUS DECK SLOW TO MOVE EAST AND DELAYED THE VFR CIGS FOR
OTM/ALO/DSM THROUGH LATE TONIGHT. FOD HAS CLEARED THE STRATUS
DECK AND MCW IS THE NEXT IN LINE TO DO SO. VFR CONDITIONS ARE
EXPECTED OVERNIGHT THROUGH SUNDAY.

&&

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

&&

$$

SHORT TERM...AWB
LONG TERM...KOTENBERG
AVIATION...PODRAZIK



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