Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 180849
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
349 AM CDT SAT APR 18 2015

.SHORT TERM /TODAY/...
ISSUED AT 348 AM CDT SAT APR 18 2015

PRECIPITATION CHANCES TODAY WILL BE MAIN FORECAST CONCERN. LARGE
UPPER LEVEL LOW PRESSURE SYSTEM WILL PUSH SLOWLY EAST FROM COLORADO.
SURFACE BOUNDARY ASSOCIATED WITH LOW CURRENTLY LOCATED FROM WESTERN
NEBRASKA TO EASTERN KANSAS HAS ONGOING CONVECTION ALONG LINE. THIS
WILL PUSH SLOWLY EASTWARD WITH LOW...BRINGING BEST CHANCES FOR
PRECIPITATION LATE IN THE DAY. MODELS CONTINUE TO BE A BIT SLOWER
WITH THIS PROGRESSION...AND HAVE CUT BACK ON BEST PRECIPITATION
CHANCES TO LATER IN THE DAY...GENERALLY ENTERING CWA NEAR 18Z.
SUBJECTIVELY ANALYZED WEAK SURFACE BOUNDARY STRETCHED FROM CENTRAL
NEBRASKA TO SOUTH CENTRAL IOWA HAS ALLOWED FOR SCATTERED SHOWERS AND
THUNDERSTORMS TO DEVELOP EARLY THIS MORNING. THIS WILL PERSIST AND
CONTINUE TO LIFT SLOWLY NORTHEAST THROUGHOUT THE MORNING HOURS.
THEREFORE...EXPECT PRECIPITATION TO COME IN TWO WAVES TODAY...WITH
EARLY MORNING PRECIPITATION CONTINUING AS SYSTEM LIFTS
NORTHEAST...AND MAY EXPAND AS BETTER FORCING ARRIVES AS LOW MOVES
EAST...AND BETTER CHANCES WITH BOUNDARY ASSOCIATED WITH LOW. HAVE
KEPT THUNDER MENTIONED TO ISOLATED AS INSTABILITY IS PRESENT BUT
GENERALLY WEAK. BETTER INSTABILITY COMES LATE IN THE
DAY...ESPECIALLY IN THE WEST AND MAY SEE MORE WIDESPREAD THUNDER IN
THE AFTERNOON. ALONG WITH WEAK INSTABILITY...SHEAR REMAINS WEAK
THOUGH...CANNOT RULE OUT AN ISOLATED SEVERE THUNDERSTORM WITH LARGE
HAIL OR DAMAGING WINDS AS THE MAIN THREATS.

.LONG TERM /TONIGHT THROUGH FRIDAY/...
ISSUED AT 348 AM CDT SAT APR 18 2015

THE UPPER LOW PRESSURE OVER COLORADO TODAY WILL BEGIN TO SHIFT
EAST TONIGHT AND TRANSITION TO AN OPEN WAVE. ONE STRONG IMPULSE
AHEAD OF THE SYSTEM WILL BE OVER WESTERN IOWA BY 00Z THIS EVENING
WITH MODEST QG FORCING AND UPPER LEVEL DIVERGENCE OVER CENTRAL AND
NORTHERN IOWA. THE MOISTURE TRANSPORT WILL BE MAXIMIZED DURING
THIS TIME NEAR THE INTERSTATE 35 CORRIDOR AND WILL LIFT NORTHEAST
THROUGH THE REMAINDER OF THE EVENING. PROFILES WILL BE QUITE
SATURATED THROUGH THE EVENING WITH PWAT VALUES NEAR 1.25 INCHES.
OVERALL INSTABILITY WILL BE RELATIVELY WEAK AND ONLY 2OO J/KG OR
LESS. CONTINUED TREND OF SHOWERS WITH ISOLATED THUNDERSTORMS
EMBEDDED IN THE ACTIVITY. SOME DRIER AIR DOES TRY TO ENTRAIN INTO
THE REGION BEHIND THIS WAVE OF PRECIPITATION AND SHOULD RESULT IN
A PERIOD OF LITTLE TO NO PRECIPITATION AFTER 06Z AND INTO SUNDAY
MORNING. FOG MAY NEED TO BE CONSIDERED YET FOR TONIGHT CONSIDERING
THE AMOUNT OF LOW LEVEL SATURATION AND WEAK SFC FLOW.

ANOTHER WAVE OF SHOWERS AND ISOLATED THUNDERSTORMS IS
EXPECTED TO DEVELOP IN ADVANCE OF A COLD FRONT MOVING ACROSS THE
STATE DURING THE DAY ON SUNDAY. PROFILES WILL CONTINUE TO REMAIN
QUITE SATURATED ON SUNDAY AHEAD OF THE BOUNDARY AND WITH A STRONG
LOW PRESSURE SYSTEM LIFTING INTO THE LOWER OHIO VALLEY DURING THE
DAY...CLOUDS SHOULD REMAIN IN PLACE AND HOLD TEMPERATURES DOWN
INTO THE 50S AND 60S. TOTAL RAINFALL AMOUNTS THROUGH SUNDAY WILL
LIKELY TOP 1 INCH IN SOME LOCATIONS. NORTHWEST WINDS BEHIND THE
BOUNDARY WILL BECOME QUITE GUSTY AND MAY APPROACH WIND ADVISORY
CRITERIA OVER THE WESTERN FORECAST AREA.

THE SYSTEM MOVING INTO THE NORTHERN PLAINS TONIGHT AND SUNDAY WILL
BECOME A LARGE CLOSED UPPER LOW THAT WILL BE THE DOMINANT WEATHER
FEATURE FOR THE STATE THOUGH MUCH OF NEXT WEEK AND KEEP THE STATE
IN CYCLONIC FLOW EARLY THEN TRANSITION TO MORE TRUE NORTHWEST FLOW
LATER IN THE PERIOD AS THE SYSTEM SHIFTS SLOWLY EAST. DRY AIR AND
PROFILES CONDUCIVE TO DEEP MIXING CAN BE EXPECTED MONDAY AND
TUESDAY ALONG WITH BREEZY TO GUSTY NORTHWEST WINDS. DEWPOINTS WILL
BE DROPPING INTO THE 20S SO THE POTENTIAL FOR TEMPERATURES TO DROP
BELOW FREEZING IS THERE MONDAY NIGHT AND TUESDAY NIGHT THOUGH
WINDS SHOULD AT 10 MPH MONDAY NIGHT WITH A GOOD PRESSURE GRADIENT
IN PLACE. THESE WINDS SHOULD PREVENT FROST FORMATION AND WILL KEEP
PROFILES MIXED ENOUGH TO HOLD TEMPERATURES UP A FEW DEGREES. THE
UPPER LOW WILL MAKE MORE PROGRESS EAST THURSDAY INTO FRIDAY THOUGH
850 MB TEMPERATURES WILL GENERALLY BE BELOW 0C THROUGH FRIDAY.
WITH THIS COLD AIR AROUND...HIGHLY LIKELY THAT THERE WILL BE ONE
TO TWO FROST EVENTS WITH THE BEST CHANCES TUESDAY NIGHT AND
WEDNESDAY NIGHT. SOME HOPE OF BREAKING THIS PATTERN INTO NEXT
WEEKEND WITH SOME HINTS AT AN OMEGA BLOCK DEVELOPING WHICH WOULD
FORCE UPPER RIDGING AND WARMER TEMPERATURES BACK INTO THE MIDWEST.

&&

.AVIATION...18/06Z
ISSUED AT 1124 PM CDT FRI APR 17 2015

A FEW ISOLATED SHOWERS AND WEAK THUNDERSTORMS HAVE DEVELOPED
ACROSS FAR SOUTHERN IOWA...WITH MID AND HIGH LEVEL CLOUDS IN
PLACE. CHANCES FOR PRECIP TO INCREASE THROUGH THE PERIOD AS BETTER
MOISTURE LIFTS INTO THE STATE...WITH THE BEST TIMES EXPECTED
DURING THE DAY SATURDAY INTO SATURDAY EVENING. MORE SPOTTY
ACTIVITY EXPECTED PRIOR TO THEN...AND COULD MAINLY BE CONFINED TO
THE WESTERN AND SOUTHERN AREAS OF THE STATE. MVFR CIGS EXPECTED
TOWARD THE END OF THE PERIOD AS LOW LEVEL MOISTURE REALLY
INCREASES. ADDITIONALLY WINDS TO PICK UP SOME AND BECOME MORE
SOUTHEASTERLY FOR SATURDAY.


&&

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

$$

SHORT TERM...AWB
LONG TERM...DONAVON
AVIATION...BEERENDS


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