Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 230504
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1204 AM CDT SAT APR 23 2016

.SHORT TERM.../TONIGHT/
ISSUED AT 352 PM CDT FRI APR 22 2016

STRATUS SHIELD ON THE BACKSIDE OF THE DEPARTING UPPER LEVEL TROUGH
HAS SLOWLY BUT STEADILY BEEN ERODING FROM THE NORTHWEST THIS
AFTERNOON AS SYNOPTIC SUBSIDENCE ENVELOPES THE REGION. THIS CLEARING
HAS BEEN UNDERDONE BY ALL SHORT RANGE GUIDANCE SOLUTIONS IN PART TO
THE 1.5 TO 2 KFT THICK CLOUDS DEPICTED BY SATELLITE THAT HAVE FAILED
TO MIX OUT TODAY. THESE THICKNESS VALUES HAVE GRADUALLY BEEN COMING
DOWN THROUGHOUT THE AFTERNOON AND IT IS EXPECTED THAT THE DECK WILL
SCATTER OUT BY SUNSET. SURFACE RIDGING OVER THE MISSOURI RIVER
VALLEY WILL SLIDE EAST THIS EVENING WITH THE RIDGE AXIS OVER THE
MISSISSIPPI RIVER BY 12Z SATURDAY. THERE IS SOME UNCERTAINTY HAS TO
HOW MUCH OF THE CLOUD DECK/MOISTURE WILL ERODE BEFORE THE PASSAGE OF
THE RIDGE AND SOUTHERLY RETURN FLOW ENSUES. HAVE THUS KEPT SOME
MENTION OF CLOUDS IN THE GRIDS OVERNIGHT IN THE SOUTH AND EAST WITH
MOST MODEL SOUNDINGS SATURATING THE 3-4 KFT AFTER MIDNIGHT.

.LONG TERM.../SATURDAY THROUGH FRIDAY/
ISSUED AT 352 PM CDT FRI APR 22 2016

RIDGE OF HIGH PRESSURE WILL SHIFT EAST OF IOWA ON SATURDAY. AS
THIS OCCURS...THE PRESSURE GRADIENT WILL BE INCREASING WITH LOW
PRESSURE MOVING EAST INTO THE WESTERN SOUTH DAKOTA AND NEBRASKA.
THIS WILL ALLOW WARM ADVECTION TO SPREAD ACROSS THE STATE AS
SOUTHERLY WINDS INCREASE. A RIBBON OF STRONGER THETA-E ADVECTION
WILL MOVE THROUGH FROM MID TO LATE AFTERNOON THOUGH THE MID LEVELS
WILL BEGIN QUITE DRY SO NOT MUCH FOR INCREASING CLOUDS UNTIL LATE
AFTERNOON. THAT SAID SOME LOWER LEVEL FLAT CUMULUS MAY DEVELOP
EARLIER IN THE DAY BENEATH THE STRONG INVERSION IN PLACE ABOVE 850
MB. STILL LOW POTENTIAL FOR A FEW ISOLATED SHOWERS TO DEVELOP LATE
IN THE DAY BUT STILL AT THIS TIME NOT HIGH ENOUGH TO INCLUDE POPS.

A CLOSED UPPER LEVEL LOW WILL BE MOVING RAPIDLY EAST THROUGH THE
INTERMOUNTAIN WEST AND INTO WYOMING SATURDAY NIGHT AND AS THIS
OCCURS...THE SOUTHWEST FLOW WILL SHARPEN AND THE LOW LEVEL JET
WILL INCREASE THROUGH CENTRAL KANSAS AND INTO EASTERN NEBRASKA.
THE LLJ WILL BE NEARLY COINCIDENT WITH THE INCREASING INSTABILITY
THROUGH THE MID MISSOURI VALLEY AND PROVIDE A FOCUS FOR ADDITIONAL
THUNDERSTORM ACTIVITY WELL NORTH INTO THE DAKOTAS. THE DYNAMICS
WILL SHIFT EAST ON SUNDAY AS THE UPPER LOW AND ITS SURFACE LOW
REFLECTION DRAW CLOSER. THERE WILL BE SOME POTENTIAL FOR SEVERE
WEATHER BY SUNDAY AFTERNOON AND EVENING...MAINLY WEST OF
INTERSTATE 35. BULK SHEAR VALUES WOULD SUGGEST POTENTIAL FOR A FEW
ROTATING UPDRAFTS THOUGH LOW LEVEL HELICITY VALUES AND MARGINAL AT
BEST LCL HEIGHTS POINT TO LOW TORNADO POTENTIAL. LARGE HAIL AND
DAMAGING WINDS WILL BE THE PRIMARY THREATS WITH STORMS.

THE DRY SLOT WILL MOVE THROUGH SUNDAY NIGHT INTO MONDAY WITH
POTENTIAL FOR LINGERING PRECIPITATION OVER FAR NORTHERN AND
EASTERN IOWA. MONDAY WILL BE WARM TO BEGIN THE DAY THOUGH A COLD
FRONT WILL BRING FALLING TEMPERATURES TO THE NORTH BY THE
AFTERNOON.

THE NEXT SIGNIFICANT STORM SYSTEM IS EXPECTED TO ARRIVE TUESDAY
NIGHT AND WEDNESDAY. STRONG THETA-E ADVECTION LIFTING THROUGH THE
STATE WILL BRING ELEVATED THUNDERSTORM POTENTIAL INITIALLY. SFC
BASED CONVECTION COULD REACH INTO SOUTHERN IOWA AND WILL DEPEND ON
PLACEMENT AND TIMING OF THE SYSTEM. A FEW SEVERE STORMS WILL BE
POSSIBLE WITH THIS EVENT. MUCH OF THE EXTENDED WILL BE COOLER WITH
HIGHS IN THE 50S AND 60S. FORTUNATELY NO FREEZING TEMPERATURES ARE
ON THE HORIZON.

&&

.AVIATION.../FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT/
ISSUED AT 1158 PM CDT FRI APR 22 2016

WILL SEE WIDESPREAD VFR CONDITIONS FOR MUCH OF THE TIME. MAIN
CONCERN WOULD BE THE DEVELOPMENT OF STATUS OVERNIGHT IN RETURN
FLOW ON BACKSIDE OF THE RIDGE AXIS. WINDS WILL GENERALLY BE LIGHT
FROM THE SOUTHEAST OVERNIGHT BUT INCREASE STEADILY ON SATURDAY AND
BE GUSTY BY AFTERNOON...ESPECIALLY WEST OF KMCW-KLWD.

&&

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

&&

$$

SHORT TERM...SKOW
LONG TERM...DONAVON
AVIATION...COGIL



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