Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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649
FXUS63 KOAX 201118
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
618 AM CDT WED MAY 20 2015

.SHORT TERM...(TODAY THROUGH FRIDAY)
ISSUED AT 327 AM CDT WED MAY 20 2015

ENDING RAIN TODAY...THEN WHEN TO INTRODUCE THUNDER CHANCES LATER
THIS WEEK...ARE THE PRIMARY FORECAST CONCERNS.

MID LEVEL WAVE WAS EJECTING THROUGH MID AMERICA THIS MORNING...
BRINGING SHOWERS TO ALL OF EASTERN NEBRASKA AND SOUTHWEST IOWA.
VORTICITY MAXIMUM WAS NOTED ALONG THE SOUTH DAKOTA BORDER IN
NORTHWEST NEBRASKA...WITH LOBE OF VORTICITY STRETCHING EAST THEN
SOUTHEAST INTO EASTERN NEBRASKA. THIS REPRESENTED THE BACK EDGE OF
RAIN...WHICH WAS ENTERING OUR WESTERN CWA AS OF 3 AM. THIS TREND
WILL CONTINUE THROUGH THE MORNING AS LOBE ROTATES NORTHEAST...BUT
WILL STILL SEE ISOLATED TO SCATTERED SHOWERS INTO THE AFTERNOON AS
VORT MAX SLIDES NEARLY DUE EAST. RAIN SHOULD BE ENDING BY THIS
EVENING IN SOUTHWEST IOWA. THOUGH RAIN WILL END...PERSISTENT CLOUD
COVER AND NORTHERLY LOW LEVEL WIND COMPONENT WILL KEEP TEMPERATURES
CONFINED TO THE LOW TO MID 50S THIS AFTERNOON.

CLOUDS WILL BE SLOW TO CLEAR FROM NORTH TO SOUTH OVERNIGHT. SOME
CLEARING IN CENTRAL AND NORTHEAST NEBRASKA WHERE COOLEST TEMPS AND
LIGHT WINDS WILL PREVAIL...COULD LEAD TO PATCHY FROST IN THOSE
NORMAL COLD AIR DRAINAGE SITES. THEN NORTHWEST WINDS THURSDAY SHOULD
SCOUR OUT REMAINING COVER. A SUBTLE INCREASE IN LOW LEVEL WARMTH
COMBINED WITH SUNSHINE AND WESTERLY WIND COMPONENT SUGGEST 10 TO 15
DEGREES WARMER HIGHS THURSDAY AFTERNOON.

WE THEN LOOK WEST AS UPPER LOW/TROUGH SETTLING INTO THE SOUTHWEST
BEGINS TO EJECT ENERGY INTO THE PLAINS. THE FIRST WAVE SHOULD MOVE
THROUGH THE CENTRAL ROCKIES THURSDAY NIGHT...BUT THEN LIFT MORE
NORTHERLY THROUGH THE HIGH PLAINS ON FRIDAY. THE SOUTHERN EXTENT OF
DAMPENING SHORTWAVE ENERGY MAY SKIRT OUR WESTERN CWA FRIDAY
AFTERNOON...BUT LAYER MOISTURE AND LOW LEVEL CONVERGENCE ARE
RELATIVELY SCANT. WILL KEEP SHOWER AND ISOLATED THUNDER CHANCES
CONFINED TO THE WESTERN CWA FRIDAY AFTERNOON.

.LONG TERM...(FRIDAY NIGHT THROUGH TUESDAY)
ISSUED AT 327 AM CDT WED MAY 20 2015

CONTINUED RAIN/THUNDER CHANCES THROUGH THE HOLIDAY WEEKEND ARE THE
MAIN CHALLENGES FOR THE LONGER TERM FORECAST. WESTERN UPPER TROUGH
WILL GRADUALLY DRIFT INTO THE ROCKIES...THEN BROADEN AND FLATTEN
WITH TIME INTO TUESDAY. SEVERAL IMPULSES ROLLING THROUGH THE GENERAL
SOUTHWEST FLOW ALOFT COULD BE THE SPARK FOR CONVECTION AT JUST ABOUT
ANY TIME. MOISTURE PROFILES BECOME MORE FAVORABLE BY SUNDAY WHEN
SURFACE DEW POINTS ARE EXPECTED TO REACH THE 60S. THE BEST
COMBINATION OF MOISTURE AND INSTABILITY APPEAR TO RESIDE JUST AHEAD
OF A COOL FRONT SETTLING INTO OUR AREA SUNDAY AFTERNOON. HOWEVER
THAT INSTABILITY IS MODEST AT BEST AND SHEAR IS NOT SUBSTANTIAL. SO
WHILE CHANCES FOR SHOWERS/STORMS WILL BE HIGH...SEVERE STORMS ARE
NOT LOOKING LIKELY. WE SHOULD SEE A RELATIVE MINIMUM IN PRECIP
CHANCES ON MONDAY BEHIND COOL FRONT. THEN GFS/ECMWF SUGGEST THAT
FRONT WILL RETURN NORTH AS A WARM FRONT ON TUESDAY...WITH ATTENDANT
MOISTURE/INSTABILITY BRINGING INCREASING RAIN CHANCES AGAIN.

&&

.AVIATION...(12Z TAFS FOR KOFK...KLNK AND KOMA.)
ISSUED AT 618 AM CDT WED MAY 20 2015

EXPECT THAT MVFR CONDITIONS WILL OCCUR MUCH OF THE MORNING...
ESPECIALLY AT KOFK AND KLNK. MAIN AREA OF RAIN HAD MOVED EAST OF
THE TAF SITES...BUT SOME SCT PCPN IS POSSIBLE INTO THE AFTERNOON.
IFR CONDITIONS EXIST TO THE WEST AND AT LEAST FOR NOW THOSE ARE
EXPECTED TO STAY TO THE WEST. CONDITIONS WILL TREND TOWARD VFR
BY LATE AFTERNOON OR EARLY EVENING.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&

$$

SHORT TERM...DERGAN
LONG TERM...DERGAN
AVIATION...MILLER



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