Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 061233
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
734 AM CDT SUN JUL 6 2014

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 311 AM CDT SUN JUL 6 2014

THERE ARE THREE PRIMARY FORECAST CHALLENGES CURRENTLY BEING
CONSIDERED:

  -HEAT INDEX VALUES TODAY
  -CONVECTION CHANCES THIS AFTERNOON AND EVENING IN THE SOUTH
  -SEVERE AND HEAVY RAIN POTENTIAL FOR MONDAY AFTERNOON AND NIGHT

AT 07Z...SURFACE COLD FRONT WAS ANALYZED FROM NORTH CENTRAL
SOUTH DAKOTA INTO FAR NORTHWEST NEBRASKA AND HAD JUST MOVE
THROUGH PINE RIDGE. FRONT SHOULD REACH SOUTHEAST NEBRASKA BY LATE
AFTERNOON. AIRMASS OVER FORECAST AREA AHEAD OF THE FRONT WILL BE
QUITE HUMID WITH DEWPOINTS IN THE LOW TO MID 70S...WITH ONLY
SLIGHT COOLING BEHIND THE FRONT. ALOFT...WEAK RIDGING WAS NOTED
UPSTREAM WITH MINOR HEIGHT RISES AT 500 MB ACROSS THE DAKOTAS INTO
NEBRASKA...WITH FAIRLY WARM MID LEVEL TEMPERATURES.

THEREIN LIES THE QUESTION OF THE PAST COUPLE OF DAYS...TRYING TO
DETERMINE WHETHER THE FRONT WILL BE ABLE TO TRIGGER CONVECTION
TODAY IN A WARM AIRMASS WITH A MODEST CAP AND A LACK OF DEEP
VERTICAL MOTION FROM ANY DISTINCT LIFTING MECHANISM OTHER THAN
THE FRONT. THE 00Z NAM AND THE 06Z RAP ARE IN GOOD AGREEMENT WITH
DEVELOPING CONVECTION ALONG THE FRONT IN THE 22Z-23Z TIME
FRAME...AND THE 00Z GFS DEVELOPS IT SLIGHTLY POST FRONTAL BETWEEN
00Z-06Z. NOT SURPRISINGLY...THE NAM AND RAP BOTH ERODE THE CAP
FROM ABOUT LINCOLN SOUTH...AND INDICATE VERTICAL MOTION ON THE
ORDER OF -4 MICROBARS/SEC THROUGH AROUND 600MB. GIVEN THESE
POSSIBLE SCENARIOS...WILL GO WITH A SLIGHT CHANCE IN SOUTHEAST
NEBRASKA/SOUTHWEST IOWA FROM 22Z-03Z.

REGARDING THE HEAT AND HUMIDITY TODAY...THE COOLING BEHIND THE
FRONT IS A CONCERN BUT NEARLY FULL SUN SHOULD KEEP TEMPERATURES
FROM DROPPING MUCH. A DEGREE OR TWO DROP IN DEWPOINTS IS EXPECTED
IN NORTHERN COUNTIES...BUT NOT IN SOUTHERN COUNTIES UNTIL WELL
AFTER THE FRONT PASSES. GENERALLY HAVE NOT MADE CHANGES TO TEMPS
TODAY...BUT DID RAISE DEWPOINTS A FEW DEGREES BASED ON READINGS
SATURDAY. BOTTOM LINE IS HEAT INDEX VALUES OF 95-100 NORTH AND
100-105 SOUTH. LOOKS LIKE MOST SOUTHERN COUNTIES WILL REMAIN JUST
SHY OF HEAT ADVISORY CRITERIA.

MODELS IN REASONABLY GOOD AGREEMENT WITH WET PATTERN FOR MONDAY
AFTERNOON INTO MONDAY NIGHT. CURRENT FORECAST HAS THIS PERIOD
HANDLED WELL. ONLY CHANGES WILL BE TO INCREASE POPS FOR NORTHWEST
AREAS MONDAY AFTERNOON...AND ALSO MENTION HEAVY RAIN MONDAY NIGHT
ESPECIALLY SOUTH OF I-80 WHERE RECENT RAINS HAVE CAUSED FLOODING
IN SOUTHWEST IOWA.

HEAVY RAIN OVER THE SOUTHERN COUNTIES LOOKS POSSIBLE GIVEN THE
STRONG FRONTAL CONVERGENCE IN THE LOW LEVELS FOR 9-12 HOURS... JET
DIVERGENCE AND SHEARED VORTICITY IN NORTHWEST FLOW CAUSING A
PROLONGED PERIOD OF LIFT...AND ABUNDANT MOISTURE/INSTABILITY. NAM
AND GFS SHOW QUITE STRONG THETA-E ADVECTION FROM 850-700. THIS IS
A CONCERN GIVEN THE CURRENT FLOODING IN THE NISHNABOTNA RIVER
BASIN IN SOUTHWEST IOWA. WPC DAY 2 EXCESSIVE RAIN GRAPHIC SUPPORTS
THIS AS WELL.

INGREDIENTS FOR SEVERE CONVECTION MONDAY AFTERNOON AND EVENING
APPEAR TO BE LINING UP...PER SPC DAY 2 DISCUSSION. INSTABILITY
AND DEEP LAYER SHEAR PARAMETERS MORE THAN SUPPORT A SEVERE WEATHER
OUTBREAK WITH UNSEASONABLY FAST UPPER FLOW. BOWING SEGMENTS ALONG
THE FRONTAL BOUNDARY IN SOUTHEAST NEBRASKA/SOUTHWEST IOWA SEEM
LIKELY.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 311 AM CDT SUN JUL 6 2014

BY LATE TUESDAY THE PRIMARY SYNOPTIC FRONT SHOULD MOVE WELL SOUTH
OF THE AREA WITH SURFACE HIGH PRESSURE MOVING INTO THE FORECAST
AREA. DRY CONDITIONS ARE EXPECTED TUESDAY NIGHT INTO WEDNESDAY. BY
THURSDAY...RETURN FLOW BRINGS MOISTURE BACK INTO THE REGION AND
THE UPPER PATTERN MAINTAINS A SOMEWHAT UNSETTLED NORTHWEST FLOW
REGIME WITH SOME POTENTIAL FOR MCS ACTIVITY...BUT CONFIDENCE IS
LOW THURSDAY INTO SATURDAY. TEMPERATURES SHOULD BE CLOSE TO
NORMAL OR A FEW DEGREES BELOW NORMAL.

&&

.AVIATION...(12Z TAFS FOR KOFK...KLNK AND KOMA.)
ISSUED AT 734 AM CDT SUN JUL 6 2014

DENSE FOG/LOW CIGS HAVE SET IN AT KOFK...RECENT OBSERVATIONS
INDICATE THIS CONDITION WILL SLOWLY IMPROVE TO VFR IN THE NEXT THREE
HOURS. LIGHT  FOG HAS BEEN REPORTED AT THE OTHER SITES AND BY 15Z
ALL THREE SITES SHOULD BE INTO VFR. A SCATTERED TO BROKEN MID DECK
WILL PUSH THROUGH THE AREA THIS AFTERNOON...BUT DO NOT ANTICIPATE
ANYTHING OTHER THAN VFR.

&&

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

$$

SHORT TERM...NIETFELD
LONG TERM...NIETFELD
AVIATION...PEARSON


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