Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 261753
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1253 PM CDT SUN JUL 26 2015

.SYNOPSIS...
ISSUED AT 319 AM CDT SUN JUL 26 2015

HAND ANALYSIS OF THE 07Z MSL DATA SHOWS A WEAK TEMPERATURE AND
PRESSURE FIELD AROUND THE AREA WITH GENERALLY LIGHT WIND. THERE IS A
TROUGH WITH A DEWPOINT GRADIENT ACROSS SOUTHEAST NEBRASKA AND A WEAK
CYCLONIC CIRCULATION OVER EAST CENTRAL SOUTH DAKOTA IN THE WAKE OF
THE OVERNIGHT CONVECTIVE SYSTEM. THERE IS ALSO A WEAK QUASI-
STATIONARY BOUNDARY ON THE HIGH PLAINS. THE HIGH PLAINS BOUNDARY IS
CHARACTERIZED BY A WIND SHIFT AND DEWPOINT GRADIENT. ALSO...RADAR
SHOWS A BOUNDARY ACROSS THE NORTHERN SANDHILLS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 319 AM CDT SUN JUL 26 2015

CONTINUING SOUTH TO SOUTHEAST FLOW WILL REINFORCE THE STRENGTH OF
THE THETA-E RIDGE ON THE HIGH PLAINS OF NORTHEAST COLORADO AND OVER
THE NEBRASKA PANHANDLE. THE WIND AND THETA-E FIELDS IN THE 0-2KM AGL
LAYER INDICATE CONVERGENCE IN THE THETA-E GRADIENT IN THE NEBRASKA
PANHANDLE AND NORTHEAST COLORADO. THIS IS LIKELY TO RESULT IN THE
DEVELOPMENT OF SCATTERED THUNDERSTORMS THIS AFTERNOON THAT MAY
CONGEAL EVENTUALLY INTO A CONVECTIVE COMPLEX. THERE IS AGREEMENT IN
THE PRECIPITATION AMOUNTS AND SURFACE FEATURES AMONG THE ECMWF...THE
CANADIAN...THE GFS AND THE NAM SO OUR CONFIDENCE IS HIGH IN THE
FOLLOWING SCENARIO. SCATTERED THUNDERSTORMS WILL DEVELOP IN THE
THETA-E GRADIENT OVER NORTHEAST COLORADO THIS AFTERNOON. THE STORMS
WILL THEN BECOME ORGANIZED INTO A CONVECTIVE SYSTEM THIS EVENING
BEFORE MAKING ITS WAY ACROSS SOUTHERN NEBRASKA. INITIALLY THE
INSTABILITTY AND 0-6KM AGL BULK SHEAR APPEARS TO SUPPORT LARGE
HAIL...BUT AS THE SITUATION EVOLVES...LOCALIZED HEAVY RAIN BECOMES
THE PRIMARY THREAT.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 319 AM CDT SUN JUL 26 2015

THE WEEK AHEAD WIL BE CHARACTERIZED BY SOME SIGNIFICANT CHANGES BY
MID WEEK BEFORE RETURNING TO A SUMMERTIME PATTERN BY NEXT WEEKEND.

MONDAY STARTS WITH AN ANOMALOUS UPPER LOW MOVING ACROSS THE PAC NW.
AND INTO THE NRN ROCKIES. TEMPS AT THE H5 LEVEL EXCEED -3SD
ACCORDING TO GEFS AND HEIGHTS EXCEEDING -2SD. RETURN INTERVALS FOR
THIS TYPE OF SYSTEM ARE IN THE NEIGHBORHOOD OF EVERY 5 TO 10 YEARS
SO AS THIS UPPER SYSTEM APPROACHES THE NRN PLAINS LATE MONDAY SFC
CYCLOGENESIS WILL DEVELOP IN WRN ND/SE MT. THE RESPONSE FURTHER
SOUTH WILL BE AN INCREASING SRLY WINDS SERVING TO TRANSPORT
PLENTIFUL LOW LEVEL MOISTURE INTO THE REGION. MODELS CONTINUE TO
STRUGGLE WITH THE AMOUNT OF MIXING THAT WILL OCCUR DURING THE DAY
MONDAY. GFS CONTINUES TO DEVELOP A MUCH DEEPER BL LEADING TO MINIMAL
CAPE AND LOWER DEW POINTS BY AFTERNOON MONDAY. THE NAM ON THE OTHER
HAND DEVELOPS A MORE SHALLOW BL AND SFC DEW POINTS HIGHER. THE NAM
THEREFORE HAS A MORE DEFINITIVE SFC TD GRADIENT LOCATED ACROSS NERN
CO AND INTO SWRN NEB...SUFFICIENT FOR CONVECTIVE INIT LATE IN THE
DAY MONDAY ACROSS SWRN NEB. THE GFS HAS A WEAKER TD GRADIENT AND HAS
WEAKER AND PERCEIVED MORE SHALLOW CONVECTION MONDAY NIGHT. BECAUSE
THIS SETUP WILL HAVE MORE POTENTIAL FOR MECHANICAL MIXING DUE TO THE
ANOMALOUS UPPER SYSTEM WOULD THINK THE SOLUTION WOULD LIE SOMEWHERE
IN THE MIDDLE BUT NOT AS DEEPLY MIXED AS GFS WOULD SUGGEST. EITHER
WAY WARM MID LEVEL TEMPS AND DRY AIR SHOULD TEMPER POTENTIAL
UPDRAFTS AND LIMIT CONVECTION TO ISOLD. TEMPS OF COURSE WILL DEPEND
ON THE DEPTH OF MIXING BUT A GOOD THERMAL RIDGE DEVELOPS AHEAD OF
THE SEWD ADVANCING FRONT AND MAY SEE A FEW 100S MONDAY AFTERNOON
FROM SW INTO PORTIONS OF THE SANDHILLS...THOUGH FOR NOW THE FCST
HAS MAINLY MID AND UPPER 90S.

AFOREMENTIONED COLD FRONT SHOULD CLEAR MOST OF THE CWA BY MID
MORNING TUESDAY. OF SIGNIFICANCE TUESDAY WILL BE THE MUCH DRIER
AIRMASS BY AFTERNOON. BOTH GFS AND NAM WOULD SUGGEST DEW POINTS IN
THE 30S MAY BE COMMON AS STRONG CAA TAKES OVER...WITH HIGHS TUESDAY
BELOW AVE FOR THIS TIME OF YEAR. BECAUSE OF THE TIMING OF THE
FRONTAL PASSAGE BEING EARLY IN THE DAY AND THE DRIER
AIRMASS...CONVECTIVE INITIATION WILL BE INHIBITED. WINDS WILL BE
BREEZY BEHIND THE FRONT. LOW DEWPOINTS REMAIN ACROSS THE AREA
TUESDAY NIGHT AND WED AS WELL WHICH MEANS MIN TEMPS WED MORNING WILL
BE COOLER THAN IN THE HUMID AIRMASS OF THE WEEKEND AND FIRST OF
THE WEEK.

AS THE ANOMALOUS UPPER LOW MOVES INTO ONTARIO AND THE HUDSON BAY
REGION BY THURSDAY...THE RIDGE AXIS WILL RETROGRADE TO THE WRN
STATES AGAIN...PUTTING THE REGION IN BROAD NW FLOW WHICH ISN/T
CONDUCIVE TO THE BEST CHANCES FOR CONVECTIVE RAINS. THE STRONG CAA
ASSOCIATED WITH THE FRONT WILL DRIVE IT WELL SOUTH INTO OK AND THE
TX PANHANDLES. MOISTURE RETURN WILL BE LIMITED UNTIL THURSDAY INTO
FRIDAY SINCE THE FRONT WILL BE SOUTH OF THE AREA. SUBTLE SHORT WAVES
WILL ROUND THE WRN STATES RIDGE AND ONCE LOW LEVEL MOISTURE IS ABLE
TO RETURN SOME POTENTIAL FOR THUNDERSTORMS WILL EXIST...HOWEVER
CONFIDENCE THAT FAR OUT ON TIMING AND LOCATION IS AVERAGE.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1253 PM CDT SUN JUL 26 2015

CONVECTIVE CHANCES ARE THE PRIMARY CONCERN FOR THE 18Z AVIATION
FORECAST. THE NEAR TERM CONVECTIVE ALLOWING FORECAST MODELS AND
SHORT TERM DETERMINISTICS ARE STRUGGLING ON COMING TO A CONSENSUS OF
WHAT IMPACTS FROM ANY POTENTIAL CONVECTION THAT WILL DEVELOP
DURING THIS FORECAST PERIOD. AS OF NOW...TWO AREAS ARE FAVORED FOR
CONVECTIVE DEVELOPMENT. FIRST OFF THE PANHANDLE OF WESTERN
NEBRASKA...AND THE SECOND OVER NORTHEASTERN COLORADO. WE
ANTICIPATED THE CONVECTION OFF THE PANHANDLE TO REMAIN ISOLATED
TO SCATTERED AND WORK EAST THROUGH THE AFTERNOON/EVENING.
ADDITIONAL CONVECTION OFF THE HIGH PLAINS OF EASTERN COLORADO MAY
SPREAD EAST ACROSS SOUTHWEST NEBRASKA THIS EVENING/OVERNIGHT WITH
GREATER COVERAGE. WHERE CONVECTION OCCURS...BRIEF IFR CONDITIONS
WOULD BE POSSIBLE.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SYNOPSIS...SPRINGER
SHORT TERM...SPRINGER
LONG TERM...JWS
AVIATION...JACOBS



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