698
FXUS63 KBIS 131117
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
617 AM CDT TUE AUG 13 2013
.UPDATE...
ISSUED AT 617 AM CDT TUE AUG 13 2013
LATEST LOCAL/REGIONAL RADAR SHOWS POTENTIAL OF ISOLATED SHOWERS
OVER BEACH WITH LATEST AWOS REPORTING BKN TO OVC CLOUDS. ISOLATED
THUNDERSTORMS OVER BAKER MONTANA SOUTH TO CAMP CROOK IN WESTERN
SOUTH DAKOTA. THESE ISOLATED THUNDERSTORMS CONTINUE TO SHOW A
SLOW BUT STEADY PROGRESS TOWARDS SLOPE AND BOWMAN COUNTIES. WILL
ADD A MENTION OF ISOLATED THUNDERSTORMS FOR FAR SOUTHWESTERN NORTH
DAKOTA WHERE MID LEVEL LAPSE RATES ARE HOLDING BETWEEN 7C TO
7.5C/KM.
MINOR UPDATE TO ADD PATCHY FOG IN THE NORTH AND EAST CENTRAL. FOG
IS BEING REPORTED FROM TIOGA EAST TO MINOT AFB. WITH TEMPERATURE/DEWPOINTS
EITHER AT SATURATION OR CLOSELY APPROACHING SATURATION...HAVE
BROAD BRUSHED AN AREA OF PATCHY FOG UNTIL 16Z FOR THE ABOVE
MENTIONED AREA. THE REST OF FORECAST REMAINS ON TRACK.
UPDATE ISSUED AT 505 AM CDT TUE AUG 13 2013
UPDATE TO MENTION ISOLATED SHOWERS EARLY THIS MORNING ACROSS FAR
SOUTHWEST NORTH DAKOTA...OVER GOLDEN VALLEY AND WESTERN SLOPE AND
BOWMAN COUNTIES. NO OTHER CHANGES.
&&
.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 312 AM CDT TUE AUG 13 2013
FORECAST HIGHLIGHTS IN THE SHORT TERM PERIOD WILL ONCE AGAIN BE
CHANCES FOR THUNDERSTORMS ACROSS THE SOUTHWEST THIS AFTERNOON AND
EVENING.
CURRENTLY...NORTHWEST FLOW ALOFT REMAINS IN PLACE ACROSS THE
NORTHERN PLAINS THIS MORNING WITH A DEEP UPPER LEVEL TROUGH OVER
THE EASTERN GREAT LAKES AND A DIRTY UPPER LEVEL RIDGE OVER THE
ROCKIES. SURFACE HIGH PRESSURE REMAINS OVER THE DAKOTAS WITH A SFC
TROUGH/QUASI-STATIONARY FRONTAL BOUNDARY STRETCHED FROM THE LEE
OF THE MONTANA ROCKIES INTO THE CENTRAL PLAINS. AS MENTIONED IN
THE PREVIOUS DISCUSSION...00Z/06Z NAM...00Z 4KM WRF...AND THE NAM
HR 4KM CONUS STILL DEPICT LIGHT PRECIPITATION DEVELOPMENT THIS
MORNING ALONG TO WEST OF THE MISSOURI RIVER WITH OTHER MODELS
REMAINING DRY. WHILE MID LEVEL CLOUD DEVELOPMENT HAS INCREASED
OVER THIS AREA THE PAST FEW HOURS WITH SCT-BKN CIGS...RADAR HAS
REMAINED VOID OF ANY ECHOS WITH THE EXCEPTION OF A BRIEF BLIP OVER
ADAMS/HETTINGER COUNTY. ONLY FORCING I CAN SEE THAT WOULD
CONTRIBUTE TO PRECIPITATION/SHOWER DEVELOPMENT IS A WEAK LLJ OF
AROUND 25KTS NOSING THROUGH THE SOUTHWEST COUNTIES. HOWEVER MODELS
PROJECT THIS FEATURE DECREASING IN MAGNITUDE WITH TIME SO WILL
KEEP THE FORECAST DRY WITH THIS ISSUANCE.
ANOTHER CONCERN EARLY THIS MORNING IS CONVECTION IN SOUTHEAST
MONTANA MOVING SLOWLY EAST TOWARDS THE WESTERN ND BORDER. THESE
STORMS ARE STILL 2-3 HOURS OUT...AND WILL FOR NOW NOT MENTION IN
THE FORECAST AS I AM NOT CONVINCED THIS ACTIVITY WILL SUSTAIN
ITSELF FOR MUCH LONGER. WILL CONTINUE TO MONITOR IN CASE AN UPDATE
BECOMES NEEDED IF THESE SHOWERS/SCATTERED THUNDERSTORMS
PERSIST...AND/OR SHOWERS DEVELOP ACROSS THE WEST AS I DISCUSSED
PRIOR.
AS YESTERDAY...SOUTHWESTERN NORTH DAKOTA WILL ONCE AGAIN SEE
INCREASING INSTABILITY NEAR THE BETTER DEEP LAYER MOISTURE IN THE
VICINITY OF THE SFC TROUGH TODAY AT PEAK HEATING...WITH RELATIVELY
STABLE CONDITIONS ELSEWHERE. WE ONCE AGAIN LACK A GOOD TRIGGER
MECHANISM FOR CONVECTION...BUT CANNOT RULE OUT EMBEDDED SMALLER
SCALE IMPULSES MOVING THROUGH THE RIDGE SPARKING A BRIEF STORM
OR TWO ALONG THE INSTABILITY AXIS WHICH CUTS THROUGH MY
SOUTHWESTERN COUNTIES. RIGHT NOW IT APPEARS THE BETTER CHANCES
WILL RESIDE WEST AND SOUTH OF NORTH DAKOTA AGAIN WHERE TWO MORE
DISTINCT IMPULSES ARE FORECAST TO TRACK (ONE OVER WESTERN MONTANA
AND THE OTHER OVER EASTERN WYOMING). WILL MAINTAIN THUNDERSTORMS
IN THE FORECAST ACROSS THE SOUTHWEST AND DRY CONDITIONS
ELSEWHERE.
.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 312 AM CDT TUE AUG 13 2013
THE OVERALL H5 PATTERN AMONGST THE GFS/ECMWF/GEM GLOBAL SHOW HEIGHTS
SLOWLY NUDGING UPWARDS AND PEAKING SATURDAY AS A MID/UPPER LEVEL
RIDGE MOVE OVERHEAD. THIS TYPE OF PATTERN WILL RESULT IN A WARMING
TREND INTO THE WEEKEND AND INTO NEXT WEEK AS DENOTED BY THE H85
TEMPERATURE FIELDS. H85 TEMPS ARE FORECAST FROM AROUND +16C IN THE
JAMES RIVER VALLEY TO +21C IN WESTERN NORTH DAKOTA WEDNESDAY
EVENING...RISING TO AROUND +24C IN THE JAMES RIVER VALLEY SATURDAY
TO +28C ACROSS THE WEST. TAKING THESE TEMPERATURES DOWN DRY
ADIABATICALLY SATURDAY YIELDS HIGHS IN THE MID 90S WEST...TO LOWER
90S CENTRAL...AND UPPER 80S IN THE JAMES RIVER VALLEY. A SHORTWAVE
TROUGH IS FORECAST TO PUSH THROUGH THE RIDGE SUNDAY
AFTERNOON/EVENING...WHICH DESPITE SUPPRESSING HEIGHTS EARLY NEXT
WEEK...H85 TEMPERATURES WILL ONLY BE SLIGHTLY AFFECTED...RESULTING
IN THE VERY WARM AIR TO CONTINUE. THUS AFTERNOON HIGHS IN THE UPPER
80S TO LOWER 90S CAN BE EXPECTED.
IN REGARDS TO PRECIPITATION CHANCES...AS THE RIDGE GETS CLOSER
WEDNESDAY AND THURSDAY...SHORTWAVE ENERGY WILL CONTINUE TO MIGRATE
ATOP THE RIDGE AND INTO WESTERN/CENTRAL NORTH DAKOTA PER GFS/ECMWF.
FOR WEDNESDAY THROUGH THURSDAY...THE WEST AND PORTIONS OF THE
NORTHERN AND EAST CENTRAL NORTH DAKOTA WILL BE THE PRIME LOCATIONS
FOR SOME THREAT OF SHOWERS/THUNDERSTORMS. AN ISOLATED SEVERE
THUNDERSTORM IS POSSIBLE DURING THIS TIME AS WELL. THURSDAY NIGHT
THROUGH SATURDAY...H7-H5 RIDGING STRONGLY DEVELOPS INTO NORTH DAKOTA
AND THIS WILL WORK TO SUPPRESS ANY THUNDERSTORM DEVELOPMENT. GFS
SOUNDINGS SHOW A DECENT CAP IN PLACE ACROSS WESTERN AND CENTRAL
NORTH DAKOTA. THE RIDGE SHIFTS EAST SUNDAY AS AN APPROACHING
SHORTWAVE TROUGH PER GFS/ECMWF SLIDES THROUGH SUNDAY/SUNDAY NIGHT.
THIS WILL RESULT IN A GOOD CHANCE OF SHOWERS/THUNDERSTORMS ACROSS
MOST OF WESTERN/CENTRAL NORTH DAKOTA. THE HEAVIEST RAINFALL IS
FORECAST TO OCCUR WITH THE MAIN SHORTWAVE ITSELF...ACROSS NORTH
CENTRAL NORTH DAKOTA SUNDAY EVENING WITH A SECONDARY MAXIMUM IN THE
JAMES RIVER VALLEY. DECENT AGREEMENT IN PRECIPITATION TOTALS AND
TIMING AMONGST THE GFS/ECMWF...WITH THE NORTH AND EAST CENTRAL
POSSIBLY IN LINE TO RECEIVE BETWEEN 0.50 AND 1.00 INCHES OF RAINFALL
WITH THIS SHORTWAVE. DRY AND WARM MONDAY AND TUESDAY.
&&
.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 617 AM CDT TUE AUG 13 2013
VFR CONDITIONS WILL PREVAIL OVER WESTERN AND CENTRAL NORTH DAKOTA
THROUGH THE 12Z TAF PERIOD. THERE WILL BE A CHANCE FOR AN ISOLATED
THUNDERSTORM AT KDIK THIS AFTERNOON AND EVENING.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...KS
SHORT TERM...NH
LONG TERM...KS
AVIATION...NH