Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 210941
AFDBIS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
441 AM CDT THU AUG 21 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 441 AM CDT THU AUG 21 2014

THE MAIN FOCUS IS FLOOD POTENTIAL LATER TODAY INTO THE WEEKEND.

THE NEXT IN A SERIES OF PRECIPITATION WAVES IS SCHEDULED TO
SPREAD INTO SOUTHWESTERN NORTH DAKOTA BEGINNING AT 21 UTC
TODAY...AT LEAST ACCORDING TO GOOD AGREEMENT AMONG THE 00 UTC
NAM/HIRES ARW AND NMM...AND 06 UTC HRRR. CONVECTION IN THESE
MODELS REACHES THE U.S. 83 CORRIDOR BY 06 UTC...WHICH DOES WELL TO
ILLUSTRATE THE RATHER SLOW PROPAGATION. ALSO CONTRIBUTING TO THE
HEAVY RAIN POTENTIAL IS THE NEAR RECORD PRECIPITABLE WATER. THE
00 UTC BISMARCK SOUNDING INDICATED 1.73 INCH PRECIPITABLE
WATER...WHICH IS 3 STANDARD DEVIATIONS ABOVE THE AUGUST MEAN.

SEE THE HYDROLOGY SECTION BELOW FOR MORE DETAILS ON FLOOD
POTENTIAL.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 441 AM CDT THU AUG 21 2014

AN ACTIVE SOUTHWESTERLY FLOW ALOFT WILL CHARACTERIZE THE UPPER
PATTERN OVER THE NORTHERN PLAINS THROUGH THE WEEKEND. QUASI-ZONAL
FLOW IS THEN PROGGED TO DEVELOP DURING THE FIRST PART OF NEXT
WEEK...WITH UPPER LEVEL RIDGING POSSIBLE BY THE MIDDLE OF NEXT
WEEK. WELL BELOW NORMAL TEMPERATURES WILL CONTINUE THROUGH THE
EXTENDED PERIOD.

THE MEDIUM RANGE MODELS CONTINUE TO PROG A LONGWAVE TROUGH
DEVELOPING OVER THE PACIFIC NORTHWEST FRIDAY. THIS WILL LEAD TO
CONTINUED SOUTHWESTERLY FLOW ALOFT AND SUBSEQUENT THUNDERSTORM
CHANCES ACROSS WESTERN AND CENTRAL NORTH DAKOTA FRIDAY.

AS THE PARENT UPPER TROUGH ENTERS MONTANA SATURDAY...THE MEDIUM
RANGE MODELS PROG HIGHER QPF AMOUNTS TO DEVELOP OVER WESTERN NORTH
DAKOTA. THE HIGHER QPF AMOUNTS ARE FORECAST TO CONTINUE OVER WESTERN
NORTH DAKOTA THROUGH SUNDAY AS THE TROUGH PIVOTS NORTH ACROSS THE
MT/ND BORDER. THIS COULD LEAD TO SOME HYDRO CONCERNS DEVELOPING
WEST. WILL CONTINUE TO MONITOR MODEL TRENDS AS THE EVENT APPROACHES.
FOR NOW WILL MENTION THE HEAVY RAIN POSSIBILITY IN THE HWO.

SOME DRYING IS THEN FORECAST SUNDAY NIGHT AS THE UPPER TROUGH/LOW
LIFTS NORTH INTO SOUTHERN MANITOBA. LOWER PRECIP CHANCES ARE
FORECAST FOR THE FIRST HALF OF NEXT WEEK AS QUASI-ZONAL FLOW ALOFT
DEVELOPS.

BY WEDNESDAY...THE LATEST GFS PROGS AN UPPER RIDGE TO DEVELOP OVER
THE ROCKIES. HOWEVER...THE ECMWF PROGS AN UPPER LOW DEVELOPING OVER
THE INTERMOUNTAIN WEST. WILL KEEP THE FORECAST DRY FOR
WEDNESDAY...BUT COULD POSSIBLY SEE PRECIP CHANCES INCREASING IF THE
ECMWF VERIFIES.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 441 AM CDT THU AUG 21 2014

IFR/LIFR CONDITIONS ARE EXPECTED AT KISN/KMOT DUE TO LOW STRATUS
AND FOG...WITH POSSIBLE MVFR CEILINGS AT KJMS/KBIS/KDIK. VFR WILL
RETURN BY 14Z. THUNDERSTORMS ARE AGAIN EXPECTED AT KDIK/KISN
BY 03Z...AND AT KBIS/KMOT BY 06Z.

&&

.HYDROLOGY...
ISSUED AT 441 AM CDT THU AUG 21 2014

ABOUT A THIRD OF THE AREA HAS RECEIVED MORE THAN THREE TIMES
THEIR NORMAL AMOUNT OF PRECIPITATION OVER THE PAST TWO WEEKS. SOIL
MOISTURE IS ANOMALOUSLY HIGH...AND THE LIKELIHOOD OF RAINFALL
CAUSING EXCESSIVE RUNOFF AND OVERLAND/SMALL STREAM FLOODING GROWS
WITH EACH PASSING THUNDERSTORM.

WE WILL USE THE PRECIPITATION FREE HOURS UNTIL THIS AFTERNOON TO
GATHER OBSERVATIONS OF HOW WELL SOILS HANDLED THE OBSERVED RAIN
RATES OF ABOUT 2.5 INCHES PER HOUR. THAT INSIGHT WILL ALLOW
BETTER JUDGMENT ON WHETHER A FLOOD/FLASH FLOOD WATCH MIGHT BE
WARRANTED FOR THIS EVENING/TONIGHT. AT THIS TIME...HOWEVER...WE
WILL CONTINUE TO USE THE HYDROLOGIC OUTLOOK/ESF TO HIGHLIGHT FLOOD
POTENTIAL.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SHORT TERM...SCHECK
LONG TERM...TM
AVIATION...SCHECK
HYDROLOGY...SCHECK



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