Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 211853
AFDBIS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
153 PM CDT THU AUG 21 2014

.UPDATE...

ISSUED AT 152 PM CDT THU AUG 21 2014

LOW CLOUDS STARTING TO BURN OFF...BUT HAVE BEEN SLOW TO DO SO.
ADJUSTED SKY GRIDS BASED ON LATEST SATELLITE AND OBS.

INCREASED POPS FAR WEST TO ACCOUNT FOR DEVELOPING CONVECTION
ACROSS FAR EASTERN MT MOVING SLOWLY EAST. DO NOT ANTICIPATE
SEVERE. TEMPERATURES WERE ALSO ADJUSTING TO TAKE INTO ACCOUNT THE
CLOUD COVER.


UPDATE
ISSUED AT 958 AM CDT THU AUG 21 2014

EXTENDED FOG MENTION THROUGH THE MORNING AND INCREASED SKY COVER.
LOW STRATUS CONTINUES TO ADVECT SOUTH ACROSS NORTH DAKOTA IN THE
WAKE OF A SURFACE TROUGH NOW OVER THE EASTERN DAKOTAS. THE LOW
CLOUDS SHOULD BURN OFF WITH TIME AS WE PROGRESS THROUGH THE
MORNING INTO THE AFTERNOON HOURS. BOUNDARY LAYER MOISTURE REMAINS
RICH TODAY AND TONIGHT...SETTING THE STAGE FOR HEAVY RAINS TONIGHT
AS A STRONG MID LEVEL WAVE APPROACHES AND MOVES NORTHEAST ACROSS
THE REGION. SEE OUR HYDROLOGIC DISCUSSION BELOW.

OTHER UPDATES MINOR. TEMPERATURES WILL GREATLY DEPEND ON CLOUD
COVER.

UPDATE ISSUED AT 642 PM CDT THU AUG 21 2014

UPDATED THE FORECAST TO ADD PATCHY TO AREAS OF MORNING FOG TO THE
FORECAST. THE FOG SHOULD BEGIN TO DISSIPATE WITHIN THE NEXT FEW
HOURS AND GIVE WAY TO PARTLY SUNNY SKIES TODAY. THE UPDATED
PRODUCTS HAVE BEEN SENT.

&&

.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 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)

ISSUED AT 152 PM CDT THU AUG 21 2014

MVFR/IFR CONDITIONS CONTINUE NORTH AND EAST THIS EARLY AFTERNOON.
STILL EXPECT CONDITIONS WILL IMPROVE AS THE DAY PROGRESSES. NEXT
AVIATION HIGHLIGHT WILL BE THUNDERSTORMS EXPECTED LATER TODAY
WEST...SPREADING EAST OVERNIGHT.



&&

.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.
&&

$$

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





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