Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 230204
AFDBIS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
904 PM CDT FRI AUG 22 2014

.UPDATE...
ISSUED AT 844 PM CDT FRI AUG 22 2014

SHORTWAVE TROUGH OVER THE SOUTHWEST US CONTINUES TO MIGRATE
NORTHWARD WITH BROAD DIFFLUENT FLOW ALOFT OVER THE NORTHERN
PLAINS THIS EVENING. WEAK WARM ADVECTION OVER A STATIONARY
FRONTAL BOUNDARY ACROSS SOUTH DAKOTA LIKELY THE SOURCE FOR SOME
PERSISTENT WEAK SHOWERS IN CENTRAL NORTH DAKOTA THAT OCCASIONALLY
FLARE UP A BIT FROM TIME TO TIME BUT HAVE NOT BEEN ABLE TO
ESTABLISH THEMSELVES. BISMARCK 00Z SOUNDING SHOWS PLENTY OF
MOISTURE WITH 1.37 PWAT WITH ABR NEARLY THE SAME AT 1.41. BOTH
HAVE GENERALLY TALL AND SKINNY CAPE SUITABLE FOR HEAVY RAIN
POTENTIAL WITH WEAK OR LITTLE CAP. CONVECTION ACROSS THE SOUTHWEST
LIKELY TO CONTINUE TO SLOWLY EVOLVE AS LAPSE RATES ARE WEAK IN THE
LOW LEVEL AND ALOFT. BUT EXPECT WE WILL BEGIN TO SEE AN INCREASE
IN SHOWERS ACROSS THE SOUTHWEST AFTER MIDNIGHT AS THE UPPER
SHORTWAVE APPROACHES. FORECAST TRENDS LOOK GOOD.

UPDATE ISSUED AT 619 PM CDT FRI AUG 22 2014

LATEST SATELLITE WATER VAPOR CHANNEL SHOWS A SIGNIFICANT SHORTWAVE
TROUGH NEAR THE FOUR CORNERS REGION MOVING NORTH. CONVECTION
BEGINNING TO INCREASE IN RESPONSE TO THE BROAD DIFFLUENT FLOW
ALOFT NORTH OF THE SHORTWAVE ACROSS WYOMING AND MONTANA. THIS
CONVECTION WILL MAKE ITS WAY INTO WESTERN NORTH DAKOTA LATE
TONIGHT. THIS SUPPORTS FORECAST TRENDS AND LENDS CONFIDENCE TO
THE CURRENT FORECAST. HIGHS TODAY WHERE COOLER THAN FORECAST WITH
HIGHS IN THE 60S WEST AND NORTH. THIS MAY BE A TREND FOR THE NEXT
FEW DAYS. THIS UPDATE WILL ADD ISOLATED SHOWERS NORTH OF BISMARCK
AND ALONG THE CANADIAN BORDER AS DEPICTED ON RADAR.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 321 PM CDT FRI AUG 22 2014

THE MAIN FORECAST ISSUE IN THE SHORT TERM PERIOD IS THE POTENTIAL
FOR FLOODING. THE DETERMINISTIC MODELS ARE COMING INTO BETTER
AGREEMENT WITH THE EVOLUTION OF A STRONG UPPER LEVEL LOW PRESSURE
SYSTEM MOVING ACROSS THE NORTHERN ROCKIES THROUGH SATURDAY THEN
LIFTING INTO THE NORTHERN PLAINS SATURDAY NIGHT INTO SUNDAY.

THERE HAS BEEN A GOOD CONSENSUS REGARDING A PRECIPITATION MAX OVER
EASTERN MONTANA. MODELS HAVE DIFFERED IN A SECOND MAX ACROSS THE
NORTHERN PLAINS. THE GFS/ECMWF/GEM WERE FARTHER EAST WITH A
SECONDARY MAX... WHILE THE NAM HAS BEEN MORE CONSISTENT WITH
BRINGING A SWATH OF HIGHER QPF ACROSS MUCH OF THE CWA. MODELS ARE
NOW MORE IN LINE WITH THE SECONDARY MAX LIFTING NORTH THROUGH
CENTRAL NORTH DAKOTA...WITH TWO DAY QPF GREATER THAN 1 INCH ACROSS
A MAJORITY OF THE CWA...AND A MAX OF OVER 2 INCHES OVER THE NORTH
CENTRAL...ENDING SUNDAY AFTERNOON.

TYPICALLY A BIG RAIN EVENT LIKE THIS IN AUGUST MIGHT NOT CAUSE TOO
MUCH OF A PROBLEM. HOWEVER...WITH OUR CURRENT SOIL MOISTURE
CONDITIONS GIVEN RECENT HEAVY RAINS...THE THREAT OF EXCESSIVE RAIN
INCREASES. WITH MANY AREA NEAR SATURATED OR SATURATED...WILL ISSUE
A FLOOD WATCH FOR MOST OF WESTERN AND CENTRAL NORTH DAKOTA. SEE
THE SEPARATE FLOOD DISCUSSION BELOW FOR ADDITIONAL DETAILS.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 321 PM CDT FRI AUG 22 2014

BY SUNDAY EVENING THE MODELS ARE DEPICTING AN UPPER LEVEL LOW OVER
EASTERN MONTANA/NORTHERN NORTH DAKOTA...WITH THE LOW LIFTING
NORTHEASTWARD INTO MANITOBA BY DAYBREAK MONDAY MORNING. MEANWHILE AN
UPPER LEVEL TROUGH REMAINS OVER THE ROCKIES. THIS TROUGH MOVES
EASTWARD ACROSS MONTANA MONDAY AND MONDAY NIGHT...AND ACROSS THE
DAKOTAS ON TUESDAY/TUESDAY NIGHT.

THUS ON SUNDAY NIGHT...THE LINGERING SHOWERS SHOULD BE MAINLY
CONFINED TO THE NORTHERN COUNTIES. SMALL CHANCES OF SHOWERS CAN BE
EXPECTED MONDAY AND TUESDAY AS THE WESTERN LONGWAVE TROUGH MOVES
THROUGH THE REGION.

WEDNESDAY UPPER LEVEL RIDGING TAKES PLACE...KEEPING THE FORECAST
AREA MAINLY DRY MID-WEEK THROUGH THE END OF THE WEEK.

REGARDING TEMPERATURES...COOLER THAN AVERAGE WITH HIGHS IN THE 60S
MONDAY AND TUESDAY...WARMING TO THE 70S WEDNESDAY...AND UPPER 70S
AND LOWER 80S BY THURSDAY/FRIDAY. LOWS IN THE 40S TO LOWER 50S
SUNDAY NIGHT AND MONDAY NIGHT...WITH LOWS IN THE 50S THROUGH NEXT
WEEK.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 844 PM CDT FRI AUG 22 2014

A WET WEATHER PATTERN WILL BRING DETERIORATING AVIATION WEATHER TO
THE REGION TONIGHT THROUGH SATURDAY. MAIN HAZARDS TO AVIATION
INCLUDE MVFR TO IFR CEILINGS IN RAIN SHOWERS AND AREAS OF FOG WITH
EMBEDDED THUNDERSTORMS. THUNDERSTORMS PRIMARILY SOUTHWEST
INITIALLY THEN SPREAD TO THE NORTHEAST SATURDAY. CONDITIONS WILL
PROGRESSIVELY FALL FROM LOW VFR TO MVFR TO IFR.



&&

.HYDROLOGY...
ISSUED AT 321 PM CDT FRI AUG 22 2014

GOING INTO THE COMING WEEKEND...THERE IS NO AREA OF THE CWA WHERE
LOCALIZED FLOODING CAN BE RULED OUT. MODERATE TO HEAVY RAINS OVER
THE PAST WEEK HAVE KEPT SOIL MOISTURE ABNORMALLY HIGH ACROSS THE
CWA. HEAVY RAINS ARE LIKELY TO OVERWHELM THE CURRENT INFILTRATION
RATES OF THE SOIL AND LEAD TO OVERLAND FLOODING AND CREATE A GREATER
THAN NORMAL RUNOFF. THIS ENHANCED RUNOFF RATES WILL ENCOUNTER
ALREADY WELL ABOVE NORMAL FLOW IN NEARLY EVERY SIGNIFICANT SMALL
STREAM AND RIVER IN THE AREA. WHILE THERE IS NO REASONABLE
EXPECTATION OF MAJOR RIVER FLOODING...AT A MINIMUM THERE WILL BE
SIGNIFICANT WITHIN BANK RISES...AND MINOR RIVER FLOODING CANNOT BE
RULED OUT.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
FLOOD WATCH FROM 1 AM CDT /MIDNIGHT MDT/ SATURDAY THROUGH SUNDAY
AFTERNOON FOR NDZ017>020-031>034-040>046-050.

FLOOD WATCH FROM SATURDAY MORNING THROUGH SUNDAY AFTERNOON FOR
NDZ001>005-009>013-021>023-035-036-047.

&&

$$

UPDATE...WAA
SHORT TERM...TWH
LONG TERM...JV
AVIATION...WAA
HYDROLOGY...TWH





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