300
FXUS63 KBIS 210921
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
421 AM CDT THU MAY 21 2026
KEY MESSAGES
- WIDESPREAD RAIN SHOWERS DEVELOPING IN WESTERN NORTH DAKOTA
LATE THIS AFTERNOON AND EVENING, CONTINUING THROUGH FRIDAY
AND SPREADING INTO CENTRAL AND EASTERN NORTH DAKOTA FRIDAY
AFTERNOON THROUGH FRIDAY NIGHT.
- MEDIUM TO HIGH CHANCES FOR AN AXIS OF AT LEAST HALF AN INCH
OF RAIN IN WESTERN NORTH DAKOTA, WITH LOW TO MEDIUM CHANCES
FOR EXCEEDING 1 INCH OF RAIN.
- NEAR TO SLIGHTLY BELOW NORMAL TEMPERATURES THROUGH FRIDAY,
WARMING TO WELL ABOVE NORMAL BY THE END OF THE HOLIDAY
WEEKEND.
DISCUSSION
ISSUED AT 421 AM CDT THU MAY 21 2026
THE MAIN STORY IN THE SHORTER TERM FORECAST PERIOD IS THE
EXPECTATION FOR BENEFICIAL RAINFALL ACROSS MUCH OF WESTERN AND
TO A LESSER EXTENT, PARTS OF CENTRAL NORTH DAKOTA LATE THIS
AFTERNOON THROUGH FRIDAY NIGHT.
SYNOPSIS: AN UPPER LEVEL LOW IS SPINNING OVER SOUTHWEST
SASKATCHEWAN EARLY THIS MORNING, WITH A TROUGH AXIS EXTENDING
SOUTHWESTWARD TO SOUTHERN IDAHO. A NEAR-STATIONARY SURFACE
TROUGH IS LOCATED FROM THE SOUTHEAST CORNER OF SASKATCHEWAN TO
NORTHEAST WYOMING. AS THE CLOSED UPPER LOW CONTINUES TO SPIN
ACROSS SOUTHERN SASKATCHEWAN THROUGHOUT THE DAY, THE BASE OF
THE UPPER TROUGH WILL DIG SOUTHEASTWARD THROUGH SOUTHERN
WYOMING AND SPIN UP ANOTHER CLOSED CIRCULATION OVER THE BLACK
HILLS FRIDAY MORNING. THE SOUTHERN CLOSED LOW IS FORECAST TO
BECOME THE PREDOMINANT FEATURE ON FRIDAY AND SPIN NORTHEASTWARD
INTO THE RED RIVER VALLEY FRIDAY NIGHT, WITH SOME UNCERTAINTY ON
THE EVOLUTION OF AND/OR INTERACTION WITH THE NORTHERN CLOSED
LOW. ALL THE WHILE, THE SURFACE TROUGH WILL BECOME INVERTED AS
IT ATTACHES TO LEE CYCLOGENESIS IN NORTHEAST COLORADO BY
TONIGHT. BY THE TIME THE COLORADO LOW EJECTS NORTHEASTWARD ON
FRIDAY, ANOTHER SURFACE LOW COULD FORM NEAR THE BLACK HILLS AND
CREATE A DOUBLE-BARREL SURFACE LOW THAT ATTENDS TO THE SOUTHERN
UPPER LOW.
THE MAIN FOCUS FOR CONTINUOUS SHOWERS THROUGH FRIDAY MORNING IS
ALONG THE INVERTED TROUGH AXIS IN WESTERN NORTH DAKOTA.
ENSEMBLE SYSTEMS CONTINUE TO HONE IN ON A CORRIDOR OF HIGHEST
RAIN AMOUNTS, BUT THERE IS STILL SOME SPREAD THAT NOW APPEARS TO
BE DEPENDENT ON MODEL RESOLUTION. GLOBAL ENSEMBLES FAVOR A
CORRIDOR OF HIGHEST MEAN QPF AND THRESHOLD PROBABILITIES FROM
AROUND LEMMON, SD TO MINOT. IN HIGH-RESOLUTION ENSEMBLES, THIS
SAME AXIS IS SHIFTED WESTWARD FROM BETWEEN BOWMAN AND HETTINGER
TO STANLEY. REGARDLESS OF LOCATION, ALL ENSEMBLE SYSTEMS SHOW
HIGH PROBABILITIES FOR AT LEAST HALF AN INCH OF RAIN AND LOW TO
MEDIUM PROBABILITIES FOR AT LEAST ONE INCH OF RAIN. BUT THE HREF
CONTAINS HIGHER PROBABILITIES FOR EXCEEDING ONE INCH, AND ITS
PROBABILITY-MATCHED MEAN QPF SHOWS A CORRIDOR OF 1.5 TO 2
INCHES, WITH LOCALIZED AREAS EVEN EXCEEDING 3 INCHES. THESE
HIGHER RAIN PROJECTIONS BY CAMS ARE UNDOUBTEDLY BEING DRIVEN BY
TRAINING CONVECTION, FOR WHICH THERE APPEAR TO BE HIGH CHANCES
OF OCCURRING THIS EVENING INTO THE OVERNIGHT HOURS. INGREDIENTS
SUPPORTING THIS INCLUDE SKINNY CAPE PROFILES WITH UP TO 1000
J/KG, HIGH DEEP-LAYER RH, AND FAVORED STORM MOTIONS PARALLEL TO
THE INVERTED TROUGH. THE MAIN RISK FROM THUNDERSTORMS WILL BE
HEAVY DOWNPOURS. THERE DOES NOT APPEAR TO BE ENOUGH SHEAR TO
SUPPORT STRONGER CONVECTION, BUT SOME SMALL HAIL AND GUSTY WINDS
CANNOT BE RULED OUT. GIVEN THE SEASONAL MOISTURE DEFICITS, THE
RISK FOR FLOODING IS VERY LOW. BUT THERE COULD BE PONDING OF
WATER IN URBAN, LOW-LYING, AND POOR DRAINAGE AREAS WHERE THE
HEAVIEST RAIN FALLS.
THE INVERTED SURFACE TROUGH IS FORECAST TO SHIFT VERY LITTLE,
IF AT ALL ON FRIDAY. THIS WILL CONTINUE TO PRODUCE SHOWERS OVER
WESTERN NORTH DAKOTA, BUT WEAKER BUOYANCY SHOULD KEEP RAINFALL
RATES LOWER ON FRIDAY. BY FRIDAY AFTERNOON, THE NEARLY-STACKED
LOW OVER SOUTH DAKOTA WILL BEGIN TO PUSH A LARGE AREA OF MOSTLY
STRATIFORM RAIN WITH SOME POSSIBLE EMBEDDED CONVECTIVE ELEMENTS
INTO SOUTH CENTRAL AND SOUTHEASTERN NORTH DAKOTA. THIS SHIELD OF
RAIN WILL PROGRESS NORTH-NORTHEASTWARD THROUGH THE EVENING AND
INTO FRIDAY NIGHT. MOST AREAS IN CENTRAL AND EASTERN NORTH
DAKOTA WILL SEE ONLY A 3-6 HOUR PERIOD OF RAINFALL AT MOST, BUT
THE WRAP-AROUND DEFORMATION ZONE COULD STALL OVER PART OF SOUTH
CENTRAL NORTH DAKOTA FOR A LONGER DURATION RAINFALL. FOR AREAS
ALONG AND EAST OF HIGHWAY 83, THERE ARE LOW (NORTH) TO MEDIUM
(SOUTH) CHANCES FOR EXCEEDING HALF AN INCH OF RAIN THROUGH
FRIDAY NIGHT, WITH ONLY VERY LOW CHANCES FOR EXCEEDING ONE INCH.
HIGH TEMPERATURES TODAY ARE FORECAST TO REACH AROUND 65 TO 70
DEGREES, EXCEPT IN THE FAR WEST WHERE THICKER CLOUD COVER AND
DEVELOPING SHOWERS COULD KEEP HIGHS CLOSER TO 60. WITH
INCREASING CONFIDENCE IN WIDESPREAD RAIN AND CLOUDS ON FRIDAY,
THE HIGH TEMPERATURE FORECAST HAS IN TURN COOLED INTO THE MID
50S TO MID 60S, WHICH MAY STILL BE A LITTLE TOO WARM. LOWS
TONIGHT SHOULD STAY IN THE 40S. FRIDAY NIGHT COULD BE COOLER,
PARTICULARLY IN THE SOUTHWEST WHERE THERE ARE HIGHER ODDS FOR
DECREASING CLOUD COVER. IF A CLEAR SKY DOES EMERGE THERE, LOWS
FALLING TO NEAR FREEZING CANNOT BE RULED OUT.
CONFIDENCE REMAINS HIGH IN A STRONG WARMING TREND THROUGH THE
HOLIDAY WEEKEND, ALONG WITH WITH DRIER CONDITIONS AS A RIDGE
TRIES TO BUILD OVER THE CENTRAL CONUS. THE PRECEDING LOW
PRESSURE SYSTEM NOW LOOKS A TAD SLOWER TO DEPART THE REGION,
WHICH COULD KEEP HIGHS ON SATURDAY IN THE MID 60S TO MID 70S AND
ALLOW DIURNAL SHOWERS TO DEVELOP. THERE COULD ALSO BE SOME
WEAKER SHORTWAVE ENERGY CROSSING THE REGION ON SUNDAY IN A
TRANSITORY QUASI-ZONAL FLOW REGIME. THE RIDGE FINALLY DOES LOOK
TO BECOME WELL ESTABLISHED ON MEMORIAL DAY, ALBEIT WITH SOME
PLACEMENT UNCERTAINTY OF ITS AXIS. THE NBM CONTINUES TO
ADVERTISE HIGHS IN THE MID 80S TO NEAR 90 FOR THE HOLIDAY. WELL
ABOVE NORMAL TEMPERATURES REMAIN FAVORED TO CLOSE OUT MAY, WITH
HIGHS MOSTLY IN THE 80S. PRECIPITATION CHANCES REMAIN UNCERTAIN
BEYOND MEMORIAL DAY, DRIVEN BY WHETHER OR HOW MUCH THE RIDGE
WILL BLOCK A DEEP WESTERN CONUS TROUGH FROM ADVANCING EASTWARD.
BUT THERE DOES APPEAR TO BE CONSENSUS FOR EITHER SOUTHWEST OR
SOUTHERLY FLOW ALOFT OVER THE NORTHERN PLAINS NEXT WEEK, WHICH
WOULD EVENTUALLY POINT TOWARDS INCREASED CHANCES FOR SHOWERS
AND THUNDERSTORMS.
AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 421 AM CDT THU MAY 21 2026
A FEW LIGHT RAIN SHOWERS ARE POSSIBLE ACROSS WESTERN AND CENTRAL
NORTH DAKOTA THIS MORNING, WITH VFR CONDITIONS EXPECTED. FROM
LATE THIS AFTERNOON THROUGH TONIGHT, A SIGNIFICANT INCREASE IN
SHOWERS IS EXPECTED ACROSS WESTERN AND INTO NORTH CENTRAL NORTH
DAKOTA, WITH EMBEDDED THUNDERSTORMS IN THE LATE AFTERNOON AND
EVENING. CEILINGS COULD FALL TO MVFR LEVELS UNDER RAIN, AND THE
HEAVIEST SHOWERS AND STORMS COULD BRIEFLY REDUCE VISIBILITY TO
IFR LEVELS. WESTERN NORTH DAKOTA WILL SEE VARIABLE WINDS AROUND
5-10 KTS THROUGH THE FORECAST PERIOD, WHILE CENTRAL NORTH DAKOTA
MAINTAINS A SOUTHERLY BREEZE, INCREASING BACK TO AROUND 15-25
KTS THIS AFTERNOON.
BIS WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...HOLLAN
AVIATION...HOLLAN
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