000  
FXUS63 KBIS 221939  
AFDBIS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BISMARCK ND  
239 PM CDT FRI OCT 22 2021  
   
SHORT TERM
 
(THIS EVENING THROUGH SATURDAY)  
ISSUED AT 239 PM CDT FRI OCT 22 2021  
 
BREEZY TO WINDY CONDITIONS EXPECTED ON SATURDAY.  
 
UPPER AIR ANALYSIS IS HIGHLIGHTED BY A MODERATELY AMPLIFIED  
PATTERN OVER THE WESTERN CONUS, WITH A DEEP PACIFIC TROUGH  
CROSSING THE WEST COAST AND A RIDGE DOWNSTREAM THROUGH THE  
NORTHERN ROCKIES. ANTI-CYCLONIC FLOW OVER THE NORTHERN PLAINS WAS  
EVIDENT ON WATER VAPOR IMAGERY AS SEVERAL VORTICITY LOBES WERE  
EXITING TO THE EAST. SUBSIDENCE AND POSSIBLY THE INFLUENCE OF  
EASTERLY UPSLOPE WINDS HAVE MAINTAINED CLOUDS THIS AFTERNOON IN  
THE CENTRAL PORTION OF THE STATE, AND WILL LIKELY LINGER IN SOME  
FORM THROUGH THE AFTERNOON. PRESSURE FALLS OVER THE FAR WEST DUE  
TO A DEEPENING SURFACE LOW OVER THE NORTHERN HIGH PLAINS HAVE  
CREATED BREEZY CONDITIONS IN THE NORTHWEST, AND WILL INCREASE  
WINDS THIS EVENING ACROSS MORE OF THE WEST AND CENTRAL AS THE  
SURFACE LOW SHIFTS EAST.  
 
SATURDAY WILL FEATURE BREEZY CONDITIONS ACROSS THE WEST AND  
CENTRAL AS A TIGHT PRESSURE GRADIENT AND MODERATELY STRONG 850MB  
WINDS WILL PROVIDE SOUTHEAST WINDS OF 15 TO 25 MPH. THE HIGH END  
WIND POTENTIAL WILL DEPEND ON BOUNDARY LAYER MIXING, WHICH IS  
UNCERTAIN GIVEN THE UNFAVORABLE FLOW DIRECTION (SOUTHEAST) AND THE  
POTENTIAL FOR CLOUD COVER LIMITING INSOLATION. THE SATURDAY  
AFTERNOON WINDS WITH THIS FORECAST WERE NUDGED ABOVE NBM, BUT  
DOESN'T QUITE GET TO ADVISORY CRITERIA YET. OTHERWISE PARTLY TO  
MOSTLY SKIES AND HIGHS IN THE 40S WILL BE THE OTHER WEATHER  
CONDITIONS, WITH CHANCES FOR PRECIPITATION INCREASING SATURDAY  
NIGHT.  
   
LONG TERM
 
(SATURDAY NIGHT THROUGH FRIDAY)  
ISSUED AT 239 PM CDT FRI OCT 22 2021  
 
A BROAD AREA OF MID LEVEL SHORTWAVE ENERGY WILL BEGIN TO SPREAD OVER  
THE NORTHERN PLAINS SATURDAY NIGHT. THE ASSOCIATED FORCING  
MECHANISMS (Q-VECTOR CONVERGENCE, PVA, WEAK ISENTROPIC ASCENT)  
SHOULD PROVIDE ENOUGH LIFT TO GENERATE AN AREA OF LIGHT  
PRECIPITATION MOVING FROM WEST TO EAST ACROSS WESTERN AND CENTRAL  
NORTH DAKOTA SATURDAY NIGHT INTO SUNDAY AFTERNOON. THESE  
PRECIPITATION CHANCES ARE SUPPORTED BY NUMEROUS ENSEMBLE DATASETS.  
SOME MODEL SOUNDINGS SHOW A DEEP ISOTHERMAL LAYER NEAR ZERO DEGREES  
CELSIUS AND/OR A LACK OF MOISTURE IN ICE-PRODUCING LAYERS ALOFT  
(COLDER THAN -10 C). BUT GIVEN FORECAST SURFACE AIR TEMPERATURES AT  
OR ABOVE FREEZING, AND WARMER GROUND TEMPERATURES AT THIS TIME OF  
YEAR, FREEZING RAIN IS NOT AN EXPECTED TYPE. SOME SNOW CANNOT BE  
RULED OUT, MAINLY ACROSS NORTH CENTRAL NORTH DAKOTA WHERE THERMAL  
PROFILES ARE SLIGHTLY COOLER. BUT AGAIN, NO IMPACTS ARE EXPECTED.  
DECREASING CLOUDS IN FAR WESTERN NORTH DAKOTA SUNDAY AFTERNOON COULD  
ALLOW HIGHS TO REACH THE 50S. OTHERWISE, 40S ARE EXPECTED.  
 
A PROGRESSIVE PATTERN WILL BRING AN AMPLIFIED, TRANSIENT RIDGE OVER  
THE NORTHERN PLAINS ON MONDAY AS A POWERFUL TROUGH DIGS INTO THE  
WESTERN CONUS. THE MAIN EXPECTED IMPACT FROM THIS SETUP IS STRONG  
SOUTHERLY SURFACE WINDS. ENSEMBLE DATASETS THAT COMPARE CURRENT  
OUTPUT TO CLIMATOLOGY (E.G., NAEFS AND ECMWF SITUATIONAL AWARENESS  
TABLES) HIGHLIGHT WESTERN NORTH DAKOTA FOR SURFACE TO 850 MB WINDS  
NEAR THE 99TH PERCENTILE, AND DETERMINISTIC GUIDANCE IS CONSISTENT  
IN SHOWING 900-800 MB WINDS AROUND 40-50 KTS. A CAPPING INVERSION  
ABOVE THE BOUNDARY LAYER AND THE LACK OF A WESTERLY COMPONENT TO THE  
WIND FIELD COULD DAMPEN BOUNDARY LAYER MIXING AND KEEP SURFACE GUSTS  
BELOW THE BOUNDARY LAYER MAXIMUM. HOWEVER, SUSTAINED SURFACE WIND  
SPEEDS TEND TO OVER-PERFORM GUIDANCE IN THESE SETUPS. THIS PERIOD  
WILL NEED TO BE MONITORED FOR POTENTIAL HEADLINES AS PROBABILITIES  
FOR ADVISORY CRITERIA WINDS CONTINUE TO SHOW AN INCREASING TREND.  
THE AFOREMENTIONED CAPPING INVERSION WILL ALSO KEEP TEMPERATURES  
COOLER THAN WHAT IS TYPICALLY SEEN IN THIS HEIGHT PATTERN AND  
THERMAL PROFILE, THOUGH THEY SHOULD STILL BE NEAR NORMAL FOR LATE  
OCTOBER.  
 
THE DEEP WESTERN CONUS TROUGH IS FORECAST TO EJECT INTO THE GREAT  
PLAINS BY WEDNESDAY, WITH A NEGATIVELY TILTED AXIS SHOWING UP IN  
ENSEMBLE MEAN HEIGHT FIELDS. THE MOST UNCERTAIN ASPECT OF THIS  
SYSTEM IS TIMING, WITH CLUSTER ANALYSIS SHOWING ECMWF ENSEMBLE  
MEMBERS FAVORING A SLOWER SOLUTION. REGARDLESS OF THE TIMING,  
ENSEMBLE SYSTEMS SHOWS HIGH CONFIDENCE IN PRECIPITATION CHANCES,  
WHICH CAN BE CONFIRMED BY AN ANALYSIS OF FORCING MECHANISMS IN  
DETERMINISTIC GUIDANCE. NBM TEMPERATURE GUIDANCE SUGGESTS MOST, IF  
NOT ALL PRECIPITATION WILL FALL AS RAIN, WITH ONLY ISOLATED MIXES OF  
SNOW POSSIBLE DURING EARLY MORNING HOURS. DESPITE THE OVERALL  
LOWERING OF HEIGHTS ALOFT, STRONGER BOUNDARY LAYER MIXING MAY  
ACTUALLY RESULT IN WARMER SURFACE TEMPERATURES THROUGH THE MIDDLE OF  
THE WEEK. IT IS ALSO LIKELY TO REMAIN WINDY AT TIMES THROUGH MID  
WEEK, PARTICULARLY WITH THE PRESSURE RISES BEHIND THE MAIN TROUGH  
AXIS. UNCERTAINTY IN THE SYNOPTIC PATTERN GROWS BY THE END OF THE  
WEEK, BUT A TRANSITION TO NORTHWEST FLOW ALOFT WITH AN UPPER LEVEL  
RIDGE OVER THE ROCKIES SEEMS TO BE A MORE LIKELY OUTCOME AT THIS  
TIME.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)  
ISSUED AT 1226 PM CDT FRI OCT 22 2021  
 
GENERALLY VFR CONDITIONS THROUGH THE TAF PERIOD, THOUGH CHANCE OF  
REDUCED CATEGORIES EARLY SATURDAY MORNING. SOUTHEAST WINDS WILL  
GRADUALLY INCREASE THIS EVENING IN THE WEST, BECOMING 15-25 KTS AT  
KDIK-KXWA AFTER 10Z. WITH SOUTHERLY WINDS DRAWING UP LOW LEVEL  
MOISTURE, MVFR CIGS MAY DEVELOP IN SOME ARES, MORE LIKELY  
SOUTHWEST. CONFIDENCE IN LOCATION AND COVERAGE IS LOW AT THIS  
TIME, BUT WILL NEED MONITORING. SOUTHEAST WINDS BEGIN TO INCREASE  
CENTRAL LATER SATURDAY MORNING.  
 

 
   
BIS WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
SHORT TERM...AE  
LONG TERM...MH  
AVIATION...AE  
 
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