212  
FXUS63 KUNR 231110  
AFDUNR  
 
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY  
NATIONAL WEATHER SERVICE RAPID CITY SD  
410 AM MST MON DEC 23 2024  
   
KEY MESSAGES
 
 
- SLIGHT CHANCES FOR FREEZING FOG/DRIZZLE ACROSS NORTHWESTERN SD  
TONIGHT  
 
- WARM TEMPERATURES AND MOSTLY DRY CONDITIONS EXPECTED THROUGH  
CHRISTMAS  
 

 
   
DISCUSSION
 
(TODAY THROUGH SUNDAY)  
ISSUED AT 318 AM MST MON DEC 23 2024  
 
SHORT WAVE RIDGING HAS BUILT ACROSS THE NORTHERN ROCKIES WITH DRY  
AIR FILTERING INTO THE REGION BEHIND A WEAK SHORTWAVE. SKIES  
ACROSS THE CWA ARE CLEAR WITH TEMPERATURES RANGING FROM THE TEENS  
TO LOW 20S ACROSS THE PLAINS AND PORTIONS OF THE BLACK HILLS TO  
THE UPPER 30S TO LOW 40S ACROSS THE EASTERN AND SOUTHERN SLOPES OF  
THE BLACK HILLS. PLEASANT AND MILD DAY ON TAP AS SHORTWAVE RIDGE  
AXIS MOVES ACROSS THE REGION, TEMPERATURES WILL RISE INTO THE  
UPPER 40S TO LOW 50S BY THIS AFTERNOON.  
 
SHORTWAVE TROUGH CROSSES THE CWA EARLY TUESDAY. AHEAD OF THE  
TROUGH, WEAK Q-VECTOR CONVERGENCE AND PERIOD OF AMPLE DEEP LAYER  
MOISTURE WILL RESULT IN SPOTTY LIGHT PRECIPITATION - MAINLY ACROSS  
NORTHEASTERN WY, THE BLACK HILLS, AND NORTHWESTERN SD. BUFKIT  
SOUNDINGS ACROSS NORTHWESTERN SD INDICATE A SHALLOW LAYER OF VERY  
MOIST AIR NEAR THE SURFACE WHICH COULD LEND TO THE DEVELOPMENT OF  
FOG/FREEZING FOG. WEAK SHEAR AT THE TOP OF THE SATURATED LAYER  
WOULD SUPPORT FREEZING DRIZZLE IN SOME AREAS AS TEMPERATURES DROP  
BELOW FREEZING TONIGHT INTO EARLY TUESDAY. FORECAST CONFIDENCE IN  
THIS SCENARIO IS LOW AS THE SATURATED LAYER NEAR THE SURFACE IS  
VERY SHALLOW -- HOWEVER HAVE OPTED TO MENTION SLIGHT CHANCES FOR  
FREEZING DRIZZLE ACROSS NORTHWESTERN SD FOR THIS FORECAST PACKAGE.  
HREF GRAND ENSEMBLE PROBS DO SHOW DECENT CHANCES OF DENSE FOG  
(50-80% PROBABILITIES OF VISIBILITY <0.5 MILES) ALONG THE EASTERN  
BOUNDARIES OF OUR CWA (SO EASTERN ZIEBACH COUNTY DOWN TO TRIPP  
COUNTY) TONIGHT INTO EARLY TUESDAY MORNING. PROBABILITIES OF DENSE  
FOG DECREASE FURTHER WEST BUT THERE ARE AREAS OF 20-40%  
PROBABILITIES ACROSS NORTHWESTERN SD INTO THE BLACK HILLS.  
 
IF PRECIP DOES OCCUR TONIGHT, CHANCES FOR MEASURABLE PRECIP  
(GREATER THAN 0.01") ARE VERY LOW WITH THE HREF GRAND ENSEMBLE  
PAINTING 10- 30% PROBS ACROSS NORTHWESTERN SD INTO THE NORTHERN  
BLACK HILLS AND NORTHEASTERN WY FOR TONIGHT THROUGH EARLY TUESDAY.  
THE LREF GRAND ENSEMBLE SEEMS EVEN MORE PESSIMISTIC ABOUT OUR  
ODDS WITH CHANCES ACROSS NORTHWESTERN SD < 5% AND 0-10% ACROSS  
NORTHWESTERN WY.  
 
SHORTWAVE RIDGING BUILDS INTO THE REGION BY CHRISTMAS WITH  
SOUTHERLY RETURN FLOW ADVECTING WARM AIR INTO THE CWA. A WEAK  
SHORTWAVE WILL CROSS THE REGION CHRISTMAS DAY, THOUGH MOISTURE  
WITH THIS SYSTEM WILL BE MINIMAL - KEEPING PRECIP CHANCES NEAR  
ZERO. A BRIEF PERIOD OF UPSLOPE ENHANCEMENT COMBINED WITH MODEST  
0-2KM RH (~70-80%) COULD SUPPORT THE DEVELOPMENT OF A FEW SNOW  
SHOWERS IN THE NORTHERN BLACK HILLS. CHANCES FOR ANY MEASURABLE  
SNOW WILL BE VERY LOW (LREF GRAND ENSEMBLE PAINTS 0-20% PROBS  
ACROSS THE BLACK HILLS).  
 
PROGRESSIVE UPPER LEVEL PATTERN CONTINUES THROUGH THE REST OF THE  
WEEK INTO THE WEEKEND WITH DETERMINISTIC GUIDANCE IN POOR  
AGREEMENT AS TO LOCATION, TIMING, AND STRENGTH OF ANY SYSTEMS.  
THIS TRANSLATES TO LOW CONFIDENCE IN PATTERN EVOLUTION AND THUS  
SENSIBLE WEATHER IMPACTS THROUGH THE REST OF THIS YEAR.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)  
ISSUED AT 410 AM MST MON DEC 23 2024  
 
VFR CONDITIONS ARE LIKELY FOR MOST OF THE AREA THRU THE PERIOD.  
HOWEVER, IFR/LIFR CIGS/VSBYS IN BR/FG ARE POSSIBLE TO PROBABLE (30  
TO 70% CHANCES) ALONG AND EAST OF A KHEI TO KICR LINE BEGINNING  
AROUND 00Z. MODEST IMPROVEMENT IS THEN EXPECTED FROM NORTH TO  
SOUTH THRU THE END OF THE PERIOD.  
 

 
   
UNR WATCHES/WARNINGS/ADVISORIES
 
 
SD...NONE.  
WY...NONE.  

 
 

 
 
DISCUSSION/KEY MESSAGES...WONG  
AVIATION...SHERBURN  
 
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