FXUS65 KCYS 042216
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
316 PM MST FRI DEC 4 2009

.SHORT TERM...TONIGHT THROUGH SUNDAY...
STRONG PRESSURE FALLS ARE OCCURRING ACROSS THE REGION AHEAD OF A
STRONG UPPER LOW DIGGING INTO THE NORTHERN ROCKIES THIS AFTERNOON.
THIS IS ACTING TO ACCELERATE THE DEEPENING OF THE LEESIDE SFC
TROUGH AND MAINTAINING THE TIGHT SFC PRESSURE GRADIENT ACROSS
CENTRAL WYOMING. THUS EXPECT THE WINDS TO CONTINUE TO BE STRONG
THROUGH THE EVENING SO WILL LET THE HIGH WIND WARNING CONTINUE
THROUGH 11 PM TONIGHT. WINDS WILL EASE SLIGHTLY OVERNIGHT AS THE
SYSTEM APPROACHES AND THE LEE SIDE TROUGH BEGINS TO SHIFT TO THE
EAST. A COLD FRONT ASSOCIATED WITH THE SYSTEM WILL TRACK SOUTH
ACROSS THE REGION SATURDAY MORNING AND WILL BE THROUGH MOST ZONES
BY MIDMORNING. WINDS WILL VEER TO THE NORTH BEHIND THE FRONT WITH
ARCTIC AIR FILTERING IN THROUGH THE DAY. THUS EXPECT SATURDAYS
MAXIMUM TEMPS TO BE EARLY ON WITH STEADY OR DECREASING TEMPS
THROUGH THE DAY. THE JET ALOFT WILL STRENGTHEN SATURDAY NIGHT AND
INTO SUNDAY AND WILL BECOME ORIENTED ROUGHLY WEST TO EAST BY THE
AFTERNOON. THIS WILL ENHANCE MOISTURE ADVECTION OFF THE PACIFIC
INTO THE CENTRAL US. THE INITIAL SHORTWAVE WILL ROTATE AROUND THE
BASE OF THE MEAN UPPER LOW SATURDAY NIGHT INTO SUNDAY. DEEPENING
UPSLOPE FLOW BEHIND THE FRONT DURING THIS TIME COMBINED WITH
INCREASING SYNOPTIC LIFT WILL INCREASE CHANCES FOR SNOW SATURDAY
NIGHT. NAM IS SHOWING INCREASING OMEGA OVERNIGHT SO EXPECT BEST
SNOW POTENTIAL LATE SATURDAY NIGHT INTO SUNDAY MORNING.

WITH VERY COLD TEMPERATURES THROUGH THE COLUMN...EXPECT SNOW RATIOS 
TO BE HIGHER THAN AVERAGE LIKELY RESULTING IN 5 TO 8 INCHES IN THE 
MOUNTAINS WITH 2 TO 4 INCHES IN THE LARAMIE FOOTHILLS AND VALLEYS BY 
LATE SUNDAY MORNING. EXPECT THE EAST FACING SLOPES OF THE LARAMIE 
RANGE TO SEE THE HIGHEST SNOW TOTALS. SNOW WILL TAPER OFF THROUGH 
THE DAY AS THE UPPER LEVEL SHORTWAVE MOVES ACROSS THE CWA...HOWEVER 
PERSISTENT UPSLOPE FLOW WILL KEEP A CHANCE FOR LIGHT SNOW THROUGH 
THE DAY SUNDAY.

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...
MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT IN THE OVERALL PATTERN 
PROGRESSION THROUGH THIS PERIOD...BUT STILL DIFFER SOME ON THE 
DETAILS. UPPER RIDGING WILL PERSIST OVER THE ERN PACIFIC THROUGH 
NEXT WEEK...WHICH WILL EFFECTIVELY MAINTAIN A DOWNSTREAM LONGWAVE 
TROUGH OVER THE LOWER 48. INITIALLY...AN UPPER LOW LOCATED OVER 
OREGON WILL DEEPEN AS IT DIGS SOUTH INTO NRN CALIFORNIA. HEIGHTS 
WILL RISE OUT AHEAD OF THIS FEATURE ACROSS THE INTERMOUNTAIN WEST. A 
PERSISTENT SFC HIGH WILL BE LOCATED ACROSS SRN ALBERTA. THIS SFC 
HIGH WILL COMBINE WITH FALLING SFC PRESSURES OVER THE GREAT BASIN TO 
PRODUCT UPSLOPE FLOW ALONG THE FRONT RANGE. ALTHOUGH THE SYSTEM 
ITSELF WILL REMAIN OVER THE GREAT BASIN FOR SUNDAY NIGHT AND 
MONDAY...INCREASING LOW-LEVEL UPSLOPE WILL COMBINE WITH INCREASING 
WEST/SOUTHWEST FLOW ALOFT FOR THE BEGINNING OF 36 TO 48 HOUR 
OVERRUNNING SET-UP. SO...EXPECT LIGHT SNOW TO INCREASE ACROSS THE 
AREA SUNDAY NIGHT AND MONDAY...ESPECIALLY IN THE MOUNTAINS...THOUGH 
EXPECT ANY ACCUMULATION DURING THIS TIMEFRAME TO REMAIN LIGHT. THE 
UPPER LOW WILL MOVE FROM THE GREAT BASIN EAST INTO COLORADO MONDAY 
NIGHT. THE GFS IS FURTHEST NORTH AND STRONGEST WITH THE SFC 
LOW...WHILE THE ECMWF IS WEAKER AND TAKES IT FURTHER SOUTH TOWARDS 
THE TX/OK PANHANDLES WITH TIME. THIS PERIOD WILL NEED TO BE 
MONITORED CLOSELY AS A SHIFT OF THE STORM TRACK WOULD HAVE IMPACT ON 
LOCATION OF BEST LIFT AND ASSOCIATED SNOW ACCUMULATIONS. FOR NOW 
HAVE CONTINUED THE TREND OF INCREASING POPS FOR MONDAY THROUGH 
TUESDAY. DRIER NORTHWEST FLOW WILL WORK IN FOR TUESDAY NIGHT THROUGH 
WEDNESDAY NIGHT...WITH ADDITIONAL MOISTURE IMPACTING MAINLY 
OROGRAPHICALLY FAVORED AREAS WEST OF THE LARAMIE RANGE FOR THURSDAY 
AND FRIDAY. TEMPERATURES WILL BE UNSEASONABLY COLD FOR MONDAY AND 
TUESDAY...WITH HIGHS ONLY CLIMBING INTO THE TEENS EAST...AND PERHAPS 
ONLY SINGLE DIGITS IN WRN AND NRN ZONES. CLOUDS WILL THIN FOR 
WEDNESDAY/THURSDAY AND WHEN COMBINED WITH WARMING MID-LEVEL 
TEMPERATURES...EXPECT HIGHS TO MODERATE BACK INTO THE UPPER 20S TO 
LOW 30S BY THURSDAY AND FRIDAY.

&&

.AVIATION...
STRONG WEST WINDS WILL GUST TO NEAR 40 TO 45 KNOTS IN AND AROUND 
AREA MOUNTAINS THROUGH THIS EVENING...BEFORE GRADUALLY SLOWING 
OVERNIGHT IN ADVANCE OF AN APPROACHING COLD FRONT. THE COLD FRONT 
WILL MOVE THROUGH KDGW BY AROUND 16Z...THROUGH KCYS/KBFF/KCDR 
BETWEEN 18 AND 20Z. VFR CONDITIONS WILL PREVAIL OVERNIGHT TONIGHT 
AND THROUGH SATURDAY MORNING...BUT WILL LOWER TO MVFR/IFR BEHIND THE 
FRONT...INITIALLY AT KDGW AND KCDR BY EARLY AFTERNOON...SPREADING 
SOUTH INTO KLAR AND KCYS BY LATE AFTERNOON. SNOW WILL BEGIN TO 
DEVELOP BEHIND THE FRONT SATURDAY AFTERNOON AND CONTINUE THROUGH 
SATURDAY NIGHT. GENERALLY 1 TO 2 INCHES CAN BE EXPECTED AT NEBRASKA 
TERMINALS...WITH 2 TO 4 INCHES AT WYOMING TERMINALS BY MID-DAY 
SUNDAY.

&&

.FIRE WEATHER...
GUSTY WESTERLY WINDS WILL CONTINUE ACROSS THE DISTRICT THROUGH THIS 
EVENING. A COLD FRONT WILL BRING INCREASING PRECIPITATION CHANCES TO 
THE AREA LATE SATURDAY AND INTO EARLY NEXT WEEK. TEMPERATURES WILL 
CONTINUE TO BE MUCH COLDER THAN NORMAL THROUGH AT LEAST THE MIDDLE 
OF NEXT WEEK.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING UNTIL 11 PM FRIDAY FOR WYZ106-WYZ110.
NE...NONE.

&&

$$

SHORT TERM/AVIATION...RJM
LONG TERM...HAHN