450
FXUS65 KCYS 040437
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1037 PM MDT SAT MAY 3 2025
KEY MESSAGES
- A PLEASANT SATURDAY EXPECTED ACROSS THE REGION AHEAD OF A
COOLER, MORE UNSETTLED PATTERN FOR SUNDAY ONWARDS.
- INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS MONDAY
THROUGH WEDNESDAY WITH SOME SNOW FOR OUR MOUNTAINOUS REGIONS.
SHORT TERM /THROUGH MONDAY/
ISSUED AT 212 PM MDT SAT MAY 3 2025
AN UPPER LEVEL RIDGE WILL RESIDE OVER THE INTERMOUNTAIN WEST THIS
AFTERNOON AND OVERNIGHT HOURS. THERE IS SOME CUMULUS DEVELOPMENT
OCCURRING OVER THE MOUNTAINS WITH A POTENTIAL WEAK SURGE OF MOISTURE
NEAR THE HIGHER ELEVATIONS. HI-RES MODELS ARE PUTTING A BRIEF SHOWER
OVER OUR MOUNTAINS BETWEEN 20 AND 0Z. THERE IS ALSO A SLIGHT VORT-
MAX THAT MOVES NORTH FROM THE COLORADO BORDER THAT MAY HELP PROVIDE
THE FORCING NEEDED FOR ANY PRECIPITATION DEVELOPMENT. HOWEVER, GIVEN
THE STOUT DRY LAYER POPS WERE REDUCED TO 15 PERCENT FOR A SLIGHT
CHANCE THESE SHOWERS OCCUR. ACCUMULATIONS WONT BE MUCH, MAYBE A
HUNDREDTH OR SO. TEMPERATURES WERE ALSO INCREASED FROM NBM GUIDANCE
GIVEN WE WERE ONLY A DEGREE OFF FROM OUR FORECASTED HIGH BY
LUNCHTIME AND STILL HAD AMPLE TIME FOR PEAK HEATING TO OCCUR. AS
CONSEQUENCE THE HIGH TEMPERATURES ARE FORECASTED TO BE IN THE LOW TO
MID 70'S ACROSS THE FORECAST AREA THIS AFTERNOON.
SUNDAY, THE UPPER LEVEL RIDGE BEGINS TO PUSH OFF TO THE EAST AS A
BOWLING BALL OF A LOW PRESSURE SYSTEM MAKES ITS WAY NORTHEAST FROM
THE SOUTHERN PACIFIC COAST. THE LOW PRESSURE SYSTEM WILL BUTT RIGHT
UP AGAINST THE RIDGE, TIGHTENING THE HEIGHT AND PRESSURE GRADIENT.
WINDS IN TURN WILL BE RATHER GUSTY EAST OF I-25 AND INTO THE
NEBRASKA PANHANDLE. WHILE THE HEIGHT GRADIENTS ARE BETWEEN -30 AND -
50 INDICATING WEAK TO MODERATE UPSLOPE, OUR IN HOUSE ALGORITHM PUTS
A 20-40 PERCENT CHANCE OF ELEVATED WINDS EAST OF LARAMIE. THE GFS
OMEGA FIELDS SHOW WEAK SUBSIDENCE ALONG THE I-80 CORRIDOR WHICH IS
PROBABLY WHY OUR ALGORITHM ISN'T TOO EXCITED ABOUT THIS POTENTIAL
WIND EVENT. THERE IS A LOW LEVEL JET BETWEEN 40 TO 50KTS THAT OCCURS
AT NIGHT BUT DUE TO THE LIMITED TO NO MIXING THAT OCCURS AT NIGHT
CONFIDENCE IS LOW FOR HIGH WINDS. THE FASTER WINDS ALSO DONT STICK
AROUND FOR VERY LONG WITH SLIGHTLY WEAKER WINDS OCCURRING DURING THE
DAY (30-40KTS). SO NO HEADLINES WERE ISSUED ON THIS SHIFT. RH VALUES
ARE ALSO GREATER THAN 20 FOR LIMITED FIRE WEATHER CONCERNS ON
SUNDAY. GIVEN THE CYCLONIC ROTATION OF A LOW OUR FLOW PATTERN WILL
BE FROM THE SOUTH USHERING IN MOISTURE FROM THE GULF. SO OUR RH
VALUES WILL LIKELY BE HIGHER THAN CURRENTLY PROGGED. SUNDAY
AFTERNOON, THE UPPER LEVEL LOW WILL SEND A VORTICITY MAX INTO OUR
REGION TO INCREASE PRECIPITATION CHANCES SUNDAY AFTERNOON AND
EVENING. CURRENTLY THE RAIN LOOKS TO BE CONFINED TO THE MOUNTAINOUS
REGIONS OF THE FORECAST AREA. SUFFICIENT ISENTROPIC LIFT AND THE
VORT-MAXES LOOK TO HELP DEVELOP THE RAIN SUNDAY AFTERNOON AND
EVENING, BUT DUE TO OUR STOUT DRY LAYER MUCH OF THE LOWER ELEVATIONS
ARE LIKELY TO REMAIN DRY. DUE TO THE OMEGA BLOCK, THIS UPPER LEVEL
LOW WILL RESIDE OVER THE INTERMOUNTAIN WEST OVER THE NEXT COUPLE
DAYS.
LONG TERM /MONDAY NIGHT THROUGH SATURDAY/
ISSUED AT 212 PM MDT SAT MAY 3 2025
MEDIUM TO LONG RANGE MODELS IN REASONABLE AGREEMENT AND SHOW A
PRETTY ACTIVE WEATHER PATTERN OVER THE NEXT WEEK OR SO. AN OMEGA
BLOCK IS FORECAST TO FORM OVER THE CENTRAL PLAINS LATE LATE THIS
WEEKEND AND EARLY IN THE WEEK. THIS WILL ALLOW THE UPPER LEVEL
TROUGH, CURRENTLY DIGGING SOUTH ALONG THE WEST COAST, TO STALL AS IT
ATTEMPTS TO EJECT EASTWARD. THIS UPPER LEVEL TROUGH IS EXPECTED TO
PERSIST ACROSS THE AREA THROUGH AT LEAST WEDNESDAY AFTERNOON, WITH
SOME ENSEMBLES SHOWING IT LINGERING ACROSS THE HIGH PLAINS INTO
EARLY THURSDAY MORNING. THIS IS EXPECTED TO RESULT IN CLOUDY/COOL
CONDITIONS WITH FREQUENT SHOWER ACTIVITY AND A DECENT CHANCE OF
THUNDERSTORMS. FOG AND LOW CLOUDS MAY ALSO PLAQUE THE REGION DUE TO
PERSISTENT EASTERLY FLOW AT THE SURFACE.
THE MORE STEADY/PERSISTENT SHOWER ACTIVITY SHOULD BEGIN LATE ON
MONDAY AS THE FIRST SET OF UPPER LEVEL DISTURBANCES/VORT MAXES
ALOFT LIFT NORTHWARD ACROSS THE EASTERN SIDE OF THE MAIN UPPER
LEVEL TROUGH/LOW. THE UPPER LEVEL LOW CENTERED NEAR THE FOUR
CORNERS REGION IS NOT EXPECTED TO MOVE MUCH MONDAY AND MONDAY
NIGHT, SO EXPECT NUMEROUS DISTURBANCES TO LIFT NORTH AND
EVENTUALLY NORTHWEST ACROSS THE AREA, AROUND THE PRIMARY LOW.
THIS WILL LIKELY BE THE FIRST OF TWO PEAKS IN PRECIPITATION
THAT MODELS ARE HINTING TOWARDS, EVEN THOUGH THERE ARE TIMING
DIFFERENCES. A QUICK LOOK AT THE 00Z NAEFS SHOW PWAT AND
SPECIFIC HUMIDITY/MIXING RATIO ABOVE THE 90TH PERCENTILE AND
EVEN CLOSING IN ON THE 99TH PERCENTILE...ESPECIALLY OVER
SOUTHEAST WYOMING AND FAR WESTERN NEBRASKA ON MONDAY AND
TUESDAY. EXPECT THE LOW LEVEL MOISTURE TO BE IN PLACE. HOWEVER,
DO NOT EXPECT IT TO RAIN ALL THE TIME. THERE WILL BE A BALANCING
ACT BETWEEN AVAILABLE FORCING AND ANY LOW TO MIDLEVEL
INSTABILITY (BOTH SURFACE-BASED AND ELEVATED/CONDITIONAL). THE
BEST CHANCE FOR HEAVIER RAINFALL APPEAR TO BE WHEN THESE TWO
INGREDIENTS COME TOGETHER, BOTH MONDAY EVENING/NIGHT AND TUESDAY
EVENING WHEN THE UPPER LEVEL LOW SLOWLY EJECTS NORTHEAST NEAR
THE COLORADO AND NEW MEXICO BORDER. DURING THE DAYTIME HOURS,
ANY BREAK IN THE CLOUDS WILL RESULT IN RAPID DESTABILIZATION OF
THE LOWER BOUNDARY LAYER AND LIKELY LEAD TO DEVELOPING SHOWERS
OR THUNDER SHOWERS. THESE FACTORS ARE WHY WE KEPT POP ABOVE 80+
PERCENT. STRONG TO SEVERE THUNDERSTORMS LOOK HIGHLY UNLIKELY IN
THIS PATTERN WITH MUCAPE LIKELY BELOW 500 J/KG AND WEAKER WINDS
ALOFT COMPARED TO THE SURFACE. THERE WILL BE SOME MOUNTAIN SNOW
WITH SNOWLEVELS HOVERING AROUND 7500 TO 8000 FEET. THE I-80
SUMMIT APPEARS TO HAVE THE BEST CHANCE TO SEE SIGNIFICANT SNOW
ACCUMULATIONS...ESPECIALLY TUESDAY AND TUESDAY NIGHT.
FOR WEDNESDAY, ALL MODELS SHOW THE UPPER LEVEL LOW EJECTING
EASTWARD AND WEAKENING ACROSS THE CENTRAL PLAINS. STILL A GOOD
CHANCE FOR RAIN SHOWERS OVER THE AREA WEDNESDAY AFTERNOON AND
EVENING. HOWEVER, MODEL SOUNDINGS ARE NOT SHOWING HARDLY ANY
INSTABILITY, SO PRECIP RATES SHOULD BE PRETTY LOW. HIGH
TEMPERATURES WILL BE COOLEST ON TUESDAY AND WEDNESDAY WITH
HIGHS STRUGGLING TO INCREASE INTO THE 50S.
FOR LATER IN THE WEEK, MODELS SHOW A WARMING TREND AS A
TRANSIENT UPPER LEVEL RIDGE AXIS PUSHES EAST ACROSS THE GREAT
BASIN REGION AND INTO THE INTERMOUNTAIN WEST. CAN'T RULE OUT
SOME SHOWERS AND THUNDERSTORMS OVER SOUTHEAST WYOMING EACH
AFTERNOON, BUT IT SHOULD BE MUCH DRIER COMPARED TO EARLIER IN
THE WEEK. HIGH TEMPERATURES WILL RETURN TO THE UPPER 60S TO MID
70S BY FRIDAY.
AVIATION /06Z TAFS THROUGH 06Z MONDAY/
ISSUED AT 1033 PM MDT SAT MAY 3 2025
A RIDGE ALOFT WILL MOVE OFF TO OUR EAST ON SUNDAY AS THE FLOW
ALOFT TURNS SOUTHERLY, AND A WEATHER DISTURBANCE BRINGS A CHANCE
OF SHOWERS AND THUNDERSTORMS SUNDAY AFTERNOON AND EVENING WEST
OF A DOUGLAS TO LARAMIE LINE.
WYOMING TAFS...CLEAR SKIES WILL PREVAIL UNTIL 15Z, THEN
SCATTERED TO BROKEN CLOUDS NEAR 10000 FEET WILL OCCUR. WINDS
WILL GUST TO 35 KNOTS FROM 15Z TO 00Z.
NEBRASKA TAFS...CLEAR SKIES WILL PREVAIL. WINDS WILL GUST TO
35 KNOTS AT CHADRON AND SIDNEY UNTIL 00Z, AND TO 35 KNOTS AT
SCOTTSBLUFF AND ALLIANCE FROM 15Z TO 00Z.
CYS WATCHES/WARNINGS/ADVISORIES
WY...NONE.
NE...NONE.
SHORT TERM...MM
LONG TERM...TJT
AVIATION...RUBIN
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