834
FXUS65 KRIW 201021
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
421 AM MDT SAT JUN 20 2026
KEY MESSAGES
- AN ACTIVE DAY TODAY AS A WEATHER SYSTEM BRINGS SOME SHOWERS
AND THUNDERSTORMS, MOST NUMEROUS IN NORTHERN WYOMING. SOME
STORMS COULD BE STRONG TO SEVERE.
- THE CHANCE OF SHOWERS AND STORMS CONTINUES SUNDAY AND MONDAY,
WITH THE BEST CHANCE ONCE AGAIN ACROSS NORTHERN WYOMING.
- ELEVATED TO NEAR CRITICAL FIRE WEATHER REMAINS LIKELY THROUGH
MONDAY, WITH TODAY AND MONDAY THE DAYS OF THE MOST CONCERN.
DISCUSSION
ISSUED AT 233 AM MDT SAT JUN 20 2026
IT IS ALWAYS RATHER INTERESTING WHEN COMING BACK FROM A VACATION TO
SEE WHAT YOU WALK INTO. THERE ARE SOME THINGS TO TALK ABOUT THIS
MORNING, AS WE LOOK TO HAVE AN ACTIVE FEW DAYS ACROSS WESTERN AND
CENTRAL WYOMING.
EVEN AT THE EARLY MORNING HOUR THIS MORNING, A SUBTLE SHORTWAVE IS
MOVING INTO WESTERN WYOMING AND BRINGING A FEW SHOWERS AND EVEN AN
ISOLATED LIGHTNING STRIKE OR TWO. THERE HAVE BEEN A FEW WIND GUSTS
WITH THIS, BUT THE MAXIMUM HAS BEEN AROUND 40 MPH OR SO. A FEW
SHOWERS WILL CONTINUE THIS MORNING, BUT THE MAIN EVENT STILL LOOKS
TO BE THIS AFTERNOON. MOST GUIDANCE CONTINUES TO FAVOR THE AREAS
EAST OF THE DIVIDE AS WELL AS WESTERN WYOMING, WHERE THE DEEPER
MOISTURE WILL BE FOUND, WITH A MAXIMUM CHANCE OF AROUND 3 OUT OF 5
ACROSS THE NORTHERN BORDER AS WELL AS JOHNSON AND NATRONA COUNTIES,
WITH TAPERING CHANCES FURTHER SOUTH AS YOU MOVE SOUTHWARD INTO THE
DRIER AIR. THE HIGHEST CHANCE WILL BE DURING PEAK HEATING, WITH A
GRADUAL DECREASE THROUGH THE EVENING. HOWEVER, A FEW SHOWERS WILL
LINGER THROUGH THE NIGHT. AS FOR THE CHANCE OF ANY STRONGER STORMS,
MOST OF THE AREA IS UNDER A MARGINAL RISK OF SEVERE THUNDERSTORMS.
THERE WILL BE DECENT FORCING AND DYNAMICS AS A SHORTWAVE WILL
APPROACH THE AREA AND THERE WILL BE A BUT OF UPPER LEVEL SUPPORT
FROM THE LEFT FRONT QUADRANT OF A JET STREAK MOVING INTO SOUTHERN
WYOMING THIS AFTERNOON. THE LIMITING FACTOR, AS IT USUALLY IS IN
THIS PART OF THE COUNTRY, IS MOISTURE. WE HAVE SEVERAL THREATS, WE
WILL TACKLE EACH ONE OF THEM INDIVIDUALLY.
SEVERE WIND GUSTS...NOT SURPRISINGLY, THIS IS THE MAIN THREAT FROM
THE STORMS, AS IT USUALLY IS IN WESTERN AND CENTRAL WYOMING. MODEL
SOUNDINGS SHOW WELL DEFINED INVERTED V SOUNDINGS ACROSS MUCH OF THE
THE AREA, WITH AN EMPHASIS ON THE SOUTHWESTERN HALF OF THE AREA.
THERE ARE STEEP LAPSE RATES AS WELL, APPROACHING 9 DEGREES CELSIUS
PER KILOMETER IN SOME LOCATIONS. IN ADDITION, SHOWER AND
THUNDERSTORM BASES LOOK TO REMAIN FAIRLY HIGH, GENERALLY MORE THAN A
MILE ABOVE THE SURFACE. DEW POINT DEPRESSIONS ARE NOT THE HIGHEST I
HAVE SEEN, BUT ARE STILL DECENT. THE LARGEST ARE IN SOUTHWESTERN
WYOMING, WHERE SOME APPROACH 60 DEGREES. DEPRESSIONS DROP TO AROUND
40 DEGREES IN CENTRAL WYOMING AND TO AROUND 30 DEGREES IN NORTHERN
WYOMING WHERE THE DEEPEST MOISTURE WILL BE FOUND. HOWEVER, ANY
SHOWER OR THUNDERSTORM COULD HAVE A STRONG WIND GUST, EVEN ANY
CUMULUS CLOUD THAT COULD COLLAPSE. THE DREADED "LITTLE GREEN BLOBS"
ARE DEFINITELY POSSIBLE THIS AFTERNOON, ESPECIALLY IN THE SOUTHERN
HALF OF OUR AREA.
HAIL...THERE IS A VERY SMALL AREA OF A MARGINAL RISK OF LARGE HAIL,
LARGELY ALONG AN EAST OF A GLENROCK TO MIDWEST INTO EASTERN JOHNSON
COUNTY. THIS DOES MAKE SENSE SINCE MOISTURE WILL BE DEEPEST IN THIS
AREA, ALONG WITH THE LOWEST CLOUD BASES. THIS IS ALSO THE LOCATION
OF THE BEST INSTABILITY, WITH CAPE VALUES APPROACHING 1000 J/KG AND
LIFTED INDICES AS LOW AS MINUS 4. JOHNSON COUNTY LOOKS TO HAVE THE
BEST CHANCE, AS MOST GUIDANCE SHOWS SOME WEAK UPSLOPE FLOW INTO THE
BIGHORNS THIS AFTERNOON, WHICH SHOULD AID IN CONVECTIVE INITIATION.
THE BEST CHANCE OF LARGE HAIL REMAINS ACROSS EASTERN WYOMING, BUT
THERE IS AROUND A 1 IN 10 CHANCE OF SOME IN OUR AREA, MAINLY ALONG
AND EAST OF INTERSTATE 25.
FLOODING...THE CHANCE OF THIS IS LOW BUT NOT ZERO, AND MAINLY IN THE
NORTHERN HALF OF THE STATE. AS FOR CLIMATOLOGY, THE PREDICTED
PRECIPITABLE WATER VALUE OF 0.63 AT 00Z THIS AFTERNOON PUTS MOISTURE
IN THE TOP 20 PERCENT OF HISTORICAL VALUES FOR THIS VALUE AND AROUND
125 PERCENT OF THE DAILY MEAN (0.50 INCHES). THE MOST LIKELY
LOCATIONS WILL BE, AGAIN ACROSS JOHNSON COUNTY, WHERE SOME AREAS
HAVE OVER AN INCH OR PRECIPITABLE WATER, AS WELL AS THE BIG HORN
BASIN. HOWEVER, THERE WILL BE SOME STEERING FLOW TODAY, SO MOST OF
THE STORMS WILL HAVE SOME MOVEMENT, MITIGATING THE THREAT SOMEWHAT.
IN ADDITION, IT HAS BEEN DRY, SO THE SOIL DOES HAVE A DECENT AMOUNT
OF CAPACITY. THE WEATHER PREDICTION CENTER DOES HAVE EASTERN JOHNSON
COUNTY UNDER A MARGINAL RISK OF EXCESSIVE RAINFALL, AND THIS LOOKS
REASONABLE GIVEN THE PATTERN.
DRY LIGHTNING AND FIRE WEATHER...THIS WILL LARGELY BE A THREAT
ACROSS THE SOUTHERN HALF OF THE AREA, WHERE CLOUD BASES WILL BE
HIGHER. THIS WILL OBVIOUSLY BRING A THREAT OF SOME FIRE STARTS,
GIVEN THE CONTINUING DROUGHT CONDITIONS ACROSS THE AREA. ELEVATED TO
NEAR CRITICAL FIRE WEATHER IS LIKELY ACROSS SOUTHERN WYOMING WHERE
WINDS GUSTING OVER 30 MPH AND HUMIDITY FALLING TO AROUND 15 PERCENT
MAY BRING ERRATIC FIRE BEHAVIOR IF ANY FIRES CAN START.
AND ONE BONUS I WILL THROW IN, TORNADOES. THE THREAT IS VERY LOW,
LESS THAN 2 PERCENT ACROSS THE ENTIRE AREA AS THE BEST
INSTABILITY AND SHEAR WILL BE ACROSS EASTERN WYOMING. LIKE MANY
OF THE OTHER THREATS, THE MAIN AREA OF CONCERN IS JOHNSON
COUNTY, WHERE THE MOST SHEAR WILL BE FOUND AND DEEPER MOISTURE
WILL ALLOW FOR LOWER CLOUD BASES AND ALLOW FOR THE POSSIBILITY
OF ANY ROTATION TO REACH THE GROUND. THIS THREAT IS BY FAR THE
LOWEST OF ALL THE THREATS THOUGH.
LOOKING FURTHER OUT, THINGS LOOK TO STAY ACTIVE OVER THE NEXT COUPLE
OF DAYS. ANOTHER SHORTWAVE WILL MOVE ACROSS THE AREA SUNDAY WITH
ANOTHER CHANCE OF CONVECTION. INSTABILITY VALUES ARE AROUND 25
PERCENT LESS WITH THIS WAVE AND THERE IS MUCH LESS JET SUPPORT. SO,
THE THREAT OF STRONG TO SEVERE THUNDERSTORMS WILL LIKELY BE LESS.
AND LIKE TODAY, THE MAIN THREAT WILL BE EAST OF THE CONTINENTAL
DIVIDE.
MONDAY HAS THE POTENTIAL TO BE A BIT MORE INTERESTING. ANOTHER
SHORTWAVE WILL BE CROSSING THE AREA. THE MAIN DIFFERENCE HERE IS
THAT THERE WILL BE MORE JET SUPPORT, WITH AN 100 KNOT JET STREAK
MOVING ALONG THE WYOMING / MONTANA BORDER. THE LIMITING FACTOR HERE
IS MOISTURE, WITH PRECIPITABLE WATER VALUES FALLING TO AS LOW AS
0.20 INCHES ACROSS WESTERN WYOMING. IF THE DRY AIR WINS OUT, THE
MAIN THREAT WOULD BE FIRE WEATHER WITH A GUSTY WIND AND LOWER
HUMIDITY WITH THE JET CLOSE BY. HOWEVER, IF MOISTURE COULD LINGER,
WE COULD HAVE A SITUATION WITH STORMS FIRING ALONG A PSEUDO DRY
LINE. THERE IS STILL A LOT OF UNCERTAINTY BUT WE WILL HAVE TO WATCH
THIS.
MORE SETTLED CONDITIONS SHOULD MOVE IN FOR TUESDAY AS A BUILDING
RIDGE BRINGS UPPER LEVEL CONVERGENCE. UNCERTAINTY INCREASES FROM
MIDWEEK ON AS SOME GUIDANCE HAS RIDGING OVER THE AREA AND ONLY
ISOLATED CONVECTION WHILE OTHERS HAVE THE AREA NEAR THE TOP OF THE
RIDGE WITH SHORTWAVES TOPPING THE RIDGE AND BRINGING A FEW CHANCES
OF CONVECTION. TEMPERATURES LOOK TO REMAIN CLOSE TO NORMAL, WITH THE
BIGGEST TEMPERATURE ANOMALIES ACROSS SOUTHERN WYOMING WHERE DRIER
AIR AND LESS CLOUD COVER SHOULD ALLOW FOR WARMER TEMPERATURES.
AVIATION /12Z TAFS THROUGH 12Z SUNDAY/
ISSUED AT 405 AM MDT SAT JUN 20 2026
AVIATION IMPACTS WILL CONTINUE THROUGH TODAY, MAXIMIZING BETWEEN
18Z SATURDAY AND 02Z ON SUNDAY. A FEW LIGHT SHOWERS WILL MOVE
THROUGH THROUGH AROUND 15Z BUT MOST PRECIPITATION SHOULD NOT
REACH THE GROUND. AN APPROACHING WEATHER SYSTEM WILL BRING A
DECENT CHANCE OF SHOWERS AND THUNDERSTORMS TODAY. THE GREATEST
CHANCE WILL BE ALONG AND NORTH OF A KJAC TO KWRL LINE, AND IN
THESE TAF SITES TEMPO GROUPS WERE MAINTAINED WITH AT LEAST A 50
PERCENT CHANCE OF A THUNDERSTORM THIS AFTERNOON. FURTHER SOUTH,
IN VICINITY OF KCPR, KRIW, KLND, KPNA AND KBPI, CHANCES ARE
GENERALLY BETWEEN 25 AND 35 PERCENT, SO PROB30 GROUPS WERE
MAINTAINED HERE. WE CAN'T RULE OUT A SHOWER OR THUNDERSTORM IN
VICINITY OF KRKS BUT WITH THE CHANCE LESS THAN 20 PERCENT WE
ELECTED TO LEAVE OUT OF THE TAF FOR NOW. A FEW SHOWERS WILL
LINGER ACROSS NORTHERN WYOMING THROUGH THE NIGHT, SO WE KEPT
VCSH IN THE NORTHERN TERMINALS AFTER 06Z.
RIW WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...HATTINGS
AVIATION...HATTINGS
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