Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 221719
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1118 AM MDT FRI AUG 22 2014

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT
A SLUG OF PACIFIC MOISTURE SWINGING AROUND THE BASE OF THE
NEGATIVELY TILTED TROUGH CLOSING OVER SEATTLE BROUGHT THUNDERSTORMS
WITH LOCALLY HEAVY RAINFALL TO THE FAR WEST VALLEYS INCLUDING THE
VCNTY OF JACKSON EARLIER THIS EVENING AHEAD OF THE EXITING
TRANSITORY RIDGE. DEBRIS SHOWERS ARE STILL CRAWLING NORTHEAST ACROSS
PORTIONS OF NW AND CENTRAL WY AS THEY STRATIFORM OUT AS THEY BISECT
THE COLD FRONT WHICH IS DRAPED FROM LND TO TMH. FOR TODAY...THE
TIGHTENING DIFLUENT SOUTHWEST FLOW AHEAD OF THE APPROACHING PAC NW
LOW WILL BRING IN ADDITIONAL PACIFIC MOISTURE BLENDING WITH A
SMIDGEN OF MONSOONAL MOISTURE RESULTING IN BANDED SHOWERS AND
ISOLATED THUNDERSTORMS TO MAINLY WESTERN AND NORTHERN WY WHERE THE
BEST DEEP MOISTURE AND CAPES WILL BE. TONIGHT WIDESPREAD SHOWERS
AND A FEW THUNDERSTORMS WILL SPREAD SOUTHEAST ACROSS THE REST OF
WYOMING AS THE 500MB LOW TRACKS TOWARD NW WY AND THE MID LEVEL
CIRCULATION TRACKS FROM THE PAC NW TO SOUTHWEST MT BY SATURDAY.
MOST OF THE PRECIP WILL BECOME STRATIFORM BY LATE TONIGHT AND INTO
SATURDAY MORNING. IN FACT...THE SNOW LEVEL SHOULD DROP TO 10K IN
THE NW MTNS BY 12Z SATURDAY. SATURDAY WILL BE A FALL LIKE DAY WITH
OUR FIRST REAL SYNOPTIC SCALE PRECIP EVENT OF THE YEAR WITH LEFT
FRONT QUAD DYNAMICS ALONG WITH QG FORCING IN NORTHERN WY. THE WRAP
AROUND ISENTROPIC LIFT SHOULD REMAIN WELL TO OUR NORTH SATURDAY
OVER N MT. IN FACT...THE TRACK OF THE MID LEVEL CIRCULATION AND
THE AFOREMENTIONED DYNAMICS WILL BE A BIT FARTHER NORTH THAN
EARLIER RUNS OF THE GFS INDICATED SO THE BEST QPF SHOULD BE IN NW
WY DURING THE NEXT 48 HOURS WHERE HPC IS INDICATING AROUND AN INCH
AND A HALF OF PRECIP WHERE ROUGHLY A HALF INCH OF RAIN HAS FALLEN
IN SOME OF THESE AREAS DURING THE LAST FEW DAYS SO THIS AREA WILL
LIKELY HAVE TO BE WATCHED. ONCE THE MID LEVEL CIRCULATION LIFTS
INTO MONTANA SATURDAY AFTERNOON AND THE TRAILING 700MB TROUGHPA
OCCURS WITH COOLING ALOFT...STRATIFORM PRECIP WILL TRANSITION TO
LOW BASED SHALLOW CONVECTION BY SATURDAY AFTERNOON BEHIND THE
TROUGHPA. THE SFC LOW IS ALSO PROGGED TO BE FARTHER NORTH AND OVER
NE WY SATURDAY AFTERNOON WITH COOLER AIR WRAPPING AROUND BEHIND
IT. SATURDAY NIGHT...AS THE SYSTEM PULLS OUT TO THE EAST...SNOW
LEVELS WILL LIKELY DROP TO AROUND 8K OVER NORTHERN WY WITH SNOW
EXPECTED ON THE HIGHER PEAKS ABOVE 10K FARTHER SOUTH OVER THE WIND
RIVER MTNS. THE BIG HORN MTNS COULD SEE AROUND 3 INCHES OF SNOW
ALONG THE HIGHER PEAKS BY SUNDAY MORNING ALONG WITH 1 TO 2 INCHES
OF SNOW OVER SOME OF THE NORTHWEST MTNS AND WIND RIVER MOUNTAINS.
PRECIP WILL CONTINUE TO TAPER OFF SUNDAY AND SUNDAY NIGHT AS THE
FLOW BECOMES MORE CONFLUENT. ONLY THE NORTHERN MTNS MAY SEE SOME
ISOLD SHOWERS WITH THE SEMI MOIST WESTERLY FLOW.

.LONG TERM...MONDAY THROUGH FRIDAY
MORE MODEL VARIATION AGAIN TONIGHT. THE GFS IS MORE PROGRESSIVE AND
WEAKER WITH OUR SYSTEM EARLY NEXT WEEK. THE EURO HAS GONE AWAY FROM
ITS CLOSED LOW OVER ERN CA AND NV THAT WE DISCARDED LAST NIGHT BUT
IS SLOWER AND STRONGER THAN THE GFS. THE GEM LOOKS A LOT LIKE THE
EURO LAST NIGHT WITH THE NEXT SYSTEM DROPPING STRAIGHT SOUTH INTO
ERN CA AND NV NEXT TUESDAY BEFORE LIFTING NE AND THEN EAST JUST TO
OUR SOUTH WEDNESDAY INTO THURSDAY. LEANING MORE TOWARDS A GFS/EURO
COMPROMISE TONIGHT WHICH PROVIDES MORE CONTINUITY. I STILL THINK
WE`LL HAVE TO WATCH THIS ONE CLOSELY FOR YET ANOTHER SIGNIFICANT
TROUGH SWINGING ACROSS MONDAY INTO TUESDAY. FOR NOW...GOING WITH
INCREASING CHANCES OF SHOWERS AND SOME THUNDERSTORMS MONDAY INTO
MONDAY NIGHT WITH THE STORM POTENTIALLY LINGERING EAST OF THE DIVIDE
INTO TUESDAY. THE MIDDLE OF NEXT WEEK STILL LOOKS CONSIDERABLY
WARMER ESPECIALLY THURSDAY AND FRIDAY. DEPENDING ON THE SYSTEM FOR
NEXT WEEKEND. FRIDAY COULD BE A VERY WARM AND WINDY DAY WITH
LOWERING RH`S EAST OF THE DIVIDE. THE GFS HAS THIS SYSTEM RACING
THROUGH FRIDAY NIGHT ALREADY. THE EURO EVOLUTION IS MUCH SLOWER WITH
THE SYSTEM NOT ARRIVING UNTIL LATE NEXT WEEKEND. CONFIDENCE LOW ON
TIMING RIGHT NOW SO MAKING MINIMAL CHANGES TO THE BLENDED FORECAST.
EITHER WAY...ACTIVE PATTERN CONTINUES WITH NO SEASONABLE WARM
WEATHER UNTIL AT LEAST THE MIDDLE OF NEXT WEEK AND POTENTIALLY ONLY
FOR A COUPLE DAYS.

&&

.AVIATION.../18Z ISSUANCE/
VFR WITH LOCAL MVFR CONDITIONS ARE EXPECTED THROUGH THE FORECAST
PERIOD WITH LOWER CIGS...SHOWERS AND THUNDERSTORMS THE WEST AND
SOUTH...SPREADING NORTHEAST ACROSS THE CENTRAL AND NORTH THIS
AFTERNOON AND EVENING AND OVERNIGHT. AREAS OF MVFR CONDITIONS WILL
OCCUR ACROSS THE REGION IN AREAS OF HEAVIER RAIN AND SMALL HAIL
ASSOCIATED WITH STRONGER STORMS...AND PERHAPS AGAIN AFTER SHOWERS
HAVE SUBSIDED WITH LOCAL BR. SHOWERS AND STORMS WILL DECREASE AFTER
06Z AND WILL BECOME ISOLATED AROUND 09Z SATURDAY. ANOTHER SURGE OF
SHOWERS AND STORMS WILL BE POSSIBLE AFTER 15Z SATURDAY ACROSS THE
SOUTH...EVENTUALLY FILLING IN NORTHWARD.

&&

.FIRE WEATHER...
THE ACTIVE AND WET PATTERN CONTINUES WITH A HIGH LIKELIHOOD OF
WETTING RAIN THROUGH SATURDAY FOR THE ENTIRE FORECAST AREA...WITH
THE MOSTLY RAIN...AND HIGH ELEVATION SNOW...POSSIBLE ACROSS THE
WEST AND NORTH. A POTENT PACIFIC STORM SYSTEM WILL APPROACH THE
AREA LATER TONIGHT WITH NUMEROUS SHOWERS AND A FEW THUNDERSTORMS
SPREADING FROM NORTHWEST TO SOUTHEAST LATER TONIGHT THROUGH FRIDAY
AND INTO SATURDAY. COOLER WEATHER WILL FILTER IN BEHIND THIS
WEATHER SYSTEM WITH SNOW LEVELS LOWERING TO 8000 FEET IN THE
NORTHERN MOUNTAINS BY LATE SATURDAY NIGHT. HIGH TEMPERATURES IN
MOST LOWER ELEVATIONS BY SATURDAY WILL STRUGGLE TO GET ABOVE 70.
WINDS WILL BE GENERALLY LIGHT EXCEPT FOR BRIEF GUSTY WINDS NEAR
THUNDERSTORMS AS WELL AS DURING THE COLD FRONTAL PASSAGE THIS
WEEKEND.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...LIPSON
LONG TERM...SKRBAC
AVIATION...JB
FIRE WEATHER...LIPSON












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