Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 230930
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
330 AM MDT SAT AUG 23 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

A BIG GLOB OF PRECIP HAS BEEN MOVING NORTH NORTHEAST ACROSS WY AHEAD
OF THE CIRCULATION SPINNING OVER IDAHO. THE LEADING EDGE OF THIS
PRECIP AREA HAD A FEW NOTEWORTHY THUNDERSTORMS THAT PRODUCED LOCALLY
HEAVY RAINFALL AND OCCASIONAL GROUND STRIKES. THESE CONVECTIVE CELLS
WERE ASSOCIATED WITH A VORT LOBE PINWHEELING AROUND THE IDAHO LOW.
BEHIND THESE CELLS...THERE HAVE JUST BEEN PROGRESSIVELY WEAKER CELLS
THAT EVENTUALLY MORPHED INTO STRATIFORM PATCHES OF LIGHT TO MODERATE
RAINFALL SPINNING AROUND THE LOW. HOWEVER...THE SIGNIFICANT
RAINFALL THAT THE MODELS HAVE BEEN PROMISING IN NORTHWEST WY HAVE
NOT OCCURRED THIS EVENING. THIS AREA OF RAINFALL WILL BEGIN TO
EXIT THE EAST HALF OF THE CWA BY 12Z THIS MORNING BY THE TIME THE
LOW REACHES NORTHWEST WY BUT SHOULD LINGER THE LONGEST WHERE THE
BEST QG FORCING WILL BE STRONGEST IN NORTHERN WY. WRAP AROUND
ISENTROPIC LIFT WILL REMAIN WELL TO OUR NORTH WELL UP INTO MT
NORTH OF THE LOW. THE MID LEVEL CIRCULATION PROGGED TO BE OVER
NORTHERN WY THIS MORNING WILL PROPAGATE AND JUMP NORTH TO MONTANA
AND WILL SWING THE TRAILING 700MB TROUGH THE THE AREA AROUND MID
DAY TODAY. BEHIND THIS TROUGH EXPECT LOW BASED AND LOW TOPPED
CONVECTION TO RAPIDLY FIRE UP WITH MANY SMALL CONVECTIVE CELLS
PRODUCING SCATTERED TO NUMEROUS RAIN SHOWERS THIS AFTERNOON. THESE
SHOWERS WILL STRATIFORM OUT TONIGHT AS THE WEATHER PULLS AWAY TO
THE NORTHEAST INCLUDING THE ASCT SFC LOW THAT WILL TRACK NORTHEAST
ACROSS NORTHEAST WY THAT WILL HELP PULL MUCH COLDER AIR AROUND
BEHIND IT OVER THE AREA. SNOW LEVELS SHOULD BE AROUND 8500 FEET
OVER YELLOWSTONE PARK BY SUNDOWN THIS EVENING AND THEN DROP TO
7500 FEET BY 12Z SUNDAY WHICH TRANSLATES INTO MOST OF THE PARK.
ACROSS THE BIG HORN MOUNTAINS...EXPECT SNOW LEVELS TO DROP FROM
10500 FEET THIS EVENING TO 8K BY 12Z SUNDAY. THEN IN THE WIND
RIVER MTNS...EXPECT SNOW LEVELS TO DROP FROM 10K THIS EVENING TO
9K 12Z SUNDAY. ANY SNOWFALL...HOWEVER...SHOULD BE LIGHT AND PATCHY
SINCE THE PRECIP WILL DISSIPATE FROM SOUTHWEST TO NORTHEAST AS THE
COLD ADVECTION TAKES PLACE FROM THE NORTH. THE MOST SNOWFALL
SHOULD FALL IN THE BIG HORN MOUNTAINS WHERE 2 TO 3 INCHES COULD
FALL OVER THE HIGHER PEAKS WHERE THE PRECIP WILL BE LAST TO CLEAR
OUT. AN INCH OR LESS IS EXPECTED OVER THE REST OF THE HIGHER PEAKS.

THEN BY SUNDAY THE FLOW WILL BECOME WESTERLY AND CONFLUENT AFTER THE
TROUPHPA WITH ONLY ISOLD SHOWERS OVER THE NORTHERN MTNS FROM SEMI
MOIST WESTERLY FLOW.

THEN ON MONDAY AND MONDAY NIGHT THE NEXT SHORTWAVE WILL DIVE INTO
THE LONG WAVE TROUGH OVER THE WESTERN STATES WITH A MID LEVEL
CIRCULATION PROGGED OVER IDAHO MONDAY. EXPECT ANOTHER BOUT OF
INCREASING SCATTERED TO NUMEROUS SHOWERS AND A FEW THUNDERSTORMS TO
OCCUR MONDAY AND MONDAY NIGHT. SNOW LEVEL COULD DROP TO 9500 ONCE
AGAIN BY 12Z TUESDAY IN THE NORTHERN MTNS.

.LONG TERM...TUESDAY THROUGH SATURDAY

A TROUGH/CLOSED LOW WILL SWING ACROSS THE ROCKIES IN THE TUESDAY AND/OR
WEDNESDAY TIME FRAME. THE TREND IS FOR A SLOWER SOLUTION WITH THE
00Z GFS BEING THE MOST PROGRESSIVE PUSHING THE TROUGH INTO THE
PLAINS BY LATE TUESDAY/TUESDAY NIGHT. ON THE OTHER HAND...THE 00Z
ECMWF AND GEM ARE SLOWER...WITH A CLOSED UPPER LOW PUSHING ACROSS
UTAH TUESDAY AND FINALLY PUSHING INTO THE FRONT RANGE OF COLORADO
WEDNESDAY AFTERNOON. DUE TO THE SLOWER TREND HAVE COOLED TEMPS AND
EXPANDED POPS TUESDAY...AND ADDED SOME SLIGHT POPS ALL THE WAY INTO
WEDNESDAY MORNING ACROSS THE EXTREME EAST/SOUTHEAST. THERE COULD
BE SOME MINOR SNOW ACCUMULATION ABOVE 10 KFT AS THIS SYSTEM MOVES
ACROSS THE FORECAST AREA.

A WARMING TREND AND DRY CONDITIONS ARE EXPECTED THURSDAY AND
FRIDAY...AHEAD OF A TROUGH THAT COULD BEGIN TO IMPACT THE AREA LATE
FRIDAY AND SATURDAY. THERE COULD BE SOME ELEVATED FIRE WEATHER
CONDITIONS...MAINLY SATURDAY AS WINDS INCREASE AND RH LOWERS AHEAD
OF THE TROUGH.

&&

.AVIATION.../12Z ISSUANCE/

A WEATHER SYSTEM WILL MOVE THROUGH WYOMING TODAY AND INTO EASTERN
MONTANA TONIGHT. SCATTERED SHOWERS AND STORMS WILL OCCUR TODAY
OVER THE REGION. AREAS OF MVFR CONDITIONS WILL OCCUR TODAY DUE TO
LOW CLOUDS. THE SHOWERS AND STORMS WILL BE ENDING IN THE SOUTH
AFTER 00Z SUNDAY. SCATTERED SHOWERS WILL CONTINUE OVER THE CENTRAL
AND NORTH THROUGH 06Z...THEN BECOME ISOLATED AFTER 06Z SUNDAY.
AREAS OF LOW CLOUDS WILL DEVELOP OVER THE NORTH AFTER 00Z CREATING
MVFR TO IFR CONDITIONS IN PLACES. THE LOW CLOUDS WILL SPREAD INTO
CENTRAL WY AFTER 06Z SUNDAY WITH AREAS OF MVFR TO IFR CONDITIONS.

&&

.FIRE WEATHER...

FIRE WEATHER CONCERNS WILL REMAIN LOW ACROSS MOST OF THE FORECAST
AREA THROUGH THE WEEKEND. THE REASON FOR THE LOW CONCERN IS THAT
MOISTURE FROM A COUPLE OF DIFFERENT SOURCES WILL CONTINUE TO
INFILTRATE THE STATE...COMBINING WITH A VIGOROUS UPPER LEVEL
DISTURBANCE TO PROVIDE FOR CONTINUED INCREASING RAINFALL CHANCES
STATEWIDE THROUGH THIS MORNING. ABOVE 9000 FEET...OVER THE NEXT
FEW DAYS/NIGHTS/...THIS YEAR`S FIRST SIGNIFICANT SNOWFALL COULD
OCCUR...WITH 1 TO 3 INCHES POSSIBLE TONIGHT. THIS PATTERN WILL
CONTINUE THROUGH SUNDAY AND POSSIBLY INTO THE BEGINNING OF NEXT
WEEK BEFORE BREAKING LATER IN THE WEEK.

&&

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

&&

$$

SHORT TERM...LIPSON
LONG TERM...WM
AVIATION...AR
FIRE WEATHER...LIPSON






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