Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 190533
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1132 PM MDT FRI JUL 18 2014

.SHORT TERM...TONIGHT THROUGH SATURDAY (ISSUED AT 159 PM MST)

WEAK FLAT RIDGING AND MODEST WARMING CONTINUES AS SW/JET STREAK
PASSES TO THE E...AND HEIGHTS/THICKNESS SLOWLY RISE/INCREASE.
UPSTREAM PUSHING THRU NRN NV AND UT...A WEAK UPR LVL SW WILL MOVE
THROUGH THE AREA THIS AFTERNOON.  THIS FEATURE WILL ARRIVE JUST AS
MAX HEATING OCCURS...AND WILL INCREASE UPR FLOW...SLIGHTLY DECREASE
UPR LVL TEMPS...AND INCREASE LAPSE RATES OVR THE SWRN/SRN ZONES. THE
MOUNTAINS OF THE AREA WILL HAVE THEIR OWN ELEVATED HEATING AND
CONVERGENCE TO TRY AND SET CONVECTION OFF. HOWEVER...W/ LITTLE
MOISTURE AROUND THE AREA THRU ANY LVL...AND LITTLE BEING ADVECTED
INTO THE FA (SLIGHTLY BETTER ACROSS THE NRN BORDER AREA). ML CAPE
WILL REMAIN LOW AT LESS THAN 200 J/ KG...PROVIDING FOR MAINLY
ISOLATED CONVECTION... AND MOST OF IT ON THE DRY SIDE WITH LITTLE
RAIN...BUT GUSTY WINDS AND LOW PRODUCTION LIGHTNING. THIS WILL
INCREASE FIRE DANGER A BIT...BUT MOST WX PARAMETERS LOOK TO REMAIN
BELOW CRITICAL LEVELS. OTHERWISE MOST OF THE WESTERN ZONES WILL
EXPERIENCE A DRY PUNCH TODAY...WITH LITTLE CHANCE OF ANY PRECIP
OCCURRING SOUTH OF YELLOWSTONE ALL THE WAY TO THE UT BORDER...AND
EAST THROUGH SWEETWATER AND FREMONT COUNTIES. WHAT ACTIVITY DOES
OCCUR LOOKS TO REMAIN QUITE ISOLATED ALONG WITH RELATIVELY LOW
LIGHTNING PRODUCTION WHICH WILL BENEFIT FIRE WX CONCERNS EVEN AS THE
REGION CONTINUES TO DRY OUT.

TONIGHT AND SAT...WV IMAGERY SHOWING DRY PUNCH FROM THE WEST PUSH
ACROSS MOST OF THE STATE THROUGH THE FCST PERIOD WITH HIGH BUT DRY
ADIABATIC LAPSE RATES BY STATE AFTERNOON...BUT NOT ENOUGH MOISTURE
ANYWHERE TO GET A SHOWER/THUNDER GOING. VERY SMALL CHANCE FOR AN
ISOLATED STORM NEAR THE WY/UT/CO BORDER REGION. BUT EVEN
THEN...HARDLY ANY PRECIP WOULD REACH THE GROUND...AND DRY LIGHTNING
PRODUCTION SHOULD ALSO BE RELATIVELY LOW WITH THIS ACTIVITY IF ONE
SHOULD DRIFT INTO SRN LINCOLN OR SWEETWATER COUNTIES.
OTHERWISE...HOT/BREEZY/ CONDITIONS ACROSS THE WEST AND SOUTH REGIONS
WILL RAISE FIRE DANGER CONCERNS...ESPECIALLY IF A FIRE CAN GET
STARTED...HOWEVER DRY FUEL STATUS IS NOT CONSIDERED CRITICAL IN
THESE ZONES AT THIS TIME. THE EASTERN ZONES...INCLUDING JOHNSON AND
NATRONA COUNTIES...WHERE DRY FUELS ARE CRITICAL AT THIS
TIME...SHOULD STILL REMAIN JUST BELOW RED FLAG CONDITIONS. WILL
MONITOR FOR CHANGING CONDITIONS.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

DRY SATURDAY NIGHT WITH MILD OVERNIGHT LOWS. SUNDAY WILL SEE
INCREASING MOISTURE FROM THE SOUTHWEST AS THE FLOW ALOFT BECOMES
SOUTHWEST. A WEATHER DISTURBANCE WILL BE MOVING NORTH THROUGH UTAH
AND NEVADA SUNDAY AFTERNOON INTO SUNDAY EVENING...THEN INTO WESTERN
WY BY MONDAY DAYBREAK. THIS WILL LEAD TO ISOLATED SHOWERS AND STORMS
FORMING OVER SOUTHWEST WY SUNDAY PM AND SPREADING NORTHWARD SUNDAY
NIGHT INTO MONDAY MORNING. MOST STORMS WILL HAVE GUSTY WIND AND THE
STRONGER STORMS WILL HAVE BRIEF HEAVY RAIN. ON MONDAY THE
DISTURBANCE WILL MOVE ACROSS NORTHERN WY AND SOUTHERN MONTANA. THUS
THE BEST CHANCE FOR SHOWERS AND STORMS WILL BE ACROSS THE NORTHERN
ZONES WITH ISOLATED AT BEST CENTRAL BASINS AND SOUTH. THE FAR WEST
WILL SEE SOME STORMS MONDAY AFTERNOON AND EVENING AS WELL AS THE
MOISTURE AXIS REMAINS OVER THAT AREA. SHOWERS AND STORMS CONTINUE
MONDAY NIGHT OVER THE FAR WEST AND NORTH...BECOMING ISOLATED AFTER
MIDNIGHT MONDAY NIGHT.

UPPER LEVEL HIGH PRESSURE BUILDS NORTH INTO WY TUESDAY BRING WARMER
700MB TEMPS INTO THE AREA. STORMS WILL BE ISOLATED AND CONFINED TO
FAR NORTHERN WY TUESDAY AFTERNOON AND NIGHT. THE MODELS ARE HINTING
AT ANOTHER WEATHER DISTURBANCE ROTATING AROUND THE WEST SIDE OF THE
UPPER HIGH FOR WEDNESDAY AFTERNOON AND NIGHT. THE GFS IS FASTER WITH
THIS DISTURBANCE THAN THE ECMWF. THE CURRENT FORECAST LOOKS GOOD SO
WILL NOT ALTER WED PM THROUGH WED NIGHT WITH THE ISOLATED STORMS
OVER THE NORTHWEST AND NORTH.

THE GFS AND ECMWF MODELS CONTINUE TO DIFFER ON THE TRACK OF A STORM
SYSTEM THAT MOVES ACROSS THE PACIFIC NW STATES WEDNESDAY NIGHT AND
ACROSS MONTANA/SOUTHERN CANADA THURSDAY. THE GFS TRACK IS STILL
SOUTH OF THE ECMWF TRACK BUT THE ECMWF TRACK IS FARTHER SOUTH ON ITS
12Z RUN THAN LAST NIGHTS 00Z RUN. THIS MAKES A DIFFERENCE IN HOW
MUCH COOL AIR MAKES IT INTO THE NORTH PART OF THE STATE THURSDAY
NIGHT AND FRIDAY. IT WILL REMAIN HOT AND DRY FOR THE CENTRAL AND
SOUTH ZONES THURSDAY WITH ISOLATED STORMS OVER THE NORTH THURS PM
AND NIGHT AS THE COLD FRONT APPROACHES AND THEN PASSES BY. FRIDAY
LOOKS DRY FOR MOST OF THE REGION WITH MAYBE ISOLATED STORMS OVER THE
FAR NORTHERN MOUNTAINS.

AS FOR TEMPS...SUNDAY THROUGH WEDNESDAY...SUMMERTIME HIGHS IN THE
80S AND 90S. AN ISOLATED 100 DEGREE HIGH NEXT WEDNESDAY COULD OCCUR
IF THE CLOUDS DO NOT INCREASE FAST ENOUGH IN THE BIGHORN BASIN.
COOLER OVER THE NORTH THURSDAY WITH MORE CLOUDS AND POSSIBLE STORMS
AND THE COOLER AIR FILTERING IN DURING THE AFTERNOON. STILL HOT
CENTRAL AND SOUTH THURSDAY. FRIDAY HIGHS WILL BE LITTLE CHANGED FROM
THURSDAY AS 700MB TEMPS ARE QUITE SIMILAR.

&&

.AVIATION.../06Z ISSUANCE/

TERMINALS WILL BE VFR THROUGH THE FORECAST PERIOD. ENOUGH SMOKE
FILTERING INTO THE REGION IN WEST-NORTHWEST FLOW ALOFT TO POSSIBLY
BRING A BRIEF PERIOD OF MVFR EARLY SATURDAY...BUT THINKING IS IT
WILL REMAIN 6SM OR BETTER. MID AND HIGH CLOUDS WILL DRIFT ACROSS THE
FORECAST AREA EARLY SATURDAY BEFORE THE UPPER FLOW BACKS TO THE
WEST. THIS WILL BRING DRIER AIR INTO THE REGION. THE ATMOSPHERE WILL
BE MORE STABLE AS TEMPERATURES WARM ALOFT AND MOISTURE IS LACKING AT
ALL LEVELS. THE NEXT OPPORTUNITY FOR CONVECTION APPEARS TO BE IN
WESTERN WYOMING LATE SUNDAY AFTERNOON. SURFACE WIND AT KBPI...
KPNA...KRKS AND KCPR WILL INCREASE BETWEEN 18Z-19Z/SAT TO 15-25KTS
WITH A FEW HIGHER GUSTS THROUGH 02Z/SUN.

&&

.FIRE WEATHER...

RELATIVELY FLAT UPPER LEVEL RIDGING CONTINUES...WITH THE WARMING AND
DRYING TREND ALSO CONTINUING ACROSS THE FORECAST AREA. ISOLATED
CHANCES FOR HIGH BASED SHOWERS AND THUNDERSTORMS WILL COME TO
PORTIONS OF SOUTH AND SOUTHEAST WYOMING AS A WEAK UPPER LEVEL
DISTURBANCE ROTATES ACROSS THE FORECAST AREA THIS AFTERNOON. THE
CENTRAL AND NORTHERN MOUNTAINS WILL ALSO HAVE AN ISOLATED CHANCE FOR
A DIURNALLY FORCED SHOWER/STORM OVER THE HIGHER REACHES. THIS
CONVECTIVE ACTIVITY WILL BE CHARACTERIZED AS HIGH BASED...WITH
LITTLE RAIN BUT GUSTY WINDS LIKELY ALONG WITH FEW TO OCCASIONAL
LIGHTNING. THESE CONDITIONS ALONG WITH  BREEZY WEST WINDS 15 TO 20
MPH AND RH VALUES DROPPING INTO THE MID AND UPPER TEENS WILL BEGIN
TO SIGNIFICANTLY ENHANCE FIRE DANGER ACROSS THE SOUTH AND SOUTHWEST
ZONES...ALTHOUGH DRY FUEL STATUS IS NOT CONSIDERED TO BE CRITICAL IN
THIS REGION AS OF YET. THROUGH THE WEEKEND...WARMING CONTINUES
SATURDAY WITH WINDS CONTINUING OUT OF THE WEST AND BREEZY IN THE
AFTERNOON...SLOWLY INCREASING FIRE DANGER/WEATHER CONCERNS AS FUELS
CONTINUE TO DRY OUT. HOWEVER...THE DEEP DRY ATMOSPHERE WILL PROMOTE
VIRTUALLY NO CONVECTION EXCEPT FOR ONLY THE SMALLEST CHANCE
SOMEWHERE NEAR THE WY/UT/CO BORDER AREA. SUNDAY...ANOTHER BUT
SOMEWHAT STRONGER UPPER LEVEL DISTURBANCE...NOW LOCATED OVER THE SRN
AZ/CA BORDER AREA...WILL MOVE INTO WYOMING FROM THE SOUTHWEST...WITH
SOME MID/UPR LVL MOISTURE IN TOW. THIS WILL PRODUCE ISOLATED TO
WIDELY SCATTERED THUNDERSTORM CHANCES AT LEAST ACROSS THE SOUTHWEST
HALF OF WYOMING. AGAIN...THESE STORMS WILL BE HIGH BASED FOR THE
MOST PART...BUT WILL HAVE A LITTLE BETTER CHANCE AT GETTING
MEASURABLE MOISTURE TO THE GROUND. WHILE THESE STORMS WILL ALSO BE
ABLE TO PRODUCE MORE IN THE WAY OF LIGHTNING...THE REGION WHERE THEY
WILL OCCUR...MAINLY SOUTH OF A ZONE 415 TO ZONE 300 LINE...SHOULD
ALSO HAVE SLIGHTLY COOLER HIGH TEMPERATURES ALONG WITH HIGHER MIN RH
VALUES...KEEPING THE FIRE DANGER ELEVATED BUT STILL BELOW RED FLAG
CONDITIONS FOR ANOTHER DAY.

&&

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

$$

SHORT TERM...BRAUN
LONG TERM...AR
AVIATION...CNJ
FIRE WEATHER...BRAUN








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