Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 132006
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
206 PM MDT SUN JUL 13 2014

.SHORT TERM...TONIGHT THROUGH MONDAY

HIGH PRESSURE OVER THE GREAT BASIN AND LOW PRESSURE OVER THE UPPER
MIDWEST WITH WYOMING IN BETWEEN THE TWO SYSTEMS WILL KEEP US IN
NORTHWEST FLOW WITH SOME CONVECTION STILL POSSIBLE THIS EVENING AS A
WEAK DISTURBANCE MOVES OVER THE RIDGE. HEIGHTS WILL CONTINUE TO
BUILD ACROSS THE WEST AS THE SUBTROPICAL HIGH SHIFTS NORTH...THIS
WILL LIMIT CONVECTION ACROSS THE SOUTHWEST...BUT IT WILL NOT BE
ENOUGH TO ERADICATE ALL ACTIVITY...JUST LIMIT IT TO PROBABLY JUST A
FEW SHOWERS THIS EVENING...AND TO A LESSER EXTENT ON MONDAY AS
ANOTHER...STRONGER WAVE FLATTENS THE RIDGE AND MAKES SHOWERS AND
STORMS MORE LIKELY AS HEIGHTS LOWER. THE DISTURBANCE ON MONDAY WILL
ARRIVE LATER IN THE AFTERNOON SO THERE COULD BE SOME INITIAL
ACTIVITY FOCUSED ON THE MOUNTAINS AS THE SURFACE HEATS UP BUT THEN
ONCE THE DISTURBANCE ARRIVES...IT COULD EXPAND THE THUNDERSTORM
ACTIVITY LATE IN THE AFTERNOON AND INTO THE EVENING...ESPECIALLY IN
YELLOWSTONE...THE ABSAROKAS AND AS FAR SOUTH AS THE WIND
RIVERS...AND INTO ADJACENT FOOTHILLS AND BASINS. ACROSS NORTHEAST
WYOMING...COOL AIR AT THE SURFACE WILL BEGIN TO UNDERCUT THE WARM
AIR ALOFT LEADING TO A PRETTY STABLE ATMOSPHERE FOR MUCH OF THE DAY
ALONG THE I25 CORRIDOR AND THE NORTHERN BIGHORN BASIN.

.LONG TERM...MONDAY NIGHT THROUGH SUNDAY

ACTIVE PERIOD TO START THE MEDIUM RANGE WITH APPROACHING UPPER LOW
CURRENTLY OFF THE WA/OR COAST. THIS UPPER LOW WILL RIDE OVER
THE RIDGE AND DROP SE THROUGH WYO COUNTRY TUESDAY AND TUESDAY NIGHT.
CURRENT TRACK PUTS IT ACROSS OUR ERN ZONES TUESDAY NIGHT. THE
LEADING EDGE OF THIS SHORTWAVE FORCING IMPACTS THE NW AT THE
BEGINNING OF MY PERIOD WITH INCREASED MOISTURE VALUES AND SOME
MODEST QG FORCING. MODIFIED SOUNDINGS GIVE SOME 500-1000 J/KG IN THE
NWRN HALF AND WILL KEEP IDEA OF SCATTERED POPS FROM THE NW DOWN INTO
MOST OF FREMONT COUNTY MONDAY EVENING. AS THE UPPER LOW APPROACHES
MONDAY NIGHT THERE IS ACTUALLY SOME ISENTROPIC UPGLIDE FORECAST
ACROSS OUR NWRN/NCNTRL ZONES. COOL FRONT SLIDES SOUTH ON BACK SIDE
OF HUGE GREAT LAKES LOW AND THEN AS THE UPPER LOW APPROACHES WE GET
SOME MODEST UPGLIDE FOR THE CODY FOOTHILLS AND ABSAROKA FOOTHILLS.
INCREASED POPS IN THIS AREA MONDAY NIGHT. SOUTHERN ARM OF THIS
FORCING WILL ALSO LIKELY SUPPORT A BAND OF SHOWERS MOVING E-NE OFF
THE WIND RIVERS AND ACROSS CENTRAL WYO MONDAY NIGHT. NAM KEEPS THE
FRONT ENTRENCHED ON TUESDAY WHILE THE GFS AND TO A LESSER EXTENT
THE EURO WASH IT OUT AHEAD OF THE NEW FRONT WITH THE UPPER LOW.
THERE WILL LIKELY BE ENOUGH SUPPORT AND WEAKER FRONT HANGING IN THE
AREA TO SUPPORT SOME MORNING SHOWERS AND ISOLATED THUNDERSTORMS
TUESDAY. AS THE UPPER LOW TRACK SE INTO NRN WYO TUESDAY AFTERNOON AND
EARLY EVENING...AIRMASS WILL DESTABILIZE AHEAD OF IT WITH BEST COMBO
OF HIGHER PWATS (AROUND AN INCH)...FRONTAL CONVERGENCE AND UPPER
DYNAMICS TO BE FROM THE SERN ABSAROKAS...SE THROUGH FREMONT AND
NATRONA COUNTIES. HIT THESE AREAS HARDER LEADING TO EVENTUAL STEADY
RAIN/SHOWERS CENTERED ON NATRONA AND FOR A WHILE JOHNSON COUNTY
OVERNIGHT TUESDAY NIGHT WITH EMBEDDED THUNDERSTORMS. NATRONA COUNTY
LOOKS BEST FOR THIS WITH UPSLOPE...CONVERGENCE ALONG THE MID LEVEL
CIRCULATION AND OVERALL FORCING FROM THE TROUGH/LOW. BUMPED UP POPS
TO LIKELY FOR TUESDAY NIGHT AND INCREASED THEM SOME INTO WEDNESDAY
MORNING. GFS SHEARS AND STRETCHES THIS LOW OUT AND LINGERS SOME
FORCING THROUGH THE DAY WEDNESDAY WITH THE NAM IS QUICKER TO BUILD
THE SHORTWAVE RIDGING IN. FORECAST STILL HAS SCATTERED CENTRAL WYO
MOUNTAIN POPS AND AROUND CASPER MOUNTAIN THAT LOOKS GOOD FOR NOW BUT
WITH ANY SLOWER MOVEMENT...WE`LL NEED TO BUMP THOSE UP EAST OF THE
DIVIDE.

FLAT RIDGE/NW FLOW HOLDS THURSDAY WITH WARMER TEMPERATURES AND
POTENTIAL WEAK SEWD MOVING DISTURBANCE. SCATTERED MOUNTAIN STORMS
WITH AT LEAST ISOLATED FOR THE LOWER ELEVATIONS OF THE NORTH LOOKS
GOOD. ANOTHER DISTURBANCE AHEAD OF A POTENTIAL STRONGER SHORTWAVE
FOR FRIDAY NIGHT OR SATURDAY SHOULD BE ENOUGH TO HELP FIRE
THUNDERSTORMS ONCE AGAIN FRIDAY. MODELS ARE STARTING TO DIVERGE MORE
SIGNIFICANTLY BY THE WEEKEND AS TO THE LOCATION AND STRENGTH OF NEXT
SHORTWAVE. THE GEM IS THE FURTHEST SOUTH AND SHARPEST WITH THIS
SYSTEM DIGGING IT INTO NRN IDAHO ON SATURDAY AND THEN WEAKENING IT
BUT MOVING IT ACROSS THE STATE LATE SATURDAY INTO SUNDAY MORNING.
THE GFS KEEPS THE ENERGY WELL TO THE N WITH JUST A SW FLOW.
HOWEVER...THE GFS THEN HAS DISTURBANCES ROTATING AROUND THE BUILDING
MONSOONAL HIGH NEAR THE 4-CORNERS. THE ECMWF IS ABOUT IN BETWEEN
THESE SOLUTIONS. BY SUNDAY...THE ECMWF IS BUILDING THE 4-CORNERS
HIGH NWD WHILE THE GFS MAINTAINS IT SW FLOW WITH POTENTIAL
DISTURBANCES. WILL NOT MAKE ANY MAJOR CHANGES AND KEEP IDEA OF
SCATTERED MOUNTAIN STORMS AND AT LEAST ISOLATED THROUGH THE LOWER
ELEVATIONS THROUGH SATURDAY AND MAYBE ADD IN SOME ISOLATED AT LEAST
IN THE MOUNTAINS FOR SUNDAY.

&&

.AVIATION.../00Z ISSUANCE/

LIGHT WINDS WITH MAINLY SKC CONDITIONS WILL OCCUR THRU THE PERIOD.
ISOLATED CONVECTION MAINLY OVER THE MOUNTAINS SHOULD DECAY
RELATIVELY QUICKLY AS THEY MOVE INTO THE LOWER ELEVATIONS. THE MAIN
HAZARD WILL BE GUSTY OUTFLOW WINDS. THE CONVECTION OUTFLOW WINDS
COULD IMPACT TERMINALS THAT DO NOT HAVE VCSH MENTIONED. ANY
CONVECTION SHOULD QUICKLY WANE THIS EVENING WITH VERY LITTLE OR NO
CONVECTION LEFT BY 03Z. -SHRA AND -TSRA WILL BE POSSIBLE AFTER 18Z
ON MONDAY AS WELL...AGAIN STORMS WILL MAINLY BE IN THE MOUNTAINS BUT
THERE WILL A LITTLE BETTER CHANCE OF THESE STORMS MAKING IT INTO THE
LOWER ELEVATIONS BETWEEN 21Z AND 03Z MONDAY.

&&

.FIRE WEATHER...

WE SHIFT TO A NORTHWEST FLOW PATTERN BY MONDAY WITH A COLD FRONT
POSSIBLY DROPPING SOUTHWEST INTO THE DIVIDE DURING THE DAY...AND
BEYOND OVERNIGHT. THIS COULD BE THE FOCUS OF ANOTHER ROUND OF WET
SHOWERS AND THUNDERSTORMS ESPECIALLY ALONG AND EAST OF THE DIVIDE.
ANOTHER WAVE OF SHOWERS AND STORMS IS POSSIBLE ON TUESDAY WITH A
GOOD CHANCE OF WETTING RAIN JUST ABOUT EVERYWHERE. RELATIVE HUMIDITY
AND WINDS ARE NOT EXPECTED TO REACH CRITICAL LEVELS FOR THE NEXT FEW
DAYS BUT THERE COULD BE GUSTY AND ERRATIC WINDS WITH THE STORMS ON
MONDAY EVEN IN AREAS WHERE THERE ARE NO STORMS EXPECTED...LIKE
AROUND RAWLINS DISPATCH. ON TUESDAY...THERE WILL BE A STEADY 15 TO
25 MPH WIND ACROSS MUCH OF RAWLINS DISPATCH AREA FOR MOST OF THE DAY
WITH A CHANCE OF THUNDERSTORMS LATE.

&&

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

$$

SHORT TERM...ALLEN
LONG TERM...SKRBAC
AVIATION...ALLEN
FIRE WEATHER...ALLEN





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