Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 272159
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
359 PM MDT FRI MAY 27 2016

.SHORT TERM...TONIGHT THROUGH MONDAY

AN EXITING WELL DEVELOPED COLD LOW OVER EASTERN COLORADO WILL
CONTINUE TO EXIT TO THE EAST. THE NEXT SIGNIFICANT UPPER LOW
EXISTS OVER SOUTHERN BRITISH COLUMBIA WITH A SLIGHTLY NEGATIVELY
TILTED TROUGH EXTENDING TO THE SOUTH OF THERE. WESTERN AND CENTRAL
WYOMING LIES BETWEEN THESE TWO LOW CENTERS WITH THE
AFOREMENTIONED TROUGH DRIVING A WEAK VORT EASTWARD NOW SITUATED
ALONG THE MONTANA IDAHO BORDER. WITHOUT MUCH FORCING FROM THESE
TWO MAIN FEATURES... WE ARE RELYING Solely ON WEAK CAPE/LIFTED
INDICES AND WEAK WESTERLY DIFLUENT FLOW ALOFT TO PRODUCE MOSTLY
CONTINUED WEAK CONVECTION FOR THE REMAINDER OF THIS AFTERNOON AND
EVENING. MOST OF THESE CELLS HAVE HAD A TOUGH TIME BREAKING AWAY
FROM THE MOUNTAINS WHERE THEY FORMED DUE TO FORCED ASCENT. SOME OF
THE TINY MORE ENHANCED CELLS HAVE MANAGED TO PRODUCE SMALL HAIL.
THE AFOREMENTIONED VORT LOBE IS HELPING TO A DEGREE. ANOTHER
TROUGH WILL SWING BY ON SATURDAY WITH SIMILAR RESULTS, WITH THE
BEST INSTABILITY WEST OF THE DIVIDE. SUNDAY WILL BE THE WARMEST
AND DRIEST DAY OF THE HOLIDAY WEEKEND AS HEIGHTS RISE AHEAD OF THE
APPROACHING CLOSED LOW THAT WILL GET DISLODGED FROM SOUTHERN
BRITISH COLUMBIA AND WILL COME SCOOTING ACROSS MONTANA MEMORIAL
DAY/MONDAY. THE ONLY CONVECTION EXPECTED SUNDAY WILL BE MOSTLY IN
THE SOUTHWEST AND NORTHEAST ZONES. THIS CLOSED LOW WILL SWING A
PROMINENT TROUGH ACROSS THE STATE FROM WEST TO EAST ACROSS
WYOMING, COMPLETE WITH A TIGHT THERMAL GRADIENT. DRIER AIR WILL
BE PUNCHING BEHIND THE TROUGH WITH MUCH HIGHER CAPES OVER THE
EASTERN ZONES WHERE THE BEST CHANCE OF ANY STRONG THUNDERSTORMS
WILL BE. HOWEVER...A BETTER CHANCE OF THUNDERSTORMS EXISTS
THROUGHOUT THE AREA...ESPECIALLY UP NORTH. THE SNOW LEVEL WILL
LIKELY DROP TO 8K IN THE NORTHERN MTNS BY THE LATTER PORTION OF
MEMORIAL DAY.


.LONG TERM...MONDAY NIGHT THROUGH FRIDAY

Main issue with the forecast is generally at the beginning of the
period in regards to where our next upper low will be Monday night
and Tuesday. The GFS is furthest south with a majority of the trough
swinging across the north half of the forecast area. The ECMWF is
furthest north in Nrn MT/Southern Canada (but trending south again)
and the GEM is about in the middle. Longer wave analysis would
support a further south solution so will keep the going forecast
unchanged. With that said, there is enough cold air to bring a quick
shot of snow to the nrn mtns Monday night. After that, the mean
ridge begins to build into the region with warming temps. Models are
trying to keep the ridge somewhat dirty with moisture spilling se
down the front side of the ridge, mainly Thursday into Friday. Going
forecast already had that handled with some isold storms in the nrn
mtns trying to spill se of the foothills late in the day. No reason
to change this.


&&

.AVIATION.../00Z ISSUANCE/

West of the Continental Divide...KJAC/KRKS/KPNA/KBPI Routes

Isolated showers and thunderstorms will prevail across the area
into this evening. The strongest storms could have brief heavy
rain, small hail and wind gusts over 40 mph through 04z. Only a
few higher mountain showers may continue overnight. Overall,
Saturday will be drier with most areas dry. Only a few mainly
mountain showers or a brief thunderstorm are possible Saturday
afternoon.

East of the Continental Divide...KCPR/KCOD/KRIW/KWRL/KLND Routes

Isolated shower and thunderstorm activity will prevail through 04z.
Isolated light rain showers may persist through 06z. Saturday will
be dry for most of the lower elevations with Johnson County being
the main exception as a cold front brings a little better chance
of afternoon showers and thunderstorms.


&&

.FIRE WEATHER...

A slow drying and warming trend will take place through the weekend.
Temperatures will slowly warm with relative humidity lowering each
day. There will still be some mainly afternoon and evening showers
and thunderstorms around, especially in and adjacent to the
mountains. Any thunderstorm could have erratic winds. Otherwise,
winds should remain light to moderate outside of showers or
thunderstorms. Coverage of thunderstorms will shrink each day with
many of the lower elevations mainly dry on Saturday and Sunday.
MORE UNSETTELED WEATHER AND SOMEWHAT COOLER WEATHER WILL RETURN
EARLY NEXT WEEK.

&&

.RIW Watches/Warnings/Advisories...
None.
&&

$$

SHORT TERM...Lipson
LONG TERM...Skrbac
AVIATION...Skrbac
FIRE WEATHER...Lipson



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