Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 280505
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1105 PM MDT FRI MAY 27 2016

.SHORT TERM...TONIGHT THROUGH MONDAY (issued at 359 PM MDT)

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.../06Z ISSUANCE/

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

Isolated showers over the northwest through Saturday morning. Then
isolated showers and storms over far north WY Saturday afternoon
into early evening. Local mvfr cigs/vsbys are possible with storms.
In southern WY Saturday afternoon isolated showers and storms will
occur into the early evening. KRKS airport will be close to this
activity and VCSH will be included in the TAF. Otherwise VFR
conditions to prevail over the region through Saturday evening.

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

Isolated showers will end by 12z in the eastern part of the area,
mainly from KBYG to KCPR. New showers and storms will develop by 18z
over the Bighorn Mountains southward to Casper. This activity will
occur through 00z Sunday and then diminish by 02z. MVFR cigs/vsbys
will be likely with storms from 18z Sat to 01z Sun. Otherwise, VFR
conditions will prevail over the rest of the area Saturday and
Saturday evening.

&&

.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 Unsettled WEATHER AND SOMEWHAT COOLER WEATHER WILL RETURN
EARLY NEXT WEEK.

&&

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

&&

$$

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



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