Area Forecast Discussion
Issued by NWS Riverton, WY

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826
FXUS65 KRIW 060528
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1128 PM MDT THU MAY 5 2016

.SHORT TERM...TONIGHT THROUGH SUNDAY

HIGH CLOUDS HAVE ENCROACHED ON THE AREA TODAY. A HARBINGER OF THE
MAJOR CHANGE THAT IS TAKING SHAPE FOR FRIDAY THROUGH THE WEEKEND.
A FEW WEAK SHOWERS ARE STARTING TO FORM AND MAIN THREAT INTO EARLY
THIS EVENING WILL BE GUSTY WIND POTENTIAL WITH AREAS OF 40-50
DEGREE SPREADS IN THE SOUTHWEST. A FEW DYING GUSTY SHOWERS MAY
EDGE EAST OF THE DIVIDE INTO EARLY THIS EVENING. NOT MUCH LIQUID
BUT SOME BRIEF STRONG WIND GUSTS AND A LIGHTNING STRIKE OR TWO. FRIDAY
IS STILL SHAPING UP TO BE QUITE THE INTERESTING DAY. LARGE UPPER
LOW MOVES INTO SOCAL WHILE SRN CANADA SHORTWAVE PUSHES A COLD
FRONT SWD ACROSS THE AREA. UPPER LOW DYNAMICS START TO PUSH INTO
THE SOUTH WITH A RATHER COMPLEX JET INTERACTION. SWRN WYOMING WILL
SEE THE DAYTIME HEATING...APPROACHING FRONT...LARGE SCALE ASCENT
WITH UPPER LOW AND POSSIBLE UPPER JET SUPPORT. JET SUPPORT IS
QUITE INTERESTING AS FIRST JET STREAK MOVES UP AND STARTS TO
ROTATE WWD ACROSS SRN ID/NRN UT AREA WHILE MAIN CYCLONIC NOSE OF
THE JET NOSES INTO FAR NRN CO. THIS SETUP PUTS SWRN WYOMING IN
POTENTIAL STRONG UPPER DIVERGENCE. NORTH OF THE FRONT...WE CAN
STILL SEE SOME STRONGER STORMS WITH GOOD DIRECTIONAL SHEAR AND
MODERATE CAPE. MARGINAL RISK HAS BEEN MOVED TO INCLUDE CASPER AND
LANDER AND IS PRETTY MUCH WHERE WE`VE HAD IT FOR 3 DAYS NOW. AS
THE UPPER LOW MOVES SLOWLY NEWD FRIDAY NIGHT...WE SHOULD SEE
SIGNIFICANT LOWER ELEVATION RAIN AROUND PARTS OF SWRN AND MOST OF
CENTRAL WYOMING...CENTERED AROUND THE WIND RIVER BASIN/LANDER
FOOTHILLS AND SURROUNDING MOUNTAINS. FRONT PUSHES SOUTH FRIDAY
PROVIDING UPSLOPE WHILE MID LEVEL E-SE FLOW CONVEYOR BELT AND
ASSOCIATED LIFT... SATURATES THE ATMOSPHERE. MID LEVEL QG FORCING
AND UPPER JET SUPPORT FOR THE FIRST HALF OF THE EVENT ALL SPELLS
SIGNIFICANT PCPN. SNOW LEVELS LOOK MAYBE A TAD LOWER THAN
YESTERDAY. THINKING 9-9.5K IN THE WINDS AT 06Z SATURDAY WITH ABOUT
1K LOWER AT TIMES IN HEAVIER SHOWERS/TSTMS. 12Z SATURDAY MORNING
SNOW LEVELS WILL PROBABLY BE CLOSE TO 8500 FEET WITH SOME LOWERING
AT TIMES IN HEAVIER PCPN. THINKING LANDER WILL DROP INTO THE 41-44
DEGREE RANGE BY SATURDAY MORNING AND THEN THINKING ABOUT 3 DEGREES
COOLER PER 1K FEET. HIGHS IN LND WILL PROBABLY ONLY BE IN THE
46-48 RANGE WITH SNOW LEVELS 8.5K GENERALLY WITH SOME LOWERING IN
HEAVIER PCPN PERIODS. ANOTHER 500 FEET OR SO LOWER SATURDAY NIGHT
AS LOW GETS CLOSER. STILL LOOKING AT 1 TO 2 INCHES ACROSS THE WIND
RIVER BASIN WITH THE HIGHER AMOUNTS FROM AROUND RIVERTON WWD WITH
2.5-3 INCHES TOWARDS LANDER AND 3-4 IN THE WINDS AND POSSIBLY SRN
ABSAROKAS. HEAVY SNOW WILL FALL BUT MOSTLY ABOVE 10K INITIALLY AND
THEN GRADUALLY A LITTLE LOWER. 1-2 FEET OF SNOW WILL CERTAINLY
FALL UP HIGH BUT MOSTLY ABOVE ROAD LEVEL. OTHER SURROUNDING AREAS
WILL ALSO SEE THE POTENTIAL FOR .75 TO 1.5 INCHES OF RAIN FROM THE
SWRN AREAS TO CODY FOOTHILLS AND OVER TO NATRONA AND JOHNSON
COUNTY AND EVEN IN SWEETWATER COUNTY. THE LEAST WILL PROBABLY BE
THE FAR NWRN AREAS AND NR5N BIGHORN BASIN WHERE AMOUNTS WILL VARY
FROM A THIRD TO TWO-THIRDS IN GENERAL. STILL UNSETTLED SUNDAY WITH
UPPER LOW LIKELY TO BE WEAKENING AND MEANDERING JUST TO OUR SOUTH.
HARD TO FCST WHERE BANDS OF PCPN WILL BE BY THEN. THEY COULD BE
CLOSER AROUND THE LOW TO MAYBE SOME OUTER BANDS WILL COME INTO
PLAY. MOST AREAS WILL HAVE A CHANCE OF CONTINUED SHOWERS AND
HIGHER ELEVATION SNOW THROUGH THE END OF THIS PERIOD. BOTTOM
LINE...A MAJOR CHANGE FROM WARM AND DRY TO COOL/COLD AND WET (AND
WHITE UP HIGH) WITH A COUPLE (TO SEVERAL) INCHES OF LIQUID
CENTERED ON FREMONT COUNTY WITH LESS AS YOU FAN OUT FROM THERE.
HIGHS IN THE 70S AND 80S WILL STRUGGLE TO BE IN THE UPPER 40S TO
UPPER 50S ON FRIDAY FOR MANY LOWER ELEVATION AREAS.

.LONG TERM...SUNDAY NIGHT THROUGH THURSDAY

A SERIES OF LOW PRESSURE TROUGHS IN NORTH NORTHWEST FLOW WILL DIG
SOUTH SOUTHEAST FROM BRITISH COLUMBIA AND ALBERTA MOVING ACROSS
WESTERN MONTANA...EASTERN IDAHO AND WESTERN WYOMING BRINGING PERIODS
OF SHOWERS AND AFTERNOON AND EVENING THUNDERSTORMS THROUGH THE
PERIOD.  TEMPERATURES WILL BE COOL AND MOST PERIODS TEMPERATURES ARE
COOLER THAN PREVIOUS FORECAST.  THE TREND IS FOR LESS PRECIPITATION
WEDNESDAY THROUGH THURSDAY BUT STILL SHOWERS AND THUNDERSTORMS WILL
BE MOVING THROUGH THE AREA WHILE BEING MOST NUMEROUS IN THE WESTERN
AND NORTHERN MOUNTAINS.

&&

.AVIATION.../06Z ISSUANCE/

WEST OF THE CONTINENTAL DIVIDE...KJAC/KRKS/KPNA/KBPI AIRPORTS

UPPER LOW ALONG THE SOUTHERN CALIFORNIA COAST WILL GRADUALLY TRACK
ONSHORE AND SPREAD MOISTURE NORTH ACROSS THE FORECAST AREA FRIDAY.
SHORTWAVE OVER EAST-CENTRAL UTAH WILL MAKE ITS WAY NORTH BY MIDDAY
FRIDAY AS COLD FRONT DROPS SOUTH TO THE EAST OF THE DIVIDE BEFORE
SWINGING AROUND THE WIND RIVER RANGE. THIS COMBINATION WILL SET THE
STAGE FOR SHOWERS AND THUNDERSTORMS...SOME POSSIBLY STRONG...AFTER
20Z/FRIDAY. MOISTURE DEEPENS DURING THE AFTERNOON AND INTO THE
EVENING HOURS. EXPECT WIDESPREAD MOUNTAIN OBSCURATIONS AFTER ABOUT
00Z/SATURDAY. HAVE KEPT LOW END VFR AT KRKS...KBPI...AND KPNA
BETWEEN 00Z-06Z/SATURDAY...ALTHOUGH MVFR WOULD BE A DISTINCT
POSSIBLITY. SURFACE WIND FROM THE EAST-NORTHEAST TO EAST-SOUTHEAST
OF 12-22KTS...HIGHER AT KRKS...WILL PROVIDE FAVORABLE SHEAR PROFILE
DURING THE AFTERNOON ACROSS SOUTHWEST WYOMING. HEAVIER PRECIPITATION
FRIDAY EVENING WILL BE SNOW ABOVE 9K FT MSL.

EAST OF THE CONTINENTAL DIVIDE...KCPR/KCOD/KRIW/KWRL/KLND AIRPORTS

UPPER LOW WILL GRADUALLY TRACK ONSHORE ACROSS SOUTHERN CALIFORNIA
TODAY WHIL CONTINUING TO SPREAD MOISTURE NORTH ACROSS THE EASTERN
GREAT BASIN INTO WYOMING. AT THE SAME TIME...A COLD FRONT WILL PUSH
SOUTH FROM MONTANA THIS MORNING. THE FRONT WILL SWEEP THROUGH THE
BIG HORN BASIN BETWEEN 11Z-14Z WITH GUSTY NORTHERLY WIND OF 15-25KTS
IN ITS WAKE. THE FRONT WILL PUSH ACROSS THE WIND RIVER BASIN BETWEEN
15Z-17Z WITH GUSTY NORTHEAST WIND. THE WIND WILL INCREASE THIS
AFTERNOON AT ALL TERMINALS AS PRESSURE GRADIENT TIGHTENS. BEST
CHANCE FOR STRONG CONVECTION WILL BE TO THE SOUTH OF A KRIW-KCPR
LINE AFTER 20Z/FRIDAY. MOISTURE DEEPENS AND MODEL SOUNDINGS SHOW
ATMOSPHERE QUICKLY SATURATING BETWEEN 23Z/FRIDAY AND
03Z/SATURDAY...PARTICULARLY AT KLND...KRIW...AND KCPR. EXPECT
WIDESPREAD MVFR WITH LOCALIZED IFR CONDITIONS NEAR THE FOOTHILLS.
MOUNTAINS WILL BE OBSCURED THROUGH THE REMAINDER OF THE FORECAST
PERIOD. HEAVIER PRECIPITATION FRIDAY EVENING WILL BE SNOW ABOVE 9K
FT MSL.

&&

.FIRE WEATHER...

AN AREA OF LOW PRESSURE WILL MOVE TOWARD WYOMING OVER THE NEXT FEW
DAYS AND BRING INCREASINGLY COOL AND WET WEATHER. A FEW AFTERNOON
THUNDERSTORMS WILL BE POSSIBLE ACROSS THE WESTERN MOUNTAINS THIS
AFTERNOON. MEANWHILE...AREAS EAST OF THE DIVIDE WILL SEE ONE MORE
WARM AND DRY DAY WITH A SOUTHWESTERLY BREEZE DEVELOPING. SOME AREAS
WILL HAVE RELATIVE HUMIDITY FALL INTO THE LOWER TEENS. WET WEATHER
WILL RETURN FRIDAY AND ESPECIALLY FRIDAY NIGHT INTO SATURDAY WITH A
WETTING RAIN LIKELY FOR MANY AREAS...ESPECIALLY EAST OF THE DIVIDE.


&&

.RIW WATCHES/WARNINGS/ADVISORIES...
FLOOD WATCH FROM SATURDAY MORNING THROUGH SUNDAY AFTERNOON FOR
WYZ007-017-018.

&&

$$

SHORT TERM...PS
LONG TERM...C.BAKER
AVIATION...CNJ
FIRE WEATHER...PS



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