Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 060942
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
342 AM MDT FRI MAY 6 2016

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT

GENERAL OMEGA BLOCK PATTERN ACROSS THE CONUS...WITH SLOW
MOVING/EVOLVING DEEP STORM SYSTEM MOVING OUT OF THE DESERT
SW...TOWARD THE CNTRL ROCKIES THRU THE FCST PERIOD...BECOMING PART
OF A POSSIBLE REX BLOCK SANDWICHED BETWEEN ANOTHER OMEGA BLOCK BY
SUNDAY. SFC CURRENTLY SHOWS HIGH P ACROSS THE GREAT BASIN WITH WEAK
LOW P OFF TO THE NE AND OVR ND...WITH A VERY WEAK TROF REACHING
INTO NERN WY.

ADDED ZONE 07 INTO THE FLOOD WATCH AREA AS COPIOUS RAINFALL OVR THE
OWL CREEK AND BRIDGER MOUNTAINS COULD BE PROBLEMATIC...AT THE VERY
LEAST PROVIDING THE IMPETUS FOR MUD AND ROCK SLIDE POTENTIAL IN THE
CANYON AREAS...IN ADDITION TO/OR IN LIEU OF FLOODING.

BOTTOM LINE...VERY WET PATTERN ABOUT DUE TO TAKE OVR NEARLY THE
ENTIRE FCST PERIOD...WITH FLOOD WATCHES POSTED FOR PORTIONS OF CNTRL
WY...INCLUDING ZONES 07 17 AND 18...BEGINNING SAT 12Z AND LASTING AT
LEAST THRU THE DAY SUNDAY.

AS THE SW CONUS LOW SLOWLY SPINS THIS WAY...PWS WILL INCREASE THRU
THE DAY...REACHING ANOMALOUSLY HIGH LEVELS BY TONIGHT...RANGING
BETWEEN 0.75 AND 1 INCH OVERNIGHT TONIGHT THRU SAT MORNING. COMBINED
WITH THE PASSAGE OF A DEVELOPING SFC FRONT TONIGHT...THIS WILL USHER
IN THE BEGINNING OF POTENTIAL FLOOD CONDITIONS BY SAT MORNING FOR
MUCH OF FREMONT COUNTY AND AT LEAST SOUTHERN HOT SPRINGS
COUNTY...AREAS FAVORED TO TAKE ADVANTAGE OF UPSLOPE CONDITIONS WITH
VIGOROUS VEERING FLOW FROM NE TO E/SFC TO H7. QPF VALUES/RANGES ARE
ACCORDINGLY HIGH WITH BETWEEN A HALF AND AND INCH EVER 6 HRS
BEGINNING TONIGHT UNTIL SAT MORNING...THEN PERHAPS A QUARTER INCH TO
A HALF INCH EVERY 6 HRS THRU SAT NIGHT. THIS WILL GIVE 2 DAY TOTAL
QFP VALUES RANGING FROM 2 TO 4 INCHES OVR THE CNTRL BASINS AND
ADJACENT MOUNTAINS. SNOWFALL WILL BE INTERESTING...ESPECIALLY DURING
THE OVERNIGHT HRS TONIGHT AND SATURDAY NIGHT...AS WARM ADVECTION
AHEAD OF THE APPROACH OF THE UPR LOW WILL KEEP SNOW LEVELS HIGH TO
BEGIN WITH...FALLING TO AROUND 8500 FEET OR SO BY SAT/SUN
MORNINGS...BUT OSCILLATING SOME BETWEEN THESE PERIODS AS THE WARM
ADVECTION BATTLES THE COLDER TEMPS NEAR THE CENTER OF THE LOW AS IT
APPROACHES. ADVISORY/WARNING ACCUMULATIONS WILL BE LIKELY OVR THE
WIND RIVER/SRN ABSAROKA MOUNTAINS THRU SUN MORNING...BUT MOST OF
HIGH AMOUNTS WILL BE LOCATED ABOVE 9500 FEET AND COME DURING THE TWO
NOCTURNAL PERIOD. WILL LET THE DAY CREW DECIDE HOW TO HANDLE THE
SNOW. FINALLY...WITH RATHER STRONG ACCENT SPREADING OVR THE FA WITH
THE APPROACH OF THE UPR LOW...THIS AFTERNOON MAY ALSO AFFORD CHANCES
FOR A FEW STRONG/MARGINALLY SEVERE THUNDERSTORMS WITH CAPE RANGING
FROM 500 TO 1500 J/KG ACROSS THE SRN AND ERN FA...COMBINING WITH
SHEAR RANGING FROM 25 TO 40 KTS BUT ONLY MARGINAL LAPSE RATES. A FEW
STORMS COULD PRODUCE STRONG WET DOWNBURSTS IN HEAVY RAIN AND SMALL
HAIL OF AROUND .75 INCH...TO SLIGHTLY LARGER. ACROSS SWEETWATER
COUNTY WHERE IT WILL BE A BIT DRIER IN THE BOUNDARY LAYER
EARLY...DCAPE COULD RANGE BETWEEN 500 AND 900 J/KG FOR A SHORT
PERIOD...PRODUCING A FEW STRONG MICROBURSTS APPROACHING SEVERE
LEVELS BY MID TO LATE AFTERNOON. ALL IN ALL..A VERY BUSY PATTERN
FOR THE NEXT FEW DAYS.

.LONG TERM...MONDAY THROUGH FRIDAY

THE MODELS KEEP SCATTERED SHOWERS AND ISOLATED STORMS ALONG AND
EAST OF THE DIVIDE MONDAY WITH DRIEST AREA BEING SW WY. THE NEXT
WEATHER SYSTEM DROPS SOUTHEAST OUT OF MONTANA MONDAY NIGHT AND
THROUGH WYOMING TUESDAY INTO TUE NIGHT. RAIN SHOWERS WITH SNOW IN
THE MOUNTAINS. RAIN COULD CHANGE TO SNOW BRIEFLY OVER THE LOWER
ELEVATIONS TUE NIGHT WITH LIGHT ACCUMULATION. WILL NEED TO WATCH
THIS MORE AS TIME GETS CLOSER. A NW FLOW ALOFT FOR WED AND THURS
WITH A MORE WEST FLOW ALOFT NEXT FRIDAY. THERE APPEARS TO BE A FEW
WEAK DISTURBANCES IN THE FLOW WED AND THURS WHICH WOULD LEAD TO
SOME CONVECTION BOTH DAYS. MOST OF THE ACTIVITY LOOKS TO BE ALONG
AND EAST OF THE DIVIDE WITH LESSER COVERAGE IN THE SOUTHWEST. NEXT
FRIDAY WOULD SEE BETTER SHOWER OR STORM COVERAGE WEST OF THE
DIVIDE VERSUS EAST OF THE DIVIDE. HIGH TEMPS WILL BE ON A YO-YO
RIDE WITH MONDAY BEING THE MILD DAY...THEN COLDER TUE AND WED. A
LITTLE WARMER NEXT THURS AND FRI.

&&

.AVIATION.../12Z 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
FROM 00Z-12Z/SATURDAY WILL BE SNOW ABOVE 9K FT MSL. BETTER CHANCE
FOR MVFR CEILINGS/VISIBILITY WILL COME BETWEEN 06Z-12Z/SATURDAY
BECAUSE OF BETTER DYNAMICS AND DEEPER MOISTURE. KJAC WILL BE THE
LEAST LIKELY LOCATION TO SEE MVFR CEILINGS AS UPPER FLOW IS NOT
AS FAVORABLE THERE.

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

UPPER LOW WILL GRADUALLY TRACK ONSHORE ACROSS SOUTHERN CALIFORNIA
TODAY WHILE 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. IFR/MVFR CEILINGS/VISIBILITY WILL
BECOME MORE WIDESPREAD BETWEEN 06Z-12Z/SATURDAY. PRECIPITATION AMOUNTS
0.50 INCHES IN 6-HOURS...DYNAMICS ARE FAVORABLE...AND UPSLOPE
FLOW WILL ENHANCE PRECIPITATION PRODUCTION.

&&

.FIRE WEATHER...

LOW FIRE DANGER FOR ALL LOCATIONS THROUGH THE WEEKEND...WITH GREEN
UP UNDERWAY AND MORE MOISTURE HEADED INTO THE REGION OVER THE NEXT
FEW DAYS. EXPECT RELATIVELY HIGH MINIMUM RH VALUES...ONLY BOTTOMING
OUT IN THE 30S TO MID 60S (PERCENT) ACROSS THE ENTIRE REGION.
SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS CAN ALSO BE EXPECTED
BY THIS AFTERNOON...WITH SHOWERS...HEAVY AT TIMES...CONTINUING TO
FALL OVER MOST LOCATIONS THROUGH AT LEAST SUNDAY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

FLOOD WATCH FROM SATURDAY MORNING THROUGH SUNDAY AFTERNOON FOR
WYZ007-017-018.

&&

$$

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



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