Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 290445
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1045 PM MDT THU APR 28 2016

.SHORT TERM...TONIGHT THROUGH FRIDAY (ISSUED AT 145 PM MDT)

VERY SLOW PROGRESSING 2/3 UPR WAVE PATTERN ACROSS THE NRN HEMISPHERE
IN PLACE WITH KLUDGEY LW TROF ACROSS THE CONUS WITH EMBEDDED DEEP
TROF AND ASSOCIATED CLOSED LOW OVER THE WEST WITH THE CENTER OF CIRC
NEAR/WEST OF THE FOUR CORNERS AREA. TWO EMBEDDED DISTURBANCES...ONE
ACROSS NRN/NERN WY WITH ANOTHER ROTATING UP FROM ERN UT/WRN CO WILL
PROVIDE MUCH OF THE IMPETUS FOR LIGHT SHRASN TODAY...MAINLY FROM THE
CNTRL BASINS SOUTH...AND ACROSS THE FAR NORTHERN PORTION OF WY
TODAY. SFC HAS MAIN SFC LOW WELL TO THE SOUTH FROM CNTRL CO TO NEAR
THE FOUR CORNERS REGION...WITH ONLY A WEAK INVERTED TROF UP INTO WRN
WY. LOW PRESSURE RESIDES OVR THE GB...WITH GENERAL HIGH P TO THE
E/NE INTO THE PLAINS....KEEPING MUCH OF THE LOW LVL FLOW ACROSS THE
FA FROM THE NORTH TO EAST.

SEASONALLY COOL/COLD CONDITIONS...FOR THE MOST PART...CONTINUE THRU
THE FCST PERIOD...WITH A RATHER PERSISTENT STRAT CU CLOUD DECK
REMAIN OVR MUCH OF WY. A FEW BREAKS IN THE CLOUDS MAY ARRIVE THIS
AFTERNOON OVER THE BASINS FOR A SHORT PERIOD BEFORE RETURN TO
OVERCAST AGAIN TONIGHT. A FEW MORE BREAKS WITH SLIGHTLY BETTER
SUNSHINE POTENTIAL WILL BE POSSIBLE FRIDAY AFTERNOON...BEFORE
CLOSING ONCE AGAIN FRIDAY NIGHT FOR MOST LOCATIONS EXCEPT PERHAPS
THE NRN BIG HORN BASIN WHICH COULD REMAIN SCATTERED OVERNIGHT.
PRECIP POTENTIAL BEST ACROSS THE SOUTH AND WEST
TODAY/TONIGHT...EITHER ASSOCIATED WITH MOIST ADVECTION AND MODEST
UPR FORCING ROTATING INTO REGION FROM UPR LOW TO THE SOUTH...OR
ALONG/NEAR THE TROF OUT WEST. FRIDAY...OTHER THAN ISOLATED VERY
LIGHT SHOWERS POSSIBLE ACROSS MOST OF THE FA HERE AND THERE...BETTER
LOCATIONS FOR MEASURABLE PRECIP WILL BE LOCATION EITHER OVR THE WRN
MOUNTAINS FRI AFTERNOON DURING THE AFTERNOON WITH THE BEST
INSTABILITY...OR ACROSS FAR ERN SWEETWATER...ERN FREMONT...AND SRN
NATRONA COUNTIES AS THE MAIN UPR LOW HEADS TOWARDS/OVR ERN
CO...SPINNING UP A LEE CYCLONE INTO THE SRN PLAINS. HOWEVER...NONE
OF THE ACTIVITY APPEARS TO BE TOO SIGNIFICANT ATTM...WITH MOST ALL
OF THE BEST DYNAMICALLY FORCED PRECIP POTENTIAL ACROSS SERN
WY...AND POINTS FURTHER SOUTH AND EAST. THRU THE 24 HRS OF THE FCST
PERIOD...SNOW ACCUMULATION SHOULD GENERALLY RANGE FROM A TRACE TO AN
INCH ACROSS THE LOWER ELEVATIONS...TO 1 TO 3 INCHES ACROSS THE
MOUNTAINS.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

A COLD LOW PRESSURE TROUGH WILL REMAIN OVER THE AREA FRIDAY NIGHT
WITH MOIST LOW LEVEL EASTERLY FLOW PRODUCING AREAS OF RAIN AND SNOW
SHOWERS OR A RAIN AND SNOW MIX.  THIS WILL CONTINUE ON SATURDAY...
SATURDAY NIGHT AND SUNDAY AS THE UPPER LOW PRESSURE AREA SPLITS
WITH THE NORTHEASTERN PART OF THE LOW EXITING TO THE EAST WHILE
A LARGE CLOSED LOW CIRCULATION REFORMS OVER THE SOUTHERN GREAT BASIN
AND DESERT SOUTHWEST WEST OF THE FOUR CORNERS AREA.  DRYING OCCURS
FROM NORTH TO SOUTH AS A DRY SURFACE HIGH PRESSURE AREA MOVES SOUTH
FROM ALBERTA ON MONDAY AND MONDAY NIGHT.  THE WEAKENING OF THE
SOUTHWEST LOW MAY BE TOO FAST AND THE MODELS START TO DIFFER WITH
THE DEMISE OF THE LOW AS AN UPPER LEVEL HIGH PRESSURE RIDGE BUILDS
INTO THE WEST.  THIS LEADS TO SIGNIFICANT DRYING AND WARMING
TUESDAY THROUGH WEDNESDAY.  WHEN THE RIDGE AXIS MOVES INTO EASTERN
WYOMING...SOUTH SOUTHWEST FLOW MOVES INTO WESTERN WYOMING WITH SOME
SHOWERS DEVELOPING WEDNESDAY NIGHT AND THURSDAY OVER THE WESTERN
MOUNTAINS.  THE SPREAD BETWEEN THE MODEL SOLUTIONS BECOMES QUITE
LARGE...BUT WITH A GENERAL LONG WAVE HIGH PRESSURE RIDGE...THE
MAIN DIFFERENCES ARE TO THE WEST AND EAST OF THE AREA WHERE LONG
WAVE TROUGHS BRACKET THE RIDGE. WEDNESDAY AND THURSDAY HIGHS WARM
NICELY INTO THE UPPER 60S AND 70S WITH THE WARMEST TEMPERATURES
IN THE BIGHORN BASIN.

&&

.AVIATION.../06Z ISSUANCE/

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

VFR TO MVFR CIGS THROUGH FRIDAY NIGHT. ISOLATED RAIN AND SNOW
SHOWERS WILL OCCUR THROUGH 15Z WITH LOCAL IFR VSBYS/CIGS. FRIDAY
AFTERNOON ADDITIONAL SHOWERS WILL DEVELOP AND CONTINUE THROUGH
FRIDAY NIGHT. EXPECT AREAS OF MVFR CIGS AND SOME MOUNTAIN
OBSCURATION. A GUSTY WIND TO CONTINUE AT KRKS THROUGH FRIDAY
AFTERNOON.

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

VFR TO MVFR CIGS ACROSS THE REGION THROUGH FRIDAY NIGHT. ISOLATED
SNOW SHOWERS OVERNIGHT IN CENTRAL WY UNTIL 15Z. THEN SCATTERED RAIN
OR SNOW SHOWERS FRIDAY AFTERNOON AND NIGHT WITH AREAS OF MVFR CIGS
AND SOME MOUNTAIN OBSCURATION.

&&

.FIRE WEATHER...

TODAY...LOW FIRE DANGER ALL LOCATIONS WITH RELATIVELY LIGHT WIND
HIGH RH VALUES...ONLY BOTTOMING OUT IN THE MID 50S TO MID 80S
(PERCENT). SMALL CHANCES FOR AN ISOLATED TO SCATTERED SHOWERS OR AN
ISOLATED THUNDERSTORM ACROSS SOUTH AND SOUTHWEST WY THIS AFTERNOON
THROUGH 4 AM. FRIDAY...FIRE DANGER CONTINUES LOW ACROSS ALL OF
WYOMING.

&&

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

&&

$$

SHORT TERM...BRAUN
LONG TERM...C.BAKER
AVIATION...AR
FIRE WEATHER...BRAUN


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