Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 211719
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1119 AM MDT SAT MAR 21 2015

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

TODAY COULD TURN OUT TO BE EVEN WARMER THAN FRIDAY IN SOME AREAS
WITH H7 TEMPS RANGING FROM 1.5C TO 2.5C. HIGH CLOUDS ARE SPILLING
OVER THE RIDGE ACROSS IDAHO AND MONTANA. THE VORT MAX JUST OFF THE
OREGON COAST WILL MOVE RAPIDLY TOWARD THE NORTHERN MONTANA BORDER
TODAY AND WILL FLATTEN THE RIDGE OVER OUR AREA. AS IT DOES...THE
CLOUDS TO THE WEST WILL SPILL INTO THE WESTERN AND NORTHERN PORTIONS
OF WYOMING ALONG WITH ISOLATED SHOWERS IN NW WY AIDED BY NEGATIVE
LIFTED INDICES AND INCREASING WEST SOUTHWEST DIFLUENT FLOW. AS
THE ASCT TROUGH AXIS SPEEDS EAST ACROSS WY TONIGHT WE WILL SEE
WIDELY SCATTERED RAIN AND SNOW SHOWERS ACROSS THE NORTHERN
MOUNTAINS WITH MORE OF THE ENERGY TO OUR NORTH OVER MONTANA AND
CANADA. ON SUNDAY MILD TEMPS WILL CONTINUE UNDER A WESTERLY FLOW.
THE COMBINATION OF AN H7 FRONT LINGERING IN NORTHERN WY ASCT WITH
TONIGHTS TROUGHPA AND NEGATIVE LIFTED INDICES IN WESTERN WY WILL
RESULT IN ISOLATED TO WIDELY SCATTERED SHOWERS MAINLY IN NORTHERN
AND WESTERN WY SUNDAY AFTERNOON. DRY CONDITIONS WITH CLEAR TO
PARTLY SKIES ARE ANTICIPATED FOR SUNDAY NIGHT. THEN MONDAY BEGINS
THE SLEW OF ACTIVE WEATHER. A DEEPER STRONGER TROUGH WILL BE
TRACKING THROUGH THE GREAT BASIN MONDAY AND WILL TRACK ACROSS THE
ROCKIES MONDAY NIGHT. THIS SYSTEM WILL SUPPLY A DEEPER LAYER OF
PACIFIC MOISTURE. THE MOISTURE...INCREASING SOUTHWEST DIFLUENT
FLOW AND THE WEAKLY UNSTABLE ATMOSPHERE WILL ADD UP TO A BETTER
CHANCE OF SHOWERS ACROSS THE CWA MONDAY WITH LIKELY POPS ACROSS
THE WESTERN MTNS. THEN ON MONDAY NIGHT THE TROUGHPA TAKES PLACE
ALONG WITH A SFC LOW TRACKING SOUTHEAST ACROSS NORTHEAST WY AND
COLDER AIR FILTERING IN FROM THE NW. THE RESULT WILL BE RAIN
TURNING TO SNOW IN THE WEST MONDAY NIGHT WITH A RAIN AND SNOW
SHOWERS IN THE NORTH...EAST OF THE DIVIDE.

.LONG TERM...TUESDAY THROUGH SATURDAY

MEDIUM RANGE MODELS ARE SHOWING A COUPLE OF QUICK MOVING
DISTURBANCES IN THE NORTHWEST FLOW IMPACTING THE COWBOY STATE
TUESDAY AND WEDNESDAY. AN ASSOCIATED WEAK/SHALLOW COLD FRONT IS
PROJECTED TO PUSH SOUTH...EAST OF THE DIVIDE TUESDAY NIGHT. BOTH
SYSTEMS WILL GIVE THE NORTHWEST AND NORTHERN MOUNTAINS A GOOD CHANCE
OF ACCUMULATING SNOW...WITH SOME SHOWER ACTIVITY SPILLING INTO THE
LOWER ELEVATIONS. DESPITE EXPECTED HIGHS IN THE 40S TO AROUND 50
ACROSS MUCH OF THE LOWER ELEVATIONS TUESDAY/WEDNESDAY...THE
PRECIPITATION TYPE IS EXPECTED TO BE MAINLY SNOW/GRAUPEL SHOWERS.
THIS IS DUE TO THE ANTICIPATED INSOLATION BEFORE...IN BETWEEN SHOWER
ACTIVITY...WITH A WELL MIXED LOWER LEVEL OF THE ATMOSPHERE WITH LOW
WET BULB ZERO HEIGHTS. IF CLOUDS ARE THICKER/LOWER THAN CURRENTLY
FORECAST...THAN MAX TEMPS WILL BE A BIT TOO WARM. ALSO...WINDY
CONDITIONS ARE EXPECTED TUESDAY.

MEDIUM RANGE MODELS THEN SUGGEST AN UPPER RIDGE BEGINNING TO BUILD
INTO THE AREA THURSDAY...BUT A RELATIVELY MOIST NORTHWEST WILL KEEP
THE THREAT OF SOME SNOW SHOWER ACTIVITY...MAINLY OVER THE NORTHERN
MOUNTAINS.  DRY AND WARM CONDITIONS ARE EXPECTED FRIDAY WITH A
RIDGE OVER THE AREA. MODELS THEN SUGGEST THE UPPER RIDGE FLATTENING
OUT SATURDAY WITH POSSIBLY SOME ACTIVITY BEGINNING TO IMPACT THE
MOUNTAINS.

TEMPERATURES ARE EXPECTED TO BE SEASONAL TUESDAY AND
WEDNESDAY...WITH ABOVE AVERAGE TEMPERATURES FRIDAY AND SATURDAY.

.AVIATION.../18Z ISSUANCE/

VFR CONDITIONS WILL OCCUR THROUGH 18Z SUNDAY. ISOLATED SHOWERS
WILL OCCUR OVER NW WY FROM 21Z UNTIL 04Z. A COLD FRONT WILL PUSH
ACROSS THE REGION AROUND 00Z IN THE WEST AND THEN ACROSS THE
CENTRAL AND EAST FROM 03Z UNTIL 08Z. EXPECT A WIND SHIFT TO THE
NORTH OR NORTHWEST AFTER THE FRONTAL PASSAGE. THE WIND BECOMES
LIGHT BY 12Z SUNDAY.

.FIRE WEATHER...

...RED FLAG WARNING UNTIL 7 PM MDT FOR NATRONA COUNTY...

 A RED FLAG WARNING TO BE ISSUED FOR THIS AFTERNOON FOR NATRONA
COUNTY FOR LOW RELATIVE HUMIDITY AND FREQUENT WIND GUSTS OF 25 TO
30 MPH.  SIMILAR WEATHER CONDITIONS ARE EXPECTED IN ZONES 279 AND
289 THIS AFTERNOON BUT THE FUELS ARE NOT CRITICAL IN THOSE ZONES.

HIGH PRESSURE WILL BE OVER THE AREA WITH DRY AND GENERALLY MILD
CONDITIONS. OVER AND NEAR THE EAST SLOPES OF THE MOUNTAINS...
BREEZY TO LOCALLY WINDY CONDITIONS CAN BE EXPECTED THIS AFTERNOON
WITH LOW RELATIVE HUMIDITY. LIGHTER WINDS WILL OCCUR IN THE
BASINS AND VALLEYS. FAIR TO GOOD SMOKE DISPERSAL IS EXPECTED. A
FEW RAIN SHOWERS ARE EXPECTED OVER THE NORTHWEST MOUNTAINS IN THE
AFTERNOON AND EARLY EVENING TODAY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING UNTIL 7 PM MDT THIS EVENING WYZ280.

&&

$$

SHORT TERM...LIPSON
LONG TERM...WM
AVIATION...C.BAKER
FIRE WEATHER...LIPSON






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