National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS65 KRIW 161733
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1130 AM MDT SUN JUN 16 2013

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

A DIRTY RIDGE TRIES TO BUILD EAST TODAY INTO THE REGION...WITH DRY
WESTERLY FLOW AT THE SURFACE AND EAST TO NORTHEASTERLY FLOW EXPECTED
TO SUPPLY THE NORTHEASTERN PORTION OF THE CWA WITH SOME LOW LEVEL
MOISTURE...THERE WILL BE SOME MOISTURE AT THE MID LEVELS ACROSS THE
REST OF THE CWA THAT COULD BE AVAILABLE FOR AFTERNOON
CONVECTION...THOUGH COVERAGE WILL BE MUCH MORE LIMITED. BROADBRUSHED
ISOLATED THUNDERSTORMS ACROSS THE LOWER ELEVATIONS OF CENTRAL AND
NORTHERN WYOMING...WITH SLIGHTLY MORE ACTIVITY EXPECTED OVER THE
HIGHER ELEVATIONS. THE EASTERLY FLOW WILL ALSO PROVIDE SOME LOW
LEVEL SHEAR TO SUSTAIN SOME OF THE STORMS THAT DO FORM
TODAY...INCREASING CHANCES OF SMALL HAIL...ESPECIALLY ALONG THE I25
CORRIDOR. OVERALL SITUATION DOES NOT LOOK SEVERE ATTM...WITH ONLY
MODEST INSTABILITY AVAILABLE. EVEN FCST DCAPE LOOKS TO REMAIN IN
CHECK AT LESS THAN 500 J/KG WEST OF THE DIVIDE...GUSTY ERRATIC NEAR
STORMS...BUT NOT SEVERE HERE. BETTER CHANCE FOR STRONG GUSTS OVER
AND NEAR/ADJACENT AREAS TO NATRONA COUNTY AS DCAPE TRENDS RISE TO
NEAR 1000J/KG.

MORE SHOWERS AND THUNDERSTORMS ARE EXPECTED ON MONDAY. COVERAGE WILL
INCREASE THROUGH THE MORNING...WITH SOME SCATTERED ACTIVITY NOTED IN
THE AFTERNOON EAST OF THE DIVIDE...WITH THE STRONGEST STORMS
EXPECTED IN NATRONA AND JOHNSON COUNTIES...AS WELL AS EASTERN
FREMONT COUNTY WHERE CAPE COULD EXCEED 1500 J/KG...BULK SHEAR
EXCEEDING 35KT AND SURFACE DEWPOINTS APPROACH 50 DEGREES.

LOWERING HEIGHTS AHEAD OF AN APPROACHING TROUGH ON TUESDAY WILL
COMBINE WITH MOIST UPSLOPE FLOW EAST OF THE DIVIDE TO ALLOW FOR
BROAD INSTABILITY OVER THE REGION...FURTHER ENHANCED BY THE PASSAGE
OF A SHORT WAVE TROUGH AHEAD OF THE MAIN TROUGH. VERY DRY SOUTHWEST
FLOW WILL LIMIT COVERAGE ACROSS THE SOUTH...BUT 45 TO 50 DEGREE DEW
POINTS EAST OF THE DIVIDE AND CAPE RISING TO 1000 J/KG AS FAR WEST
AS THE CONTINENTAL DIVIDE TO ABOVE 2000 J/KG ALONG THE I25 CORRIDOR
SHOULD INCREASE COVERAGE THERE. SHEAR IS SOMEWHAT LIMITED...ON THE
ORDER OF 10 TO 15 KT OVER MUCH OF THE AREA...SO THAT SHOULD PREVENT
STORMS FROM BECOMING TOO ORGANIZED.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

OUR MAIN WEATHER MAKER THROUGH THIS PERIOD WILL BE AN UPPER LOW
SPINNING NEAR 45N/138W EARLY THIS MORNING.  THIS LOW WILL MOVE INTO
THE NW U.S. WEDNESDAY WITH THE SURFACE LOW OUT AHEAD OVER MONTANA.
THIS SETUP WILL PUT MOST OF WYOMING IN THE WARM SECTOR WHERE VERY
DRY AND BREEZY/WINDY CONDITIONS WILL BE THE RULE ALONG WITH AN
INCREASED FIRE RISK.  A FEW THUNDERSTORMS WILL BE POSSIBLE ACROSS
THE NORTH BUT MOST OF THIS ACTIVITY WILL BE OVER MONTANA.

THE UPPER LOW WILL LIFT ACROSS NW MONTANA ON THURSDAY WITH ITS
ASSOCIATED COLD FRONT PUSHING ACROSS THE WEST AND FAR NORTH...ALONG
WITH COOLER TEMPERATURES AND SLIGHT CHANCES OF THUNDERSTORMS.
DRY...WARM AND BREEZY TO WINDY CONDITIONS WILL PREVAIL ACROSS SOUTH
AND CENTRAL WYOMING.

SPREAD INCREASES BETWEEN THE GFS AND ECMWF OVER THE WEEKEND WITH THE
GFS PROGRESSING THE UPPER LOW FASTER ACROSS SOUTH CENTRAL
CANADA...INTO SOUTHERN MANITOBA BY SUNDAY WHILE THE ECMWF SHOWS MORE
OF A REX BLOCK...HIGH OVER LOW...ACROSS ALBERTA/SASKATCHEWAN.
FORECAST LEANS TOWARD SLOWER PROGRESSION...KEEPING SLIGHT CHANCES OF
THUNDERSTORMS ACROSS THE NORTH ALONG WITH COOLER TEMPERATURES WHILE
THE SOUTH AND CENTRAL REMAIN DRY WITH OVERALL ABOVE NORMAL
TEMPERATURES.

&&

.AVIATION.../18Z ISSUANCE/
SLIGHT INSTABILITY AND SOME MID-LEVEL MOISTURE WILL RESULT IN SOME
HIGH-BASED SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND EVENING
MAINLY VCNY AND NORTH OF A KJAC-KLND-KCPR LINE. HOWEVER...COVERAGE
WILL ISOLATED WITH VERY LITTLE CHANCE NEAR KRKS. TERMINALS NEAR THE
MOUNTAINS LATE AFTERNOON AND EVENING WILL HAVE BETTER CHANCES AT
CONVECTION OCCURRING NEARBY. NORTHERN WIND RIVER BASIN TERMINALS
INTO BIG HORN BASIN WILL BE SOMEWHAT PROTECTED BY MUCH STRONGER
STABILITY. HOWEVER...EVEN THESE TERMINALS MAY GET SOME GUSTY
CONDITIONS LATER THIS EVENING. WHERE STORMS ARE ABLE TO
FORM...EXPECT GUSTY ERRATIC OUTFLOWS.  ISOLATED STORMS THAT GO UP IN
THE VCNY AND EAST OF INTERSTATE 25 COULD PRODUCE THE STRONGEST BRIEF
WIND BURSTS. SOME OF THESE STORMS MAY PRODUCE BRIEF MVFR OR IFR
CONDITIONS IF CLOSE ENOUGH TO ANY ONE TERMINAL. MOST ACTIVITY WILL
DIMINISH ACROSS WESTERN TERMINALS NEAR SUNSET...WHILE ISOLATED
SHOWERS/STORMS MAY PERSIST LONGER IN VCNY AND EAST OF INTERSTATE 25.

&&

.FIRE WEATHER...

A RIDGE ACROSS THE AMERICAN SOUTHWEST WILL FIGHT TO MAINTAIN ITSELF
FOR THE NEXT WEEK OR SO...WITH A FEW WAVES RIPPLING ALONG THE
PERIPHERY OF THE RIDGE. OVERALL IT WILL BE DRY WITH MINIMUM RH
VALUES FALLING INTO THE SINGLE DIGITS ACROSS THE SOUTHERN ZONES.
SOME MODERATE INCREASE IN MOISTURE WILL BRING ISOLATED TO WIDELY
SCATTERED SHOWERS AND THUNDERSTORMS INTO THE FORECAST FOR THE NEXT
FEW AFTERNOONS AND EVENINGS...ESPECIALLY OVER AND NEAR THE MOUNTAIN
RANGES AND THE LOWER ELEVATIONS EAST OF THE DIVIDE.

&&

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

$$

SHORT TERM...ALLEN
LONG TERM...AEM
AVIATION...BRAUN
FIRE WEATHER...ALLEN