773 FXUS65 KRIW 101023 AFDRIW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 323 AM MST TUE FEB 10 2015 .SHORT TERM...TUESDAY THROUGH THURSDAY NIGHT JUST ABOUT ALL OF THE WEATHER CONCERNS ARE FOR TODAY FOLLOWED BY A QUIETER PERIOD FOR MIDWEEK. THE FIRST CONCERN IS WHAT TO DO ABOUT THE HIGHLIGHTS. AS FOR THE HIGH WIND WARNING...THE HIGH WINDS HAVE YET TO MATERIALIZE. ALMOST ALL THE MODELS SHOW 700 MILLIBAR WINDS BEGINNING TO DECREASE SO THESE WILL LIKELY BE CANCELLED WITH THE ISSUANCE OF THE MORNING PACKAGE. AS FOR THE WINTER WEATHER ADVISORY THE POCATELLO RADAR IS NOT VERY IMPRESSIVE SO UNLESS ACTIVITY PICKS UP IN THE NEXT HOUR THESE WILL BE CANCELLED AS WELL. THE TREND FOR THE DAY SHOULD BE FOR DECREASING COVERAGE AS UPPER LEVEL ENERGY AND A TROUGH MOVES OUT OF THE AREA. SHOWERS WILL LINGER TODAY BUT NOTHING HEAVY IS ANTICIPATED. AS FOR EAST OF THE DIVIDE...THIS LOOKS TO BE THE MOST ACTIVE DAY OF THE NEXT SEVERAL. A COLD FRONT WILL DROP SOUTHWARD ACROSS THE AREA TODAY. WIDESPREAD HEAVY PRECIPITATION IS NOT EXPECTED. HOWEVER...THERE ARE A COUPLE OF INTERESTING FACTORS. ONE IS THAT WITH THE UNSTABLE NORTHWEST FLOW...THIS IS A GOOD SET UP FOR CONVECTIVE SHOWERS. WITH THE WARMER TEMPERATURES SOME OF THESE MAY FALL AS RAIN RATHER THAN SNOW. THE NAM ACTUALLY HAS AN AREA OF HEAVIER SNOW IN THE LEE OF THE ABSAROKAS. HOWEVER...THIS IS THE 6Z RUN AND THE MID RANGE RUNS ARE SOMEWHAT UNRELIABLE. NEVERTHELESS...SOME MORE PERSISTENT SHOWERS ARE POSSIBLE ALTHOUGH PINPOINTING THEM IS IMPOSSIBLE UNTIL THEY ARE SHOW UP. ALSO SOMETHING INTERESTING...THE MODELS SHOW THE LIFTED INDICES FALLING TO NEAR OR IN SOME CASES SOMEWHAT BELOW ZERO. THERE WERE A FEW THUNDERSTORMS ACROSS IDAHO YESTERDAY. SO...ALTHOUGH WE ARE NOT CONFIDENT ENOUGH TO PUT IT IN THE GRIDS...I WOULD NOT BE SURPRISED TO A SEE A FEW LIGHTNING STRIKES...ESPECIALLY WITH SOME SUN THIS MORNING. THESE SHOWERS SHOULD WANE THIS EVENING AS THE FRONT MOVES AWAY AND WE LOSE DAYTIME HEATING. TEMPERATURES WILL BE A BIT COOLER THAN RECENT DAYS...BUT STILL ABOVE NORMAL. AND WITH THE NORTHWEST FLOW...THERE WILL BE GUSTY WINDS ACROSS JOHNSON COUNTY WITH THE COLD ADVECTION BEHIND THE FRONT. MID LEVEL WINDS DO NOT SUPPORT HIGH WINDS...BUT THERE COULD BE SOME GUSTS TO 40 TO 45 MPH OR SO. THINGS REALLY QUIET DOWN FOR WEDNESDAY AND ESPECIALLY THURSDAY AS RIDGING AGAIN ESTABLISHES ITSELF ACROSS THE WEST AS A HIGHLY AMPLIFIED PATTERN DEVELOPS WITH A DEEP TROUGH ACROSS THE EASTERN UNITED STATES. TEMPERATURES WILL BE COOLEST FOR WEDNESDAY WITH SOME WEAK COLD ADVECTION CONTINUING. AS FLOW TURNS MORE SOUTHWESTERLY FOR THURSDAY...TEMPERATURES WILL AGAIN RISE WITH 50S A GOOD POSSIBLY ACROSS MANY OF THE LOWER ELEVATIONS. .LONG TERM...FRIDAY THROUGH TUESDAY SYNOPSIS...A RIDGE OF HIGH PRESSURE WILL BRING DRY AND UNSEASONABLY MILD WEATHER ON FRIDAY. A DISTURBANCE MOVING OVER THE RIDGE WILL BRING SLIGHT CHANCES RAIN AND SNOW ACROSS THE NORTHERN MOUNTAINS OVER THE WEEKEND WITH BREEZY/WINDY CONDITIONS THROUGH THE WIND CORRIDORS. A CANADIAN COLD FRONT WILL MOVE SOUTH ACROSS CENTRAL WYOMING ON MONDAY BRINGING A CHANCE OF UPSLOPE SNOW AND MUCH COLDER TEMPERATURES INTO TUESDAY. DISCUSSION...GFS AND ECMWF ARE IN GOOD OVERALL AGREEMENT WITH TRANSITIONS IN LONGWAVE PATTERN ACROSS NORTH AMERICA THROUGH THE PERIOD. UPPER RIDGE AXIS IS FORECAST TO BE CENTERED ALONG THE 115W MERIDIAN ON FRIDAY WITH A COUPLE OF PACIFIC SHORTWAVES RIDING OVER AND FLATTENING THE RIDGE OVER THE WEEKEND. BY LATE SUNDAY...HIGH AMPLITUDE RIDGE IS EXPECTED TO RE-FORM OVER THE EASTERN PACIFIC...PHASING WITH UPPER HIGH OVER KAMCHATKA. THIS CHANGE WILL ALLOW ARCTIC AIR TO SPILL DOWN FURTHER WEST ALONG THE EAST SLOPES OF THE CONTINENTAL DIVIDE EARLY NEXT WEEK. THE ECMWF IS A BIT MORE AGGRESSIVE...OR AROUND 6 HOURS FASTER...THAN GFS BRINGING ARCTIC FRONT SOUTH INTO THE NORTHERN ROCKIES SUNDAY NIGHT AND MONDAY. THESE DIFFERENCES WILL NOT AFFECT THE OVERALL FORECAST PICTURE THIS FAR OUT. THE COLD FRONT WILL LIKELY BRING FALLING TEMPERATURES THROUGH THE DAY MONDAY ACROSS NORTH AND CENTRAL WYOMING ALONG WITH SNOW SPREADING NORTH TO SOUTH. AREAS OF SNOW...ESPECIALLY IN UPSLOPE FAVORED AREAS...MAY LAST WELL INTO TUESDAY WITH ARCTIC SURFACE HIGH PRESSURE SLIDING SOUTH ACROSS THE BORDER INTO WESTERN NORTH DAKOTA 00Z WEDNESDAY. ON A POSITIVE NOTE(S)...DEPENDING ON ONE'S PERSPECTIVE OF COURSE...THE DEEPER ARCTIC AIR IS EXPECTED TO SWING DOWN WELL TO OUR EAST ACROSS THE NORTHERN PLAINS INTO THE GREAT LAKES...AND A MILDER PACIFIC AIRMASS IS EXPECTED TO PUSH BACK ACROSS WYOMING ON WEDNESDAY. && .AVIATION.../12Z ISSUANCE/ EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES VFR CONDITIONS WILL PREVAIL THROUGH 00Z. SOME MOUNTAIN SNOW WILL OCCUR THROUGH 06Z WED WITH AREAS OF MVFR CONDITIONS VCNTY OF THE MOUNTAINS. ISOLATED RAIN OR SNOW SHOWERS FOR THE LOWER ELEVATIONS UNTIL 00Z WED. AFTER 00Z WED AREAS OF MVFR CONDITIONS WILL DEVELOP AS CEILINGS DROP AND ISOLATED RAIN AND SNOW SHOWERS OCCUR THROUGH 09Z WED. WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES VFR TO MVFR CONDITIONS WILL OCCUR THROUGH 00Z WED. MOUNTAIN SNOW WILL OCCUR WITH MVFR/IFR CONDITIONS VCNTY OF THE MOUNTAINS. TERMINAL SITES MAY BE IMPACTED BY SNOW SHOWERS THROUGH 00Z WED WITH POTENTIAL MVFR CONDITIONS. AFTER 00Z WED VFR CONDITIONS WILL PREVAIL WITH ISOLATED SHOWERS OVER THE MOUNTAINS. && .FIRE WEATHER... WINDS WILL DECREASE TODAY AS MID LEVEL WINDS DECREASE. A COLD FRONT WILL DROP SOUTHWARD ACROSS THE AREA AND BRING THE RISK OF SHOWERS...ESPECIALLY DURING THE AFTERNOON AND EVENING. RIDGING WILL REESTABLISH ITSELF ACROSS THE AREA FOR WEDNESDAY INTO THE WEEKEND AND BRING MAINLY DRY AND QUIET WEATHER. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...HATTINGS LONG TERM...AEM AVIATION...AR FIRE WEATHER...HATTINGS