Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 171549
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
849 AM MST WED DEC 17 2014

.SYNOPSIS...A SERIES OF WEAK WEATHER SYSTEMS WILL CROSS THE
REGION THROUGH THURSDAY. HIGH PRESSURE WILL RETURN FOR FRIDAY.

&&

.DISCUSSION...WATER VAPOR LOOP SHOWS A SHORTWAVE RIDGE
OVERHEAD...WITH ANOTHER WEAK SPLITTING TROUGH APPROACHING FROM
WEST. AMDAR 400-250MB WIND OBSERVATIONS INDICATE A 75-110KT
CYCLONIC JET FROM NORTHERN CALIFORNIA INTO NORTHERN MEXICO.
GOES/GPS/RAP/12Z RAOB INDICATE THE PRECIPITABLE WATER VALUE RANGES
BETWEEN 0.08" NORTHEAST MOUNTAINS...TO 0.45" SOUTHERN VALLEYS.
BLENDED PRECIPITABLE WATER PRODUCT SHOWS AN INCREASE IN MOISTURE
FROM THE WEST WITHIN THE TROUGH AXIS...WITH OVER 150% OF NORMAL
ACROSS MUCH OF THE WEST.

BASED ON SURFACE OBSERVATIONS AND WEBCAMS EARLY THIS
MORNING...BUMPED UP POPS ACROSS THE SOUTH. RAP/HRRR-3KM AND HIGH
RESOLUTION WRF MODELS REMAIN ACTIVE THIS AFTERNOON AND SPREAD
NORTHWARD INTO CENTRAL MOUNTAINS...THOUGH PRECIPITATION MAY TURN
SHOWERY WITH THE PASSAGE OF THE WAVE.

MEANWHILE INVERTED CONDITIONS ACROSS THE NORTH...MOST NOTABLY ALONG
THE WESTERN SHORE OF THE GREAT SALT LAKE WITH COOLER TEMPERATURES
AND POCKETS OF DENSE FOG. HAVE ADDED TO THE FORECAST FOR THE
REMAINDER OF THE MORNING.

PREVIOUS DISCUSSION FOLLOWS...THE SPLITTING MID-LEVEL TROUGH
CURRENTLY ALONG THE OREGON/CALIFORNIA COAST WILL CONTINUE TO SPLIT
AND WEAKEN AS IT TRACKS SLOWLY THROUGH THE GREAT BASIN LATER TODAY
THROUGH THURSDAY. THE STRONGEST AND BEST ORGANIZED DYNAMIC
FEATURES WILL REMAIN IN THE SOUTHERN BRANCH OF THE SPLIT OVER
ARIZONA. FURTHER NORTH A TANGLE OF WEAK VORTICITY MAXIMA WILL
HOVER OVER SOUTHERN/CENTRAL UTAH THE NEXT COUPLE OF DAYS.

THE BEST CHANCE AT PRECIP WILL REMAIN ACROSS FAR SOUTHERN UTAH NEAR
THE BASE OF THE SPLIT TROUGH AND COLD AIR ALOFT. WEAK SYNOPTIC-SCALE
LIFT ACROSS THE SOUTH SHOULD BE SUFFICIENT FOR WIDESPREAD...ALBEIT
LIGHT PRECIP THROUGH MIDWEEK. HAVE BOOSTED POPS A BIT ACROSS THE
SOUTH...BUT WILL KEEP SNOW TOTALS IN THE MOUNTAINS AND QPF VALUES ON
THE LOW SIDE. UP NORTH PLENTY MOISTURE WILL BE IN PLACE...BUT WITH
NO ADVECTION OF ANY KIND IT LOOKS UNLIKELY THAT ANY MORE THAN
ISOLATED LIGHT PRECIP WILL DEVELOP IN THE CORE OF THE SPLIT TROUGH
OVER UTAH.

ONE LAST SHORTWAVE WILL DIG SOUTHEAST ACROSS UTAH LATE WEDNESDAY
NIGHT/THURSDAY. THIS FEATURE WILL ARRIVE AHEAD OF THE STRENGTHENING
UPPER RIDGE ADVANCING THROUGH THE REGION. FAIRLY MOIST WESTERLIES
WILL FOLLOW THE REGION THROUGH THE BASIN...WITH EMBEDDED SHORTWAVES
RACING EAST THROUGH THE NORTHERN ROCKIES/NORTHERN GREAT BASIN. FAR
NORTHERN UTAH WILL LIKELY BE GRAZED BY THESE PASSING FEATURES...WITH
WEAK DYNAMIC AND THERMALLY GENERATED LIFT BRING PERIODS OF LIGHT
RAIN/SNOW TO THE FAR NORTH THROUGH AT LEAST FRIDAY NIGHT.

AFTER THE BRIEF RIDGING OVER THE CWA ON FRIDAY A WEAK
SHORTWAVE...STRONGER ON THE EC...WILL MOVE ACROSS THE NORTHERN HALF
OF THE CWA WITH SLIGHT CHANCE POPS IN THE VALLEYS AND CHANCE IN THE
MOUNTAINS. WITH H7 TEMPS IN THE -6 TO -8 DEGREE RANGE THE NORTHERN
VALLEYS WILL LIKELY SEE A RAIN SNOW MIXTURE OR EVEN JUST SNOW IN THE
COLDER VALLEYS. AFTER THIS FEATURE EXITS THE REGION STRONG RIDGING
WILL OCCUR ALONG THE WEST COAST WHICH WILL BE FAR ENOUGH WEST TO
KEEP NORTHERN UTAH UNDER AN EXTENDED PERIOD OF WARM ADVECTION
PRECIPITATION. ON SUNDAY A WEAK DISTURBANCE IS FORECAST TO BE
EMBEDDED IN THIS NORTHWEST FLOW BY BOTH THE EC AND GFS. THEREFORE
HAVE BOOSTED POPS FROM THE SOUTHERN WASATCH FRONT AND MOUNTAINS
NORTHWARD. MODELS SHOW THAT THIS FLOW IS ASSOCIATED WITH AN
ATMOSPHERIC RIVER ORIGINATING OVER THE PACIFIC AND ITS TRAJECTORY
ACROSS SOUTHERN OREGON AND NORTHERN NEVADA IS FAVORABLE FOR BETTER
THAN AVERAGE PRECIPITATION AMOUNTS FOR NORTHERN UTAH. THIS MOIST
NORTHWEST FLOW REMAINS ACROSS NORTHERN UTAH AND SOUTHWEST WYOMING
THROUGH MONDAY INTO TUESDAY...ALBEIT WITH A GRADUAL WEAKENING TEND.
SOUTHERN HALF OF THE CWA WILL REMAIN DRY AND MILD THROUGH THIS
PERIOD WITH QUITE A BIT OF CLOUDS ACROSS CENTRAL AREAS BUT SOUTHERN
UTAH SHOULD HAVE MOSTLY CLEAR SKIES FROM SUNDAY NIGHT THROUGH
WEDNESDAY.

BOTH THE EC AND GFS SHOW A SIGNIFICANT TROUGH OVER THE PACIFIC
NORTHWEST WEDNESDAY WITH THE ASSOCIATED 700 MB BAROCLINIC ZONE
PUSHING INTO NORTHERN PORTIONS OF THE CWA WEDNESDAY NIGHT. TOO EARLY
TO GET EXCITED FOR A WHITE CHRISTMAS OVER MOST OF UTAH BUT AT LEAST
THE MODELS ARE SHOWING SOME POTENTIAL.

&&

.AVIATION...LIGHT AND VARIABLE SURFACE WINDS WILL CONTINUE AT THE
KSLC TERMINAL THIS MORNING BEFORE BECOMING A PREVAILING NORTHWEST
BETWEEN 18-20Z. PERIODIC CIGS TO 6500 FT AGL WILL CONTINUE THROUGH
18-19Z BEFORE SCATTERING OUT FOR THE AFTERNOON HOURS.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...NONE.
WY...NONE.
&&

$$

PUBLIC...ROGOWSKI/CONGER/STRUTHWOLF
AVIATION...MERRILL

FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)

FOR FREQUENTLY ASKED QUESTIONS ABOUT THE AREA FORECAST DISCUSSION
VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY/GENERAL/AFD_FAQS.PHP (ALL LOWER CASE)


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