Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 161540
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
840 AM MST TUE DEC 16 2014

.SYNOPSIS...THE UPPER LEVEL TROUGH OVER THE EASTERN PACIFIC TODAY
WILL SEND A SERIES OF WEAK WEATHER SYSTEMS ACROSS THE REGION
THROUGH THURSDAY. HIGH PRESSURE WILL RETURN FOR FRIDAY.

&&

.DISCUSSION...
WATER VAPOR LOOP SHOWS A RIDGE PROPAGATING INTO THE ROCKIES...WITH A
WEST COAST TROUGH. THE FIRST EJECTING WAVE WAS CROSSING CENTRAL
NEVADA. AMDAR 400-250MB WIND OBSERVATIONS INDICATE A 100-150KT
ANTICYCLONIC JET FROM THE FOUR CORNERS INTO THE MIDDLE MISSISSIPPI RIVER
VALLEY. A NORTHERLY 110-165KT WAS WELL OFF THE PACIFIC COAST.
GOES/GPS/RAP/12Z RAOB INDICATE THE PRECIPITABLE WATER VALUE RANGES
BETWEEN 0.15" MOUNTAINS...TO 0.40" MOST VALLEYS. BLENDED
PRECIPITABLE WATER PRODUCT SHOWS AN INCREASE IN MOISTURE FROM THE
WEST WITHIN THE TROUGH AXIS.

RAP SHOWS UPSTREAM WAVE WILL TRANSLATE NORTHEAST OVER NORTHWEST UTAH
THIS AFTERNOON. THIS SHOULD BE THE FOCUS FOR THE HIGHEST CHANCE OF
PRECIPITATION WITH THE RAFT RIVER MOUNTAINS LIKELY TO SEE
SEVERAL INCHES OF SNOW. OTHERWISE CLOUDY AND WARM.

PREVIOUS DISCUSSION FOLLOWS...
A MOIST SOUTHWEST FLOW ALOFT EXISTS ACROSS THE GREAT BASIN AHEAD
OF THE NEGATIVE-TILT SPLIT TROUGH EXTENDING FROM THE GULF OF
ALASKA TO THE CENTRAL CALIFORNIA COAST. WEAK VORTICITY MAXES
EJECTING NORTHEAST AHEAD OF THE TROUGH WILL BRING AREAS OF LIGHT
PRECIP TO MAINLY NORTHERN UTAH TODAY.

ONE FEATURE WHICH IS SOMEWHAT LOST IN THE CLOUD FIELD OVER SOUTHWEST
UTAH WILL LIFT INTO NORTHEAST UTAH THIS MORNING. WEAK DYNAMIC LIFT
WORKING WITH ADEQUATE MOISTURE WILL GENERATE LIGHT PRECIP ACROSS
CENTRAL THEN NORTHEAST UTAH THIS MORNING.

A MORE ACTIVE VORTICITY MAX EXITING THE CENTRAL SIERRAS WILL TAKE
AIM ON NORTHEAST NEVADA/NORTHWEST UTAH LATER THIS MORNING THROUGH
EARLY THIS EVENING. ALREADY SEEING A FEW RADAR RETURNS MOVING OUT OF
WEST-CENTRAL UTAH...WITH MUCH GREATER AREAL COVERAGE NOTED TO THE
WEST OVER NEVADA. STRONGER DYNAMIC LIFT ALONG WITH COLDER AIR ALOFT
AND A DEEPER MOISTURE LAYER SHOULD BRING A GREATER AREA OF PRECIP
INTO NORTHERN UTAH BY THIS AFTERNOON...AND ON THROUGH THE EARLY
EVENING HOURS. THE HEAVIEST RAIN/SNOW WILL LIKELY STAY NEAR THE COLD
POOL ALOFT AND STRONGEST DYNAMIC LIFT OVER THE FAR NORTHWEST PORTION
OF THE STATE. DRIER AIR AND DYNAMIC SUBSIDENCE TRAILING THIS FEATURE
SHOULD BRING AN END TO MOST IF NOT ALL PRECIP UP NORTH BY LATE
TONIGHT.

THE NEXT VORTICITY MAX CURRENTLY NEAR 41/131 WILL FOCUS OVER
SOUTHERN UTAH ON WEDNESDAY. THIS SYSTEM WILL HOLD TOGETHER WELL AS
IT ENTERS CALIFORNIA...THEN WEAKEN A BIT AS IT SPLITS MOVING INTO
THE WESTERN GREAT BASIN TONIGHT. THE FEATURE WILL STILL HAVE SOME
KICK AS IT TRACKS EAST ACROSS SOUTHERN NEVADA AND THEN NORTHERN
ARIZONA. SUFFICIENT DYNAMIC LIFT AND COLD AIR ALOFT WILL FIND A
STILL FAIRLY MOIST AIRMASS ACROSS SOUTHERN UTAH WEDNESDAY THROUGH
EARLY THURSDAY. LOOKING AT THE DEVELOPMENT OF WIDESPREAD LIGHT TO
MODERATE PRECIP NORTH AND EAST OF THE VORTICITY MAX BEGINNING EARLY
WEDNESDAY. COLDER TEMPERATURES ALOFT ALONG WITH FAIRLY STRONG
SYNOPTIC-SCALE LIFT SHOULD PROMOTE SNOW AS THE MAIN PRECIP TYPE
OUTSIDE OF THE LOWER VALLEYS NEAR THE ARIZONA BORDER. SEVERAL INCHES
OF SNOW COULD FALL ACROSS THE SOUTHERN MOUNTAINS THROUGH EARLY
THURSDAY.

LINGERING SHOWER ACTIVITY SHOULD WIND DOWN THURSDAY AFTERNOON AS
HIGH PRESSURE ALOFT SHIFTS EAST INTO THE GREAT BASIN. THIS HIGH WILL
CENTER ACROSS UTAH FOR FRIDAY...MAINTAINING DRY/STABLE CONDITIONS
HEADING INTO THE WEEKEND.

BOTH THE EC AND GFS START SATURDAY OFF WITH THE CWA UNDER A FLAT
RIDGE BUT THEN HAVE A WEAK DISTURBANCE MOVING SOUTHEAST ACROSS
NORTHERN UTAH BY 00Z SUNDAY. THE EC HAS BEEN MORE CONSISTENT WITH
THIS FEATURE AND THE GFS NOW HAS BOUGHT OFF ON  THIS DISTURBANCE AS
WELL. HOWEVER...THE LATEST 06Z GFS IS ACTUALLY STRONGER AND MOVES IT
ACROSS SOUTHWESTERN WYOMING AND NORTHEAST UTAH LATE SATURDAY VERSES
THE EC WHICH HAS THE MAIN ENERGY MOVING INTO WEST CENTRAL UTAH.
FORECAST IS BASED ON A BLEND OF THE EARLIER GFS AND EC
SOLUTIONS...BUT LATEST GFS WOULD ARGUE FOR HIGHER POPS OVER THE
NORTHERN MOUNTAINS.

A RIDGE GRADUALLY BUILDS INTO CALIFORNIA AND NEVADA SUNDAY THROUGH
TUESDAY WITH UTAH ON THE EASTERN FRINGE WHICH MEANS ANY WEAK
DISTURBANCE RIDING OVER THIS RIDGE WILL KEEP NORTHERN UTAH UNDER A
SOMEWHAT ACTIVE WARM ADVECTION PATTERN. HAVE KEPT NEAR CLIMO POPS
FOR THE NORTHERN THIRD OF THE CWA FOR THIS REASON WHILE THE SOUTHERN
TWO THIRDS OF THE CWA SHOULD BE DRY WITH TEMPERATURES ABOVE NORMAL.
THE ACTIVE NORTHWEST FLOW ACROSS NORTHERN UTAH WILL KEEP A FAIR
AMOUNT OF CLOUDS AROUND WHICH WILL PREVENT ANY VALLEY INVERSION FROM
DEVELOPING...CONSEQUENTLY ABOVE NORMAL TEMPERATURES ACROSS THE NORTH
AS WELL. TEMPERATURES WILL TAKE A RUN INTO THE LOWER 50S ACROSS THE
CENTRAL AND SOUTHERN WASATCH FRONT MONDAY AND TUESDAY.

&&

.AVIATION...LIGHT AND VARIABLE WINDS WILL CONTINUE AT THE SLC
TERMINAL THROUGH THE MORNING. THERE IS A 30 PERCENT CHANCE WINDS
WILL BECOME WEST TO NORTHWEST FOR A PERIOD BETWEEN 22Z-02Z. CEILINGS
ARE EXPECTED TO FALL TO NEAR 5000 TO 6000 FEET AGL BETWEEN 23-02Z.

&&

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

$$

PUBLIC...ROGOWSKI/CONGER/STRUTHWOLF
AVIATION...KRUSE

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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