Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 311142
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
442 AM MST SAT JAN 31 2015

.SYNOPSIS...AN UPPER LOW CENTERED ACROSS SOUTHERN NEVADA WILL
MOVE SOUTH INTO NORTHWEST MEXICO THIS EVENING. A MOIST WEST
NORTHWEST FLOW ALOFT ACROSS THE NORTHERN GREAT BASIN WILL BRING
LIGHT PRECIPITATION TO NORTHERN UTAH AND SOUTHWEST WYOMING EARLY
IN THE UPCOMING WEEK.

&&

.SHORT TERM (THROUGH 00Z WEDNESDAY)...THE STATIONARY UPPER LOW
CURRENTLY CENTERED ON THE SOUTHERN TIP OF NEVADA WILL MOVE SOUTH
INTO NORTHWEST MEXICO IN RESPONSE TO THE UPPER RIDGE NOSING INTO
THE PACIFIC NORTHWEST. THIS UPPER RIDGE WILL REMAIN A FAIRLY LOW
AMPLITUDE FEATURE AS A SERIES OF SHORTWAVES CREST THE RIDGE AND
THEN DIG SOUTHEAST INTO THE CENTRAL CONUS.

A BROAD AREA OF LIGHT TO MODERATE VALLEY RAIN AND MOUNTAIN SNOW
PERSISTS ACROSS MUCH OF SOUTHERN AND EASTERN UTAH THIS MORNING.
MOIST MID-LEVEL SOUTHERLY FLOW ALONG THE EAST FLANK OF THE UPPER
LOW RUNNING OVER THE TOP OF THE LOW-LEVEL NORTHEAST FLOW HAS
CREATED THE LARGE-SCALE TO SUPPORT THE WIDESPREAD PRECIP. THE
MID-LEVEL SOUTHERLY WILL BEGIN TO BREAK DOWN AFTER MID-MORNING AS
THE UPPER BEGINS TO TRACK SOUTH AND A DRIER DEEP LAYER NORTHERLY
FLOW DEVELOPS. PRECIP WILL END FROM NORTH TO SOUTH DURING THE
DAY...WITH PRECIP LIKELY ENDING BY EARLY THIS EVENING. THE CURRENT
WINTER WEATHER ADVISORY HAS BEEN LEFT IN PLACE WITH THE CURRENT
FORECAST PACKAGE...THOUGH IT WILL LIKELY BE TAKEN DOWN A LITTLE
EARLIER THAN THE CURRENT LATE AFTERNOON EXPIRATION.

THE UPPER RIDGE NOSING INTO THE NORTHERN HALF OF THE WESTERN
CONUS TODAY WILL REMAIN A RELATIVELY LOW AMPLITUDE FEATURE DURING
THE FIRST HALF OF THE UPCOMING WEEK. A SERIES OF FAST MOVING
SHORTWAVE RUNNING OVER THE TOP OF THE RIDGE WILL GRAZE NORTHERN UTAH
AND SOUTHWEST WYOMING EARLY IN THE WEEK. HAVE BUMPED POPS UP A BIT
ACROSS A BROADER AREA OF THE NORTH OWING TO SUFFICIENT DYNAMIC
AND THERMALLY DRIVEN LIFT AND THE AVAILABLE PACIFIC MOISTURE. THE
PRECIP TYPE SHOULD REMAIN AS RAIN IN THE VALLEYS...WITH SNOW OR A
RAIN/SNOW MIX IN THE HIGHER VALLEYS AND MOUNTAINS. CENTRAL AND
SOUTHERN UTAH WILL REMAIN A BIT TOO FAR SOUTH FOR ANY PRECIP...BUT
WILL SEE SOME CLOUD COVER AND CONTINUED MILD TEMPERATURES EARLY IN
THE WEEK.

&&

.LONG TERM (AFTER 00Z WEDNESDAY)...THE MOIST WEST-NORTHWESTERLY FLOW
CONTINUES OVER THE NORTHERN PORTIONS OF THE FORECAST AREA ON TUESDAY
NIGHT...THOUGH THE EXACT EVOLUTION OF THIS SET-UP HEADING INTO
WEDNESDAY IS STILL UNCERTAIN. THE GFS HAS BEEN PROMOTING THE IDEA OF
A SHORTWAVE DIVING INTO UTAH EARLY WEDNESDAY...BRINGING COLD
ADVECTION AND AN INCREASE IN PRECIP TO THE AREA. MEANWHILE...THE
ECMWF KEEPS ANY SHORTWAVES NORTH AND EAST OF THE AREA...AS THE RIDGE
BEGINS TO BUILD AND SHIFT OVER THE GREAT BASIN IN A QUICKER
FASHION...WHICH PROMOTES WARM ADVECTION OVER NORTHERN UTAH.

DESPITE THESE FAIRLY SIGNIFICANT DIFFERENCES IN DETAILS...LINGERING
MOISTURE CAUSES BOTH GLOBAL MODELS TO KEEP CONTINUED PRECIPITATION
OVER THE UTAH/IDAHO BORDER TUESDAY NIGHT AND WEDNESDAY...SO HAVE
INCREASED POPS A BIT THROUGH THIS PERIOD. OTHERWISE...THE FORECAST
IS A COMPROMISE BETWEEN THESE TWO SOLUTIONS...WITH TEMPS AND SNOW
LEVELS TILTED A LITTLE TOWARD THE COLDER GFS.

MODELS RE-CONVERGE FOR WEDNESDAY NIGHT AND THURSDAY...WITH A HIGHER
AMPLITUDE RIDGE SHIFTING OVER THE FORECAST AREA BY THURSDAY
AFTERNOON. WITH INCREASING SOUTHWESTERLY FLOW AND STRONG WARM
ADVECTION ASSOCIATED WITH THIS RIDGE...HAVE KEPT TEMPS QUITE A BIT
ABOVE SEASONAL NORMALS FOR THURSDAY AND FRIDAY.

HEADING INTO THE WEEKEND...MODELS AGREE THAT THE RIDGE WILL LIKELY
FLATTEN ACROSS THE WEST...WHICH COULD ALLOW SOME ADDITIONAL MOISTURE
AND WEAK SHORTWAVES TO MIGRATE ACROSS THE FORECAST AREA...ESPECIALLY
SATURDAY OR SATURDAY NIGHT. HAVE PUSHED POPS A LITTLE HIGHER AND
CLOSER TO CLIMATOLOGY UNTIL THE DETAILS OF THIS WAVE GETS SORTED
OUT. LOOKING PAST DAY 7...BOTH THE GFS AND EC PUSH A SHORTWAVE INTO
THE GREAT BASIN ON MONDAY...WITH A GENUINE COLD FRONT ON OUR
DOORSTEP BY 00Z TUESDAY. WHILE THIS STORM DOES NOT LOOK LIKE THE
STRONGEST THING IN THE WORLD AND IS ALL THE WAY OUT IN DAY 10...IT
IS AT LEAST INTERESTING TO SEE A LEGITIMATE PROGRESSIVE TROUGH IN
THE MODELS AGAIN.

&&

.AVIATION...CEILINGS AT THE SLC TERMINAL ARE EXPECTED TO RISE ABOVE
7000FT BETWEEN 12Z AND 16Z...WITH ONLY A SLIGHT CHANCE THAT CIGS
REMAIN BELOW THAT LEVEL THROUGH 18Z. NORTHERLY WINDS WILL PERSIST AT
THE TERMINAL THROUGH THE DAY...AND COULD EVEN BECOME GUSTY AT TIMES
AFTER 17Z.


$$

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER WEATHER ADVISORY UNTIL 4 PM MST THIS AFTERNOON FOR UTZ010-
     013-517-518.

WY...NONE.
&&

$$

SHORT TERM...CONGER
LONG TERM/AVIATION...SCHOENING

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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