Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 161219 AAA
AFDSLC

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
619 AM MDT THU APR 16 2015

.UPDATE...PERSISTENT SNOW ACROSS SWRN WY IS CREATING WINTER
DRIVING CONDITIONS ALONG I-80 EAST OF EVANSTON. EXPECT THIS TO
CONTINUE THRU ABOUT MID MORNING BEFORE INSOLATION THRU THE CLOUDS
HEATS ROAD SURFACES SUFFICIENTLY TO MELT MOST OF THE SNOW. PRECIP
COULD CONTINUE THRU THE AFTN BUT SHOULD MELT AS IT FALLS. SO HAVE
UPDATED TO RAISE POPS AND ISSUE A WINTER WEATHER ADVISORY FOR
THIS MORNING FOR OUR WY ZONE.

&&

.SYNOPSIS...A COLD UPPER LOW WILL REMAIN NEAR THE FOUR CORNERS
AREA TODAY THEN DRIFT SLOWLY EAST TONIGHT THROUGH FRIDAY. A COOL
NORTHWEST FLOW WILL DEVELOP FOR THE WEEKEND.

&&

.SHORT TERM (THRU 00Z MON)...THE COLD UPPER LOW IS CENTERED NEAR
LAKE POWELL EARLY THIS MORNING WITH MOISTURE CONTINUING TO WRAP
AROUND THE NORTH AND WEST SIDES OF THIS FEATURE. CONSIDERABLE
CLOUDINESS AND AREAS OF SNOW ARE IN THIS MOIST FLOW AND SHOULD
PERSIST THROUGH THE DAY AS THE LOW MOVES ONLY VERY SLOWLY SEWD.
HAVE KEPT THE EXISTING WINTER WEATHER HIGHLIGHTS IN PLACE ALTHO
ROADS HAVE BEEN JUST WET OUTSIDE OF THE AREAS OF HEAVIER SNOW AND
THIS SHOULD BECOME EVEN MORE THE CASE ONCE THE SUN IS UP. ALSO THE
AIRMASS IS FORECAST TO GRADUALLY WARM TODAY AND SNOW LEVELS WILL
BE RISING ABOVE MOST VALLEY FLOORS BY AFTN. HAVE ALLOWED THE
HIGHLIGHT FOR THE NRN MTNS TO EXPIRE FOR THESE REASONS.

VALLEY TEMPS THIS MORNING ARE BELOW FREEZING IN SOME AREAS AND A
FEW SPOTS HAVE REACHED 28 F OR BELOW. WILL LEAVE THE EXISTING
FREEZE WARNING IN PLACE AS TEMPS COULD STILL BRIEFLY TOUCH 28 IN A
FEW MORE LOCATIONS.

PRECIP WILL DIMINISH OVER THE WEST TONIGHT BUT CLOUDS AND ISOLATED
SHOWERS COULD LINGER THRU FRI NIGHT. TEMPS WILL ALSO WARM SOMEWHAT
TODAY AND FRI AND REMAIN WARMER TONIGHT. THESE FACTORS WILL LIMIT
THE HARD FREEZE THREAT TO THE COLDER CENTRAL AND SWRN VALLEYS AND
WILL ALLOW DAY CREW TO ASSESS THE NEED FOR ANOTHER WARNING.

A COOL NORTHERLY FLOW DEVELOPS ACROSS THE CWA ONCE THE LOW MOVES
AWAY. A WEAK WAVE IN THIS FLOW COULD BRING SOME INSTABILITY AND A
THREAT OF ISOLATED SHOWERS TO THE NERN CWA SAT AFTN AND
OVERNIGHT SAT NIGHT. A WEAK LOW DEVELOPS OVER THE GREAT BASIN OUT
OF THIS WAVE ON SUN AND BRINGS A THREAT OF WEAK CONVECTIVE SHOWERS
TO MORE OF THE CWA SUN.

.LONG TERM (AFTER 00Z MONDAY)...THE OPERATIONAL GFS SHOWS THE TAIL
END OF A WEAK TROUGH MOVING ACROSS THE REGION SUNDAY NIGHT WHILE
APPEARS TO BE AN OUTLIER COMPARED TO THE GFS ENSEMBLE AND THE EC.
THEREFORE THE EXTRA COOLING AT H7 BY THE GFS WAS IGNORED AND WENT
WITH THE EC H7 FORECAST WHICH WAS STILL A DEGREE COOLER THAN
PREVIOUS FORECAST SO ENDED UP LOWERING TEMPS BY A DEGREE OR TWO FOR
MONDAY UNDER THE CONTINUED NORTHERLY FLOW.

THE RIDGE MOVES OVER UTAH MONDAY NIGHT BUT BY TUESDAY A WEAK TROUGH
MOVING ACROSS CALIFORNIA IS EXPECTED TO CREATE A DEFORMATION AXIS
ACROSS UTAH. NOT REALLY CONFIDENT THAT THIS WILL HAPPEN BUT THE GFS
HAS SHOWN THIS FEATURE OVER THE LAST SEVERAL RUNS SO DECIDED TO PUT
SOME TOKEN POPS IN OVER THE MOUNTAINS. AS THIS TROUGH MOVES A LITTLE
CLOSER ON WEDNESDAY I INCREASED THE POPS OVER THE CENTRAL AND
NORTHERN MOUNTAINS SOME BUT NOT MUCH SINCE THE EC HAS MORE OF A
RIDGE STILL OVER THE CWA.

BY THURSDAY THE EC MOVES A CLOSED LOW OVER SOUTHERN CALIFORNIA WHILE
THE NEW 06Z GFS IS STRONGER WITH ITS CORE OF THE LOW OFF THE COAST
BUT THERE IS A LOBE OF ENERGY STRETCHING EAST INTO WESTERN ARIZONA
WHICH PLACES THE ENTIRE CWA UNDER A INCREASINGLY MOIST CYCLONIC
FLOW. HAVE GONE WITH LOW END POPS FOR VALLEYS AND CHANCE POPS IN THE
MOUNTAINS. CONFIDENCE IS LOW FOR THIS EXTENDED PERIOD AS MODELS ARE
NOT IN SYNC.


&&

.AVIATION...BROKEN TO AT TIMES SCATTERED CIGS AROUND 500 FT AGL ARE
EXPECTED TO OCCASIONALLY MOVE ACROSS THE SLC TERMINAL THROUGH ABOUT
14Z BEFORE DISSIPATING. AFTER 15Z CIGS SHOULD REMAIN ABOVE 7K FT AGL
BUT THERE IS A 40 PERCENT CHANCE OF CIGS OCCASIONALLY BEING NEAR 5K
FT AGL. WINDS WILL REMAIN NORTHERLY THROUGH TODAY WITH AN INCREASE
IN SPEEDS THIS AFTERNOON.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...HARD FREEZE WARNING UNTIL 9 AM MDT THIS MORNING FOR UTZ001>005-
     011>016.

     WINTER WEATHER ADVISORY UNTIL 11 AM MDT THIS MORNING FOR UTZ015-
     016.

     WINTER WEATHER ADVISORY UNTIL 5 PM MDT THIS AFTERNOON FOR UTZ010-
     517-518.

WY...WINTER WEATHER ADVISORY UNTIL 11 AM MDT THIS MORNING FOR WYZ021.

&&

$$

SHORT TERM...WILENSKY
LONG TERM/AVIATION...STRUTHWOLF

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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