Area Forecast Discussion
Issued by NWS Salt Lake City, UT

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS65 KSLC 212218
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
418 PM MDT THU MAY 21 2015

.SYNOPSIS...THE LOW PRESSURE SYSTEM OFF THE CALIFORNIA COAST WILL
MOVE INLAND TONIGHT...THEN TURN NORTHEAST AND SLOWLY TRACK NORTHEAST
THROUGH THE GREAT BASIN THIS WEEKEND.

&&

.SHORT TERM (THROUGH 06Z MONDAY)...THE UPPER LOW CENTERED JUST OFF
THE CENTRAL CALIFORNIA COAST THIS AFTERNOON WILL TAKE A TURN TO
THE EAST-SOUTHEAST INTO SOUTHERN CALIFORNIA LATER TONIGHT. FROM
THERE THIS LOW WILL MOVE INTO NORTHWEST ARIZONA FRIDAY NIGHT...
THEN TURN TO THE NORTHEAST AND TRACK SLOWLY THROUGH THE SOUTHERN
AND EASTERN GREAT BASIN THIS WEEKEND.

AHEAD OF THIS UPPER LOW AT LEAST TWO OR THREE VORTICITY LOBE WILL
EJECT OUT OF THE PARENT LOW AND TRACK NORTH ACROSS UTAH TONIGHT
THROUGH EARLY FRIDAY. THIS DYNAMIC SUPPORT FOR LIFT WORKING WITH
THE FAIRLY MOIST AND UNSTABLE AIR MASS ALREADY IN PLACE WILL
PRODUCE PERIODIC SHOWERS/THUNDERSTORMS. GOOD UPPER DIVERGENCE WILL
ALSO SUPPORT DEEP CONVECTION CAPABLE OF PRODUCING HEAVY
RAIN/SMALL HAIL WITH THE STRONG CONVECTIVE ELEMENTS.

THE SLOW NORTHEAST PROGRESSION OF THE UPPER LOW THROUGH SOUTHERN
AND EASTERN UTAH WILL LEAD TO A PROLONGED PERIOD OF VALLEY RAIN
AND HIGH ELEVATION SNOW THIS WEEKEND. SOLID SYNOPTIC-SCALE LIFT
AND MORE THE ADEQUATE MOISTURE SHOULD HAVE LITTLE TROUBLE GENERATE
WIDESPREAD PRECIPITATION BEGINNING LATE FRIDAY NIGHT AND
CONTINUING INTO AT LEAST SATURDAY EVENING.

WILL CONCENTRATE THE HEAVIEST PRECIP IN THE AREAS NORTH AND WEST
OF THE UPPER LOW WHERE DEEP LAYER AND MOIST WARM ADVECTION WRAP
AROUND EXISTS. THESE AREAS OF THERMALLY-DRIVEN LIFT HAVE BEEN
RATHER PROLIFIC IN THE AMOUNT OF PRECIP GENERATED IN RECENT
STORMS...AND SEE NO GOOD REASON TO DEVIATE FROM THIS THINKING AT
THIS TIME. QUESTION RIGHT NOW IS WHICH MODEL...EITHER THE GFS OR
THE ECMWF...IS THE ONE TO FOLLOW WITH THIS STORM. THE MAIN
DIFFERENCE COMES WITH THE ORIENTATION OF THE WARM ADVECTION. THE
GFS MAINTAINS A MORE NORTH-NORTHWEST ORIENTATION WITH FAIRLY
STRONG THERMAL ADVECTION INTO AND WEST OF THE WASATCH RANGE
SATURDAY. THE ECMWF IN CONTRAST HAS SOME EASTERLY COMPONENT TO THE
ADVECTION WHICH WOULD FOCUS CLOSER TO THE NEVADA BORDER. THE TRACK
OF THE UPPER LOW...THOUGH FAIRLY SIMILAR IN BOTH MODEL...WOULD
TEND TO SUPPORT THE ECMWF MORE THAN THE GFS. THE CURRENT FORECAST
WOULD STILL MAINTAIN WIDESPREAD AND SUBSTANTIAL PRECIP...THOUGH
QPFS WILL BE SCALED DOWN A BIT ALONG THE URBAN CORRIDOR IN THE
THIS FORECAST PACKAGE.


.LONG TERM (AFTER 06Z MONDAY)...SIMILAR DIFFERENCES EXIST REGARDING
SHORT WAVE EVOLUTION ACROSS THE WESTERN CONUS IN THE LATEST 12Z RUNS
AS THE PREVIOUS FEW. BOTTOM LINE HOWEVER WILL CONTINUE TO FOCUS ON
UNSETTLED WEATHER ACROSS THE AREA AS A MEAN LONG WAVE WILL REMAIN IN
PLACE ACROSS THE WESTERN CONUS THROUGH THE PERIOD.

PRIMARY DIFFERENCE TO BEGIN THE LONG TERM PERIOD REVOLVES AROUND THE
HANDLING OF CUT OFF LOW THAT IS CURRENTLY SPINNING ALONG THE BRITCOL
COASTLINE /AND WILL REMAIN DOING SO FOR THE NEXT FEW DAYS/. THE GFS
CONTINUES TO WANT TO SHEAR A PORTION OF THIS LOBE SOUTHEAST OVER THE
WEEKEND AND INTO OUR AREA EARLY MONDAY MORNING KICKING THE PREVIOUS
UPPER LOW EAST. ECMWF CONTINUES TO TAKE THIS ENERGY IN A MORE LESS
CONSOLIDATED STATE TO OUR WEST...ROTATING IT THROUGH THE BASE OF THE
LONGWAVE. ALTHOUGH BOTH RETAIN FAIRLY WET SOLUTIONS...CONFIDENCE IS
LOW REGARDING PLACEMENT AND POTENTIAL SIGNIFICANCE OF PRECIP ATTM...
BUT FELT IT REASONABLE TO CONTINUE AN INCREASING TREND TO POPS
MONDAY /ESPECIALLY NORTH/.

THEREAFTER MODEL SPREAD ACTUALLY DECREASES THROUGH MIDWEEK. THE
GFS/ECMWF BOTH INDICATE TO SOME REGARD THE PRIMARY BRITCOL LOBE WILL
THEN MEANDER SLOWLY SOUTHEAST AND MERGE WITH A WEAK SOUTHERN BRANCH
SHORT WAVE THAT WILL BE UNDERCUTTING THE MEAN EASTERN PACIFIC RIDGE.
ALTHOUGH HEIGHTS WILL BE ATTEMPTING TO BUILD FROM THE SOUTHEAST AND
SOME WARMING OF TEMPS LOOKS LIKELY...VICINITY OF THESE FEATURES AND
RATHER DEEP MOISTURE IN PLACE NOW LOOKS TO MAINTAIN A GOOD CHANCE OF
FAIRLY WIDESPREAD CONVECTION ACROSS THE NORTHERN HALF OF THE AREA
FOR THE MIDWEEK PERIOD. OPTED TO BUMP POPS BOTH TUE/WED AS SUCH.

&&

.AVIATION...SOUTHWESTERLY WINDS THAT WILL BE GUSTY AT TIMES ARE
EXPECTED TO PREVAIL AT THE KSLC TERMINAL FOR THE NEXT FEW HOURS.
ANOTHER BAND OF IS SHOWERS APPROACHING FROM THE SOUTH AND WILL MOVE
THROUGH THE TERMINAL BY 2330Z BRINGING LIGHT RAIN SHOWERS...AIDING
TO MAINTAIN THIS WIND DIRECTION. UPON PASSAGE OF THESE SHOWERS TO
THE NORTH WINDS ARE EXPECTED TO RETURN TO THE NORTHWEST FOR THE
01Z TO 03Z WINDOW...BEFORE AGAIN RETURNING TO THE SOUTH OVERNIGHT.

&&


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

$$

SHORT TERM...CONGER
LONG TERM/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)



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.