Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 061617
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
1017 AM MDT WED MAY 6 2015

.SYNOPSIS...THE MOIST AND UNSTABLE AIRMASS ACROSS THE AREA THIS
MORNING WILL GRADUALLY DRY THROUGH THURSDAY. A COLD UPPER LOW
WILL MOVE SOUTH FROM THE PACIFIC NORTHWEST AND SETTLE INTO THE
GREAT BASIN FOR FRIDAY THROUGH THE UPCOMING WEEKEND.

&&

.DISCUSSION...MORNING WATER VAPOR AND H5 ANALYSIS DEPICT THE DEEP
PACNW LOW DIVING SOUTH THROUGH WASHINGTON AND OREGON. STARTING TO
NOTE THE BEGINNINGS OF INCREASED DIVERGENCE ALOFT WITHIN HEIGHT
FIELDS ACROSS THE FAR NORTHWEST COINCIDENT WITH A NET
STRENGTHENING OF THE ENTRANCE REGION OF THE UPPER JET ON THE
DOWNSTREAM SIDE OF THIS LOW. A WEAK SHORT WAVE ON A LINE FROM JUST
SOUTH OF ELY TO ROUGHLY RICHFIELD IS DRAPED ALONG THE LEADING EDGE
OF A DRIER MID LEVEL INTRUSION IMPINGING FROM THE SOUTHWEST.

TWO AREAS TO NOTE REGARDING NEAR TERM CONVECTIVE POTENTIAL AND
ASSOCIATED PRECIP...THE NORTHWEST AND CENTRAL UTAH. BEST BET FOR
ISOLATED THUNDER THIS MORNING EXISTS ACROSS THE NORTHWEST WITHIN
AFOREMENTIONED DIFFLUENT ZONE. HAVE NOTED SOME DEVELOPMENT OVER
THE LAST HOUR AND HAVE INCREASED POPS AND ADDED MENTION OF THUNDER
THERE FOR THE REMAINING MORNING HOURS. FURTHER SOUTH AND
EAST...COINCIDENT WITH THE SHORT WAVE LIFTING SLOWLY
NORTH...NUMEROUS SHOWERS EXIST DUE TO WEAK FORCING DRIVEN BY THE
WAVE AND TIGHTENING MOISTURE GRADIENT AS THE DRIER AIR FILTERS IN.
GOING FORECAST HANDLES THIS WELL.

GREATEST CONVECTIVE THREAT MOVING FORWARD THROUGH THE AFTERNOON
AND EVENING WILL REMAIN FOCUSED ALONG THE NORTHERN/EASTERN
PERIPHERY OF THE WAVE LIFTING NORTH...SHOULD BE OVERHEAD KSLC LATE
AFTERNOON/EARLY EVENING AND SOUTHWEST WYOMING BY LATE EVENING.
EXPECTING AN INCREASINGLY FOCUSED AREA OF RAIN WITH EMBEDDED
THUNDER TO DEVELOP ALONG THIS FEATURE...LOCALLY HEAVY RAIN A
POTENTIAL WITH LCL LEVELS NEAR 750 M AND PWAT RUNNING 1 TO 2
STANDARD DEVIATIONS ABOVE NORMAL. DEEPEST/STRONGEST CONVECTION
WILL LIKELY REMAIN ACROSS THE WESTERN DESERTS /ESPECIALLY NW/
WHERE COMBINATION OF GREATEST INSTABILITY AND UPPER LEVEL FORCING
EXIST.

OUTSIDE OF AFOREMENTIONED NEAR TERM CHANGES AND SUBTLE SKY/QPF
UPDATES PREVIOUS FORECAST REMAINS ON TRACK. FORECAST PROBLEM OF
THE DAY WILL SHIFT TO THE APPROACH AND PASSAGE OF THE PACNW LOW
THAT WILL IMPACT THE REGION FRIDAY THROUGH MUCH OF THE WEEKEND.

PREVIOUS DISCUSSION FOLLOWS...

LOOKING AT A LONG DURATION PRECIP EVENT IMPACTING MUCH OF THE
STATE FRIDAY THROUGH AT LEAST SATURDAY EVENING. THE LATEST
VERSIONS OF THE GFS/ECMWF APPEAR QUITE SIMILAR BOTH IN TERMS OF
TIMING AND TRAJECTORY OF THE UPPER LOW ACROSS THE GREAT BASIN
THROUGH SATURDAY EVENING. THE BROAD AREA OF SYNOPTIC-SCALE LIFT
GENERATED BY THE UPPER LOW COMBINED WITH THE LONG DURATION OF THE
EVENT WILL LEAD TO MANY AREAS OF CENTRAL AND NORTHERN UTAH
RECEIVING SUBSTANTIAL PRECIP THROUGH SATURDAY EVENING.

A SLOW MOVING TROUGH WILL BE LOCATED ACROSS THE INTERIOR WEST AT
THE START OF THE LONG TERM FORECAST PERIOD. THIS TROUGH WILL
GRADUALLY MOVE EASTWARD TOWARD THE CENTRAL PLAINS THROUGH THE DAY
SUNDAY...WITH ENOUGH REMNANT MOISTURE IN PLACE TO CONTINUE THE
THREAT OF CONVECTION ACROSS MAINLY THE HIGHER TERRAIN.

RIDGING IS EXPECTED TO BUILD INTO THE REGION MONDAY...PROVIDING A
BREAK IN THE UNSETTLED CONDITIONS THROUGH TUESDAY. A PACIFIC TROUGH
MOVING AROUND THE TOP OF THE RIDGE THROUGH THE NORTHERN
INTERMOUNTAIN REGION MAY IMPACT THE AREA WEDNESDAY. MODEL TO MODEL
CONSISTENCY HAS IMPROVED FOR THE MONDAY TO TUESDAY PERIOD...BUT IS
STILL A BIT LACKING FOR THE WEDNESDAY SYSTEM. LEFT LOW POPS ACROSS
THE MOUNTAINS OF NORTHERN UTAH MONDAY AND TUESDAY...AS A FEW
AFTERNOON SHOWERS/THUNDERSTORMS WILL BE POSSIBLE. INCREASED POPS
BACK TO CLIMO FOR WEDNESDAY...BUT NOT CONFIDENT ENOUGH IN THE
EVOLUTION OF THE PATTERN AT THIS POINT TO INCREASE POPS ANY FURTHER.

&&

.AVIATION...SHOWERS LOOK TO DEVELOP ALONG THE MOUNTAINS SURROUNDING
THE KSLC TERMINAL MIDDAY. FLOW SHOULD MAINLY REMAIN FROM THE SOUTH
TODAY...PERHAPS GUSTY ON ARRIVAL OF MORE WIDESPREAD RAIN FROM THE
SOUTH MID TO LATE THIS AFTERNOON. THE RISK OF NORTHWEST FLOW
PERSISTENT AND STRONG ENOUGH FOR OPERATIONAL CONCERNS THIS AFTERNOON
IS 10 PERCENT. THERE IS A 30 PERCENT CHANCE OF EMBEDDED
THUNDERSTORMS AFFECTING THE AIRFIELD WITH LOWERING
VISIBILITY/CEILING...GUSTY WIND AND LIGHTNING THREAT MID TO LATE
THIS AFTERNOON.

&&

.FIRE WEATHER...A DISTURBANCE WILL PIVOT NORTHWARD TODAY FROM SOUTH
CENTRAL UTAH EARLY THIS MORNING INTO NORTHERN UTAH THIS EVENING. AS
IT DOES SO...A GUSTY DRYING SOUTH WIND WILL DEVELOP ACROSS SOUTHERN
UTAH. THIS WILL LIMIT ANY CONVECTION TO ISOLATED COVERAGE AT BEST.
NUMEROUS TO WIDESPREAD PRECIPITATION IS EXPECTED TO DEVELOP ACROSS
CENTRAL UTAH MIDDAY...LIFTING INTO NORTHERN UTAH THIS AFTERNOON AND
EVENING. A WIDESPREAD SOAKING RAIN IS EXPECTED ACROSS THE
NORTH...WITH SECONDARY CONCERNS BEING CLOUD TO GROUND
LIGHTNING...LOCALLY GUSTY WINDS...AND SMALL HAIL. SNOW LEVEL IS
AROUND 8500FT.

THE DRYING TREND CONTINUES TOMORROW...WITH GUSTY SOUTHERLY WINDS FOR
MUCH OF THE REGION. CONVECTION WILL BE MOST PRONOUNCED EAST OF
INTERSTATE 15 AND NORTH OF INTERSTATE 70 TOMORROW AFTERNOON.

A LARGE COOL SPRING STORM WILL ARRIVE FROM THE WEST COAST FRIDAY...
GRADUALLY CROSSING THE EASTERN GREAT BASIN THROUGH THE WEEKEND.
EXPECT TO SEE MUCH COOLER CONDITIONS WITH WIDESPREAD PRECIPITATION RE-
DEVELOPING ACROSS THE REGION. SNOW LEVELS LOWER TO 6-7KFT FRIDAY
NIGHT AND SATURDAY.

&&

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

$$

PUBLIC/AVIATION/FIRE WEATHER...MERRILL/ROGOWSKI
PREVIOUS DISCUSSION...CONGER/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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