Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 172256
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
456 PM MDT SUN AUG 17 2014

.SYNOPSIS...AN UPPER LEVEL RIDGE OF HIGH PRESSURE OVER THE AREA
TODAY WILL MOVE EAST ON MONDAY. SOUTHERLY FLOW AHEAD OF AN UPPER
LEVEL LOW ALONG THE CALIFORNIA COAST WILL SPREAD DEEP MOISTURE
BACK INTO THE REGION LATE MONDAY AND TUESDAY.

&&

.DISCUSSION...UPPER LEVEL RIDGE REMAINS CENTERED OVER THE FOUR
CORNERS THIS AFTERNOON WITH AN UPPER LEVEL LOW CLOSING OFF ALONG
THE PACIFIC NORTHWEST COAST. DRY WEST-SOUTHWEST FLOW ALOFT
CONTINUES OVER THE STATE AND HAS USHERED IN PRECIPITABLE WATER
VALUES LESS THAN .50" ACROSS MUCH OF WESTERN UTAH. GOES SOUNDER
PRECIPITABLE WATER IMAGERY INDICATES THAT THERE IS STILL A POCKET
OF VALUES NEAR .75" ACROSS EAST CENTRAL UTAH. WEAK INSTABILITY IS IN
PLACE OVER THE HIGHER TERRAIN IN EASTERN UTAH...AS WELL AS IN
EXTREME NORTHWEST UTAH...THIS AFTERNOON AND EXPECT ISOLATED
STORMS INTO THE EVENING IN THESE LOCATIONS. STORMS SHOULD QUICKLY
DISSIPATE AFTER SUNSET.

MONDAY...UPPER LEVEL RIDGE SLIDES EAST AS CUTOFF LOW MOVES DOWN
THE CALIFORNIA COAST. THIS ALLOWS SOUTHERLY FLOW TO DEVELOP AND
BRING MONSOON MOISTURE BACK INTO SOUTHERN UTAH BY AFTERNOON. GFS
AND NAM GUIDANCE INDICATE THAT PRECIPITABLE WATER VALUES
APPROACHING 1" WILL SPREAD IN TO FAR SOUTHERN UTAH BY LATE
AFTERNOON. BELIEVE THAT SHOWERS AND THUNDERSTORMS WILL DEVELOP
OVER SOUTHERN UTAH DURING THE AFTERNOON AS MOISTURE SURGES
NORTH AND HAVE INCLUDED CHANCE POPS IN THE SOUTHERN MTNS AND
INCREASED POPS IN SOUTH CENTRAL AND SOUTHWEST VALLEYS. WILL LIKELY
BE THE WARMEST DAY OF THE WEEK ACROSS NORTHERN UTAH WITH SLIGHTLY
ABOVE NORMAL TEMPERATURES AS MID LEVEL THERMAL RIDGE MOVES OVER
THE AREA.

MONDAY NIGHT AND TUESDAY...MOISTURE SURGES ALL THE WAY INTO
NORTHERN UTAH BY TUESDAY MORNING. WITH ELEVATED INSTABILITY IN
PLACE THROUGH THE NIGHT ON MONDAY AND DEEP MOISTURE MOVING
NORTH...ANTICIPATE THAT SHOWERS WILL CONTINUE THROUGH THE
NIGHT. ACCORDINGLY HAVE SPREAD THE CHANCE OF PRECIP NORTH...AT
LEAST TO THE SOUTHERN WASATCH FRONT BY MORNING.

ANTICIPATE GREATER COVERAGE OF PRECIP ON TUESDAY WITH PRECIPITABLE
WATER VALUES UP AROUND AN INCH OVER MUCH OF THE STATE. MODELS ALL
AGREE THAT A SHORTWAVE WILL EJECT NORTHEAST AS THE CUTOFF LOW
MOVES DOWN THE COAST. THIS WILL SUPPLY LARGER SCALE FORCING AS IT
MOVES THROUGH UTAH AND SHOULD LEAD TO MORE EXTENSIVE CLOUD COVER
AND PRECIPITATION ACROSS THE STATE ON TUESDAY. GIVEN THE AVAILABLE
MOISTURE...FLASH FLOODING IS CERTAINLY A POSSIBILITY...BUT
WIDESPREAD CLOUD COVER MAY LIMIT SBCAPE AND CORRESPONDINGLY
UPDRAFT STRENGTH. STILL...POTENTIAL IS THERE FOR FLASH
FLOODING...ESPECIALLY FOR THE MOST PRONE AREAS...SUCH AS SLOT
CANYONS AND RECENT BURN SCARS.

WEDNESDAY THROUGH SUNDAY...MEDIUM RANGE MODELS IN AGREEMENT THAT
MONSOON SURGE IS RELATIVELY SHORT-LIVED AS FLOW ALOFT TURNS
SOUTHWESTERLY ON WEDNESDAY AND THE AIRMASS BEGINS TO DRY. SOME
CONCERN THAT THE MODELS ARE OVER AGGRESSIVE WITH THE DRYING...AS
IS OFTEN THE CASE. FOR NOW LEFT MENTION SHOWERS AND THUNDERSTORMS
PRIMARILY CONFINED TO THE HIGHER TERRAIN...BUT WOULD NOT BE
SURPRISE TO SEE THE MOISTURE LINGER...ESPECIALLY IN ERN UT.

ECMWF AND GFS IN RELATIVE AGREEMENT ON THE DEVELOPMENT OF AN
UPPER LEVEL TROUGH OVER THE PAC NW AND NRN INTERMOUNTAIN REGION
DURING THE LATTER HALF OF THE WEEK. THIS DEEPENING FEATURE WILL
KEEP TEMPERATURES A LITTLE COOLER AS LOWER HEIGHTS OVERSPREAD THE
REGION. HOWEVER...THE MODELS ARE STILL STRUGGLING TO CAPTURE THE
EVOLUTION OF THE CUT-OFF LOW OFF OF THE CALIFORNIA COAST. THE GFS
NOWS SWINGS IT THROUGH THE GREAT BASIN WHILE THE EC RETROGRADES
IT OFF THE COAST. THIS IS A REVERSAL FROM YESTERDAY/S 1200 UTC
RUNS. THIS REMAINS A LOW CONFIDENCE ASPECT OF THE FORECAST...WHICH
HAS AN IMPACT ON THE LIKELIHOOD OF PRECIPITATION HEADING INTO THE
WEEKEND. FOR NOW WITH SOME RESIDUAL MOISTURE IN PLACE....AND
UNCERTAINTY REGARDING THE EVOLUTION OF THE CUTOFF LOW...HAVE KEPT
SLIGHT CHANCE POPS CONFINED TO THE HIGHER TERRAIN.

&&

.AVIATION...VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD AT THE
KSLC TERMINAL. NORTHWEST WINDS ARE EXPECTED TO BECOMING SOUTHEAST
BETWEEN 0300-0400-UTC. HOWEVER...THERE IS A 20 PERCENT CHANCE THAT
THIS WIND SHIFT WILL HOLD OFF UNTIL AFTER 0400 UTC.

&&

.FIRE WEATHER...DRY AIR MASS OVER REGION TONIGHT WILL YIELD TO AN INCREASINGLY
MOIST SOUTHERLY FLOW BY MIDDAY MONDAY. SOUTHERN UTAH WITH SEE AN INCREASE
IN RELATIVE HUMIDITY VALUES AS WELL AS ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS. DEEPER MOISTURE WILL ARRIVE MONDAY NIGHT AND SPREAD ACROSS
THE ENTIRE REGION TUESDAY WITH SCATTERED SHOWERS AND THUNDERSTORMS ACROSS
MOST VALLEYS AND EVEN NUMEROUS SHOWERS AND THUNDERSTORMS OVER THE HIGHER
TERRAIN. THIS SURGE WILL LINGER INTO TUESDAY NIGHT BUT A DRIER SOUTHWESTERLY
FLOW WILL GRADUALLY MOVE IN WEDNESDAY THROUGH THURSDAY. A COOLER AND DRIER
AIR MASS IS EXPECTED BY THE WEEKEND.


&&

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

$$

PUBLIC...GRAHAM
FIRE WEATHER...STRUTHWOLF
AVIATION...GRAHAM

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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