Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 250159
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
759 PM MDT WED SEP 24 2014

.SYNOPSIS...HIGH PRESSURE WILL BUILD INTO THE AREA THROUGH LATE
WEEK. A PATTERN CHANGE IS EXPECTED THIS WEEKEND AS A FALL LIKE
PACIFIC SYSTEM MOVES THROUGH THE EASTERN GREAT BASIN. COOL AND
UNSETTLED CONDITIONS WILL CONTINUE THROUGH MIDWEEK OF NEXT WEEK.

&&

.DISCUSSION...WATER VAPOR LOOP SHOWS AN AMPLIFIED RIDGE OVER THE
ROCKIES WITH A LARGE CLOSED LOW OFF THE PACIFIC NORTHWEST. AMDAR
400-250MB WIND OBSERVATIONS REVEAL A CYCLONIC 100-140KT JET OVER
THE PACIFIC NORTHWEST. GOES/GPS/RAP/00Z RAOB INDICATE THE
PRECIPITABLE WATER VALUE RANGES BETWEEN 0.25" SOUTHWEST VALLEYS TO
0.55" MOST OTHER VALLEYS.

SATELLITE IMAGERY VOID OF ANY DETECTABLE CLOUD COVER. WITH THE
AMPLIFIED RIDGE OVERHEAD...WENT AHEAD WITH CLEAR SKIES OVERNIGHT.

MOST AREAS HAVE SEEN DEWPOINTS FALL 5 TO 10F DURING THE PAST 24HRS.
00Z KSLC RAOB SHOWS LOW LEVEL WINDS VEERING INDICATING WARM
ADVECTION...WHILE BOTH RAP AND NAM INDICATE THE 850-700MB THICKNESS
INCREASES ACROSS NORTHERN UTAH OVERNIGHT. CLEAR SKIES AND DRYING
WILL BE COUNTERACTED BY LOW LEVEL WARMING. SO EXPECT TEMPERATURES
OVERNIGHT TO BE SIMILAR TO SLIGHTLY WARMER THAN LAST NIGHT.

&&

.PREVIOUS DISCUSSION...THE LARGE SCALE PATTERN ACROSS THE WESTERN
CONUS CONTINUES TO AMPLIFY AT THIS TIME. INTERIOR RIDGE AXIS AND
CIRCULATION CENTER CONTINUES TO GRADUALLY SHIFT EAST PER H5
ANALYSIS AND IS NOW CENTERED ACROSS EASTERN UTAH. UPSTREAM A DEEP
CLOSED LOW OFF THE BRITCOL COASTLINE CONTINUES TO DIG SOUTH ALONG
THE COAST AIDED BY A NEAR 150KT JET CORE PUNCHING DOWN THE
BACKSIDE OF THE LONGWAVE. MINIMAL CHANGE TO THIS AMPLIFIED PATTERN
WILL OCCUR OVER THE NEXT 48 HOURS...THOUGH SHORT WAVE ENERGY AT
THIS TIME NEAR THE ALEUTIAN ISLANDS WILL FORM A NEW LOW CENTER OFF
THE CALI COAST COME FRIDAY. THIS LOW WILL BE THE FEATURE TO IMPACT
THE GREAT BASIN STATES THIS WEEKEND.

IN THE NEAR TERM...VERY WARM TEMPS AND INCREASINGLY WINDY EXPECTED
TOMORROW THROUGH FRIDAY. H7 TEMPS AND DEEP MIXING OF SOUTHERLY FLOW
ALOFT WILL AID SUPERADIABATIC SURFACE TEMPS ALLOWING HIGHS SOME 10
TO 20 DEGREES ABOVE NORMAL TOMORROW...ONLY A FEW DEGREES COOLER
FRIDAY. H7 FLOW RAMPING UP TO 30 PLUS KNOTS AND A TIGHTENING MSLP
GRADIENT WILL SUPPORT GUSTS NEAR 40 MPH ACROSS THE WESTERN VALLEYS
EACH AFTERNOON.

PROLONGED SOUTH TO SOUTHWESTERLY FLOW ALOFT WILL EVENTUALLY TAP INTO
MODEST SUBTROPICAL MOISTURE FRIDAY. PWAT PER GUIDANCE WILL TREND TO
INCREASE RAPIDLY WITH AFTERNOON VALUES IN THE .8 TO .9 RANGE. THIS
COMBINED WITH MODEST INSTABILITY AND SUFFICIENT SHEAR WILL ALLOW FOR
A THREAT OF CONVECTION...SOME ORGANIZED...ACROSS MAINLY THE WESTERN
HALF OF THE AREA.

12Z ECMWF CONTINUED TO TREND TOWARDS THE LAST SEVERAL GFS
OUTPUTS...MORE PROGRESSIVE AND NOW IN LINE WITH THE GFS REGARDING
AFOREMENTIONED TROUGH EVOLUTION FRIDAY NIGHT THROUGH SUNDAY. BUMPED
POPS UP SIGNIFICANTLY ACROSS THE WEST FRIDAY NIGHT THROUGH SATURDAY
AS MODELS ARE CONSISTENT IN STRONG DIFFLUENCE ALOFT AREAWIDE...WITH
A SLOW MOVING WEST TO EAST MID LEVEL COLD FRONTAL PASSAGE FOCUSING
WIDESPREAD PRECIP FOR MUCH OF THE DAY. GFS/ECMWF QPF SUGGEST UP TO 2
INCHES PRECIP IN THE NORTH AND AROUND 1 IN THE SOUTH DURING BY
SATURDAY EVENING.

UPPER LOW WILL CHURN THROUGH THE FORECAST AREA THEREAFTER...SHIFTING
FRONT/DIFFLUENCE DOWNSTREAM ALLOWING A NET DECREASE IN HEAVY PRECIP
FROM WEST TO EAST LATE SATURDAY INTO SUNDAY. COLD CORE INSTABILITY
WILL MAINTAIN SCATTERED PRECIP SUNDAY AS THE LOW CENTER LIFTS
NORTHEAST THROUGH THE AREA...FOCUSED PRECIP NORTH...WITH SNOW LEVELS
LOWERING TO OR JUST BELOW 9KFT BY LATE DAY. SLOW MOVING NATURE AND
TRACK OF SYSTEM WILL ALLOW FOR A PERIOD OF WRAP AROUND PRECIP
THROUGH MONDAY AS THE LOW LIFTS INTO SOUTHERN MT. SNOW LEVELS
POSSIBLY DIPPING TO 8KFT EARLY MONDAY THOUGH ACCUMULATIONS DO NOT
APPEAR TO BE OVERLY SIGNIFICANT AT THIS TIME.

GLOBAL MODELS SUGGEST A CONTINUATION OF COLD/UNSETTLED CONDITIONS
THROUGH MIDWEEK OF NEXT WEEK AT LEAST AS THE LONG WAVE TROUGH
REMAINS IN PLACE ACROSS THE INTERIOR WEST THROUGH THAT TIME.
DIFFERENCES ARISE IN DETAILS REGARDING SHORT WAVE ENERGY/PASSAGE
BETWEEN THE GFS/ECMWF BUT THE BIG PICTURE REMAINS
CONSISTENT...UNSETTLED AND QUITE COOL.

&&

.AVIATION...SOUTHERLY WINDS WILL CONTINUE AT THE SLC TERMINAL
THROUGH THE OVERNIGHT HOURS. WINDS WILL LIKELY BECOME GUSTY AFTER
ABOUT 12-14Z THURSDAY MORNING.

&&

.FIRE WEATHER...HIGH PRESSURE WILL SHIFT EAST TONIGHT ALLOWING
A DEEP LAYER SOUTHERLY FLOW TO DEVELOP AND STRENGTHEN ACROSS
THE REGION THROUGH THE REMAINDER OF THE WEEK. THIS WILL RESULT
IN LOCALLY WINDY CONDITIONS ACROSS THE WESTERN VALLEYS. A
POTENT PACIFIC STORM SYSTEM WILL MOVE INTO THE GREAT BASIN
BEGINNING LATE FRIDAY...THEN SLOWLY CROSS THE REGION DURING
THE UPCOMING WEEKEND. THIS WILL BRING WIDESPREAD WETTING
RAINS SATURDAY INTO SATURDAY NIGHT. PRECIPITATION CHANCES
WILL BECOME FOCUSED ACROSS NORTHERN UTAH SUNDAY INTO
MONDAY...WITH SNOW LEVELS FALLING TO NEAR 9000 FEET DURING
THIS TIME.

&&

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

$$

PUBLIC...ROGOWSKI/MERRILL
FIRE WEATHER...SEAMAN
AVIATION...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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