Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 290207
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
807 PM MDT SAT MAR 28 2015

.SYNOPSIS...A COLD FRONT WILL SWEEP SOUTH ACROSS SOUTHERN UTAH
TONIGHT. A WEAK WEATHER DISTURBANCE OFF THE CALIFORNIA COAST WILL
MOVE EAST INTO SOUTHERN UTAH BY SUNDAY NIGHT. HIGH PRESSURE ALOFT
WILL RETURN TO THE AREA BY LATE MONDAY.

&&

.DISCUSSION...WATER VAPOR LOOP SHOWS A TROUGH SHEARING OVER
NORTHERN UTAH WITH THE MAJORITY OF THE ENERGY PROGRESSING THROUGH
THE NORTHERN ROCKIES. AMDAR 400-250MB WIND OBSERVATIONS SHOW A
90-115KT WESTERLY JET OVER THE PACIFIC NORTHWEST AND NORTHERN
ROCKIES. GOES/GPS/RAP/00Z SLC RAOB INDICATE THE PRECIPITABLE WATER
VALUE RANGES BETWEEN 0.10"- 0.15" FAR NORTHWEST UTAH...TO
0.33"-0.50" ACROSS MOST OTHER VALLEYS EXCEPT DIXIE. BLENDED TOTAL
PRECIPITABLE WATER PRODUCT INDICATES AN ABNORMALLY MOIST AIRMASS
OVER THE NORTHERN ROCKIES...AND AN ABNORMALLY DRY AIRMASS OVER THE
DEEP SOUTHWEST ALONG WITH THE WESTERN GREAT BASIN.

KEPT MENTION OF ISOLATED RAIN/SNOW SHOWERS IN THE HIGHER TERRAIN
THROUGH THE EVENING PER RADAR TRENDS. SHORT RANGE ENSEMBLES INDICATE
INSTABILITY WANES SIGNIFICANTLY AFTER SUNSET SO CONVECTION SHOULD
DECAY BY LATE EVENING.

OTHERWISE RAP 850-700MB THICKNESS/SATURATED EQUIVALENT POTENTIAL
TEMPERATURE/STREAMLINES INDICATE THE COLD FRONT WILL MAKE IT THROUGH
SOUTHERN UTAH OVERNIGHT. WITH A NORTHERLY PRESSURE GRADIENT
DEVELOPING AS HIGH PRESSURE BUILDS IN...INCREASED WINDS IN TYPICAL
DOWNSLOPE/CANYON LOCATIONS ACROSS SOUTHERN UTAH LATE TONIGHT.

OTHERWISE JUST TOUCHED UP TEMPERATURE CURVE WITH LATEST OBSERVATIONS
AND SHORT TERM LAMP GUIDANCE. REST UNCHANGED.

PREVIOUS DISCUSSION FOLLOWS...

THE SURFACE COLD FRONT CURRENTLY OVER THE SOUTHERN WASATCH FRONT
WILL CONTINUE SOUTH THROUGH ALL BUT EXTREME SOUTHERN UTAH OVERNIGHT.
LOW-LEVEL COLD ADVECTION SUPPORTING THE FRONT GENERATING FAIRLY
STRONG POST-FRONTAL NORTHWEST WINDS AT THIS TIME. SUSPECT THAT THESE
WINDS WILL BECOME LESS STRONG AS THE COLD ADVECTION BECOMES LESS
STRONG ACROSS CENTRAL/SOUTHERN UTAH LATER TONIGHT.

CONVECTION SPRINGING UP ALONG AND AHEAD OF THE FRONT STRUGGLING TO
GENERATE EVEN LIGHT PRECIP. THE SUPPORTING MID-LEVEL SHORTWAVE WILL
CONTINUE TO SHEAR TO THE EAST THROUGH THE NORTHERN ROCKIES...
LEAVING LITTLE IN THE WAY OF DYNAMIC SUPPORT OVER COLD AIR ALOFT TO
SUPPORT CONVECTION. WILL KEEP A FEW EVENING SHOWERS MENTIONED IN THE
FORECAST...WITH THIS ACTIVITY CONFINED TO THE NORTHEAST AND CENTRAL
MOUNTAINS.

FOR SUNDAY THE VARIOUS MODEL GUIDANCE CONTINUE TO DEVELOP CONVECTIVE
PRECIP ACROSS THE SOUTHERN/CENTRAL MOUNTAINS DURING THE AFTERNOON.
WHAT LITTLE MOISTURE THAT DOES EXIST WILL POOL OVER SOUTHERN UTAH
NORTH OF THE SURFACE BOUNDARY NEAR THE ARIZONA BORDER. WEAK LOW-
LEVEL CONVERGENCE INDICATED IN THE GUIDANCE MAY FIND SOME SUPPORT
FOR LIFT FROM THE SHORTWAVE CURRENTLY OFF THE CENTRAL CALIFORNIA
COAST. THIS SHORTWAVE IS SCHEDULED TO DRIFT EAST ALONG THE BOUNDARY
LATE SUNDAY AFTERNOON THROUGH EARLY MONDAY. SUSPECT THAT THE MODELS
ARE A BIT TOO AGGRESSIVE GENERATE PRECIP...BUT WILL INCLUDE THE
POSSIBILITY OF LIGHT PRECIP FOR THE MOUNTAINS IN THE CURRENT
FORECAST PACKAGE.

A LOW AMPLITUDE RIDGE AXIS WILL SHIFT EAST ACROSS THE GREAT BASIN
LATE MONDAY THROUGH EARLY TUESDAY. AN INCREASINGLY WARM SOUTHWEST
FLOW ALOFT TRAILING THE RIDGE WILL BRING BREEZY AND WARM CONDITIONS
TO MUCH OF UTAH TUESDAY AFTERNOON.

BOTH THE GFS AND EC HAVE A COLD FRONT MOVING INTO NORTHERN PORTION
OF THE CWA TUESDAY NIGHT WITH DECENT BAROCLINICITY BUT NEITHER SHOW
MUCH IN THE WAY OF QPF. LEFT THE SLIGHT CHANCE POPS IN FOR NOW.
HOWEVER IF THE UPSTREAM TROUGH BECOMES STRONGER THIS WILL TEND TO
WEAKEN THE FIRST TROUGH ON WEDNESDAY AND CONSEQUENTLY REDUCE THE
SHOWER THREAT.

WEDNESDAY WILL BE A COOLER DAY BUT WITH TEMPERATURES STILL ABOUT 5
TO 10 DEGREES ABOVE NORMAL.

THE NEXT UPSTREAM TROUGH LOOKS STRONGER AND WILL LIKELY BRING
TEMPERATURES DOWN TO NEAR NORMAL THURSDAY WITH THE BULK OF
PRECIPITATION OVER THE NORTHERN HALF OF THE CWA. HAVE INCREASED POPS
OVER NORTHERN HALF OF CWA BUT BECAUSE THERE IS ABOUT 30-50 METER
VARIATION IN THE 500 MB HEIGHTS IN THE GFS MODEL RUNS OVER UTAH
THURSDAY NIGHT WANTED TO LEAVE ROOM FOR THE POSSIBILITY OF A WEAKER
SYSTEM MOVING THROUGH.

SNOW LEVELS COULD LOWER TO NEAR THE VALLEY FLOORS OF NORTHERN UTAH
BY THURSDAY NIGHT. DEPENDING ON CLOUD COVER SUB FREEZING
TEMPERATURES ARE POSSIBLE LATE THURSDAY NIGHT OVER MANY VALLEY
EXCLUDING DIXIE. COOL TEMPERATURES WILL LINGER THROUGH FRIDAY BUT
TEMPERATURES ARE EXPECTED TO REBOUND NICELY SATURDAY THROUGH
SUNDAY.

&&

.AVIATION...A NORTHWEST WIND UNDER CLEAR SKIES WILL PERSIST AT
THE KSLC TERMINAL THROUGH MUCH OF THE NIGHT. WINDS MAY BECOME
LIGHT AND VARIABLE OR TURN LIGHT SOUTHERLY AROUND SUNRISE.

&&

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

$$

PUBLIC...ROGOWSKI/CONGER/STRUTHWOLF
AVIATION...ROGOWSKI

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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