Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 231516
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
916 AM MDT MON MAR 23 2015

.SYNOPSIS...A COLD FRONT WILL CROSS NORTHERN AND CENTRAL UTAH
TODAY. A SECOND SYSTEM WILL CROSS MAINLY NORTHERN UTAH AND
SOUTHWEST WYOMING TUESDAY. STRONG HIGH PRESSURE ALOFT WILL RETURN
FOR THE LATTER HALF OF THE WEEK.

&&

.DISCUSSION...WATER VAPOR LOOP SHOWS A NEGATIVELY TILTED TROUGH
OVER THE PACIFIC NORTHWEST INTO THE EASTERN GREAT BASIN. AMDAR
400-250MB WIND OBSERVATIONS SHOW A 75-115KT CYCLONIC JET FROM
NORTHERN CALIFORNIA INTO THE CENTRAL ROCKIES. GOES/GPS/RAP/12Z SLC
RAOB INDICATE THE PRECIPITABLE WATER VALUE RANGES BETWEEN
0.15-0.20" EASTERN AND SOUTHERN MOUNTAINS TO 0.33-0.50" VALLEYS.
BLENDED TOTAL PRECIPITABLE WATER PRODUCT INDICATES AN ABNORMALLY
MOIST AIRMASS ACROSS THE NORTHERN ROCKIES AND GREAT BASIN.

RAP 850-700MB THICKNESS/SATURATED EQUIVALENT POTENTIAL
TEMPERATURE/STREAMLINES INDICATE THE FRONTAL ZONE WILL SHIFT FROM
THE WASATCH FRONT AT 15Z TO ABOUT INTERSTATE 70 BY LATE AFTERNOON.

INHERITED FORECAST HAD A GOOD HANDLE ON POP DISTRIBUTION...JUST
INCREASED ACROSS EASTERN FORECAST AREA PER OBSERVATIONS THIS MORNING
AND A BIT FURTHER SOUTH PER RAP/HRRR/LOCAL WRF THIS AFTERNOON.

HIGHER RESOLUTION GUIDANCE SUGGESTS THAT AS THE DAY PROGRESSES
PRECIPITATION WILL BECOME MORE CONVECTIVE. WHILE THIS INHERENTLY
STARTS TO DIMINISH PRECIPITATION DISTRIBUTION AT ANY ONE TIME...THERE
IS ENOUGH STORM MOTION AND COVERAGE TO MAINTAIN LIKELY POPS.

SNOW LEVELS NEAR 7500FT PRE-FRONTAL ARE FORECAST TO FALL TO BETWEEN
6000-6500FT AS THE DAY PROGRESSES. ROADS EVEN IN SOUTHWEST WYOMING
ARE CURRENTLY JUST WET. SOME BRIEF IMPACT DUE TO SLUSH POSSIBLE ON
HIGHER PASSES BUT SOLAR INSOLATION AND INITIALLY WARM ROADS SHOULD
MITIGATE MOST OF THE IMPACT.

09Z SHORT RANGE ENSEMBLES SHOW GREATER INSTABILITY AND THUNDER
PROBABILITIES THAN PRIOR RUNS. UPDATED TO ADD ISOLATED THUNDER TO THE
FORECAST...WITH A THUNDERSTORM ALREADY MOVING THROUGH DAVIS COUNTY.

HIGH TEMPERATURES LOOKED GOOD...ADJUSTED TEMPERATURE CURVE WITH
OBSERVATIONS AND LAMP GUIDANCE.

PREVIOUS DISCUSSION FOLLOWS...

A LOW AMPLITUDE TROF IS MOVING INTO THE GREAT BASIN EARLY THIS
MORNING AND IS FORECAST TO CROSS THE CWA DURING THE DAY. THIS WAVE
SENDS A COLD FRONT THRU NRN/CENTRAL UT TODAY PASSING SLC AROUND MID
MORNING WITH A BAND OF PRECIP ACROSS THE NORTH. AT THIS TIME IT
APPEARS THE MOST WIDESPREAD PRECIP WILL BE STARTING WITH THE FRONT
AND LINGERING INTO THE AFTN THEN TURNING MORE OROGRAPHIC AND SHOWERY.

SNOW TOTALS IN THE MTNS SHOULD BE MOSTLY 6 INCHES OR LESS THROUGH
THIS EVENING AND EXPECT LITTLE IMPACT ON TRAVEL AS MOST OF THIS
FALLS DURING THE DAYLIGHT HOURS AND ROAD SURFACES ARE STARTING
FAIRLY WARM.

A SECOND SHORT WAVE SENDS A WARM FRONT THRU NRN UT TUE MORNING THEN
A COLD FRONT THRU THE ENTIRE CWA TUE NIGHT. PRECIP WITH THE WARM
FRONT WILL BE LIMITED TO AREAS MAINLY NORTH OF ABOUT I-80 AND ANY
SUPPORT FOR SHOWERS ALONG THE COLD FRONT QUICKLY WANES ONCE IT
REACHES CENTRAL UT. A LITTLE SNOW COULD REACH DOWN TO THE BENCHES IN
SALT LAKE AND DAVIS COUNTIES EARLY TUE AS WELL AS THE CACHE VALLEY
BUT EXPECT NO ACCUMULATION. THE MTNS WILL PICK UP SEVERAL MORE
INCHES BUT WITH LITTLE IMPACT ANYWHERE SOUTH OF ABOUT LOGAN SUMMIT
AND NOT MUCH EVEN THERE.

A FEW SHOWERS COULD LINGER OVER THE NORTH WED WITH A COOL DRY
NORTHERLY FLOW FORECAST FOR THE REST OF THE CWA. LOCAL GUSTY WINDS
ARE POSSIBLE IN THE USUAL DOWNSLOPE AREAS BUT SPEEDS WILL STAY SUB
ADVISORY.

HIGH PRESSURE IS PROGGED TO MOVE BACK IN STRONGLY BEHIND THE EXITING
TROUGH WEDNESDAY NIGHT/EARLY THURSDAY WHICH SHOULD BRING AN END TO
ANY LINGERING SHOWERS ACROSS NORTHERN UTAH. THE STRENGTHENING RIDGE
WILL ALLOW FOR A QUICK WARMING TREND FOR THE LATTER HALF OF THE WEEK
WITH MAXES ONCE AGAIN CLIMBING TO AT LEAST 15F ABOVE SEASONAL NORMS
FOR THE UPCOMING WEEKEND.

GLOBAL MODELS CONTINUE TO INDICATE A STORM SYSTEM OFF THE CALIFORNIA
COAST IMPACTING THE STATE EARLY NEXT WEEK. HOWEVER...EC/GFS DISAGREE
ON THE DETAILS AND RUN-TO-RUN CONSISTENCY REMAINS QUITE POOR. LATEST
GFS IS MORE FAVORABLE FOR PRECIPITATION...BRINGING THE SYSTEM
DIRECTLY ACROSS THE STATE SUNDAY NIGHT/MONDAY AS THE CLOSED LOW
BECOMES AN OPEN WAVE. EC IS A BIT SLOWER WITH THE SYSTEM AND TRACKS
IT ACROSS SOUTHERN ARIZONA AS AN OPEN WAVE. REGARDLESS...HAVE ADDED
SOME POPS IN FOR DAY 7 AS ALL GUIDANCE FOR THAT PERIOD INDICATES AT
LEAST SOME INSTABILITY.

&&

.AVIATION...PERIODS OF CEILINGS BELOW 7000FT WILL BE POSSIBLE AT THE
SLC TERMINAL THROUGH TODAY...AS SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS CONTINUE ACROSS NORTHERN UTAH. MVFR CONDITIONS ARE
ALSO POSSIBLE IF A HEAVIER STORM MOVES DIRECTLY OVER THE TERMINAL.
NORTHWEST WINDS ARE GENERALLY EXPECTED TO PREVAIL THROUGH AT LEAST
04Z TUESDAY...BUT THERE IS A SLIGHT CHANCE OF ERRATIC WINDS DUE TO
SHOWER ACTIVITY.

&&

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

$$

PUBLIC...ROGOWSKI/WILENSKY/TRAPHAGAN
AVIATION...SCHOENING

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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