Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 131514
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
914 AM MDT MON APR 13 2015

.SYNOPSIS...HIGH PRESSURE ALOFT ACROSS UTAH TODAY WILL BE
FOLLOWED BY A COLD AND STRONG PACIFIC STORM SYSTEM AFFECTING THE
REGION TUESDAY THROUGH WEDNESDAY NIGHT. HIGH PRESSURE ALOFT WILL
RETURN LATE IN THE WEEK.

&&

.DISCUSSION...
WATER VAPOR LOOP SHOWS RIDGING OVER THE INTERIOR WEST WITH A COLD
STORM OFF THE BRITISH COLUMBIA COAST. AMDAR 400-250MB WIND
OBSERVATIONS SHOW A SOUTHWESTERLY 90-120KT JET INTO THE PACIFIC
NORTHWEST AND SOUTHWEST CANADA. GOES/GPS/RAP/12Z SLC RAOB INDICATE
THE PRECIPITABLE WATER VALUE RANGES BETWEEN 0.10"-0.15"
MOUNTAINS...TO 0.20"-0.25" ACROSS MOST VALLEYS. BLENDED TOTAL
PRECIPITABLE WATER PRODUCT INDICATES MUCH LOWER THAN TYPICAL
VALUES ACROSS THE WEST COAST/GREAT BASIN/SOUTHWEST CONUS...WITH
HIGHER THAN NORMAL VALUES ACROSS WESTERN CANADA AND THE NORTHERN
ROCKIES WITH A PACIFIC TAP INTO BRITISH COLUMBIA.

GOING FORECAST IN GOOD SHAPE. UPDATING TO EXPIRE THE HARD FREEZE
WARNING AS TEMPERATURE CLIMB BACK TOWARD FREEZING ACROSS THE CACHE
VALLEY AND SANTAQUIN/NEPHI AREAS.

SHORT RANGE ENSEMBLES INDICATE WEAK INSTABILITY THIS
AFTERNOON...WITH LOCAL WRF MODELS SHOWING A BIT OF MOISTURE AT
500MB...SO ADDED SOME BUILDING CUMULUS TO THE SKY GRID ACROSS
EASTERN MOUNTAINS THIS AFTERNOON. OTHERWISE IT WILL BE SUNNY AND
WARM.

HIGH WIND AND WINTER WEATHER TUESDAY INTO THURSDAY WILL BE THE FOCUS
FOR THE AFTERNOON PACKAGE.

&&

PREVIOUS DISCUSSION...
THE LOW-AMPLITUDE UPPER RIDGE OVER UTAH WILL SHIFT OFF TO THE
EAST THIS MORNING AHEAD OF A VERY COLD AND ENERGETIC PACIFIC
TROUGH SCHEDULED TO ARRIVE OVER UTAH TUESDAY NIGHT. TEMPERATURES
WILL INCREASE SUBSTANTIALLY TODAY AS A WARM SOUTHWEST FLOW ALOFT
DEVELOPS OVER THE STATE THIS AFTERNOON. A BREEZY AND MILD NIGHT
WILL FOLLOW AS THE TROUGH CONTINUES TO ADVANCE THROUGH THE GREAT
BASIN.

VERY WINDY CONDITIONS WILL DEVELOP ACROSS THE FORECAST AREA ON
TUESDAY. A STRONG COLD FRONT SUPPORTED BY SOLID LOW-LEVEL COLD
ADVECTION WILL PRESS EAST ACROSS NEVADA TONIGHT...SETTLING INTO
NORTHEAST NEVADA BY EARLY TUESDAY. AHEAD OF THE FRONT THE NEAR 700MB
WINDS WILL RANGE BETWEEN 35 AND 45 KNOTS ACROSS WESTERN UTAH DURING
THE MORNING...LEADING TO AN START TO STRONG SOUTH WINDS DURING THE
MORNING. GOOD LATE MORNING AND AFTERNOON MIXING AHEAD OF THE
ADVANCING FRONT WILL LEAD TO VERY STRONG AND GUSTY SURFACE WINDS
ACROSS MUCH OF THE STATE. AT THIS POINT IN APPEARS TO BE A SOLID
WIND ADVISORY OR MARGINAL HIGH WIND EVENT FOR THE WESTERN VALLEYS
PRE-FRONTAL. SOUTHERN AND EASTERN UTAH APPEAR TO BE MORE IN LINE FOR
A HIGH-END WIND ADVISORY EVENT TUESDAY AFTERNOON AND EARLY EVENING.
IN THE POST-FRONTAL ENVIRONMENT STRONG LOW-LEVEL COLD ADVECTION AND
A TIGHT SURFACE GRADIENT WOULD SUPPORT A BRIEF PERIOD OF HIGH WINDS
ACROSS NORTHWEST UTAH DURING THE LATE AFTERNOON AND EVENING HOURS.
THIS POST-FRONTAL AREA WILL BE THE MOST LIKELY AREA TO REACH HIGH
WIND CRITERIA ASSOCIATED WITH THE COLD FRONT. WILL LEAVE THE HIGH
WIND WATCH UP FOR NOW...THOUGH SUSPECT THAT ONLY THE NORTHWEST
DESERTS AND A FEW OTHER WIND PRONE AREAS OF NORTHWEST AND WEST-
CENTRAL UTAH WILL MEET CRITERIA. OTHER AREAS OF THE WATCH WILL
LIKELY END SOLID ADVISORY-LEVEL CRITERIA.

SOLID FRONTAL LIFT SUPPORTED BY A RAPIDLY DESTABILIZING AIRMASS WITH
ARRIVAL OF THE MID-LEVEL COLD AIR IN THE TROUGH SHOULD PRODUCE DEEP
CONVECTION ALONG AND BEHIND THE SURFACE FRONT LATE TUESDAY AFTERNOON
AND EVENING. A BRIEF BUT INTENSE CONVECTIVE PRECIP EVENT ASSOCIATED
WITH THE FRONT WILL PUT DOWN A COUPLE OF QUICK INCHES OF SNOW IN THE
MOUNTAINS...WITH RAIN AND/OR SNOW SHOWERS IN THE VALLEYS/FOOTHILLS.
PRECIP COULD DECREASE IN INTENSITY/AREAL COVERAGE BEHIND THE FRONT
FOR A TIME LATE TUESDAY NIGHT...THEN RETURN AGAIN AS WIDESPREAD SNOW
SHOWERS ACROSS NORTHERN/CENTRAL UTAH AS THE TROUGH EVOLVES INTO A
CLOSED LOW SQUARELY OVER THE REGION LATE TUESDAY NIGHT/WEDNESDAY.
THE LATEST RUNS OF THE GFS ARE CLEARLY MORE FAVORABLE FOR PRECIP
ACROSS NORTHERN UTAH AS THE CENTER OF THE NOW DEVELOPED UPPER LOW
POSITIONS ACROSS SOUTHWEST WYOMING OR NORTHEAST UTAH. THE RESULTANT
UNSTABLE NORTH-NORTHWEST FLOW WOULD BE IDEAL FOR MODERATE TO HEAVY
PRECIP ACROSS PORTIONS OF NORTHERN UTAH THAT FAVOR THIS PATTERN.
SIGNIFICANT SNOW ACCUMULATIONS ARE LIKELY FOR THE NORTHERN MOUNTAINS
THROUGH WEDNESDAY EVENING. CENTRAL UTAH WILL BE ON THE SOUTHERN
FRINGE OF THE HEAVIER PRECIP...AND AS SUCH WILL SEE SIGNIFICANTLY
LESS ACCUMULATIONS OUTSIDE OF THE MOST FAVORED NORTH AND NORTHWEST
SLOPES.

PRECIP WILL BEGIN TO WIND DOWN LATE WEDNESDAY NIGHT AS THE UPPER LOW
SETTLES INTO A POSITION OVER OR A BIT TO THE SOUTH OF THE FOUR
CORNERS REGION. EASTERN AND SOUTHERN UTAH COULD STILL SEE ORGANIZED
PRECIP RESULTING FROM THE SYNOPTIC SCALE LIFT ASSOCIATED WITH THE
UPPER LOW. INSTABILITY SHOWERS WILL LINGER OVER THE NORTH THROUGH
EARLY THURSDAY. AN ANTICYCLONIC NORTHERLY FLOW DEVELOPING BEHIND THE
FOUR CORNERS UPPER LOW WILL BRING AN END TO PRECIP ACROSS THE NORTH
LATE THURSDAY.

CLOSED LOW OVER THE GENERAL WESTERN NEW MEXICO REGION WILL BE CLOSE
ENOUGH TO SOUTHEASTERN PORTION OF CWA TO HAVE INSTABILITY SHOWERS
CONTINUING INTO THE EVENING. THE EC IS A LITTLE MORE EXCITED ABOUT
THIS AS FAR AS PRODUCING QPF BUT THE GFS IS ACTUALLY COLDER ALOFT
OVER SOUTHEAST UTAH WHICH MAKES ME BELIEVE THAT AT LEAST ISOLATED
SHOWERS WILL OCCUR.

&&

.AVIATION...THE SLC TERMINAL WILL SEE VFR CONDITIONS AND MOSTLY
CLEAR SKIES THROUGHOUT THE DAY. SOUTHEAST WINDS ARE EXPECTED TO
SWITCH TO THE NORTHWEST BETWEEN 20Z AND 22Z. THERE IS A 20 PERCENT
CHANCE THE SWITCH WILL BE LATER THAN EXPECTED OR WILL NOT OCCUR AT
ALL.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...HIGH WIND WATCH FROM TUESDAY MORNING THROUGH WEDNESDAY MORNING
     FOR UTZ011>013-019>021.

     WINTER STORM WATCH FROM TUESDAY MORNING THROUGH WEDNESDAY
     AFTERNOON FOR UTZ007>010-517.

     HIGH WIND WATCH FROM TUESDAY MORNING THROUGH TUESDAY EVENING FOR
     UTZ001>006-014>016.

     HIGH WIND WATCH FROM TUESDAY MORNING THROUGH WEDNESDAY MORNING
     FOR UTZ518.

WY...HIGH WIND WATCH FROM TUESDAY MORNING THROUGH TUESDAY EVENING FOR
     WYZ021.

&&

$$

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

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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