Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 211209
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
509 AM MST WED JAN 21 2015

.SYNOPSIS...A WEATHER DISTURBANCE WILL TRACK EAST ACROSS NORTHERN
ARIZONA AND IMPACT EXTREME SOUTHERN UTAH THROUGH THIS MORNING. HIGH
PRESSURE ALOFT WILL EXPAND ACROSS THE WESTERN STATES DURING THE
LATTER HALF OF THE WEEK.

&&

.SHORT TERM (THROUGH 12Z SATURDAY)...A COUPLE OF SYNOPTIC SCALE
FEATURES TO NOTE ON WATER VAPOR IMAGERY THIS MORNING. THE FIRST IS A
TROUGH CURRENTLY CENTERED OVER THE LAKE MEAD AREA WHICH HAS SPREAD
CLOUDS ACROSS SOUTHERN UTAH. WARMER SOUTHWEST FLOW AHEAD OF THIS
FEATURE IS INTERACTING WITH THE OLD FRONTAL BOUNDARY NEAR THE
UTAH/ARIZONA BORDER TO PRODUCE A BAND OF PRECIPITATION. BULK OF THIS
IS OCCURRING OVER ARIZONA PER RADAR IMAGERY...WITH JUST WEAK ECHOES
ASSOCIATED MORE WITH LOW CLOUDS AND VIRGA THAN MEASURABLE
PRECIPITATION OVER SOUTHERN UTAH. THESE ECHOES ARE ALREADY WEAKENING
OVER SOUTHERN UTAH AS THE TROUGH CONTINUES ON A SOUTHEAST TRAJECTORY
TODAY.

THE SECOND FEATURE OF NOTE IS A TROUGH CURRENTLY OVER WESTERN
MONTANA AND WYOMING WHICH IS PROGGED TO CARVE BACK INTO FAR
NORTHEASTERN UTAH AS IT PHASES WITH THE AFOREMENTIONED WAVE. THIS
WILL BRING A NORTH TO NORTHEASTERLY FLOW TO MUCH OF THE FORECAST
AREA TODAY AND KEEP A COOLER AIRMASS IN PLACE. HOWEVER...THE BEST
UPPER SUPPORT AND MOST OF WHAT LITTLE IN THE WAY OF MOISTURE IS
ASSOCIATED WITH THIS STORM WILL REMAIN EAST OF UTAH. THIS WILL KEEP
MOSTLY SUNNY SKIES OVER THE NORTHERN PORTIONS OF THE FORECAST AREA
FOR TODAY...BUT DESPITE THE SUNSHINE...THE COOL AIRMASS WITH H7
TEMPERATURES BETWEEN -8 AND -12Z WILL HOLD MAXES CLOSER TO NORMAL.
HOWEVER...THE ENHANCED NORTHEASTERLY FLOW AND ASSOCIATED NORTHERLY
GRADIENT WILL LIKELY BRING GUSTY CANYON WINDS TO WASHINGTON COUNTY
LATE THIS EVENING AND OVERNIGHT.

AN UPPER RIDGE WILL BUILD BACK INTO THE AREA FOR TOMORROW...LEADING
TO STRENGTHENING INVERSIONS WHICH WILL HOLD VALLEY TEMPERATURES DOWN
DESPITE H7 TEMPERATURES CLIMBING BACK TO AROUND -4C. THE RIDGE
PATTERN WILL BE INTERRUPTED BY ANOTHER WEAK SPLITTING STORM SYSTEM
FOR FRIDAY WHICH WILL BRING LITTLE MORE THAN A WEAK DRY COLD FRONT
TO THE AREA.

&&

.LONG TERM (AFTER 12Z SATURDAY)...THE GFS...ECMWF AND CANADIAN
MODELS ARE ALL SIMILAR IN THE HANDLING OF A ELONGATED TROUGH
SPLITTING AS IT RETROGRADES SOUTHWEST OFF THE BAJA COAST AND
UNDERNEATH THE WEST COAST RIDGE SATURDAY. THE RIDGE CONTINUES TO
MOVE EAST INTO THE GREAT BASIN FOR SUNDAY AND MONDAY BRINGING DRY
AND MODERATELY MILD CONDITIONS TO THE REGION.

BY MONDAY NIGHT THE UPPER LOW OFF THE NORTHERN BAJA COAST BECOMES AN
OPEN WAVE AS IT GETS PICKED UP BY THE UPSTREAM TROUGH NEAR 140W AND
MOVES NORTHWARD UP THE WEST SIDE OF THE RIDGE INTO SOUTHERN
CALIFORNIA TUESDAY AND AS A MUCH WEAKENED TROUGH BY THE TIME IT
REACHES OREGON WEDNESDAY. THIS FEATURE WILL BRING INCREASING
MOISTURE...AND A WEAKENING COLD FRONT...THROUGH UTAH ON SOUTHWEST
FLOW TUESDAY INTO WEDNESDAY. SINCE WE WILL BE ON THE EASTERN FRINGE
OF THIS SYSTEM THE MOISTURE IS EXPECTED TO BE LIMITED BUT GIVEN ALL
THREE MEDIUM RANGE MODELS SHOWING A SIMILAR EVOLUTION AND LIGHT
PRECIP...HAVE EXPANDED THE SLIGHT CHANCE POPS OVER MOST OF THE
SOUTHERN TWO THIRDS OF THE CWA TUESDAY WITH SOME CHANCE POPS IN THE
SOUTHERN MOUNTAINS. DUE TO THE H7 TEMPS COOLING TO AROUND 1C OR 0C
HAVE ADDED MENTION OF SNOW TO THE HIGHER TERRAIN ABOVE 8000 FT.

MOISTURE IS EXPECTED TO SPREAD SWIFTLY NORTHWARD AND BE OVER
NORTHERN HALF OF THE CWA EARLY TUESDAY NIGHT WITH POPS IN THE SLIGHT
CHANCE CATEGORY. BY WEDNESDAY ONLY THE NORTHERN MOUNTAINS AND
SOUTHWEST WYOMING WILL HAVE A SLIGHT CHANCE OF ANY PRECIP. AS THE
RIDGE BUILDS IN FROM THE SOUTH DRYING WILL TAKE PLACE OVER THE
SOUTHERN TWO THIRDS OF THE CWA.

TEMPERATURES ARE EXPECTED TO BE ABOVE NORMAL THROUGHOUT THIS PERIOD.
THE WARMEST DAY WILL BE MONDAY WHEN TEMPERATURES REACH 10-15 DEGREES
ABOVE AVERAGE ACROSS THE ENTIRE CWA.

&&

.AVIATION...LIGHT NORTH-NORTHWEST WINDS ARE EXPECTED TO CONTINUE AT
THE KSLC TERMINAL THROUGH TODAY WITH A SHIFT TO SOUTHEAST AFTER
ABOUT 04Z TONIGHT. VFR CONDITIONS WILL PREVAIL THROUGH THE TAF
PERIOD.

&&

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

$$

CHENG/STRUTHWOLF

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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