Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 010255
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
755 PM MST SAT JAN 31 2015

.SYNOPSIS...HIGH PRESSURE WILL BUILD INTO THE AREA FROM THE NORTH
TONIGHT. A MOIST WEST NORTHWEST FLOW WILL DEVELOP ACROSS THE
NORTHERN GREAT BASIN MONDAY AND CONTINUE INTO WEDNESDAY.

&&

.DISCUSSION...WATER VAPOR LOOP SHOWS A RIDGE BUILDING IN FROM
THE WEST...AS A STRONG WAVE PROPAGATES SOUTHEAST OVER WYOMING
WITHIN THE NORTHERN STREAM TROUGH AND A CLOSED LOW SINKS INTO
MEXICO. AMDAR 400-250MB WIND OBSERVATIONS INDICATE A 75-125KT
ANTICYCLONIC JET FROM BRITISH COLUMBIA ACROSS THE NORTHERN ROCKIES
AND INTO CENTRAL CALIFORNIA. GOES/GPS/RAP/00Z RAOB INDICATE THE
PRECIPITABLE WATER VALUE RANGES BETWEEN 0.05-0.15" NORTHERN
MOUNTAINS...TO 0.50-0.60" FAR SOUTHERN VALLEYS. BLENDED TOTAL
PRECIPITABLE WATER PRODUCT INDICATES VALUES MUCH ABOVE NORMAL TO
OUR SOUTH AND EAST...WITH A MUCH DRIER AIRMASS TO OUR NORTHWEST.

UPDATED TO REMOVE ALL MENTION OF POPS AS HIGH PRESSURE BUILDS IN
SURFACE AND ALOFT.

DOWNSLOPE/CANYON WINDS ARE ELEVATED ACROSS PRONE AREAS OF EAST
CENTRAL AND SOUTHERN UTAH AS THE HIGH BUILDS IN. VALUES OF 30 TO 40
MPH FOR GUSTS ARE MOST COMMON.

ADJUSTED SKY COVER TO ACCOUNT FOR SATELLITE TRENDS. APPEARS BEST
DRYING TAKING PLACE ACROSS THE WESTERN VALLEYS. REMOVED FOG MENTION
THERE. BUT HAVE MENTION NEAR RICKFIELD...LAKE POWELL...GREEN
RIVER...UINTA BASIN...CACHE VALLEY AND WASATCH BACK AFTER MIDNIGHT
THROUGH TOMORROW MORNING. 00Z RAOB SHOWS STRONG INVERSION WILL
CONTINUE TO LOWER BELOW RIDGETOPS WITH SIGNIFICANT DRYING TAKING
PLACE IN THE MOUNTAINS OVERNIGHT.

TWEAKED TEMPERATURES BASED ON LASTEST LAMP GUIDANCE.

PREVIOUS DISCUSSION FOLLOWS...
THE SHORT WAVE RIDGE CROSSING UT FROM THE NORTH AT THIS TIME IS
GENERATING STRONG DRYING AND SUBSIDENCE WITH CLEARING SKIES ACROSS
THE CWA. AN AREA OF STRATUS WILL LINGER ALONG AND WEST OF THE I-15
CORRIDOR FROM ABOUT PROVO SOUTH INTO THE NIGHT BUT SHOULD
DISSIPATE AFTER MIDNIGHT. PRECIP HAS COME TO AN END ACROSS THE CWA
AND ALLOWED THE REMAINING WINTER WEATHER HIGHLIGHT TO EXPIRE.

A FAIRLY TIGHT NORTHERLY SURFACE GRADIENT IS IN PLACE ACROSS THE CWA
THIS AFTN AND WILL PERSIST ACROSS CENTRAL AND SRN UT TONIGHT. THIS
SHOULD BRING ENOUGH MIXING TO THESE AREAS TO SUFFICIENTLY DRY LOWER
LEVELS AND PRECLUDE MUCH FOG DEVELOPMENT TONIGHT. LEFT A MENTION IN
SOME AREAS TO ALLOW FOR LOCAL GROUND FOG IF THE WINDS DROP OFF
SOONER. ALSO HAVE A MENTION OF FOG IN THE COLDER NRN VALLEYS.

THE UPSTREAM RIDGE JUST OFF THE COAST TODAY CROSSES THE CWA ON SUN
AND FLATTENS RAPIDLY SUN NIGHT AS A WEAK WAVE PASSES MAINLY TO OUR
NORTH. THIS WAVE DOES PUSH SOME MOISTURE INTO FAR NRN UT BRINGING A
THREAT OF LIGHT PRECIP.

THIS PATTERN OF AN INCREASINGLY MOIST WNWLY FLOW OVER NRN UT
CONTINUES THRU TUE WITH A CONTINUED CHANCE OF VALLEY RAIN AND MTN
SNOW FROM ABOUT SLC NORTH. DONT EXPECT ENOUGH MTN ACCUMULATION FROM
THESE WEAK WAVES TO WARRANT ANY HIGHLIGHTS AND VALLEY PRECIP SHOULD
STAY AS RAIN.

SIGNIFICANT MODEL DIFFERENCES PLAGUE THE BEGINNING OF THE LONG TERM
FORECAST PERIOD. THE 06Z GFS AND 00Z EC AND THE 12Z GFS AND 12Z EC
REMAINED OUT OF SYNC IN A SIMILAR MANNER...WITH THE GFS CONTINUING
TO DEPICT A HIGHER AMPLITUDE RIDGE OVER THE EASTERN PACIFIC/PACIFIC
COAST THAN THE EC. THE MAIN IMPACT FROM THIS HIGHER AMPLITUDE RIDGE
IS THE GFS HAS A MORE SIGNIFICANT SYSTEM DIGGING INTO THE EASTERN
GREAT BASIN AND ROCKY MOUNTAIN STATES. THE EC...WITH THE LOWER
AMPLITUDE RIDGE...BRINGS A WEAKER BRUSH-BY SYSTEM THROUGH THE
INTERMOUNTAIN REGION WHICH PRIMARILY IMPACTS AREAS NORTH OF UTAH.

LOOKING AT ENSEMBLE DATA FROM THE GEFS...GFS AND CANADIAN...MUCH OF
THE GUIDANCE SUPPORTS A HIGHER AMPLITUDE RIDGE OVER THE EASTERN
PACIFIC/PACIFIC COAST. GIVEN THIS DATA...DECIDED TO CONTINUE THE
TREND OF LEANING TOWARD THE GFS. THIS WOULD BRING A STRONGER AND
COLDER SYSTEM INTO THE CWA TUESDAY NIGHT INTO WEDNESDAY WITH A
HIGHER THREAT OF PRECIPITATION THAN THE EC SOLUTION WOULD INDICATE.

FOLLOWING THIS SYSTEM...A LARGE RIDGE IS EXPECTED TO BUILD INTO THE
WESTERN UNITED STATES WITH LITTLE CHANCE OF PRECIPITATION EXPECTED
WEDNESDAY THROUGH FRIDAY. MUCH OF THE LONGER RANGE MODEL GUIDANCE
INDICATES A MORE ZONAL PATTERN WILL DEVELOP NEXT WEEKEND...SOMEWHAT
INCREASING THE THREAT OF PRECIPITATION ACROSS NORTHERN UTAH.

&&

.AVIATION...NORTHWEST WINDS ARE EXPECTED AT THE SLC TERMINAL
UNTIL ABOUT 07-08Z THEN SHIFT TO THE SOUTHEAST. THERE IS A 30
PERCENT CHANCE OF SWITCHING EARLIER. CLOUDS WILL INCREASE SUNDAY
AFTERNOON BUT CEILINGS ARE EXPECTED TO REMAIN ABOVE 7K FT AGL
THROUGH THE END OF THE TAF PERIOD.

&&

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

$$

PUBLIC...ROGOWSKI/WILENSKY/KRUSE
AVIATION...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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