Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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862
FXUS65 KSLC 120246
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
746 PM MST THU FEB 11 2016

.SYNOPSIS...HIGH PRESSURE WILL REMAIN OVER THE INTERMOUNTAIN WEST
THROUGH FRIDAY. A COUPLE OF WEAK WEATHER DISTURBANCES WILL CROSS
NORTHERN UTAH THIS WEEKEND.

&&

.DISCUSSION...WATER VAPOR LOOP SHOWS A RIDGE DOMINATING THE WEST.
AMDAR 400-250MB WIND OBSERVATIONS PLACE A 80-135KT ANTICYCLONIC
JET FROM WESTERN CANADA OVER THE NORTHERN ROCKIES AND INTO THE
GREAT LAKES. GOES/HRRR/GPS/00Z SLC RAOB INDICATE THE PRECIPITABLE
WATER VALUE RANGES BETWEEN 0.15"-0.25" MOUNTAINS...TO 0.35"-0.50"
NORTHERN/WEST CENTRAL VALLEYS.

WITH AN INVERSION IN PLACE...MAIN CONCERN IS HAZE/FOG/STRATUS AND
TEMPERATURES. THE BASE OF THE INVERSION HAS LOWERED TO 850MB WITH A
STRENGTH OF 10.7C...WHICH IS SLIGHTLY WEAKER THAN YESTERDAY MORNING.

STRATUS DECK CONTINUES ITS HOLD OVER THE WEST DESERT AND INTO THE
WASATCH FRONT...BUT HAS RECENTLY BECOME OBSCURED DUE TO CIRRUS ON
SATELLITE IMAGERY. THESE HIGH CLOUDS MAY HELP TO KEEP THE FOG FROM
BECOMING SO DENSE IN SOME LOCATIONS.

HAVE ADJUSTED FOG WORDING TO AREAS OF DENSE FOG ALONG THE LAKESHORE
AND BENCHES WHERE TERRAIN INTERSECTS STRATUS. DID THE SAME ACROSS
WEST CENTRAL UTAH AND THE SANPETE VALLEY WHERE PREVIOUS NIGHTS HAVE
SHOWN SOME OF THE WORSE VISIBILITIES...ADJACENT TO UTAH VALLEY.

ONLY OTHER CHANGE WAS TO ADJUST THE TEMPERATURE/DEWPOINT/RH AND
APPARENT TEMPERATURE CURVES WITH LATEST OBSERVATIONAL AND LAMP
GUIDANCE THROUGH THE MIDDLE OF THE NIGHT.

&&

.PREVIOUS DISCUSSION...
A STRONG RIDGE REMAINS IN PLACE OVER THE GREAT BASIN THIS
AFTERNOON...KEEPING A STABLE AIRMASS IN PLACE. TEMPERATURES AT
700MB REMAIN QUITE MILD...GENERALLY BETWEEN 2 TO 5C ACROSS THE
FORECAST AREA. AS A RESULT...MOST HIGHER ELEVATION SITES CONTINUE
TO SEE DRY AND MILD CONDITIONS. HOWEVER...LOWER VALLEYS OF MAINLY
NORTHERN AND CENTRAL UTAH REMAIN MIRED IN INVERSIONS WITH FOG AND
LOW STRATUS. SATELLITE TRENDS DO INDICATE THE STRATUS ERODING A
BIT ALONG THE EDGES THIS AFTERNOON...BUT NOT ENOUGH TO
SIGNIFICANTLY AFFECT TEMPERATURES.

EXPECT THE STRATUS TO CONTINUE OVERNIGHT WITH FOG INCREASING IN
COVERAGE AFTER SUNSET DESPITE INCREASING HIGH CLOUDS HELPING TO
LIMIT RADIATIVE COOLING SOMEWHAT. NOT ISSUING ANY FOG HIGHLIGHTS
WITH THIS PACKAGE EVEN THOUGH SOME DENSE FOG IS EXPECTED.
RATHER...WILL ALLOW LATER SHIFTS TO MONITOR TRENDS AS THE HIGH
CLOUDS MAY AFFECT THE COVERAGE OF DENSE FOG. NOT LOOKING AT ANY
SIGNIFICANT CHANGES IN THE WEATHER FOR TOMORROW.

FOR THE WEEKEND...A COUPLE OF WEAK STORM SYSTEMS ARE STILL EXPECTED
TO GRAZE NORTHERN UTAH. BECAUSE THESE STORMS ARE NOT VERY
STRONG...THEY ARE NOT EXPECTED TO SWEEP AWAY THE INVERSIONS.
RATHER...COOLER AIR ALOFT WILL GRADUALLY ERODE THE INVERSIONS FROM
ABOVE. THE SATURDAY STORM IS ONLY EXPECTED TO PUT A SMALL DENT IN
THE INVERSION AND NOT EXPECTED TO PRODUCE MUCH IF ANY IN THE WAY OF
PRECIPITATION. THE STORM ON SUNDAY WILL BE A BIT COOLER...USHER IN
STRONGER WINDS ALOFT AND SOME LIGHT PRECIPITATION FOR THE NORTH. THE
WINDS ARE NOT EXPECTED TO MIX DOWN TO THE VALLEY BOTTOMS SO AS A
RESULT THE INVERSIONS MAY NOT COMPLETELY ERODE AWAY.
NEVERTHELESS...WITH THE LATEST EC COMING IN STRONGER WITH THE STORM
THAN THE 00Z RUN...THE POTENTIAL FOR A SIGNIFICANT IMPROVEMENT TO
AIR QUALITY SEEMS MORE LIKELY.

LOW AMPLITUDE RIDGING CENTERED OVER THE NORCAL COAST WILL
MAINTAIN A SOMEWHAT PROGRESSIVE NORTHWESTERLY FLOW ALOFT EARLY
NEXT WEEK. REMNANT MOISTURE FROM THE PREVIOUS SHORT WAVE AND WEAK
JET SUPPORT ALOFT MAY MAINTAIN ISOLATED MOUNTAIN SNOW SHOWERS
ACROSS THE FAR NORTH MONDAY INTO THE OVERNIGHT HOURS...BUT LARGELY
LOOKING AT A SOMEWHAT IMPROVED AND PARTIALLY MIXED
ENVIRONMENT...WITH DRY CONDITIONS DOMINATING. AXIS OF
AFOREMENTIONED RIDGE WILL TREND TO SHIFT INLAND AND OVERHEAD
THROUGH THE MIDWEEK PERIOD ALLOWING ANOTHER ROUND OF RISING
HEIGHTS AND SUBSIDENT WARMING...THIS LIKELY STRENGTHENING
INVERSIONS ACROSS THE VALLEYS AND BASINS ONCE AGAIN. THIS
SAID...NET STRENGTH AND AMPLITUDE OF THIS RIDGE WILL BE WEAKER
THAN THE CURRENT SITUATION...AND RESIDENCE TIME QUITE A BIT
SHORTER.

GLOBAL MODELS DO PICK UP ON A NET PATTERN CHANGE ACROSS THE WESTERN
CONUS LATE NEXT WEEK AS MEAN FLOW ACROSS THE EASTERN PACIFIC
TRANSITIONS MORE ZONAL DRIVING AT LEAST THE REMNANT ENERGY OF AN
ADEQUATE TROUGH INLAND INTO THE EASTERN GREAT BASIN.
EVOLUTION...TIMING AND AMPLITUDE OF THIS REMAINS LOW CONFIDENCE AT
THIS TIME DUE TO SUBSTANTIAL SPREAD IN GUIDANCE...BUT THE LIKELIHOOD
OF HAVING SOME SEMBLANCE OF A TROUGH MOVE THROUGH IN THE THU OR FRI
TIMEFRAME LOOKS LIKE A DECENT BET. THE COMBINATION OF INCREASED FLOW
ALOFT AND CLOUD COVER AHEAD OF THIS COMBINED WITH MODEST CAA AT THE
LOW/MID LEVELS DURING PASSAGE MAY HAVE A NOTABLE AFFECT ON THE
PERSISTENT INVERSIONS AT THAT TIME.

&&

.AVIATION...PREVAILING IFR CONDITIONS IN HAZE/FOG AND LOW STRATUS
ARE EXPECTED TO REMAIN IN PLACE AT THE KSLC TERMINAL THROUGH THE
VALID TAF PERIOD. DENSE FOG IS EXPECTED TO ONCE AGAIN CREEP INTO THE
NORTHWESTERN PORTION OF THE AIRFIELD TONIGHT...AND A 60 PERCENT
CHANCE EXISTS THAT THIS FOG WILL SPREAD ACROSS THE AIRFIELD SOMETIME
WITHIN THE 09Z-14Z WINDOW.

&&

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

$$

PUBLIC...ROGOWSKI/CHENG/MERRILL
AVIATION...KRUSE

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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