Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 200845
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
245 AM MDT MON OCT 20 2014

.SYNOPSIS...A DRY AND MILD SOUTHWESTERLY FLOW WILL DEVELOP AHEAD
OF A PACIFIC TROUGH WHICH WILL CROSS NORTHERN UTAH TUESDAY. ANOTHER
COLD FRONT IS FORECAST NEXT WEEKEND.

&&

.SHORT TERM (THROUGH 12Z THURSDAY)...
WATER VAPOR LOOP SHOWS A CLOSED LOW OVER NORTHERN MEXICO...A
RIDGE OVER THE NORTHER ROCKIES...AND A TROUGH OFF THE PACIFIC
NORTHWEST. AMDAR 400-250MB WIND OBSERVATIONS REVEAL A CYCLONIC
100-120KT JET OFF THE PACIFIC NORTHWEST COAST. GOES/GPS/RAP/00Z
RAOB INDICATE THE PRECIPITABLE WATER VALUE RANGES BETWEEN 0.25"
NORTHEAST MOUNTAINS...TO 0.60" VALLEYS.

TODAY IS A TRANSITION DAY AS WE GET INTO A PRE-FRONTAL REGIME.
HEIGHTS/PRESSURE BEGIN TO FALL AS A WAVE EJECTS FROM THE PACIFIC
TROUGH TOWARD NORTHERN CALIFORNIA. SOUTHERLY FLOW DEVELOPS IN
RESPONSE...WITH A SOUTHEASTERLY PRESSURE GRADIENT SETTING UP.

EXPECT MOST ALL VALLEYS TO REALIZE BETTER MIXING TODAY WITH WARMER
TEMPERATURES THE RESULT WITHIN THE THERMAL RIDGE. 700MB TEMPERATURES
ARE SHOWN TO RISE TO ABOUT +8C PER THE RAP.

ANTICIPATE AFTERNOON BUILDUPS ON THE HIGHER TERRAIN. 00Z NAM AND
LATEST HIGH RESOLUTION LOCAL WRF RUNS INDICATE A CHANCE FOR
MEASURABLE PRECIPITATION...WITH THE 21Z SHORT RANGE ENSEMBLES
INDICATING ENOUGH DESTABILIZATION TO JUSTIFY A 20 POP FOR THE
MOUNTAINS.

INDICATE RISING POP CHANCES FOR THE SOUTHEAST VALLEYS THIS
EVENING...NORTH TOWARD PRICE AFTER MIDNIGHT. THIS IS SUPPORTED BY
THE LOCAL HIGH RESOLUTION WRF MODELS...00Z NAM...WITH THE SHORT
RANGE ENSEMBLES ALSO INDICATING RISING INSTABILITY ACROSS THE
EASTERN ZONES FROM SOUTH TO NORTH OVERNIGHT.

GREATEST POPS ARE FORECAST TUESDAY AND TUESDAY EVENING WITH THE
FRONTAL PASSAGE. QPF WILL BE LIMITED AS THE UPPER LEVEL SYSTEM
QUICKLY LIFTS INTO THE NORTHERN ROCKIES LIMITING INSTABILITY.
STILL...GENERATE ENOUGH INSTABILITY FOR PRECIPITATION GENERATION
ALONG WITH JUSTIFYING A MENTION OF THUNDER. MODELS ALL FAIRLY
CONSISTENT SHOWING BEST COVERAGE AND QPF EAST OF THE WASTACH
MOUNTAINS AS THE TROUGH INTERACTS WITH POOLING MOISTURE ALONG THE
COLORADO BORDER.

MUCH OF THE COLDER AIR REMAINS NORTH OF THE IDAHO BORDER.
STILL...SNOW LEVELS LOOK TO LOWER TO ABOUT 10KFT TUESDAY. THIS COULD
HAVE SOME IMPACT ON THE MIRROR LAKE HIGHWAY IN THE UINTA
MOUNTAINS...WHERE SNOWFALL COULD AMOUNT TO 3-5" ON A SNOWBOARD.
ROADS ARE WARMER AND WITH MUCH OF THE EVENT DURING THE
DAYTIME...SOLAR INSOLATION SHOULD ALSO HELP TO COUNTERACT IMPACTS
EXCEPT PERHAPS DURING PEAK INTENSITY.

END PRECIPITATION LATE TUESDAY EVENING...WITH SHORTWAVE RIDGING
BUILDING IN FOR WEDNESDAY. A MOIST WESTERLY PACIFIC FLOW LOOKS TO
SUPPLY MID AND HIGH LEVEL CLOUDINESS ACROSS THE NORTH WEDNESDAY
NIGHT.

&&

.LONG TERM (AFTER 12Z THURSDAY)...
HIGH PRESSURE IS EXPECTED TO BUILD OVER THE FORECAST AREA
THURSDAY THROUGH THE FIRST HALF OF THE WEEKEND...RESULTING IN DRY
AND STABLE CONDITIONS WITH MAXES UP TO 10F ABOVE SEASONAL NORMALS
BY SATURDAY. GLOBAL MODELS REMAIN IN FAIRLY GOOD AGREEMENT THAT
THE RIDGE WILL SHIFT EAST LATE SATURDAY...ALLOWING A PACIFIC STORM
SYSTEM TO MOVE THROUGH SATURDAY NIGHT AND SUNDAY. GUIDANCE DOES
CONTINUE TO DISAGREE A BIT ON THE TIMING...WITH THE LATEST GFS
JUST A LITTLE BIT FASTER THAN THE EC...BUT BOTH BRING A DECENT
AMOUNT OF MOISTURE AND A WELL DEFINED COLD FRONT INTO AT LEAST
NORTHERN AND CENTRAL UTAH. THE FRONT IS PROGGED TO DROP 700 MB
TEMPS FROM THE +6 TO +8C RANGE TO AS LOW AS -5 OR -6C BY SUNDAY
AFTERNOON. HAVE COOLED TEMPERATURES DOWN IN THE EXTENDED AND
MAINTAINED GOING POPS FOR NORTHERN AND CENTRAL UTAH FOR THE LATTER
HALF OF THE WEEKEND.

&&

.AVIATION...THE SLC TERMINAL WILL SEE VFR CONDITIONS THROUGHOUT THE
DAY WITH SOME SCATTERED CLOUDS THIS AFTERNOON. SOUTHEAST WINDS ARE
EXPECTED TO SHIFT TO THE NORTHWEST LATER THAN USUAL...BETWEEN 21Z
AND 23Z. HOWEVER...THERE IS A 30 PERCENT CHANCE THAT WINDS WILL
REMAIN SOUTHERLY THROUGHOUT THE DAY.

&&

.FIRE WEATHER....MILD WITH A SOUTH BREEZE DEVELOPING TODAY...AHEAD OF
A COLD FRONT CROSSING UTAH TOMORROW. ONLY A SMALL CHANCE OF A
MOUNTAIN SHOWER THIS AFTERNOON. MUCH BETTER CHANCE FOR
PRECIPITATION TOMORROW ESPECIALLY ACROSS NORTHERN UTAH. SNOW
LEVEL AROUND 10KFT. FRONT WILL ALSO BRING A NOTABLE INCREASE IN
HUMIDITY ACROSS MUCH OF THE STATE INTO MID WEEK.

TEMPERATURES REBOUND GRADUALLY LATE WEEK WITH DECREASING HUMIDITY.
ANOTHER WET COLD FRONT EXPECTED NEXT WEEKEND. SOUTHERLY WINDS MAY
BECOME GUSTY AHEAD OF THE FRONT.

&&

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

$$

SHORT TERM/FIRE WEATHER...ROGOWSKI
LONG TERM/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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