Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 300256
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
856 PM MDT FRI AUG 29 2014

.SYNOPSIS...HIGH PRESSURE OVER THE REGION WILL SHIFT EAST THROUGH
TONIGHT. A STORM SYSTEM WILL BRING A COLD FRONT THROUGH NORTHERN
AND CENTRAL UTAH SATURDAY AND SUNDAY. A MORE STABLE AIRMASS WILL
RETURN FOR THE EARLY TO MIDDLE PART OF THE UPCOMING WEEK.

&&

.DISCUSSION...WATER VAPOR LOOP SHOWS A RIDGE HAS BUILT INTO THE
EASTERN GREAT BASIN FROM SOUTHERN CALIFORNIA...WITH A TROUGH OVER
THE PACIFIC NORTHWEST. IN BETWEEN...A SEVERAL DISTURBANCES ARE
APPROACHING NORTHERN UTAH FROM NORTHERN CALIFORNIA. AMDAR
400-250MB WIND OBSERVATIONS REVEAL A 50-85KT ANTICYCLONIC JET FROM
NORTHERN CALIFORNIA INTO THE FOUR CORNERS. A SECOND CYCLONIC JET
OF SIMILAR MAGNITUDE IS OVER THE PACIFIC NORTHWEST INTO WESTERN
CANADA. GOES/GPS/RAP/00Z RAOB INDICATE THE PRECIPITABLE WATER
VALUE RANGES BETWEEN 0.4" NORTHEAST MOUNTAINS TO 0.8" WESTERN
VALLEYS.

INCREASED CLOUD COVER AS SATELLITE SHOWS COPIOUS MID AND HIGH LEVEL
MOISTURE STREAMING INTO NORTHERN UTAH FROM NORTH CENTRAL CALIFORNIA.
THIS WILL HELP TO KEEP TEMPERATURES WARMER OVERNIGHT. INCREASED
SOUTHERLY WINDS IN THE HIGHER TERRAIN LATER TONIGHT AHEAD OF AN
APPROACHING COLD FRONT.

DECIDED TO ADVERTISE A SLIGHT CHANCE OF A SHOWER OVERNIGHT NORTH OF
INTERSTATE 70. PLENTY OF INSTABILITY ON THE 00Z KSLC RAOB...THOUGH
BOTH SHORT RANGE ENSEMBLES AND RAP INDICATE INSTABILITY WANES LATE
THIS EVENING...THUS DID NOT MENTION THUNDER. STILL...APPROACHING
DYNAMICS OF AFOREMENTIONED DISTURBANCES AND PROXIMITY OF THE UPPER
LEVEL JET TO CONTEND WITH. THOUGH IT IS NOTEWORTHY THAT CURRENT HRRR-
3KM RUN DOES NOT SHOW ANY CONVECTION AFTER MID EVENING. ELECTED TO
INCLUDE MENTION OF LOCALLY GUSTY WINDS GIVEN INVERTED-V SOUNDING
WITH MAINLY THE MID LEVELS MOISTENING TONIGHT. EARLIER DEEPER
CONVECTION CERTAINLY DISPLAYED THIS THREAT WITH WIND GUSTS OF 40+
MPH AND EVEN 1 SEVERE REPORT.

&&

.PREVIOUS DISCUSSION...HIGH PRESSURE OVER THE FORECAST AREA HAS
BEGUN TO SHIFT EAST THIS AFTERNOON AS A PACIFIC NORTHWEST STORM
SYSTEM MOVES ONSHORE. SOME SHORTWAVE ENERGY MOVING THROUGH THE RIDGE
HAS ALLOWED A FEW SHOWERS AND THUNDERSTORMS TO DEVELOP OVER THE
HIGHER TERRAIN OF UTAH...PRIMARILY OVER THE UINTAS. THE POSSIBILITY
OF CONVECTION OVER THE TERRAIN CONTINUES THROUGH THE EVENING AND
OVERNIGHT HOURS AS THE WAVE MOVES THROUGH. OTHERWISE...SKIES HAVE
BEEN PARTLY CLOUDY WITH TEMPERATURES TOPPING OUT A FEW DEGREES ABOVE
SEASONAL NORMS.

THE PACIFIC NORTHWEST STORM SYSTEM WILL TRACK EAST OVER THE LABOR
DAY WEEKEND...MOVING ACROSS NORTHERN UTAH SATURDAY AND SUNDAY AS IT
DOES SO. THIS WILL BRING A COLD FRONT INTO NORTHERN AND CENTRAL UTAH
AS WELL AS SOUTHWEST WYOMING. LATEST GUIDANCE IS TRENDING A BIT
SLOWER WITH THE SYSTEM...WITH THE FRONT NOT REALLY ENTERING
NORTHWEST UTAH UNTIL SATURDAY EVENING. BECAUSE OF
THIS...TEMPERATURES ARE EXPECTED TO REMAIN ON THE MILD SIDE DURING
THE DAY SATURDAY. WITH SHORTWAVE ENERGY FROM THE STORM SYSTEM
APPROACHING DURING THE AFTERNOON...THE THREAT OF CONVECTION
CONTINUES OVER THE NORTHERN UTAH MOUNTAINS. TIGHTENING GRADIENT
AHEAD OF THE FRONT WILL LIKELY RESULT IN SOME BREEZY
WINDS...ESPECIALLY OVER SOUTHERN UTAH.

THE FRONT IS PROGGED TO MOVE THROUGH NORTHERN UTAH SATURDAY
NIGHT...STALLING OVER CENTRAL UTAH SUNDAY MORNING. THE MAIN TROUGH
ALSO MOVES THROUGH NORTHERN UTAH DURING THE OVERNIGHT HOURS...WHICH
WILL BE THE BEST TIME FOR PRECIP TO DEVELOP. HOWEVER...DUE TO
RELATIVE LACK OF MOISTURE THINK COVERAGE WILL BE SCATTERED AT BEST.
MORNING FORECAST PACKAGE COVERED THE THREAT WELL AND MADE LITTLE IN
THE WAY OF CHANGES TO POPS FOR THE AFTERNOON PACKAGE.

THE MUCH COLDER AIRMASS WILL BE IN PLACE FOR THE NORTH DURING THE
DAY SUNDAY...WITH 700 MB TEMPS DROPPING FROM AROUND +12C TO AS LOW
AS +4C...RESULTING IN MAX TEMPS AROUND 10F BELOW SEASONAL NORMS.
COOLING WILL BE LESS SIGNIFICANT OVER CENTRAL UTAH...WITH ALMOST NO
CHANGE IN TEMPERATURES BETWEEN SATURDAY AND SUNDAY OVER SOUTHERN
UTAH AS CONDITIONS REMAIN DRY AND MILD.

ONE LAST WAVE IS EXPECTED TO GRAZE NORTHERN UTAH SUNDAY NIGHT/MONDAY
MORNING BEFORE THE TROUGH FULLY EXITS...BUT DRY CONDITIONS WILL
ALLOW FOR LITTLE...IF ANY...PRECIPITATION. MODELS AGREE THAT A DRIER
AND MORE STABLE NORTHWEST FLOW WILL MOVE IN BY MONDAY
AFTERNOON...ALLOWING FOR A WARMING AND DRYING TREND THROUGH AT LEAST
THE MIDDLE OF THE UPCOMING WEEK. GLOBAL MODELS INDICATING THE RIDGE
FLATTENING A BIT BY THURSDAY AS A PACIFIC NORTHWEST TROUGH MOVES
WELL NORTH OF THE AREA...PERHAPS CURBING THE WARMING TREND.

&&

.AVIATION...EXPECTING AN INCREASE IN MID LEVEL CLOUDS AND AN
ENHANCED SOUTHERLY WIND OVERNIGHT AT THE SLC TERMINAL. WIND GUSTS
MAY INCREASE TO NEAR AIRPORT WEATHER WARNING LEVELS AROUND
SUNRISE. 20 PERCENT CHANCE OF A GUSTY SHOWER OVERNIGHT.

&&

.FIRE WEATHER....TWO WEAK DISTURBANCES ARE BRINGING ISOLATED SHOWERS
AND STORMS THIS AFTERNOON TO THE NORTHEAST AND NORTHWEST
RESPECTIVELY. SPOTTY WETTING RAINS ARE POSSIBLE WITH THESE STORMS
THROUGH THIS EVENING BUT THEY WILL TREND TO DISSIPATE WITH SUNSET. A
NET DRYING TREND WILL CONTINUE TOMORROW AS SOUTHERLY WINDS RAMP UP
ACROSS THE AREA AHEAD OF AN APPROACHING COLD FRONT. COULD SEE SOME
AREAS IN THE WESTERN VALLEYS APPROACH OR EXCEED CRITICAL FIRE
WEATHER CONDITIONS OF LOW RH AND GUSTY WINDS TOMORROW AFTERNOON BUT
FUELS REMAIN AT LEAST SOMEWHAT WET FROM RECENT RAINS. THE COLD FRONT
WILL MOVE INTO CENTRAL UTAH SATURDAY NIGHT SPREADING ISOLATED TO
WIDELY SCATTERED SHOWERS TO PRIMARILY THE NORTH/NORTHWEST BUT
POTENTIAL OF WETTING RAINS REMAINS LOW. COOLER AND MORE STABLE
CONDITIONS WILL EXIST ACROSS THE NORTH SUNDAY AND MONDAY WHILE THE
SOUTH WILL REMAIN WARM AND DRY. HIGH PRESSURE WILL RETURN NEXT WEEK
FURTHER DRYING ALL AREAS...AND SOUTHERLY WINDS LOOK TO BECOME GUSTY
ONCE AGAIN MID TO LATE WEEK.

&&

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

&&

$$

PUBLIC...ROGOWSKI/TRAPHAGAN
FIRE WEATHER...MERRILL
AVIATION...ROGOWSKI

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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