Area Forecast Discussion
Issued by NWS Salt Lake City, UT

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS65 KSLC 300307
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
907 PM MDT FRI APR 29 2016

.SYNOPSIS...THE NEXT PACIFIC STORM SYSTEM WILL SETTLE INTO THE
ARIZONA THIS WEEKEND AND IMPACT MUCH OF SOUTHERN AND EASTERN UTAH
INTO EARLY NEXT WEEK. HIGH PRESSURE ALOFT WILL RETURN TO THE
INTERIOR WEST BY THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...
WATER VAPOR LOOP SHOWS NEXT UPSTREAM SYSTEM APPROACHING FROM
EASTERN OREGON. AMDAR 400-250MB WIND OBSERVATIONS PLACE A
NORTHWESTERLY 100- 130KT JET OVER WESTERN CANADA AND THE WESTERN
GREAT BASIN. GOES/HRRR/00Z KSLC RAOB INDICATE THE PRECIPITABLE
WATER VALUE RANGES FROM 0.10"-0.35" MOUNTAINS TO 0.55"-0.80" MOST
VALLEYS.

DIFFLUENCE ALOFT...JET NOSING IN AND INSTABILITY PROBABILITIES FROM
THE SREF ALL FAVOR CONVECTION ALONG WESTERN UTAH. INCREASED POPS
ALONG THE WEST DOWN TO ST GEORGE...BUT SHOW DISSIPATING CONVECTION
ALONG AND EAST OF THE WASATCH.

HIGH ELEVATION...ABOVE 7500 FT...COULD SEE A QUICK 1-3" OF SNOWFALL
ACROSS THE CENTRAL AND SOUTHERN MOUNTAINS.

LATEST 3KM WRF MODELS RUN LOCALLY UTILIZING THE GFS AND NAM AGREE
WELL WITH THE HIGH WIND WATCH AREA AND TIMING. IT WILL ALSO LIKELY
BE BREEZY IN THE SALT LAKE AND UTAH VALLEYS. DAVIS COUNTY NORTHWARD
WILL LIKELY SEE SOME DAMAGING WINDS...WITH FALLING TREES A CONCERN
CONSIDERING THE MOIST SOILS.

&&

.PREVIOUS DISCUSSION...
A STILL MOIST AND SOMEWHAT UNSTABLE AIR MASS SUPPORTED BY A WEAK
SHORTWAVE MOVING SOUTHEAST THROUGH NORTHWEST UTAH WILL GENERATE
SCATTERED CONVECTION THROUGH EARLY THIS EVENING. MUCH OF THIS
CONVECTION WILL DISSIPATED EARLY THIS EVENING...WITH LINGERING
ACTIVITY REMAINING NEAR THE PASSING SHORTWAVE.

THE NEXT SHORTWAVE MOVING SOUTHEAST THROUGH WESTERN OREGON LATE THIS
AFTERNOON WILL DEVELOP INTO A CLOSED CIRCULATION OVER SOUTHERN
NEVADA LATE TONIGHT...THEN CONTINUE SOUTHEAST INTO ARIZONA SATURDAY.
CONVECTION ASSOCIATED WITH THIS FEATURE WILL EXPAND ACROSS NEVADA
THIS EVENING...WITH SOME SPILL OVER INTO FAR WESTERN UTAH LATE
TONIGHT. NOT ANTICIPATING AN EASTWARD EXPANSION OF THE CONVECTION
ACROSS UTAH OVERNIGHT AS THE TRAJECTORY OF THE UPPER LOW REMAIN
OUTSIDE OF UTAH. ONCE THE UPPER LOW SETTLES IN ARIZONA SATURDAY THE
BROAD AREA OF SYNOPTIC-SCALE LIFT AND AVAILABLE MOISTURE WILL
GENERATE AN INCREASE IN PRECIP ACROSS THE SOUTHERN UTAH AND THROUGH
THE CENTRAL MOUNTAINS. THE UPPER LOW WILL GRADUALLY WEAKEN AS IT
DRIFT NORTH TOWARD THE FOUR CORNERS SUNDAY. THE ASSOCIATE PRECIP
WILL REMAIN CLOSE TO THE RESIDUAL LOW CENTER OVER SOUTH-CENTRAL
THROUGH EAST-CENTRAL UTAH SUNDAY AFTERNOON AND EVENING. RESIDUAL
SHOWERS WILL PERSIST INTO MONDAY...THOUGH THIS ACTIVITY WILL BE
CONFINED TO THE EASTERN/CENTRAL MOUNTAINS AND LARGELY DRIVEN BY
DIFFERENTIAL HEATING.

THE BIG ISSUE IN THE SHORT TERM REMAINS THE POTENTIAL FOR DOWNSLOPE
WIND EVENT ACROSS FAR NORTHERN UTAH LATE SATURDAY NIGHT THROUGH
SUNDAY. THE UPPER LEVEL PATTERN OF HIGH PRESSURE CENTERED ACROSS
SOUTH-CENTRAL CANADA AND THE UPPER LOW OVER THE CENTRAL PLAINS
STATES WILL CREATE A DEEP LAYER EASTERLY FLOW ACROSS WYOMING AND
BACK INTO FAR NORTHERN UTAH THIS WEEKEND. EAST WINDS BETWEEN 40 AND
50 KTS NEAR 700 MB WITH STRONG COLD ADVECTION AND A FAVORABLE
NORTHEAST SURFACE PRESSURE GRADIENT BOTH POINT TOWARDS HIGH WINDS
FOR THE NORTHERN WASATCH FRONT AND CACHE VALLEY LATE SATURDAY NIGHT
THROUGH SUNDAY.

THE PATTERN SETTING UP DOES HAVE ITS PLUSES AND MINUSES WHEN IT
COMES TO A DOWNSLOPE HIGH WIND EVENT. ON THE PLUS SIDE THERE IS A
GOOD STABLE LAYER FORECAST TO BE ABOVE THE TERRAIN WITH FAIRLY
STRONG UPSTREAM COLD ADVECTION TAKING PLACE. THE SURFACE PRESSURE
GRADIENT OF 8-10 MB BETWEEN CENTRAL WYOMING AND NORTHERN UTAH IS
ADEQUATE TO SUPPORT HIGH WINDS. ON THE MINUS SIDE THE SURFACE
PRESSURE IS JUST ADEQUATE.

THE EVENT WILL LARGELY DEPEND ON THE UPPER LEVEL PATTERN REMAINING
FAVORABLE OVER THE WEEKEND. INITIALLY THE EASTERLY FLOW IS SUPPORTED
BY THE HIGH PRESSURE OVER SOUTH-CENTRAL CANADA AND THE UPPER LOW
MOVING INTO THE CENTRAL PLAINS. BY THE BEGINNING OF THE EVENT THE
CANADIAN HIGH SHIFTS WEST TO THE NORTHERN ROCKIES AND THE ARIZONA
LOW DRIFTS NORTH TO SUSTAIN THE DEEP EASTERLY FLOW ALOFT. IF THIS
PATTERN TRANSITION FAILS TO MATERIALIZE...THE HIGH WIND EVENT COULD
FIZZLE. AT THIS POINT CONFIDENCE THAT THE HIGH WIND EVENT WILL OCCUR
IS REASONABLY HIGH BASED ON RUN-TO-RUN CONSISTENCY OF THE GLOBAL
MODEL THE PAST SEVERAL RUNS. HAVE ISSUED AN HIGH WIND WATCH FOR LATE
SATURDAY NIGHT THROUGH SUNDAY FOR THE NORTHERN WASATCH FRONT AND
CACHE VALLEY. POINTS TO THE SOUTH ALONG THE URBAN CORRIDOR MAY SEE
MORE OF A CANYON WIND EVENT...WITH WIND GUSTS GENERALLY EXPECTED TO
REMAIN NEAR OR BELOW WHAT WOULD MEET WIND ADVISORY CRITERIA.

THE BROAD...DISSIPATING TROUGH IS EXITING THE REGION TO THE EAST
LATE MONDAY...WITH DRIER AIR GENERALLY WORKING INTO UTAH FROM THE
WEST. HOWEVER...MODELS ALREADY HAVE MAJOR DISCREPANCIES HEADING INTO
TUESDAY...AS THE GFS AND CANADIAN SLOWLY BUT SURELY BUILD HIGH
PRESSURE OVER THE REGION...WHILE THE ECMWF BRINGS A CLOSED LOW INTO
SOUTHWEST WYOMING AND NORTHERN UTAH FROM THE NORTHEAST MONDAY NIGHT
THROUGH WEDNESDAY.

THE ECMWF DEFINITELY SEEMS TO BE AN OUTLIER...BUT CANNOT RULE IT
OUT...ESPECIALLY SINCE IT HAS HAD THE SAME SOLUTION AT LEAST A
COUPLE RUNS IN A ROW. HAVE MAINTAINED SOME LOW-END POPS AND CLOUD
COVER IN THE NORTHEASTERN PORTIONS OF THE CWA TUESDAY AFTERNOON TO
ACCOUNT FOR THE EC...BUT HAVE GENERALLY KEPT THE TEMPERATURES

&&

.AVIATION...THERE IS A 30 PERCENT CHANCE THAT SHOWERS WILL IMPACT
THE SLC TERMINAL THROUGH THE REMAINDER OF THE EVENING...AND AN
EVEN LOWER CHANCE THAT A THUNDERSTORM COULD DIRECTLY IMPACT THE
AREA. BRIEF ERRATIC WINDS ARE THE MOST LIKELY IMPACT...PARTICULARLY
THE POSSIBILITY OF AN OUTFLOW BOUNDARY FROM THE NORTHWEST BETWEEN
03Z AND 07Z. OTHERWISE...EXPECT WINDS TO SWITCH TO THE SOUTHEAST
AROUND 02-04Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...HIGH WIND WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY
     AFTERNOON FOR UTZ001-002.

WY...NONE.
&&

$$

PUBLIC...ROGOWSKI/CONGER/SCHOENING
AVIATION...SCHOENING

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)


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.