Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 211052
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
452 AM MDT TUE APR 21 2015

.SYNOPSIS...HIGH PRESSURE ALOFT WILL BUILD EAST INTO THE GREAT BASIN
TODAY. A LOW PRESSURE SYSTEM OFF THE SOUTHERN CALIFORNIA COAST WILL
ALSO MOVE INLAND TODAY...THEN TURN NORTH AND IMPACT MUCH OF THE AREA
MIDWEEK.

&&

.SHORT TERM (THROUGH 00Z SATURDAY)...UTAH REMAINS UNDER A WEAK
NORTHWEST FLOW ALOFT THIS MORNING WHILE AN UPSTREAM RIDGE SLOWLY
SHIFTS INTO THE GREAT BASIN. MEANWHILE...A CLOSED LOW IS
UNDERCUTTING THIS RIDGE AND ADVANCING INTO FAR SOUTHERN CALIFORNIA.
MOSTLY CLEAR SKIES AREAWIDE THIS MORNING BUT ENOUGH LINGERING
MOISTURE REMAINS IN PLACE THAT A FEW SHOWERS/THUNDERSTORMS ARE STILL
POSSIBLE WITH DAYTIME HEATING. ADDITIONALLY...SOUTHWEST UTAH COULD
SEE A BIT BETTER COVERAGE OF SHOWERS TODAY AS THE UPPER LOW
CONTINUES TO APPROACH THE AREA. OTHERWISE...EXPECT A SLIGHT WARMING
TREND OVER MUCH OF THE AREA UNDER THE BUILDING RIDGE TODAY.

EXPECT SOME NOCTURNAL SHOWERS TO LINGER TONIGHT AS THE
AFOREMENTIONED LOW EJECTS ACROSS SOUTHERN NEVADA. THIS LOW WILL THEN
FILL AND WEAKEN...WITH THE REMNANTS LIFTING ACROSS UTAH TOMORROW.
MODELS CONTINUE TO SUPPORT INCREASED COVERAGE OF PRECIPITATION
DURING THIS TIME. AS THIS WAVE EXITS TO THE NORTH LATE WEDNESDAY
NIGHT...ANOTHER CLOSED LOW WILL TAKE ITS PLACE OVER SOUTHERN
CALIFORNIA. THIS LOW WILL THEN TRACK ACROSS ARIZONA AS AN OPEN-WAVE
TROUGH THROUGH THURSDAY NIGHT. MOISTURE DRAWN IN FROM THE SOUTH WILL
HELP BRING AN EVEN BETTER CHANCE OF SHOWERS TO THE AREA DURING THIS
TIME. GFS/EC IN GOOD GENERAL AGREEMENT WITH THIS EVOLUTION...EXCEPT
THE TROUGH TRACKS A BIT FARTHER SOUTH IN THE EC.

DESPITE SHORTWAVE RIDGING ON FRIDAY...ANOTHER UPSTREAM TROUGH
APPROACHING THE AREA WILL RESULT IN SOUTHWEST FLOW ACROSS MUCH OF
WESTERN UTAH. THIS WILL ALLOW THE MOISTURE TAP TO CONTINUE...WITH
PWAT INCREASING TO AROUND A HALF INCH BY FRIDAY AFTERNOON PER
GFS/NAM. AS SUCH...ANOTHER ROUND OF SCATTERED SHOWERS WILL BE IN
STORE FOR THE AREA. WITH THE MOISTURE PROVIDING ENOUGH CLOUD COVER
TO REDUCE SURFACE HEATING AND WITH THE AIRMASS COOLING
SLIGHTLY...EXPECT TEMPERATURES TO START TRENDING GRADUALLY DOWNWARD
FOR THE LATTER PART OF THE WEEK.

.LONG TERM (AFTER 00Z SATURDAY)...GENERAL CONSENSUS IN GLOBAL MODELS
CONTINUE TO SUGGEST UNSETTLED AND SLIGHTLY COOLER CONDITIONS ACROSS
MUCH OF THE AREA THROUGH SATURDAY AS A RELATIVELY MOIST
NORTHWESTERLY FLOW WITH EMBEDDED SHORT WAVE ENERGY SETS UP. DECENT
CURVATURE IN H5 FIELDS COUPLED WITH PASSAGE OF WEAK SHORT WAVE
ENERGY AND H7 CAA WOULD IMPLY POTENTIAL FOR PERIODS OF MORE FOCUSED
PRECIP...BEST BET ON TIMING THIS WOULD BE SATURDAY AFTERNOON THOUGH
SOME SPREAD IN GLOBALS REMAIN REGARDING DETAILS IN TRACK/TIMING OF
THIS MID/UPPER FORCING. HAVE CONTINUED TO UP POPS FOR SATURDAY AND
MAINTAINED A COOLING TREND IN TEMPS.

HIGH PRESSURE IS EXPECTED TO BUILD INTO AND THROUGH THE EASTERN
GREAT BASIN STATES LATE WEEKEND INTO EARLY NEXT WEEK. THIS
SAID...MODELS BECOME OUT OF PHASE EARLY/MID WEEK AS THE GFS
CONTINUES TO SIGNIFY A BROAD LONG WAVE TROUGH TRANSITIONING INTO THE
PACNW STATES...WHILE THE ECMWF PLACES A RIDGE AXIS OF DECENT
AMPLITUDE ALONG THE WEST COAST. NEEDLESS TO SAY CONFIDENCE IN EVEN
THE LARGE SCALE PATTERN EVOLUTION AT THAT TIME IS LOW.

&&

.AVIATION...OPERATIONAL WEATHER CONCERNS WILL REMAIN MINIMAL AT THE
KSLC TERMINAL TODAY. LIGHT SOUTHEAST SURFACE WINDS ARE EXPECTED TO
SWITCH TO THE NORTHWEST BETWEEN 18-20Z PER NORM...AND VFR CONDITIONS
WILL BE MAINTAINED UNDER LARGELY CLEAR SKIES.

&&

.FIRE WEATHER...A WEAK UPPER LOW OVER SOUTHERN CALIFORNIA WILL BEGIN
TO SPREAD MOISTURE IN FROM THE SOUTH TODAY. ISOLATED TO WIDELY
SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO BUILD OVER THE
TERRAIN OF THE SOUTH THIS AFTERNOON THEN GRADUALLY SPREAD NORTH INTO
CENTRAL PORTIONS OF THE DISTRICT TONIGHT AS THE LOW MOVES NORTHEAST
INTO SOUTHERN NEVADA. THIS LOW WILL THEN SLOWLY CHURN EAST THROUGH
THE DESERT SOUTHWEST THROUGH THURSDAY MAINTAINING PRIMARILY
DIURNALLY DRIVEN SHOWER AND THUNDERSTORM THREATS DURING THE
AFTERNOON/EVENING EACH DAY. A TRAILING DISTURBANCE WILL LIKELY
SPREAD MORE WIDESPREAD PRECIP INTO THE AREA SATURDAY BEFORE HIGH
PRESSURE BUILDS BACK INTO THE EASTERN GREAT BASIN FOR THE LATTER
HALF OF THE WEEKEND.

&&

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

$$

CHENG/MERRILL

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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