Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 180930
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
330 AM MDT MON MAY 18 2015

.SYNOPSIS...A STORM SYSTEM OVER CENTRAL CALIFORNIA THIS MORNING WILL
MOVE INTO UTAH FROM THE SOUTHWEST AND IMPACT THE STATE LATER
TODAY THROUGH TOMORROW. THE NEXT STORM SYSTEM WILL ARRIVE LATE IN
THE WEEK AND IMPACT MUCH OF UTAH THROUGH AT LEAST THE FIRST HALF
OF THE WEEKEND.

&&

.SHORT TERM (THROUGH 12Z WEDNESDAY)...
WATER VAPOR LOOP SHOWS AN EXPANSIVE CLOSED LOW CENTERED OVER
CENTRAL CALIFORNIA. AMDAR 400-250MB WIND OBSERVATIONS SHOW A
75-115KT CYCLONIC JET FROM THE EASTERN PACIFIC INTO NORTHERN
ARIZONA. GOES/GPS/RAP/00Z SLC RAOB INDICATE THE PRECIPITABLE WATER
VALUE RANGES BETWEEN 0.25"-0.50" MOUNTAINS...TO 0.50"-0.75" ACROSS
THE VALLEYS.

ACTIVE DAY FOR SHOWERS AND THUNDERSTORMS ACROSS THE REGION. PLENTY
OF DYNAMICS WITH INCREASING DIFFLUENCE ALOFT...AND THE EXIT REGION
OF THE UPPER LEVEL JET PIVOTING ACROSS THE FOUR CORNERS THIS
AFTERNOON. RAISED POPS ACROSS THE NORTH AND WEST WHICH SHOULD BE IN
A FAVORABLE POSITION. HIGH RESOLUTION GUIDANCE SUGGESTS MORE
SCATTERED ACTIVITY ACROSS THE SOUTHEAST THIS AFTERNOON. SNOW LEVELS
SHOULD BE BETWEEN 8-9KFT.

SHORT RANGE ENSEMBLES INDICATE SHEAR VALUES RISE SIGNIFICANTLY THIS
AFTERNOON PARTICULARLY ACROSS THE EASTERN ZONES...WITH VALUES ABOVE
30KTS LIKELY AND 40KTS POSSIBLE BY EVENING. THUS...EXPECTING MORE
ORGANIZED AND LONGER LIVED STORMS ACROSS THE EASTERN ZONES...WHERE
HAIL AND STRONG GUSTY WINDS WILL BE POSSIBLE. COLUMN MOISTURE IS
RICH...BUT SURFACE DEWPOINTS ARE LARGELY IN THE 40S. WHILE WARM
CLOUD DEPTH LOOKS MEAGER ON RAP BUFKIT FORECAST SOUNDINGS...CANNOT
RULE OUT A FEW STORMS PROVIDING LOCALLY HEAVY RAINFALL.

EFFECTIVE SHEAR DECREASES SIGNIFICANTLY TUESDAY AS THE COLD CORE OF
THE STORM SYSTEM MOVES OVERHEAD. THE NORTH LOOKS MOST FAVORABLE FOR
CONVECTION BASED ON THE TRACK OF THE MID LEVEL CIRCULATION
CENTER...WITH ACTIVITY MORE ISOLATED CLOSER TO THE ARIZONA BORDER.

.LONG TERM (AFTER 12Z WED)...
SHORT WAVE RIDGING OVER THE AREA WED MORNING WILL RETREAT EWD WED
AFTN AS THE NEXT CLOSED LOW IN THE ERN PAC STARTS TO MOVE INLAND.
CONVECTION WED SHOULD BE MORE ISOLATED AND LIMITED TO THE TERRAIN
BUT ITS FORECAST TO PICK UP WED EVE AND OVERNIGHT AS A SHORT WAVE
EJECTING OUT OF THE UPPER LOW CROSSES THE ERN GREAT BASIN.

GFS AND EC IN PRETTY GOOD AGREEMENT ON TRACKING THIS LOW THRU SRN CA
FRI AND ACROSS NRN AZ FRI NIGHT THEN LIFTING IT THRU ERN UT AND
FORMING A NEW CENTER OVER WY ON SAT. THIS LOW WILL KEEP CONVECTION
QUITE ACTIVE ACROSS THE CWA THU THRU FRI WITH ANOTHER WRAP AROUND
RAIN EVENT FORECAST FOR THE CWA ON SAT. SO HAVE NUDGED POPS UPWARD
THRU THIS TIME FRAME BUT STILL KEPT COVERAGE IN THE SCATTERED
CATEGORY FOR NOW.

MODELS THEN DIVERGE AFTER SAT WITH THE EC FARTHER SOUTH WITH THE
EVOLUTION OF A CLOSED LOW THAT ENTERS THE PACNW STATES SAT NIGHT.
THE EC DROPS THIS LOW INTO NRN NV BY SUN MORNING AND IT REMAINS MORE
OR LESS IN PLACE INTO MON. THIS KEEPS A COOL SHOWERY PATTERN IN
PLACE ACROSS THE CWA SUN INTO MON. MEANWHILE THE GFS KEEPS THIS LOW
OVER THE PACNW THRU MON WITH A DRIER AND WARMER SWLY FLOW OVER THE
CWA. THIS SOLUTION KEEPS SUN MOSTLY DRY AND GENERATES ONLY ISOLATED
MTN CONVECTION MON. NEITHER SOLUTION IS FAVORED SO HAVE KEPT SOME
LOW POPS IN THE FORECAST SUN/MON AS A COMPROMISE TOWARDS THE EC BUT
CONFIDENCE IS LOW THAT WE WILL SPOIL THE ENTIRE MEMORIAL DAY
WEEKEND.

&&

.AVIATION...VFR CONDITIONS WILL PREVAIL AT THE KSLC TERMINAL. CIGS
SHOULD REMAIN ABV 6000 FT THROUGH THE MORNING THEN WILL OCCASIONALLY
FALL BELOW THAT LEVEL IN SHOWERS AFTER ABOUT 19Z. WINDS WILL BE
MOSTLY SOUTHERLY BUT WILL BE VARIABLE IN DIRECTION AT TIMES DUE TO
PASSING SHOWERS. ISOLATED THUNDERSTORMS ARE POSSIBLE AFTER ABOUT 19Z
AND COULD BRING GUSTY ERRATIC WINDS AS THEY PASS NEAR OR OVER THE
AIRFIELD.

&&

.FIRE WEATHER...COOL AND MOIST CONDITIONS WILL BE THE RULE THROUGH
THE EARLY PORTION OF THE WORK WEEK. CONVECTION WILL BE FAIRLY
WIDESPREAD...PROVIDING A GOOD CHANCE FOR A WETTING RAIN. SNOW LEVEL
IS BETWEEN 8-9KFT.

A WARMING AND DRYING TREND IS FORECAST FOR THE SECOND HALF OF THE
WORK WEEK...THOUGH AFTERNOON SHOWERS AND THUNDERSTORMS WILL REMAIN A
POSSIBILITY.

THE NEXT STORM ARRIVES FOR THE HOLIDAY WEEKEND. EXPECT ANOTHER COOL
AND WET PERIOD ACROSS THE REGION.

&&

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

$$

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

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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