Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 161037
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
437 AM MDT TUE SEP 16 2014

.SYNOPSIS...HIGH PRESSURE ALOFT CENTERED ACROSS UTAH WILL SHIFT
EAST OF THE STATE LATE WEDNESDAY. TROPICAL MOISTURE POOLED TO THE
SOUTH OVER ARIZONA WILL SPREAD INTO SOUTHERN UTAH WEDNESDAY NIGHT
AND THEN COVER MUCH OF UTAH THURSDAY THROUGH THURSDAY NIGHT.

&&

.SHORT TERM (THROUGH 06Z SATURDAY)...HIGH PRESSURE ALOFT ACROSS
THE INTERIOR WEST WILL CONTINUE TO STRENGTHEN AS IT GRADUALLY
SHIFT EAST THROUGH WEDNESDAY. THIS EVENTUAL SHIFT OF THE UPPER
RIDGE TO THE EAST WILL OPEN UP THE GREAT BASIN FOR A NORTHWARD
SURGE OF TROPICAL MOISTURE ASSOCIATED WITH ODILE WEDNESDAY NIGHT
THROUGH THURSDAY.

A SLOW BUT STEADY INCREASE IN MOISTURE THE PAST COUPLE OF DAYS HAS
BROUGHT PWAT VALUES UP INTO /.70/ TO /.80/ INCH RANGE ACROSS MUCH
OF THE STATE. THE RESULT OF THIS INCREASED MOISTURE HAS BEEN FOR
A MODEST INCREASE IN WEAK CONVECTION WITH LIGHT SHOWERS AND/OR
VIRGA AND ONE OR TWO THUNDERSTORMS DURING THE AFTERNOON AND EARLY
EVENING HOURS. SUSPECT THIS TREND WILL CONTINUE THROUGH WEDNESDAY.

THE FOCUS WILL SHIFT TO THE IMPACTS BROUGHT ABOUT BY NOW TROPICAL
STORM ODILE. THIS TROPICAL STORM CURRENTLY MAKING ITS WAY INTO THE
NORTHERN GULF OF CALIFORNIA IS FORECAST TO CONTINUE NORTHEAST
INTO SOUTHEAST ARIZONA...THEN TURN EAST ACROSS NEW MEXICO BY
THURSDAY. MODEL GUIDANCE MAINTAINS A FAIRLY WELL-DEFINED
CIRCULATION CENTER WITH THIS STORM AS IT CROSSES INTO SOUTHEAST
ARIZONA. THE MEAN LAYER EASTERLIES ON THE NORTH SIDE OF THE CENTER
ACROSS NORTHERN ARIZONA WILL SERVE TO HOLD THE TROPICAL MOISTURE
NEAR THE UTAH/ARIZONA BORDER AND POINTS SOUTH THROUGH THE DAY
WEDNESDAY.

THE TROPICAL MOISTURE SHOULD FINALLY BE TAPPED WEDNESDAY NIGHT
AHEAD OF THE ADVANCING MID-LEVEL EASTERN PACIFIC TROUGH ARRIVING
ALONG THE WEST COAST. THE LATEST GFS AND ECMWF FROM THE 00Z RUN
PAINT A SIMILAR PICTURE WITH THE TROUGH REACHING THE WESTERN GREAT
BASIN LATE THURSDAY NIGHT...THEN SPLITTING ON FRIDAY WITH A CLOSED
LOW DEVELOPING SOMEWHERE AROUND THE SOUTHERN CALIFORNIA AREA
FRIDAY NIGHT.

THE INCREASING TROPICAL MOISTURE AHEAD OF THE ADVANCING TROUGH
WILL SPAWN A RAPID INCREASE IN CONVECTIVE PRECIP ACROSS MAINLY
THE WESTERN HALF OF UTAH THURSDAY THROUGH THURSDAY NIGHT. THE
INITIAL PERIOD OF THE SURGE WORKING IN CONCERT WITH ANY WEAK
SHORTWAVE EJECTING OUT AHEAD OF THE MAIN TROUGH SHOULD PRODUCE
SHOWERS AND STORMS CAPABLE OF ISOLATED HEAVY AND INTENSE RAINFALL
ACROSS SOUTHWEST AND/OR WEST-CENTRAL UTAH LATE THURSDAY AFTERNOON
AND EVENING.

THE FOCUS FOR WIDESPREAD AND POTENTIALLY HEAVY RAINFALL SHOULD
SHIFT INTO NORTHERN UTAH LATE THURSDAY NIGHT THROUGH FRIDAY. AT
THAT TIME THE NORTHERN PORTION OF THE SPLITTING TROUGH WILL BE
SHEARING EAST ACROSS NORTHERN UTAH...SUPPLYING THE NECESSARY
DYNAMIC AND THERMAL SUPPORT FOR DECENT SYNOPTIC-SCALE LIFT. A
FAVORABLE POSITION OF THE EXIT REGION TO THE UPPER JET MAY ALSO
SUPPORT STRONG CONVECTION LATE THURSDAY NIGHT THROUGH EARLY FRIDAY
MORNING.

DRIER AND MORE STABLE AIR BEHIND THE TROUGH WILL BRING AN END TO
MOST CONVECTIVE PRECIP ACROSS NORTHERN UTAH FRIDAY NIGHT. THE
REMAINDER OF UTAH WILL REMAIN IN A STILL MOIST ENVIRONMENT WITH
SCATTERED AREAS OF LIGHT TO MODERATE PRECIP EXPECTED FRIDAY
EVENING.

&&

.LONG TERM (AFTER 06Z SATURDAY)...SIGNIFICANT DIFFERENCES IN GLOBAL
GUIDANCE REMAIN REGARDING THE EVOLUTION OF THE PACIFIC TROUGH
CLOSING OFF TO OUR SOUTHWEST FOR FRIDAY NIGHT THROUGH THE UPCOMING
WEEKEND. THE 00Z ECMWF CONTINUES TO HOLD/RETROGRESS THIS LOW OFF
THE CALIFORNIA COAST INTO EARLY NEXT WEEK...MAINTAINING A DRY
FORECAST LOCALLY THROUGH THE WEEKEND. THE GFS IN CONTRAST HINTS AT
THIS LOW REMAINING NEARLY STATIONARY OVER SOUTHERN CALIFORNIA...
ALLOWING MOISTURE TO BE DRAWN BACK NORTH INTO SOUTHERN UTAH
SUNDAY BEFORE OPENING UP THE LOW AND LIFTING IT NORTHWARD THROUGH
THE AREA SUNDAY NIGHT. LEFT SLIGHT CHANCE POPS ACROSS PRIMARILY
THE SOUTHERN THIRD TO ACCOUNT FOR THIS BUT DO NOT HAVE MUCH
CONFIDENCE AT ALL AS MANY GEFS MEMBERS SUPPORT THE ECMWF. THE
ECMWF SUGGESTS ANY NET INCREASE TO POPS HOLDS OFF UNTIL TUESDAY
AFTERNOON AND WOULD NOT BE SURPRISED IF THIS SLOWER SOLUTION PANS
OUT EVENTUALLY.

&&

.FIRE WEATHER...HIGH PRESSURE STRENGTHENING ACROSS THE REGION FROM
THE SOUTH WILL KEEP TEMPERATURES QUITE WARM FOR THIS TIME OF YEAR.
READINGS WILL CONTINUE TO RUN 5 TO 10 DEGREES ABOVE NORMAL. THE
PEAK HEATING HOURS WILL AID A FEW MOUNTAIN BUILDUPS ACROSS THE
UINTAS SOUTH TO THE SOUTHERN MOUNTAINS TODAY/TOMORROW. THE WETTING
RAIN POTENTIAL WILL REMAIN LOW AS THESE STORMS SHOULD REMAIN QUITE
SHALLOW IN NATURE AND DRY SURFACE CONDITIONS WILL PERSIST. DEEPER
TROPICAL MOISTURE WILL BE DRAW NORTH AHEAD OF AN APPROACHING
PACIFIC TROUGH THURSDAY/FRIDAY. THIS MOISTURE WILL INCREASE THE
POTENTIAL FOR WETTING RAINS ACROSS MUCH OF THE DISTRICT LATE IN
THE WEEK.

&&

.AVIATION...OPERATIONAL WEATHER CONCERNS ARE EXPECTED TO REMAIN
MINIMAL AT THE KSLC TERMINAL THROUGH THE VALID TAF PERIOD. SOUTHEAST
SURFACE WINDS ARE EXPECTED TO SWITCH TO THE NORTHWEST BETWEEN 19-20Z
PER NORM AND VFR CONDITIONS WILL HOLD UNDER MOSTLY CLEAR SKIES.

&&

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

$$

CONGER/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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