FXUS65 KSLC 151217
AFDSLC
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
510 AM MST TUE DEC 15 2009
.SYNOPSIS...HIGH PRESSURE WILL REMAIN OVER THE AREA INTO THE
WEEKEND. HOWEVER...MOIST WESTERLY FLOW THROUGH THE NORTHERN
INTERMOUNTAIN REGION WILL ALLOW A SERIES OF WEAK STORM SYSTEMS TO
GRAZE NORTHERN UTAH TODAY THROUGH THURSDAY.
&&
.DISCUSSION...FLAT UPPER LEVEL RIDGE REMAINS IN PLACE OVER THE GREAT
BASIN THIS MORNING. MID-LEVEL ISENTROPIC UPGLIDE WILL CONTINUE INTO
TONIGHT AS MOISTURE OVERSPREADS FAR NORTHERN UTAH. ANTICIPATE
INCREASING CLOUD COVER ACROSS THE NORTH TODAY WITH A CHANCE OF
PRECIPITATION IN THE EXTREME NORTH BY LATE THIS AFTERNOON.
GFS AND NAM CONTINUE TO INDICATE VERY MODEST FORCING AS SEVERAL WEAK
SHORTWAVES GRAZE FAR NORTHERN UTAH OVER THE NEXT SEVERAL DAYS.
AIRMASS IS RATHER STABLE...SO RESPONSE TO MINIMAL FORCING SHOULD NOT
BE PARTICULARLY ROBUST. ALL OF THESE WEAK WAVES ARE MOVING THROUGH
THE MEAN RIDGE POSITION IN THE GREAT BASIN. WITH A STRONG SURFACE
HIGH IN PLACE ACROSS WESTERN COLORADO AND EASTERN UTAH AND THE UPPER
LEVEL RIDGE OVER THE GREAT BASIN THESE WAVES ARE ABLE TO BASICALLY
TOP THE RIDGE WITH VERY LITTLE SOUTHWARD PUSH.
HOWEVER...VERY MOIST FLOW WILL CONTINUE ACROSS THE FAR NORTH
THROUGH WEDNESDAY NIGHT AND WILL CONTINUE WITH IDEA OF SLIGHT TO LOW
CHANCE VALLEYS POPS IN THE FAR NORTH WITH A LITTLE HIGHER POPS IN
THE FAR NORTHERN MOUNTAINS. THE GREATEST THREAT FOR DECENT
PRECIPITATION AMOUNTS WOULD APPEAR TO BE IN THE RAFT RIVER RANGE IN
THE NORTHWEST CORNER OF THE STATE. THE PERIODS WITH THE BEST CHANCE
TO PRODUCE PRECIPITATION OVER A LITTLE LARGER AREA...EVEN IF IT IS
LIGHT...APPEAR TO BE TONIGHT AND WEDNESDAY NIGHT WHEN BOTH THE GFS
AND NAM INDICATE MODEST 500-300 MB DIV-Q FORCING AS WEAKENING
SHORTWAVES MOVE ACROSS NORTHERN UTAH. VALLEY PRECIPITATION TYPE
REMAINS A BIT TRICKY WITH SOME AREAS BEING MIXED OUT WHILE OTHERS
REMAIN INVERTED.
FOG CONTINUES IN NUMEROUS INVERTED VALLEYS THIS MORNING AND BELIEVE
THAT AREAS SUCH AS THE UINTA BASIN AND CACHE VALLEY WILL HAVE A
DIFFICULT TIME MIXING OUT OVER THE NEXT SEVERAL DAYS. WITH THE
INVERSION IN PLACE IN SEVERAL AREAS HAVE CONTINUED THE MENTION OF
FOG IN THESE AREAS OVER THE NEXT COUPLE OF DAYS. HOWEVER...IT WOULD
SEEM THAT WITH THE INCREASE MID AND HIGH CLOUD COVER THE THREAT
WOULD DIMINISH WITH TIME.
GFS AND ECMWF REMAIN IN DECENT AGREEMENT THROUGH FRIDAY AS SHARP
RIDGE BUILDS OVER THE GREAT BASIN TOWARD THE END OF THE WEEK. THE
00Z GFS WAS MUCH FASTER BRINGING THE LARGE SCALE RIDGE INTO THE
GREAT BASIN OVER THE WEEKEND AS AN UPPER LEVEL TROUGH EJECTED
NORTHEAST OUT OF THE GREAT LAKES REGION. THIS ALLOWED UPPER LOW TO
MOVE INTO THE PACIFIC NW OVER THE WEEKEND AND INTO THE GREAT BASIN
EARLY IN THE WEEK. HOWEVER...THE 06Z GFS RUN TRENDED STRONGLY
TOWARD THE 00Z ECMWF SOLUTION AND IS NOW KEEPING THE RIDGE IN PLACE
OVER THE GREAT BASIN INTO EARLY NEXT WEEK. HOWEVER...CONFIDENCE IN
THE ULTIMATE EVOLUTION OF THE PATTERN EARLY NEXT WEEK REMAINS A BIT
LOW AS THE ECMWF AND GFS ENSEMBLES CONTINUE TO SHOW CONSIDERABLE
SPREAD IN THE TIMING OF THE RIDGE BREAKDOWN IN THE WEST. WITH THIS
UNCERTAINTY IN MIND HAVE NUDGE TOWARD CLIMATOLOGICAL POPS EARLY NEXT
WEEK.
&&
.AVIATION...THE SLC TERMINAL WILL SEE VFR CONDITIONS AND CEILINGS
ABOVE 7000FT AGL THROUGH AT LEAST 21Z TODAY. LOWER CLOUDS WILL MOVE
IN THIS EVENING...WITH A 60 PERCENT CHANCE OF 6000FT CEILINGS OR
LOWER AFTER 00Z WEDNESDAY. SURFACE WINDS ARE EXPECTED TO REMAIN OUT
OF THE SOUTH THROUGH THE DAYLIGHT HOURS TODAY...WITH A 30 PERCENT
CHANCE THAT WINDS WILL SWITCH TO LIGHT NORTHERLY BETWEEN 21Z AND 23Z
TODAY.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...NONE.
WY...NONE.
&&
$$
PUBLIC...GRAHAM
AVIATION...SCHOENING
FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)
