Area Forecast Discussion
Issued by NWS Pocatello, ID

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521
FXUS65 KPIH 060220
AFDPIH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
820 PM MDT THU MAY 5 2016

.UPDATE...TEMPERATURES THIS EVENING HAVE ALREADY DROPPED 5 TO 8
DEGREES FROM THE HIGHS THIS AFTERNOON AND THE FIRST SPOKE OF
ENERGY OFF THE LOW ENTERING CALIFORNIA HAS MOVED NORTH...SO HAVE
REMOVED MENTION OF THUNDERSTORMS FOR THE NEXT FEW HOURS. THE NEXT
SPOKE SWINGS NORTH TO NEAR THE SOUTHERN IDAHO BORDER CLOSE TO
SUNRISE. MOISTURE WILL BE INCREASING AND AIRMASS BECOMES MORE
UNSTABLE EARLY SO A SLIGHT CHANCE OF THUNDERSTORMS IN THE SOUTH
CENTRAL HIGHLANDS AND NORTHERN WASATCH WAS INCLUDED IN THE
FORECAST. RS

&&

.PREV DISCUSSION... /ISSUED 112 PM MDT THU MAY 5 2016/

SHORT TERM...TONIGHT THROUGH SUNDAY.
UPPER LOW OFF THE CALIFORNIA COAST PUSHES INLAND TONIGHT AND INTO
SOUTHERN UTAH BY SATURDAY. SOUTHERLY FLOW AHEAD OF THIS LOW WILL
SPREAD EXTENSIVE MOISTURE INTO IDAHO. MOST ACTIVITY TO WEST TODAY
AND THIS EVENING EXPECT NOTHING MORE THAN ISOLATED SHOWERS AND
THUNDERSTORMS MAINLY IN THE EASTERN HIGHLANDS. EXPECT SHOWER
ACTIVITY TO INCREASE OVERNIGHT WITH WIDESPREAD SHOWERS AND
THUNDERSTORMS EXPECTED FRIDAY AFTERNOON. INCLUDED POTENTIAL FOR
HEAVY RAIN AND SMALL HAIL FRIDAY AFTERNOON AND EARLY EVENING.
EXPECT WIDESPREAD SHOWERS AND THUNDERSTORMS TO CONTINUE FRIDAY
NIGHT AND SATURDAY AS WELL. THE REGION IS IN A MARGINAL RISK FOR
SEVERE THUNDERSTORMS FRIDAY SO MONITOR CONDITIONS CLOSELY FRIDAY
AFTERNOON.  EXPECT LINGERING SHOWER AND THUNDERSTORM ACTIVITY
SUNDAY AS WELL BUT NOT NEARLY AS WIDESPREAD AS FRIDAY AND
SATURDAY. TEMPERATURES WILL BEGIN TO COOL OFF WITH WIDESPREAD
CLOUD COVER AND RAIN WITH HIGHS DROPPING TO NEAR NORMAL BY
SATURDAY AND SUNDAY. COULD SEE SOME STRONG EAST TO NORTHEAST WINDS
ESPECIALLY IN THE NORTHERN SNAKE PLAIN AS WELL LATE FRIDAY.
GK

LONG TERM...SUN NIGHT THROUGH NEXT THU NIGHT. EXTREMELY WET
CONDITIONS FROM THE NEARBY CLOSED LOW OF THE NEAR TERM FORECAST WILL
TURN EASTWARD IN ITS MOVEMENT AND AFTER SUN NIGHT WILL HAVE
CONSIDERABLY LESS PRECIPITATION AND CLOUDS. HOWEVER...THE TIMING OF
AN UPSTREAM LOW IN THE NORTHERN BRANCH OF THE JETSTREAM HAS CHANGED
SIGNIFICANTLY...CONTINUING A TREND FROM THE PREVIOUS GUIDANCE RUN.
IT IS ARRIVING FASTER AND DIGGING FARTHER SOUTH...ON BOTH THE GFS
AND THE ECMWF...AND PRODUCING A WETTER AND COLDER FORECAST THAN
PREVIOUS THINKING. HAVE INCREASED POPS AND CLOUDS FOR THE PERIOD MON
AFTERNOON/EVE THROUGH WED MORNING TO MATCH THE PRESENT TRENDS. TUE
MAY NOW BE THE COLDEST DAY OF THE NEXT SEVEN WITH THIS COLD-CORE LOW
AND NORTHERLY AIRFLOW ONCE THE CENTER HAS PASSED TO THE EAST. SNOW
LEVELS COULD DROP TO MID-SLOPES ON MOUNTAINS...ESPECIALLY ALONG THE
ID-MT BORDER. MON STILL LOOKS WINDY OR VERY WINDY AS A SPEED MAX
MOVES ALONG THE SOUTHERN BOTTOM END OF THE CLOSED LOW AND RIGHT
OVERHEAD OF THE SOUTHWEST ZONES IN THE FORECAST AREA. MESSICK

AVIATION...LOW APPROACHING FROM THE SOUTH HAS DEVELOPED SOME LOW-
LEVEL WINDSHEAR WITH SOUTH WIND ALOFT AND NORTH WIND AT THE
SURFACE...BUT THE SURFACE WIND SHOULD WEAKEN. THEY WILL SHIFT TO THE
SOUTH AND INCREASE DURING THE EVENING. ONLY SCATTERED LIGHT -SHRA
EXPECTED DURING THE AFTERNOON AND EVENING...AND MAINLY EVENING. THE
DELAY OF THE PRECIPITATION MEANS THAT KBYI AND KPIH WILL LIKELY MISS
TS ACTIVITY AND SO HAVE REDUCED THEM TO VCSH PHRASING...BUT
INSTABILITY LASTS LONGER FOR KIDA AND SO HAVE KEPT A BRIEF PERIOD OF
VCTS THERE. GUSTY SOUTHERLY WIND OVERNIGHT...ESPECIALLY FOR KBYI AND
KPIH WITH SOME DOWNSLOPE/FOEHN WIND EFFECTS. THE -SHRA AND -TSRA
SHOULD DEVELOP DURING THE AFTERNOON ON FRI...WITH ALL AIRDROMES IN
THE THREAT AREA FOR TSRAGR WITH GUSTS TO 60KT NEAR CB CLOUDS. MESSICK

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$



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