Area Forecast Discussion
Issued by NWS Boise, ID

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000
FXUS65 KBOI 280330
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
830 PM MST TUE JAN 27 2015

.DISCUSSION...AT 8 PM MST LIGHT PCPN IN IDAHO SOUTH AND EAST OF A
LINE THROUGH THE OWYHEES...BOISE...IDAHO CITY...STANLEY.  THE PCPN
WAS SPREADING NNE AS A WEAK UPPER LOW IN NRN NV MOVES TOWARD
YELLOWSTONE BY MIDNIGHT...AND THEN INTO MONTANA OVERNIGHT AS A
WEAKENING OPEN TROUGH.  CURRENT FORECAST DESCRIBES TRENDS WELL.
HIGH PRESSURE ALOFT WILL REBUILD BEHIND THE DEPARTING TROUGH.  LOW
LEVEL MOISTURE AND THE INVERSION WILL HELP DEVELOP VALLEY FOG AGAIN
TONIGHT BUT HIGHER CLOUDS WILL OPPOSE DEVELOPMENT...SO PATCHY FOG IS
A REASONABLE FORECAST.  FOG AGAIN WEDNESDAY NIGHT...POSSIBLY MORE
THAN CURRENTLY FORECAST BUT WILL LEAVE THAT TO THE NEXT CREW WITH
ALL THE 00Z GUIDANCE.

&&

.AVIATION...MVFR/IFR AND LOCAL LIFR CONDITIONS IN FOG AND STRATUS
WILL PERSIST THROUGH WEDNESDAY MORNING ACROSS SOUTHWEST IDAHO...
MAINLY FROM KBOI EAST AND SOUTH. EXPECT AREAS OF LIGHT RAIN...WITH
SNOW ABOVE 7K FT MSL...UNTIL AROUND 09Z. ALSO EXPECT PATCHY IFR/LIFR
STRATUS AND FOG IN EASTERN OREGON INCLUDING THE KBNO AREA. SURFACE
WINDS...LIGHT AND VARIABLE. WINDS ALOFT...NORTHWEST 10-20 KTS UP
THROUGH 10K FT MSL.

&&

.PREV DISCUSSION...
SHORT TERM...TONIGHT THROUGH THURSDAY...VISIBILITY HAS IMPROVED
OVER THE TREASURE VALLEY...BUT FOG AND LOW STRATUS REMAIN. BOISE
SOUNDING FROM THIS MORNING STILL SHOWING A STRONG INVERSION BUT
SOME UNCERTAINTY IF THE DENSE FOG WILL REDEVELOP TONIGHT AS CLOUDS
CONTINUE TO INCREASE OVER THE AREA AHEAD OF AN APPROACHING WEAK
UPPER LEVEL LOW. WILL KEEP A MENTION OF PATCHY FOG IN THE FORECAST
FOR THE SNAKE RIVER VALLEY BUT THERE COULD BE ISOLATED POCKETS OF
DENSE FOG. SATELLITE AND RADAR SHOWING THE WEAK UPPER LEVEL LOW
CONTINUING TO MOVE NORTH WITH PRECIPITATION ALREADY SPREADING
INTO SOUTHWEST IDAHO ALONG THE NEVADA BORDER. BULK OF THE
PRECIPITATION WITH THIS SYSTEM WILL BE MAINLY OVER EASTERN IDAHO
WITH THE HIGHEST CHANCE OF PRECIPITATION IN THE MAGIC VALLEY...
DECREASING WEST AND NORTH TOWARD THE IDAHO/OREGON BORDER WITH DRY
CONDITIONS OVER SOUTHEAST OREGON. PRECIPITATION WILL DECREASE OVER
THE AREA WEDNESDAY MORNING WITH DECREASING CLOUDS THROUGH THE DAY.
SKIES WILL LIKELY CLEAR ENOUGH OVER SOUTHEAST OREGON AND THE LOWER
TREASURE VALLEY WEDNESDAY NIGHT ALLOWING FOR FOG TO REDEVELOP.
EXPECT TEMPERATURES TO REMAIN ABOVE NORMAL THROUGH THURSDAY.

LONG TERM...THURSDAY NIGHT THROUGH TUESDAY...MODELS ARE IN ABOVE-
AVERAGE AGREEMENT THROUGH SUNDAY. AN UPPER LEVEL LOW WILL MOVE
THROUGH THE DESERT SW...LEAVING US IN WEAK FLOW ALOFT THU NIGHT AND
FRI. NW FLOW ON THE EAST SIDE OF AN INCOMING RIDGE TAKES HOLD
SATURDAY...BRINGING DRY CONDITIONS INTO SUNDAY. WHILE BOTH THE EC
AND GFS BRING MOISTURE INTO THE REGION SUNDAY NIGHT...THEY DIVERGE
IN THE THICKNESS FIELD STARTING SUNDAY. FOR THE CHANCE OF PRECIP WE
ARE FORECASTING FOR SUNDAY NIGHT THROUGH TUE...THE ECM INDICATES IT
MIGHT BE COLD ENOUGH FOR SNOW IN THE SNAKE RIVER VALLEY...WHILE THE
GFS INDICATES RAIN. FOR NOW...HAVE SPLIT THE DIFFERENCE AND GONE
WITH RAIN. WE HAVE NOT PUT FOG OR STRATUS IN THE VALLEYS IN THE LONG
TERM...BUT THE CHANCE FOR FOG IS THERE.  IT WILL DEPEND IN PART ON
HOW MUCH PRECIPITATION IS GENERATED BY THE SYSTEM MOVING THROUGH
TONIGHT.

&&

.AIR STAGNATION...INVERSION WILL WEAKEN TONIGHT AS CLOUDS AND
PRECIPITATION SPREAD OVER THE AREA. MIXING HEIGHTS WILL REMAIN
BELOW 2000 FEET AGL AT LEAST THROUGH THURSDAY. ANY RAINFALL WILL
INCREASE SURFACE MOISTURE AND WILL AID IN THE REDEVELOPMENT OF
FOG AND LOW CLOUDS ACROSS LOWER VALLEYS.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
OR...NONE.

&&

$$

WEATHER.GOV/BOISE

DISCUSSION...LC
AVIATION.....JT
PREV SHORT TERM...JA
PREV LONG TERM....SP/WH
AIR STAGNATION....JA



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