212  
FXUS66 KOTX 181721  
AFDOTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SPOKANE WA  
ISSUED BY NATIONAL WEATHER SERVICE PENDLETON OR  
920 AM PST SAT NOV 18 2017  
   
SYNOPSIS
 
 
DRY CONDITIONS AND SEASONABLE TEMPERATURES WILL PREVAIL TODAY AND  
TONIGHT. PRECIPITATION CHANCES WILL INCREASE SUNDAY AFTERNOON  
INTO SUNDAY NIGHT. MODERATE TO HEAVY MOUNTAIN SNOW IS EXPECTED  
SUNDAY NIGHT OVER THE CASCADES AND MONDAY IN THE IDAHO PANHANDLE  
MOUNTAINS. A MILD AND WET STORM SYSTEM TUESDAY INTO WEDNESDAY WILL  
BRING ANOTHER ROUND OF RAIN TO THE REGION.  
 

 
   
DISCUSSION
 
A LOW AMPLITUDE MID/UPPER RIDGE WILL CROSS THE  
REGION TODAY, FLATTENING OUT TONIGHT INTO EARLY SUNDAY. EXPECT  
DRY CONDITIONS AND SEASONABLE TEMPERATURES AREA WIDE UNDER THIS  
REGIME. NO SIGNIFICANT CHANGES TO THE ONGOING FORECAST IS  
EXPECTED THROUGH TONIGHT.  
 
FOR SUNDAY THROUGH MONDAY NIGHT...A GULF OF ALASKA TROUGH WILL  
DIG OFF THE BC COAST, WITH A SIGNIFICANT SHORTWAVE TROUGH ENTERING  
THE AREA LATE SUNDAY, EXITING INTO WESTERN MT BY MONDAY NIGHT.  
INITIAL PRECIP WILL MOVE INTO THE CASCADES EARLY SUNDAY,  
GRADUALLY SPREADING EAST INTO THE COLUMBIA BASIN SUNDAY  
AFTERNOON/EVENING, AND ACROSS SOUTHEAST WA AND THE CENTRAL ID  
PANHANDLE SUNDAY NIGHT. A DEEP MOIST FLOW WILL RESULT IN A  
SUSTAINED PERIOD OF PRECIP FOR ALL AREAS SUNDAY NIGHT INTO MONDAY.  
STORM TOTAL LIQUID AMOUNTS WILL RANGE FROM 0.75 TO 1.50 INCHES  
FOR THE EAST SLOPES OF THE CASCADES AND THE CENTRAL/NORTHERN ID  
PANHANDLE MOUNTAINS, TO 0.25 TO 0.50 INCHES FOR THE FOOTHILLS, AND  
0.10 TO 0.25 INCHES FOR THE COLUMBIA BASIN. SIGNIFICANT MOUNTAIN  
SNOWS WILL BE POSSIBLE DOWN TO PASS LEVELS AND WILL MONITOR FOR  
WINTER WEATHER HIGHLIGHTS.  
 
MONDAY NIGHT THROUGH FRIDAY...STORM SYSTEM RESPONSIBLE FOR THE  
WET AND SNOWY WEATHER SUNDAY NIGHT/MONDAY MOVES TREKS AWAY TO THE  
SOUTHEAST AND IN TURN ITS CONNECTION TO SUBTROPICAL MOISTURE MAKES  
A SIMILAR EXIT AWAY FROM THE AREA. THE SITUATION GETS A BIT  
COMPLICATED HOWEVER DUE TO MODEL DIFFERENCES AS THE GFS ALLOWS FOR  
A DISTINCT 12 HOUR OR SO BREAK DUE TO TRANSIENT SHORTWAVE RIDGING  
WHILE THE MORE FAVORED ECMWF PASSES YET ANOTHER DISTURBANCE  
THROUGH THE AREA. WILL CONTINUE THE STRATEGY UTILIZED IN THE  
PREVIOUS FORECAST BY UTILIZING A BLEND OF THE TWO WHICH WILL FOCUS  
THE HIGHER POPS PRIMARILY OVER THE SOUTHERN PORTION OF THE  
FORECAST AREA MONDAY NIGHT. A WELL MAINTAINED SIGNIFICANT  
SUBTROPICAL MOISTURE FEED OFF THE COAST GETS BETTER RESOLVED  
TUESDAY AND BY TUESDAY AFTERNOON THERE ARE HINTS FROM EARLIER  
MODELS THAT THE TIP OF THE MOISTURE STREAM MAY MAKE ENOUGH  
PROGRESS EASTWARD TO STREAM MOISTURE NORTHEAST AND OVER THE NORTH  
CASCADES AND SOME DISTANCE INTO THE COLUMBIA BASIN AND OKANOGAN  
HIGHLANDS. THE PLUME HAS A GOOD NORTH TO SOUTH ORIENTATION TO IT  
SUCH THAT BY TUESDAY NIGHT INTO WEDNESDAY THERE WILL BE MINIMAL TO  
NO DOWNSLOPING EFFECT IN THE LEE OF THE CASCADES WHEN A LOW  
PRESSURE SYSTEM TIED INTO THE PLUME PASSES THROUGH. THIS WILL  
RESULT IN SUBSTANTIAL PRECIPITATION WITH VERY HIGH SNOW LEVELS (AS  
HIGH AS 7-9 THOUSAND FEET MSL) AND WARM TEMPERATURES. THIS WARM  
WET RAINFALL WILL AID IN COMPACTING THE MOUNTAIN SNOW AT HIGHER  
ELEVATIONS AND MAY WORK TO ERODE A GOOD AMOUNT OF IT FROM ABOUT  
4500 FEET MSL AND BELOW. IN FACT THE SEVEN DAY TEMPERATURE  
FORECAST SHOULD PEAK WITH WEDNESDAYS HIGH TEMPERATURE. THE RAIN  
AND THE RESULTING MOUNTAIN RUNOFF IS LIKELY TO RESULT IN HIGHER  
STREAMFLOW WEDNESDAY AND THURSDAY BUT THERE IS ENOUGH SNOW IN THE  
MOUNTAINS TO ABSORB A SIGNIFICANT QUANTITY OF THE SNOW AND SLOW  
THE RUNOFF TO JUST RESULT IN A SLIGHT BUMP IN TERMS OF STREAMFLOW  
INCREASE BUT NOTHING TO SUGGEST ANY MAIN STEM RIVER FLOODING. POPS  
REMAIN SOMEWHAT HIGH FOR WEDNESDAY NIGHT INTO THURSDAY AS THERE  
MODELS HINT AT ADDITIONAL DISTURBANCES DIGGING INTO THE WEAKENING  
REMNANTS OF THE PLUME REMAINING OFF THE COAST BUT GOING WITH THE  
IDEA THAT THE MOISTURE PLUME IS PRETTY MUCH WORN OUT AT THIS POINT  
IN TIME THE EXPECTATION IS SOME SLIGHT COOLING AND LOWERING OF  
SNOW LEVELS SHOULD TAKE PLACE. WILL SHOW A FURTHER DECREASE IN  
POPS COUPLED WITH SOME WARMING FOR THURSDAY NIGHT INTO FRIDAY AS  
MODELS HINT AT DISTURBANCES DIGGING SOUTHWARD IN THE LARGE  
OFFSHORE TROF THAT COULD FURTHER INTERRUPT/DIVERT ANY MOISTURE  
STREAM POSITIONED BETWEEN THE LARGE OFFSHORE TROF AND NARROW  
INLAND RIDGING WHICH WOULD LIMIT THE MOISTURE ANY DISTURBANCES  
PASSING THROUGH EASTERN WASHINGTON AND NORTHERN IDAHO WOULD HAVE  
TO WORK WITH.  
 

 
   
AVIATION
 
18Z TAFS: A FLAT RIDGE WILL PERSIST THROUGH SUNDAY WITH  
ABUNDANT MID AND HIGH LEVEL CLOUDS PASSING THROUGH THE REGION. AREAS  
OF MVFR CONDITIONS DUE TO STRATUS ARE DISSIPATING THIS MORNING. DC  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
SPOKANE 43 30 44 36 44 34 / 0 0 20 90 40 30  
COEUR D'ALENE 41 30 43 35 42 33 / 0 0 20 90 50 30  
PULLMAN 44 32 47 36 46 37 / 0 0 10 100 60 40  
LEWISTON 49 32 50 40 51 39 / 0 0 10 90 60 40  
COLVILLE 39 28 40 33 41 32 / 0 10 50 100 50 20  
SANDPOINT 39 27 41 34 39 30 / 10 0 20 100 60 30  
KELLOGG 38 26 42 32 39 33 / 10 0 10 100 80 40  
MOSES LAKE 46 29 46 35 48 31 / 0 0 20 60 10 10  
WENATCHEE 44 31 43 33 45 33 / 0 0 30 50 10 10  
OMAK 41 30 40 31 42 33 / 0 10 50 70 10 10  
 

 
   
OTX WATCHES/WARNINGS/ADVISORIES
 
 
ID...NONE.  
WA...NONE.  

 
 

 
 
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