922  
FXUS65 KMSO 261007  
AFDMSO  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MISSOULA MT  
407 AM MDT THU APR 26 2018  
   
DISCUSSION
 
HIGH PRESSURE WILL REMAIN THE DOMINANT FORCE AT PLAY  
THROUGH FRIDAY LEADING TO ABUNDANT SUNSHINE WHICH WILL SUPPORT CONTINUED  
ABOVE NORMAL TEMPERATURES. WHILE RECORD TEMPERATURES WILL REMAIN  
FAR FROM REACH, THE RAPID ASCENT FROM THE 50S LAST WEEKEND TO SOME  
30 DEGREES WARMER BY FRIDAY WILL FEEL DOWNRIGHT HOT TO MANY FOLKS.  
 
A SIGNIFICANT PATTERN CHANGE IS STILL EXPECTED TO BEGIN ON  
SATURDAY, THOUGH TIMING OF THIS SLOWLY APPROACHING COLD FRONT AND  
UPPER LEVEL STORM SYSTEM REMAIN CHALLENGING WITHIN THE LATEST  
MODEL RUNS. WHILE INCREASING HIGH/MID LAYER CLOUDS ARE EXPECTED  
FRIDAY AFTERNOON, LIMITED LOW LEVEL MOISTURE ADVECTION SHOULD  
INHIBIT ANY CONVECTIVE DEVELOPMENT AND THUS CHANCES FOR  
PRECIPITATION WERE TAPERED BACK UNTIL EARLY SATURDAY MORNING  
ACROSS CENTRAL IDAHO AND SATURDAY AFTERNOON ACROSS THE REST OF  
WESTERN MONTANA.  
 
BY SATURDAY AFTERNOON THERE APPEAR TO BE SEVERAL INGREDIENTS  
(VERTICAL WIND SHEAR, UPPER LEVEL JET PLACEMENT, INCREASING LOW  
LEVEL MOISTURE, POSSIBLE ENERGY PULSES & APPROACHING SLOW MOVING  
COLD FRONT) WHICH COULD PROVE FAVORABLE FOR OUR FIRST DECENT  
CHANCE FOR THUNDERSTORM DEVELOPMENT ACROSS THE NORTHERN ROCKIES.  
BUT THESE STORMS SHOULD BE QUITE LIMITED IN STRENGTH GIVEN THE  
TIME OF YEAR AND MAINLY CAPABLE OF GUSTY OUTFLOW WINDS OF 40 MPH  
AND SOME HEAVY RAIN. MODELS DO SUPPORT SLOW MOVING CONVECTION  
DEVELOPING AND PRODUCING THE FIRST AREA OF HEAVIER PRECIPITATION  
ALONG THE IDAHO/MONTANA BORDER, BITTERROOT & PARTS OF SW MONTANA  
SATURDAY NIGHT INTO SUNDAY MORNING.  
 
SUNDAY AND MONDAY CAN BE SUMMED UP WITH TWO WORDS: WET AND COOL.  
THE LOW PRESSURE SYSTEM OVER THE AREA CLOSES AND PARKS ITSELF OVER  
THE NORTHERN ROCKIES. THIS WILL RESULT IN WIDESPREAD STEADY  
PRECIPITATION AND MUCH COOLER TEMPERATURES. MODELS ARE VERY  
CONSISTENT SHOWING SIGNIFICANT WRAP AROUND MOISTURE. THE HEAVIEST  
PRECIP AMOUNTS IN THIS FEATURE WILL DEPEND ON WHERE THE LOW  
PRESSURE MOVES. CURRENTLY MODELS ARE IN SOME AGREEMENT SHOWING THE  
LOW SHIFTING NORTHEAST WHICH WOULD GIVE NORTHWEST MONTANA THE  
HEAVIEST PRECIPITATION, WITH AN INCH EXPECTED IN THE VALLEYS AND A  
POTENTIAL FOR 2 INCHES IN THE MOUNTAINS OVER THIS 48 HOUR PERIOD.  
 
FURTHER ANALYSIS OF THE HYDROLOGIC FORECAST AND IMPLICATIONS OF  
THE ABOVE MENTIONED HOT WEATHER AND PRECIPITATION ARE DISCUSSED IN  
THE HYDROLOGY SECTION BELOW.  
 
LATE MONDAY INTO TUESDAY THE LOW EXITS EAST OF THE REGION. HOWEVER  
IT WILL STILL INFLUENCE OUR WEATHER WITH UNSETTLED, SHOWERY  
PRECIPITATION. NEXT WEEK MODELS ARE INDICATING ANOTHER RIDGE  
DEVELOPING BY WEDNESDAY OR THURSDAY WHICH WOULD RETURN NICE  
WEATHER AND BOOST TEMPERATURES BACK TO ABOVE NORMAL READINGS.  
 

 
   
AVIATION
 
LIGHT WINDS AND CLEAR/SUNNY SKY CONDITIONS WILL YIELD  
NO SIGNIFICANT CONCERNS FOR AVIATION INTERESTS ACROSS THE NORTHERN  
ROCKIES.  
 

 
   
HYDROLOGY
 
DAYTIME HIGH AND OVERNIGHT LOW TEMPERATURES RUNNING  
10 TO 20 DEGREES ABOVE NORMAL THESE NEXT FEW DAYS WILL BEGIN THE  
FIRST SIGNIFICANT SNOW MELT CYCLE OF THE 2018 HYDRO SEASON. AS A  
RESULT, FAIRLY RAPID RISES ARE EXPECTED BY FRIDAY ON MOST AREA  
STREAMS, CREEKS AND RIVERS. FURTHERMORE, A DEEPENING UPPER LEVEL  
LOW PRESSURE SYSTEM IS FORECAST TO PRODUCE WIDESPREAD, SLOW  
MOVING CONVECTIVE PRECIPITATION ACROSS MUCH NORTHERN ROCKIES  
WATERSHED THIS WEEKEND. THE ADDITION OF 1 TO PERHAPS OVER 2 INCHES  
OF RAIN IN COMBINATION WITH THIS WEEK'S SNOW MELT COULD PUSH A FEW  
RIVERS (YAAK, FISHER, CLARK FORK & SOUTH FORK OF CLEARWATER RIVER)  
TOWARDS FLOOD STAGE OVER THE WEEKEND. IT'S LOOKING MORE LIKE THE  
HEAVIEST PRECIPITATION AMOUNTS WILL BE FOCUSED ACROSS NORTHWEST  
MONTANA.  
 

 
   
MSO WATCHES/WARNINGS/ADVISORIES
 
 
MT...NONE.  
ID...NONE.  

 
 

 
 
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