FXUS65 KBOI 091541

AFDBOI



Area Forecast Discussion

National Weather Service Boise ID

941 AM MDT Fri May 9 2025



.DISCUSSION...Seeing an increase in high level moisture and

cloud cover this morning (some evidence seen in early morning 

KBOI wx balloon trace) as the upper ridge axis shifts eastward. 

Otherwise warming trend will continue today with highs running 

about 10 degrees warmer than yesterday. Still looking at

Saturday being the hottest day with afternoon thunderstorms

possible over higher terrain of SW Idaho. Current forecast for

today is on track. 



&&



.AVIATION...VFR with high clouds filling in this evening.

Elevated smoke from area burns in the vicinity of KMYL-KONO. 

Surface winds: E- SE 5-15 kt in the Snake Plain, elsewhere 

variable less than 10 kt. Winds aloft at 10kft MSL: SW 15-25 kt.



.KBOI...VFR. variable less than 5 kt this morning, becoming E-SE

5-8 kt.



.WEEKEND OUTLOOK...Saturday will be warm and dry with increasing  

clouds and a slight chance of showers and thunderstorms near the

Boise Mountains and ID/NV border late afternoon into evening. 

On Sunday afternoon, a cold front will move from SE OR into SW 

ID, bringing a chance of showers and thunderstorms (40-50% 

chance) with gusty westerly winds, lowering ceilings, and 

mountain obscuration. 



&&



.PREV DISCUSSION...

SHORT TERM...Today through Sunday night...Today and Saturday 

are expected to be the warmest days of the season so far, with 

temperatures running 10 to 15 degrees above normal under a 

strengthening upper-level ridge to the east.



On Saturday, a deepening upper-level low approaching the 

Pacific Northwest coast will enhance southwesterly flow and draw

in additional mid- and upper-level moisture. This will tighten 

the pressure gradient, resulting in breezy southerly winds 

across the region. The combination of downslope flow and warm 

air will push valley temperatures to near-record levels, with 

highs in the low 90s. While moisture remains limited, there 

appears to be enough elevated moisture (precipitable water 

values in the 60th percentile) and instability (CAPE around 250 

J/kg) to support isolated thunderstorm development, especially 

over the higher terrain of southwest Idaho where orographic lift

will aid initiation.



By Sunday, steeper lapse rates and increased upper-level support

from a strengthening southwesterly jet will spread across much

of the region ahead of the incoming low. Although moisture

continues to be a limiting factor, lift and shear should be

sufficient to support additional thunderstorm development, again

favoring the higher elevations during the afternoon and evening.

Inverted-V soundings indicate that stronger storms could produce

gusty outflow winds. Temperatures on Sunday will be about 10

degrees cooler than Saturday, but still remain roughly 10

degrees above normal.



LONG TERM...Monday through Friday...Wetter, cooler, and windy 

weather is in store for much of the long term as a deep upper level 

low slowly moves east. Temperatures hold steady at just a few 

degrees below normal, but about 15-20 degrees cooler than the warmer 

days in the short term. The weather will be most active Monday 

through Wednesday, with afternoon gusts of 20-30 mph and 

precipitation each day. During this period, valleys have a 30-40% 

chance of precipitation each day and mountains have a 50-70% chance, 

highest in the afternoons. Convection may struggle with clouds and 

colder surface temps, but models show marginal CAPE Monday and 

Tuesday afternoons so thunderstorms and strong showers can't be 

written off. Cold temps will drop snow levels to 6000-7000 ft MSL, 

so high elevation passes could see a couple inches of wet snow 

accumulation.



The upper level low will moves east Wednesday night, and model 

solutions diverge significantly Thursday and Friday. We are likely 

to see temps consistent with those earlier in the weak as the flow 

among models is mostly zonal. Clouds are also likely to stick 

around, but the most uncertainty lies in the chance of 

precipitation. The EC has another low amplifying as it moves onto 

the coast bringing more precip Friday evening, while the GFS shows a 

weak shortwave and a much lower chance of precipitation.



&&



.BOI WATCHES/WARNINGS/ADVISORIES...

ID...None.

OR...None.



&&



$$



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DISCUSSION...DG

AVIATION.....SA

SHORT TERM...JDS

LONG TERM....JM