Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Boise Idaho
313 am MST Friday Dec 20 2013
Short term...today through Saturday...a cold dry air mass is in
place this morning with temperatures in the single digits and teens
throughout southeast Oregon and southwest Idaho. These colder
temperatures are setting the stage for a winter weather event that will
impact travel for most of the area starting late this afternoon
and continuing through Saturday morning. Latest model runs are a
tad slower in spreading the snow from northwest to southeast...but overall there
is not much change...especially with regard with quantitative precipitation forecast/snowfall
amounts. It appears that the snow will not get into the Boise
metropolitan until after 5 PM...but it will reach the lower Treasure
valley near Ontario by then. Highs will only be in the 20s so
roads will become snow-covered by late evening. Snow amounts high
enough to warrant a Winter Weather Advisory for the Boise/west
central mountains this afternoon through tonight. Snowfall totals
will average 2-3 inches in the valleys...3-6 inches in the
mountain valleys /such as McCall/...and 6-12 inches in the
mountains. Winds will increase across the southern areas with
blowing/drifting snow expected in the southwest Idaho Highlands
and southern Twin Falls County. The southern portion of the
western Magic Valley /including Twin Falls/ will likely see some
blowing snow as the winds increase overnight. Winds are not
expected to be a factor for most of the remainder of southwest
Idaho. Snow will diminish for the bulk of southeast Oregon/SW Idaho on
Saturday...but lingering snow showers and gusty winds for blowing
snow will continue across the southern Idaho Highlands and western
Magic Valley through Saturday morning. Showers will diminish
Saturday afternoon as the northwest flow becomes drier. Temperatures on
Saturday will not be as cold with highs generally in the 30s.
Long term...Saturday night through Thursday...the unsettled
pattern will continue through Tuesday under northwest flow aloft.
Enough Pacific moisture will be transported across our area for
scattered mountain snow showers each day. A disturbance embedded
in the flow will increase chances of precipitation Monday
afternoon through Tuesday morning bringing a chance of rain and
snow showers to the lower valleys mainly Monday night. By
Wednesday a ridge of high pressure will move over our area from
the west...providing dry weather for the rest of the week.
Temperatures will remain near normal through Tuesday...but
Wednesday through Thursday the inversion will return...lowering
readings to around 5 degrees below normal.
Aviation...VFR conditions will prevail across most of our area
through this morning. After 18z an approaching warm front will
spread snow with deteriorating conditions across eastern Oregon...
the central Idaho mountains...and the Treasure valley...with
widespread mountain obscuration and IFR/local LIFR conditions
across the entire area after 00z. Surface winds will be southeast
to southwest 5-15 kts except 10-20 kts across higher terrain.
Northwest winds aloft will increase to 40 kts at 10k feet mean sea level by
Idaho...Winter Weather Advisory from 11 am this morning to 5 am MST
Winter Weather Advisory from 8 PM this evening to 11 am MST
Winter Weather Advisory from 5 PM this afternoon to 5 am MST
Or...Winter Weather Advisory from 11 am MST /10 am PST/ this morning
to 5 am MST /4 am PST/ Saturday orz062>064.