Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Riverton Wyoming
445 am MDT sun Mar 9 2014
Short term...today through Tuesday night
winds are beginning to pick up in the Cody foothills and the
surrounding mountains. Earlier Clark east gusted from the west at
55 miles per hour where the temperature has warmed to 57 degrees. Gap flow seems to
be the culprit with a 14c temperature spread prognosticated from ynp to Clark.
Clark east would be more likely to blow than Clark west with gap
flow. Mountain wave potential does not look impressive. Will let the
High Wind Warning run through this morning for the Cody foothills.
As for the High Wind Warning for the Green Mountains and Natrona County
in effect for this morning...a tight surface pressure gradient of 15mb
from gcc to rks as well as 50 knot 700 mb winds mixing down should
encourage strong winds to blow through that wind corridor with
outer drive already seeing gusts of 66 miles per hour just south of Casper.
Otherwise today is shaping up to be a fairly warm and dry day for
much of the County Warning Area for early March with 700 mb temperatures of 3c expected over
Natrona Colorado...0.5c for central Wyoming and -3c in western Wyoming which will
translate to highs in the 60s expected in cpr/byg...50s central
basins and in the 40s at the lower elevations west.
The ridge currently over US now will move east and flatten today
with the westerly Pacific flow increasing with some isentropic lift
developing in far western Wyoming out ahead of the next approaching
upstream trough off the Pacific coast. This will result in an
increasing chance of rain and snow in northwest Wyoming later this afternoon.
Snow levels today should be around 7k. Light rain and snow should
continue in the far west tonight and into Monday morning with the
westerly upslope flow continuing. As the Pacific trough approaches
the precipitation in western Wyoming will increase in coverage and
intensity Monday afternoon. By early Monday evening the snow will
lower to the valley floor around sunset by 00z Tuesday. Snow will
continue in the west through Monday night. Advisory amounts appear
likely in the west from tonight through Monday night. However...the
snowfall in the valleys will likely melt as fast as it piles up at
the lower elevations. An associated 700 mb circulation will track south-southeast
across central Wyoming on Monday nt...across Shoshoni if you take the
track literally...with a surface low tracking south across Johnson
and Natrona counties. An associated cold front will move south
Monday night. The front will help spread snowfall to areas east of
The Divide Monday night. Moderately strong q vector forcing and the
700 mb circulation will enhance the snowfall...especially east of The Divide.
After the 700 mb circulation shifts to the south...the upslope flow will
deepen and strengthen for accumulating snowfall east of The
Divide...especially in the upslope favored areas from lnd to cpr.
The aforementioned dynamics will help seed the lower deck of upslope
induced snow clouds. The precipitation will be all snow across the whole
County Warning Area Monday night and into Tuesday with 700 mb temperatures falling to the minus
low teens. Have indicated advisory snow amounts for the mountains
and elevated basin areas along and south of The Owl creek mountains and
along and east of the Big Horn Mountains with most of the snow occurring
late Monday night and Tuesday morning. The track of the associated
vorticity maximum is favorable for snowfall in Lander. Snow will diminish
Tuesday afternoon. Clearing will take place Tuesday night with fog
developing late with favorable soundings supporting fog along with
clear skies and fresh snow cover. Should see lows in the single
digits in the far west by 12z Wednesday.
Ice jam flooding remains an issue in the Big Horn basin and
Johnson County. Urban and Small Stream flooding associated with
melting snow remains a threat in the west today.
Long term...Wednesday through Sunday
a chilly start to medium range period behind our early week snow.
Morning fog is quite possible in the freshly snow covered areas
where winds are light and a generally clear sky will exist.
Temperatures will be slow to rebound Wednesday in the snow covered
areas but it's still March so temperatures will still warm into the
30s and 40s. Ridge flattens allowing a northwest flow to develop for the
second half of the week with a couple weak disturbances producing
probably nothing more than some passing clouds until Saturday when a
stronger southeastward moving disturbance is forecast to move through. So
warmer Thursday and Friday and then a little colder and potentially
unsettled across the north and east with rain and snow showers or
rain showers turning to snow showers on Saturday. Models have been
changing a lot in this developing northwest flow so confidence is still
low on timing and details for next weekend yet. As of now...that
is the only day with any real chance of precipitation in the
east of The Divide...kcod/kcpr/klnd/kriw/kwrl routes
VFR conditions will occur today and tonight. Gusty wind conditions
around the kcod and kcpr terminal site through most of the period.
Strong middle level wind speeds will occur which will cause some wind
shear at times over the near the mountains.
West of The Divide...kbpi/kjac/kpna/krks routes
Patchy fog may occur in the valleys until 16z with local MVFR to IFR
conditions. Otherwise VFR conditions will occur at most terminal
sites through the period. At the kjac terminal site clouds will be
lowering by 00z as rain and snow develops in the northwest mountains after
22z. Snow will occur in the northwest mountains after 01z through 12z
Monday. Conditions at kjac terminal site will lower to MVFR by 06z
Monday as snow develops...with possible IFR conditions by 12z Monday.
inversions and poor smoke dispersal are expected this morning in
the basins and valleys. Strong west southwest winds will blow
today from South Pass to Casper as well as along the Cody
foothills and East Slope of the Continental Divide. Highs will
range from the 60s east...50s central and 40s low elevations of
the west. Areas of light snow will develop later this afternoon in
western Wyoming today with the snowfall becoming steadier and
heavier tonight and into Monday along with a mix of rain and snow
or all rain at times in the western valleys. All snow will
continue Monday night and spread to areas east of The Divide
Monday night and Tuesday. Significant accumulation is expected
east and west of The Divide. Clearing will take place with fog
developing Tuesday night. Inversions and poor smoke dispersal are
expected late Tuesday night and Wednesday morning in the basins
High Wind Warning until 9 am MDT this morning wyz002-003.
High Wind Warning until noon MDT today wyz019-020.