Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
936 PM CST Thursday Dec 5 2013
no big changes to previous forecast except to nudge low temperatures up a
bit with edge of middle-high level clouds from system to the south
pushing over region from time to time. Still looking at lows in
the single digits inland...though a little closer to +10 than
previous forecast...and in the teens along the lake. Occasionally
gusty west-northwest winds will keep wind chills between 0 and 10
VFR through the period with northwest winds in the 10 to 20 knot
range slowly easing through the day and into the evening Friday.
no change to current headline...though next shift may cancel at
330 am issuance if downward trend on latest NAM and rap forecast
soundings pan out. Will let them assess full 00z model suite.
Previous discussion... /issued 333 PM CST Thursday Dec 5 2013/
Tonight and Friday...forecast confidence medium to high
A dry Arctic airmass will dominate. 925 temperatures drop off to -12 to
-17c tonight with some mixing to keep winds up a bit. Single digit
lows will be common across southern WI. Models try to thicken up the
cirrus canopy riding SW/NE in the upper flow and this appears
plausible given upstream cloud trends. Not much change into Friday
with more cold and only some middle/high clouds brushing the south.
Highs mostly in the teens.
Friday night through Saturday night...forecast confidence high
Northwesterly winds will maintain an Arctic airmass over southern WI during this
period. A 1040 mb high will finally arrive for Sat nt but middle to
upper level clouds will increase during the night as warm
advection begins ahead of a large polar trough moving into the
central and southern rockies. Single digit lows with highs in the teens
Long term...Sunday through Thursday...forecast confidence medium
The extended models are in fairly good agreement of an impressive
warm advection pattern developing sun and sun nt with the passage
of the shortwave trough sun nt. The dendrite growth zone is
approximately 200 mb thick with this system but also notice the
greatest lift is above the dendrite zone. Lake enhancement will
also be a factor and will focus more over Ozaukee and Sheboygan
counties as long as the 1000-850 mb flow remains southeasterly. Took a
model consensus of quantitative precipitation forecast which yielded around 0.20 inches and
applied a snow ratio around 17 or 18 to 1. This yields snow totals
of 3-4 inches but then added a couple inches due to lake
enhancement over Sheboygan and Ozaukee counties. The details of
the 1000-850 mb onshore flow will be the key to the placement of
the lake enhanced snows and it is possible warning criteria could
Northwesterly flow aloft and Arctic air to continue the remainder of the
week. A weak Alberta clipper may bring a light amount of snow late
Monday nt and Tuesday. Arctic high pressure to prevail Wednesday and Thursday.
Aviation/00z tafs/...tight pressure gradient continues between low
pressure lifting northeast of Lake Superior and high pressure in the
plains. Expect the winds to ease tonight into Friday as the gradient
relaxes a bit. Just some jet related ac/cirrus racing northeastward into southern
WI from the Central Plains.
Marine...Small Craft Advisory conditions tonight with brisk west
winds. Winds will slowly diminish tonight as the strong low near
Lake Superior moves northeast toward James Bay Canada.
Lm...Small Craft Advisory until 6 am CST Friday for lmz643>646.
tonight/Friday and aviation/marine...collar
Friday night through Thursday...gehring