Scientific Forecaster Discussion
fxus63 kmqt 180742
Area forecast discussion
National Weather Service Marquette Michigan
342 am EDT Fri Oct 18 2019
Short term...(today and tonight)
issued at 341 am EDT Friday Oct 18 2019
Rap and msas analyses show ridging from the surface up through the
mid and upper levels this morning from northern Ontario southward
through the upper Midwest. With mostly clear skies and winds nearly
calm on land, we're off to a seasonably cold start this moring.
Plenty of locations across the interior are in mid to upper 20s. 30s
are hanging on along the lakeshores and across the south-central
and east where some low-level clouds remain. But even in these areas
there should be enough scattering out for further cooling as the low-
level ridge axis shifts overhead. Some widely-scattered high clouds
are moving into the area now, which will slow down the cooling
somewhat, but not prevent mid 20s lows over the interior west.
That will be but a memory by this afternoon, however. As ridging
shifts to the east, the surface pressure gradient increases quickly
ahead of an area of low pressure developing in the Central Plains.
Stiff southerly winds will develop today, which will both advect
warmer air in aloft and help mix out the low levels leading to a
fairly warm day. Leaned on the warm side of guidance (generally
towards the bias-corrected mos) given that days with stiff
southerlies and warming aloft can often overperform on temps. The
only limiting factor will be cloud development downwind of Lake
Michigan. The guidance is fairly split on how thick this gets.
Frictional convergence along with positive moisture advection could
trap enough moisture around and below an inversion above about 3 kft
for thicker than expected clouds over the central and east and thus
cooler temps than currently forecast. On the flip side, in the
absence of these clouds temps could get even warmer than is in the
grids right now if deeper mixing is realized.
The low level jet moves from west to east across the u.P. From late afternoon
today through the overnight. Where its passage coincides with deeper
diurnally driven mixing (i.E. Where it's still daylight when it
passes overhead) have gone fairly bullish with gusts - 30 kts or
more at iwd - though this is well within the guidance envelope.
Expect that winds will stay up overnight and continue to gust in the
favored downslope areas right into Saturday morning, with some 25-30
kt gusts possible in those spots as well from late this evening
through early Saturday morning.
No rain is expected today; by tonight models hint at enough low to
mid-level Theta-E advection ahead of a precursor short wave for
light scattered showers over the west about 03-09z - enough to
warrant chance pops, anyway. The main show will be during the day
Saturday... more on that in the long-term.
Long term...(saturday through thursday)
issued at 217 am EDT Friday Oct 18 2019
Upper air pattern consists of a broad 500 mb trough across the
western and central U.S. With a ridge in the ern U.S. 12z Sat.
There is a shortwave in the plains 12z Sat that moves into the upper
Great Lakes Sat night and then the through digs into the plains on
sun into Sun night. Deeper moisture and 850-500 mb q-vector
convergence moves through on Sat in a narrow band and both move out
on Sat night. Dry weather on sun and then next chance of pcpn moves
in late Sun night.
In the extended, the GFS and European model (ecmwf) show a deep 500 mb trough across
the plains 12z Mon with a closed 500 mb low over SW Minnesota/northwest Iowa. This
upper low heads slowly northeast 12z Tue to Northwest Lake Superior and
then due north Wed towards Hudson Bay. More upper troughing then
moves into the northern plains 12z Thu and this into the area on
Fri. The system on Mon and Tue looks to have strong wind. Active and
wet weather pattern will continue with temperatures near normal.
Aviation...(for the 06z tafs through 06z Friday night)
issued at 138 am EDT Friday Oct 18 2019
VFR conditions will prevail at kiwd/kcmx/ksaw once a drier/warmer
air mass spreads over the area this morning. Before then, some
shallow fog/br may has developed at ksaw which should persist off-
and-on through sunrise, but stay IFR or better for the most part. S
to se winds will become gusty to 15-25kt today as a low pres trough
moves E across the plains. With inversion in place and low-level
wind Max shifting E into the upper lakes this evening, low level wind shear will
develop at kiwd/kcmx.
Marine...(for the 4 am Lake Superior forecast issuance)
issued at 341 am EDT Friday Oct 18 2019
As a trough approaches from the west, winds will become southeast today
then S tonight and increase to around 20 kts on the westenr lake and
25-30 kts east, with a few gale force gusts to 35 kts possible east
tonight. Expect these to be widely scattered and only for a brief
period of a few hours, so did not feel a Gale Warning was needed.
Behind the trough, winds become SW and relax back to 20 kts or less
by late Saturday, then even further to around just 10 kts for
Sunday. The next fall-like system moves in early next week with southeast
gales probable on the Eastern Lake Monday, then more widespread northwest
to west gales probable Tuesday on the back side of the system.