Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Marquette Michigan
459 am EDT Wednesday Sep 17 2014
Short term...(today and tonight)
issued at 456 am EDT Wednesday Sep 17 2014
Latest water vapor imagery and RUC analysis shows a shortwave moving
into western Ontario with its associated upper jet maximum passing across the tip
of James Bay. 850 mb fgen along the systems cold front is supporting
band of rain showers from just north of Minnesota bdr extending across north central and
Eastern Lake Superior as noted on Canadian radar mosiac. Some of these
rain showers have brushed the Keweenaw peninsula early this morning and low
clouds have reached into kcmx as well. Otherwise the rest of the County Warning Area
has stayed dry thus far.
Today...as the Ontario shortwave dives across the northern tip of Lake
Superior later this morning it will help drive the cold front across
Upper Michigan late this morning into the afternoon hours. Models show
supporting 850 mb fgen forcing for rain showers activity generally weakening
and moving east by late morning with departing shortwave and associated
upper jet maximum as cold front slowly begins to shift south across the
area. Since the models indicate the best fgen forcing generally
staying out over Lake Superior or north of the lake through late
morning have kept higher chance/likely probability of precipitation well north over Lake
Superior this morning with only slight chance to low chance probability of precipitation brushing
the Keweenaw peninsula and the far NE County Warning Area. The rest of the County Warning Area should
stay generally dry today as fgen will be weakening quickly along the
front as it begins to move south across Upper Michigan this afternoon.
Since cold frontal passage will be later in the day for all but the
northwest quarter of the County Warning Area...expect temperatures to warm up into the 60s over
scntrl and eastern portions of the County Warning Area with the coolest temperatures (around
50f) across the Keweenaw peninsula. Temperatures across the north will likely
fall into the 40s in the afternoon under a brisk developing nearly wind and
stratus deck following frontal passage.
Tonight...Canadian high pressure building across the area and
becoming centered NE of Lake Superior will bring clearing skies and
light easterly winds. Precipitable waters less than 30 percent of normal or less than
25 inch will allow for ideal radiational cooling conditions. Expect
freezing to below freezing temperatures across much of the interior of the
Upper Michigan. Have posted freeze warnings for the interior western counties
and have frost advisories out for the rest of the County Warning Area with the
exception of Keweenaw County.
Long term...(thursday through tuesday)
issued at 303 am EDT Wednesday Sep 17 2014
Not much change in thinking from previous shift. Thursday will start with
lingering cold and frost from Wednesday night as a 1025mb surface high will be
centered just NE of the County Warning Area at 12z Thursday. The high will move to New
England...while strengthening to 1030mb...by 12z Friday while a surface
trough moves to the Dakotas. Return flow/warm air advection will just be starting
late Thursday...so dry air lingering over the region will make for mostly
sunny skies on Thursday. Temperatures on Thursday will top out in the middle to upper
Moisture begins to increase Thursday night as the return flow
increases...but most precipitation looks to hold off until Friday when ample
moisture will be established...a series of shortwave troughs begins
a trek across the area...and the pressure gradient/return flow
increases. Models are in good agreement on the start time of precipitation
Friday in the warm air advection regime...but how things shape up on Friday and
especially the end time of precipitation on Sat night or sun is more
uncertain. Even though models agree that the strongest shortwave
will enter the region late Sat into Sat night...models disagree with
each other and from run to run due to the complex nature of phasing
the three waves over the area. Will likely not have greater
certainty on end time of precipitation until closer to the weekend. Have
the greatest probability of precipitation from late Friday through Sat. Continued to have
chances for thunderstorms late Friday into Sat night when some elevated
instability is expected...no severe weather is expected though.
850mb temperatures will top out around 15c Friday night into Sat...resulting
in high temperatures in the middle 60s to low 70s /which is around average/.
The airmass will be colder sun through Tuesday under stronger northwest flow
along and incoming surface high pressure...resulting in cooler and drier
conditions Monday and Tuesday.
Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 721 PM EDT Tuesday Sep 16 2014
VFR conditions will prevail at kiwd/kcmx/ksaw tonight as low levels
remain dry. Cold front currently over Ontario will drop S into
portions of northern Upper Michigan tonight before stalling as subtle surface low
pressure develops and tracks east-southeast along front toward the upper Great
Lakes. It is expected that low clouds and band of rain that will
develop north of front will pass just north of kcmx late tonight. As the
very weak surface low passes Wednesday morning...cold front will push
S...bringing low MVFR ceilings to all terminals. IFR not out of the
question at kcmx and especially ksaw which will see a more direct
upslope wind after frontal passage.
Marine...(for the 4 am Lake Superior forecast issuance)
issued at 456 am EDT Wednesday Sep 17 2014
Expect winds generally 10-20kt as the front stalls over the lake
early this morning. Front will get a push S late this morning into
the afternoon with NE winds behind the front increasing to 15-25kt for
at least a time. Over far Western Lake Superior...coastal
convergence/funneling may result in winds briefly as high as 30kt.
Winds will then diminish to under 20kt tonight/Thursday as high pressure
settles over northern Ontario in the vicinity of Lake Superior. As the high
then shifts toward New England and a low pressure trough approaches from
the west...S winds will increase Thursday night/Fri. With S winds a more
favorable direction for stronger winds over Eastern Lake Superior than
over the west...winds should reach 20-30kt over the Eastern Lake on Friday.
Although winds will diminish on Sat as the trough arrives over the
upper lakes...west to northwest winds will again increase to as high as
20-30kt behind the trough Sat night/sun.
frost advisory from midnight EDT /11 PM CDT/ tonight to 10 am
EDT /9 am CDT/ Thursday for miz003-005>007-012>014-085.
Freeze warning from 11 PM EDT /10 PM CDT/ this evening to 10 am
EDT /9 am CDT/ Thursday for miz002-004-009>011-084.