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Area forecast discussion 
National Weather Service Gaylord Michigan
217 PM EDT Monday Sep 1 2014

issued at 311 am EDT Monday Sep 1 2014

A cold front will push through northern Michigan late this afternoon
and late this evening. Showers and thunderstorms will accompany the
front...with a chance for some of the storms to become severe. The
severe threat is primarily damaging winds...and mainly in northern
lower Michigan. Large hail is also possible.

Tuesday will be rather quiet with just a small chance for light rain
showers. Warm and breezy conditions develop Wednesday and Thursday
with the next chance of showers and thunderstorms beginning late
Wednesday night. Cooler and drier conditions developing Friday and
into the weekend.


issued at 1155 am EDT Monday Sep 1 2014

Some latest thoughts on convective evolution. Short wave and
associated batch of precipitation now making inroads into northwest lower
Michigan. Several convective segments have developed rapidly ahead
along the leading edge...likely along the back edge of a pocket
of steeper lapse rates aloft that was already in place this morning.
Storm Prediction Center mesoscale-analysis reveals between 500 to 1000 MUCAPE across northern
lower Michigan...but paltry MLCAPE...suggesting this initial
convection is largely elevated. But...with an axis of effective
bulk shear values running 40 to 50 knots now edging into the
region with this batch of precipitation...could still get some organized
updrafts/hail producers over the next few hours. As inland warming
continues along with increasing MLCAPE values...stronger wind
gusts also possible. Will continue to monitor.

Update issued at 100 am EDT Monday Sep 1 2014

Progressive open short wave trough in the northern/Central Plains this
morning with a vorticity center advancing across the Iowa/
Minnesota area...pushing into Wisconsin. Strong jet core punching
across Central Plains with some semblance of upper jet coupling
over Wisconsin. A couple distinct batches of showers and embedded
thunderstorms across western Upper Michigan and down
through Wisconsin...and second batch through Missouri.

Across the Great Lakes...surface low lifting NE through Ontario. Warm
front stretches across northern Michigan (evident around 750 mb on the
12z apx sounding) and cold front stretching down through western
Wisconsin. 12z apx sounding also reveals an elevated mixed layer
between 850 mb and 650 mb with bubbly altocumulus castellanus moving through northern
Michigan (often a precursor to severe weather). But meanwhile...with
initial boundary layer heating...low stratus has been expanding
quickly northward across northern lower Michigan over the last few
hours...which will of course hinder heating for awhile.

Rest of today...favorable conditions are in place for severe
weather. 50 knots or so of middle level flow develops across the area
this afternoon resulting in 40 to 50 knots 0-6km bulk shear.
Meanwhile...upper jet core punches in across northern lower Michigan
around middle afternoon with attending middle level short wave lifting up
through Upper Michigan. So...good kinematics in place with decent
synoptic forcing rolling through and steeper lapse rates aloft
already in place. However...with early heating and bump in the
boundary layer...quite a bit of stratus has expanded up through northern
lower Michigan over the last few hours which obviously will impede
daytime heating/destabilization. On top of that...initial batch of
showers and thick higher cloud cover is already moving across Lake
Michigan and will overspread the region.

Will see how things play out as there are various possibilities. But
first thoughts are we will once again be faced with a heating/
destabilization problem across northern Michigan which will obviously
reduce our severe weather threat. In fact...northern lower Michigan may
end up largely split once again as one round of precipitation runs up
through Upper Michigan into Canada while stronger convection takes
off this afternoon across the Midwest into the lower lakes. Will
continue to monitor trends.


Short term...(today through tonight)
issued at 311 am EDT Monday Sep 1 2014

..severe thunderstorms possible this afternoon...

High impact weather potential: thunderstorms expected today...some
of which could be severe with damaging winds and large hail.

Early morning analysis reveals a rather robust axis of height falls
impinging on the southwest lakes...on the southern tail of a broader
upper trough swinging through the upper Midwest. A cold front as of
06z is snaking from Western Lake Superior down into the Texas
Panhandle...with several areas of enhanced convection occurring
along this feature...though most areas along the front are receiving
rain in some form. Helping the cause is a nocturnal enhancement of
the low level jet poking from central Iowa up into Wisconsin and
helping maintain eastward progress of what was already a long-lived
mesoscale convective system feature emanating from the Central Plains. With that said...this
feature is showing signs of weakening as the better low level jet convergence
is lifting northward through the upper Great Lakes that is helping
transport an axis of much steeper middle level lapse rates up in our
direction and quelling the overall amount of elevated instability
available in advance of this feature. In addition...the current mesoscale convective system
is running squarely into a tremendously drier airmass...with a
notable pocket of very dry 850-750mb dew points residing over much
of northeast Illinois into much of eastern Wisconsin (not to mention
northern michigan).

Of course with today being the big Holiday and unofficial sendoff to
Summer...all eyes will be on convective potential through the day.
At the moment...and based on upstream appears our
dry forecast before 16z/noon should hold just fine. Above-mentioned
pocket of drier air aloft will work across the area through the
morning...while the axis of better height falls lifts toward the
southwest lakes. As that additional round of convection
will likely get going from parts of central Iowa up into western
Wisconsin...probably sending some thicker cirrus in our direction.
That setup should allow for a good deal of surface heating as
pronounced thermal ridging arrives just ahead of a cold front
marching through Wisconsin by 18z. Given good mixing into a core of
800 mb temperatures nearing 17c aloft...highs could theoretically push as high
as the middle or even upper 80s...particularly for northeast lower on
downslope southerly flow.

All the while...moisture transport will ramp up aloft...while
surface dew points creep back through the 60 to perhaps near
70...fueling increasing MLCAPE values up toward 1500+ j/kg. Add the
arrival of a 55 knot middle level jet core from 18-00z and likely
development of inland pre-frontal thermally-driven troughing...and
upstream convection should have little difficulty propagating and/or
redeveloping into northern Michigan from about noon Onward. Deep
shear vectors parallel to the front support more of a linear
convective structure...though with some supercellular elements
certainly possible given more than sufficient deep shear for updraft
rotation. Initial middle level dry air axis should support a wind
threat with any storms from precipitation loading...while shear and
evaporative cooling potential (wet bulb zero heights around
11-12kft) lend credence to a larger hail potential. Going severe
weather chances will remain in all products as the setup certainly
looks as good of one we have seen all Summer season.

May see a trailing axis of rain behind the primary convective line
into the evening and early overnight hours...courtesy of enhanced
jet dynamics aloft working squarely across the area. This is a very
similar setup to the ongoing upper miss valley mesoscale convective system early this
morning. As that jet axis gradually works east and overtakes
northern Michigan...rain chances should propagate southeastward
through 09z before ending altogether as drier air and waning forcing
arrive by sunrise. Do have some concerns we may see some thicker
stratus fire off in a still quite moist environment...but a lack of
significant cooling below 900mb (often the calling card for northern
Michigan Summer stratus - see yesterday) yields hope things may
gradually clear out from northwest to southeast.

Long term...(tuesday through sunday)
issued at 311 am EDT Monday Sep 1 2014

..eyes on Thursday night potential round of storms...

Impacts: storms Thursday afternoon and Thursday night. Exact details
tbd...but there is an expectation of a lot of wind in the

Synoptic pattern/evolution

A very fast/progressive flow aloft with broad low amplitude trough
to ridge to trough evolution. The most significant upper trough and
associated cold front set for Thursday into Friday. Late periods
ending in a trend toward longer period ridging and surface high
pressure...with Summer trying not to look for the exit door toward
meteorological fall.

Main forecast concerns: possible elevated light rain showers Tuesday
and more importantly...shower and storm evolution for late Wednesday
night into Friday morning.

Tuesday through wednesday:

Cold front from Monday will be east of US with some likely higher
level clouds still grazing areas near Saginaw Bay early Tuesday
morning. A new development in some of the data suggests some low to
middle level cloud arriving quickly associated with
weakish looking shortwave and middle level jetlet. The air mass will be
on the dry side of the spectrum...but pretty steep lapse rates
around 6.5c/km and a bit of added low to middle level moisture results
in a handful of MUCAPE (~400 j/kg) arriving more so Tuesday
afternoon in peak heating. Surface dew points likely in the lower 50s...but
some light rain showers...high based...are possible. Introduced a
small 20 percent chance. High north the middle-upper 70s. Gonna keep
Tuesday night precipitation free until more detail can be gleaned from the
data....especially timing. Heights rise at least overnight...with
surface high pressure becoming more of an influence into Wednesday.
Highs Wednesday rising into the upper 70s to lower 80s.

Wednesday night through friday:

Surface high pressure to depart rather quickly with fast flow aloft. Surface
low pressure from the Central Plains and an associated warm front
lift into the region Thursday...with the system cold front overhead
Friday around daybreak and exiting by Friday afternoon. Timing of
course in question. Some warm advection showers and eventual chance
at some storms develop by late Wednesday night and into Thursday
morning. This is all dependent on timing...but clouds and precipitation to
wane into the afternoon...while gusty and warm conditions develop.
Convection expected to fire in the deeper instability ahead of the
front out across Wisconsin Thursday afternoon...which could make a
run at US as early as Thursday evening. Confidence is on the low end
of the scale for the following: lots of wind aloft...and if we can
generate the instability with low level moist advection...and height
falls Thursday evening...may be looking at some pretty good storm
potential. With the above scenario...instability storm strength and
coverage decreasing overnight...but some showers rolling through
overnight and into Friday morning with the surface cold front. Clearing
in the afternoon. Highs Thursday into the upper 70s and lower half
of the 80s....cooling off to the upper 60s and 70s Friday.

Friday night through monday:

Shortwave trough with the Thursday night storms expected to lift out
of the region with a trend toward rising heights and another period
of ridging...especially by late weekend into early next work week.
This period though dominated by surface high pressure...outside of what
seems to be an insignificant potential shallow surface cold front
Saturday (may be north of US in canada). The idea here is to be
cooler with highs generally in the middle 60s and lower 70s.


Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 2 PM EDT Monday Sep 1 2014

Line of strong thunderstorms now advancing through north central
lower Michigan and will impact pln/apn terminal sites through 20z
or so. Line of storms already east of tvc/mbl. But additional
showers and possibly a few storms may re-develop later this
afternoon and move through this a cold front swings
through the region. After that...a period of VFR-MVFR conditions will
follow overnight...but VFR conditions will be found on Tuesday.


issued at 311 am EDT Monday Sep 1 2014

A cold front will makes its approach into the afternoon and evening
hours today...delivering a round or two of showers and thunderstorms
to all the waters of northern Michigan. Some of these storms could
produce winds in excess of 40 knots and large hail. Outside of any
storms...southerly winds will increase to 15-25 knots through the
day...strongest on Lake Michigan where Small Craft Advisory
conditions will be felt. Winds will be slightly lower on Lake Huron
and Whitefish Bay...though some gusts to around 25 knots are
certainly possible where the flow will remain locally backed more
southeasterly and will channel up against the coastline. Winds will
diminish quickly behind the front overnight...and remain mainly
below 15 knots into midweek as high pressure briefly works through
the region.


Apx watches/warnings/advisories...
LH...Small Craft Advisory until 8 PM EDT this evening for lhz345>349.
Lm...Small Craft Advisory until 8 PM EDT this evening for lmz323-341-
Ls...Small Craft Advisory until 8 PM EDT this evening for lsz321.



short term...Lawrence
long term...smd

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