Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Gaylord Michigan
154 PM EDT Sat Aug 30 2014
issued at 218 am EDT Sat Aug 30 2014
Slow moving low pressure will meander through northern Michigan
today...delivering several additional rounds of showers and
thunderstorms. Conditions will briefly dry out for Sunday as high
pressure arrives...with another period of showers and storms
anticipated for Labor Day ahead of an approaching cold front. Dry
and more seasonable conditions will return behind that front for the
first part of the work week.
issued at 154 PM EDT Sat Aug 30 2014
..severe storm threat increasing...
Previous forecast thinking appears on track. Morning batch of
showers/thunder has exited and thicker cloud cover is slowly
eroding allowing temperatures to creep through the 70s. Conditional
instability following suite with MLCAPE values creeping up over
500 j/kg over the southeast counties per Storm Prediction Center mesoscale-analysis and limited
cinh. Decent parameters in place for strong to sever storms over a
chunk of northern lower Michigan with strong middle level winds and effective
bulk shear values approaching 40 knots...reflected in Storm Prediction Center updated
day one outlook and recently issued sels mesoscale discussion. With further heating
and incoming short wave out of Wisconsin...still think storms will
take off over northern lower Michigan within the next few hours.
In the process of launching 18z special balloon flight...
Update issued at 1019 am EDT Sat Aug 30 2014
Satellite imagery/upper air progg charts revealing middle level
short wave center over southern Wisconsin...lifting northeast and small
upper jet core in the Midwest punching up into lower Michigan.
Associated broad surface low analyzed over NE Wisconsin along pseudo
stationary front stretching up into east-central Upper Michigan
roughly up through the Munising area. Latest moisture surge ahead
of the short wave/surface troughs underway this morning...driving a
line of showers and some embedded thunderstorms North/East through
the County Warning Area.
Have added some timing detail to the forecast for the next few
hours as follows. Latest moisture surge/associated showers and
thunder pushing through the northern/eastern parts of the County Warning Area and
will be largely exiting the region by noon. That will give a large
part of the County Warning Area US another lull in the action through midday
barring any additional spotty showers that may pop in this soupy
airmass. But...expect things to fill back in this afternoon as
upstream short wave tracks up through Northern Lake Michigan and we get
some boost from jet exit region forcing from upper jet core
punching into lower Michigan.
Bigger question is...will we see severe weather? Respectable 40-50
knot middle level flow will be in place across lower Michigan this
afternoon with resulting 0-6km bulk shear values pushing 35 to 40
knots over the east/southeast part of the County Warning Area. Enough to support organized
updrafts (and hence why Storm Prediction Center has a "see text" over southern lower mi).
Question for US is the usual one...will we get enough heating to
generate decent instability. Quite a bit of cloud cover stretches
down through the lower lakes although there are some breaks and
thinning of the cloud cover behind this mornings line of showers.
While we will not get full sun obviously...enough heating and lack
of rainfall should result in 75 to 80 degree temperatures...warmest over
the southeast toward Saginaw Bay...and potentially around 2k j/kg of
MLCAPE. If that materializes...severe possibilities will increase
for the afternoon with wind the main threat and again over the
east/southeast part of northern lower Michigan. Will see how it GOES.
Short term...(today through tonight)
issued at 218 am EDT Sat Aug 30 2014
..periods of showers and storms...
Impacts: lightning. Severe storms not expected. Possible? Sure.
Current weather and synoptic pattern:
Split flow in the upper levels...with a faster more zonal flow
across Canada...and a broad trough pushing a shallow cold front
eastward into Western Lake Superior. At the same time...a shortwave
trough is spinning near Iowa/MO with a slow moving warm front just off
to our SW. There is some vorticity being ejected into northern Michigan
at this time...with an axis of deeper moisture and resultant band of showers
and possible rumble or two of thunder. This is seen on recent area
VAD wind profiles showing a secondary weaker...yet strengthening low level jet
focusing some low level lift into our neck of the Woods (the main
low level jet and stronger downstairs forcing in NE of us). This secondary low level jet
is just one of several subtleties in the low level pattern. There
are also several ill-defined surface circulations on the frontal
boundary. These subtleties are rather insignificant compared to the
upper forcing of divergence and DPVA in stronger channeled 500 mb flow
into all of the western Great Lakes. This is where the greatest
coverage of showers was located...and increasing instability/storms
due to height falls. Everything is progressive...slowly translating
east. As stated yesterday...the atmosphere is pretty darn
moist...and any little bit of forcing will lead to the development
of showers...that is what we are seeing moving into northern lower
A very mild night with cloudy skies/moist atmosphere...readings were
steady/very slowly falling into the middle and upper 60s.
Synoptic pattern/weather evolution:
Axis of deeper moisture on nose of strengthening secondary low level jet will
continue to lift NE out of northern Michigan by daybreak. Some isolated
thunderstorms possible within this band of showers. Nothing too
heavy from a quantitative precipitation forecast Point of View. Too difficult to determine any
forcing until the main show arrives later this morning/afternoon.
As stated above...the atmosphere is very moist (pwats >1.75") and it
will not take much to fire off at least isolated rain showers. So
chances for rain have to be included this morning. The progressive
upper level forcing/troughs/sfc fronts will all be translating
toward northern Michigan through the day...arriving in eastern upper
12z-16z....around midday in far northern lower...and the remainder of the
area this afternoon. The upper divergence is expected to wane through
the morning...but likely lead to some forcing assistance across
eastern upper...and likely only some minimal diurnal heating to help
things this afternoon for northern lower. Regardless...we have the deep
moisture (possibly up to 2" precipitable waters for a period of time)...height
falls from the shortwave trough and low level convergence from the
surface front and weakish low pressure to bring periods of showers and
some thunderstorms. Things will wane through the night with the
departure of all said synoptic features. Cannot rule out absolutely
zero chances for rain overnight as there will be some >1" precipitable waters and
potential residual surface troughing around with middle level shallow
ridging nut until 09-12z. Only very small chances for rain.
Not much in the way of heating today with what should be a mainly
cloudy day. Temperatures are already in the middle to upper 60s and
only a short time of any thinning or breaks in the overcast will be
able to easily get temperatures into the middle and upper 70s. More solid low
level overcast in eastern upper. Will go middle-upper 60s there...with
low to middle 70s northern lower.
If we do get into the middle to upper 70s which theoretically would be
across NE lower before the stronger forcing arrives in the
afternoon. Modifying forecast soundings reveal 1500 j/kg (possibly more
in low 80s). Low level flow is not as backed as it was across
Wisconsin yesterday (where there was a confirmed tornado...but we
do have low lcl's and slightly strengthening low to middle level winds
with 35 to 40kts of 0-6km bulk shear. Freezing levels of 15kft do
come down to just under 14kft. This will help in a hail threat...but
chances for any severe weather...hail/wind or a tornado...are pretty
low. Maybe we can get enough instability to draw down some gusty
winds to 40 miles per hour...maybe half inch hail.
Lows tonight in the upper 50s/low 60s eastern upper...where shallow
cool advection with lingering bl moisture will lead to stratus. This
thicker low level stratus will also develop most all northern lower with
just slightly less cooling. 60-65f there.
Long term...(sunday through friday)
issued at 218 am EDT Sat Aug 30 2014
..an active welcome to meteorological autumn...
High impact weather potential: a round or two of thunderstorms
expected for Labor Day...along with quite windy conditions through
the day. Depending on the timing of said storms...an impact to
larger outdoor events may exist...with wind perhaps an issue for the
bridge walk as well.
Pattern summary: upper trough plaguing the region through tonight
will depart early Sunday...leaving a very brief period of shortwave
ridging in its wake. An axis of sharp height falls will quickly work
east through the northern plains and western lakes Sunday
night...arriving here Monday with a cold front in Tow. After
that...the overall upper flow pattern is expected to significantly
flatten out over the entire lower 48 through much of the work
week...favoring a rather tight thermal gradient somewhere near the
area and perhaps delivering several chances for additional rain.
However...confidence is low and it won't take much flattening of a
very broad eastern Continental U.S. Ridge to drive cooler air into northern
Michigan and favor better rain chances to our south.
A look at the forecast details...
Sunday-Sunday night: relatively quiet conditions for the Middle Point
of the Labor Day weekend as transient low/middle level shortwave
ridging builds overhead. As discussed yesterday...have some big
concerns about very pesky low stratus overstaying its welcome
through at least a part of the day...courtesy of a quick shot of
much cooler sub-900mb air slicing in beneath residual warmth aloft.
Have seen this so many times this Summer that it's not even
funny...and the fact that current (and last night's) satellite
trends favored widespread Post-frontal stratus...confidence is
heightened quite a bit. That junk should mix out with time through
the day (i hope!)...leaving a rather seasonable day with highs in
the lower half of the 70s. Any diurnal shower threat looks very
limited given an influx of relatively drier boundary layer air
through the day (dew points back into the upper 50s/low 60s).
Similarly...should be a little more comfortable night Sunday night
with clear skies/light winds...at least the first half of the
night...promoting some decent radiational cooling.
Monday/Labor Day-Monday night: the period of most interest due to
plenty of outdoor activities as we bid adieu to the official Summer
season...not the least of which is of course the Mackinac Bridge
walk. At the moment...based on consensus timing...it appears that
the morning hours will be mainly dry and just increasing windy...as
the flow aloft ramps up considerably in advance of our upstream
trough and cold front. Sharper Theta-E axis leaning back toward the
area does give some pause...as the chance for an initial morning
round of convection is not zero. However...the better shot will
probably wait until the sharper height falls/low level frontal
convergence work through the western lakes into late afternoon...
arriving here into early evening per 00z model consensus. This setup
continues to have some severe storm potential...with a nice corridor
of enhanced deep layer shear working out ahead of the forcing
boundary...while timing of upstream convective development should
occur around peak heating. For the bridge walk and any other outdoor
events...currently it would appear temperatures will be rising through the
60s/low 70s in the morning with winds gusting up to around 30 miles per hour as
deeper mixing ensues into a core of 40 knots aloft. Chances for rain
will continue into the first part of Monday night...ending rapidly
from west to east behind the front as sharp cooling and drying gets
Tuesday-friday: looking like a nice stretch of weather for back to
school time into midweek as northern Michigan sits on the far
northern fringe of broad upper ridging centered over the southeast
states. All the while...low level ridging is prognosticated to work through
the region into Wednesday night. Quite the significant drier airmass
is also forecast to make an appearance...suggesting that any rain
threat will remain off to our west nearer an axis of building heat
and moisture slowly working back into the upper Midwest by late
Wednesday. That axis may try to lean in our direction toward
Thursday or Thursday night...though confidence remains quite low
regarding the timing of additional rain chances. There should be
quite the tight thermal gradient not terribly far away into late
week and next weekend as cooler air circulates through southern
Canada while heat/humidity build north along the Southeast Ridge.
However...the placement of that feature and associated better rain
chances remains highly in question...with various pieces of guidance
really wavering over the last 48 hours. Based on everything I have
seen over the past few days...combined with northern Michigan climatology
and recent trends this year...it would seem reasonable to assume
that cooler air will more than likely dominate much of the County Warning Area...in
line with the more persistent European model (ecmwf) and GFS ensemble mean. That
would favor a dry forecast over much of northern Michigan...and
simply out of not wanting to clutter the forecast with very low
chance probability of precipitation that are extremely low confidence...will opt for dry
conditions at this point. The exception will be late Friday into
Friday night with hints of a cold front pressing into the area.
Temperatures look to remain quite seasonable...with highs generally in the
70s and lows in the 50s...perhaps cooler Tuesday night with the high
Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 154 PM EDT Sat Aug 30 2014
Thunderstorms expected to develop across northern lower Michigan over
the next few hours...with apn the most likely terminal site to get
storms. Otherwise...a mix of MVFR to VFR flight conditions will
persist through the afternoon...reduced to possible IFR with any
showers or storms that move through.
Tonight...front will slowly sag through the region with showers
diminishing. But...cooler air undercutting moist boundary layer
will lead to IFR conditions at the terminal sites later this
evening through Sunday morning. Slow improvement through the
morning hours Sunday.
issued at 218 am EDT Sat Aug 30 2014
Periods of rain and scattered non-severe thunderstorms will cover
much of the nearshores through today and into this evening...as weak
low pressure and a shallow cold front work into the region. Stable
conditions over the lakes have thwarted any potential advisory level
winds ahead of the front. Gradient weakens heading through the
afternoon and tonight while winds shift out of the W-NW.
A quiet Sunday will lead into the next front and period of showers
and storms arriving on Labor Day Monday. A similar set up with
potential advisory level winds being stopped by too much Overlake
Generally quiet conditions Tuesday-Wednesday. Maybe next chance of
precipitation late this coming work week.